Study On Stability And Support Measures Of Side-slope-upward In Tunnel Section Of A Shallow Buried Unsymmetrical Pressure Tunnel

Because it is difficult to ensure the stability of the shallow slope at the tunnel entrance section of the shallow buried bias curve,the form of the slope support and the method of tunnel excavation are slightly improper,which will cause the deformation,cracking and even landslides of the side slope.Therefore,in this paper,based on the Jiabin Road Tunnel of the South Approach of the Jialing River Bridge tunnel project in Chongqing,this paper studies the stability and support measures of the slope at the entrance of the shallow tunnel under-biased tunnel.The thesis adopts theoretical analysis and numerical simulation,on-site.The combined research methods of monitoring are used to study the relationship between supporting measures,support parameters,tunnel excavation methods and the stability of the side slope,hoping to provide reference for the design and construction of similar projects in the future.The research content and conclusions of this paper are as follows:(1)In this paper,the unbalance thrust method and the MIDAS/GTS NX numerical simulation method of the limit equilibrium theory are respectively applied to the stability calculation of the unsupported slope after the tunnel is cut open.On this basis,the possible slope support is adopted.Supporting parameters(supported by anti-sliding piles,combined supporting with anchored piles,combined supporting of anchored piles and anchored frames)supporting parameters(length of pile,distance between piles,inclination angle of anchor cable,anchorage force of anchor cable,frame beam and The anchor cable spacing,etc.)was studied and optimized,and it was concluded that the combined support scheme of anchored pile and anchored cable frame had the best support for slope support.It is proposed that the length and spacing of anti-sliding piles are not linear with the displacement of the slope and the slope stability coefficient.Under the same conditions,when the cable inclination angle is between 15 and 30,changing the inclination angle of the anchor cable is more effective than changing the anchorage force of the anchor cable.It is recommended that the prestressing strength of the single hole not exceed 300 k N.In order to avoid the group anchor effect,the distance between the anchor cable frame and the anchor cable cannot exceed 2.0m.Finally,the best support parameters are obtained.(2)Based on this premise,the numerical simulation analysis of the full-section method,the up-and-down step method,the CD method,and the double sidewall guide pit method for the tunnel section of the shallow-buried pressured tunnel was carried out to compare and analyze the effects of four different excavation methods.Deformation and stress characteristics of the surrounding rock.It is proposed that the Jiabin Road tunnel in Chongqing is optimally excavated using the step method.At the same time,due to the influence of the bias voltage,the horizontal displacement field and the stress field all have an asymmetry distribution phenomenon,and the minimum principal stress of the surrounding rock in each key position of the tunnel structure is obtained.Distribution law,different excavation method under the minimum principal stress of the wall with the excavation footage rule,and the inversion of the arch position of the maximum tensile stress,the left wall position to produce the maximum compressive stress,construction should be timely support to avoid dangerous situations.(3)During construction,on-site dynamic monitoring was conducted on the tensile force of anchorage cable,the settlement of the surface of the mouth and the slope of the dome,and the horizontal convergence.The law of the tension of the anchor cable tension after locking was obtained and the regression equation was used.Regression analysis predicts the deformation and stability of surrounding rock,and obtains the time when each section tends to be stable,and the relationship between the tunnel's buried depth and the cumulative value of vault and the rate of crown subsidence over time;monitor results and values.The simulation results are compared and analyzed to verify the correctness of the numerical simulation excavation scheme.It is shown that the engineering numerical simulation and regression prediction have important reference significance for the project.