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工程中多采用基础上拔静载试验中基础顶部荷载-位移曲线获取基础的承载力,忽略了基础周围土体的变形破坏过程,而实际工程中均是基础周围地基土体发生破坏。为研究扩底基础与其周围土体在抗拔承载特性方面的差异,以黄土地基中的9个扩底基础为研究对象,通过现场全尺寸基础的上拔静载试验,分别获得基础顶部与地表的上拔荷载-位移曲线,并进一步对基顶与地表处的荷载-位移曲线变化特征、抗拔承载力取值进行对比分析。结果表明,两处的荷载-位移曲线变化特征相似,相同上拔荷载作用下地表处的位移量均小于基础处位移量,差异以初始弹性阶段变形最为突出;两者在弹性极限荷载Q_(L1)取值方面,相差较大,但随着地基基础由弹性向塑性发展,差异逐渐减小,两者塑性极限荷载Q_(L2)取值基本相同。结合上拔扩底基础的破坏模式,分析出上述差异主要由于基础与周围土体之间变形不协调所致,加载初期基础顶部的上拔位移包括基础拔出量和上部土体压缩量,当上部土体压密后压缩变形消失,地基基础成为一个整体,上拔基础与周围土体的变形趋于协调。
In engineering, the load-displacement curve on the basis of top load-displacement curve is mostly used to obtain the bearing capacity of the foundation, while the deformation and failure process of the soil around the foundation is ignored. In actual engineering, the soil around the foundation is damaged. In order to study the difference of pull-out and load-bearing characteristics between expanded foundation and its surrounding soil, 9 expanded bases in loess foundation were selected as the research object. Based on the full-scale on-site static load test, And the load-displacement curve at the top of the base and the ground surface, and then the change characteristics of load-displacement curve and the value of anti-pull bearing capacity were compared and analyzed. The results show that the load-displacement curves of the two sections have similar changing characteristics. The displacements of the ground surface under the same uplift load are all less than those at the base. The differences are most prominent in the initial stage of elastic deformation. ), The difference is larger, but with the foundation of the foundation from elastic to plastic development, the difference decreases gradually, the plastic ultimate load Q_ (L2) values of the two basically the same. Based on the failure mode of the foundation, the differences are mainly attributed to the uncoordinated deformation between the foundation and the surrounding soil. The uplift displacement at the top of the foundation during initial loading includes the amount of foundation pull-out and the amount of compression of the upper soil. Compaction deformation of the upper soil after the collapse of the disappeared, the foundation of the foundation as a whole, the basic pull-ups and the surrounding soil deformation tends to be coordinated.