Abstract
China has a vast territory,with significant differences of internal and external forces such as lithology,geological structure,and climate in different regions,resulting in distinct regional characteristics in karst development.The Qinling Mountains is the north-south demarcation line in China,with complex topography,geological structure,and widespread distribution of soluble rocks.Consequently,karst in this region is an unavoidable problem in the construction of various projects.The development of karst may lead to reservoir leakage,posing a constraining influence on the construction of pumped-storage power station reservoirs.However,the current research on the characteristics of karst development at specific engineering sites in the Qinling area is relatively limited,and there is not much research on the impact of karst development characteristics on the permeability of the rock body in the reservoir areas.To provide a valuable supplement and reference for the study of karst development in the Qinling area,and to establish a reliable foundation for the design of pumped-storage reservoirs,leakage prevention and control,and risk assessment,this study takes limestone of a pumped-storage reservoir located in the Qinling Mountains of southern Shaanxi Province as the research object.Utilizing drilling,borehole TV imaging and in-situ pressure water tests,this study comprehensively evaluates the water permeability performance of the rock body.By integrating the characteristics of karst development,the research summarizes and analyzes the distribution patterns of limestone karst development in the study area.The permeability of the rock body is evaluated in conjunction with karst development characteristics,leading to the following conclusions:
The linear karstification rate of three boreholes in the study area is greater than 10％,with an encounter rate of 47.1％.This indicates a strong degree of karst development.Using the contour line of 3％ karstification rate as the boundary,the study area is divided into two karst zones:Zone Ⅰ and Zone Ⅱ which includes Zone Ⅱ-1 and Zone Ⅱ-2.The karst in Zone Ⅰ is strongly to moderately developed,with a relatively high concentration of caves in the borehole area.In contrast,the karst in Zone Ⅱ is weakly developed,and caves are seldom found in the borehole area.The depth of the karst caves is predominantly distributed between 10 m and 60 m underground,representing a typically shallow-buried karst system.The karst caves are distributed in a moniliform shape,with ZK107 and ZK113 being the most prominent,where seven caves are vertically distributed in a single borehole area.The gray oolitic limestone caves are the most developed,followed by brownish-red fine-crystalline limestone caves,while argillaceous limestone caves are not developed.The development of karst caves is consistent with the solubility pattern of limestone.In addition,the karst fissures are generally developed in all borehole areas,and can be categorized into two types:joint-solution fissures and solution fissure zones.These fissures are commonly filled with mud,calcium and calcite.
Comprehensive analysis shows that the permeability performance of the rock body in the study area is jointly influenced by the karst development characteristics,the integrity of the rock body,and the filling characteristics.The logarithm of the average permeability(lg10q)exhibits a linear relationship with the linear karstification rate,which is expressed by the equation:lg(q)=A·Rlk+B,where Rlk denotes the linear karstification rate,and A and B are constants.The ratio coefficient A indicates the influence of karst development on the permeability of the rock body,with a calculated value equal to 3.39.Overall,the rock bodies in the study area demonstrate a pattern whereby the increase of karst development correlates with greater permeability of the rock body.A comparison shows that in moderately permeable rock bodies,karst development is primarily weak.In contrast,in strongly and very strongly permeable rock bodies,karst development is predominantly strong to moderate.The permeability of the rock body exhibits a clear linear trend,correlating with an increase in the linear karstification rate.Constant B reflects the effect of the integrity degree of the rock body on the permeability performance.Specifically,relatively intact rock bodies exhibit moderate to strong permeability(Constant B=1.58),while fractured and broken rock bodies indicate extremely strong permeability(Constant B=3.46).In addition,the filling characteristics of protogenesis fissures and karst caves can cause fluctuations in permeability.When the protogenesis fissures and karst caves are not filled,permeability tends to be high;however,when they are densely filled,the permeability will significantly decrease.关键词
抽水蓄能水库/溶洞/岩溶裂隙/透水性能/秦岭Key words
pumped-storage upper reservior/karst cave/karst fissure/water permeability/the Qinling Mountains分类
水利科学
