A direct shear test is one which is conducted in the field or in the laboratory to determine the capacity of materials- usually soil or rock, to resist shear.
The property of shear strength of soil or rock type is one of the major properties that are to be taken into consideration by engineers when considering the construction of structures that are dependent on the shearing resistance of the given soil or rock type. Some such conditions are calculating slope stability or determining the capacity to support foundations.
An Apparatus for conducting a Direct Shear Test consists of multiple components, one of which is a box that comes in a square like or circular shape and is segmented into two compartments. It is basically a box which splits horizontally. The sample that you want tested is to be put in this box. Thereafter, two kinds of forces are applied on the box to determine the shear strength of the material. There is a constant downward load that the sample or specimen is subjected to, while an increasing degree of horizontal force i.e. a force parallel to the surface of the specimen is applied on one of the two halves of the box. This leads to the two parts of the shear box to be “pulled apart”. These two forces create a shear failure that runs along the meeting points of the two halves of the box. The apparatus records the value of normal load as well as the shear force. Controlling the speed at which horizontal force is applied, determines the degree of strain.
A loading unit is another component of the apparatus. It is usually provided with roller strips or V strips to ensure that the shear box which rests on it has frictionless movement. The loading unit is also provided with load yokes to ensure balance to it. There is also a lead screw which connects to the shear box structure and helps applying shear stress.
In order to arrive at a decisive conclusion about the shear strength of a specimen, the test is usually carried out thrice, each time with different degrees of vertical load. This allows engineers to graphically chart out a distinctive “failure envelope” and consequently make well informed plans and designs for slopes, dams or foundations.
Though a shear test can be performed to measure the shear strength of different surfaces, they are mostly conducted to measure the amount of shear strength that sandy materials have.
The property of shear strength of soil or rock type is one of the major properties that are to be taken into consideration by engineers when considering the construction of structures that are dependent on the shearing resistance of the given soil or rock type. Some such conditions are calculating slope stability or determining the capacity to support foundations.
An Apparatus for conducting a Direct Shear Test consists of multiple components, one of which is a box that comes in a square like or circular shape and is segmented into two compartments. It is basically a box which splits horizontally. The sample that you want tested is to be put in this box. Thereafter, two kinds of forces are applied on the box to determine the shear strength of the material. There is a constant downward load that the sample or specimen is subjected to, while an increasing degree of horizontal force i.e. a force parallel to the surface of the specimen is applied on one of the two halves of the box. This leads to the two parts of the shear box to be “pulled apart”. These two forces create a shear failure that runs along the meeting points of the two halves of the box. The apparatus records the value of normal load as well as the shear force. Controlling the speed at which horizontal force is applied, determines the degree of strain.
A loading unit is another component of the apparatus. It is usually provided with roller strips or V strips to ensure that the shear box which rests on it has frictionless movement. The loading unit is also provided with load yokes to ensure balance to it. There is also a lead screw which connects to the shear box structure and helps applying shear stress.
In order to arrive at a decisive conclusion about the shear strength of a specimen, the test is usually carried out thrice, each time with different degrees of vertical load. This allows engineers to graphically chart out a distinctive “failure envelope” and consequently make well informed plans and designs for slopes, dams or foundations.
Though a shear test can be performed to measure the shear strength of different surfaces, they are mostly conducted to measure the amount of shear strength that sandy materials have.