Theoretical Analysis of Rock Blasting Damage in Construction of Tunnels Closely Under-Passing Sewage Box Culverts

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.