Research On The Model Test Of Soil Deformation Under The Condition Of Pumping And Recharging

With the accelerating process of urbanization in China and the excessive exploitation of groundwater resources,land subsidence has evolved into an increasingly serious geological disaster,and this phenomenon is particularly serious in economically developed and densely populated areas.Related departments have adopted strict control groundwater exploitation and measures such as artificial recharge of groundwater,which effectively slows down the ground subsidence disaster.Are these measures scientific and reasonable?And If groundwater cannot be used in ground subsidence area?To solve these problems,it requires profound study on ground subsidence mechanism to guide the rational exploitation of the ground subsidence.By observing the land subsidence characteristics of Suzhou-Wuxi-Changzhou area,a series of similar laboratory model tests were carried out.And these model tests through the use of BOTD A optical fiber technology,preliminary revealed the deformation mechanism between aquifer and aquitard,and the paper achieved the following results:(1)In this study,a series of model tests of soil deformation under the condition of pumping and recharging were designed.Test equipment and procedures,such as model box design,soil material selection,soil layers design,sensor cable selection,layered settlement devises design and the design of water head control and measuring devices,were all determined.(2)In order to ensure that soil has a good density and uniformity,a method of hierarchical and quantitative soil compaction was taken.Considering one-dimensional deformation measurement characteristics of the fiber-optic,sensing optical fiber cables installed in the model were tightened.During the phase of soil filling,some resin-made disc were installed on optical fibers,which solved the problem of fibers coupled with soil.To verify the accuracy and reliability of optical fiber data,two identical fiber and six layered settlement devices were installed in the model.(3)According to the change of water level in model under the condition of pumping and recharging,the paper explained the flow path of water in the soil layers,thus revealed the water level variational rule of the aquifers and aquitard.Combined with laboratory test and characteristics of land subsidence in the actual field,the process land subsidence caused by excessive pumping of underground water was divided into the following three stages.The First Stage:In the early stage of artificial exploitation of groundwater,the confined aquifer were pumped in elastic range.When the aquifer water level decreases,the pore water pressure were decreases as well,meanwhile the effective stress were increased.The Second Stage:As groundwater continued extraction,when the phenomenon that aquifer recharge rate was less than the pumping speed appeared,the pressure above the aquifer framework will getting bigger and bigger.At this time,the aquifers have to absorbed water from the aquitard layer,and this "suction force" was formed by the water head difference and negative pressure during the pumping of aquifers.The Third Stage:As the groundwater flow from aquitard to aquifer in a large number,some unsaturated zones appeared in aquitard,which was the reason of significant compression in aquitard.Aquifer water level can be quickly restored in the process of artificial recharge,meanwhile the pore water pressure in the aquifer also restored quickly and started again under pressure.By contrast,the water level recovery in aquitard was a slow process.In the third stage of land subsidence,the structure of clay soil in aquitard were damaged and can't restored.(4)According to the analysis of test data,the accuracy and reliability of the data monitored by optical fiber by were verified,and test results showed that the main areas of soil deformation in land subsidence process were located in the aquitard,and the main areas of soil deformation in aquitard were located in unsaturated zones.