Microstructure characteristic and mechanical behavior of mudstone under water environment

Under water environment, the mudstone has poor properties, such as hydrophilicity, expansibility and disintegration, which are of great challenges in the supporting design and excavation of underground openings. This paper aims at the study of water-weakening mechanism of the mudstone by several experimental methods. (1) Powder X-ray diffraction was conducted to obtain the mineral composition. (2) The uniaxial compression of mudstones in five conditions with water contents respectively nearly 0 (dry state), 1.04%, 1.32%, 1.75%, 1.88% (saturated state) were discussed. (3) The changes of microstructure in different water contents were studied by scanning electron microscope. The results show that the mudstone mainly contains chlorite, quartz, illite and calcite with the contents about 25%, 20%, 25%, 17% respectively, mixed up with small amount of feldspar, dolomite and hematite account for 5%, 5%, 3% respectively. With the increase of water contents, the water film between mineral particles becomes thicker and the mudstone starts to expand which lead to the uneven inner-stress. Meanwhile, part of colloidal substance is dissolved and the joints become loose. All of these lead to form a lot of micro-pores that damage the internal structure system. As a result, the peak strength and the mechanical parameters gradually decline with water contents increase until to a stable state.