Research Of The Karst Development Law And Three-dimensional Visualization In A Construction Site Foundation In Kunming

The research area is located in the southwestern margin of the first-order tectonic unit Yangtze-Huaihe Platform,which is about 170 km from the eastern side of the Sanjiang fold system,with a complex crustal dynamics background.The geological structure in the area is quite complex.Baiyi-transverse thrust fault,thrust nappe structure,Baoxianghe fault and other secondary faults intersect here,which lead to the development of karst topography in the area.In view of the importance of the project in the research area and the complexity of the site karst foundation,the study of the karst development law and three-dimensional visualization in the research area is not only of great geological significance,but also of great practical significance.In this paper,the methods of in-situ geological survey,mapping,drilling-geophysical data in-depth evaluation are combined to accurately identify the physical and geographic environment,geological environment conditions and hydrogeological characteristics of the engineering site,which then described the karst morphology of the site area and its surrounding areas.The horizontal zoning,vertical zoning and deep karst description of the research area are also.The law of karst development can be used to study the influencing factors and karstification of karst development in this area.On the basis of comprehensive analysis,a three-dimensional stratum structure model of the site is constructed by coupling borehole data,engineering geological profile,topographic geological map and other metadata.According to the three-dimensional model,the karstification of the site has been discussed,and the stability of the surrounding rock of the site karst cave is simulated.Through the analysis and research of the foregoing,the following conclusions and research results have been achieved:?1?The foundation of the site is generally characterized by a ternary structure of"clay+pebble bed+bedrock".The lithology of the foundation is dolomite-limestone????₁lS?of the Cambrian Longwangmiao Formation in the north-east and siltstone,fine sandstone and a small amount of shale and dolomite in the Cambrian Canglangpu Formation????₁c?in the south-west.The karst forms around the project area are mainly depressions,water-falling caves and funnels with relatively small ratio of long axis to short axis.The karst in the foundation of area is strongly developed,and the main forms are karst holes,karst fissures,karst caves and karst fractured zones.?2?Based on the linear karst rate of boreholes,the karst development in the field area is divided into four zones:extremely strong,intense,medium and weak.The degree of karst development is stronger in the north-east side than that in the south-west side of the site,which is more intense in the side near the Baoxiang River.Vertically,the karst area is divided into two vertical zones:strong karst zone and relatively weak karst zone.The lower limit elevation of the main body of the strong karst zone is about 1915 m,the karst development degree in the south-east side of the site near the Baoxianghe fault is higher than that in the north-west side.The possibility of large-scale deep karst development below the base level of regional erosion?Dianchi Basin?is small.?3?The Baiyi-Hengchong fault,D^P?Z^?nappe structure and Baoxianghe fault all contribute to the intense karstification of???₁lS in the research area,in which the latter two play a decisive role.The D^P?Z^?nappe structure caused the fragmentation of the Cambrian strata underlying the nappe boundary,which provided the basic support for the karstification of the strata.The Baoxianghe fault was formed after the formation of Dianchi basin,which is characterized by old age,low grade and small scale,but played a decisive role in the development of the Cambrian strata karst in the engineering area.This is mainly reflected in the intensification of the fragmentation of the foundation rock mass with the development of the Cambrian strata,assisting the Karst water's discharge into Dianchi Lake and breeding Baoxiang River Basin.?4?Groundwater activities in the research area also greatly promoted the development of karst foundation in the site area.The studied site is located in the groundwater runoff area,and its groundwater mainly receives the recharge of Baoxiang River and atmospheric precipitation,thus runs through the cross section of Chestnut Garden by normal runoff mode and eventually flows into Dianchi Lake.The karst water movement is mainly horizontal movement,and the main migration space is the karst pipeline,which included the karst space of centimeter scale.The groundwater runoff is slow and mainly laminar flow,especially the water flow of the centimeter scale dissolution space.The groundwater level in the engineering area is subject to the Baoxiang River.?5?The karstification analysis based on the three-dimensional stratigraphic structure model shows that the karstification degree on the north-east side of the site is higher than that on the south-west side,and nine of the sites are the most developed,which is consistent with the spatial variation of the ground lithology?stratigraphic unit?.The karstification degree in the part of the site is intenser than others due to the influnce of the fault structure.The karstification degree on the side of the site near the Baoxiang River is intenser than that of other places.?6?The numerical simulation based on the three-dimensional field model?generalized model?shows that the stress distribution characteristics of surrounding rock of flat-shaped karst cave are significantly different from those of circular and elliptical underground caverns such as tunnels.Controlled by the shape of karst caverns,the lateral stress is greater than that of the top and bottom.At the same time,the stability of surrounding rock of karst cave is closely related to the size of long and short axes and the thickness of roof.