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扩径率和入岩深度是影响岩基挖孔基础抗拔承载特性的两个重要因素。通过开展8个不同扩径率、不同入岩深度挖孔基础的现场真型上拔静载试验,从荷载位移变化规律、抗拔承载力和地基岩体破坏模式三方面分析了扩径率与入岩深度对基础抗拔承载特性的影响,结果表明扩径率对荷载位移曲线初始线性阶段影响显著。采用图解法分别获得代表基础低、中、高3种承载能力的抗拔承载力Q_(L1)、Q_(DLI)、Q_(L2),分析表明,随着扩径率与入岩深度的增加,基础抗拔承载力均有不同程度提高,但两种因素对基础承载力影响机制不同,扩径率可明显提高初始弹性阶段的承载力Q_(L1),而入岩深度可明显提高塑性阶段的承载力Q_(DLI)和Q_(L2)。通过分析地基破坏时地表岩体裂缝的分布特征,得出岩基中上拔岩体的破坏模式与基础结构型式无关,均是从基底开始出现裂缝,沿着一定角度的开口延伸至地面,直至地基发生破坏,并且破坏范围随着入岩深度的增加而减小。综合考虑基础施工安全性、经济性和机械化程度,建议优先选择加深入岩深度的措施来提高基础抗拔承载力。
The rate of expansion and the depth of rock entry are two important factors that affect the uplift and load-bearing characteristics of foundation excavation. By carrying out the on-site true-type pull-out static load test with eight different diameter expansion rates and different depths of rock excavation, the relationship between the expansion ratio and the increase rate of tensile deformation is analyzed from the variation of load displacement, The results show that the diameter expansion rate has an obvious influence on the initial linear phase of load displacement curve. The bearing capacity Q L1, Q DL DL and Q L2 of the bearing capacity of three kinds of low, medium and high load bearing foundation are obtained by the graphic method. The analysis shows that with the increase of the rate of expansion and the depth of rock entry, , And the basic pull-out bearing capacity all increased to some extent. However, the influence mechanism of the two factors on the foundation bearing capacity is different. The expanding rate can obviously increase the bearing capacity Q L1 of the initial elastic stage, while the depth of rock entry can obviously improve the plasticity stage Of bearing capacity Q_ (DLI) and Q_ (L2). By analyzing the distribution characteristics of the cracks in the surface rock mass when the foundation is broken, it is concluded that the failure mode of the rock mass in the rock mass is irrelevant to the foundation structure type. Cracks start from the basement and extend to the ground along an angle opening until The foundation is damaged, and the damage area decreases with the depth of the rock. Considering the safety, economy and mechanization of foundation construction, it is suggested that the measures of deepening the depth of rock entry be given priority to improve the basic pull-out bearing capacity.