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目的:探讨中密和密实砂液化场地混凝土低承台群桩和地基动力响应存在的差异性,并揭示引起这种差异性的原因,以期获得加密后砂土液化场地混凝土低承台群桩和地基动力反应的基本特征与规律。创新点:1.利用振动台试验,成功实施中密和密实砂液化场地低承台群桩基振动台试验;2.基于试验结果,对比中密和密实砂层液化场地群桩和地基的动力响应规律,考察两种液化场地条件下群桩效应基本特征。方法:1.通过对比白噪声扫频,获得中密砂和密实砂层液化场地下体系模态参数的差异性(图2和表1);2.通过对比砂层孔压、加速度和位移(图3–8),获得中密砂和密实砂液化场地动力反应显著的差异性;3.基于上部结构和承台的位移与加速度,讨论中密砂和密实砂液化场地上部结构动力反应与回复力特性(图9和10);4.基于桩上记录的应变时程,考虑桩的非线性,反算混凝土桩的弯矩时程,对比两类场地群桩弯矩存在的差异性,获得两类场地对群桩效应的影响效应(图12–14)。结论:1.密实砂液化场地加速度在砂层液化后未出现弱化现象,表现出明显的循环流动性,密实砂液化场地比中密砂液化场地刚度更大;2.上部结构动力响应与砂土密实状态密切相关;3.中密砂液化场地桩的最大弯矩发生在土层分界处,而密实砂液化场地中桩的最大弯矩发生在桩头处;4.群桩效应在密砂层中更显著,而在中密砂层并不显著。
Objective: To explore the differences of dynamic response between low pile cap pile and subgrade in medium density and dense sand liquefaction site, and to reveal the reasons for this difference. Basic Features and Regularities of Foundation Dynamic Response. Innovative points: 1. Using shaking table test, the successful implementation of medium and dense sand liquefaction site pile caps pile platform shaking table test; 2. Based on the test results, the contrast between dense and dense sand liquefied ground piles and foundation dynamic Response law, study two kinds of liquefied site under the conditions of group pile basic characteristics. Methods: 1. By comparing the white noise sweep frequency, the difference of modal parameters of the subsoil liquefaction field in the medium and tight sand was obtained (Figure 2 and Table 1); 2. By comparing the pore pressure, acceleration and displacement Figure 3-8) to obtain significant differences in the dynamic response of the medium and tight sand liquefaction sites. 3. Based on the displacement and acceleration of the superstructure and caps, the dynamic response and recovery of the superstructure in the tight sand and the tight sand liquefaction site (Figure 9 and 10); 4. Based on the time history of strain recorded on piles, taking into account the nonlinearity of piles and calculating the bending moments of concrete piles, Effect of two types of sites on pile group effects (Figure 12-14). The conclusions are as follows: (1) The acceleration of liquefaction site does not appear to be weakened after sand liquefaction, and shows obvious cyclic fluidity. The density of dense sand liquefaction site is more than that of middle tight sand liquefaction site.2. Dense state of liquefaction site is closely related to the dense state; 3. The maximum bending moment of pile in liquefaction site of middle density sand occurs at the boundary of soil layer, while the maximum bending moment of middle pile in dense sand liquefaction site occurs at pile tip. In the more significant, while the sand in the sand is not significant.