SHEAR STRENGTH TEST OF SOIL – ADVANTAGES, LIMITATIONS & APPLICABILITY

SHEAR STRENGTH TEST OF SOIL – ADVANTAGES, LIMITATIONS & APPLICABILITY

SHEAR STRENGTH TEST OF SOIL

The choice of appropriate shear strength tests for a particular project depends on the soil type, whether the parameters will be used in a total or effective stress analysis, and the relative importance of the structure. Common laboratory tests include direct shear, triaxial, unconfined compression, and laboratory vane shear test. The applicability, advantages and disadvantages for each test are summarized in following table.

TABLE

SUMMARY OF COMMON SHEAR STRENGTH TESTS
Test Type	Applicability	Advantages	Disadvantages
Direct Shear Test	a. Effective strength parameters for coarse grained and fine grained soils	a. Simple and inexpensive b. Thin sample allows for rapid drainage of fine grained soils	a. Only for drained conditions b. Failure plane forced to occur at joint in box c. Non-uniform distribution of stress and strain d. No stress-strain data
Triaxial Shear Test	a. Effective and total strength parameters for coarse-grained and fine-grained soils b. Compared to direct shear tests, triaxial tests are preferred for fine-grained soils	a. Easy to control drainage b. Useful stress-strain data c. Can consolidate sample hydrostatically or to in situ Ko state of stress d. Can simulate various loading conditions	a. Apparatus more complicated than other types of tests b. Drained tests on fine grained soils must be sheared very slowly
Unconfined Compression Test	a. Undrained shear strength of 100% saturated samples of homogenous, unfissured clay b. Not suitable as the only basis for design on critical projects	a. Very rapid and inexpensive	a. Not applicable to soils with fissures, silt seams, varves, other defects, or less than 100% saturation b. Sample disturbance not systematially accounted for
Lab Vane Shear Test	a. Undrained shear strength of 100% saturated samples of homogenous, unfissured clay b. Not suitable as the only basis for design on critical projects	a. Very rapid and inexpensive	a. Not applicable to soils with fissures, silt seams, varves, other defects, or less than 100% saturation b. Sample disturbance not systematially accounted for