Research on Construction Methods and Stability of the Large-section Tunnels with Shallow Tunneling Excavation Method
|School||Xi'an University of Architecture and Technology|
|Course||Bridge and Tunnel Engineering|
|Keywords||large-section shallow excavation construction methods monitoring stability|
With the accelerated process of urbanization in China, subway plays anincreasingly important role in addressing the increasingly prominent urban transportproblems. Building tunnels in densely populated, heavy traffic, buildings and facilitiesover the city, the specificity of construction environment determines the complexity ofsurrounding rock deformation and supporting structure force in tunnel constructionprocess. Especially in shallow large-section tunnel excavation, the fields of surroundingrock displacement and stress are complicated, having a great impact on the surfaceenvironment and buildings, and initial supporting deformation is large and difficult tocontrol, which causes tunnel to collapse and has an impact on construction safety, soselecting a reasonable construction method is the key to the tunnel construction. Basedon the Harbin subway project, combining the methods of finite element numericalsimulation and field monitoring data analysis, this paper has done some research onconstruction methods and stability of the large-section tunnels with shallow tunnelingexcavation method, the most important conclusions are summarized as follows:1. Simulating the construction process of the CRD method with the finite elementsoftware, through the analysis of calculation results, found that the deformation ofsurrounding rock caused by the upper soil of the tunnel excavation is large, where thevault settlement value is13.1mm, the arch bottom uplift value is10.2mm, the largestincrease in ground subsidence is7.0mm caused by the upper soil of the right pilottunnel excavation, temporary vertical and initial supporting junctions appear stressconcentration, and temporary vertical supporting structures need to withstand greaterbending moments and axial compression. 2. By analyzing the numerical simulation of construction process of the both-sidesdrift method,found that vault settlement value is14.7mm, the arch bottom uplift valueis12.9mm, the largest increase in ground subsidence is7.7mm caused by the uppersoil of the center-upper pilot tunnel excavation, the supporting structure (includinginitial supporting and temporary supporting)corresponding to center-upper pilot need towithstand greater bending moments and axial compression in this phase, the bendingmoment and axial force, respectively, to achieve the maximum bending moment of thesupporting structure0.88times,0.95times the maximum axial compression during thewhole construction phase.3. Through the comparative analysis of surrounding rock displacement field, stressfield and supporting structure internal force status, found that the CRD method andboth-sides drift method are not very different in terms of surrounding rock displacementfield control, but in terms of surrounding rock stress field control and supportinginternal force state, which is superior to the former, so the both-sides drift method isbasically superior to the CRD method.4. The variation of tunnel clearance convergence, vault settlement, and groundsettlement caused by construction with the both-sides drift method are obtainedfollowing a large number of monitoring data analysis, the law of the interaction betweenthe first pilot tunnel excavation and later pilot tunnel excavation, and the stability ofsurrounding rock deformation of the construction phase is discussed in terms of thedisplacement and the displacement rate changes.