邻既有地铁地下结构抽排承压水的影响分析

Influence analysis of pumping and discharging confined water from underground structure adjacent to existing subway

抽排地下承压水对周边敏感建筑物一直是比较忌讳的,一般情况采取封闭式进行。但若仅基坑局部落深处抽排承压水,涉及范围较小,盲目地采取全封闭止水帷幕必然会造成较大的经济浪费,明显是不合适的。以邻近南京地铁11号线基坑工程为例,为降低基坑落深区承压水抽排对已建地铁地下结构产生影响,当抗突涌安全系数与允许值相差较小时,提出了落深区注浆压重取消抽排;当抗突涌安全系数与允许值相差较大时,必要时可设置降压井,但水头降深严格按实际需求设置。通过Visual MODFLOW软件计算分析发现,承压水降压范围和降深较小时,开放式抽排承压水对临近敏感建筑物影响相对可控,可为类似工程提供一定的借鉴。

Pumping underground confined water has always been taboo for surrounding sensitive buildings.Generally,it is carried out in a closed manner.However,if only the confined water is pumped from the deep of the foundation pit,the scope involved is small,and the blind adoption of fully closed water stop curtain will inevitably cause great economic waste,which is obviously inappropriate.Taking the foundation pit project adjacent to Nanjing Metro Line 11 as an example,in order to reduce the impact of confined water pumping in the deep area of the foundation pit on the underground structure of the built subway,when the difference between the anti surge safety factor and the allowable value is small,it is proposed to cancel pumping by grouting weight in the deep area;when the safety factor against sudden surge differs greatly from the allowable value,step-down wells can be set if necessary,but the head drawdown shall be in strict accordance with the actual demand.Through the calculation and analysis of Visual MODFLOW software,it is found that when the pressure reduction range and depth of confined water are small,the impact of open pumping and drainage of confined water on adjacent sensitive buildings is relatively controllable,which can provide some reference for similar projects.