Strength Weakening Effect of High Prestatically Loaded Marble Subjected to Low-Frequency Dynamic Disturbance under Point Load

Wuxing Wu,Fengqiang Gong,Nan Jiang

doi:10.1155/2021/5529897

Abstract

The deep high prestatically loaded rock is often subjected to low-frequency dynamic disturbance and exhibits unusual strength characteristics, and thus, it is important to investigate the strength characteristics under the coupling effect of prestatic load and low-frequency dynamic disturbance loading conditions. In this study, a series of point load tests were conducted on the high prestatically loaded marble subjected to low-frequency disturbance by the MTS system, focusing on exploring the role of prestatic load level and low-frequency disturbance frequency in the process of rock strength change. Based on the average static failure load (Fmax) of samples under the static point loading, the high prestatic load levels (Fp) were selected as 70%, 80%, and 90% of Fmax, the corresponding low-frequency dynamic disturbance was loaded by sinusoidal waves with amplitudes of 60%, 40%, and 20% of Fmax, and the low-frequency dynamic disturbance frequencies (f) are 1, 2, 5, and 10 Hz. The change curve of the point load strength with the prestatic load level or the disturbance frequency was analyzed, which indicates that the point load strength under the coupled high prestatic load and low-frequency dynamic disturbance load was significantly lower than that under the pure static loading, presenting a significant point load strength weakening effect. Only when Fp or f reaches a certain level, the point load strength decreases significantly as f or Fp increases. Moreover, the point load strength weakening rate was proposed to characterize the degree of strength weakening. The comprehensive analysis demonstrates that Fp has a greater effect on the point load strength weakening effect than f, which is mainly reflected in the point load strength weakening level dominated by the Fp, and the weakening degree is affected by f.

Highlights

With the decrease of shallow mineral resources and the increasing demand for underground space, more and more underground projects extend to great depth. e deep surrounding rock has been subjected to high static stress before excavation [1,2,3] and undergoes various forms of dynamic disturbance during the excavation process [4, 5], resulting in the high static load surrounding rock in a stress state coupled with high static load and dynamic disturbance load
Comparison of the point load strength under the traditional static loading and the point load test under the coupled static-dynamic loading shows that the point load strength has obvious strength weakening effect. e existing literature has confirmed that the tensile strength of rock shows obvious strength weakening effect under the coupled staticdynamic loading [32]
Gong et al [32] carried out a Brazilian disk (BD) test on prestatically loaded BD samples subjected to low-frequency dynamic disturbance, and systematically analyzed the characteristics and mechanism of tensile strength changes, and the main conclusions are shown in Figure 11. e tensile strength of the BD sample under the pure static state is 4.89 MPa, but when FP is 90% under the coupled static-dynamic loading, the tensile strength decreases with f until it reaches 4.32 MPa at f 50 Hz, showing obvious strength weakening effect

Summary

Introduction

With the decrease of shallow mineral resources and the increasing demand for underground space, more and more underground projects extend to great depth. e deep surrounding rock has been subjected to high static stress before excavation [1,2,3] and undergoes various forms of dynamic disturbance during the excavation process [4, 5], resulting in the high static load surrounding rock in a stress state coupled with high static load and dynamic disturbance load. Liu et al [8] pointed out in detail that the high prestressed rock is in the coupled static-dynamic stress state during deep rock engineering excavation. Ese studies have clearly pointed out that the deep high prestatically loaded surrounding rock is often subjected to dynamic disturbance, under the coupling stress state of the high prestatic load and dynamic disturbance. Compared with pure static or pure dynamic stress state, the failure characteristics of the deep high prestatically loaded surrounding rock under the dynamic disturbance are obviously different, which cannot be explained reasonably by traditional rock mechanics theory [2, 6]. Erefore, knowledge of the high prestatically loaded rock subjected to dynamic disturbance on deep rock fracture characteristics and mechanical behaviors has significance for the construction of deep underground rock engineering Compared with pure static or pure dynamic stress state, the failure characteristics of the deep high prestatically loaded surrounding rock under the dynamic disturbance are obviously different, which cannot be explained reasonably by traditional rock mechanics theory [2, 6]. erefore, knowledge of the high prestatically loaded rock subjected to dynamic disturbance on deep rock fracture characteristics and mechanical behaviors has significance for the construction of deep underground rock engineering

Results

Discussion

Conclusion