HOW TO DETERMINE THE STABILITY OF THE EARTH SLOPES.

The resistance in sliding of grain particles of a soil mass depends upon the angle of internal friction. It is usually considered that the value of the internal friction is almost independent of the normal pressure but varies with the degree of packing of the particles, ie with the density. The soils subjected to the higher normal stresses will have lower moisture contents and higher bulk densities at failure than those subjected to lower normal stresses and the angle of internal friction may thus change. The true angle of internal friction of clay is seldom zero and may be as much as 26degree . The angle of internal friction of granular soils are determined with description and outlines of some of the more important tests necessary for required density and the moisture content like, Proctor compaction test, Moisture content determination, Measurements of compaction in the field, Consolidation test, Liquid limit test, Plastic limit test. The behavior of soil under loading is very complex, Soils of different types differs considerably in their resistance to deformation when stressed and such deformation depends upon the moisture content, bulk density, angle of internal friction of the soils and the method in which the load is applied. The tests used to determine the strength properties of soil can be divided into three broad groups, Shear tests, Bearing tests and the penetration tests. The object of shear tests is to determine, (1) The ultimate bearing capacity of the soil mass for the design of footings and other foundations (2) The stability of the earth slopes (3) The estimation of earth pressure on retaining walls, footings and sheet pilings, etc and (4) For the design of thickness of airfield and road pavements. It determine the value of the apparent cohesion and angle of shearing resistance of soil under known test conditions. All stability in soil is derived from the shearing strength. The shear resistance is composed of two parts, the resistance of soil grains to sliding over each other and the cohesion existing between the soil particles. The resistance to sliding is dependent upon the angle of internal friction. A granular soil develop friction between the soil particles only under the application of a normal load but in cohesive soil there is resistance against sliding of the cohesive soils and is called cohesion. Clays have a resistance to shearing due to their cohesive strength. Shearing strength is dependent on and varies directly as the coefficient of friction and cohesion of the soil. There are several methods of testing the shear strength of a soil in a laboratory and the most common being the, Shear box test, Triaxial test, Unconfined compression test and the Vane test.