基于微水试验的北京大兴隐伏岩溶裂隙渗透系数求取方法

Determination of Permeability Coefficient of Concealed Karst Fractures Using Slug Test in Daxing of Beijing

微水试验是进行岩土体渗透性测试的重要技术手段与方法。选取北京大兴隐伏奥陶系灰岩岩溶裂隙含水层作为目标层,依据现场条件选择生产井,利用水位自动监测装置记录停泵水位恢复法,HSZK振荡试验法与注水试验法进行微水试验应用研究,发现获得的目标层渗透系数小于传统抽水试验结果。分析认为造成这种差异的原因在于不同试验方法的影响半径不同,而微水试验结果更能体现试验点岩土体的渗透性。此外,在裂隙与岩溶介质中运用微水试验要尽量减小、避免皮肤效应的影响,选择试验方法时要保证水位瞬时变化的实现,对于主裂隙,可以借助栓塞进行分段试验。

Slug test is an important method to determine the permeability of rock and soil masses.In this paper,the permeability of the concealed Ordovician karst-fractured limestone aquifer in Daxing of Beijing was estimated.The production wells were selected according to the in-situ conditions,and the slug test design included the pump-off water level recovery method recorded by auto-monitoring system,HSZK oscillation method,and injection method.The results showed that the permeability obtained from the slug test is less than that determined by the conventional pumping test.The discrepancy was mainly due to the difference of influence radius in different test methods,and slug test can reflect the permeability at the local scale more accurately.Additionally,it is necessary to reduce or avoid the well skin effect while performing the slug test in the fracture and karst medium.The realization of instantaneous water level change needs to be conducted when designing the slug test and the plug-sealing sectional test can be used in the main fractures.