基于HS-Small模型的基坑近接桥桩开挖变形影响区研究

Analysis of influenced zone of foundation pit excavation adjacent to bridge pile foundation using HS-Small constitutive model

针对苏南某地铁高架线路邻近的基坑工程,根据国内外取值经验及土工试验结果,初步拟定各典型土层的HS-Small本构模型参数,基于基坑的地表沉降和围护结构水平变形的实测数据,采用有限元方法对开挖过程进行位移反分析,以此对HS-Small模型参数进一步优化和校准。在该基础上建立了基坑近接地铁桥梁桩基开挖有限元模型,对桥桩变形的影响区进行研究。结果表明,(1)当桥桩与基坑间距小于0.6倍基坑深度时,桩基沉降并未随间距增加产生明显减小趋势。当桥桩与基坑间距大于0.6倍基坑深度时,桩基沉降随间距增加而迅速收敛,桥桩水平位移也呈现处相似的分段变化规律,其临界点位于1.0倍坑深处;(2)近接开挖施工对桩基水平位移相较于竖向沉降更易超限,桥桩与基坑间距大于1.37倍基坑深度时,桩基变形不超过规范限值。桥桩与基坑间距大于1.90倍基坑深度时,桩基变形不超过警戒值(极限值的60%);(3)将桥桩变形的影响范围划分为A、B、C三级分区,并提出了相应的工程防护措施。

Taking a close range excavation to a metro line in southern area of Jiangsu province as the research object, a set of HS-Small constitutive model parameters are proposed preliminarily by empirical methods and soil tests. And then, based on the measured data of horizontal deformation of retaining structures and ground surface settlement in the field, inversion analysis is carried out to replay the excavation process by finite element method in order to further optimize and calibrate HS-Small model parameters. On this basis, the finite element model of the adjacent excavation of subway bridge pile foundation is built;and the influenced area of the existing pile deformation is established. The results show that:(1) When the spacing between pile and pit is less than 0.6 times of the depth of foundation pit, pile foundation settlement doesn’t perform an obvious trend to decrease;but when the spacing between pile and pit is more than 0.6 times of the depth of foundation pit, the settlement of pile foundation quickly decreases;pile horizontal displacement also shows similar pattern, but the critical point is located on the 1 times of the depth of foundation pit.(2) The close range excavation has a more obvious effect on pile horizontal displacement than vertical settlement;but when the pile-pit spacing is greater than 1.37 times of the depth of excavation, the deformation of pile foundation will not exceed the limit value;when the pile-pit spacing is greater than 1.90 times of the depth of excavation, the deformation of pile foundation will be less than the warning value(60% of the limit value).(3) The influenced zone of pile foundation deformation is divided into three grades as A, B and C, and the protection measures are put forward accordingly.