Research On Surrounding Rock Deformation Law During The Gradient Bias Multi-arch Tunnel Construction

In recent years,multi-arch tunnel is more and more being applied to the particular geological because of the advantages of its linear flow,covering an area of less,high space utilization,convenient connection hole line and avoiding the tunnel portal separated roadbed and bridge,which has brought good economic and technical effects for the country's engineering construction.However,the special structure of multi-arch tunnel has also led to the complex stress state and the difficulty of construction.The Daniu mountain tunnel on the Guangzhou-Zhongshan-Jiangmen highway is a two-way six lanes multi-arch tunnel,which designs total length of 341 m,maximum depth more than 45 m,minimum depth less than 5 m,the largest span more than 16 m.The entrance and exit zone of tunnel are shallow under unsymmetrical pressure,the embedded depth of the tunnel showed a trend of obvious incremental change direction along the tunnel,and the tunnel construction process involves four different excavation methods,all above put forward high request to the construction of engineering.In order to delve into the gradual unsymmetrical pressure,multi-arch tunnel deformation characteristics of surrounding rock under different construction methods,this paper study on deformation monitoring of tunnel construction process on the basis of Daniu mountain tunnel engineering example.In addition,the paper use two different tunnel excavation construction process of the three-dimensional finite element numerical analysis on the design change scheme.Using the above study contents,the results are as follows:(1)The spatial distribution of the vertical deformation and horizontal deformation are affected by gradient bias,properties of surrounding rock and supporting intensity together.For the middle drift,the supporting intensity is the most important factor on the vertical deformation.The stronger the supporting intensity,the smaller the deformation.And lateral deformation is sensitive to change with external disturbances.For the main hole,the vertical deformation of the entrance and exit zone of shallow bias with buried depth increases,the bias on lateral deformation value has amplification effect.When the benching tunneling method is used in the middle of main hole,the deformation of the first tunnel was affected obviously by double holes superimposition effect than the following holes.(2)The ground displacement of the middle drift is positively correlated to the cover depth change.The ground movement of the main hole and the cover depth change are correlated negatively.(3)K3+043 section pressure test research shows the surface depth is one of the most important factors affecting the contact pressure distribution.(4)The results of three-dimensional finite element numerical analysis as follows: Single wall heading construction method of the excavation period of impact on the surrounding rock is shown as: lateral drift > the main hole on the steps > the main hole down the steps;The benching tunneling method of the excavation period of impact on the surrounding rock is shown as: the right hole up the steps > right hole down the steps.