| In the construction of super long highway tunnel,many auxiliary caverns are often added.Restricted by the topography and other factors,some auxiliary caverns are close to each other and combined with the main tunnel to form a high-density cross underground cavern group.The excavation of cross tunnel will cause the surrounding rock to be disturbed for many times,and the variation of stress is different,so it is difficult to describe quantitatively.It is an extremely complex mechanical transformation process.Therefore,the stability of cross tunnel construction has become a key factor affecting the success or failure of Tunnel Group Engineering.Based on the underground cavern group project of Funiu Mountain super long highway tunnel of Zhengzhou Xi’an expressway,this paper adopts the method of field test and finite element simulation to study the law of displacement field,stress field of surrounding rock and safety change of supporting structure caused by cross construction of cavern groups:(1)Based on the comprehensive evaluation and classification of surrounding rock in the scope of underground cavern group,the original construction scheme of cavern group is optimized and improved,and the supporting scheme of air supply and exhaust intersection is designed;(2)Based on the monitoring data collected by the dynamic construction of the cross tunnel,the variation characteristics of the displacement,pressure and arch stress of the existing tunnel surrounding rock caused by the excavation of the intersection are analyzed.It is found that the influence of cross tunnel excavation on the displacement of surrounding rock of existing caverns is mainly reflected in the sudden increase of arch roof settlement,small convergence change on the surrounding rock around the tunnel,and the change of displacement of surrounding rock of the section has significant spatial distribution heterogeneity;due to the influence of the excavation of the main tunnel at the intersection,the surrounding rock pressure of the existing tunnel is concentrated on the side of the main tunnel face close to the excavation,showing obvious characteristics of bias pressure distribution.After the section steel arch is excavated at the intersection,the structural safety grade of the arch frame decreases from safety to basic safety;(3)By using the finite element software MIDAS GTS/NX formation-structure method is used for funiu underground cavities 3-d excavation simulation,from two aspects: global and local analysis of calculation results,the study of underground cavities cross construction impact on the stability of surrounding rock and supporting,and introduce the damage evaluation method for the phase of the initial supporting structure safety.It is found that the maximum settlement value of intersection # 6 is 15.9mm,which is located in the arch of the main tunnel of the intersection,and the maximum settlement value of other intersections is located in the arch of the intersection junction.The tensile stress of surrounding rock is mainly between0.049 MPa and 1.648 MPa.The tensile stress concentration area is generated at the arch waist of the intersection and the side wall of the main hole of the 5 # and 7# air supply outlet,and the compressive stress concentration area is generated at the side wall and corner of the lower part of the intersection.Both # 6 exhaust duct side near the intersection of 25 m within the scope of acceptor hole and dealership tunnel excavation effect significantly,with the main tunnel excavation both the monitoring cross section at the beginning of the minimum safety factor by64.8%,8.3% lower tunnel excavation,each part of the monitoring cross section in the early stage of the excavation support minimum safety factor were greater than 1.53,meet the design specification requirements.(4)Through numerical simulation,the influence factors of construction stability and scheme optimization of "cross" intersection with special form of plane intersection are studied.Three groups(12 working conditions)are set up.The displacement field,stress field and support strength field of surrounding rock produced by excavation of "cross" tunnel are simulated and analyzed under different construction methods,construction sequence scheme and length of support reinforcement section Influence of internal force of retaining structure.After comparison and selection,it is suggested that the excavation scheme of "ten" intersection is as follows: firstly,the inclined shaft is excavated,then the backstage step method is transferred to the main tunnel,and the large and small mileage ends are excavated respectively,and finally the cross passage is connected.The reinforcement scheme of intersection support is as follows: the inclined shaft and main tunnel of intersection are set with 5m reinforcement section,and the cross passage is not set with reinforcement section;... |
PDF Full Text Request