. OBJECTIVE

To determine the parameter of shear strength of soil, cohesion, c and angle of friction, .

INTRODUCTION

The test is carried out on either undisturbed samples or remolded samples. To facilitate the remolding purpose, a soil sample may be compacted at optimum moisture content in aCompaction mould. Then specimen for the direct shear test could be obtained using the correctcutter provided. Alternatively, sand sample can be placed in a dry state at a required density, in the assembled shear box.

A normal load is applied to the specimen and the specimen is sheared across the pre-determined horizontal plane between the two halves of the shear box. Measurements of shear load, shear displacement and normal displacement are recorded. The test is repeated foe two or more identical specimens under different normal loads. From the results, the shear strength parameters can be determined.

Apparatus

PROCEDURES1.Internal measurement is verify by using vernier calipers. The length of the sides, L andthe overall depth, B.2.Base plate is fixed inside the shear box. Then porous plate is put on the base plate. Perforated grid plate is fitted over porous so that the grid plates should be at right anglesto the direction shear.3.Two halves of the shear boxis fixed by means of fixing screws.4.Forsandysoil,compactsoilinlayerstotherequired density in shear box.5.Mount the shear box assembly on the loading frame.

6.The dial is set of the proving ring tozero7.The loading yoke is placed on the loading pad rdg7olpoiuytrewqThe correct loading is applied to the hanger pad.

9.Carefully the screws clamping the upper half is removed to the lower half.10.The test is conducted by applying horizontal shear load to failure. Rate strain should be0.2mm/min11.Readings for the Shear force is taken at every 0.5mm displacement.Conduct test on three identical soil samples under different vertical compressive stresses,

7.0DISCUSSIONThe direct shear test is suited to the relatively rapid determination of the the parameter of the shear strength of soil, to find the value of cohesion and also to find the angle of friction. At the end of result we had plot the graph, which is the graph of shear stress versus strain. The graph will gained us to value offriction angle. (Refer to the graph).At these 3 samples which are 1.75kg, 2.5 kg and 3.25kg there are no error data obtained. The value obtained from the dial gauge showed increases directly. This is because the dial gauge reading has increased the time by the time. The cohesion of soil and the angle of friction of soil are determined. The angle of friction isthe angle of the linear line produced (lines slope). From the graph, thecohesion of soil is 0.0kN/m2as the sample of soil used is sand. As we know that sand is type of coarse grained soil andit is assume cohesion less. Form the graph, the angle of friction is 35.The direct shear test hasadvantages and disadvantages. It is simple and fast especially for sands. The failure that occurs isalong a single surface, which approximatesobserved slips or shear type failure in natural soils

8.0CONCLUSIONDirect shear test is useful when cohesion less soils are to be tested. In this test thefailure plane is forced to occur at a predetermined location where both normal and shearstresses are acting; the sample is placed in a closed shear box, fixed at the base with the topfree to translate under a horizontal force. The two portions of the box are spaced by using spacing screws to reduce the friction. The space should be at least as large as the largest sandparticle. Theboxis thenplacedin thedirect shearapparatus, andincreasing horizontal load is applied with constant corresponding vertical load, and the horizontal deformation shall be recorded by using the dial gage. For each test shear stress-strain diagram is drawn in order to find out the ultimate stress, then the shear failure envelope is drawn by relating each ultimate shear stress to the normal stress corresponding to it in at least three tests. The direct shear test can be used to measure the effective stress parameters of any type of soil as long as the pore pressure induced by the normal force and the shear force candissipate with time. For the experiment we use the clean sands as a sample, so there is noproblem asthe porepressure dissipates readily.However, inthe caseof highly plasticclays,it is merely necessary to have asuitable strain rate so that the porepressure can dissipate withtime.Direct shear tests can be performed under several conditions. The sample isnormally saturated before the test is run. The test can be run at the in-situ moisture content.Before we find the value of cohesion and friction angle, we must plot the graph from the datathat we get from the experiment. The results of the tests on each specimen are plotted on agraph with the peak (or residual) stress on the x-axis and the confining stress on the y-axis.The y-intercept of the curve which fits the test results is the cohesion, and the slope of theline or curve is the friction angle.

Referene

[1] Importance of shear strength of soil | Civil Engineering Terms. 2015.Importance of shear strength of soil | Civil Engineering Terms. [ONLINE] Available at:http://www.civilengineeringterms.com/soil-mechanics-2/importance-of-shear-strength-of-soil/. [Accessed 05 June 2015].