Analysis of the Influence of Coverage Span Ratio on the Stability of Surrounding Rock in Subway Tunnel Chambers
Due to the limitation of topographic conditions and the need of function,the buried depth and span of underground engineering often vary greatly,so it is of great significance to study the influence of the ratio of cover to span on the stability of surrounding rock of tunnel.This paper deduced a formula of surrounding rock pressure by combining with Terzaghi theory and used the finite element simulation method based on mesh adaptive partition technology to systematically study the stability of surrounding rock of rectangular caverns with different coverage span ratio from the aspects of surface ultimate bearing capacity,displacement response,stress response and surrounding rock plastic zone.The results show that:under the condition of gradeⅣ surrounding rock,the surrounding rock pressure of rectangular cavern increases with the increase of span ratio,when the coverage span ratio H/D reaches 2,the surrounding rock pressure gradually tends to be stable.When the coverage span ratio H/D is less than 2,the collapse failure of the rectangular cavern is easy to occur to the ground surface in the limit state.When the coverage span ratio H/D is greater than 2,the pressure arch effect appears above the cavern vault.Therefore,the ratio between depth and span equaling to 2 can be used as a reference standard to divide the depth of deep and shallow buried caverns under grade Ⅳ surrounding rock conditions.
underground cavityratio between depth and spanfinite elementTerzaghi theorypressure arch effect
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