Uniaxial compression tests and cyclic loading acoustic emission tests were conducted on 20%, 40%, 60%, 80%, dry and saturated muddy sandstone by using a creep impact loading system to investigate the mechanical properties and acoustic emission characteristics of soft rocks with different water contents under dynamic disturbance. The mechanical properties and acoustic emission characteristics of muddy sandstones at different water contents were analysed. Results of experimental studies show that water is a key factor in the mechanical properties of rocks, softening them, increasing their porosity, reducing their brittleness and increasing their plasticity. Under uniaxial compression, the macroscopic damage characteristics of the muddy sandstone change from mono-bevel shear damage and ‘X’ type conjugate bevel shear damage to a roadway bottom-drum type damage as the water content increases. Dynamic perturbation has a strengthening effect on the mechanical properties of samples with 60% and less water content, and a weakening effect on samples with 80% and more water content, but the weakening effect is not obvious. Macroscopic damage characteristics of dry samples remain unchanged, water samples from shear damage and tensile–shear composite damage gradually transformed into cleavage damage, until saturation transformation monoclinic shear damage. The evolution of acoustic emission energy and event number is mainly divided into four stages: loading stage (I), dynamic loading stage (II), yield failure stage (III), and post-peak stage (IV), the acoustic emission characteristics of the stages were different for different water contents. The characteristic value of acoustic emission key point frequency gradually decreases, and the damage degree of the specimen increases, corresponding to low water content—high main frequency—low damage and high water content—low main frequency—high damage.

Improving the safety and stability of soft surrounding rock with nonlinear large deformation gives a strong guarantee for the safe mining and sustainable development of deep coal mines. In order to control the nonlinear large deformation of the surrounding rock in a deep soft rock roadway, this paper discusses the nonlinear large deformation mechanism and coupling support countermeasures of a typical engineering application at Xin’an coal mine in Gansu province, China. The series of experiments and theoretical analysis described in this paper reveal the phenomena, properties, and reasons for the nonlinear large deformation of soft surrounding rock in detail. Then, the type of nonlinear large deformation mechanism is determined and transformed from a composite one to a simple one. Based on experimental results and mechanism transformation, a suitable coupling support countermeasure, which contains the Constant Resistance Large Deformation (CRLD) bolt, steel mesh, floor hollow grouting cable, and steel fiber concrete, is proposed to reduce the nonlinear large deformation and the potential risk during mining. The application shows that the coupling support countermeasure can effectively reduce the nonlinear large deformation of the surrounding rock and help to maintain the stability of the deep soft rock roadway at Xin’an coal mine.

Anisotropic discontinuity exists widely in rock masses of mines, tunnels, slopes, water conservancy and hydropower projects. The shear characteristics of bolted anisotropic rock joints are extremely important for the stability design of engineering rock mass. However, few scholars have studied the bolted anisotropic rock joint. The different rock properties on both sides of the rock joint, especially the different rock strengths, will greatly affect the deformation characteristics and failure mode of the rock mass. Based on this, a series of shear tests were carried out on the bolted anisotropic rock joint under different normal stresses, and the characteristics of shear stress–shear displacement curve, shear strength, failure characteristics of the rock joint and deformation characteristics of the bolt are discussed. λ is defined as the strength ratio of upper and lower rock on the structural surface. The results show that the effect of λ on the shear stress–shear displacement curve is not obvious at the pre-fracture stage. The shear stress–shear displacement curve at the pre-breaking stage of the bolt presents a softening stage when the normal stress is equal to 0.5 MPa, tends to be horizontal when the normal stress is equal to 1 MPa and presents a hardening stage when the normal stress is greater than 1 MPa. After the bolt is broken, the shear stress–shear displacement curve presents a stepped-down descent. With the increase in λ, the breaking shear stress of the bolt increases. Elliptic failure occurs on the surface of the bolted anisotropic rock joint, and the length of the major axis of the ellipse decreases with the increase in λ value and normal stress. The bolts with different λ values of anisotropic rock joint show “Z-shaped” tensile bending deformation characteristics after shear fracture, and the horizontal and vertical components of the bolt deformation decrease with the increase in λ value and normal stress. The fracture shear displacement of the bolt increases with the increase in normal stress and decreases with the increase in λ value. The research results are helpful to further understand the shear mechanical characteristics and differences of bolted rock joints and provide a reference for solving the engineering problems of the composite layered rock mass.