Correct Answer - Option 3 : Triaxial test

__Concept-__

Shear strength of soil is given by τ’ = C’ + σ’ tan φ

Where τ’ = Effective shear strength, C’ = Effective cohesion, σ’ = Effective stress, φ = Angle of internal friction

**Here C’ and φ are the shear strength parameter of the soil.**

Triaxial shear strength test on soil measures the mechanical properties of the soil.

In this test, soil sample is subjected to stress, such that the stress resulted in one direction will be different in perpendicular direction.

The material properties of the soil like shear resistance, cohesion and angle of internal friction are determined from this test. The test is most widely used and is suitable for all types of soils.

**Vane shear test** –

It is used to determine the undrained shear strength of soils especially soft clays.

This test can be done in laboratory or in the field directly on the ground. Vane shear test gives accurate results for soils of low shear strength (less than 0.3 kg/cm^{2}).

**Compaction test-**

Compaction test of soil is carried out using Proctor’s test to understand compaction characteristics of different soils with change in moisture content.

Compaction of soil is the optimal moisture content at which a given soil type becomes most dense and achieve its maximum dry density by removal of air voids.