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

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