Abstract This paper presents a probabilistic limit state framework for the evaluation of the base resistance of drilled shafts in soft rock. In situ load tests and the Griffith fracture theory are used to evaluate the mode of failure for the rock mass under the drilled shaft base. The base resistance or the limit state in the context of this paper is defined by the contact pressure at which load induced vertical to subvertical cracks form and the contact pressure-displacement relationship passes into a steep and fairly straight tangent. The parameters affecting the base resistance are evaluated using an in situ load test database. A statistical approach using the maximum likelihood method is utilized for the development of the design model for the base resistance. Reliability analysis is used to calibrate the corresponding resistance factors. The in situ load tests and the Griffith fracture theory suggest that the soft rock mass underlying the drilled shaft base primarily fails by the formation of vertical to subvertical cracks. Field observations indicate that the displacements in the underlying rock mass are largely in the vertical direction and that the base displacements required to mobilize the proposed base resistance are generally less than 30 mm. Load test data show that the base resistance is chiefly related to the unconfined compressive strength of soft rock. The calculated resistance factors are found to slightly decrease with increase in the span length of the structure and increase with the increase in the foundation redundancy.

中文翻译：

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使用原位载荷测试的软岩中钻孔轴的基础阻力：一种极限状态方法

摘要 本文提出了一个概率极限状态框架，用于评估软岩中钻孔轴的基础阻力。原位载荷试验和格里菲斯断裂理论用于评估钻孔轴基下岩体的破坏模式。在本文的上下文中，基础电阻或极限状态由载荷引起的垂直到近似垂直裂纹形成时的接触压力定义，接触压力-位移关系变为陡峭且相当直的切线。使用原位负载测试数据库评估影响基极电阻的参数。使用最大似然法的统计方法用于开发基极电阻的设计模型。可靠性分析用于校准相应的电阻系数。原位载荷试验和格里菲斯断裂理论表明，钻孔轴基下方的软岩体主要通过形成垂直到近垂直的裂缝而失效。现场观察表明，下伏岩体的位移主要在垂直方向上，并且调动所建议的基础阻力所需的基础位移一般小于 30 mm。荷载试验数据表明，基底阻力主要与软岩的无侧限抗压强度有关。发现计算的阻力系数随着结构跨度长度的增加而略有下降，并随着基础冗余度的增加而增加。