深基坑多层承压含水层中混合井降水技术优化研究

Optimization of Precipitation Technology of Mixed Wells in Multi-layer Confined Aquifers of Deep Foundation Pits

对于多层承压含水层中的深基坑工程而言,水文地质条件复杂,基坑施工常因隔水层厚度不足或水力坡降过大导致坑底突涌,盲目地进行坑内降水又会造成基坑渗流场突变、基坑内外水位差过大等问题。因此,地下水的有效控制成为基坑开挖成败的关键。以某深基坑降水工程为实例,通过理论计算并结合数值模拟研究了不同承压非完整井的相关参数,包括滤管数量、位置和长度,揭示了相关参数对减压降水效果的影响,优化了隔、降组合降水措施。结果表明:采用混合井双滤管复合结构深井时降水成效显著,且第一、二承压含水层上、下分层滤管长度比接近1∶1时达到最优值,此时理论计算结果与数值模拟结果的相对误差最小,仅为6.81%,故对处于多层承压含水层等复杂水文地质条件下的深基坑工程可结合实际地层结构借鉴混合井分层滤管长度最优比值进行降水设计。

For deep foundation pit projects built in multi-layer confined aquifers,the hydrogeological conditions are complex.Due to insufficient water barrier thickness or excessive hydraulic gradient,excavation of a foundation pit often results in water-inrush at the bottom of the foundation pit.However,blind precipitation in a foundation pit causes unexpected change in seepage field and excessive water level difference between inside and outside of the foundation pit.Therefore,effective control of groundwater becomes the key to the success of a foundation pit excavation.Based on a precipitation engineering example of a foundation pit,this paper aims to study the relevant parameters of different confined incomplete wells,such as the number,location and length of the filter tubes with both theoretical foundation and numerical simulation.Eventually,the paper reveals the influence of related parameters on the depressurization precipitation effect,and optimizes the water proof and precipitation measures.The results show that the uses of mixed wells and double filter tube composite structure have significant precipitation efficiency in deep wells.The optimal value is reached when the length ratio of the upper and lower stratified filter tubes in the first and second confined aquifers is close to 1∶1.The minimum error value between numerical and theoretical is 6.81%.For the precipitation design of deep foundation pit projects under complex hydrogeological conditions,such as multi-layer confined aquifers,the optimal ratio design of the mixed well layered filter tube can be used in combination with the actual strata structure.