Unloading effect of roadway excavation based on simulation method in similar material

Abstract

Dynamic unloading is instantaneous, and the transient unloading effect has important influence on deep rock blasting excavation. In order to study the deformation law and failure mechanism of surrounding rock under dynamic excavation with unloading condition. And tunderstand further dynamic characteristics and the dynamic effects of transient unloading in rock mass excavation. There used a self-developed simulation test device for simulating the process of dynamic excavation in confining pressure loading. The experimental model was made similar material, and used the test device to impact it. It focus on monitoring the unloading effect in real time with the help of strain gauge, high-speed camera and fiber grating sensor. These devices that monitored effective strain-time curves, crack propagation image and the tensile state or compressive state of rock mass after excavation. The test results show that surrounding rock stress of model have experienced five stages that were called initial stress stage, dynamic loading stage, dynamic unloading stage, initial stress unloading stage and creep stage respectively. After model was impacted, each monitoring point occured different strain variation, and some occured compressive strrain, others occured tensile strain. The whole model in compressived state. The model showed creep phenonmen after excavation. Through observing crack propagation image, crack propagation process shown clearly. Firstly, radial cracks were rapidly generated during dynamic excavation. Then, with the free face increase constantly, the stored energy of surrounding rock of model was rapidly released toward the free face, resulting in annular crack occured. Annular crack belongs to tensile faiure, which was generated in vertical radial crack direction and propagated along the adjacent radial crack. Finally, annular crack was parallelled with the free face. The simulation test device system monitored the unloading effect of rock-like marterial well in whole time. Unloading strain value varied with distance, the rock mass model can be divided into near unloading area, middle unloading area and far unloading area after excavation.

Keywords

• dynamic excavation
• surrounding rock-like material
• loading of double
• unloading
• crack