Dynamic evolution characteristics of ground collapse of covered karst based on particle flow
Karst collapse represents a significant geological hazard,predominantly occurring in regions characterized by the presence of soluble rock formations,including carbonate rocks,calcareous clastic rocks and salt rocks,among others. The characteristics of karst collapse fall into three key attributes:a hidden spatial distribution,a sudden occurrence and a periodic recurrence over time. These attributes can collectively challenge the construction of major infrastructure in karst areas. A karst collapse disaster along the railway will potentially pose a significant threat to the safe construction and continued operation of the high-speed railways. During both the construction and operational phases of railways in karst areas,pumping and discharging groundwater,along with altering hydrodynamic conditions,have been identified as key factors contributing to karst collapse. The most widely used numerical simulation method is the finite element method (FEM),which is based on the assumption of a continuous medium. FEM simplifies a complex problem by breaking it down into more manageable components. It conceptualizes the solution domain as a collection of small interconnected sub-domains called finite elements. For each element,a suitable (simpler) approximate solution is assumed,and the conditions necessary for solving the overall domain are derived. However,soil is not a continuous medium;therefore,a model based on FEM is unable to simulate the local instability of a collapsed soil body,the damage process at a mesoscopic scale,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 caves 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,in which a contact bonding model was also introduced. This model assumed that the filler in the cave was entirely washed away due to the erosive effect of groundwater seepage. Additionally,the vacuum suction and erosion effect inside the cave were not taken into consideration during the simulation period. The effect of groundwater on soil strength was 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 can elucidate the dynamic evolution process and deformation characteristics of karst collapse from a mesoscopic view. Furthermore,the influence of various sizes of cave openings,thicknesses of overburden layers and groundwater levels on the deformation of the overlying karst collapse has been investigated. The migration laws of soil particles under the influence of different factors have been analyzed.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:equilibrium of stress-formation of stress arch-destruction of stress arch-equilibrium of stress again-…-fracture of stress arch. The internal stress of the soil body demonstrates the following pattern: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 cave is,the greater the depth and range of surface subsidence become,which in turn increases the likelihood of collapse. A reduction in the thickness of an overburden layer may cause a more pronounced surface subsidence,thereby increasing the likelihood of collapse. Similarly,an elevated water level may contribute to a more rapid expansion of the soil cave,which in turn will cause a more pronounced surface subsidence and an increased propensity for collapse. The relationship between surface subsidence and thickness of overburden layer is not significant when the thickness of the latter is large. The study provides a comprehensive account of the karst collapse evolution from a mesoscopic perspective,offering insights into prevention and mitigation of karst collapse during the construction and operation of high-speed railways.
covered karstexpansion of soil caveparticle flownumerical simulationdynamic evolution
万方数据
维普
