Mechanical Behavior of Claystone in Lateral Decompression Test and Thermal Effect

Based on a theoretical analysis of stress evolution in surrounding rocks of an underground cavity during excavation, a series of lateral decompression (LD) tests are designed and performed in this study to investigate the mechanical behavior of the Callovo-Oxfordian (COx) claystone. The mean stress is kept constant in each LD test. A number of unloading-reloading cycles are included in each LD test. Furthermore, to evaluate the effect of temperature on mechanical strength and elastic properties of the COx claystone, the LD tests are performed under five different values of temperature from 20 to 90 degrees C. The shear strength as well as failure pattern in the LD tests are analyzed. The variation of elastic moduli is determined and analyzed from the unloading-reloading cycles. The effect of temperature on both the shear strength and elastic moduli is identified and characterized. The COx claystone showed a shear failure in the LD tests, and the failure was characterized by the creation of a localized macro-crack and of a damaged zone with many micro-cracks around the macro-crack. The temperature increase induced a degradation of the shear strength of the COx claystone. An obvious mechanical damage of elastic properties was observed in the COx claystone during the shear stress loading in the LD tests. This damage was more important in the lateral direction than the axial one, leading to an induced anisotropy of the material.