考虑旋挖桩承载特性及实时钻进过程的终孔深度确定

Determination of final digging depth considering bearing behavior of rotary digging pile and real-time digging process

鉴于旋挖钻机施工的优越性,旋挖桩基的运用越来越广泛,但钻进过程中的终孔深度确定是当前亟待解决的关键课题。为了确定旋挖钻进终孔深度并提高施工的时效性,以高压变电站软质岩土深回填区的旋挖桩为研究对象,结合实际地质勘测资料建立桩-地层接触效应的三维数值模型,通过单一桩的沉降、轴力及负摩阻力响应验证计算模型的可靠性。并研究不同嵌岩深度的旋挖桩承载力,其结果表明,较大的嵌岩深度提高了桩体抗压刚度,减小了桩顶沉降,但同一荷载下的负摩阻力分布范围较大,导致桩体抵抗外荷载的能力有所降低,可见合理的嵌岩深度设计是关键。进一步基于比功模型及旋挖钻进实时监测信息,优化各类地层的比功阈值区间,确定持力层深度及终孔深度。结合地勘资料比较实际旋挖钻进深度与计算嵌岩深度,两者是吻合的,验证了上述方法的的准确性及可靠性,其方法可为复杂地层的旋挖钻进终孔深度设计及桩承载力评价提供技术手段。

Rotary digging piles are widely used due to the superiority of the rotary digging machine,however,the final depth during digging is a key topic to be solved.To determine the final digging depth and improve the digging efficiency of the rotary digging machine,take a rotary digging pile in the deep backfilled areas case study,a 3-D numerical model considering pile-formation contact effect based on the real geological materials has been proposed to simulate the response of the pile settlement,axial force and negative friction resistance.And then,the pile bearing capacity considering different embedded depth has been deeply studied to show shat that larger embedded depth increases the pile stiffness and decreases the pile settlement,however,the range of the negative friction under the same load will be enlarged resulting in decreasing the pile bearing capacity,so the rational embedded depth is the most significant.In addition,using the formation energy model and real-time monitoring information to optimize the threshold value of the formation energy for some formations and determine the bearing layer and the final digging depth,correspondence of the real digging depth and the calculated depth based on geological information has been compared and proved the accuracy and the reliability of the proposed method.Therefore,the above method can be used to design the final digging depth and assess the piles bearing capacity in the complex formations.