Triaxial shear testing is a geotechnical laboratory test used to determine what are referred to as soil strength properties – namely the cohesion and angle of internal friction of the soil. From these parameters, an engineer can determine soil bearing capacity, predict how the soil will interact with vertical structures (such as shoring, retaining walls, deep foundations), and estimate frictional resistance to sliding. The sample set is prepared from intact or compacted soil cores that are roughly 1 to 2 times diameter in height. The cores are tested one at a time, by placing inside a rubber membrane, and then surrounded by a pressurized cylindrical water tank. Once the soil has been consolidated to the desired confining pressure, the sample is slowly displaced in vertical compression. The resistance pressure of the soil to this movement is recorded at frequent time intervals to determine the displacement distance at the peak level of resistance.
