4. DIRECT SHEAR TEST ON SAND
The shear strength, S, of sand can be expressed by the equation:
S= σ’ tan ϕ
Where:
S= shear strength.
σ’ = effective normal stress.
ϕ = angle of friction of soil.
The angle of friction, ϕ, is a function of the relative density, of compaction of sand,
grain size, shape and distribution in a given soil mass.
Equipment:
1. Direct shear test machine (strain controlled)
2. Balance sensitive to 0.1 g
3. Large porcelain evaporating dish
4. Tamper (for compacting sand in the direct shear box).
5. Spoon
Figure below shows a direct shear test machine. It consists primarily of a direct shear box
which holds the soil specimen, it is split into two halves (top and bottom), The top and
bottom halves of the shear box can be held together by two vertical pins; electric load cell to
measure the horizontal load applied to the specimen; two transducer (one horizontal and one
vertical) to measure the deformation of the soil during the test; and a yoke by which a
vertical load can be applied to the soil specimen. A horizontal load to the top half of the
shear box is applied by a motor and gear arrangement. In a strain-controlled unit, the rate of
movement of the top half of the shear box can be controlled.
The shear strength, S, of sand can be expressed by the equation:
S= σ’ tan ϕ
Where:
S= shear strength.
σ’ = effective normal stress.
ϕ = angle of friction of soil.
The angle of friction, ϕ, is a function of the relative density, of compaction of sand,
grain size, shape and distribution in a given soil mass.
Equipment:
1. Direct shear test machine (strain controlled)
2. Balance sensitive to 0.1 g
3. Large porcelain evaporating dish
4. Tamper (for compacting sand in the direct shear box).
5. Spoon
Figure below shows a direct shear test machine. It consists primarily of a direct shear box
which holds the soil specimen, it is split into two halves (top and bottom), The top and
bottom halves of the shear box can be held together by two vertical pins; electric load cell to
measure the horizontal load applied to the specimen; two transducer (one horizontal and one
vertical) to measure the deformation of the soil during the test; and a yoke by which a
vertical load can be applied to the soil specimen. A horizontal load to the top half of the
shear box is applied by a motor and gear arrangement. In a strain-controlled unit, the rate of
movement of the top half of the shear box can be controlled.
