密砂中圆形锚上拔承载力尺寸效应分析

通过模型试验和有限单元法分析了密砂中圆形锚板上拔承载力的尺寸效应问题。分别对直径为20,50,400 mm的锚板在埋深比为2～6时进行拉拔试验,获得上拔力和位移关系曲线及极限上拔力。基于不同埋深比时板径与上拔承载力系数关系曲线,可发现:相同埋深比时,随着锚板直径增加,上拔承载力系数逐渐减小;且随着埋深比增加,此现象愈明显。考虑密砂强度随应变发展而出现的软化现象,对理想弹塑性Mohr-Coulomb模型进行改进,基于改进的模型对上述12个拉拔试验进行有限元数值模拟,同时与理想弹塑性模型模拟结果进行比较。结果表明:理想弹塑性模型严重高估锚板上拔承载力,而考虑土体软化的模型能够模拟锚板上拔过程中破坏面上土体强度逐渐发挥的过程,计算得到的极限承载力与试验结果吻合较好。尺寸效应产生的原因一方面由于应力水平对土体强度的影响,另一方面由渐进破坏引起;埋深比越大,随着锚板直径增加,周围土体依次进入破坏的过程愈加明显。

Scale effects of uplift capacity of circular anchors in dense sand

The scale effects of uplift capacity of circular anchors in dense sand are studied by means of the model tests and finite element method. The pullout tests on the circular anchors with the diameters of 20, 50 and 400 mm as well as the embedment ratios of 2~6 are carried out, where the curves of uplift resistance and displacement and ultimate uplift capacity are obtained. It is seen from the test results that the breakout factor decreases with the increase in anchor diameter under the same embedment ratio, and the phenomenon is more obvious with larger embedment ratio. Numerical analysis for the pullout tests is performed based on the modified Mohr-Coulomb model which can reflect the strain softening of dense sand, and the results are compared with those based on the elastic-perfectly plastic Mohr-Coulomb model. It is shown that the numerical results based on elastic-perfectly plastic model overestimate the uplift capacity of anchors remarkably, while the simulations based on the modified Mohr-Coulomb model can reveal the process of mobilizing soil strength to the peak value, and thus the numerical results agree well with the test ones. The reasons causing the scale effects are the soil strength dependent on stress level and the progressive failure during pullout. The process that the soils surrounding the anchors reach failure step by step becomes more and more obvious with the increase of anchor diameter when the embedment ratio is relatively large.