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CHAPTER: 1
SOIL MECHANICS( B.Tech. Hons.Civil) Question: 1. Describe in Detail that the soil is used as construction material? Ans: The soil can be considered as the oldest and the most complex of the construction materials used by engineers. Unless if the structure is built on hard rock, every structure, whether it is a building of any kind, a bridge, a dam, a railroad, an airport, or a hydraulic structure, rest on soil therefore, the choice of an adequate foundation on the soil is must for construction of project. The stability and function of a structure depend upon the behavior of the soil upon which it is built. Because of ignorance of the principles of soil mechanics, Engineers have been faced, in the past, in various parts of the world with an increasing number of failures due to following problems.
- Unanticipated action of water.
- Frost action in soils.
- Unexpected settlements of soils.
- Lateral displacement of soil.
- Other unexpected performance of the soil. Many earth dams have collapsed because engineers were unable to find the accurate
performance of compacted soil. The collapse of tunnels, bridge piers and abutments, and the failure of many earth retaining structures and various structures have been occurred because Engineers were unable to evaluate satisfactory how much pressure this soil would exert on these structures under various conditions. Differential settlements of the foundations under large engineering structures were directly responsible for serious structural damage. Q : 2 Explains that the Problems/Properties of soils and foundation are very difficult and Complex as compared with the superstructure. Ans. The mechanical properties of soils are more complex and difficult to determine than those of steel, concrete, or wood. No material has greater variation of properties than soil, because it is not a manufactured standard product like steel. This is because the soil with which the engineer must work was placed by nature in a great variety of kinds and conditions. Thus it can be understood that soils produce the most serious problems of design because it is not homogeneous. Soil investigations and knowledge of the physical and mechanical properties of soil can help to protect the owner of a building and the engineer in charge from unforeseeable conditions and the troubles that usually occurred to them. In the course of time engineers have learned that the problems dealing with soils and foundations are
once, that the “Opponent Soil” has buried the results of their work; and that the “Opponent Water” flowing out of every pore of the soil and every hole in the soil, has washed away the results of all their efforts. It is therefore the duty of every engineer who erects structures supported on soil to understand clearly that water and soil are natural opponents. Moreover, because the civil engineer in charge is the man who is responsible for the final success or failure of a structural project, it is also his duty to gain a proper and thorough knowledge and understanding of the principles of mechanics. In modern times the civil engineer should rely less upon rule of thumb; Soil mechanics has developed from practical necessity. Since its development it has been proved that soil mechanics has saved this nation millions of dollars. If we think about the damaged roads and other structures which have failed, the reconstruction of which requires much money and effort, shows us the important of soil mechanics. CHAPTER: 3 SOIL MECHANICS Question: 1. Define soil mechanics and explain it in detail. Ans: Soil mechanics can be defined as that discipline of engineering sciences which studies
theoretically and practically soils, by means of which and upon which engineers build their structures. Soil mechanics sometimes also called Geo- technique. The soil mechanics treats soil as a construction material. Behavior of soil under static and dynamic load, as well as under the influence of water and temperature, is studied theoretically and experimentally by using knowledge of soil mechanics, it also studies the mutual interaction of structure and soil. Soil mechanics is the application of the laws of mechanics and hydraulics to engineering problems dealing with sediments and other unconsolidated accumulations of solid particles produced by the mechanical and chemical disintegration of rocks regardless of whether or not they contain an admixture of organic. “Soil Mechanics” is that discipline of engineering science which deals with the properties, behavior & performance of soil as a structural material. The practice of engineering which applies the principles of soil mechanics to the design of engineering structures is called soil engineering. Purpose: The purpose of soil mechanics is to replace by scientific methods the design applied in foundation engineering in the past. Q: 2. Describe the objective of soil mechanics in detail.
Question: 3. Explain that what problems related to soil should be considered before execution of any project? Ans: Following are some soil mechanics problems: A. How deep borings for soil exploration should be made. B. What is the bearing capacity of a soil on its surface and at carious depths to carry various loads? C. What is the load to be applied on a particular soil? D. What is the intensity and what is the stress distribution in a soil induced by various kinds of loading. E. How thick should be a layer of a good soil over a poor one in order to prevent other foundation form punching. F. Does a soil possess properties (friction and cohesion) which will assure satisfactory stability for foundations? G. How much counterweight should be placed as a remedial measure against lateral motion of soil, masses in order to maintain the stability of a structure? H. When does settlement cease. I. What is the mutual interaction between soil and foundation, and what kinds and magnitude stresses are induced in the foundation and soil of a rigid highway or runway pavement due to schemes under consideration?
J. What is the frost penetration depth? K. What will be the effect on pavement of frost heave and thaw. L. What remedial measures can be taken to prevent frost damage? M. How suitable is a particular soil as a base for highways, railway and the construction of dams. N. Does the soil in question swell, or shrink and how much. O. What treatment should be given to such soils? P. To what degrees can a waterlogged soil be drained? CHAPTER: 4 ( B. Tech Hons. Civil) SOIL MECHANICS Q: 1. Define soil and write a detail note on its formation. Ans. Definition: Soil is a material upon which or by which engineer build his structure.
In soil engineering a sharp demarcation between rock and soil is no longer made. In this sense the term soil is adopted and used also in soil mechanics, and in this book only the engineer’s definition of the terms soil is to be understood from as engineer’s viewpoint( soil is a material by means of which and upon which he builds his structures) c) Formation of soil: d) Soil which is a complex mixture of inorganic matter that may or not contain decomposed organic residues and other substances and which blankets the earth’s crust, is formed by the process f weathering, (disintegration and decomposition) of rocks and minerals through the action of many natural physical or mechanical and chemical agents into smaller and smaller particles The factors of weathering in the process of soil formation may be atmospheric, such as the work of temperature wind and water erosion and transportation by the water and glaciers; plant and animal life;
Question: 2. Distinguish between Glacial Soil & Alluvial Soil: Ans. A). Glacial Soils: The soil, which have been transported & deposited by glaciers. The glacial ice sheet filled up river valleys with the so-called glacial drift. Glacial drift is the glacial deposit formal types of the superficial material of rock debris of any sort, handled in any way, by the glacier-for example by erosion, transportation, deposition from ice, or running melt waters emanating from the ice. Glacial deposits consist of boulders, rock fragment, gravel, sand, silt, and clay in various proportions. The position of the southern boundary of the continental glacier is distinctively recognized by the geologic feature called the terminal moraine. The landform of the terminal moraine consisting of glacial debris material is characterized by irregular, hills. Their width varies from one to two miles, and their height can be about 30m. One of the engineering aspects of terminal moraine soil materials containing salty clay and clay is the disposal of domestic wastes by means of domestic septic tanks. Septic tanks built in clayey soils, soils which by nature are of low permeability, may function improperly, thus creating unpleasant odors another engineering aspect of glacial soils relative to foundation engineering is the thickness of the glacial drift. One ridges of bedrock the glacial drift may be
sediment (silt) and a thinner and darker verve which is the winter sediment (clay) when the finer sediment settled out at low velocities of flow beneath the frozen surface of the lake. This brief review on glacial soils may be summarized like this; glacial soils are important sources of soil as a construction material for earthwork, as a foundation material and as an aggregate for concrete. b) Residual Soils: Residual soils are those which have been left in place as a result of decay of the underlying parent rock below the ground surface. In glaciated areas residual soils are buried by glacial drift because there may be more than one terminal moraine. The parent materials of soils are igneous rocks such as granite (or) basalt and sedimentary rocks such as limestone and sandstone. c) Wind-Borne Soils: Under this group two kinds of soils material are present namely; the loess and dune sand. wind-borne soils are ones which have been transported and laid down by atmospheric currents such as winds, loess is wind-blown silty clay, light in color porous and coherent ,loess as a construction material is relatively unknown to engineers. Loess often may turn out to be a very dangerous material for dams’ highways and as a support of foundations
particularly when wet dunes develop and where loose sand is exposed to wind. Question: 4. Define the following?
- Bed rock
- Boulders
- Boulder clay
- Calcareous
- Caliches
- Cobbles
- Gumbo
- Humus
- Loam
- Loess DEFINITIONS:
- Bed Rock: Bed Rock Is any layer of rock either at the surface or beneath superficial deposits of soil. Bedrock may be soft or hard.
- Boulders: Boulders Are detached rock fragments larger than 300mm in diameter. Boulder clay is a mixture of an unstratified semi metal deposit of glacial clay, containing unsorted rock fragment of all sizes ranging from boulders, Cobbles, gravel, sand, and clay, the particles of which are cemented by calcium carbonate.
- Boulder Clay: It is a mixture of an unstratified semi metal deposit of glacial clay. Containing unsorted rock fragments of sizes ranging from boulders, cobbles, and gravel to finely pulverized clay material.
- Loam: It is a mixture of sand, silt, and clay, sometimes containing some organic matter, such as humus. The terms sand, silt, and clay here refer to the particle size.
- Loess: Denotes a uniform, and usually range between 0.01mm to 0.05mm. The color of loess is yellowish light brown. Loess is encountered in dry continental regions. Slopes of cuts made in it are able to stand nearly vertically. Question: 5. a ) Differentiate between Cohesive & Non-Cohesive Soil ‘b’ Define the following marl, mud, peat, pebbles, quicksand. Ans: a) Cohesive Soils: The soils possessing cohesion are called cohesive soils.there are two types of cohesions (1) True cohesion the intermolecular attraction of the soil particles for each other throughout the soil mass in called true cohesion. 2 Apparent Cohesion: Binding of the soil mass together by the action of surface tension farces of the soil moisture is called apparent. Non-Cohesive Soils: The soils which have been formed by the uncemented weathered rock particles is called Non-Cohesive Soils for example gravel sand. B).
- Marl: Is a very loose term denoting deposits which consist of mixtures of sands, or clays or loam. The proportion of carbonate lime, however, may not fall below about 15% nor dos the quantity of clay rise above 75%.
- Mud: Designates a mixture of silt or clay with water. The constancy of mud is an almost fluid mass.
- Peat: Is an organic soil formed of vegetal matter under conditions of excessive moisture, as found in swamps. Peat is very compressible, and therefore unsuitable for supporting even the lightest foundations.
- Pebbles: Are a constituent part of gravels with diameters about 50mm to 75mm.
- Quicksand: Is not a special type of soil, but a condition. Any granular material through which an upward flow of water takes place may become “Quick” under proper hydraulic conditions. Q - 6 Write a note on the Following (1) Soil Profile (2) Lime Soil (3) Hard Pan (4) Till Ans (1) Soil Profile: It is a vertical cross section of the actual soil strata at a given site showing a natural sequence and thickness of soil layers below the ground surface
Subject Soil MECHANICS B.TECH (HONs. Civil) 2006 Some Physical Properties of Soil Q-1. Define the following (1) mechanical composition of a soil (2) soil phases (3) soil texture (4) specific gravity of a soil. Ans. mechanical composition of a soil The physical makeup of a mineral soil is termed as mechanical composition
2. Soil Phases Definition. Any homogeneous part of a soil system different from other parts of the system and separated from them by abrupt transition such as the solid soil particles and liquid water. Soil system ordinarily has three phases namely a. The solid phase b. The liquid phase. c. The gaseous or vapor. d. 3. Soil Structure. Definition: the shape, size and distribution of soil particles and the proportion of soil material of each size present in any given sample is called the soil structure terzaghi described three types of structure given below.
a. Granular or single – grained structures b. Honeycomb or cellular structures and c. Flocculent structures.
- Specific Gravity The specific gravity G of dry solids of a soil is defined as the ration of the density Ys of a given volume of the soil solids to the greatest density Yw (at +4°c) of an equal volume of pure water. G = Weight of soil particles in grams = Ys Ws (1) (Volume of soil particles) (1.000) ______ Vs Ys yw Where Ys = unit weight of soil solids = Ws = _Weight of Solid (Soil) Vs Vol. of Soil Yw = unit weight of water Ws = VsYs also Vs = Ws ________________________ (2) G.W The quantity G is dimensionless and it shows how many times heavier the substance of the solid
