第九章_地面沉降.pptVIP

REDUCING FUTURE SUBSIDENCE In some areas where ground-water pumping has caused subsidence, the subsidence has been stopped by switching from ground-water to surface-water supplies. If surface water is not available, then other means must be taken to reduce subsidence. Possible measures include reducing water use and determining locations for pumping and artificial recharge that will minimize subsidence. Optimization models coupled with ground-water flow models can be used to develop such strategies. * 地面沉降的控制与治理—可能发生地面沉降的地区 对可能发生的地区，硬预测地面沉降的可能性和危害程度： 估算沉降量，预测其发展趋势 结合水资源评价，研究确定地下水资源的合理开采方案 采取适当的建筑措施，预先对可能发生地面沉降量作充分考虑 图中的G-G’线将代表由土层自重所造成的总应力线 H-C 线则将代表土层中的天然孔隙水压力线 持续开采，导致地下水继续降低，如1 部分停止开采，水位缓慢上升，如2 、 3、4 完全停止开采，恢复到最初状态，如5 Land Subsidence From Ground-Water Pumping CAUSE OF LAND SUBSIDENCE FROM GROUND-WATER PUMPING CAUSE OF LAND SUBSIDENCE FROM GROUND-WATER PUMPING Land subsidence is the lowering of the land-surface elevation from changes that take place underground. Common causes of land subsidence from human activity are pumping water, oil, and gas from underground reservoirs; dissolution of limestone aquifers (sinkholes); collapse of underground mines; drainage of organic soils; and initial wetting of dry soils (hydrocompaction). Land subsidence occurs in nearly every state of the United States.(figure 1). CAUSE OF LAND SUBSIDENCE FROM GROUND-WATER PUMPING Overdrafting of aquifers is the major cause of subsidence in the southwestern United States, and as ground-water pumping increases, land subsidence also will increase. In many aquifers, ground water is pumped from pore spaces between grains of sand and gravel. If an aquifer has beds of clay or silt within or next to it (figure 2), the lowered water pressure in the sand and gravel causes slow drainage of water from the clay and silt beds. The reduced water pressure is a loss of support for the clay and silt beds. Because these beds are compressible, they compact (become thinner), and the effects are seen a