Numerical simulation of deformation in the development strata of karst caves for slab foundations and the control of safe distance

HUANG Yunlong; GAO Bin; ZHOU Hang; YU Zhe; HE Wen

doi:10.11932/karst20250110

Abstract：Karst areas are widely distributed throughout China,and karst caves are a common karst form in these regions.As China's economy continues to develop and the demand for rural revitalization intensifies,infrastructure,such as transmission lines,often has to traverse karst areas.In the entire process of infrastructure construction,ensuring the safety of foundations in karst strata is of utmost importance.The existence of karst caves significantly increases the complexity of the deformation of slab foundations.Unfortunately,the failure modes and deformation mechanisms of these foundations in such environments remain unclear.This lack of understanding makes it extremely difficult to propose targeted prevention and control measures in engineering practice.To address this issue,finite element software PLAXIS 2D is employed to establish a numerical model of the slab foundation of electric power towers in karst strata.This model is used to simulate the development of shear bands and load-displacement curves,thereby elucidating the failure mechanisms and conducting analysis on bearing characteristics of slab foundations in karst strata. Against the backdrop of real-world projects,finite element software is utilized to determine the most adverse simulation working conditions.Key factors including relative locations,sizes,and burial depths of karst caves,have been studied to determine their influence on the deformation of transmission tower foundations.Through this research,the deformation mechanism and bearing performance of slab foundations under various load combinations,different locations of karst cave,and varying sizes of karst caves have been examined.Based on the criterion—the limit value of foundation inclination in the serviceability limit state—the failure range of slab foundations in karst strata was delineated.This delineation may provide a crucial basis for the site selection of slab foundations in karst strata.The study results show that the locations,sizes,and load types of karst caves significantly influence the development of shear bands and the failure mechanisms of foundation soil.Affected by the locations of karst caves and the varying tension and compression loads on both sides,slab foundations exhibit diverse failure modes and bearing characteristics.Whether it involves a compression-compression combination or a tension-compression combination,the shear strain will pass from the compressed side of the foundation close to the karst cave into the karst cave.This may result in the formation of an arc-shaped shear band between the karst cave and the foundation.The most unfavorable situation occurs when a karst cave is developed directly beneath a compressed foundation.In terms of the bearing capacity of the foundation in karst strata,this capacity increases as the ratio of diameter(D)to width(B)decreases.Therefore,in practical engineering,the width of the slab should be maximized relative to the diameter of the karst cave.When the ratio D/B exceeds 1,further increase of the width of the slab foundation does not significantly enhance the bearing capacity of the foundation.Additionally,the larger the radius of the karst cave and the closer it is to the foundation,the more pronounced the impact on the inclination of the transmission tower.However,it is important to note that the influence of karst caves on transmission towers is limited to a specific range.Based on the numerical results,a safety design diagram of transmission tower foundations in karst strata is proposed,delineating the safety area of slab foundations.This design diagram aids to determine the construction locations of transmission towers,which can help reduce both line costs and expenses related to karst cave treatment,providing valuable reference for line site selection.This method can provide significant guidance for the site selection of slab foundations of electric power towers in similar karst strata and the management of karst caves. For the site selection of slab foundations for electric power towers,engineers can utilize the analysis results generated by this method to comprehensively consider various factors and select the most appropriate construction location.This approach can effectively minimize the risk of foundation deformation and enhance the stability and safety of electric power towers.At the same time,this method also helps to plan and design foundation structures in advance,allowing for better adaptation to the special geological conditions of karst strata.This approach also minimize uncertainties and difficulties during subsequent construction phrases.In terms of the management of karst caves,this method provides a basis for formulating scientific and reasonable treatment plans.According to the influence of karst caves on the inclination of transmission towers and the relationship between foundation bearing capacity and parameters related to karst caves,targeted measures such as filling and reinforcement can be implemented.In addition,by delineating the failure range of slab foundations in karst strata,the areas requiring focused attention and treatment can be identified more clearly,thereby enhancing the efficiency and effectiveness of karst cave treatment.