Research On Deformation Rules And Support Techniques For The Ridge Section Of Muzhailing Soft Rock Tunnel With High Geostress

The Muzhailing tunnel of Lanzhou-Chongqing railway, which is located in Gansu Province, is evaluated as "high risk tunnel" by the ministry of railways. After entering ridge section of Muzhailing Tunnel, we encountered many difficulties in construction.This paper is based on project of the ridge section of Muzhailing tunnel, combined with the construction method and monitoring measurement project of the tunnel, numerical simulation method is used to study the deformation rule and the mechanical characteristics of the surrounding rock and lining structure of the high geostress soft rock tunnel, as well as the support techniques.Focusing on problems of deformation for primary supports and crack for secondary lining, the following researches are carried out:(1) Introducing the geological lithology, tectonic stress and ground conditions of Muzhailing tunnel, combined with theoretical calculations, so that the strength parameters, deformation parameters and lateral pressure coefficient of the surrounding rock are determined.(2) By using the monitoring data and numerical simulation method, analysis is conducted to investigate the characteristics and deformation rule of the ridge secton of Muzhailing soft rock tunnel with high ground stresses.(3) Analysing the mechanical characteristics of the surrounding rock and lining structure of the tunnel. The paper has analyzed the effect of stress relaxation area and found out elasticity modulus, stress relaxation area thickness, the lateral pressure coefficient and tunnel shape on the surrounding rock and lining structure stress influence. Finally we started from the aspects of stress relaxation area, determined the lining cracking reasons.(4) From aspects of primary supports deformation, primary supports stress, surrounding rock stress and surrounding rock mass plastic zone, we compared the pilot enlarging tunnel with circular cross-section and the 3-bench method. In the end, by using of the concept of stress relaxation area, we evaluated the safety of lining structures.