Behavior of seismic-acoustic parameters during deforming and failure of rock samples, large blocks and underground opening: base for monitoring

Abstract

Construction of engineered projects, such as underground spaces, tunnels, machine halls etc. is connected with variations in stress-state and deformations of large volumes of rock mass. Latter can results in damage of rocks, their collapse into underground space, danger for equipment and risk for human life. To avoid such consequences different in situ geotechnical and geophysical monitoring is carried out during construction and exploitation of underground structures. Geophysical monitoring is based on observations for behavior of elastic shear- and longitudinal wave velocities (Vs and Vp, respectively) and microseismic activity. Behavior of the elastic velocities during deforming of the rock depends on type of the future failure that, in turn, is defined by structure and properties of medium and characteristics of stress state σ3/σ1 and hydrostatic pressure. These velocity variations are defined by difference in effective parameters of forming microfractures, whose geometry is distinguished at different modes of stress-state. At that character of interaction between microfractures determines type of the macrofailure. We studied behavior of longitudinal wave velocities during loading of rock samples, large blocks and underground opening orienting measurements along maximum (σ1) and minimum (σ3) stresses. It is shown that velocity variations along maximum stress is more informative at elastic phase of rock deformations (velocity increases), whereas velocity variations along axis of minimum stress is more informative at the stage of nonlinear deformation of rock (velocity begin decrease). These regularities are well appeared at deforming of large blocks and unloading of rock mass in underground openings. This knowledge should be used at planning and performing of monitoring of stability of underground structures.