Experimental Study on Stratigraphic Subsidence Induced by Sand Leakage in Tunnel Lining Cracks

In order to study the problem of strata subsidence caused by sand leakage in tunnel lining cracks in sandy soil, a set of sand (water) leakage visualization test system for underground engineering which could change the size of circular leakage opening was designed. The sand flow pattern under different working conditions was obtained. It was shown that the sand inrush process could be divided into four stages: initial stage, induced stage, diffusion stage and stable stage. The influence of the diameter of the leakage opening and the thickness of soil layer on the sand inrush and the sandy soil subsidence was studied. When the diameter of the sand leakage opening was same, the influence range of the subsidence increased with the increase of the thickness of soil layer. When the thickness-to-span ratio reached 21.4, the sand layer only subsided. No sand inrush occurred. When the thickness-to-span ratio continued to increase to 25.7, the sand layer did not subside. When the thickness of the sand layer was same, the diameter of the columnar region in the vertical subsidence zone increased with the increase of the diameter of the sand leakage opening. The subsidence range induced by the circular sand leakage opening was rounded on the top plane, and the quadratic surface was approximated on the section. The subsidence range of the soil was related to the shape failure angle of the collapsed surface. The shape failure angle of the collapsed surface was about 13° larger than the natural angle of repose of the soil. This provided a reference for the prevention and control of stratigraphic subsidence caused by the sand leakage of tunnel lining cracks in sandy soil layers.