摘要
深基坑抽水常可导致多含水层水位同时下降,并由此诱发邻近桩承建筑明显沉降;然而,基坑抽水施工时却难以获取邻近建筑桩基的荷载传递数据,该条件下的桩基受力变形特性与桩-土相互作用机理尚不十分清楚。为此,文章在天津某多含水层基坑工程场地开展了现场抽水试验,分析抽水过程中邻近桩承建筑沉降的发展规律,并基此建立三维有限元模型,进一步研究不同抽水工况下邻近群桩受力变形特性与荷载传递规律。研究表明:多含水层体系基坑抽水过程中,邻近桩承建筑沉降随时间的发展相对于坑内水位下降来说呈现出明显的非同步性和滞后性,这是由于基坑外各含水层在其间弱透水层的水力阻隔作用下呈现出不同步的水位下降(浅层水位下降滞后于深层水位下降),相应地,浅层含水层中桩侧摩阻力(或负摩阻力)发挥也将滞后于深层含水层中桩侧摩阻力发展,因而导致了桩承建筑在坑内水位稳定后的持续沉降,桩身轴力也为此不断增大。另外,研究还发现基坑抽水可引起邻近建筑群桩发生偏向基坑的侧移,且群桩中不同位置基桩的侧移模式不同,靠近基坑的基桩呈悬臂式侧移,而远离基坑的基桩呈鼓肚式侧移,由此而引发不同位置基桩产生不同程度的附加弯矩。在密集城市环境中的建筑桩基结构设计中,若该建筑周边已明确规划有大型建筑设施时,可适度考虑放大先建建筑桩基结构设计弯矩与轴力以确保建筑结构在后续邻近地下施工过程中的稳定安全,但与此同时,应更加注重后建基坑的变形监测与控制。
Deep foundation pit dewatering often results in simultaneous drawdown of water levels in multiple aquifers,causing apparent settlement of adjacent pile-supported building.However,it is difficult to obtain the load-transfer data of adjacent pile foundations during dewatering,and the pile deformation characteristics and pile-soil interaction mechanism under this condition are not quite clear.Hence,in this study,a pumping test was carried out for a foundation pit constructed in stratum with multi-aquifer in Tianjin;the settlement development of adjacent pile-supported building during the pumping test was analyzed.Based on the pumping test,a three-dimensional finite element model for fluid-solid coupling was established to investigate the load-deformation property and load-transfer mechanism of adjacent pile group under different dewatering conditions.Results indicate that during the pumping process of foundation pit in multi-aquifer system,the settlement of adjacent pile-supported building exhibits obvious delayed and asynchronous behaviors compared with the drawdown of groundwater inside the foundation pit due to the hydraulic barrier of the aquitard between the multi aquifers,causing the asynchronous drawdown of water level in each aquifer(i.e.,drawdown in shallow aquifer lags behind that in deep aquifer).Accordingly,the development of pile shaft resistance(or negative friction)in shallow aquifers may lag behind that in deep aquifers,leading to the continuous settlement of pile-supported buildings after the water level inside the pit is stabilized;meanwhile,the pile axial force is continuously increased.Additionally,results also show that the pumping of foundation pit may cause the lateral deflection of piles towards the pit,but the deflection patterns of piles at different locations of the pile group are different;typically,the pile near the foundation pit moves in the cantilever mode,while the pile far away from the pit moves much in deep location,causing different additional pile bending moments at different locations.In the design of pile foundation in crowded urban environment,if there are planned large buildings or facilities around the construction site,the design values of the bending moment and axial force of the building pile can be appropriately enlarged to ensure the stability and safety of the building in subsequent adjacent construction;meanwhile,greater attention shall be paid to the deformation monitoring and control during the subsequent adjacent construction.
作者
曾超峰
孙海昱
薛秀丽
宋伟炜
雷勇
陈秋南
Zeng Chaofeng;Sun Haiyu;Xue Xiuli;Song Weiwei;Lei Yong;Chen Qiunan(Hunan Provincial Key Laboratory of Geotechnical Engineering for Stability Control and Health Monitoring,Hunan University of Science and Technology,Xiangtan 411201,China)
出处
《土木工程学报》
EI
CSCD
北大核心
2023年第8期164-173,183,共11页
China Civil Engineering Journal
基金
国家自然科学基金(51978261,51708206)
湖南省教育厅资助项目(21A0290,20A190)。
关键词
基坑降水
多含水层体系
建筑桩基变形
荷载传递
轴力与弯矩
foundation pit dewatering
multi-aquifer system
pile foundation deformation
load transfer
axial force and bending momen
