含水层越流情况下基坑降水引发变形机理及控制措施  

Mechanisms and countermeasures of deformation induced by dewatering of excavation in leaky aquifers

作　　者：栗晴瀚 张静涛[2] 郑刚[1,3] 程雪松[1,3] 雷亚伟 孙颜顶 贾建伟 刘晓敏 Li Qinghan;Zhang Jingtao;Zheng Gang;Cheng Xuesong;Lei Yawei;Sun Yanding;Jia Jianwei;Liu Xiaomin(Key Laboratory of Coast Civil Structure Safety of Ministry of Education,Tianjin University,Tianjin 300350,China;China Construction Second Engineering Bureau LTD,Beijing 100160,China;School of Civil Engineering,Tianjin University,Tianjin 300350,China;China Construction Sixth Engineering Bureau LTD,Tianjin 300457,China)

机构地区：[1]天津大学滨海土木工程结构与安全教育部重点实验室,天津300350 [2]中国建筑第二工程局有限公司,北京100160 [3]天津大学建筑工程学院,天津300350 [4]中国建筑第六工程局有限公司,天津300457

出　　处：《土木工程学报》2023年第5期89-101,共13页China Civil Engineering Journal

基　　金：中国建筑第二工程局有限公司科技资助计划(91110000100024296D200003);中建股份科技研发计划资助(CSCEC-2021-Z-(25));国家自然科学基金(52178343)。

摘　　要：在天津等沿海地区,地层中通常分布有多个承压含水层,由于隔水层厚度不均匀,且常包含粉土、粉砂透镜体,各含水层间存在水力联系的现象较普遍。天津某地铁车站基坑开挖前的降水试验中,基坑外水位发生大幅下降,实测地连墙侧移与坑外地表沉降分别达到允许变形的29.0%和73.5%。基于此案例,采用三维有限元对含水层越流情况下基坑降水引发的变形机理、规律和影响区进行研究,并对降水引发坑外沉降的控制措施进行了对比研究。结果表明,含水层越流导致基坑内外存在水力联系时,坑内降水引发的坑外沉降由支护结构侧移和水位下降共同导致,沉降区根据诱发机理可分为两部分,距基坑2倍降水深度以内为支护结构侧移和水位下降复合影响区,以外为水位下降影响区。降水井底部弱透水层高渗透性引发越流将增大坑内水位降深,从而增大地连墙变形及其引发的坑外沉降。地连墙墙趾处弱透水层高渗透性引发越流将增大基坑内外水力联系及坑外沉降,但会减小地连墙变形。对于含水层越流风险高的地层,疏干降水建议采用“深浅井”方案以更好地实现按需降水和基坑变形控制;回灌和加深止水帷幕截断基坑内外水力联系均可较好控制坑外水位下降,但切断水力联系会导致支护结构侧移增大,对于复合影响区内沉降控制效果较回灌差,且成本相对较高。研究成果以期为软土地区复杂水文地质条件下的基坑降水变形控制提供参考。In coastal areas,such as Tianjin,there are multiple confined aquifers in strata.Because the thickness of the aquitard is not uniform,and it often contains pockets of silt or silt sand,the phenomenon of hydraulic connection between aquifers is very common.In a dewatering test of a subway station in Tianjin before the excavation,the groundwater level(GL)outside the excavation decreased significantly.The measured diaphragm wall deformation(δ_(H))and settlement outside the excavation(δ_(v))reached 29.0%and 73.5%of the allowable values,respectively.Based on the case,the mechanisms,rules,and influence zones of deformation induced by excavation dewatering in leaky aquifers were studied by three-dimensional finite element model.Furthermore,the control measures forδ_(v)induced by dewatering were compared.The results show that when the leaky aquifer induces hydraulic connection between the soil mass inside and outside the excavation(HC),δ_(v)can be caused by O and GL drop,and the zone of settlement can be divided into two parts based on the mechanism.The zone within a distance two times the dewatering depth from the excavation is the composite influence zone of δ_(H) and GL drop,and the zone outside is the influence zone of CL drop.The cross-flow caused by the high permeability of aquitard at the bottom of the dewatering well may increase the GL drop in the excavation,which results in the increase of On andδ_(v).The cross-flow caused by the high permeability of aquitard at the toe of the diaphragm wall increase the HC andδ_(v),but it reduces On.For the strata with high risk of cross-flow,it is suggested to adopt the‘deep and shallow wells'to control the GL andδ_(v).The GL drop outside the excavation can be well controlled by groundwater recharge or lengthening waterproof curtain to cut off the HC.However,cutting off the HC may increase the Sq induced by dewatering,which leadsδ_(v)induced by dewatering to be greater than that with groundwater recharge in the composite influence zone and the relatively higher cost

关 键 词：含水层越流 基坑降水 地连墙变形 沉降 回灌 

分 类 号：TU463[建筑科学—结构工程]