Stratigraphic response and control measures induced by excavation of shallow underpass tunnels

Tunneling through existing buildings in shallow soft rock strata is a key and difficult issue in tunnel construction. To investigate the disturbance and deformation mechanism of soft rock stratum in the tunnel underpass project, based on the Longquanshan Tunnel, a more suitable construction method for shallow tunnel underpassing existing buildings was proposed - the New Sidewall (NS) method. Using FLAC3D, a refined numerical model of a shallow tunnel passing under a glass trestle was established to study the disturbance effect of different construction methods on the soft ground layer and the degree of influence of the glass trestle piles. The applicability and control effect of the work method was verified combined with on-site monitoring data. Results indicate that the large deformations and other engineering problems in the tunnel are mainly caused by the weak surrounding rocks in the shallow inlet section. The cover layer of the shallow buried section is thin and unable to form an arch, and the original three-step method is ineffective in controlling deformation. The deformation of the surrounding rock is controlled significantly when high-pressure rotary jet grouting piles are used to reinforce the ground layer in the tunnel section. However, the deformation is still large when using the Cross Diaphragm (CRD) method, Center Diaphragm (CD) method, and three-step method. The NS method has the advantages of optimized zoning of the palm face and a temporary support structure for large deformations. The proposed NS method of construction can effectively reduce excavation disturbance, control the deformation of surrounding rock and surface, and ensure the safe operation of the glass stack.