砂性土中钢管桩水平承载特性模型试验

Small-scale model tests of lateral bearing capacity of steel pipe in sand

为探究不同桩径的钢管桩水平承载特性及桩土相互作用机理,通过水平荷载作用下钢管桩承载特性的模型试验和PIV(particle image velocimetry)成像技术,研究桩径对钢管桩水平承载特性的影响及桩土界面受力机理。室内试验包括半模型和全模型试验,半模型试验主要分析桩在加载至破坏过程中桩侧位移的变化情况,全模型试验主要分析桩在加载至破坏过程中桩侧位移、弯矩及桩身剪力的变化情况。试验中通过采集桩身各截面应变、桩顶应力、桩顶及土层沉降、桩周土压力等数据实现对桩土相互作用过程的观测,并通过对试验数据的处理和分析,得到水平荷载作用下桩-土相互作用的规律。结果表明,桩径大小对其水平承载力影响较大,尺寸效应的影响在非线性阶段表现十分明显;钢管桩在水平荷载作用下其最大弯矩点在桩身中部靠上位置,且随着荷载的增加最大弯矩点向下移动,故在设计过程中可重点验算桩身中部附近的抗弯承载力;桩的刚柔性也是影响桩内力分布及桩侧土体发挥的关键因素;桩侧土体位移主要集中于5倍桩径以上位置,浅层土体对于抵抗水平荷载发挥关键性作用。

In order to study the lateral bearing characteristics of steel tubular piles and the mechanism of pile-soil interaction with different pile diameters,in this study,small-scale model method tests and PIV(particle image velocimetry)imaging technology were used to analyse the lateral bearing characteristics of steel tubular piles and the soil-pile interaction of pipe piles with different diameters.The laboratory tests included half model and full model tests.The half model test mainly analyzed the change of pile side displacement from loading to failure,while the full model test mainly analyzed the change of pile side displacement,bending moment and shear force of pile body from loading to failure.At the same time,pile-soil interaction process was observed by collecting the strain data of each pile body section,pile top stress,settlements of pile top and soil layer,and earth pressure around the pile.Through the processing and analysis of the test data,the law of pile-soil interaction under the action of horizontal load was obtained.According to the test results,it is concluded that the pile size has a great influence on its lateral bearing capacity.When the pile diameter is doubled,the horizontal bearing capacity is multiplied,and the size effect is very obvious in the nonlinear stage.Under the action of lateral load,the maximum bending moment of steel pipe pile is located at the upper position of the middle part of pile body,and the maximum bending moment moves downward with the increase in load,so the bending capacity near the middle part of the pile body is checked during the design process.The rigidity and flexibility of steel tubular pile have a great influence on the distribution of shear stress on pile body.For flexible pile,the bottom position of pile body is more complicated,while,for rigid pile,the displacement is more inclined to the rotation of rigid body,so the maximum shear stress is near the pile bottom.The soil displacement on the pile side mainly focuses on the position above 5 times the pile diameter,and the shallow soil plays a key role in resisting the horizontal load.