Influence of pipe jacking excavation in overlying quicksand layer on surface settlement and numerical analysis

Abstract

The cause of quicksand in soil depends on the nature of soil. Under the action of permeability, quicksand is easy to occur when the pore ratio of soil is large, the water content is large, the clay content is small, the silt content is large, the permeability coefficient is small and the drainage performance is poor. Therefore, quicksand phenomenon is easy to occur in fine sand, silt and loam, but whether quicksand phenomenon occurs or not also depends on certain external conditions, that is, the hydrodynamic pressure (permeability) generated by the seepage of groundwater in the soil. When the upward seepage force of unit granular soil is greater than or equal to its own gravity, the soil will suspend and move. In the process of underground engineering construction, if the problem of quicksand is not solved, the structure will displace with the flow of sand layer, which will change the bearing layer of the foundation and do great harm to the structure. This phenomenon should be eliminated. Practice shows that many accidents of underground structures are related to quicksand caused by the change of seepage conditions during construction. The disturbance of soil in pipe jacking construction is the fundamental cause of soil deformation. It destroys the original natural equilibrium state of soil, changes the stress-strain state of soil, and makes the undisturbed soil experience complex stress paths such as extrusion, shear and deformation. In this paper, a numerical model is established to analyze the surface settlement trend of pipe jacking in quicksand covered stratum, and the methods of grouting behind pipe jacking wall and excavation surface stability measures are verified to control the settlement measures in the construction process.