.
Task 01:
a) Explain the rock cycle in the earth's crust by analyzing its formation.
Elements are chemically combined to form minerals. Minerals are physically combined to form rocks. In another word the solid mineral material forming part of the surface of the earth and other similar planets, exposed on the surface or underlying the soil or oceans.
Rocks can be classified into three groups:
Ø Igneous
Ø Sedimentary
Ø Metamorphic.
u Igneous: Igneous rock (derived from the Latin word ignites meaning fire) is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava. Igneous rock may form with or without crystallization, either below the surface as intrusive (Platonic) rocks or on the surface as extrusive (volcanic) rocks. This magma can be derived from partial melts of existing rocks in either a planet's mantle or crust. Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Igneous rocks are formed from the solidification of molten rock material. There are two basic types.
u Intrusive igneous rocks crystallize below Earth's surface, and the slow cooling that occurs there allows large crystals to form. Examples of intrusive igneous rocks are diorite, gabbro, granite, pegmatite, and peridotite.
u Extrusive igneous rocks erupt onto the surface, where they cool quickly to form small crystals. Some cool so quickly that they form an amorphous glass. These rocks include andesite, basalt, obsidian, pumice, rhyolite, scoria, and tuff.
Sedimentary Rocks: Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles (detritus) to settle in place. The particles that form a sedimentary rock by accumulating are called sediment. Before being deposited, the sediment was formed by weathering and erosion from the source area, and then transported to the place of deposition by water, wind, ice, mass movement or glaciers, which are called agents of denudation. Sedimentation may also occur as minerals precipitate from water solution or shells of aquatic creatures settle out of suspension.
Metamorphic Rocks: Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form".The original rock (protolith) is subjected to heat (temperatures greater than 150 to 200 °C) and pressure (1500 bars),[2] causing profound physical and/or chemical change. The photolith may be a sedimentary rock, an igneous rock or another older metamorphic rock.
b) Examine mode of formation and classification. 1) Igneous rocks with details of minerals. 2) Sedimentary rocks and their diversity. 3) Metamorphic rocks and grades of metamorphism.
Examine mode of formation and classification
Rocks are formed in three main ways and are classified accordingly. Igneous rocks form from molten material called magma. Sedimentary rocks form from sediments deposited out of water or the air. Metamorphic rocks form from the alteration of other rocks through temperature and pressure induced changes in the minerals.
· Igneous rocks with details of minerals.
Igneous Rocks Mode of Formation with Detail of Minerals: Igneous rocks are formed from cooling molten rock called magma. Minerals crystallize and interlock as the melt cools and solid rock forms. Eventually the entire melt forms a cool solid rock composed of crystals with no open spaces and usually showing no preferred grain alignment.
The rock may be entirely composed of one mineral but is usually made of several mineral types. The composition and range of types of minerals is determined by the magma. The size of the crystals is determined by the cooling history. In general, slow cooling will result in large crystals forming while rapid cooling will produce smaller crystals. Very rapid cooling may result in non-crystalline glass forming as part of or even all of the rock. If some slow cooling is followed by rapid cooling a fine grained rock with a scattering of larger crystals, called a porphyry, can result.
Magma can be intruded into other rocks within the crust or it can be erupted onto the surface. Intrusive igneous rocks, sometimes called plutonic rocks, are often coarse grained while the extrusive igneous rocks erupted or extruded at a volcano are often fine grained. When erupted magma flows across the landscape it is called lava. Lava cools to form a solid volcanic rock but magma explosively erupted is blasted into fragments that rain back down on the landscape, sometimes as unconsolidated debris but sometimes still hot enough to weld back into a mass of solid rock. Explosively formed volcanic rocks are called pyroclastic.
Volcanic rocks often contain gas bubbles, some glassy material and fragments of other rocks caught up in the explosive acts of formation. Plutonic rocks sometimes also contain rock fragments that have fallen into the intruding magma and not melted before it cooled. They are called xenoliths.
Common igneous rocks include granite, basalt, andesite and rhyodacite.
· Sedimentary rocks and their diversity.
Sedimentary rocks mode of formation and their diversity. Sedimentary rocks form from sediments deposited from water or air. Each grain in the rock was originally separate from all the others. When it stopped moving it settled down, touching several other grains but leaving pores spaces between the grains in places where they cannot touch.
Compaction under the weight of the accumulating sediments may have distorted soft grains, reduced the porosity and increased the cohesion between grains. Minerals precipitating out of watery solution filling the pores may have formed a cement, further securing the minerals to each other to form a solid rock. Sedimentary rocks can also be formed from evaporation or precipitation from a saturated mineral solution.
Based on their composition, sedimentary rocks are classified as organic, clastic, or non-clastic.
a. Organic sedimentary rocks are derived from organisms, and examples of these are coal and limestone. Limestone is a rock that contains many fossils and is made of calcium carbonate and microscopic shells.
b. Clastic sedimentary rocks like conglomerates and shale are formed from any size particle of pre-existing rock. Conglomerate rock has rounded pebbles cemented together in a matrix. Shale, on the other hand, is clay that had been hardened and tuned into rock.
c. Non-clastic or chemical sedimentary rocks: result from the evaporation of a saturated mineral solution. Rock gypsum and rock salt are examples of these rocks.
Most of the rocks found on the Earth’s surface are sedimentary even though sedimentary rocks only make up less than 5% of all the rocks that make up Earth. Furthermore, around 65% are classified as mud rocks, such as mudstone, shale and siltstone. Sandstones are from 20 to 25%, and carbonate rocks like limestone and dolostone are 10 to 15%. Sedimentary rocks form at or near the Earth’s surface.
Common sedimentary rocks include sandstone, mudstone, conglomerate and limestone. Grains in a sedimentary rock can be either distinct minerals or fragments of rocks. Either way, they have usually been sourced from the weathering and erosion of other rocks.
· Metamorphic rocks and grades of metamorphism.
Metamorphic: form from other rocks, including other metamorphic rocks. When rocks are deeply buried, intruded by magma or are caught up in large tectonic processes they experience large changes in temperature and / or pressure. Many minerals respond to theses changes by changing their crystal size and crystal type but some assemblages of minerals undergo more radical changes. Without actually melting, some mineral assemblages redistribute the elements within the starting minerals to form new suites of minerals that are more stable at the new pressures and temperatures.
Metamorphic rocks formed from magmatic intrusions heating country rock (the cool rock around the magma) are called thermal or contact metamorphic rocks. Metamorphic rocks resulting from wide spread temperature and pressure changes caused by tectonic processes are called regional metamorphic rocks. Some minerals may also separate into distinct layers, especially where the temperature and pressure changes have been extreme. Common metamorphic rocks include marble, slate, schist and gneiss.
Grade of metamorphism.
The grade of metamorphism is primarily controlled by temperature. As temperature increases, the grain size of the minerals in a metamorphic rock increases.
The most common names are derived from the metamorphism of shale. At low grades of metamorphism (typically around 300o C), one of the first chemical reactions to take place converts clay minerals that formed during weathering, into micas such as muscovite (white mica) and chlorite (green mica). If these mica minerals grow during deformation, they will be aligned with their sheets perpendicular to the maximum compressive stress, thus imparting a foliation to the rock. At these low temperatures, however, the micas do not grow large enough to be seen with the naked eye. You can tell they are there because the rock brakes along the foliation planes. Such a low-grade metamorphic rock exhibiting a foliation, but with minerals too small to be seen with the naked eye is called slate.
At higher grades of metamorphism, typically in the temperature range of 400 to 600o C, the micas grow large enough to be clearly visible to the naked eye, and consequently the foliation becomes obvious. These rocks are know as schist. At the very highest grades of metamorphism, typically with temperatures near or above 700o C, metamorphic segregation occurs, and produces rocks known as gneiss.
1.2 | Describe the common rock forming minerals and their susceptibility to weathering?
The technical definition of a mineral is elegant: a naturally occurring crystalline solid. That definition calls for a bit of commentary, though. By “crystalline” is meant that the atoms of the mineral are arranged in a regular three-dimensional array, called its crystal structure. Most of the common minerals are of a class called silicate minerals. Silicate minerals have as their basic building blocks a polyatomic (five-atom) unit, called a silica tetrahedron, that consists of one atom of silicon, relatively small, surrounded by four atoms of oxygen, relatively large, to give the shape of a tetrahedron. The five atoms are bonded very strongly together. The atoms in mineral crystals are held together by strong forces called bonds. An understanding of the nature of bonds necessitates some familiarity with atomic structure.
Some of important types of minerals
· Ferromagnesian silicates (“femags”): This collection of minerals (olivines,pyroxenes, amphiboles, biotite, and certain metamorphic minerals) contain iron and/or magnesium, in various proportions, as their main positive ions.
· Micas: Micas consist of sheets of polymerized silica tetrahedrons, each with three of their four oxygens shared, with various positive ions between the sheets
· Quartz: Quartz, with the simple formula SiO2, is a network silicate mineral with a three-dimensional network of silica tetrahedra, with all of the oxygens shared with adjacent tetrahedra
· Carbonates: The calcium carbonate minerals calcite and aragonite, along with the calcium–magnesium mineral dolomite, are the main minerals in chemically precipitated carbonate sedimentary rocks, and they are common as well in sediments in the warm and shallow oceans
Weathering
It is the term used for the chemical decomposition and physical disintegration of bedrock at and just below the earth’s surface. Weathering acts upon all bedrock near the surface, although with greatly varying nature and rate depending upon a number of factors. Weathering, in the usually accepted sense, acts upon rock that is close enough to the surface to be affected not only by active circulation of surface derived waters but also by such things as temperature changes and plant growth.
Weathering is traditionally subdivided into two
· chemical weathering
· physical weathering
Physical Weathering
The mechanical breakup or disintegration of rock doesn't change mineral makeup. It creates broken fragments or “detritus.” which are classified by size:
· Coarse-grained – Boulders, Cobbles, and Pebbles.
· Medium-grained – Sand
· Fine-grained – Silt and clay (mud).
Physical weathering takes place by a variety of processes. Among them are:
· Development of Joints - Joints are regularly spaced fractures or cracks in rocks that show no offset across the fracture (fractures that show an offset are called faults).
o Joints form as a result of expansion due to cooling or relief of pressure as overlying rocks are removed by erosion.
o Igneous plutons crack in onion like “exfoliation” layers. These layers break off as sheets that slide off of a pluton.
o Joints form free space in rock by which other agents of chemical or physical weathering can enter.
· Crystal Growth - As water percolates through fractures and pore spaces it may contain ions that precipitate to form crystals. As these crystals grow they may exert an outward force that can expand or weaken rocks.
· Thermal Expansion - Although daily heating and cooling of rocks do not seem to have an effect, sudden exposure to high temperature, such as in a forest or grass fire may cause expansion and eventual breakage of rock. Campfire example.
· Root Wedging - Plant roots can extend into fractures and grow, causing expansion of the fracture. Growth of plants can break rock - look at the sidewalks of New Orleans.
· Animal Activity - Animals burrowing or moving through cracks can break rock.
· Frost Wedging - Upon freezing, there is an increase in the volume of the water (that's why we use antifreeze in auto engines or why the pipes break in New Orleans during the rare freeze). As the water freezes it expands and exerts a force on its surroundings. Frost wedging is more prevalent at high altitudes where there may be many freeze-thaw cycles.
Chemical Weathering
Since many rocks and minerals are formed under conditions present deep within the Earth, when they arrive near the surface as a result of uplift and erosion, they encounter conditions very different from those under which they originally formed. Among the conditions present near the Earth's surface that are different from those deep within the Earth are:
· Lower Temperature (Near the surface T = 0-50oC)
· Lower Pressure (Near the surface P = 1 to several hundred atmospheres)
· Higher free water (there is a lot of liquid water near the surface, compared with deep in the Earth)
· Higher free oxygen (although O2 is the most abundant element in the crust, most of it is tied up bonded into silicate and oxide minerals - at the surface there is much more free oxygen, particularly in the atmosphere).
Because of these differing conditions, minerals in rocks react with their new environment to produce new minerals that are stable under conditions near the surface. Minerals that are stable under P, T, H2O, and O2 conditions near the surface are, in order of most stable to least stable:
· Iron oxides, Aluminum oxides - such as hematite Fe2O3, & gibbsite Al(OH)3.
· Quartz*
· Clay Minerals
· Muscovite*
· Alkali Feldspar*
· Biotite*
· Amphiboles*
· Pyroxenes*
· Ca-rich plagioclase*
· Olivine*
(Note the minerals with a *. These are igneous minerals that crystallize from a liquid. Note the minerals that occur low on this list are the minerals that crystallize at high temperature from magma. The higher the temperature of crystallization, the less stable are these minerals at the low temperature found near the Earth's surface)
Types of Chemical Weathering Reactions
· Hydrolysis - H+ or OH- replaces an ion in the mineral. Example:
· Leaching - ions are removed by dissolution into water. In the example above we say that the K+ ion was leached.
· Oxidation - Since free oxygen (O2) is more common near the Earth's surface, it may react with minerals to change the oxidation state of an ion. This is more common in Fe (iron) bearing minerals, since Fe can have several oxidation states, Fe, Fe+2, Fe+3. Deep in the Earth the most common oxidation state of Fe is Fe+2.
Rock
Primary Minerals
Residual Minerals*
Leached Ions
Granite
Feldspars
Clay Minerals
Na+, K+
Micas
Clay Minerals
K+
Quartz
Quartz
---
Fe-Mg Minerals
Clay Minerals + Hematite + Goethite
Mg+2
Basalt
Feldspars
Clay Minerals
Na+, Ca+2
Fe-Mg Minerals
Clay Minerals
Mg+2
Magnetite
Hematite, Goethite
---
Limestone
Calcite
None
Ca+2, CO3-2
*Residual Minerals = Minerals stable at the Earth's surface and left in the rock after weathering.
Since chemical weathering occurs on the surface of minerals, the water and acids that control chemical weathering require access to the surface. Physical weathering breaks the rock to provide that surface. Fracturing the rocks, as occurs during jointing, increases the surface area that can be exposed to weathering and also provides pathways for water to enter the rock. As chemical weathering proceeds, new softer minerals, like oxides or clay minerals, will create zones of weakness in rock that will allow for further physical weathering. Dissolution of minerals will remove material that holds the rock together, thus making it weaker.
Factors that Influence Weathering
· Rock Type & Structure
o Different rocks are composed of different minerals, and each mineral has a different susceptibility to weathering. For example, a granite consisting mostly of quartz is already composed of a mineral that is very stable on the Earth's surface, and will not weather much in comparison to limestone, composed entirely of calcite, which will eventually dissolve completely in a wet climate.
o Bedding planes, joints, and fractures, all provide pathways for the entry of water. A rock with lots of these features will weather more rapidly than a massive rock containing no bedding planes, joints, or fractures.
· Slope - On steep slopes weathering products may be quickly washed away by rains. On gentle slopes the weathering products accumulate. On gentle slopes water may stay in contact with rock for longer periods of time, and thus result in higher weathering rates.
· Climate- High amounts of water and higher temperatures generally cause chemical reactions to run faster. Thus warm humid climates generally have more highly weathered rock, and rates of weathering are higher than in cold dry climates. Example: limestones in a dry desert climate are very resistant to weathering, but limestones in a tropical climate weather very rapidly.
1.3 | Evaluate the common usage of rock and un-cemented sediments for construction.
In geology, rock or stone is a naturally occurring solid aggregate of one or more minerals or mineraloids. For example, the common rock granite is a combination of the quartz, feldspar and biotite minerals. The Earth's outer solid layer, the lithosphere, is made of rock. Rocks have been used by mankind throughout history. From the Stone Age, rocks have been used for tools. The minerals and metals found in rocks have been essential to human civilization. Rocks normally consist of several minerals, some essential, some accessory. A rock may be thought of as a "mineral environment." Each rock type was formed under certain specific conditions, resulting in the formation of a fairly predictable group of minerals.
Serial
No.
Rock and Un-Cemented Sediment
Common usages for construction.
1
LIMESTONE:
A sedimentary rock
it is used mainly in the manufacture of Portland cement, the production of lime, manufacture of paper, petrochemicals, linoleum, fiberglass, glass, carpet backing and as the coating on many types of gum.
2
CONGLOMERATE
A sedimentary rock
It is a coarse-grained clastic sedimentary rock that is composed of a substantial fraction of rounded to subangular gravel-size clasts, e.g., granules, pebbles, cobbles, and boulders, larger than 2 mm (0.079 in) in diameter.
Conglomerate can be crushed to make a fine aggregate that can be used where a low-performance material is suitable. Many conglomerates are colorful and attractive rocks that are rarely used as an ornamental stone for interior use
A sedimentary rock with a variable hardness, consisted of rounded or angular rock or mineral fragments cemented by silica, lime, iron oxide,
3
SANDSTONE:
A sedimentary rock
Generally thick-bedded, varicolored, rough feel due to uneven surface produced by breaking around the grains.
Sandstone is relatively soft, making it easy to carve. It has been widely used around the world in constructing temples, homes, and other buildings. It has also been used for artistic purposes to create ornamental fountains and statues.
Some sandstones are resistant to weathering, yet are easy to work. This makes sandstone a common building and paving material including in asphalt concrete.
the smooth sandstones used for formations of walls, pillars, ceilings and balustrades
4
GRANITE:
An igneous rock
An igneous-plutonic rock, medium to coarse-grained that is high in silica, potassium, sodium and quartz but low in calcium, iron and magnesium. It is widely used for architectural construction, ornamental stone and monuments.
Granite dimension stone is used in buildings, bridges, paving, monuments and many other exterior projects. Indoors, polished granite slabs and tiles are used in countertops, tile floors, stair treads and many other design elements.
5
PUMICE:
An igneous rock
PUMICE: An igneous-volcanic rock, it is a porous, brittle variety of rhyolite and is light enough to float. It is formed when magma of granite composition erupts at the earth’s surface or intrudes the crust at shallow depths. It is used as an abrasive material in hand soaps, emery boards, etc.
In construction pumice is used in the following applications:
· Production of light weight building blocks
· Production of light weight concrete
· Floor insulation and filling purposes
6
GABBRO:
An igneous rock
GABBRO: An igneous-plutonic rock, generally massive, but may exhibit a layered structure produced by successive layers of different mineral composition.
It is widely used as crushed stone for concrete aggregate, road metal, railroad ballast, etc. Smaller quantities are cut and polished for dimension stone (called black granite).
The main features of Gabbro crushed stone is its hardiness, strength, and density. Crushed stone made of Gabbro-Diabase is ideal for the construction of water-based projects due to its low water absorption rate. does not require the use of expensive additives that are usually necessary when using crushed granite.
Gabbro- stone can be used in road construction, production of asphalt mixes, production of ready-mixed concrete for industrial and civil construction, production of high-strength concrete, general building, and as an anti-icing agent for gritting roads.
7
BASALT: An igneous rock
BASALT: An igneous volcanic rock, dark gray to black, it is the volcanic equivalent of plutonic gabbro and is rich in ferromagnesian minerals. Basalt can be used in aggregate.
Basalt is used for a wide variety of purposes. It is most commonly crushed for use as an aggregate in construction projects. Crushed basalt is used for road base, concrete aggregate, asphalt pavement aggregate, railroad ballast, filter stone in drain fields and may other purposes. Basalt is also cut into dimension stone. Thin slabs of basalt are cut and sometimes polished for use as floor tiles, building veneer, monuments and other stone objects
8
SCHIST:
Metamorphic
SCHIST: A metamorphic uneven-granular, have graphite and used as building stones.
Generally used as a decorative rock, e.g. walls, gardens etc; high percentage of mica group minerals precludes its use in the construction and roading industries.
9
GNEISS:
Metamorphic
GNEISS: A metamorphic uneven granular medium to coarse grained crystalline with more or less parallel mineral orientation. Colors are too variable to be of diagnostic value. Due to physical and chemical similarity between many gneisses and plutonic igneous rocks some are used as building stones and other structural purposes.
10
QUARTZITE:
A metamorphic or sedimentary rock
QUARTZITE: A metamorphic or sedimentary rock with crystalline texture, consists of rounded quartz grains cemented by crystalline quartz, generally white, light gray or yellow to brown. Same uses as sandstone.
This stone is stronger than any granite or marble; it contains approximately 98% quartz, making it one of the most durable stones known to man.
Many famous buildings and installations are made from Shoksha. Examples of these include St. Isaac’s Cathedral in Saint Petersburg, Lenin’s Mausoleum in Red Square in Moscow, the tomb of Napoleon in Paris, and many more.
Red quartz crushed stone can be used for landscaping, general building, road construction, grave and memorial decoration, and more
11
MARBLE:
Metamorphic
MARBLE: A metamorphic even-granular grain to medium grained and may be uneven granular and coarse grained in calc-silicate rock. The normal color is white but accessory minerals act as coloring agents and may produce a variety of colors. Depending upon its purity, texture, color and marbled pattern it is quarried for use as dimension stone for statuary, architectural and ornamental purposes. Dolomite rich marble may be a source for magnesium and is used as an ingredient in the manufacture of refracting material
Task 02
2.1 Explain the protocol for describing a soil deposit using nine characteristics as specified in BS 5930 and also produce possible soil description for any two soil deposits in line with BS 5930 site investigation recommends.
BS system for description and classification
The British Soil Classification System (BSCS) which was introduced in the British Standard Code of Practice for Site Investigations, BS 5930:1981 is reviewed. An account is given of the development of the BSCS from the previous British system of CP 2001; the reasons for changes are explained, and comparison is made with similar systems in use in America, France, Germany, Switzerland, and Japan. New features of the system are that it is metricized, its groups are fully defined, description of the grading of course materials is improved, fuller description is possible of coarse soils containing an appreciable proportion of fines and of fine soils containing an appreciable proportion of gravel or sand, the classification of fine soils is extended to provide for materials of very high and extremely high plasticity, the presence of organic matter can be indicated in any type of soil, and materials containing boulders and cobbles can be classified. Without the use of a satisfactory system of description and classification, the description of materials found on a site would be meaningless or even misleading, and it would be difficult to apply experience to future projects.
BS description system
An endorsed protocol for describing a soil deposit uses nine characteristics; therefore these are described in the following order:
· Compactness :
e.g. loose, dense, slightly cemented
· Bedding structure :
e.g. homogeneous or stratified; dip, orientation
· Discontinuities :
spacing of beds, joints, fissures
· Weathered state :
degree of weathering
· Colour :
main body color, mottling, humic
· Grading or consistency:
e.g. well-graded, (a good representation of all particle sizes from largest to smallest) poorly-graded; (a limited representation of grain sizes) soft, firm, hard
· SOIL NAME :e.g. GRAVEL, SAND, SILT, CLAY; (upper case letters) plus silty-, gravelly-, with-fines, etc. as appropriate
· Soil class:
(BSCS) designation (for roads & airfields) e.g. SW = well-graded sand. Terrestrial raw soils= layer less than 5cm thick. Lithomorphic Soils: These are shallow soil In colluvium more than 40cm thick
· Geological stratigraphic name:
Well-known names of geological stratigraphic like e.g. London clay, the Lambeth Group (known as the Woolwich and Reading Beds), Dartford Heath Gravel, Swanscombe, etc.
Note: Not all characteristics are necessarily applicable in every case.
Example:
(i) Loose homogeneous reddish-yellow poorly-graded medium SAND (SP), Flood plain alluvium
(ii) Dense fissured unweathered greyish-blue firm CLAY. Oxford clay.
Definitions of terms used in description
A table is given in BS 5930 Site Investigation setting out a recommended field identification and description system. The following are some of the terms listed for use in soil description:
1. Particle shape :
angular, sub-angular, sub-rounded, rounded, flat, elongate
Rounded
Sub rounded
Sub angular
Angular
2. Compactness :
loose, medium dense, dense (use a pick or driven peg, or density index )
3. Bedding structure :
homogeneous, stratified, inter-stratified
4. Bedding spacing :
massive(>2m), thickly bedded (2000-600 mm), medium bedded (600-200 mm), thinly bedded (200-60 mm), very thinly bedded (60-20 mm), laminated (20-6 mm), thinly laminated (<6 mm).
5. Discontinuities:
i.e. spacing of joints and fissure: very widely spaced (>2m), widely spaced (2000-600 mm), medium spaced (600-200 mm), closely spaced (200-60 mm), very closely spaced (60-20 mm), extremely closely spaced (<20 mm).
6. Colours :
red, pink, yellow, brown, olive, green, blue, white, grey, black
7. Consistency:
very soft (exudes between fingers), soft (easily moldable), firm (strong finger pressure required), stiff (can be indented with fingers, but not molded) very stiff (indented by sharp object), hard (difficult to indent).
8. Grading :
well graded (wide size range), uniform (very narrow size range), poorly graded (narrow or uneven size range).
9. Composite soils: In SANDS and GRAVELS: slightly clayey or silty (<5%), clayey or silty (5-15%), very clayey or silty (>15%)
In CLAYS and SILTS: sandy or gravelly (35-65%)
10. Man- made soil: These are soils formed in material modified or created by human activity. They result from abnormal management practices such as the addition of earth containing manures or refuse. i.e.: Disturbed soils: at least 40cm of artificially displaced material.
11. Peat soils:
a) Firm: Fiber’s already compressed together
b) Spongy: Very compressible and open structure
c) Plastic: Can be molded in hand and smears in fingers
d) Fibrous: Plant remains recognizable and retains some strength
e) Amorphous: No recognizable plant remains
British Soil Classification System
The recommended standard for soil classification is the British Soil Classification System, and this is detailed in BS 5930 Site Investigation. Its essential structure is as follows:
Soil group
Symbol
Recommended name
Qualifying terms
Degree of permeability
Coarse soils
Fines %
High
GRAVEL
G
GW
0 - 5
Well-graded GRAVEL
W
GPu/GPg
0 - 5
Uniform/poorly-graded GRAVEL
pu
G-F
GWM/GWC
5 - 15
Well-graded silty/clayey GRAVEL
W
GPM/GPC
5 - 15
Poorly graded silty/clayey GRAVEL
p
GF
GML, GMI...
15 - 35
Very silty GRAVEL [plasticity sub-group...]
H
GCL, GCI...
15 - 35
Very clayey GRAVEL [..symbols as below]
H
SAND
S
SW
0 - 5
Well-graded SAND
W
Low
SPu/SPg
0 - 5
Uniform/poorly-graded SAND
Pu
S-F
SWM/SWC
5 - 15
Well-graded silty/clayey SAND
W
GPM/GPC
5 - 15
Poorly graded silty/clayey SAND
P
SF
SML, SMI...
15 - 35
Very silty SAND [plasticity sub-group...]
H
SCL, SCI...
15 - 35
Very clayey SAND [..symbols as below]
H
Fine soils
>35% fines
Liquid limit%
SILT
M
MG
Gravelly SILT
MS
Sandy SILT
Very low
ML, MI...
[Plasticity subdivisions as for CLAY]
CLAY
C
CG
Gravelly CLAY
G
Practically impermeable
CS
Sandy CLAY
S
CL
<35
CLAY of low plasticity
L
CI
35 - 50
CLAY of intermediate plasticity
I
CH
50 - 70
CLAY of high plasticity
H
CV
70 - 90
CLAY of very high plasticity
V
CE
>90
CLAY of extremely high plasticity
E
Organic soils
O
[Add letter 'O' to group symbol]
high
Peat
Pt
[Soil predominantly fibrous and organic]
Very low
2.2 | Classify the provided course soil based on the results of a dry-sieving test obtained as below by plotting a computer printed grading curve against % finer in y-axis and particle size in x-axis.
Sieve mesh
size (mm)
Mass
retained (g)
Percentage
retained
Percentage
finer (passing)
14.0
0
0
100.0
10.0
3.5
1.2
98.8
6.3
7.6
2.6
86.2
5.0
7.0
2.4
93.8
3.35
14.3
4.9
88.9
2.0
21.1
7.2
81.7
1.18
56.7
19.4
62.3
0.600
73.4
25.1
37.2
0.425
22.2
7.6
29.6
0.300
26.9
9.2
20.4
0.212
18.4
6.3
14.1
0.150
15.2
5.2
8.9
0.063
17.5
6.0
2.9
Pan
8.5
2.9
TOTAL
292.3
100.0
The soil comprises: 18% gravel, 45% coarse sand, 24% medium sand, 10% fine sand, 3% silt, and is classified therefore as: a well-graded gravelly SAN.
2.3 A stratum of sand 2.5 m thick overlies a stratum of saturated clay 3 m thick. The water table is 1 m below the surface. For the sand, Gs = 2.65, e = 0.50 and for the clay Gs = 2.72, e = 1.1. Calculate the total and effective vertical stresses at depths of 1 m, 2.5 m and 5.5 m below the surface assuming that the sand above the water table is completely dry. ( yw = 9.81 kN/m³ ).
ANSWER
Specific gravity of sand Gs = 2.65
Specific gravity of clay Gs = 2.72
Void ratio of sand e = 0.50
Void ratio of clay e = 1.1
yw = 9.81 kN/m³
Sketch as mentioned above,
For Clayey Layer
Calculation of dry and saturated unit weight of Clay
ysat = (G + e) yw
1 + e
= (2.72 + 1.1) 9.81
1 + 1.1
= (3.82) 9.81
2.10
2
= 1.82 x 9.81
= 17.85 KN/m
y = ysat - yw
= 17.85 – 9.81
= 8.04 KN/m2
For Sandy Layer
Calculation of dry and saturated unit weight of Sand
ysat = (G + e) yw
1 + e
= (2.65 + 0.50) 9.81
1 + 0.50
= (3.15) 9.81
1.50
2
= 2.10 x 9.81
= 20.60 KN/m
y = ysat - yw
= 20.60 – 9.81
= 10.79 KN/m2
For Sandy Stratum above water table
ydry = (G) yw
1 + e
= (2.65) 9.81
1 + 0.50
= (2.65) 9.81
1.50
2
= 1.75 x 9.81
= 17.22 KN/m
At 5.5m below the Ground level
Total Pressure (δ5.5) = 17.845(3) + 20.60 (1.5) + 17.22
= 53.54 + 30.90 + 17.22
= 101.66 KN/m2
Pore Pressure (h5.5) = h yw
Note h = 3 + 1.5 = 4.5
= 4.5 (9.81)
= 44.15 KN/m2
Net Effective Pressure δ = Total Pressure - Pore Pressure
= 101.66 - 44.15
= 57.51 KN/m2
At 2.5m below the Ground level
Total Pressure (δ2.5) = 20.60(1.5) + 17.22
= 30.90 + 17.22
= 48.12 KN/m2
Pore Pressure (h2.5) = h yw
Note h =1.5 = 1.5
= 1.5 (9.81)
= 14.72 KN/m2
Net Effective Pressure (δ2.5) = Total Pressure - Pore Pressure
= 48.12 - 14.72
= 33.40 KN/m2
At 1m below the Ground level
Total Pressure (δ1) = 1 (1) + 17.22
= 1 + 17.22
= 17.22 KN/m2
Pore Pressure (h1) = h yw
Note h = 0
= 0 (9.81)
= 0 KN/m2
Net Effective Pressure (δ1) = Total Pressure - Pore Pressure
= 17.22 - 0
= 17.22 KN/m2
Task 03:
3.1 Explain the Geotechnical design parameters like shear strength, compressibility and permeability. Also explain the common methods for its determination.
Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. Geotechnical engineering is important in civil engineering, but also has applications in military, mining, petroleum and other engineering disciplines that are concerned with construction occurring on the surface or within the ground. Geotechnical engineering uses principles of soil mechanics and rock mechanics to investigate subsurface conditions and materials; determine the relevant physical/mechanical and chemical properties of these materials; evaluate stability of natural slopes and man-made soil deposits; assess risks posed by site conditions; design earthworks and structure foundations; and monitor site conditions, earthwork and foundation construction.
The final properties to be used for design should be based on the results from the field investigation, the field testing, and the laboratory testing, used separately or in combination. Site performance data should also be used if available to help determine the final geotechnical properties for design. The geotechnical designer’s responsibility is to determine which parameters are critical to the design of the project and then determine those parameters to an acceptable level of accuracy.
Shear strength: In engineering, shear strength is the strength of a material or component against the type of yield or structural failure where the material or component fails in shear. A shear load is a force that tends to produce a sliding failure on a material along a plane that is parallel to the direction of the force. When a paper is cut with scissors, the paper fails in shear.
In structural and mechanical engineering, the shear strength of a component is important for designing the dimensions and materials to be used for the manufacture or construction of the component (e.g. beams, plates, or bolts). In a reinforced concrete beam, the main purpose of reinforcing bar (rebar) stirrups is to increase the shear strength.3
TYPE OF SHEAR STRENGTH
Direct Shear Test
The test is carried out on a soil sample confined in a metal box of square cross-section which is split horizontally at mid-height. A small clearance is maintained between the two halves of the box.The soil is sheared along a predetermined plane by moving the top half of the box relative to the bottom half. The box is usually square in plan of size
60 mm x 60 mm. A typical shear box is shown.
If the soil sample is fully or partially saturated, perforated metal plates and porous stones are placed below and above the sample to allow free drainage. If the sample is dry, solid metal plates are used. A load normal to the plane of shearing can be applied to the soil sample through the lid of the box.
Tests on sands and gravels can be performed quickly, and are usually performed dry as it is found that water does not significantly affect the drained strength. For clays, the rate of shearing must be chosen to prevent excess pore pressures building up.
As a vertical normal load is applied to the sample, shear stress is gradually applied horizontally, by causing the two halves of the box to move relative to each other. The shear load is measured together with the corresponding shear displacement. The change of thickness of the sample is also measured.
A number of samples of the soil are tested each under different vertical loads and the value of shear stress at failure is plotted against the normal stress for each test. Provided there is no excess pore water pressure in the soil, the total and effective stresses will be identical. From the stresses at failure, the failure envelope can be obtained.
The test has several advantages:
• It is easy to test sands and gravels.
• Large samples can be tested in large shear boxes, as small samples can give misleading results due to imperfections such as fractures and fissures, or may not be truly representative.
• Samples can be sheared along predetermined planes, when the shear strength along fissures or other selected planes are needed.
The disadvantages of the test include:
• The failure plane is always horizontal in the test, and this may not be the weakest plane in the sample. Failure of the soil occurs progressively from the edges towards the centre of the sample.
• There is no provision for measuring pore water pressure in the shear box and so it is not possible to determine effective stresses from undrained tests.
• The shear box apparatus cannot give reliable undrained strengths because it is impossible to prevent localised drainage away from the shear plane.
Triaxial test
The triaxial test is carried out in a cell on a cylindrical soil sample having a length to diameter ratio of 2. The usual sizes are 76 mm x 38 mm and 100 mm x 50 mm. Three principal stresses are applied to the soil sample, out of which two are applied water pressure inside the confining cell and are equal. The third principal stress is applied by a loading ram through the top of the cell and is different to the other two principal stresses. A typical triaxial cell is shown.
The soil sample is placed inside a rubber sheath which is sealed to a top cap and bottom pedestal by rubber O-rings. For tests with pore pressure measurement, porous discs are placed at the bottom, and sometimes at the top of the specimen. Filter paper drains may be provided around the outside of the specimen in order to speed up the consolidation process. Pore pressure generated inside the specimen during testing can be measured by means of pressure transducers.
The triaxial compression test consists of two stages:
First stage: In this, a soil sample is set in the triaxial cell and confining pressure is then applied.
Second stage: In this, additional axial stress (also called deviator stress) is applied which induces shear stresses in the sample. The axial stress is continuously increased until the sample fails.
During both the stages, the applied stresses, axial strain, and pore water pressure or change in sample volume can be measured.
Test Types
There are several test variations, and those used mostly in practice are:
UU (unconsolidated undrained) test: In this, cell pressure is applied without allowing drainage. Then keeping cell pressure constant, deviator stress is increased to failure without drainage.
CU (consolidated undrained) test: In this, drainage is allowed during cell pressure application. Then without allowing further drainage, deviator stress is increased keeping cell pressure constant.
CD (consolidated drained) test: This is similar to CU test except that as deviator stress is increased, drainage is permitted. The rate of loading must be slow enough to ensure no excess pore water pressure develop
A. Permeability test
A measure of the ability of water to flow through the soil. It is expressed in units of velocity ,
In soils, the permeant or pore fluid is mostly water whose variation in property is generally very less. Permeability of all soils is strongly influenced by the density of packing of the soil particles, which can be represented by void ratio (e) or porosity (n).
Permeability value depends on the average size of the pores and is related to the distribution of particle sizes, particle shape and soil structure. The ratio of permeabilities of typical sands/gravels to those of typical clays is of the order of 106. A small proportion of fine material in a coarse-grained soil can lead to a significant reduction in permeability.
For different soil types as per grain size, the orders of magnitude for permeability are as follows:
Soil
k (cm/sec)
Gravel
100
Coarse sand
100 to 10-1
Medium sand
10-1 to 10-2
Fine sand
10-2 to 10-3
Silty sand
10-3 to 10-4
Silt
1 x 10-5
Clay
10-7 to 10-9
Field Tests for Permeability
Field or in-situ measurement of permeability avoids the difficulties involved in obtaining and setting up undisturbed samples in a permeameter. It also provides information about bulk permeability, rather than merely the permeability of a small sample.
A field permeability test consists of pumping out water from a main well and observing the resulting drawdown surface of the original horizontal water table from at least two observation wells. When a steady state of flow is reached, the flow quantity and the levels in the observation wells are noted.
Two important field tests for determining permeability are: Unconfined flow pumping test, and confined flow pumping test.
Unconfined Flow Pumping Test
In this test, the pumping causes a drawdown in an unconfined (i.e. open surface) soil stratum, and generates a radial flow of water towards the pumping well. The steady-state heads h1 and h2 in observation wells at radii r1 and r2 are monitored till the flow rate q becomes stead
Confined Flow Pumping Test : Artesian conditions can exist in a aquifer of thickness D confined both above and below by impermeable strata. In this, the drawdown water table is above the upper surface of the acquifer
Compressibility
When a soil layer is subjected to vertical stress, volume change can take place through rearrangement of soil grains, and some amount of grain fracture may also take place. The volume of soil grains remains constant, so change in total volume is due to change in volume of water. In saturated soils, this can happen only if water is pushed out of the voids. The movement of water takes time and is controlled by the permeability of the soil and the locations of free draining boundary surfaces.
It is necessary to determine both the magnitude of volume change (or the settlement) and the time required for the volume change to occur. The magnitude of settlement is dependent on the magnitude of applied stress, thickness of the soil layer, and the of the soil.
When soil is loaded undrained, the pore pressure increases. As the excess pore pressure dissipates and water leaves the soil, settlement takes place. This process takes time, and the rate of settlement decreases over time. In coarse soils (sands and gravels), volume change occurs immediately as pore pressures are dissipated rapidly due to high permeability. In fine soils (silts and clays), slow seepage occurs due to low permeability.
Components of Total SettlementThe total settlement of a loaded soil has three components: Elastic settlement, primary consolidation, and secondary compression.
Elastic settlement is on account of change in shape at constant volume, i.e. due to vertical compression and lateral expansion. Primary consolidation (or simply consolidation) is on account of flow of water from the voids, and is a function of the permeability and compressibility of soil. Secondary compression is on account of creep-like behaviour.
Primary consolidation is the major component and it can be reasonably estimated. A general theory for consolidation, incorporating three-dimensional flow is complicated and only applicable to a very limited range of problems in geotechnical engineering. For the vast majority of practical settlement problems, it is sufficient to consider that both seepage and strain take place in one direction only, as one-dimensional consolidation in the vertical direction.
a) Explain the rock cycle in the earth's crust by analyzing its formation.
Rocks can be classified into three groups:
b) Examine mode of formation and classification. 1) Igneous rocks with details of minerals. 2) Sedimentary rocks and their diversity. 3) Metamorphic rocks and grades of metamorphism.
1.2 | Describe the common rock forming minerals and their susceptibility to weathering?
Because of these differing conditions, minerals in rocks react with their new environment to produce new minerals that are stable under conditions near the surface. Minerals that are stable under P, T, H2O, and O2 conditions near the surface are, in order of most stable to least stable:
|
· Iron oxides, Aluminum oxides - such as hematite Fe2O3, & gibbsite Al(OH)3.
· Quartz*
· Clay Minerals
· Muscovite*
· Alkali Feldspar*
· Biotite*
· Amphiboles*
· Pyroxenes*
· Ca-rich plagioclase*
· Olivine*
(Note the minerals with a *. These are igneous minerals that crystallize from a liquid. Note the minerals that occur low on this list are the minerals that crystallize at high temperature from magma. The higher the temperature of crystallization, the less stable are these minerals at the low temperature found near the Earth's surface)
Types of Chemical Weathering Reactions
· Hydrolysis - H+ or OH- replaces an ion in the mineral. Example:
· Leaching - ions are removed by dissolution into water. In the example above we say that the K+ ion was leached.
· Oxidation - Since free oxygen (O2) is more common near the Earth's surface, it may react with minerals to change the oxidation state of an ion. This is more common in Fe (iron) bearing minerals, since Fe can have several oxidation states, Fe, Fe+2, Fe+3. Deep in the Earth the most common oxidation state of Fe is Fe+2.
Since chemical weathering occurs on the surface of minerals, the water and acids that control chemical weathering require access to the surface. Physical weathering breaks the rock to provide that surface. Fracturing the rocks, as occurs during jointing, increases the surface area that can be exposed to weathering and also provides pathways for water to enter the rock. As chemical weathering proceeds, new softer minerals, like oxides or clay minerals, will create zones of weakness in rock that will allow for further physical weathering. Dissolution of minerals will remove material that holds the rock together, thus making it weaker.
Factors that Influence Weathering
· Rock Type & Structure
o Different rocks are composed of different minerals, and each mineral has a different susceptibility to weathering. For example, a granite consisting mostly of quartz is already composed of a mineral that is very stable on the Earth's surface, and will not weather much in comparison to limestone, composed entirely of calcite, which will eventually dissolve completely in a wet climate.
o Bedding planes, joints, and fractures, all provide pathways for the entry of water. A rock with lots of these features will weather more rapidly than a massive rock containing no bedding planes, joints, or fractures.
· Slope - On steep slopes weathering products may be quickly washed away by rains. On gentle slopes the weathering products accumulate. On gentle slopes water may stay in contact with rock for longer periods of time, and thus result in higher weathering rates.
· Climate- High amounts of water and higher temperatures generally cause chemical reactions to run faster. Thus warm humid climates generally have more highly weathered rock, and rates of weathering are higher than in cold dry climates. Example: limestones in a dry desert climate are very resistant to weathering, but limestones in a tropical climate weather very rapidly.
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1.3 | Evaluate the common usage of rock and un-cemented sediments for construction.
Serial
No.
Rock and Un-Cemented Sediment
Common usages for construction.
1
LIMESTONE:
A sedimentary rock
it is used mainly in the manufacture of Portland cement, the production of lime, manufacture of paper, petrochemicals, linoleum, fiberglass, glass, carpet backing and as the coating on many types of gum.
2
CONGLOMERATE
A sedimentary rock
It is a coarse-grained clastic sedimentary rock that is composed of a substantial fraction of rounded to subangular gravel-size clasts, e.g., granules, pebbles, cobbles, and boulders, larger than 2 mm (0.079 in) in diameter.
Conglomerate can be crushed to make a fine aggregate that can be used where a low-performance material is suitable. Many conglomerates are colorful and attractive rocks that are rarely used as an ornamental stone for interior use
A sedimentary rock with a variable hardness, consisted of rounded or angular rock or mineral fragments cemented by silica, lime, iron oxide,
3
SANDSTONE:
A sedimentary rock
Generally thick-bedded, varicolored, rough feel due to uneven surface produced by breaking around the grains.
Sandstone is relatively soft, making it easy to carve. It has been widely used around the world in constructing temples, homes, and other buildings. It has also been used for artistic purposes to create ornamental fountains and statues.Some sandstones are resistant to weathering, yet are easy to work. This makes sandstone a common building and paving material including in asphalt concrete.
the smooth sandstones used for formations of walls, pillars, ceilings and balustrades
4
GRANITE:
An igneous rock
An igneous-plutonic rock, medium to coarse-grained that is high in silica, potassium, sodium and quartz but low in calcium, iron and magnesium. It is widely used for architectural construction, ornamental stone and monuments.
Granite dimension stone is used in buildings, bridges, paving, monuments and many other exterior projects. Indoors, polished granite slabs and tiles are used in countertops, tile floors, stair treads and many other design elements.
5
PUMICE:
An igneous rock
PUMICE: An igneous-volcanic rock, it is a porous, brittle variety of rhyolite and is light enough to float. It is formed when magma of granite composition erupts at the earth’s surface or intrudes the crust at shallow depths. It is used as an abrasive material in hand soaps, emery boards, etc.
In construction pumice is used in the following applications:
· Production of light weight building blocks
· Production of light weight concrete
· Floor insulation and filling purposes
6
GABBRO:
An igneous rock
GABBRO: An igneous-plutonic rock, generally massive, but may exhibit a layered structure produced by successive layers of different mineral composition.
It is widely used as crushed stone for concrete aggregate, road metal, railroad ballast, etc. Smaller quantities are cut and polished for dimension stone (called black granite).The main features of Gabbro crushed stone is its hardiness, strength, and density. Crushed stone made of Gabbro-Diabase is ideal for the construction of water-based projects due to its low water absorption rate. does not require the use of expensive additives that are usually necessary when using crushed granite.
Gabbro- stone can be used in road construction, production of asphalt mixes, production of ready-mixed concrete for industrial and civil construction, production of high-strength concrete, general building, and as an anti-icing agent for gritting roads.
7
BASALT: An igneous rock
BASALT: An igneous volcanic rock, dark gray to black, it is the volcanic equivalent of plutonic gabbro and is rich in ferromagnesian minerals. Basalt can be used in aggregate.
Basalt is used for a wide variety of purposes. It is most commonly crushed for use as an aggregate in construction projects. Crushed basalt is used for road base, concrete aggregate, asphalt pavement aggregate, railroad ballast, filter stone in drain fields and may other purposes. Basalt is also cut into dimension stone. Thin slabs of basalt are cut and sometimes polished for use as floor tiles, building veneer, monuments and other stone objects
8
SCHIST:
Metamorphic
SCHIST: A metamorphic uneven-granular, have graphite and used as building stones.
Generally used as a decorative rock, e.g. walls, gardens etc; high percentage of mica group minerals precludes its use in the construction and roading industries.
9
GNEISS:
Metamorphic
GNEISS: A metamorphic uneven granular medium to coarse grained crystalline with more or less parallel mineral orientation. Colors are too variable to be of diagnostic value. Due to physical and chemical similarity between many gneisses and plutonic igneous rocks some are used as building stones and other structural purposes.
10
QUARTZITE:
A metamorphic or sedimentary rock
QUARTZITE: A metamorphic or sedimentary rock with crystalline texture, consists of rounded quartz grains cemented by crystalline quartz, generally white, light gray or yellow to brown. Same uses as sandstone.
This stone is stronger than any granite or marble; it contains approximately 98% quartz, making it one of the most durable stones known to man.Many famous buildings and installations are made from Shoksha. Examples of these include St. Isaac’s Cathedral in Saint Petersburg, Lenin’s Mausoleum in Red Square in Moscow, the tomb of Napoleon in Paris, and many more.
Red quartz crushed stone can be used for landscaping, general building, road construction, grave and memorial decoration, and more
11
MARBLE:
Metamorphic
MARBLE: A metamorphic even-granular grain to medium grained and may be uneven granular and coarse grained in calc-silicate rock. The normal color is white but accessory minerals act as coloring agents and may produce a variety of colors. Depending upon its purity, texture, color and marbled pattern it is quarried for use as dimension stone for statuary, architectural and ornamental purposes. Dolomite rich marble may be a source for magnesium and is used as an ingredient in the manufacture of refracting material
BS system for description and classification
e.g. loose, dense, slightly cemented
e.g. homogeneous or stratified; dip, orientation
spacing of beds, joints, fissures
degree of weathering
main body color, mottling, humic
e.g. well-graded, (a good representation of all particle sizes from largest to smallest) poorly-graded; (a limited representation of grain sizes) soft, firm, hard
(BSCS) designation (for roads & airfields) e.g. SW = well-graded sand. Terrestrial raw soils= layer less than 5cm thick. Lithomorphic Soils: These are shallow soil In colluvium more than 40cm thick
Well-known names of geological stratigraphic like e.g. London clay, the Lambeth Group (known as the Woolwich and Reading Beds), Dartford Heath Gravel, Swanscombe, etc.
(i) Loose homogeneous reddish-yellow poorly-graded medium SAND (SP), Flood plain alluvium
(ii) Dense fissured unweathered greyish-blue firm CLAY. Oxford clay.
angular, sub-angular, sub-rounded, rounded, flat, elongate
Rounded
Sub rounded
Sub angular
Angular
loose, medium dense, dense (use a pick or driven peg, or density index )
homogeneous, stratified, inter-stratified
massive(>2m), thickly bedded (2000-600 mm), medium bedded (600-200 mm), thinly bedded (200-60 mm), very thinly bedded (60-20 mm), laminated (20-6 mm), thinly laminated (<6 mm).
i.e. spacing of joints and fissure: very widely spaced (>2m), widely spaced (2000-600 mm), medium spaced (600-200 mm), closely spaced (200-60 mm), very closely spaced (60-20 mm), extremely closely spaced (<20 mm).
red, pink, yellow, brown, olive, green, blue, white, grey, black
very soft (exudes between fingers), soft (easily moldable), firm (strong finger pressure required), stiff (can be indented with fingers, but not molded) very stiff (indented by sharp object), hard (difficult to indent).
well graded (wide size range), uniform (very narrow size range), poorly graded (narrow or uneven size range).
In CLAYS and SILTS: sandy or gravelly (35-65%)
Soil group
Symbol
Recommended name
Qualifying terms
Degree of permeability
Coarse soils
Fines %
High
GRAVEL
G
GW
0 - 5
Well-graded GRAVEL
W
GPu/GPg
0 - 5
Uniform/poorly-graded GRAVEL
pu
G-F
GWM/GWC
5 - 15
Well-graded silty/clayey GRAVEL
W
GPM/GPC
5 - 15
Poorly graded silty/clayey GRAVEL
p
GF
GML, GMI...
15 - 35
Very silty GRAVEL [plasticity sub-group...]
H
GCL, GCI...
15 - 35
Very clayey GRAVEL [..symbols as below]
H
SAND
S
SW
0 - 5
Well-graded SAND
W
Low
SPu/SPg
0 - 5
Uniform/poorly-graded SAND
Pu
S-F
SWM/SWC
5 - 15
Well-graded silty/clayey SAND
W
GPM/GPC
5 - 15
Poorly graded silty/clayey SAND
P
SF
SML, SMI...
15 - 35
Very silty SAND [plasticity sub-group...]
H
SCL, SCI...
15 - 35
Very clayey SAND [..symbols as below]
H
Fine soils
>35% fines
Liquid limit%
SILT
M
MG
Gravelly SILT
MS
Sandy SILT
Very low
ML, MI...
[Plasticity subdivisions as for CLAY]
CLAY
C
CG
Gravelly CLAY
G
Practically impermeable
CS
Sandy CLAY
S
CL
<35
CLAY of low plasticity
L
CI
35 - 50
CLAY of intermediate plasticity
I
CH
50 - 70
CLAY of high plasticity
H
CV
70 - 90
CLAY of very high plasticity
V
CE
>90
CLAY of extremely high plasticity
E
Organic soils
O
[Add letter 'O' to group symbol]
high
Peat
Pt
[Soil predominantly fibrous and organic]
Very low
Sieve mesh
size (mm) |
Mass
retained (g) |
Percentage
retained |
Percentage
finer (passing) |
14.0
|
0
|
0
|
100.0
|
10.0
|
3.5
|
1.2
|
98.8
|
6.3
|
7.6
|
2.6
|
86.2
|
5.0
|
7.0
|
2.4
|
93.8
|
3.35
|
14.3
|
4.9
|
88.9
|
2.0
|
21.1
|
7.2
|
81.7
|
1.18
|
56.7
|
19.4
|
62.3
|
0.600
|
73.4
|
25.1
|
37.2
|
0.425
|
22.2
|
7.6
|
29.6
|
0.300
|
26.9
|
9.2
|
20.4
|
0.212
|
18.4
|
6.3
|
14.1
|
0.150
|
15.2
|
5.2
|
8.9
|
0.063
|
17.5
|
6.0
|
2.9
|
Pan
|
8.5
|
2.9
| |
TOTAL
|
292.3
|
100.0
|
2
2
2
3.1 Explain the Geotechnical design parameters like shear strength, compressibility and permeability. Also explain the common methods for its determination.
The test is carried out on a soil sample confined in a metal box of square cross-section which is split horizontally at mid-height. A small clearance is maintained between the two halves of the box.The soil is sheared along a predetermined plane by moving the top half of the box relative to the bottom half. The box is usually square in plan of size
60 mm x 60 mm. A typical shear box is shown.
If the soil sample is fully or partially saturated, perforated metal plates and porous stones are placed below and above the sample to allow free drainage. If the sample is dry, solid metal plates are used. A load normal to the plane of shearing can be applied to the soil sample through the lid of the box.
The soil sample is placed inside a rubber sheath which is sealed to a top cap and bottom pedestal by rubber O-rings. For tests with pore pressure measurement, porous discs are placed at the bottom, and sometimes at the top of the specimen. Filter paper drains may be provided around the outside of the specimen in order to speed up the consolidation process. Pore pressure generated inside the specimen during testing can be measured by means of pressure transducers.
Test Types
There are several test variations, and those used mostly in practice are:
Soil
k (cm/sec)
Gravel
100
Coarse sand
100 to 10-1
Medium sand
10-1 to 10-2
Fine sand
10-2 to 10-3
Silty sand
10-3 to 10-4
Silt
1 x 10-5
Clay
10-7 to 10-9
Field Tests for Permeability
Field or in-situ measurement of permeability avoids the difficulties involved in obtaining and setting up undisturbed samples in a permeameter. It also provides information about bulk permeability, rather than merely the permeability of a small sample.
A field permeability test consists of pumping out water from a main well and observing the resulting drawdown surface of the original horizontal water table from at least two observation wells. When a steady state of flow is reached, the flow quantity and the levels in the observation wells are noted.
Two important field tests for determining permeability are: Unconfined flow pumping test, and confined flow pumping test.
Unconfined Flow Pumping Test
In this test, the pumping causes a drawdown in an unconfined (i.e. open surface) soil stratum, and generates a radial flow of water towards the pumping well. The steady-state heads h1 and h2 in observation wells at radii r1 and r2 are monitored till the flow rate q becomes stead
In this test, the pumping causes a drawdown in an unconfined (i.e. open surface) soil stratum, and generates a radial flow of water towards the pumping well. The steady-state heads h1 and h2 in observation wells at radii r1 and r2 are monitored till the flow rate q becomes stead
Components of Total SettlementThe total settlement of a loaded soil has three components: Elastic settlement, primary consolidation, and secondary compression.
3.2 Discuss the methods of ground investigation and/or in-situ sample acquisition and testing
The level of detail and quality of information available about ground conditions will influence the project team’s ability to develop an appropriate, efficient and easy to implement design and to deal with issues that may arise during construction work, such as the presence of faults, underground obstructions, groundwater, and so on without incurring unnecessary costs or delays.
Ground investigations are a means of determining the condition of the ground, ideally before beginning construction works. They focus specifically on intrusive geotechnical work such as trial pits and boreholes, and so differ from wider ‘site investigations’ which tend to involve the collation of more general information from the client, from desk studies, walkover surveys and so on.
Ground investigations can help determine:
• Water table level and water flow.
• The nature of faults, fissures and voids in the underground.
• Ground layer thicknesses and the mechanical properties of soil.
• Detailed information about soil and ground samples.
There are a number of techniques that can be used for ground investigations, either individually or in combination. When deciding on the nature, scope and level of detail of ground investigations, consideration should be given to the positive influence information can have on reducing project risks, rather than just the costs of the investigations themselves.
Trial pits and trenches
Trial pits and trenches are a means of investigating shallow ground conditions and developing an understanding of the profile of soils within the ground. They can be particularly useful where buried structures or contamination is suspected or needs further investigation.
They can be excavated by hand or backhoe excavator, generally to a depth of up to 3.5-4.5 m. Trial pits and trenches can be more cost effective than boreholes but they do not allow for the same depth.
Window sampling, windowless sample boreholes and dynamic probing
Window sample and windowless sample boreholes can be a quick and economical method for obtaining soil samples, which are recovered by inserting tubes of varying lengths into the ground. They are generally restricted to shallow depths but are suited to sites with limited access, sloping sites, and where minimal disturbance is required. This is a particular advantage with window sampling which uses tubes with longitudinal openings cut into them and are inserted using either hand-held pneumatic samplers or tracked percussive samplers.
Dynamic probes use similar plant to provide strength profiles of the ground and enable a range of instrumentation to be installed such as piezometers, gas and groundwater monitoring wells and so on.
Light cable percussive boreholes
Light cable percussive boreholes can be suitable for sites that have poor access or low headroom. Tripod rigs are used to drill boreholes of up to 450 mm diameter and depths of up to 70 m. This can be a relatively economical technique and is suitable for weaker soils and where high-quality samples are required.
Rotary boreholes
Rotary boreholes are used where drilled exploration through rock and other solid geological formations such as dense gravel is required. Depths of up to 100 m can be achieved. Bedrock samples can then be taken to the laboratory for examination.
Rotary open-hole boreholes are drilled where an understanding of the presence of voids is more important than the structural details of the ground, and are typically used in areas where mine workings are likely.
Rotary cored boreholes are drilled when the structural details of the underlying rock are required. A core barrel is lowered into the drilled hole and a flush circulated with air/mist or water.
Sonic drilling
Sonic drilling involves sending high frequency mechanical oscillations down a drill string to the bit. These vibrations fluidize soil particles at the face of the bit which allows for easy penetration through most geological formations where other techniques may be less successful, particularly where the strata is varied. The specific geological conditions will determine the precise frequency to be used.
IN-SITU TESTS ON SOIL
In situ testing is a division of field-testing corresponding to the cases where the ground is tested in-place by instruments that are inserted in or penetrate the ground. In-situ tests are normally associated with tests for which a borehole either is unnecessary or is only an incidental part of the overall test procedure, required only to permit insertion of the testing tool or equipment. The role of specialized in-situ testing for site characterization and the research and development of in-situ techniques has received considerable attention over the last 15 years or so. The use of specialized in-situ testing in geotechnical engineering practice is rapidly gaining increased popularity. In Europe, specialized in-situ testing has been commonly used for more than 25 years. Improvements in apparatus, instrumentation, and technique of deployment, data acquisition and analysis procedure have been significant. The rapid increase in the number, diversity and capability of in-situ tests has made it difficult for practicing engineers to keep abreast of specialized in-situ testing and to fully understand their benefits and limitations.
ADVANTAGES
Ø Tests are carried out in place in the natural environment without sampling disturbance , which can cause detrimental effects and modifications to stresses, strains, drainage, fabric and particle arrangement
Ø Continuous profiles of stratigraphy and engineering properties/characteristics can be obtained.
Ø Detection of planes of weakness and defects are more likely and practical
Ø Methods are usually fast, repeatable, produce large amounts of information and are cost effective
Ø Tests can be carried out in soils that are either impossible or difficult to sample without the use of expensive specialized methods
Ø A large volume of soil may be tested than is normally practicable for laboratory testing. This may be more representative of the soil mass.
DISADVANTAGES
Ø Samples are not obtained; the soil tested cannot be positively identified. The exception to this is the SPT in which a sample, although disturbed, is obtained.
Ø The fundamental behavior of soils during testing is not well understood.
Ø Drainage conditions during testing are not known
Ø Consistent, rational interpretation is often difficult and uncertain
Ø The stress path imposed during testing may bear no resemblance to the stress path induced by full-scale engineering structure
Ø Most push-in devices are not suitable for a wide range of ground conditions
Ø Some disturbance is imparted to the ground by the insertion or installation of the instrument
Ø There is usually no direct measurement of engineering properties. Empirical correlations usually have to be applied to interpret and obtain engineering properties and designs
3.3 Carry out the calculations to determine requested soil properties from the following data provided from laboratory measurements.
a) A sample of soil was placed in a tin container and weighed, after which it was dried in an oven and then weighed again. Calculate the water content of the soil.
Weight of empty tin
|
= 14.00 g
|
Weight of tin + moist soil
|
= 37.82 g
|
Weight of tin + dry soil
|
= 34.68 g
|
b) A soil specimen had a volume of 89.00 ml, a mass before drying of 174.00 g and after drying of 158.00 g; the water content was 10 %. Determine the bulk and dry densities and unit weights.
a. Calculate the water content of the soil.
WI=Weight of empty tin =14.00g
W2=Weight of tin + moist soil = 37.82g
W3=Weight of tin + dry soil= 34.68g
W4= W2-W1= 23.82g
W5=W3-W1=20.68g
(WC)Water content =w5/w4x 100= 20.68/23.82x100=86.82
Weight of empty tin
|
= 14.00 g
|
Weight of tin + moist soil
|
= 37.82 g
|
Weight of tin + dry soil
|
= 34.68 g
|
Solution to 3.3a
Weight of empty tin
|
= 14.00 g
|
Weight of tin + moist soil
|
= 37.82 g
|
Weight of tin + dry soil
|
= 34.68 g
|
Water Content, W = (Mass of Water) / (Mass of Dry Soil)
= (37.82 – 34.68) / (34.68 – 14.00)
= 3.14 / 20.68 = 0.152
Percentage water content = 15.2 %
B. A soil specimen had a volume of 89.00 ml, a mass before drying of 174.00 g and after drying of 158.00 g; the water content was 10 %. Determine the bulk and dry densities and unit weights.
Solution to 3.3b
Bulk density
ρ = (mass of specimen) / (volume of specimen)
= 174.00 / 89.00 g/ml
= 1.955 Mg/m³
[1 g/ml = 1 Mg/m³]
Unit weight
Note the gravitational Acceleration have a standard value of 9.80665m/s²
Approximately = 9.81m/s²
γ = 9.81m/s² x ρ Mg/m³
γ = 9.81m/s² x 1.955 Mg/m³
= 19.17kN/ m³
Dry density
ρd = (mass after drying) / (volume)
= 158.00 / 89.00 g/ml
= 1.775 Mg/m³
ρd = ρ / (1 + w)
= 1.955 / (1 + 0.1)
= 1.955 / 1.1 Mg/m³
= 1.777 Mg/m³
Dry unit weight
γd = γ / (1 + w)
=19.17 / (1 + 0.1)
= 19.17 / 1.1
= 17.43 kN/ m³
Task 04
4.1 Evaluate various laboratory tests to determine shear strength.
Shear strength may be defined as the resistance to shearing stresses and a consequent tendency for shear deformation.
Soil derives its shearing strength from the following
1.resistance due to interlocking of particles
2.frictional resistance between the individual soil grains
3.adhesion between soil particles or cohesion
PRINCIPAL PLANES AND PRINCIPAL STRESSES
At a point in a stressed material, every plane will be subjected to a normal or direct stress and a shearing stress. A principal plane is defined as a plane on which the stress is fully normal or one which does not carry shearing stress. The normal stress acting on this principal planes are known as principal stresses. There exist three principal planes at any point in a stressed material. These three principal planes are mutually perpendicular. In the order of decreasing magnitude the principal planes are designated as major principal plane, minor principal plane and intermediate principal plane and the corresponding principal stresses are designated in the same manner.
From this figure,
These equations will give the stresses on the inclined plane making an angle with the major principal plane.
MOHR’S CIRCLE
Otto Mohr, a German scientist devised a graphical method for the determination of stresses on a plane inclined to the major principal planes. The graphical construction is known as Mohr’s circle. In this method, the origin O is selected and the normal stresses are plotted along the horizontal axis and the shear stresses on the vertical axis.
To construct a Mohr circle, first mark major and minor principal stress on X axis, Mark the centre point of that as C. A circle is drawn with c as centre and CF as radius. Each point on the circle gives the stresses ? and ? on a particular plane. The point E is known as the pole of the circle.
1.Mohr’s circle can be drawn for stress system with principal planes inclined to co-ordinate axes
2.Stress system with vertical and horizontal planes are not the principal planes
MOHR-COULOMB THEORY
The soil is a particulate material. The shear failure in soils is by slippage of particles due to shear stresses. According to Mohr, the failure is caused by a critical combination of normal and shear stresses. The soil fails when the shear stress on the failure plane at failure is a unique function of the normal stress acting on that plane. Since the shear stress of the failure plane is defined as the shear strength (s) the equation for that can be written as
S= f ( )
The Mohr theory is concerned with the shear stress at failure plane at failure. A plot can be made between the shear stresses and the normal stress at failure. The curve defined by this is known as the failure envelope.
The shear strength of a soil at a point on a particular plane was expressed by Coulomb as a linear function of the normal stress on that plane as,
In this C is equal to the intercept on Y axis and phi is the angle which the envelope make with X axis
DIFFERENT TYPES OF SHEAR TESTS AND DRAINAGE CONDITIONS
The following tests are used to measure the shear strength of the soil
1.Direct shear test
2.Triaxial compression test
3.Unconfined compression test
4.Vane shear test
Depending upon the drainage conditions, there are three types of tests
·Unconsolidated-Undrained condition
·Consolidated – Undrained condition
·Consolidated-Drained condition
DIRECT SHEAR TEST
Apparatus
The test is conducted in a soil specimen in a shear box which is split in to two halves along the horizontal plane at its middle. The size of the shear box is 60 x 60 x 50 mm. the box is divided horizontally such that the dividing plane passes through the centre. The two halves are held together by locking pins the box is also provided with gripper plates plain or perforated according to the testing conditions
Test
A soil specimen of size 60 x 60 x 25 mm is taken. It is placed in the direct shear box and compacted. The upper grid plate, porous stone and pressure pad is placed on the specimen. Normal load and shear load is be applied till failure
Presentation of results
·Stress – strain curve
·Failure envelope
·Mohr’s circle
Merits
1.the sample preparation is easy
2.as the thickness of the sample is very less, the drainage is quick
3.it is ideally suited for conducting drained tests on cohesionless soils
4.the apparatus is relatively cheap
Demerits
1.the stress conditions are known only at failure
2.the stress distribution on the failure plane is not uniform
3.the area of shear gradually decreases as the test progresses
4.the orientation of the failure plane is fixed
5.control of drainage conditions is very difficult
6.measurement of pore water pressure is not possible
TRIAXIAL COMPRESSION TEST
It is used for the determination of shear characteristics of all types of soils under different drainage conditions. In this a cylindrical specimen is stressed under conditions of axial symmetry. In the first stage of the test, the specimen is subjected to an all-round confining pressure on the sides, top and bottom. This stage is known as the consolidation stage. In the second stage of the test called shearing stage, an additional axial stress called deviator stress is applied on the top of the specimen through a ram. Thus the total stress in the axial direction at the time of shearing is equal to the confining stress plus the deviator stress. The vertical sides of the specimen are principal planes. The confining pressure is the minor principal stress. The sum of the confining stress and deviator stress is the major principal stress. Triaxial apparatus consists of a circular base with a central pedestal. The specimen is placed on the pedestal. The pedestal has one or two holes which are used in the drainage function or pore pressure measurement. A triaxial cell is placed to the base plate. It is a Perspex cylinder. There are three tie rods which support the cell. A central ram is there for applying axial stress. An air release valve and an oil release valve are attached to the cell. The apparatus also have special features like,
·Mercury control system
·Pore water pressure measurement device
·Volume changes measurement
Triaxial test on cohesive soil
CU, UU and CD tests can be conducted on soil specimen. The specimen is placed in the pedestal inside a rubber membrane. The confining pressure and axial pressure is applied till failure.
Triaxial test on cohesionless soil
The procedure is same as that in the cohesive soil only the sample preparation is different. A metal former, a membrane and a funnel are used for the sample preparation.
Merits
1.There is complete control over the drainage conditions
2.Pore pressure changes and volumetric changes can be measured directly
3.The stress distribution in the failure plane is uniform
4.The specimen is free to fail on the weakest plane
5.The state of stress at all intermediate stages up to failure is known
6.The test is suitable for accurate research work
Demerits
1.The apparatus is elaborate, costly and bulky
2.The drained test takes a longer period as compared with that in a direct shear test
3.The strain condition in the specimen are not uniform
4.It is not possible to find out the cross sectional area of the specimen accurately under large strains
5.The test simulates only axi symmetric problems
6.The consolidation of the specimen in the test is isotropic whereas in the field, consolidation is generally anisotropic.
Computation of various parameters
1.Post consolidation dimensions
1.Cross sectional area during shearing stage
1.Stresses
Deviator stress=P/A
Principal stresses
4. Compressive strength
The deviator stress at failure is known as the compressive strength of soil
Presentation of results of triaxial test
·Stress-strain curves
·Mohr envelopes in terms of total stress and effective stress
UNCONFINED COMPRESSION TEST
The unconfined compression test is a special form of triaxial test in which the confining pressure is zero. The test can be conducted only on clayey soils which can stand without confinement. There are two types of UCC machines machine with a spring and machine with a proving ring
A compressive force is applied to the specimen till failure. The compressive load can be measured using a proving ring.
Presentation of results
In this test the minor principal stress is zero. The major principal stress is equal to the deviator stress. The Mohr circle can be drawn for stress conditions at failure.
Merits
1.The test is convenient, simple and quick
2.It is ideally suited for measuring the unconsolidated undrained shear strength of intact saturated clays
3.The sensitivity of the soil can be easily determined
Demerits
1.The test cannot be conducted on fissured clays
2.The test may be misleading for soils of which the angle of shearing resistance is not zero.
VANE SHEAR TEST
The undrained strength of soft clays can be determined in a laboratory by vane shear test. The test can also be conducted in the field on the soil at the bottom of bore hole. The apparatus consists of a vertical steel rod having four thin stainless steel blades or vanes fixed at its bottom end. Height of the vane should be equal to twice the diameter. For conducting test in a laboratory, a specimen of diameter 38mm and height 75mm is prepared and fixed to the base of the apparatus. The vane is slowly lowered in to the specimen till the top of the vane is at a depth of 10 to 20 mm below the top of the specimen. The readings of the strain indicator and torque indicator are taken
Shear strength S
Where T =Torque applied
D = Diameter of vane
H1= Height of vane
Merits
1.The test is simple and quick
2.It is ideally suited for determination of the in-situ undrained shear strength of non fissured, fully saturated clay
3.The test can be conveniently used to determine the sensitivity of the soil
Demerits
1.The test cannot be conducted on the fissured clay or the clay containing silt or sand laminations
2.The test does not give accurate results when the failure envelope is not horizontal
4.2 Laboratory Test /field test to determine permeability and consolidation tests.
a) For a field pumping test, a well was sunk through a horizontal stratum of sand 14m thick and underlain by a clay stratum. Two observation wells were sunk at horizontal distances of 16 m and 34 m respectively from the pumping well. The initial position of the water table was 2.2 m below ground level. At a steady-state pumping rate of 1800 litres/min, the drawdowns in the observation wells were found to be 2.45 m and 1.20 m respectively. Calculate the coefficient of permeability of the sand.
Answer;
K = q x Log e (r2)
2
|
2
|
(r1)
r ( h2 - h1 )
Note: q = 1800 Litres / min
r1 = 16m
r2 = 34m
h1 = 14.5 – 2.2 – 2.45 = 9.85m
h2 = 14.5 -2.2 -1.2 = 11.1m
-3
|
1800 x 10 = 30 x 10 = 0.0030
60
K = q x Log e (r2)
2
|
2
|
(r1)
r ( h2 - h1 )
= 0.0030 x log e 34
2
|
2
|
16
r ( 11.1 ) - ( 9.85 )
= 0.0030 x log e ( 2.125 )
r (123.21) – (97.0225)
= 0.0030 x log e ( 2.125 )
r (26.1875)
-4
|
-2
|
= 2.80 x 10 m/s = 1.40 x 10 cm/s
b) A 3.3 m thick layer of saturated clay in the field under a surcharge loading will achieve 90% consolidation in 86 days in double drainage conditions. Find the coefficient of consolidation of the clay.
Drainage Layer
3.3m Clay Layer
Drainage Layer
As a clay layer has two way drainage, d = 3.3
2
H = 1.65m = 165cm t90
= 86 days = 86 x 24 x 60 x 60 seconds
For 90% Consolidation (U = 90%)
T90 = Cv t90
H2
Cv t90 = T90 H2
t90
T90 = 1.781 – 0.933 Log(10) = 0.848
T90 = 0.848
2
|
Cv = 0.848 x (165)
86 x 24 x 60 x 60
= 0.848 x 27225
7430400
= 23086.8
7430400
-3
|
2
|
= 0.00310707364
= 3.10 x 10 cm /s
c) Evaluate the following labortary data to determine the permiability co-efficent at 20 °C for the tested sample.
CONSTANT HEAD METHOD
DATA SHEET
Date Tested: 30 - june -2016
Tested By: Maruf Ahmed
Register Number: Q/CE/16/02/08
Sample Number: B-1, ST-10, 8’-10’
Visual Classification: Brown medium to fine sand, poorly graded, subrounded, dry.
Initial Dry Mass of Soil + Pan (M1) = 1680.0 g
Length of Soil Specimen, L = 17 cm
Diameter of the Soil Specimen (Permeameter), D = 6.4 cm Final Dry Final Dry Mass of Soil + Pan (M2) = 875.6 g
Dry Mass of Soil Specimen (M) = 804.4 g
Volume of Soil Specimen (V) = 546.96 cm3
Dry Density of Soil (ρd) = 1.47 g/cm3
Trial Number
|
Constant Head, h (cm)
|
Elapsed Time, t (seconds)
|
Outflow Volume, Q (cm3)
|
Water Temp., T (C)
|
KT
cm/sec
|
K20
cm/sec
|
1
|
30
|
84
|
750
|
24
|
0.157
|
0.143
|
2
|
50
|
55
|
750
|
24
|
0.144
|
0.131
|
3
|
60
|
48
|
750
|
24
|
0.137
|
0.125
|
4
|
70
|
38
|
750
|
24
|
0.149
|
0.136
|
Average K20= 0.134cm/sec
Note: Use properties of distribution of water issued during the class activity.
values on the Data Sheet.
Dry Mass of Soil Specimen (M) = 804.4 g
M = M1 - M2
= 1680.0g – 875.6g
= 804.4g
Volume of Soil Specimen (V) = 546.96 cm3
Volume of soil used from: V = LA.
Note:
Length of Soil Specimen, L = 17 cm
2
|
π |
A = cross-sectional area of permeameter ( 4 D , D= inside diameter of the permeameter)
π = 3.143
Diameter of the Soil Specimen (Permeameter), D = 6.4 cm
3.143 × 6.4 × 6.4 = 128.73728 = 32.18432
4 4
Volume of Soil Specimen (V) = LA
= 17 × 32.18432
= 547.13 cm3
Dry Density of Soil (ρd) = M
ρd = v
= 804.4
547.13
= 1.47 g/cm3
K T= QL
Ath
Where:
K = coefficient of permeability at temp T, cm/sec.
π |
L = Length of specimen in centimeters
3
|
3
|
A = cross-sectional area of permeameter ( 4 D , D= inside diameter of the permeameter)
Q = Volume of discharge in cm (Assume 1mL = 1 cm )
t = time for discharge in seconds
h= hydraulic head difference across Length L, in cm of water; or it is equal to the vertical distance between the constant funnel head level and chamber overflow level.
1. K T= QL
Ath
Where Q = 750
L= 17
A = 32.18
t = 84
h = 30
= 750 x 17
32.14 x 84 x 30
= 12750
81093.6
= 0.157cm/sec
Reference:
1. https://en.wikipedia.org/wiki/Igneous_rock
3. Dr. Leslie Davison, University of the West of England, Bristol, May 2000
in association with Prof. Sarah Springman, Swiss Federal Technical Institute, Zurich.
in association with Prof. Sarah Springman, Swiss Federal Technical Institute, Zurich.
4. Avery, B.W. (1980) Soil Classification for England and Wales (Higher Categories). Soil Survey Technical Monograph No. 14. Harpenden.
5. Clayden, B. and Hollis, J.M. (1984) Criteria for Differentiating Soil Series. Soil Survey Technical Monograph No. 17. Harpenden.
8. https://en.wikipedia.org/wiki/Igneous_rock
10.
