Experimental Study On Aquitards Compaction Caused By Water Pumping In Aquifers

In the context of rapid economic development,human demand for groundwater resources is growing,but excessive extraction of groundwater will cause a large area of land subsidence which would threaten the people's lives and property losses,affecting the sustainable development of the city.Therefore,mastering the occurrence and development mechanism of land subsidence is of great significance for the prevention and treatment of land subsidence.In this paper,two kinds of advanced distributed fiber sensing technology-Brillouin Optical Time Domain Analysis(BOTDA)and Distributed Temperature System(DTS)are used in the experiment.Based on the experimental study,the coupling process of water field and deformation field during the development of ground subsidence are studied,and the characteristics and laws of the aquitards deformation in the shallow depth caused by water release are revealed.The research work and achievements of the paper are as follows:(1)The main causes and hazards of ground subsidence are analyzed,and the technical means and problems of ground subsidence monitoring are summarized.The principle and technical advantages of several distributed optical fiber sensing technologies are introduced.The solution to monitoring land subsidence used by optical fiber was proposed;(2)The distribution characteristics of aquitards in the ground subsidence are introduced,especially the stratigraphic distribution of Quaternary in the Yangtze River Delta and the basic properties of aquifers and the role of the aquifers in the process of land subsidence;(3)Soil model containing aquifer experiment was designed.The geotechnical parameters of the model soil samples were determined by the laboratory test.The two kinds of special sensing cables,such as the polyurethane fiber optic cable and the carbon fiber heating cable,which were suitable for the indoor strain test and the water field monitoring were developed.(4)Based on the soil model test during water pumping process and the detailed analysis of the test results,the mathematical model of the soil hydrogeology was established,and the strain field and water field of the soil model were studied in time and space.The change law of the water field and the strain field of the aquitards during the water pumping process was studied emphatically.It is found that the deformation distribution of aquitards in the soil model presents large at the edge of model and small at the middle,and the deformation rate decreases with time.And its deformation mechanism is explained.