采空区上方高速铁路桥梁群桩基础模型试验研究

目前有关采空区桥梁群桩基础的受力机制和沉降特性的研究成果还十分匮乏。以合肥－福州高速铁路官山底特大桥采空区群桩基础为原型进行缩尺模型试验研究。根据相似理论计算出模型相似常数，试验确定相似材料后进行模型制作，通过多级荷载试验获取了桩的内力，桩间土的应力，桩、承台、土和采空巷道顶板的沉降3大类数据，得出了模型中桩和桩间土的荷载特性和基础沉降规律。研究表明：采空区对桩承载力的影响与荷载大小成反比关系；所有桩均未出现桩侧负摩阻力，穿过采空区的桩的侧摩阻力分布重心下移程度较正常地层桩明显；采空区群桩不均匀沉降存在临界荷载值，超过此值后，采空区顶板岩土层与基础下正常岩土层的差异沉降不再增加。基于试验结果和理论分析，建立了以现有规范为基础的采空区单桩承载力计算公式和采空区群桩沉降计算公式。

Model test on pile group foundation of a high-speed railway bridge above a goaf

Limit research effort has been made to explore the mechanism and settlement of high-speed railway bridge above goaf. With the pile group foundation of Guanshandi bridge in Hefei-Fuzhou high-speed railway as a prototype, a model test is carried out. According to the similarity theory, the similarity constants are derived and the similarity model materials are produced; and then the model setup is made. Based on multistage loading tests, three types of data are achieved including the internal forces of piles, stresses of soil among piles and the settlements of pile, pile caps, roof of goaf, the behaviors of piles and soils among piles as well as the settlement of goaf roof are determined. It can be found that the influence of goaf on the bearing capacity of pile is inversely proportional to the load. For all model piles, no negative skin friction is found to occur along pile shaft; and the center of the distributed skin friction in goaf descends significantly compared to those of the conventional piles. There is a critical value for the uneven settlement of pile group above goaf. If the settlement exceeds the critical value, the uneven settlement will stop growing. In addition, according to the test results and theoretical analysis, the equations for calculating bearing capacity and settlement of pile group above goaf are proposed based on the current code.