Dynamic response analysis of shallowly buried water pipelines in liquefiable sites with impervious weak layers

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.