Effect of loading rate and time delay on the tangent modulus method (TMM) in coal and coal measured rocks

Abstract Non-destructive techniques of in-situ stress measurement from oriented cored rocks have great potential to be developed as a cost cost-effective and reliable alternative the conventional overcoring hydraulic fracturing methods. The tangent modulus method (TMM) is one such technique that can applied measure stresses. Like deformation rate analysis (DRA), rock specimen subjected two cycles uniaxial compression stress-tangent curve for obtained stress–strain curve. A bending point in first cycle observed, separating it second cycle. separation between curves assumed previously maximum stress. number experiments were conducted on coal measured (sandstone limestone) understand effect loading conditions time delay. specimens preloaded, cyclic compressions under three different modes loading, four strain rates, delays up week. occurred approximately at pre-stress levels all modes, no was observed points TMM. However, clear delay TMM, contradicting DRA results. This could due sensitivity TMM range its applicability, which need further investigation measurement.