The accelerated creep plays an important role in the disasters of soft-rock tunnels under high stress. However, most of previous studies only involved attenuation creep and uniform creep. Large deformation disasters of soft rock occurred during the tunneling process in the Qianzhou–Sanyangchuan Tunnel, Gusu Province, China. In the paper, we developed the nonlinear generalized Nishihara rheological model with non-stationary parameter creep (NGNRM) to simulate the accelerated creep behaviors of soft rocks under high stress, and implemented it in ABAQUS, to reveal the mechanism of large deformation of soft rock. We proposed the multi-objective back analysis method of surrounding rock mechanical parameters based on the eXtreme Gradient Boosting and the non-dominated sorting genetic algorithm-II. In addition, the orthogonal test design method was used to determine the main parameters affecting the displacement of the tunnel. Using the proposed method, we can evaluate the large deformation mechanism of deep soft rock tunnels, and scientifically determine when to reinforce to prevent a large deformation disaster of the tunnel.
With the large-scale construction of urban traffic tunnels in China, it has become common to underpass existing buildings and structures such as sewage box culverts and pipelines using the drilling-blasting method. How to analyze accurately the blasting damage of surrounding rock and reasonably determine the safe distance between tunnel and box culvert or pipelines is an urgent issue to be solved. In this paper, the Cowper-Symonds plastic kinetic hardening model was improved using both rock initial damage degree and damage modification coefficient considering rock residual strength. The proposed model was implemented into LS-DYNA. The proposed damage model was used to evaluate the blasting construction of rock tunnels closely under-passing sewage box culverts. The results of numerical simulation using the proposed damage model shows that the blasting damage range of rock with a damage degree of more than 0.5 very significantly reduces from 1.0 m to 0.3 m as the spacing between the box culvert and the tunnel increases from 1.0 m to 4.0 m, and the evolution process of rock blasting damage can be well-presented. Moreover, the safe distance between tunnel and box culvert in blasting construction can be reasonably determined to be no less than 4.0 m. The findings in this paper could be significant for guiding the blasting construction of rock tunnels closely under-passing sewage box culverts.
Slotting-blasting is the most critical technology in the construction of rock tunnels using the drilling and blasting method. At present, there is no effective method to simulate the effect of slotting-blasting. In this paper, we proposed that the weight coefficient of tension damage or compression damage is calculated by the proportion relation of current principal stresses, and the damage properties of rock were denoted by the tension-compression weighted damage variable. The blasting damage constitutive model of rock was established by coupling the tension-compression weighted damage variable and the classical PLASTIC_KINEMATIC model. The proposed method was used to simulate tunnel slotting-blasting and investigate the rock damage evolution law in slotting-blasting construction. The numerical simulation of the explosive blasting test shows that the proposed method may effectively simulate the slot cavity formation process, the blasting damage law and the dynamic response characteristics of surrounding rock in slotting-blasting construction. The findings in this paper could be significant for the slotting-blasting design of rock tunnels.
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