Magnetic resonance approach to identify the types of inrush hazards in constructing tunnel: I. Characterizing and modelling

Abstract

Inrush hazards like water and mud inrush can cause great loss of life and property, which should be predicted in advance during tunneling. To identify types of inrush hazards, investigating water-bearing condition and filling materials inside hazardous bodies is required. Thus, after detecting hazardous bodies by using methods like resistivity method, seismic method and transient electromagnetic method, more hydrogeological information is need to conduct further investigation of filling materials inside hazardous bodies. We aim to identify the types of inrush hazards by investigating the water-bearing condition of filling materials utilizing magnetic resonance sounding (MRS). We developed a methodology, through which hazardous bodies and the inside filling materials can be characterized by electrical resistivity, water content and MRS relaxation distribution. Based on multi-exponential scheme, we made a function, describing the distribution of MRS relaxation, to characterize the scale and uniformity of pore size. By numerical modelling of hazardous bodies that can cause water inrush, mud inrush and debris inflow, MRS responses corresponding to different types of inrush hazards were simulated. The results have shown that the MRS response can be affected by variations of electric resistivity, water content and MRS relaxation distribution resulting from the water-bearing condition related to different types of inrush hazards. Besides, by considering water content inside the surrounding rock, the influence of which is illustrated to be obvious in the area near the transmitting loop. In this paper, MRS have been proven as a capable and reliable technique to identify types of inrush hazards. The characterization of water-bearing condition in front of tunnel face and the modelling of hazardous bodies can be realized by using the method presented in this paper.