Impact shaking test on excess pore pressure development and water film generation in layered sands

Layered structure in sand deposits is prevalent not only in reclaimed soils but also in natural alluvial soils. Liquefaction tests by a self-developed impact load system were carried out to investigate the excess pore water pressure (EPWP) generation and related liquefaction mechanism in layered sands, considering cases of uniform, two layered and interlayered sand columns respectively. Results show that the EPWP of saturated sands under impact loading presents two phases: transient response and steady-state response. For sands without interlayer, lower-permeability soil layer determines the rate of EPWP dissipation and lower permeability can result in smaller value of steady pore pressure but longer duration of that. For interlayered sands, presence of less permeable interlayer will prolong the total duration of pore pressure dissipation, and there is a significant “high pore pressure” sustained period during the dissipation stage of pore pressure, which is unfavorable for the liquefaction. Also, the presence of a less permeable interlayer within the sand deposit can lead to formation of water film underneath the interlayer. Besides, theoretical analysis of EPWP and water film under the same conditions are made, and it shows a good consistency between theoretical and test results, which verifies the rationality and reference value of the test analysis in this paper. •Dissipation mode of excess pore water pressure under different soil distribution conditions and sand types were analyzed.•Less permeable interlayer in sand deposit will result in long duration of“high EPWP ”and water film, which were studied.•Theoretical analysis of excess pore pressure and water film was conducted and compared with test results for verification.