地铁车站深基坑降水诱发沉降机制及计算方法

MECHANISM OF DEWATERING-INDUCED GROUND SUBSIDENCE IN DEEP SUBWAY STATION PIT AND CALCULATION METHOD

上海地铁9号线宜山路车站多点位移计高精度监测成果显示,上海软土地区承压水减压诱发沉降存在着分层沉降分异(分叉)和各层分层沉降之和与地面沉降量值不等的现象。承压水减压中地面沉降与分层沉降的机制可以用高、低渗透-压缩性地层组合、深源减压-上覆地层逆回弹、深源固结-变形协调、渐进边界机制来解释。通过区分层内压缩和单点沉降,假定逆回弹和固结同时发生,但可以分别计算,固结的渐进性体现在渗流场计算中按照水位等值线进行的层内小层划分,采用顶板逆回弹系数对分层总和法进行修正。在修正的分层总和法中,只要合理确定顶板逆回弹系数,就能够准确地计算单点沉降,进而计算地面沉降产生的量值。在固结诱发的层顶单点沉降小于变形协调诱发的层底沉降时,一定的土层条件下可能产生含水层的部分膨胀。

Monitoring data in Yishan Road station deep pit, subway No.9, Shanghai, China with multiple position extensometers indicate that the subsidence caused by dewatering of confined water has different rules： the accumulative multi-layered settlement is not equal to ground subsidence and some strata are not compressed but expansive. The mechanism is explained by combination of high-lower seepage characters, dewatering in deep confined aquifer-inversed rebound of overlaying strata, consolidation from deep-coordination of deformation and gradual boundary. The subsidence caused by dewatering in deep subway station pit is calculated by the accumulation method of each layer according to specification. A modified calculation method is established. Firstly, the single point deformation and compression in each layer are defined according to the law of inversed rebound, supposing that the inversed rebound and consolidation appear simultaneously but can be calculated separately： and the inversed rebound is measured by inversed rebound index. And the gradual consolidation is considered by layer division. When the inversed rebound value is greater than consolidation one, the strata will expand. The ground subsidence can be precisely predicted by the method when the inversed rebound index and drawdown are measured or calculated reasonably.