Study On Construction Method Of Sandy Mudstone Chamber With Super-large Cross Section

Shallow-buried large section sandy mudstone chamber construction is the hot and difficult problem in the construction of tunnel and underground construction in Chongqing city.At present,it is often constructed by double-side wall guide method,such as Chongqing Metro Station,About 342.46m2,the top cover of the cavern is 16.5m in thickness,the excavation width is 23.44 m,the excavation height is 20.71 m and the length is 214.004 m.The lithology of the surrounding rock is sandy mudstone,the area overpass,the expressway,the long distance station and the high building The As the double-side wall guide pit construction steps are complex,often lead to long construction period,large investment.In view of this,this paper takes the excavation of the Phoenix station as an example to study the construction method of the sandy mudstone caverns with shallow cross section.The main contents and conclusions are as follows:(1)By comparing the upper temporary steel support + lower double side wall guide method and the traditional double side wall guide pit construction process,we can see the upper temporary steel support + lower double side wall guide method and the traditional double side wall construction Method compared with a large operating space,construction speed,short duration,low cost characteristics,can reduce the duration of about one-third.(2)Taking the construction of Fenghuang station as an example,the stress of the surrounding rock of the caverns during the construction of two methods is studied by two-dimensional and three-dimensional numerical simulation method for double-side wall guide method and upper temporary steel support + lower double-,Soil deformation and displacement,the initial force and other forces were compared and analyzed,the two methods of rock and structural force and displacement characteristics are as follows:(1)the upper temporary steel support + the lower side of the double-wall guide pit method vault displacement of the two major changes occurred in the demolition of the upper core soil stage and the removal of temporary vertical steel support stage,double-wall guide pit method in the maximum displacement of the arch in the Finally,remove the core soil stage.The maximum dome displacement caused by the two methods is similar,and the double-wall guide method is smaller.The removal of the core soil has a great impact on the settlement caused by the two methods.(2)In the use of the upper temporary steel support + lower double side wall guide method,the absolute value of the stress is basically greater than the use of double-wall guide hole excavation.But the maximum compressive stress values are within safe limits.(3)The numerical results show that the maximum initial support force and the initial bending moment are very close to each other.Obviously,the mechanical response of the modified method can meet the standard of the traditional double-wall guide pit construction method.Through the numerical simulation of the comparative analysis,we can see that as long as the strict control of construction,double wall guide pit method can also be characterized by improved safety method,on the other hand to improve the work can be completed in the initial support after the implementation of temporary steel support As for the double-side wall guide method,the operating space is wider,the construction time is more sufficient and the flexibility is higher.(3)The steel support spacing of the upper temporary steel support + the lower double side wall guide method is optimized.Based on the analysis results,it is suggested that the upper temporary steel support + lower double side wall guide method should be used in the sandy mudstone geological condition Should be 8 ~ 12 m.(4)By comparing the two kinds of methods to monitor the measured data,the maximum surface subsidence is 12.3mm and the maximum dome settlement is 17.8mm.The maximum settlement of the surface is 12.6mm,Settling 10.5mm.Two kinds of engineering settlement value is less than the monitoring measurement specification control value of 30 mm.It can be seen that the effect of the modified method on the settlement control of strata and vaults in sandy mudstone chamber is equivalent to that of double-wall guide.