地铁深基坑抽灌一体化地下水位变化规律分析

对软土地区狭长地铁深基坑进行降水作业时, 基坑降水会使悬挂式止水帷幕墙底的承压含水层水头下降, 达到开挖要求。但同时受绕流作用的影响, 也会导致坑外承压水层向坑内补给, 造成坑外水位降低, 威胁基坑周边构筑物的安全。为防止坑外水位过度降低, 拟采用坑内降水、坑外回灌的抽灌一体化施工来控制不同开挖深度下坑内、坑外水位, 文章通过 Visual MODFLOW 软件对上海某地铁狭长深基坑进行分析, 探究其在抽灌一体化施工过程中的水位响应规律。结果表明: 对坑外承压水层的补给可以有效抬升其水位; 承压水层的降水过程响应较为敏感, 在 $ 4 \sim 6 $ h 达到最大降深, 因此回灌井应同步开启; 回灌过程中可能会导致水位不降反升, 对周边构筑物同样会造成影响, 实际施工过程中应予以控制。

When dewatering operations are conducted on long and narrow deep foundation pits for subway excavations in soft soil areas, the dewatering process reduces the water head of the confined aquifer beneath the suspended waterproof curtain wall, thereby meeting excavation requirements. However, simultaneously, the influence of seepage flow may cause recharge from the confined aquifer outside the pit into the pit, leading to a decline in the groundwater level outside the pit and posing potential risks to the safety of adjacent structures. To prevent excessive drawdown of the groundwater level outside the foundation pit, an integrated approach combining dewatering inside the pit and recharge outside the pit is proposed, aiming to regulate water levels both inside and outside the pit at varying excavation depths. Visual MODFLOW software is employed to simulate and analyze the hydrological responses during the implementation of integrated pumping and recharge measures in a long and narrow deep foundation pit associated with a subway project in Shanghai. The results indicate that the recharge of the confined aquifer outside the excavation pit can effectively elevate the groundwater level. The confined aquifer exhibits a more sensitive response during the dewatering process, with the maximum drawdown occurring within four to six hours; therefore, it is recommended to operate the recharge process in a long and narrow deep foundation pit under the conditions of a long and narrow deep foundation pit. charge wells synchronously. During the recharge process, the water level may rise rather than decline, potentially affecting nearby structures. This phenomenon should be closely monitored and controlled during actual construction.