重庆中梁山岩溶地面塌陷特征及形成机理

Characteristics and formation mechanism of karst ground collapse in Zhongliangshan area,Chongqing

通过详细调查重庆中梁山地区的岩溶地面塌陷灾害情况,分析出该区地面塌陷特征及形成机理。结果表明:岩溶地面塌陷主要分布在嘉陵江组中的地势低洼处、断层和溶槽处,多发生在降雨量大和地下水水位陡降时期,是自然因素和人类活动共同作用下的结果,数量较多,以土洞型为主;其致塌的力学机制以真空吸蚀作用和潜蚀作用为主,多种作用为辅;在具备岩溶塌陷发生的地质条件下,隧道建设过程中的强排水、降雨和村级公路修建与运营过程中会诱发岩溶地面塌陷的发生。根据岩溶地面塌陷的致塌力学机制和诱发因素,提出预防降雨形成的地表水过度聚集,隧道建设避免地下水陡降,村级公路和隧道选址避开岩溶发育区域等措施,以防止岩溶地面塌陷发生。

Zhongliangshan area,located in the west of the main city of Chongqing,seriously hinders the traffic de⁃velopment of this city,and hence affects its economic activities.In recent years,with the rapid development of Chongqing's economy as well as its traffic construction,a number of traffic tunnels and village roads have been planned and built in Zhongliangshan area.During their construction and operation,327 ground collapses occurred,which seriously damaged the geological and ecological environment.Therefore,through the detailed geological investigation of the ground karst collapse in Zhongliangshan area of Chongqing,this study systematically analyzes the characteristics and formation mechanism of the collapse in this area.The results show that in terms of distribution characteristics,ground karst collapses are mainly distributed in the low-lying areas of Jialingjiang formation,the developing areas of faults and solution grooves,and the area slightly covered by silty clay.In terms of formation time,ground karst collapses mainly form during heavy rainfall and in the period when the groundwater level drops sharply due to the heavy drainage during tunnel construction.In Zhongliangshan area,the geological conditions for the formation of ground karst collapse are sufficient.Firstly,the limestone in Jial⁃ingjiang formation in Zhongliangshan area is pure in texture,and many faults and joints are developed.Secondly,the surface water and groundwater resources are abundant,and the intense karstification forms a large number of karst space,which provides favorable room for ground karst collapse.The intensive exchange of atmospheric pre⁃cipitation,surface water and groundwater provides dynamic conditions for ground rock collapse.The Quaternary overburden with the characteristics of coarse structure at the bottom and fine structure at the top provides favor⁃able conditions for the formation of karst collapse.The inducing factors of ground karst collapse mainly include the heavy drainage leading to the sharp drop of groundwater level in the process of tunnel construction,heavy rainfall and the construction and operation of village roads.There are four types of mechanical mechanisms of sur⁃face karst collapse,i.e.,latent erosion,vacuum suction,erosion of the increasing rainfall load and surface wa⁃ter,and load and vibration.The comparison of the number of collapses produced by different mechanical mecha⁃nisms shows that the ground karst collapse produced by latent erosion and vacuum suction is widely distributed with the largest number.Hence,these two factors are the main mechanical mechanisms of collapse in this study area.According to the collapse mechanical mechanism and inducing factors of ground karst collapse,it is pro⁃posed that the careful dynamic observation of groundwater in this study area should be conducted in the process of tunnel construction,so as to avoid rapid and excessive discharge of groundwater and to prevent the sudden drop of groundwater level.During heavy rainfall,a reasonable drainage system should be established to avoid the excessive accumulation of surface water flowing to low-lying places and to avoid the increase of the overburden self-weight.In the site selection of village roads and tunnels,geological survey should be strengthened to avoid unfavorable sections in karst development areas and in high incidence areas of ground collapse,so as to prevent the occurrence of ground karst collapse.These research results provide theoretical basis and technical support for the protection of geological environment in this area.