Cambrian Karst And Karst Water Environmental Characteristics And Its Suitability With The Tunnel Engineering In Yunnan-Guizhou Area

In Yunnan-Guizhou, influenced by factors of special plateau climate, thesedimentary environment, the tectonic movement and etc., Cambrian strata presentregional characteristics of the soluble and insoluble rock interbedded, and whose karstare also obviously different from other soluble rocks with thick layers. Therefore, it ismeaningful for the scientific research and the engineering construction to study thelaw of karst and karst water in Yunnan-Guizhou area.Through referring to relevant information and analyzing and studying scientificresearch and engineering practice subjects in related Cambrian strata areas, withCambrian system of Yunnan-Guizhou area as the research object, This articlepinpoints geological environment conditions, Cambrian sedimentary characteristicsand hydrogeology conditions in Yunnan-Guizhou, and in which the Cambrian karst ispartitioned based on karst stratigraphic associations and valley cutting conditions. Thelaws of karst and karst water in different zones are studied. The suitability rules of thekarst water environment and tunnel projects are further studied combining withrelated engineering examples in the Cambrian strata in Yunnan-Guizhou area——theDawu mountain tunnel in the eastern of Yunnan and the Maoping mountain tunnel inthe northeastern of Guizhou. The results are as follows：(1)The Cambrian sedimentary in Yunnan-Guizhou area experienced "a large andtwo small" marine transgression-regression cycle, and which outcrops in the northernand the mid-northeastern of Guizhou, the eastern, the southeastern and the Baoshanbasin of Yunnan. Karst stratigraphic associations are Pure carbonate rocks, interbedded pure carbonate rocks and interbedded impure carbonate rocks; Accordingto the topography and hydrological characteristics, the Cambrian strata areas can bedivided into deep cutting zones and shallow cutting areas, in which the northern ofGuizhou, the southeastern and Baoshan basin of Yunnan are deep cutting areas; themid-northeastern of Guizhou and the eastern of Yunnan are shallow cutting areas;(2)Cambrian karst is partitioned into five districts based on karst stratigraphicassociations and valley cutting conditions: district Ⅰ with deep cutting valley andpure carbonatite in the northern of Guizhou, district Ⅱ with shallow cutting valleyand pure carbonatite in the mid-northeastern of Guizhou, district Ⅲ with shallowcutting valley and interbedded impure carbonatite in the eastern of Yunnan, district Ⅳwith deep cutting valley and interbedded pure carbonatite, district Ⅴ with deepcutting valley and interbedded impure carbonatite. Then, the development laws ofkarst and the karst water in five districts are analyzed, as follows: district Ⅰ: thesurface karst and the underground karst develop well. The underground water is insolution holes-fissures and caves-tunnels, which is recharged by rain, and drains intothe deep cutting valleys which are as the local discharge datums. District Ⅱ: karst inthe surface develops well. The scale and the depth of the underground karst forms issmall and shallow. The underground water is in solution holes-fissures and infissures-caves, and supplied by water drops, and runoff and drain satteredly. DistrictⅢ: karst develops weakly. The underground water is in fissures, which is rechargedby rain, and discharge satteredly. The water is restricted in independent small unit bythe aquiclude layers. District Ⅳ: the surface karst and the underground karst withmultilayers develop well. The type of the ground water mainly is the karst water incarbonatite. The water is recharged by rain, staged migration, and discharged by shortunderground rivers and springs with big flow. District Ⅴ: karst in the surfacedevelops weakly. Only several karstic caves and sink holes underground with smallscale. The ground water is in fissures and recharged by rain and surface water, runoffin fissures and discharge scatteredly as springs in valleys and faults.(3)The relationship between the karst water environment and the tunnelengineering are two cases: near deep cutting valley and in shallow cutting areas. Theirsuitability in different karst stratigraphic associations is further analyzed:①near thedeep cutting valley: the influence of the karst and karst water environment on theprojects mainly is the stability of the roof and floor of the tunnel, when in the vadosezone, the tunnel may occurs small-scale water bursting; the impact of the tunnel project on the karst water environment mainly is water pollution and water loss in thevadose zone.②in the shallow cutting areas: the influence of the karst and karst waterenvironment on the projects mainly includes water bursting, engineering structurecorroded by water and the stability of the tunnel roof and floor; the impact of thetunnel project on the karst water environment mainly includes water table decline,water loss and water pollution.(4)The suitability rules of Cambrian karst water environmental and the tunnelengineering in Yunnan-Guizhou area are analyzed by examples. The conclusions areas follows: under certain conditions, the karst development degree is positivelycorrelated with massive water bursting events; the stability of surrounding rock is badin areas with severe karst development, which influences greatly on the stability of thetunnel’s roof and floor; The construction of the tunnel projects will influence greatlyon the water along the lines.