Dynamic response analysis of shallowly buried water pipelines in liquefiable sites with impervious weak layers
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摘要: 由于特殊层理结构、不透水层的水力阻隔及其下形成的“水夹层”等因素的共同作用，可液化夹层土场地浅埋输水管道动力响应较复杂。通过一系列含不透水软弱层的可液化场地浅埋输水管道振动台试验，对比分析土体的加速度发展规律、管道竖向位移、管-土界面超孔压响应及管壁动土压力等，探讨管道上浮的机理及及含不透水层场地管道抗浮性能增强机制。试验结果表明，管道上、下动土压力差是导致管道发生上浮的主要原因，且管道上浮速率与其受到的动土压力差呈正相关性；软弱不透水层隔绝了场地上、下砂层的水力梯度，减小了管道上、下侧的动土压力差，从而降低管道位移，提高管道的抗震稳定性；不透水层厚度会显著影响管道的变形模式，无不透水层场地中管道应变较大且呈现出明显的非对称特性，而不透水层厚度较大工况的管道变形较为规则。Abstract: Due to the combined effects of special bedding structures, hydraulic barriers in impermeable layers and the formation of "water interlayers", the dynamic responses of shallowly buried water pipelines in liquefiable interlayer soil sites are complex. A series of shaking table tests on the shallowly buried water pipelines in liquefiable sites with impermeable weak layers are conducted to compare and analyze various aspects, including soil acceleration responses, development patterns of dynamic pore pressure, vertical displacements of pipelines, excess pore pressure responses at the pipe-soil interface and dynamic earth pressures on pipeline walls. The uplift mechanisms of underlying pipelines and the enhancement of anti-uplift performance in sites with impermeable layers are investigated. The results show that the differential dynamic earth pressures between the above and below pipelines are primarily responsible for pipeline uplift. Furthermore, there exists a positive correlation between the uplift rate and the differential dynamic earth pressures. The presence of impermeable layers isolates hydraulic gradients between the upper and lower sand layers within the site, reducing the differential dynamic earth pressures at both sides of the pipelines, decreasing their displacement and improving the seismic stability. Moreover, the absence or thickness of impermeable layers significantly influences the deformation patterns. The absence of an impermeable layer results in larger strains on the pipelines, accompanied by noticeable asymmetric characteristics. As the thicknesses of the impermeable layers increase, the deformations of the pipelines become more regularized.
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图 7 管道上下两侧动土压力差和管道上浮速度
Figure 7. Dynamic earth pressure differences and uplift velocities of pipelines
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图 8 动土压力差对管道上浮的影响
Figure 8. Effects of differential dynamic earth pressures on uplift velocity of pipelines
表 1 模型试验相似关系
Table 1 Similarity relationship of model tests
物理量 相似关系 相似比 长度Sl Sl 1/20 密度Sρ Sρ 2/1 重量加速度Sg Sg 1 弹性模量SE SlSρ 1/10 应力Sσ SESε 1/10 应变Sε 1 1 频率Sf √Sa/Sl 4 加速度Sa Sg 1 
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表 2 砂土基本物理性质指标
Table 2 Physical properties of sand
不均匀系数Cu 曲率系数Cc 相对质量密度Gs 最大孔隙比emax 最小孔隙比emin 3.37 0.89 2.72 0.62 0.27
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表 3 黏土基本物理性质指标
Table 3 Physical properties of clay
含水率w/% 天然重度γ/(kN·m-3) 相对质量密度Gs 液限wL/% 塑限wP/% 塑性指数IP 46.8 17.8 2.71 41.03 24.76 17.27
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表 4 振动台试验工况
Table 4 Summary of shaking table tests
工况 不透水层厚度/mm 加载幅值/g 1 0 0.16 2 20 0.16 3 50 0.16
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