Study On The Mechanical Characteristics Of The Supporting Structure In The Construction Stage Of The Composite Curved Middle-wall Multi-arch Tunnel

In recent years,with the expansion of China’s highway construction scale,the number of highway tunnels has increased dramatically.Affected by factors such as terrain and land occupation,more and more attention has been paid to the construction of multi-arch tunnels.Most of the early-arch double-arch tunnels were mainly monolithic middle-wall multi-arch tunnels.With the extension of the operating time,the monolithic middle-wall multi-arch tunnels exposed serious diseases.Subsequently,the compound middle-wall double-arch tunnel was gradually applied to the design and construction of the double-arch tunnel.Compared with the integral middle wall double arch tunnel,the overall performance of the composite middle wall double arch tunnel during operation is relatively good.Due to the relatively late appearance of the tunnel form,the research results of its mechanical mechanism are relatively small,and further research is needed.This paper relies on the gold-tip composite curved middle-wall double-arch tunnel project under construction,based on literature review,field investigation,mathematical statistics,numerical analysis,and on-site monitoring.The mechanical characteristics are systematically researched in order to reveal the mechanical mechanism of the compound curved middle wall double-arch tunnel,and provide a theoretical basis for the management of tunnel structural diseases in the operation stage.The main research contents and conclusions are as follows:1.Combined with the disease detection data of 8 composite curved middle wall double arch tunnels,and compared with the integrated straight middle wall tunnel and separated tunnel lining disease data,the general law of composite curved middle wall tunnel lining diseases was obtained.,And analyzed the cause of the disease.The study believes that the complicated surrounding rock-supporting relationship near the partition wall is the main reason for the serious disease on the side of the partition wall of the double-arch tunnel.2.Based on the numerical method,the change law of the stress and displacement of the partition wall and supporting structure of the compound curved middle wall double-arch tunnel under different working conditions is analyzed,and the composite curved middle wall and the integral straight middle wall are compared and analyzed.The stress and displacement changes of the partition wall and the supporting structure during the construction of the arch tunnel mainly draw the following conclusions:(1)Bias has an adverse effect on the stress of the composite curved middle wall and supporting structure,which is mainly manifested in the overall displacement of the tunnel to the shallow buried side,the periphery of the shallow buried side converging,and the outer arch waist and side walls.Longitudinal cracks are prone to occur at the adjacent locations.At the same time,the bias increases the deflection of the partition wall to the shallow buried side.The relative displacement of the wall top and the foot of the wall increases,which is likely to cause diseases.The topographic bias and the bias caused by construction The bias condition of the partition wall is intensified,and the stress value of the first excavation side is greater than that of the excavation side.(2)Through a comparative analysis of the composite and integral middle-wall double-arch tunnels,it is found that the wall displacement of the composite middle wall is smaller.Taking the wall foot as an example,the vertical displacement of the wall foot of the composite middle wall is an integral 30 %,The lateral displacement is 20% of the integral type,and the relative displacement of each part of the composite middle wall is smaller.Diseases are likely to occur on the top and toe of the monolithic middle wall,which is consistent with the results of the disease investigation in Chapter 2.Compared with the monolithic middle wall,the stress value of the monolithic middle wall is relatively small.70% of the type,the supporting structure is 90% of the integral type,but the middle of the wall and the top of the composite curved wall is still a high incidence area of disease.(3)Based on the on-site monitoring methods,the mechanical characteristics of the partition wall and supporting structure of the gold-tipped composite curved middle-wall double-arch tunnel are analyzed.The main conclusions are as follows: the overlying biased layer of the tunnel significantly affects the mechanical performance of the tunnel structure,and the overall tunnel The displacement to the shallow buried side occurred.The pressure on the deep buried side tunnel and the partition wall on the same side was greater than that on the shallow buried side.The surrounding rock pressure,the pressure between the two support layers,and the stress on the second lining showed similar characteristics.The stress in the middle of the wall is large and the wall is biased.Obtaining the complex surrounding rock-supporting relationship near the partition wall is the main reason for the serious disease on the side of the partition wall of the double-arch tunnel.