Rockburst Analysis And Engineering Application Of Damage-based Circular Tunnel

In the mountainous area of western China,steep slopes and ravines are very common.It is inevitable that road construction will take the form of deep and long tunnels across mountains and valleys.Especially in the Sichuan-Tibet Railway,potential rockburst proneness brings many problems to route selection,design and construction of the tunnel.In addition,there are different ideas about the essential conditions and the prediction standard of rock burst.Therefore,there is an urgent need for studying the geostress characteristic and rockburst prediction methodin order to provide a scientific basis for railway route selection and feasibility studies.1.Based on the Gu-Tao criterion and analytical solution about the occurrence of rockburst in the damaged circular cavern,taking a tunnel in the southwest China as the application object,and collecting the rockburst case of Jinpin-II Hydropower Station and Erlangshan highway tunnel to make rockburst prediction.On the basis of the threshold of the stress-strength ratio criterion,the coefficients a₁,a₂,a₃ related to the mechanical characteristics about the the pre-peak and post-peak stage of the stress-strain curve are introduced.The research results show the lateral pressure coefficient k is related to the coefficients a₁,a₂,a₃.Then,using the quantitative relations to modify the rockburst criterion.2.The modified rockburst criterion on the damage-based analytical solution of the circular cavern has the same physical meaning as the stress-strength ratio criterion,and considers the influnce of the in-situ stress on the rockburst.To verify the validity of this modified rockburst criterion,the Daxiangling tunnel rockburst case was used to make a comparative analysis.It shows that the verified results were basically consistent with the actual rock burst section and grade of the Daxiangling tunnel.This modified method can also effectively predict rockburst disasters.3.According to the preliminary survey data of the tunnel,combined with the hydraulic fracturing method,the measured in-situ stress value of the tunnel was obtained.Using the finite element numerical analysis software named COMSOL Multiphysics,a three-dimensional model of the tunnel was inversely analyzed to obtain in-situ stress field of the tunnel.The changes trend of the in-situ stress also reveals the strong tectonic activity in the study area.4.Finally,the modified rockburst criterion was used to predict the rockburst grade of the tunnel,combined with the brittleness,integrity,mechanical properties and energy storage conditions of the rock.And the influence of various factors such as lithology difference,burial depth,stress and other factors are all considered.