Engineering geological investigations indicate that confined water exists in the stratum during the warm season in permafrost regions and in underground engineering employing artificial ground freezing (AGF) to isolate groundwater, causing significant upward deformation of the stratum and frost damage to engineering structures. However, limited studies have explored the effect and mechanism of hydraulic pressure on ice growth during soil freezing upwards. Therefore, this study designs and conducts four groups of bottom-up freezing tests under various hydraulic pressures, and develops a model to investigate the mechanism of hydraulic pressure on ice growth, based on the theory that liquid water migrates towards the ice lens through an unfrozen water film. The experimental results, including thermal regime, frost heave, cryo-structure, and water redistribution are analyzed systematically, which show the frozen depth, frost heave increment, ice lens thickness, and the layered water content in the samples all increase with hydraulic pressure. The model is validated with experimental data, and the calculation results demonstrate that the ice growth rate increases with hydraulic pressure due to a higher pore water pressure (PWP) gradient in the unfrozen water film. Thus, the characteristics and mechanisms of ice growth in the stratum, accelerated by hydraulic pressure, are clarified. Finally, the applications and implications of this study to engineering geology are discussed, which contribute to a better understanding of ground ice formation in permafrost regions and frost damage prevention in underground engineering performing AGF.

Liquefaction behaviors of sand deposits with impervious stratum are quite different from that of homogeneous geological conditions. However, the micro- liquefaction behaviors of the interlayered deposits have been infrequently documented. This study introduces a novel experimental methodology aimed at examining the influence of silt interlayer on the liquefaction mechanisms of sand deposits from both macro and micro perspectives. In the experiments, the Excess Pore Water Pressure (EPWP) was analyzed in conjunction with recorded micro liquefaction images. The migration mechanism of fine sand particles beneath the silt interlayer was revealed. The existence of low permeability interlayer leads to prolonged retention of EPWP beneath the silt interlayer. Substantially, the water film on the base of the interlayer is demonstrated to be the mixture of pore water and silt particles flowing with high velocity under seismic motions, thereby resulting in significant strain localization. An agminated zone of loose fine sand particles is usually generated beneath the silt interlayer after the dissipation of EPWP.

Offshore foundations usually experience long-term cyclic loading, where the weakly bound water at the soil-structure interface can be transformed into free water. The free water enriched at the soil-structure interface would influence the mechanical characteristics of the soil near the interface, weakening the interface strength and posing a significant threat to the safety and stability of offshore foundations. This study proposed a novel concept, i.e. the characteristic water film thickness, to quantify the enrichment degree of water film at the soil-structure interface under cyclic loading. A series of cyclic shearing tests were carried out by using self-developed cyclic loading equipment combined with a small constant temperature centrifuge. The influence of different clay and salt contents on the characteristic water film thickness was investigated and analyzed. It was found that both the kaolin and salt contents significantly impacted the characteristic water film thickness, where it was positively correlated with the kaolin content while negatively correlated with the salt content. The research outcome enriched the understanding of the weakening mechanism underlying the load and deformation transfer between soil-structure interface.

Civil excavation projects frequently yield substantial excess spoil, posing challenges to sustainable construction. This study explores repurposing such spoil for creating controlled low strength material (CLSM), emphasizing the novel use of polycarboxylate superplasticizer (PCE) to reduce the water requirement. The work also distinctively utilizes water film thickness (WFT) theory to elucidate the effects of PCE dosage and WFT on material properties, thereby advancing CLSM mix design. First, using an experimental approach, a series of fresh CLSM samples are prepared, with varying the water-to-solid ratio (W/S) and PCE dosage, to evaluate their packing density, WFT, flowability, and bleeding rate. It is demonstrated that both packing density and WFT experienced a non-linear increase with rising PCE dosage. Regression analysis of the experimental data reveals that the flowability and bleeding rate linearly increase with the rising WFT, and the enhancements are more pronounced at higher PCE dosage. Notably, at a given WFT, the impact of PCE dosage on flowability and bleeding rate reduce as WFT decreases. Additionally, the research identifies specific WFT thresholds correlating with maximum flowability and a 5% bleeding rate. These thresholds mark the critical point at which WFT ceases to influence flowability and delineate the maximum WFT that satisfies the bleeding rate requirements, respectively. These insights are important for optimizing the design of CLSM with PCE in terms of flowability and bleeding rate.

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.

The existence of intercalation in sandy soil affect the pore pressure development in saturated sandy soil, thereby impacting the deformation of sandy soil layer. In order to study the pore pressure change during the liquefaction of sandy soil under different intercalation conditions such as location, thickness and type, a liquefaction test of laminated sand under impact load was conducted. This study involved establishing a theoretical model of saturated sandy soil with intercalations and comparing the test results with the theoretical analysis. The findings reveal that the development of pore pressure of saturated sandy soil containing intercalated layers exhibits three stages: rapid rise, rapid dissipation, and slow dissipation. In cases involving high-permeability intercalations, a higher location of the intercalation results in a shorter rapid dissipation time of pore pressure below it, leading to a faster convergence to a stable value. However, the total dissipation time shows no significant change. Conversely, for low-permeability intercalations, an increase in the height or thickness of the intercalation accelerates the rate of rapid dissipation phase of pore pressure above the intercalation, prolongs the stable phase of pore pressure dissipation, and linearly increases the total dissipation time of pore pressure. Additionally, a water film forms below the low-permeability intercalation, and increasing the intercalation height or thickness extends the duration of the water film, with the water film formation primarily affected by the intercalation thickness.. The test results are more consistent with the theoretical analysis, indicating the reliability of the test. The test results align more closely with the theoretical analysis, indicating the reliability of the test.