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本文通过厦门某项目大直径(超)长灌注桩桩端有无注浆、不同持力层的对比静载试验以及基坑底大吨位(6000kN)抗拔试验,分析研究大直径(超)长灌注桩的竖向承载性能,得出以下结论和建议:抗压桩、抗拔桩均存在侧阻力时间效应因素的影响而降低桩侧摩阻力,当暴孔约9d,抗压桩桩侧摩阻力降低约23%,抗拔桩桩侧摩阻力降低约1/3;采用S-lgP法和经验参数法(结合静载试验)分离桩侧摩阻力和桩端阻力,表明大直径超长灌注桩即使是嵌岩桩通常也属于端承摩擦桩,侧摩阻力先于端阻力发挥,故应先满足桩身压屈变形,才能保证桩端阻力的发挥;不管是抗压桩还是抗拔桩,可优先考虑桩侧注浆,可较大幅度提高桩侧摩阻力,而不要盲目增加桩长或嵌岩深度;桩侧抗拔土阻力峰值对应的桩顶上拔量同样约为0.02D,当桩周土层为全风化岩—强风化岩时,抗拔系数约为0.60。
In this paper, the large-diameter (super) long bored pile in Xiamen project with or without grouting pile, the contrast test of different bearing strata and the pull-up test of large tonnage (6000kN) The vertical bearing capacity of cast-in-situ piles has the following conclusions and recommendations: Both the anti-pressure piles and the anti-pull piles have the influence of time-dependent factors of lateral drag, Drag reduction of about 23%, anti-pull pile lateral friction reduced by about 1/3; using S-lgP method and empirical parameter method (combined with static load test) to separate pile-side friction and pile-end resistance, Even if the pile is a rock-socketed pile, it usually belongs to the end-bearing friction pile, and the side frictional resistance is exerted prior to the end resistance. Therefore, it is necessary to satisfy the buckling deformation of the pile in order to ensure the resistance of the pile at the end. , Can give priority to pile side grouting, can greatly enhance pile side frictional resistance, but do not blindly increase the pile length or embedded rock depth; pile top pullout soil resistance peak corresponding to the top of the pile pull is about the same as about 0.02D, When the soil around the pile is a fully weathered rock-strong weathered rock, the anti-pull coefficient is about 0.60.