嵌岩扩底抗拔桩承载特性现场试验研究

Field test study on bearing capacity of rock-embedded under-reamed uplift piles

依托国网路平―富乐500kV双回线路工程中嵌岩抗拔桩极限载荷试验,针对其中3根嵌岩扩底抗拔桩,对其桩顶荷载位移关系曲线、桩身轴力及桩身侧摩阻力等特性进行分析。结果表明,对所处岩土层相同、桩长接近的抗拔桩,嵌岩扩底抗拔桩较等截面桩不但能够显著提高极限抗拔荷载,而且能够有效降低桩顶位移。扩大头所处岩层性质对其所能提供的抗拔力影响较大,处于中风化岩层中的扩大头所提供的抗拔力要显著大于位于强风化岩层中的扩大头所提供的抗拔力。对同为扩底型的嵌岩抗拔桩,桩长较短时,扩大头提供的抗拔力占桩体极限抗拔荷载的比例更高,扩大头的扩底作用更显著。对于扩大头位于中风化岩层且扩大头上部等截面段具有一定厚度的黏土层与强风化岩层的抗拔桩,其等截面段与黏土层、强风化岩层接触部分极限侧摩阻力可在规范建议标准值的基础上,根据工程实际适当提高。

Based on the ultimate load test of the national power grid of 500 kV transmission line project from Luping to Fule,this paper carried out the ultimate load test of 3 rock-socketed piles with enlarged base.The load-displacement curves,distribution of axial force of pile shaft and shaft resistance were investigated.Results show that,when the piles located in the same layer of rock-soil and the length are reached,the enlarge base pile can not only increase the ultimate uplift bearing capacity,but also reduce the displacement of pile top than the pile of uniform section.The properties of the rock mass of the enlarged head have great influence on the uplift force.For the rock socketed uplift pile with enlarged bottom,the uplift force of the enlarged head is higher than that of the ultimate uplift load of the pile,and the expansion action of the enlarged head is more significant.The uplift pile of a clay layer with a certain thickness and a strong weathered layer in a medium weathered layer with enlarged head and a uniform section at the upperend of the enlarged head,the limit side friction of the section with the clay layer and the strong weathered rock layer can be improved appropriately according to the actual situation of the project on the basis of the recommended by the building codes.