加载条件对土拱效应影响的Trapdoor模型试验研究
Trapdoor model tests on impact of loading conditions on soil arching effect
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摘要: 土拱效应是一种土中应力的重分布现象,它是由土与土中结构物间刚度的差异而引起的。目前关于循环荷载对于土拱效应影响的研究十分有限。使用铝棒相似土代替砂土作为填料,通过自制的模型试验装置进行了土体自重、表面静荷载及循环荷载作用下的平面应变Trapdoor模型试验,利用土拱率作为土拱效应强弱的衡量指标,对比研究了不同加载条件对土拱效应的影响,并将试验所得结果与前人的研究成果进行了对比验证。结果表明,静荷载与循环荷载均会削弱已有稳定“土拱”,削弱程度随荷载幅值及频率的增大而增大,随荷载作用面积的增大而减小。相同荷载水平下,循环荷载对土拱效应的削弱较静荷载更强,两者间的差异随荷载幅值的增大而减小,随荷载频率的增大而增大,且峰值荷载下的差异小于零荷载下的差异。总体而言,Evans提出的土拱率计算公式能够较好地用于土体自重及静荷载作用下的Trapdoor试验中土拱率的预测,而对于循环荷载作用下的情况,还有待对计算公式进行进一步地改进。Abstract: The soil arching effect is a redistribution of the stress in soil. It is caused by the rigidity difference between the soil and the structures in the soil. The studies so far about the impact of cyclic loading on the soil arching effect is very limited. A custom-made apparatus is used to conduct plain-strain trapdoor model tests under soil self-weight, static loading and cyclic loading to study the impact of different loading conditions on the soil arching effect. The analogical soil of aluminum rods is used as the fill instead of sand. The parameter of the soil arching ratio is used to evaluate the soil arching effect. The test results from this study are compared with those from the previous studies. It is indicated that both static loading and cyclic loading reduce the existing steady soil arching. The reduction of the soil arching effect increases with the loading magnitude and frequency and decreases with the loading area. Under the same loading level, the cyclic loading reduces the soil arching effect more than the static loading. The difference of reduction caused by them decreases with the loading magnitude and increases with the loading frequency. Besides, the difference under the peak pressure is less than that under the zero pressure. On the whole, the expressions given by Evans18 can well predict the soil arching ratios in the trapdoor tests under soil self-weight and static loading. However, an improvement of the expressions is necessary for the trapdoor tests under cyclic loading.