黄土斜坡桩基竖向荷载传递规律现场试验研究

Field experimental study of transmitted characteristics of pile foundation under vertical load in loess slope

结合某黄土斜坡桥梁桩基工程,对同一坡度相近位置的两根桩基开展现场试验,研究其在不同竖向荷载工况下的桩身上、下坡面两侧的轴力、桩侧摩阻力及桩侧土压力的传递规律与分布特征。试验表明:桩基荷载传递具有明显的区域性,第1区域是从桩顶至约3倍桩径深度处,此区域上坡面桩侧轴力较下坡面相应位置小,且其轴力随深度递减幅度及侧摩阻力发挥程度均较下坡面桩侧大;第2区域是从约3倍桩径至10倍桩径深度处,桩身上坡面一侧竖向受力减小幅度小于桩基下坡面一侧,但此时下坡面桩侧摩阻力发挥幅度大于桩基上坡面一侧;第3区域是从约10倍桩径直至桩端,该区桩身两侧轴力差异不大,摩阻力发挥幅度相近,荷载平衡协调且向下传递稳定。针对斜坡桥梁桩基上、下坡面两侧所受土压力的不均匀性,对设计桩基竖向承载力进行了一定程度地折减,并对计算公式作了相应修正,研究结论可供类似工程参考、借鉴。

Combined with the pile foundation engineering constructed in loess slope for supporting super bridge, field experiments on two neighboring piles at the same slope region are conducted to investigate transmitted characteristics as well as distribution feature of axial force, skin friction and lateral earth pressure of both upslope side and downslope side under different vertical load cases. The test results show that load transmitting of pile foundation can be obviously classified into 3 regions. The first region covers from pile head to about the depth of three times pile diameter; within this region, the axial force developed in pile upslope side is less than corresponding position at downslope side; moreover, its decrease extent with pile depth and work efficiency of skin friction are greater than pile downslope side. The second region is within about pile depth of three times to ten times pile diameter, which shows a less axial force decrease extent with pile depth in upslope side and higher work efficiency of skin friction along downslope side at the same elevation. The third region starts from the pile depth of about ten times pile diameter and ends with pile tip. For pile body in this region, the difference of axial force and skin friction for two sides at the same elevation are insignificant;and the load from super region could be even and well-distributed transmitted downwards. For the special issue of uneven earth pressure of pile foundation installed in loess slope, certain reduction in some degree for vertical bearing capacity of pile design is conducted;and some necessary revision of the calculation formula is made. The acquired study results can provide a reference for other similar pile foundation.