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将饱和软黏土中钻孔灌注桩孔壁稳定性问题视为半无限体内柱形孔的卸荷收缩问题。基于SMP准则改进的修正剑桥模型,采用应力空间变换方法推导了柱孔卸荷收缩问题的弹塑性解答,得出了孔壁临塑支护荷载和孔壁颈缩的解析表达式。在此基础上,提出了维持孔壁稳定所需最小泥浆重度和孔壁稳定安全系数的计算方法,并对影响钻孔稳定性的因素进行了研究。研究结果表明,饱和软黏土中钻孔灌注桩孔壁卸荷屈服后,孔壁周围土体处于弹塑性状态,钻孔颈缩量大,孔壁稳定安全系数较小;在泥浆支护条件下,饱和软黏土中钻孔灌注桩孔壁稳定性取决于土体重度、超固结比、土体内摩擦角及泥浆重度等因素,而与钻孔深度和孔径无关;土体超固结比和内摩擦角越大,维持钻孔稳定所需的临界支护压力和最小泥浆重度越小。在实际工程中,应在保证最小泥浆重度的条件下结合工程具体情况合理选取泥浆比例。
The problem of hole wall stability of bored pile in saturated soft clay is considered as unloading and shrinkage problem of semi-infinite cylindrical hole. Based on the modified Cambridge model improved by SMP criterion, the elastoplastic solution to the unloading and shrinkage problem of the column hole is deduced by using the stress-space transformation method. The analytical expressions of the plastic-plastic retaining wall load and the neck shrinkage are obtained. On this basis, the calculation method of the minimum mud weight and the safety factor of the hole wall to maintain the stability of the hole wall is proposed, and the factors affecting the stability of the hole are also studied. The results show that the soil surrounding the hole wall is elasto-plastic after the unloading of the hole wall in the saturated soft clay, and the amount of neck shrinkage is large and the safety coefficient of the hole wall is small. Under the condition of mud support The hole wall stability of cast-in-place bored pile in saturated soft clay depends on factors such as soil mass, overconsolidation ratio, soil internal friction angle and mud weight, but not related to drilling depth and pore size. The larger the internal friction angle, the smaller the critical support pressure and the minimum mud weight required to maintain the stability of the borehole. In the actual project, the proportion of mud should be selected reasonably according to the specific conditions of the project under the condition of guaranteeing the minimum mud weight.