Study on the dynamics response characterstics of covered soil-cave type karst collapse under train vibration environment

SHI Hai; JIA Zhilei; BAI Mingzhou; ZHANG Ye; SUN Zibing

doi:10.11932/karst20250210

Abstract：Karst collapse represents a significant geological hazard,predominantly occurring in regions characterised by the presence of soluble rock formations,including carbonate rocks,calcareous clastic rocks and salt rocks,among others.Karst collapse are characterised by three key features,a hidden spatial distribution,a sudden onset and periodic recurrence over time.These attributes collectively pose a considerable challenge for the construction of major infrastructure projects in karst areas.The karst collapse disaster along the railway has the potential to pose a significant threat to the safe construction and sustained operation of the high-speed railway project.The extraction and discharge of groundwater,along with the alteration of hydrodynamic conditions during both the construction and operational phases of the railway in the karst area,have been identified as key factors contributing to the karst collapse.The most prevalent numerical simulation method is the Finite Element Method(FEM),which is predicated on the assumption of a continuous medium.The FEM involves replacing a complex problem with a simpler one and then solving it.It views the solution domain as consisting of a number of small interconnected sub-domains called finite elements,assumes a suitable(simpler)approximate solution for each element,and then deduces the conditions that are satisfied for solving the domain in general.However,soil is not a continuous medium,and a model based on the FEM is unable to simulate the local instability of a collapsed soil body,the mesoscopic-scale damage process,and other phenomena. In light of the dearth of sufficient attention to the temporal effects and fine-scale mechanisms of the karst collapse process in current studies,this paper aims to elucidate the dynamic evolution laws and mesoscopic-scale collapse mechanisms of the expansion of overlying karst soil cavities around the railway.A typical karst collapse site,namely the Beijing-Shanghai high-speed railway(Jiangxi section),was selected as the basis for calibrating the strength parameters of the collapsed soil body.This was achieved through a particle flow(PFC2D)compression test,which also introduced a contact bonding model.This model assumed that the filler in the cavern is entirely washed away due to the erosive effect of groundwater seepage.Additionally,the vacuum suction and erosion effect inside the cavern were not considered during the simulation period.The effect of groundwater on soil strength is simulated by reducing the contact strength between particles below the modelled water level.In conclusion,a coupled flow-solid model of overlying karst collapse has been established,which elucidates the dynamic evolution process and deformation characteristics of karst collapse from a mesoscopic view.Furthermore,the influence of varying cavern opening sizes,overburden layer thickness and water table height on the deformation characteristics of the overlying karst collapse has been investigated,as well as the migration law of soil particles under the influence of different factors. The study demonstrates that during the evolution of overlying karst collapse,the contact force between particles undergoes a series of changes,which can be described approximately as follows,'stress equilibrium-stress arch formation-stress arch destruction-stress equilibrium again-…-stress arch fracture'.The internal stress of the soil body demonstrates a pattern of'compressive stress gradually decreasing,tensile stress gradually increasing,and tensile stress disappearing'.Additionally,the surface subsidence and porosity of the soil body tend to increase in conjunction with the collapse evolution process.It can be observed that the larger the opening of the cavern,the greater the depth and range of ground subsidence,which in turn increases the likelihood of collapse.A reduction in the thickness of the cover layer results in a more pronounced surface subsidence,thereby increasing the likelihood of collapse.Similarly,an elevated water table leads to a more rapid expansion of the soil hole,which in turn causes a more pronounced surface subsidence and an increased propensity for collapse.The relationship between surface settlement and cover layer thickness is not significant when the latter is of greater thickness.The study provides a comprehensive account of the karst collapse evolution process from a mesoscopic perspective,offering insights that can inform disaster prevention and the mitigation of surrounding karst collapse risks during the construction and operation of high-speed railway projects.