Study On Collapse Mechanism Of Soil Subgrade Of City Roads By Water Erosion

In recent years, there have been many ground collapse accidents in our countrycity roads. The disaster is sudden, concealed, and highly destructive. Its influence onthe road is mainly manifested in the phagocytosis of personnel and vehicles. At thesame time the subsidence accident also affects the safety of upper structure, which hasdrawn wide attention from all sectors of society.In this paper, it takes city pavements as the research background, to study therelationship between underlying cavities and pipeline leakage erosion of city road, andto understand the relationship between seepage water flow, pipeline fracture spacing,erosion time and underground cavity expansion shape and size, and to discusses themechanism and influence factors of road collapse accident, providing theoretical basisfor preventing such disasters. The main works of the thesis are as follows:First of all, this paper studied the laws of Water erosion causing the undergroundcavity of drainage pipeline and water supply pipeline respectively, usingsemi-structural model and under the condition of the fixed flow of about230ml/s. It isconcluded that drainage pipeline will generally form an empty and flat ellipsoid in theground, and the fastest erosion speed is nearly1.7m/h， and after the water supply linefracture due to the enormous pressure, there were large area surface water.Then, in order to understand the mechanism of ground collapse, the paperanalyzed the ground subsidence sedimentation, the surface stress and the plastic zonedistribution, with the ANSYS finite element method. The main conclusions are asfollows: among other things, with the increase of the length of the underground cavity,the surface settlement increases, and the subsidence funnel formation is deeper,eventually collapse occurs. When the ground collapses, the length is about15m (thedepth is3m) in the numerical simulation. We believe that the main failure form ofground collapse is shear failure, and the subsidence surface is cylindrical. The signs ofcity road collapse before the performance are the rapid development of road surfacedisplacement and surface cracks, which often means the rapid development of thedamage area below.Third, using the method of numerical simulation and orthogonal test, the paperstudied the main influence factor about the critical depth. The main conclusions:among the influence factors of city road collapse, the reduction factor has the greatestimpact, followed by the width to length ratio, the last high length ratios. While the main geometrical index (short side length) is fixed, we can conclude that more flat andstrip the underground cavity is, more easily the ground subsidence will occur (shortside fixed).Finally, by using numerical simulation method, the ground collapse conditionswith hardened layer and without hardened were tested. the main conclusions: Themain function of the hardened layer is to improve the formation of stiffness, resultingin more smooth pavement in the condition of adverse load, so that people can drivemore comfortably, but it also increases the soil load value, resulting in the subgradesoil is more easily to be crushed.