Development and Numerical Modeling Approached to Individual Rock Test Chamber Based on In-situ Condition Preserved

Better understanding mechanical behavior of in-situ rocks is significant for oil exploration and underground mining. Traditional coring samples fail to keep the fidelity that can represent in-situ conditions such as underground temperature, pore pressure, and stress level, so in-situ condition-preserved coring technology was developed and realized. How to test these novel in-situ condition-preserved coring samples is of great concern due that existing experimental devices cannot be adopted to load them directly. In this manuscript, an innovative pseudo-triaxial apparatus was presented which can apply various loading on these in-situ condition-preserved rock samples and investigate their mechanical behavior. This apparatus called as Separatable Pressure-preserved Testing Capsule (SPTC in short form) can be used by putting it into any existing uniaxial test machine just with some simple connecting. To achieve pressure-preserved loading, balance chambers and an oil bag are introduced as two critical structures. The design concept was demonstrated and discussed. Moreover, shapes, dimensions, and materials of the testing capsule are determined after a serial of numerical simulations using the FEM software COMSOL. Furthermore, numerical simulations of rock samples with and without pore pressure were carried out under hydrostatic pressure and deviatoric stress loading. The results show that the safety strength measured from non-pressure-preserved rock samples is relatively large than that from pressure-preserved rock samples. Such improper estimation might cause mistaken design that probably result in the occurrence of underground engineering disasters. These simulation results also verify that such apparatus used to test pressure-preserved rock samples is necessary to obtain the veritable mechanical parameters of in-situ rocks.