Method for determining safe vertical distance between shield and karst cave in sand karst stratum

Abstract

The invention provides a method for determining a safe vertical distance between the shield and karst cave in the sand karst stratum. The method comprises the following steps: firstly, surveying the field geology of a project; secondly, establishing a finite element analytical model by utilizing three-dimensional finite element modeling software for simulating a karst cave, the excavation face balance, the stratum loss, a lining and slag cart and the shield tunnel construction excavation; thirdly, calculating the vertical displacement of shield tunnel excavation on the karst cave under different working conditions; and fourthly, making a normalized relational graph of the karst cave roof sedimentation and the distance between the karst cave and the tunnel. The method sufficiently takes shield tail volume loss into consideration when the karst cave is positioned under a tunnel during shield tunnel construction, and calculates a safe vertical distance formula for the tunnel excavation influenced karst cave by analyzing the normalized relation among karst cave roof sedimentation, vertical distance between the karst cave and the tunnel and the diameter of the karst cave; and the formula is simple and clear, is beneficial to quick and intuitive judgment of a field engineer, and can be used for improving the construction efficiency.

Description

technical field [0001] The invention relates to a method in the technical field of underground building construction, in particular to a method for determining the safe vertical distance between a shield tunnel and a karst cave in an overlying sandy-soil karst composite stratum. Background technique [0002] Karst is a landform that is eroded and destroyed by surface runoff and groundwater flow. Karst strata are distributed in many provinces in my country. With the development of urbanization, many cities need a large amount of underground space and urban subway construction, so it is inevitable to carry out tunnel construction in the overlying sandy soil karst composite stratum. Shield tunneling is carried out in the overlying sandy-soil karst composite stratum. The karst caves are distributed irregularly in the karst stratum. The tunnel excavation will disturb the surrounding soil. When there are karst caves under the tunnel, the excavation process may cause The cave defo...

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Problems solved by technology

[0003] After searching the existing literature, it is found that the Chinese patent application publication number is "CN103577642A", and the patent name is a method for determining the safety distance between hidden karst caves and newly built mountain tunnels. The finite element model of the distance between the cave and the tunnel is simulated for the finite element solution of the tunnel construction sequence, and the plastic strain energy of the rock layer between the hidden cave and the tunnel is calculated after each distance reduction, and the distance between the cave and the tunnel and the plasticity of the rock layer between the hidden cave and the tunnel are established. The deformation and strain energy change sequence, and then calculate the energy mutation characteristic value, when the energy mutation characteristic value is less than or equal to 0, output the safety distance between the hidden karst cave and the tunnel.” This method uses the energy mutation between the hidden karst cave and the tunnel as the safety distance criterion, and determines the The safety distance is smaller than the safety distance determined by the conventional plastic zone criterion, but it is mainly aimed at the safety distance of mountain tunnels, and does not consider the construction of shield tunnels in the overlying sandy soil karst composite strata and the volume loss of shield tails, and the modeling and calculation processes are relatively complex. Complicated, not conducive to quick and intuitive judgments by field engineers, poor operability, and relatively low efficiency

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