考虑气相堵塞的土样渗透试验分析

地面沉降是一种严重的地质灾害现象,对区域经济和社会生产都会造成严重影响。目前很多地区采取了回灌地下水等措施,以达到抑制区域地面沉降的目的。但是,由于回灌水水质与原有地下水存在差异,回灌水的含气量往往比原有地下水高许多,不可避免的会在土体孔隙中发生更明显的气相堵塞现象,从而削弱回灌效果。结合了常州代表性土样,通过曝气装置,采用含氧量作为分析指标,进行了渗透系数试验研究,分析气相堵塞现象对不同土体渗透系数的影响规律。研究表明气相堵塞随土粒粒径减小更加显著,细粒土样渗透系数均呈一阶负指数衰减规律变化,经历一定时间其渗透将趋于稳定。研究结果对于选择回灌水参数、深化理解地面沉降机理具有明显的现实性意义。

Study of Soil Permeability Considering the Gas Blocking

Land subsidence is the sinking of land surface.The occurrence and continuation of land subsidence have a serious impact on the regional economic and social development.Land subsidence in some regions is caused by exploiting groundwater.Changzhou City,underlain by a multi-layered aquifer system in Quaternary sediments in the Great Yangtze River Delta region,experienced a maximum land subsidence rate of 147 mm/a in the early 1980s due to excessive groundwater extraction.Land subsidence is caused by the withdrawal of groundwater.When large amounts of groundwater is pumped from the aquifers beneath,water is pulled out of the many layers of clay,which allows the clay to compact under the weight of everything above them.Because of the regional scale of the groundwater exploitation,cone of depression and land subsidence occur.In the process of groundwater recharge,there is more gas in water,and gas blocking inevitably occurs,which has great impact on groundwater recharge and the natural flow of groundwater,especially in the soil layers filled with clay or silt sand.The penetration tests of gravelly sand,fine sand and clay show gas blocking is obvious,particularly evident in clay.The test results show that the attenuation of permeability coefficient gets stable after a certain time,which shows a first-order exponential decay.The results have obvious practical significance for selecting injection water parameters and controlling land subsidence in the future.