Equipment and Techniques

Equipment & Techniques

Unconfined Compressive Strength is an index of the mechanical behaviour of rock. It is the most frequently used strength test. The test points out irregularities which may be present in the test specimen which is important when characterizing the strength of a particular rock. The specimen is loaded between steel platens until the peak load is reached.

Triaxial testing is a compression test of a cylindrical rock specimen under confining pressure where the loading path is followed by a computer. This test aims to simulate the conditions which may occur to an in-situ rock material where it is subjected to a confining pressure and deviatoric stress.

Tensile Strength testing determines the splitting tensile strength in a rock by diametral line compression of a disk.

Point Load Index is a simplification of uniaxial strength testing which gives an accurate strength index in harder rocks. This test can be carried out on any size of specimen. The specimen is compressed between two conical points loaded from a hydraulic pump. The sample fails at low applied force due to tensile failure over the area between the points.

Direct Shear is an important parameter for stability analysis for mine design. Internal and external shear strength can be measured. Internal shear strength is measured from intact rock and external is measured along a structural defect from the rock. Any shape of sample can be tested, it is cast in a concrete mold casing.
A shear force is applied by a hydraulic jack which acts in the plane of shearing to measure shear and normal forces as well as lateral displacement.

Long term creep provides an estimate to the performance of pillars, at depth, in weak rocks, especially evaporites. Strain-time curves are produced under a maintained stress which determines the critical crack density level.

Slake Durability Index is used to estimate the durability of weak rocks by two cycles of wetting and drying with abrasion.

Ultrasonic Velocity Testing provides a measurement of the velocity of sound waves in a core speciman. The velocity which stress waves are transmitted through the rock are dependant on the elastic properties of the spaciman. This test yields compression and shear wave velocities, Young's Modulus of Elasticity, Modulus of Rigidity, Poisson's Ratio, Lame's Constant and Bulk Modulus. This test is a useful prediction of static properties.

Acoustic Emision is produced by rapid microcrack growth and is associated with the brittle fracturing process in rock. This test provides information on the failure process in rock.