GE
Various applications of geo-technical engineering are as follows: Foundation design Pavement design Design of earth dam Earth retaining structure Design of embankments Design of underground structures Bearing capacity is one of the most important property considered in foundation design as foundation is important element of all civil engineering structures The area of the foundation will depend upon bearing capacity of soil. If we increase area of foundation, the intensity of load i.e., compressive stress is within limit of the bearing capacity. is the foundation will be safe and problem of settlement is solved. For every structure, building, bridge: highway, dam etc. Soil is ultimate foundation material which support any structure and proper functioning of any structure. Thus, one can say life of structure depends upon the foundation strong will be the foundation more will be the life of structure. So, it is therefore, necessary to have sound knowledge of soil, i.e., bearing capacity of soil, the pattern of stress distribution in the soil beneath the loaded area, the probable settlement of the foundation, effect of ground water and effect of vibration also its shrinkage and swelling etc. A pavement may be of any type rigid or flexible, its performance depends upon the subsoil on which it rests. The thickness of pavement depends upon certain properties of sub soil, which should be determined before the design is made. Also, while designing the pavement various points related with soil like frost, heave a thaw with their related problems of frost damage to pavements, frost penetration depth, remedial measures to prevent it, problem of pumping and suitability of soil as a construction material for constructing highways, railways etc. should be decided. Soil is the only material required for the construction of earth dam thus thorough knowledge of soil mechanics is required. Since various types of soil is used in the construction of the earth dam, it is necessary to determine the soils properties, index properties such density, plasticity characteristics and specific gravity, particle size distribution and gradation of the soil, permeability, consolidation and compaction characteristics and shear strength parameter under various drainage condition. The example of earth retaining strictures are gravity retaining wall, anchored bulk heads and cofferdams. The active and passive earth pressures and the safe critical heights of an open cut form the important properties in the design of earth retaining wall. Permeability of the soil retained behind the wall is also important for the drainage of the retained earth. Thus, knowledge of soil structure interaction is essential to design properly the retaining structures subjected to soil loadings. A thorough knowledge of shear-strength and related properties of soil is essential to design the slope and height of the embankment and cutting. The shear strength of soil reduces due to the seepage of water, this while excavating this factor must be taken into account. Thus, knowledge of soil mechanics is important in design of embankments and excavation to face above situation and problems like seepage, caving in etc. and also action to increase the soil strength and to reduce the seepage forces, action to drain the subsoil water etc. The examples of underground structures include tunnels, underground buildings, drainage structures and pipelines. Thus, for design of such structure a thorough knowledge of soil structure interaction is essential as such structures are subjected to sail loading. Also, one must have knowledge of stearing strength, angle of repose and frictional coefficient is essential and to solve problem such as seepage, caving in etc. and also to improve the properties of soil to increase shear strength and reduce seepage. Thus, from above examples it is clear that the soil mechanics is important in various field of construction. Single grained structure Honeycomb structure Flocculent structure Dispersed structure Composite structure When each panicle of soil scales out of suspension separately and independently then such soil structure is known as single grained structure. The gravitational forces acting on the particles of soil cases the settlement. The specific surface of all particles is comparatively less, thus the surface forces are too small to be considered. These surface forces are neglected for all practical purpose in case of course grained soils (Diameter> 0.02 m). Such soil particle has high void ratio when the deposits in a loose state and low void ration in a dense state. Honeycomb structure is seen in the soil particles having diameter between 0.0002-0.02 mm, usually observed in silts. In case of such soils, both gravitational forces and surface forces plays an important role. The soil particles settle due to gravitational forces and the surface forces at the contact area, are large enough compared to the submerged weighs to prevent the grains from rolling down immediately. The grains which are in contact are beld together until miniature arches are formed, with relatively large void space which is formed as honeycomb structure. In such type of structure comparatively large amount of water is enclosed within voids. Such type of structure has high voids ratio. Flocculent structure is formed when there is an edge contact between the clay platelets. The attractive electrical forces between adjacent soil particles at the time of deposition, is the basic reason for the formation of such type of structure. As the concentration of dissolved minerals is the water increases, the tendency of flocculation also increases. Flocculent structures are usually observed in clays with fine particles. Dispersed structure is also seen in clays with fine particles. The repulsion electrical forces between adjacent soil particles at the time of deposition are responsible to form dispersed structure. Usually along the coast in narrow tidal plains marine clays are found. Marine clay may contain organic matter and also very soft clay. Marine clay has low shear strength and high compressibility. Because of above properties, such clay has problems to be used as construction material or as a foundation material. Black cotton soils are usually found in Maharashtra, Madhya Pradesh, Karnataka, Andhra Pradesh, Tamil Nada and Uttar Pradesh. Black cotton soil (Indian name) is also known as Expansive soils. In India they cover an area of approximately 3,00,500 Sq. Km. This soil is formed from basalt or trap. Black cotton soil is characterized by swelling and shrinkage because it contains clay mineral montmorillonite. As the volume of black cotton soil changes it is most susceptible to damage the light loaded structure. Under-reamed piles are considered most suitable as foundations for houses and other light structures constructed en such soil. These piles are taken to depths below the zone of seasonal variation in moisture content. These soils are usually found in Kerala, Karnataka, Maharashtra, Orissa and west Bengal. In India they cover an area of about 100,000 Sq. Km. The decomposition of rock, removal of the bases and silica and formation of oxides of iron and aluminium at the top of the soil profile are responsible for formation of laterites. Like all residual soils, laterites show variability in their properties, depending upon the stage of weathering. Alluvial soils are formed in large parts of Northern India lying North of Vindhya satpura range in the Indo-Gangetic and Brahmaputra flood plains. The alluvial deposits extend from Assam in the East to Punjab in the west. The deposits have alternating layers of sand, silt and clay. Such soils are found in large parts of Rajasthan. They cover an area of about 500,000 sq.m. They are formed under highly arid conditions. Dune sand is a non-plastic uniformly graded, fine sand. Some of the problems associated with this soil are stabilization, settlement perviousness etc. Boulder deposits are found in the sub-Himalayan regions of Himachal Pradesh and Uttar Pradesh. River flowing in hilly terrains and near foot hills are responsible to deposit large quantities of boulders. The properties of these deposits depend on the relative proportions of the boulders and the soil matrix. These deposits have higher angles of shearing resistance. By visual inspection one can judge the coarse grain soil by its grading and can classify soil as well-graded, uniformly graded or poorly graded. Grains can be defined on the field based on their shape, usually term used to describe the grain shape are angular, sub-angular and rounded. Based on the colour of soil at field, soil can be expressed as white, yellow, brown, red brown etc. The term compact and loose are used to determine in-situ strength of deposit of coarse-grained soil. The structure of coarse-grained soils recognized in the field can be described as homogeneous or stratified. If soil contains some organic matter; it should be indicated. If it has some fines, and not causing cohesion, it should also be noted. Index properties such as bulk density, specific gravity, void ratio, porosity, water content, degree of saturation etc. These properties affect the other mere complex properties such as permeability, shear strength, compressibility, bearing capacity etc. Hence index properties form the important basic step of investigation. Most of the index properties are determined in the laboratory, but sometimes field tests are also deemed to be important. For collecting the samples for determination of index properties, the site investigation and subsoil exploration is thus found to be necessary. This is the most preliminary purpose of soil investigation. Bearing capacity goes on increasing with depth in most soils. As we go deeper and deeper, we encounter soil with more and more bearing strength. The bearing strength required for a particular structure must be available. Thus, the bearing capacity is estimated at a particular depth and then it can be actually tested by various tests available, of which plate load test is an important one. Thus, the site investigations are very important for determining the bearing capacity of soil. Soil contains different layers or strata below the surface and are arranged in different ways. The strata may be continuous, displaced by a crack or fault, at different angles, separated by a dyke arranged in the form of folds etc. The arrangement of strata hollows the ground level is called stratification. The properties of the soil like permeability or bearing capacity depend on the orientation and nature of the stratification. When we take boreholes at the foundation level, or when we dig bore holes or test-pits, this arrangement is clearly visible by the side of the bore holes or test-pits. Thus, by taking numerous boreholes, a geological map of the underground strata can be prepared. This will give a complete idea of the stratification of soil. Thus, investigations enable us to find the hidden features below the ground level. Seepage is important in case of earth danis, wears and aprons on permeable foundation. Soil which has same permeability in y direction i.e., in gravitational direction, and in x direction i.e., direction perpendicular to gravity is called isotropic soil. Soil which has different coefficients of permeability Kx and Ky is called anisotropic soil. The net effect can be considered as a two-dimensional flow which can be analysed by Laplace equation and flow-net technique. The effective flow will be the seepage flow. During detailed investigation of soil and subsoil, field tests will give realistic picture reinforced by laboratory tests conducted on soil samples, both disturbed and undisturbed, obtained from sub-soil explorations. Thus, for seepage control, the detailed investigations will give a fair basis for further analysis. Problem soils are those which have uncommon behaviour when confronted with various parameters whether natural or artificial. Mainly two conditions come under this category When water seeps through sand and comes to the surface, the head with which it comes out of the surface is called the exit gradient. Due to large increase in exist gradient, more than the critical gradient, effective submerged weight of sand may become zero due to upward force of seepage. Thus, de sand comes to the surface continuously and appears to boil. This condition called the quick sand condition and if it occurs below foundations, it will be dangerous. This soil is not weak in bearing capacity, nor it is excessively permeable. The problem in black cotton soil is the disproportionate volume change which occurs upon change in moisture content. This soil swells to a very high degree, even up to double the original volume upon double the original volume upon being saturated with moisture and shrinks equally largely when it loses the moisture. It may become even up to half its saturated volume when dried completely. Due to this property, the foundations resting on this type of soil will be subjected to large alternate movements during rainy season and summer. Hence special remedial measures must be taken when it is inevitable to build foundations on black cotton soil. Thus, brings out the necessity of soil and subsoil investigations. Simplest method of soil stabilization is compaction. The term stabilization is generally used when compaction is enhanced by some other method or when it is enhanced by adding some substance as an admixture. In any case, he its compaction or stabilization, the properties of soil such as maximum dry density (MDD), Optimum Moisture Content (OMC), permeability, drainage characteristic etc. must be determined to a fine degree. Doing such an investigation it will achieve much desired effects to a large extent within the least expense. Even the decision of whether to go for compaction or not, whether simple compaction or stabilization is required etc. depend on investigations of soil and subsoil carried out in details to a meticulous degree of perfection. The soil mass in general is a three-phase system composed of soil, liquid and gaseous matter. The solid phase comprises of mineral, organic matter or both. The mineral portion consists of particles of different size and shapes. The organic fraction is the plant and animal residue which may be present in various stages of decomposition. The solids enclose the open spaces termed as voids. The liquid phase is generally water and fills partly or wholly the voids. The gaseous phase, usually air, occupies the voids not filled by water. The relative volume wise and weight wise proportions of the three phases in a soil mass are important factors influencing its physical properties. It is therefore necessary to study them. Though the three phases precut cannot be separated as shown in below Fig. for better understanding they are shown as occupying separate spaces. The diagrammatic representation of the different phase present in a soil mass is called the phase diagram. When it is fully saturated i.e., all the voids are filled with water and thus gaseous phase is absent and the soil becomes a two-phase system. This property depends upon; The mode of soil formation. Soil history Soil structure. Such properties are usually determined by undisturbed samples or preferably from in-situ tests. This property depends upon does not individual grains and depend on the mode of soil formation. Such properties are usually determined by disturbed samples. Determination of water content by oven-drying method as per IS code 1S-2809-1972 This is the commonly adopted and simplest method for determination of water content of a soil sample in the laboratory. The method basically consists of drying a weighed moist sample of soil, in an oven at a controlled temperature for a period of 24 hours, after which the dry weight of the sample is taken. The drying of soil is recommended at a temperature of 105°C 110°C as temperatures M higher than 110°C may break the crystalline structure of clay particles result in loss of water of crystallization thus giving wrong results. A lower temperature of 60° is recommended for highly organic soils as at 110°C, oxidation of organic matter may take place. Sand and gravels require less time to dry i.e., 4 to 6 hours but routine laboratory procedure is fo. drying for 24 hours at 105°C-110°C. A clean, non-corrodible container is weighed within 0.01 gm accuracy. About 30-40 gm of moist soil sample is placed in it and weighed accurately. It is then placed in the oven for drying at 110°C for 24 hours. In order to determine the plastic limit about 15 gm of air-dried soil sample passing through IS sieve 425 u is taken and is mixed with a sufficient quantity of water which would enable the soil mass to become plastic enough to be easily shaped into a ball. A portion of the ball is taken and rolled on a glass plate with the palm of the hand into a thread of uniform diameter. When a diameter of 3 mmn is reached, the soil is remoulded into a ball. The process of making the thread and remoulding is continued till the sample at a diameter of 3 mm just start crumbling. Some of the crumbled pieces are then taken for water content determination by oven drying method. The test is repeated twice more with fresh samples and the average of the three values is taken as the plastic limit. A steel rod of 3 nun diameter kept by the side of the glass plate helps in comparing the thread diameter easily. The core cutter method consists of driving a core cutter of known volume usually 1000 CC into the soil after placing it on cleaned soil surface. The core cutter is usually provided with 125 mm high dolly. The driving of core cutter is accomplished by hitting the dolly mounted on the core cutter with the rammer. The cutter filled with the soil is removed by cutting under it with a knife or sharp edge. The extra soil is trimmed off. The cutter with the soil is weighed. The volume of the core cutter is calculated from the inner dimensions. The weight of empty core-cutter is also taken. Then the inside unit weight is determined by dividing the weight of soil in the core-cutter by the volume of the core-cutter. For determining the dry unit weight, a piece of the soil is taken and its water content determined by oven drying method. Then the dry density can be found from the bulk density as follow: Bulk density 
=mass of wet soil / volume of core cutter About 30 gms of soil sample passing 425-micron sieve is taken in an evaporating disk. The soil is mixed with sufficient quantity of water to bring the soil to a consistency that it may flow. The soil mixture is placed in the shrinkage dish in three equal quantities so as to fill the dish. The excess soil is removed and the dish is weighed with the soil. The soil pat is allowed to dry till the colour changes from dark to light. The dish is placed in the oven at 110°C till its weight become constant. The shrinkage dish is weighed with dry sample and the volume of dry pat of soil is measured displacement of mercury. The shrinkage limit is calculated as shown in Fig. Fig. shows the arrangement for shrinkage limit test. Fig. shows the phase diagrams. Fig represents the soil sample in plastic state which fill the container of know volume V1 and weighs w1. As the sample is gradually dried, the water content at a certain stage becomes equal to the shrinkage limits as in Fig. This method can be used in both field as well as in laboratory. The method makes use of fact that when water reacts with calcium carbide (CaC2) acetylene gas (C2H2) is generated. CaC2+2H2O=C2H2+Ca (OH)2 Pressure is exerted by acetylene gas produced. The instrument used in this method is rapid moisture tester. The dial gauge attached to the moisture tester is used to measure this pressure. The soil sample of 6 grams is taken in the test cylinder containing calcium carbide. The soil sample is required to be ground and pulverized. The steel halls are also used to serve the purpose in case of cohesive and plastic soils. The quantity of gas produced is indicated on the dial gauge in terms of pressure. From calibrated scale of pressure gauge the moisture content (m) based on total mass is determined. The water content (w) based on dry mass is calculated as, The prepared sample is completely dried in sun or by air drying. Its strength is tested by breaking lump between fingers Resistance to breaking, termed as dry strength is a measure of the plasticity and is considerably influenced by the colloidal fraction content of the soil. If the dry sample can be easily powdered it is said to have low dry strength, thus indicates silt or sandy silt. If considerable finger pressure is required to break the lump, it has medium dry strength, thus indicates silty clays and clays of low plasticity. If the lump cannot be powered by fingers at all, it has a high dry strength which represents a lightly plastic clay. The presence of water-soluble cementing materials, such as calcium carbonate or iron oxides, may also cause high dry strength. Soil with high strength is treated with a little line hydrochloric acid. A strong reaction indicates that the strength may be due lo calcium carbonate as cementing agent rather than colloidal clay.
Unit - 1
Introduction and Index Properties
Q1) What are the applications of Geotechnical Engineering to Civil Engineering?
A1)
1. Foundation design:
2. Pavement Design:
3. Design of Earth Dam
4. Earth Retaining Structure:
5. Design of Embankments:
6. Design of Underground Structures:
Q2) What are the types of Soil structure?
A2) The following types of soil structure are generally recognized
1. Single grained structure:
Fig. Single grained structure
2. Honeycomb structure:
Fig. Honeycomb structure
3. Flocculent structure:
Fig. Flocculent structure
4. Dispersed structure:
Fig. Dispersed structure
Q3) Which are the major soil deposits in India?
A3) The major soil deposits in India are as follows:
1.Marine deposits:
2. Black cotton soil:
3. Laterites and lateritic soil
4. Alluvial deposits
5. Desert soils
6. Boulder deposits
Q4) What are the identification methods of coarse-grained soil?
A4) Grading:
Grain shape:
Colour:
Strength and structure:
Presence of fines:
Q5) What is the purpose of soil exploration?
A5) 1. For finding Index properties:
2. To determine bearing capacity for foundation design:
3. To know stratification:
4. For seepage control:
5. For treating problem soils:
(a) The quick sand condition
(b) The black cotton soil
6. For enhancing properties by compaction and stabilization:
Q6) What is three phase soil system?
A6)
Q7) What are the index properties of soil?
A7) The index properties are sometimes divided into two:
1) Properties of soil mass
2) The properties of individual particle size.
1) Properties of soil mass:
2) The properties of individual particle size:
Q8) Explain Over drying method?
A8)
Q9) Explain plastic limit?
A9)
Fig.: Plastic limit determination
Q10) Explain Core cutter method?
A10)
ρ= 
(g/cm3)
Bulk unit weight, r= 9.81 ρ kN/m
Where w=water content
The core-cutter is shown in Fig.
Fig. Core cutter
Q11) Explain Shrinkage limit?
A11)
Fig. Shrinkage limit apparatus
Q12) Explain Calcium Carbide method?
A12)
W = 
W= 
x 100 %
Q13) Explain dry strength test?
A13)
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