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2020 Vol. 39, No. 4

Display Method:
Key scientific issues in research on landslide hazard induced by underground mining in mountainous areas with coal-bearing strata of southwestern China
LI Jun, CHU Hongliang, LI Bin, HE Kai, GAO Yang
2020, 39(4): 453-466. doi: 10.11932/karst20200401
Abstract:
Underground mining activities often trigger large-scale landslide on mountain slopes, causing casualties and property losses. Based on the analysis of the development characteristics of landslide hazard induced by underground mining, this paper considers that such landslide hazard often occur in the cliff belts of fold wings and core composed of layered carbonate rock and clastic rock strata in mountainous area with coal-bearing strata of southwestern China, which is closely related to factors such as topography, stratum structure and underground mining engineering activities. It is pointed out the following processes that large-scale landslide hazard induced by thin seam mining,(1) The overlying rock roof collapses and the overburden rock roof separates, and the stress transfer from the bottom to the top in and between the overburden rock in the goaf after the mined-out; (2)The formation of underground water migration channels accelerates the failure and expansion of rock mass structures on a larger scale, accelerating the loosening and failure of rock mass structural planes;(3) The uneven settlement of the overburden rock strata leads to fractures at the foot of the slope, and the large-scale rock mass structural surface of the mountain body gradually deforms under tension shear or compression shear, eventually resulting cumulative damage and large-scale landslide hazard. At the same time, this study suggests that the calculation method of traditional empirical formula is no longer applicable to this type of landslide hazard induced by underground mining.It is recommended to develop the research on following key scientific issues, including the interaction relationship between the geological structure and the landslide hazard induced by underground mining of the karst mountainous area with coal-bearing strata of southwestern China, the cumulative fracture damage and rock mass loosening in the upper part of thin seam goaf, fracture expansion and karst conduit flow, the chain response mechanism of fracture flow change of upper mountain in the mined area of thin ore bed, and the evaluation method of landslide hazard induced by underground mining,etc. The purpose is to promote the the development of prevention and mitigation work of geological hazard induced by underground mining.
Identification of large-scale landslide hazards based on differences of geological structure prone to sliding and multiple-source data in karst mountainous areas
HE Kai, LI Bin, ZHAO Chaoying, GAO Yang, CHEN Liquan, LIU Pengfei
2020, 39(4): 467-477. doi: 10.11932/karst20200402
Abstract:
The geological environment in karst mountainous areas of southwest China is complex and fragile, where large landslide hazards are common. The inaccurate geological cognition of karst mountainous area will directly lead to the lack of disaster identification ability. Based on the three kinds of main geological structures, exposed karst cliffs, complex rock formations and non-exposed karst slopes, which are prone to sliding in the karst mountainous areas of China, more applicable identification and detection methods of multiple-source data are discussed in this paper. For the karst cliff composed by thick layers of carbonate with small spatial impact area, the satellite-ground combination identification method is more applicable. The trend of dynamic deformation can be measured with the GNSS detection method, then the possible failure modes can be prejudged preliminarily. At the same time, it can help to make vector correction to the displacement from InSAR interpretation, to improve the degree of identification of the areas with the same or similar SAR observation conditions. For geological hazards with large spatial impact areas, the remote sensing technology based on InSAR is preferred to obtain surface deformation. For large deformation areas with high risk, the possible initiation mechanism can be studied or inversion analyzed in combination with the structure models liable to slide and external influence factors. The displacement identification method focuses on the increment of surface deformation is not applicable to the sudden landslides without enough early deformation. In view of such potential geological hazards, a comprehensive identification system can be constructed through multiple-source and multiple-dimensional monitoring, so as to explore a new way of landslide hazards identification and data analysis.
Geological models classification of deformation and failures for collapses and landslides in karst mountainous areas
GUO Jingyun, LI Shouding, LI Bin, LI Xiao, BI Xingtao, FANG Ranke
2020, 39(4): 478-491. doi: 10.11932/karst20200403
Abstract:
The special engineering hydrology structure in karst mountainous areas results in extremely developed geological disasters such as collapses, landslides and debris flow, which bring about serious casualties and economic and social losses. It is of great theoretical and application values for risk prevention and management in such areas to study characteristics of these hazards and establish corresponding geological models. This article systematically analyzes the geological background, influencing factors and dynamics and kinematics characteristics of collapses and landslides in the study area, and establishes geological models of deformation and failures taking the formation and evolution of typical collapses and landslides as examples. Results show that, (1) the factors that affect and reflect the characteristics of collapses and landslides can be divided into basic factors including gravity potential energy, rock group structure, karst structural planes, slope topography, slope stucture; and influencing factors such as hydrogeological conditions, engineering activities, earthquakes, rainfall and deformation movement characteristics (movement forms and deformation mechanisms). Based on these, a comprehensive index system of collapses and landslides is established. (2) Systematic analyis on each element in the model system suggests that the occurrence of collapse and landslide hazards is the result of the combination and interaction of various elements. (3) Combined with typical cases of collapse and landslide hazards in the study area, five typical geological models are established. They are the high potential energy-anti-dipping-rainfall induced high-speed long-distance landslide-debris flow model, high potential energy-oblique tilting direction-mining induced high-speed long-distance landslide model, ultra-high potential energy-lateral steep seismic induced high-speed long-range landslide model, high potential energy mining induced high-speed collapse-debris flow model, and the low potential energy-differential weathering collapse model. These geological models lay the foundation for subsequent physical simulation, numerical modeling, stability calculation and deformation and failure prediction. The next step is to build more comprehensive models of collapse and landslide hazards in the study area and carry out the risk classification of these hazards.
Review on the connotation and methods of emergency investigations to geological hazards in mountainous area
WANG Yu, HUANG Cheng, ZHOU Cuiqiong, YANG Yingdong, XIAO Huazong, YAN Xiangsheng, ZHANG Lingze, WANG Yuqin
2020, 39(4): 492-499. doi: 10.11932/karst20200404
Abstract:
Emergency investigations of geological hazards are immediate surveys to sudden geological hazards or dangerous situations. Real-time information should be provided timely during the survey period of one to several days, and the emergency investigation report should be submitted as soon as possible, so as to provide scientific basis and technical support for emergency rescue and management of geological hazards. Such emergency surveys are divided into two types,single point and a mass of geological hazards survey according to the technical conditions of surveys. This paper describes the main workflow of surveys including basic data preparation, on-site coordination meetings, decision-making and coordination arrangement, satellite and UAV remote sensing surveys, field emergency surveys, data integration research and report compilation, as well as the main working methods of each link. In general a geological hazard emergency survey adopts convenient and effective methods, such as field investigations and visits, geological mapping and satellite positioning, high-resolution satellite remote sensing, and aerial photography by UAV. In addition, the basic rules, methods and technical requirements of geological hazard emergency survey in mountainous areas are analyzed and reviewed in detail in this paper.
Experimental study on nonlinear flow properties of pipe-fissure water in carbonate rocks during failures
SUN Huan, LIU Xiaoli, WANG Enzhi, LIU Chi, ZHANG Jianmin
2020, 39(4): 500-508. doi: 10.11932/karst20200405
Abstract:
This study focus on nonlinear flow properties of pipe-fissure water in carbonate rocks during failures. A visible flow experiment was carried out to observe pipe-fissure water during rock failures. Flow transition patterns of pipes and fissures water were quantitatively described according to the experiment data of flows in rocks under multi-level loading. The results show that the pipe fluid pattern is closely related to the roughness of the pipe-wall. The laminar flow at primarily cracks changes gradually into the transition flow at broken rocks. Pipe spalling can induce fluid pattern alternation with time duration. The precursory characteristics of transition fluid patterns of the pipe and fissure express as the critical point of flows. Pipe flow transforms into fissure flow with a feature of fractional evolution during carbonate rocks failure. The fractional index can be quantitatively used to define the critical transition process of the pipe into fissure flow.
Experimental study on the deformation mechanism of upper-hard and lower-soft gently dipping rock on high slopes under the mining effect
ZHONG Zuliang, WANG Nanyun, LI Bin, LIU Xinrong, Cui Fangpeng, YANG Zhongping
2020, 39(4): 509-517. doi: 10.11932/karst20200406
Abstract:
Complex geological environments characterize karst mountainous areas in southwest China with frequent underground mining activities and large-scale landslide hazards. The purpose of this work was to understand the law of slope subsidence and ground fissure development during mining activities under the upper-hard and lower-soft gently dipping rock slopes. Taking the Pusa collapse in Guizhou Provinceas an example, using similar-model experiments, we studied the surface settlement, internal displacement, interlayer pressure variation rule and features of mining ground fissure development of the slope body under mining activities. The results show that under the action of underground mining, the surface settlement and internal displacement of the slope body increase linearly with the growth of mining length. When the mining length is about 16 times of the mining height, the surface settlement of the test model increases sharply with cracks appearing. The closer the measurement point to the ground fissure, the greater the settlement change rate. The location of ground fissures and the maximum change rate of surface settlement appear roughly in the same area. When the driving face is advancing, the unloading area appears in the roof rock above the goaf where the compressive stress decreases, while the rock mass above the mining face has the interlayer compression area where compressive stress increases. Outside the mining height range of about 20 times above the goaf, the interlayer pressure in the test model is less affected by the disturbance of underground mining activities. The research in this paper has a certain reference significance for the early identification and failure mechanism analysis of landslides under underground mining activities in karst mountainous areas of southwest China.
Monitoring the Jianshanying landslide in a karst mountainous area of Guizhou by optical remote sensing
CHEN Liquan, ZHAO Chaoying, REN Chaofeng, WANG Peijie, CHEN Xuerong, CHEN Hengyi
2020, 39(4): 518-523. doi: 10.11932/karst20200407
Abstract:
Landslides in karst mountainous areas of southwest China induced by underground mining can cause huge economic losses and casualties. Such hazard is characterized by large deformation gradients and serious collapse of the surface. This work takes the Jianshanying mining-induced landslide as an example to realizes the quantitative 2D time-series deformation monitoring of the landslide by optical sub-pixel correlation methods based on multiple optical images. First, multiple historical archives of Google earth images and UAV images are used to detect the damage of the surface, showing that the 1# landslide area has undergone significant surface deformation in 2013, becoming increasingly serious over time. Then, the 2D deformation time series of the 1# landslide area from July 31, 2016 to March 22, 2020 is inverted based on the Sentinel-2 data. Results indicate that the horizontal deformation in this area tended to be larger in the slope direction as well as in the east-west and north-south directions over time. The deformation continued to increase over time, and the maximum cumulative deformation reached 44 m and -58 m, respectively. Therefore, the large-gradient deformation monitoring of the landslide disaster in Guizhou karst mountainous areas can be realized by using optical remote sensing technology, which is important to the monitoring and early warning of landslides in similar areas.
Discrete element modelling on dynamic triggering mechanism of the Pusa landslide in Nayong county, Guizhou Province
CUI Fangpeng, LI Bin, YANG Zhongping, WU Lele, LI Ning, PENG Jianquan
2020, 39(4): 524-534. doi: 10.11932/karst20200408
Abstract:
This paper presents a discrete element modeling using UDEC software to reproduce the dynamic response of the Pusa landslide triggered by the combination of goafs, deep major karst cracks, heavy rainfall and continual blasts during underground coal mining. Based on the reproduction, the dynamic triggering mechanism and the key contributing factors of the landslide are analyzed. The results show that caving, crack and deformation zones that developed in the strata overlying goafs during mining coal seams expand up gradually below the slope. The deformation zone meets the toe of the original slope after mining of the uppermost coal seam. Meanwhile, an obvious progressive deformation zone develops in the original slope containing the deep karst fractures. The deformation behaves as a wholly downward and clockwise movement. On the condition of the heavy rainfall, a continuous progressive deformation zone develops in the slope that has been influenced by the goafs. The deformation continues to behave more downward and clockwise movement as a whole. Finally, while the continual stope blasts, as the key contributing factor for the landslide, during the underground coal mining, the slope that has been influenced by the goafs and the heavy rainfall enters multiple-phase dynamic response stages including further progressive damage deformation, critical collapse, shattering, ejecting and compaction. Simultaneously, the whole slope exhibits a downward, apart break and clockwise rotation. These results modeling would provide a support for control of similar landslides.
Impact and scraping effects of the high-elevation,long-runout "7.23" landslide in Shuicheng , Guizhou
GAO Haoyuan, GAO Yang, HE Kai, LI Bin, ZHAO Zhinan, CHEN Lichuan, WANG Yongfu
2020, 39(4): 535-546. doi: 10.11932/karst20200409
Abstract:
This paper analyzes the Shuicheng"7.23" landslide in Guizhou, 2019. Based on the field survey, Unmanned Aerial Vehicle(UAV) images and numerical simulation, the movement process, and impact and scraping effects of this landslide are characterized. Results suggest that, (1) the Shuicheng"7.23" landslide sliding volume is about 70×104 m3, with the horizontal slide distance 1,360 m, elevation difference 430 m between the front and the toe, and the equivalent friction angle 19°, implying a typical high-level, long-distance slope slide; (2) After the initiation of the slide, it hit the convex ridge, scraped the residual slope soil of the surface, disintegrated and formed a debris flow, resulting in a maximum scraping depth of 11 m; (3) The numerical simulation shows that the maximum velocity of the landslide is 30 m?s-1, the maximum kinetic energy is 8,900 kJ, the scrap volume is 46×104 m3, and the deposit volume is 116×104 m3, with an obvious amplifying effect of hazard; (4) The impact and scraping process of the Shuicheng landslide can be divided into 3 stages, impact insertion, shear nappe and mixed accumulation of sliding debris.
Current situation of research on failure mechanism and stability of rock slopes under hydraulic action
LIU Xinrong, XIONG Fei, LI Bin, YANG Zhongping, ZHOU Xiaohan
2020, 39(4): 547-558. doi: 10.11932/karst20200410
Abstract:
Water is one of the important factors triggering landslides, and its physical, chemical and mechanical effects on rock mass determine the slope stability. Based on the current domestic and foreign research status and study cases of rock-slope landslides, this paper summarizes the hydraulic hazard-causing mechanism and the main failure models of rock-slope failure, and reviews the analysis methods of rock slope stability considering hydraulic action. It is generally accepted that the hydrostatic pressure generated by water to the sliding body (push of the rock mass side, uplift pressure of the sliding surface and buoyancy of rock mass) and hydrodynamic pressure (penetration outward the slope) are the main mechanisms of hydraulically induced rock-slope landslides. From the perspective of seepage flowing-stress coupling, the influence of water seepage on slope stability can be comprehensively evaluated. The rock mass structure of the slope determines the hydraulic action mode and the failure mode of the slope. The main forms of instability failure of rock slopes considering hydraulic action include bed slip, horizontal sliding, wedge sliding and perilous rock collapse. The stability analysis methods for rock slopes under hydraulic action mainly include the limit equilibrium method, the finite element strength reduction method, the perilous rock stability analysis method based on fracture mechanics, and the seepage-stress coupling model analysis method, among which the first two methods are widely used.
Characteristics and the hazard-inducing effect of groundwater systems in Zongling high-level landslide areas
Yi Lianxing
2020, 39(4): 559-566. doi: 10.11932/karst20200411
Abstract:
Taking two landslide areas of the Zongling collapse-landslide zone in Nayong county, Guizhou province as examples, this work conducted hydrogeological surveys, hydrodynamic field analysis, hydrochemistry research and flow dynamic comparative analysis to examine the hazard-inducing effect of groundwater. Results show that, (1) under natural conditions, there are three relatively independent groundwater systems in the collapse-landslide zone, while coal mining activities have changed the groundwater runoff-discharge direction, making the upper bedrock fissure water and middle karst water recharge into the lower bedrock fissure water, finally discharging to the surface from the pit or spring; (2) Flow dynamics and the variation of calcium ion content indicate that middle karst water in the rainy season recharges into the goaf tunnel in a injection form. They also show that vertical fractures developed in the shallow part of the slope body in the old Zongling town landslide area, as well as in the shallow to deep part of the slope body in the Zuojiazhai landslide area; (3) The groundwater flow in the Zongling landslide body is dominated by unsaturated groundwater seepage movement, no saturated groundwater flow field, thus no effect of the hydrodynamic driving landslides; (4) In the process of hazard initiation or triggering of the collapses and landslides in the Zongling area, groundwater plays a major role in accelerating and promoting development of vertical fractures and sliding structural plane, rock mass failure and instability. These research results are of certain significance to studies of the mechanism of collapses-landslides in the Zongling area and other karst mountainous areas with similar conditions in southwest China.
Karstification and slope failure in carbonate areas of Three Gorges Reservoir
CHEN Xiaoting, HUANG Bolin, LI Bin, ZHANG Peng, QIN Zhen
2020, 39(4): 567-576. doi: 10.11932/karst20200412
Abstract:
A large number of karst unstable banks in the gorge area of the Three Gorges Reservoir stand on both sides of the main stream of the Yangtze River, endangering the safety of the golden waterway. Based on field survey, exploration and mechanical analysis, this work analyzes the relationship between karstification and slope failure in the carbonate areas of the Three Gorges Reservoir. The field survey shows that there are many unstable slope phenomena related to karst caves, dissolution fissures, dissolution zones, dissolution troughs, dissolution ditches and other surface karstification on the carbonate bank slope. There are 186 karst potential geo-hazards in Wu Gorge, including 37 potential landslides and 6 large-scale dangerous rock masses. The mechanical analysis of rock mass indicates that the joints / cracks will gradually expand due to the decrease of effective stress and strength under heavy rainfall, impounding and rock mass degradation. At the same time, the crack growth rate of rock mass deterioration in the water level fluctuation zone is about 1,300 times higher than the average dissolution rate in the Three Gorges, which greatly accelerates the evolution process of unstable rock mass which has entered the yield state. Dissolution is the most basic action of karst bank slopes, and the long-term fluctuation of reservoir water accelerates the evolution of karst bank slopes. This study provides technical support for the identification and disaster prevention and mitigation of unstable banks in the gorge section of the Three Gorges Reservoir area.
Evaluation method of development degree based on features of intense dissolution layer
CAO Xianfa, LIU Yukang, LIU Zhikui, ZHANG Binghui
2020, 39(4): 577-583. doi: 10.11932/karst20200413
Abstract:
It is common to make errors in the selection of building foundation in karst terrains. The root reason is that the practical difficulty of karst treatment in foundation cannot be reasonably reflected by the existing evaluation of karst development degree. Taking New Terminal of Nanning Wuxu International Airport as an engineering case, this article analyzes the limitation of the existing evaluation indices of karst degree, demonstrates the advanced rationality of using intense dissolution layer’s thickness as the evaluation index of karst degree, and proposes the recommended standard of this evaluation. Results show that the intense dissolution layer, divided by the curve of dissolution ratio depth distribution in a foundation, comprehensively considers the main depth range of dissolution degree of rock surface and the development of cave dissolution, and its distribution characteristics can reflect the depth range of most complex karst foundation. As the evaluation index of karst degree, it is reasonable. Its recommended values are suggested as follows, when the thickness of an intense dissolution layer is less than 3.0 m, more than or equal to 3.0 m and less than 6.0 m ,and more than or equal to 6.0 m, the karst degree can be determined as weak development, medium development and strong development, respectively.
Stability of foundation rock mass beneath the A4 rescue platform in the Ruyifeng scenic spot, Yangshuo, Guilin
XIE Yanhua, ZHANG Binghui, SUN Gangchen, LIU Baochen, CHEN Xuandong, FAN Xindong
2020, 39(4): 584-591. doi: 10.11932/karst20200414
Abstract:
This work makes an assessment of the stability of the rock mass beneath the A4 rescue platform during the construction of the Ruyifeng scenic spot project in Yangshuo, Guilin. It builds on the combination of the methods of field surveys and theoretical analysis including stereographic projection qualitative analysis, the limit equilibrium method and finite element numerical simulation. The results show that the rock mass beneath the A4 rescue foundation is in an unstable state thus needs to be reinforced. Additionally, we puts forward the reinforcement treatment measures so as to provide theoretical support and scientific basis for the treatment of later possible collapse of the dangerous rock, which would be a certain reference for the stability research of similar rock masses in karst areas.
Features of karst development and geotechnical effects in the Liaoshan Tunnel on the E-Han expressway
LI Fangtao, LI Huangming, HU Zhiping, CHEN Nannan, YAN Changgen
2020, 39(4): 592-603. doi: 10.11932/karst20200415
Abstract:
The Liaoshan tunnel on the E-Han expressway is located in a karst area of southwest China with frequent geological hazards. Based on the investigation of the geological environment in the karst area,this work clarified the characteristics of karst development in the tunnel site area,analyzed its law and controlling factors,and examined its effects on the site. The results show that the karst morphology in the tunnel site area is diverse,characterized by multiple scales,diversity,and dense development. The karst shows significant selectivity,directionality,layering,heterogeneity,and system coherence and other laws,in which stratigraphic lithology and its combination are the material basis,topographic features and geological structural characteristics are the dominant conditions,and hydrogeological conditions are the decisive factors. The engineering effects of karst development are mainly expressed in 3 aspects, the stability of the tunnel,karst gushing water inrush and effect of tunnel life cycle. The existence of bad karst geological bodies and karst water-rich spaces can easily induce stability problems such as large cave deformation and karst collapses at the bottom of the tunnel as well as local static karst water outbursts and lake water flood and mud flooding disasters,sometimes even affecting the stability and durability of the tunnel structure during the operation period.
Study on the characteristics of karst water system and tunnel route selection in Wanshoushan area, Yunnan Province
REN Yanan, WAN Junwei, HUANG Kun, HE Xinhui
2020, 39(4): 604-613. doi: 10.11932/karst20200416
Abstract:
During construction of tunnels in karst areas, geologic hazards, such as water bursting and mud invasion, often occur threatening the project and people’ safety. Thus the optimization of tunnel line is very important. Taking the Wanshoushan tunnel of the Sanqing expressway in Yunnan as an example, this work conducted a large-scale hydrogeological survey around the tunnel site. The purpose was to clarify the spatial distribution of the karst water system and cycle features of karst underground water, study the relationship between the different tunnel schemes and spatial position of the karst water system, and predict possible karst water hazards related with these schemes. On the basis of this research, the quantitative assessment indexes for comparison of tunnel line schemes were determined, which were the number of faults running through by the tunnel, the karst aquifer length through which the tunnel extends, maximum water bursting pressure and maximum amount of water invasion. Then using the analytic hierarchy process method,we established a comprehensive assessment model for the tunnel line in the karst area, which would help choose the best scheme of the tunnel line from candidates. The results show that the scheme C possesses relatively better hydrogeological conditions and least risk of karst water bursting or mud invasion.
Finite element analysis on safety thickness of the inrush prevention layer in rock beds of the small Three Gorges karst tunnel
ZHANG Qiao
2020, 39(4): 614-621. doi: 10.11932/karst2020y33
Abstract:
In view of the geotechnical characteristics of the karst in the small Three Gorges tunnel, the finite element method is used to establish a numerical calculation model of a typical tunnel section to analyze the variation laws of tunnel surrounding rock displacement and plastic zones when the water filled karst cave is located in different directions and distances of the tunnel. Then in combination with the displacement change of surrounding rock and the distribution of plastic zones, the minimum safe thickness of the rock layer to prevent water inrush from the surrounding rock of the tunnel is determined. The research results show that under the action of karst water pressure, when the cavity diameter ratio is fixed, the influence of the karst cave on the tunnel is gradually weakened as the cave gradually moves away from the tunnel. When the interval diameter ratio is fixed, the larger the diameter of the karst cave, the more obvious the influence on the tunnel. At the same time, according to the displacement of surrounding rock and the calculation results of plastic zones, the minimum inrush prevention thickness of the tunnel surrounding rock is obtained. The research results can provide technical support for the safe construction in the small Three Gorges karst tunnel.
Prediction of karst surface subsidence risk in the Fankou lead-zinc mine area based on PCA-PSO-SVM
ZHOU Aihong, NIU Pengfei, YUAN Ying, HUANG Hucheng
2020, 39(4): 622-628. doi: 10.11932/karst2020y30
Abstract:
Karst surface subsidence is a dynamic geological phenomenon with the characteristics of concealment and suddenness, which results from the joint effect many factors. Thus, it is difficult to accurately predict the risk of surface subsidence by the conventional simple mathematical model. In this paper, the Principal Component Analysis (PCA) is used to extract five principal components from 11 influencing factors, including groundwater level, fluctuation range of groundwater level and water supply, so as to make a new interpretation of the principal components leading to the risk of surface subsidence. Additionally, the Support Vector Machine (SVM) method optimized by Particle Swarm Optimization (PSO) is introduced to establish a PCA-PSO-SVM model for prediction of risk of karst surface subsidence. Finally, combined with the engineering example of the Fankou lead-zinc mine, the prediction results by the above proposed model are compared with those obtained by the single SVM model. The results show that the PCA-PSO-SVM risk prediction model has higher accuracy, which can provide a basis for prevention and control of karst surface subsidence.