Experimental Study on the Vertical Deformation of Soils due to Groundwater Withdrawal

Abstract

Severe land subsidence caused by groundwater exploitation is one of the anthropogenic environmental problems. Even when groundwater exploitation has been limited or prohibited in some areas, it will continue in some water-deficient areas for a long time. Therefore, it is a challenge to reasonably exploit groundwater and not to cause severe land subsidence. A physical model test was conducted in this paper to simulate the extraction and recharge of groundwater, and to observe the soil deformation characteristics and the change of the pore water pressure. Based on the test results, the mechanism of land subsidence was investigated and different pumping modes were involved including the single-well pumping, single-well pumping and recharging, and double-well pumping and recharging tests. The tests indicated that the sand layer and clay layer had different pore water pressure change and deformation characteristics. In the sand layer, the pore water pressure decreased when pumping and increased when pumping stopped. In the clay layer, however, pore water pressure first increased rapidly and then decreased when pumping, and it decreased rapidly and then increased after pumping stopped. The variation of pore water pressure in the clay layer was consistent with the Mandel’s effect and was related to the distance to the pumped layer. The further the distance was, the longer the Mandel effect lasted. The sand layer mainly exhibited elastic deformation and the clay layer almost exhibited plastic deformation. The clay layer showed clear hysteresis. The hysteresis time was increased with the distance from the pumped sand layer. In addition, the results indicated that the three pumping modes could reduce land subsidence. With regard to the pumpage and land subsidence, the double-well pumping and recharging mode was better than the other two. With pumping or pumping and recharging together, the increasing rate of vertical displacement became smaller and gradually reached a stable state. In general, these three modes were reasonable for groundwater exploitation, and could effectively control land subsidence.