Abstract
The essence of roadway excavation is a process of unloading at the periphery, and the influence of unloading paths on surrounding rock damage is directly related to the selection of support design and construction technology. The real stress state of surrounding rock is often affected by different excavation conditions in the actual construction process. Therefore, a testing system of excavation and unloading model was developed to simulate the unloading process of the arch roadway under different excavation conditions. Small hollow cylindrical specimens used in this experiment were made of cement mortar. The load at the inner cavity of specimens was removed under the constant action of external pressure and axial force to simulate the real excavation unloading process. The deformation, the failure modes, and the acoustic emission evolution characteristics at the inner of specimens were obtained under unloading conditions using the strain and acoustic emission monitoring systems. The experimental results indicate that deformation laws of surrounding rock were similar under different unloading rates and initial geostresses, but failure modes and acoustic emission characteristics were quite different. Compared with that of slow unloading, the damage of surrounding rock under rapid unloading mainly accumulated after unloading, and it is easier to induce rockburst after unloading. As initial geostress increased, the occurring time of the main fracture may be delayed relatively, and the phenomenon that the distribution range of peak frequency expanded and the amplitude rose gradually can be regarded as the precursor information of the main fracture occurring. This study can be used to provide experimental support for the failure and supporting design of surrounding rock in deep underground engineering.
Highlights
With the development of the economy, the construction of underground chambers is gradually developing into the deep under the background of huge energy demand. e excavation unloading of the roadway will lead to the redistribution of the surrounding rock stress and the release of strain energy. e effects caused by different excavation unloading methods of roadway are quite different, which threaten the stability of the surrounding structure and endanger the safety of the workers [1,2,3]. erefore, it is of great theoretical significance and engineering value to investigate the influence of excavation unloading rates on deformation and damage evolution characteristics of roadway surrounding rock under different initial geostresses
A radial strain refers to the strain generated along the radius direction at the measuring point inside the surrounding rock, while tangential strain refers to the strain generated in the direction perpendicular to the radius. e solid line means that the strain was generated under a slow unloading rate (0.05 MPa/s) at different measuring points, and the dotted line means that the strain was generated under a rapid unloading rate (2 MPa/s) at different measuring points
Excavation unloading model experiments of the arch roadway that were conducted by the self–developed laboratory test system using the small hollow cylindrical specimens were performed to investigate the effects of unloading rates on surrounding rock deformation and acoustic emission (AE) features under different geostresses
Summary
With the development of the economy, the construction of underground chambers is gradually developing into the deep under the background of huge energy demand. e excavation unloading of the roadway will lead to the redistribution of the surrounding rock stress and the release of strain energy. e effects caused by different excavation unloading methods of roadway are quite different, which threaten the stability of the surrounding structure and endanger the safety of the workers [1,2,3]. erefore, it is of great theoretical significance and engineering value to investigate the influence of excavation unloading rates on deformation and damage evolution characteristics of roadway surrounding rock under different initial geostresses.A large number of studies have shown that stress redistribution can cause the initiation and extension of cracks in roadway surrounding rock under excavation unloading, and the damage degree of surrounding rock is closely related to the selection of unloading stress paths and unloading rates [4, 5]. E excavation unloading of the roadway will lead to the redistribution of the surrounding rock stress and the release of strain energy. Erefore, it is of great theoretical significance and engineering value to investigate the influence of excavation unloading rates on deformation and damage evolution characteristics of roadway surrounding rock under different initial geostresses. A large number of studies have shown that stress redistribution can cause the initiation and extension of cracks in roadway surrounding rock under excavation unloading, and the damage degree of surrounding rock is closely related to the selection of unloading stress paths and unloading rates [4, 5]. Advances in Civil Engineering different unloading rates and confining pressures using finegrained granite cube samples to study the effects of unloading velocities and stress paths on the degree of rock failure. Du et al [8] investigated the failure behaviors of different types of rock by using a novel testing system coupled to true-triaxial static loads and local dynamic disturbances and found that similar evolution law of cracks occurred in rock specimens. ese results indicate that it is pretty important to consider the real stress state of roadway excavation when the influence of unloading stress paths on the mechanical behaviors of rocks is investigated
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