扩径率与入岩深度对岩基挖孔基础抗拔承载特性影响的试验研究

Experimental investigation of influence of embedment depth and expanding ratio upon ultimate uplift resistance of hole digging foundation in rock

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 expanding ratio and the embedment depth in rock are considered as the two most significant factors influencing the ultimate uplift resistance of the hole digging foundation in rock. In order to investigate the influence of the embedment depth in rock and the expanding ratio upon the ultimate uplift resistance of the hole digging foundation in rock, the uplift static load tests of full-size foundations in site are carried out to analyze the response of displacement verse load, the ultimate uplift resistance of the hole digging foundation and the failure mode of foundation rock mass with different expanding ratios and different embedment depths in rock. Results show that the expanding ratio has the significant impact on load-displacement curve in initial liner phase, Using graphic method, three different parameters Q(L1), Q(DLI), Q(L2) representing uplift bearing performance of low, medium and high respectively are achieved. Further analysis shows that the ultimate uplift resistance will increase with the increase of the expanding ratio and the depth of the rock respectively. But the difference of influence mechanism is found that the Q(L1) value representing lower uplift resistance in initial elasticity phase are affected obviously by the expanding ratio; and the Q(DLI), Q(L2) values representing medium and higher uplift resistance respectively in plasticity phase are affected significantly by the embedment depth in rock. Through the analysis of the distribution of surface cracks in the rock mass on ground damage characteristics, the following conclusions can be achieved. The failure mode of the rock mass upper foundation had nothing to do with the foundation structure style. Cracks are generated from the bottom edge of foundation at first, and then extended to the ground along opening with a predetermined angle until failure of foundation occurs. At the same time, destroy range decreases with the increase of the embedment depth in rock. Comprehensive considering construction safety, economy and mechanization degree, measures to increase the embedment depth in rock shall be preferred.