Water absorption/dehydration by NMR and mechanical response for weakly cemented mudstones subjected to different humidity conditions

Abstract

Mudstones of Bayanhua Formation are characterized by high porosity, large content of swelling clay minerals, and weak cementation due to its late diagenesis in Wujianfang Basin, eastern Inner Mongolia, China. Mechanical properties heavily deteriorate during water absorption or dehydration, resulting in underground engineering instability. To study water absorption/dehydration and mechanical response for weakly cemented mudstones, two sets of weathering routes, namely, higher relative humidity (RHs) and lower RHs, are performed by using a self-developed weathering instrument, which can achieve environmental control and real-time weight measurement. The water migration is logged by nuclear magnetic resonance (NMR). Finally, uniaxial compression tests are carried out on weathered samples to study their mechanical properties. The results show that dehydration occurs even under the 70% RH condition, due to their higher initial water content of more than 10%, and the dehydration content is exponential over time under the 60% RH condition. Variations of T2 spectrum reflect the water migration when the surrounding humidity changes. The maximum peak of the transverse relaxation time (T2) moves left during dehydration and shifts to the right when adsorbing water. The uniaxial compressive strength (UCS) does not increase with the decreasing RH at any time, which is distinct from elasticity modulus (E). There is a critical RH at 50%, indicating that damages accumulate when the RH is lower than 50%. Tensile fracture occurs for the most types of weathered samples, and shear failure only occurs under the drying condition.