Experimental Studies On The Problem Of Tianjin Binhai New Area In Dewatering

With the Binhai New Area central business district (ultrahigh, versize, super-deepbuildings) to accelerate the pace of construction, the deep foundations are more and more,and the depth is deeper, because of the complexity of engineering geology and hydrogeologyconditions in the area, the foundation has great danger. Although accumulated someexperience in the work, but there are still many problems: regional hydrogeologicalparameters are unclear, pit inrushing evaluation is still blank, surrounding land subsidencecaused by pit precipitation and reasonable curtain depth study are still lacking. This topic forthe above problems, through the multiple holes pumping tests learned: the aquifer withconstruction-related in this area is a semi-confined aquifer system of the multi-layer structurevertical flow, near the Haihe river, the Haihe river can be used as constant-head rechargeboundary; according to Bolton,Newman and Hantush models obtained accurate regionalhydrogeological parameters (hydraulic conductivity, permeability, storage coefficient,vertical flow parameter), these studies provided reliable information for the foundation pitdewatering design. By pumping tests preliminary proved that the central business district areless consolidated soft soil area, elastic deformation and less consolidated compressionaccount for the main ingredient in the early settlement of foundation pit dewatering impacton the surrounding area, representing an important component of the total settlement amount.Through the study of groundwater confined characteristics, can be get the laws of differentdepth foundation’s basal possibility inrushing: critical excavation depth of pit inrushingranged between13.5~18.0m, when excavation depth of10m (two basement), thesemi-confined water which following pit floor does not cause pit Inrushing, and does notbuck; when excavation depth of15m (three basement), the individual site may happen pitinrushing, we suggested that doing hydrological geological investigation before decidingwhether to buck; when excavation depth is greater than20m (four basement and more), itwill cause the pit inrushing, so must buck. By monitoring data for the excavation to start thenumerical simulation analysis, summarized the influence laws of pit precipitation ongeological environment: settlement range caused by pumping test and pit precipitation isabout400m; in freedom site, single well short-term pumping test most can produce about5mm ground subsidence, group wells short-term pumping tests can produce a maximum ofabout22mm ground subsidence, and has gentle setting funnel; pit precipitation duringconstruction can produce a maximum of about30~40mm ground subsidence; outside thescope of about four times excavation depth, the land subsidence caused mainly by foundationpit dewatering. We analyzed the impact of waterproof curtain depth to land subsidenceoutside the pit when foundation pit dewatering: for hanging waterproof curtain, withwaterproof curtain deepens, the semi-confined water’s landing funnel scope becomessmaller, land subsidence scope and maximum value around foundation will be smaller; forfour basement foundation, in order to control ground subsidence outside the pit byprecipitation, waterproof curtain should be set at a depth of at least40m above (waterproofcurtain into the semi-confined aquifer layer is greater than half the length of semi-confinedaquifer thickness); when using pensile curtain, waterproof curtain control effects of landsubsidence, long strip pit is better than square pit. Above studies have certain guidingsignificance for the central business district of foundation pit dewatering project.