Study On Grouting Technology Of Rock-soil Interface In Covered Karst Development Area

With the rapid development of China's economy and the intensification of infrastructure construction,karst,as a special geological condition,has attracted increasing attention in water conservancy and civil engineering construction.Especially in covered karst development area,soil caves are easily formed due to the effects of overlying soil and groundwater.Soil cave in karst area refers that under certain hydrogeological conditions,the overburden soil on the upper part of soluble rock is eroded and destroyed,forming filled or unfilled caves,thus causing ground deformation and destruction,which is the reflection of karst phenomenon in soil layer.Soil cave has the characteristics of shallow burial,rapid development and low strength of soil layer roof,which has a great impact on soil stability and the damage of its surface appendages.At present,the treatment of soil cave in karst area is mainly based on the experience of engineering designers for qualitative treatment.However,different technicians have different treatment methods.Some tend to be conservative and cause economic waste.Some are too risky and cause construction accidents.Therefore,the research on the mechanism of soil cave development and how to manage soil caves in karst area safely,reliably,economically and reasonably to ensure the safety of the project are important topics to be studied in China's economic construction.Firstly,on the basis of consulting the research results of domestic and foreign scholars on karst phenomenon,this paper takes Tai 'an City as the research object,discusses the mechanism of soil cave development in the research area,carries out innovative design on static pressure grouting,and proposes a rock-soil interface grouting technology.The main findings are as follows:(1)Based on the analysis of the hydrogeological data of Tai'an City and the previous research results,it is concluded that the surface water in the study areas mainly affects the development of soil cave by changing the state of soil mass and the weight of soil mass in the process of seepage,while the groundwater exerts different forces to affect the development of soil caves during the rapid decline and frequent fluctuation of water level.(2)Based on the data of karst development geology,groundwater exploitation and subsidence in the study area,the geological structure of Tai'an City is simplified into a "one-dimensional" weak permeable geological model,and the development mechanism of soil caves in Tai'an City is proposed as follows: the development model of soil cave is dominated by "undermining-disintegration" and combined with multiple factors.(3)The innovative design of static pressure grouting is carried out,and a rock-soil interface grouting technology is put forward.The key technology of sealing karst cave entrance with dry kelp and the main mechanism of rock-soil interface grouting technology are elaborated in detail: plugging and blocking effect;horizontal curtain effect;infiltration and filling effect,and grouting parameters are determined theoretically.(4)Taking the foundation treatment of an apartment building in the South Campus of Shandong Agricultural University as an example,the feasibility of the grouting technology of geotechnical contact surface proposed in this paper is verified.The research results of soil cave development mechanism and rock-soil interface grouting technology in the research area proposed in this paper provide theoretical basis for the study of soil cave formation and development mechanism in the covered karst development area,and offer an economic,reasonable and efficient method for soil cave treatment in the area,providing reference and guidance for the engineering construction in such soil cave development area in the future.