Measuring pore-water pressure (PWP) in frozen soils poses significant challenges in geotechnical testing experiments, and understanding PWP is crucial for unraveling the mechanism of frost heave generation in cold regions. This paper aims to clarify the development pattern of PWP in frozen soil through laboratory tests, specifically focusing on excess PWP generated under dynamic loading. Seven sets of triaxial tests were conducted to investigate the variations in excess PWP and deformation influenced by temperature, dynamic stress amplitude, and dry density. The results reveal that excess PWP in warm saturated frozen soil undergoes two stages: pore pressure increase and dissipation. The change of external factors mainly affects the peak value of excess PWP and the change rate of excess PWP. Unlike unfrozen soil, excess PWP has a small dissipation rate after the peak and may remain dynamically stable in the later stage of loading. In addition, two empirical models of excess PWP applicable to saturated frozen soils were proposed based on the developmental patterns of excess PWP in frozen soils, and the feasibility was validated using the results obtained from laboratory tests. The model is of great significance for predicting the development of excess PWP in frozen soil under dynamic load.

Under traffic load, earthquake load, and wave load, saturated sand foundation is prone to liquefaction, and foundation reinforcement is the key measure to improve its stability and liquefaction resistance. Traditional foundation treatment methods have many problems, such as high cost, long construction period, and environmental pollution. As a new solidification method, enzyme-induced calcium carbonate precipitation (EICP) technology has the advantages of economy, environmental protection, and durability. Through a triaxial consolidated undrained shear test under cyclic loading, the impacts of confining pressure (sigma 3), cementation number (Pc), cyclic stress ratio (CSR), initial dry density (rho d), and vibration frequency (f) on the development law of pore water pressure of EICP-solidified sand are analyzed and then a pore water pressure model suitable for EICP-solidified sand is established. The result shows that as sigma 3 and CSR increase, the rise rate of pore water pressure of solidified sand gradually accelerates, and with a lower vibration number required for liquefaction, the anti-liquefaction ability of solidified sand gradually weakens. However, as Pc, rho d, and f rise, the increase rate of pore water pressure of solidified sand gradually lowers, the vibration number required for liquefaction increases correspondingly, and its liquefaction resistance gradually increases. The test results are highly consistent with the predictive results, which show that the three-parameter unified pore water pressure model is suitable for describing the development law of A-type and B-type pore water pressure of EICP-solidified sand at the same time. The study results provide essential reference value and scientific significance in guidance for preventing sand foundations from liquefying.

The generation mechanism of pore pressure plays an essential role in understanding the liquefaction behavior of sand under cyclic loading. Extensive undrained simple shear tests were undertaken to study the pore pressure and shear strain development characteristics of calcareous sand reinforced by fibers. The results show that the deformation patterns of the tested calcareous sand gradually shift from brittle to ductile failure as fiber content increases. The mechanism of pore pressure generation in calcareous sand subjected to cyclic loading is quite distinct from that of siliceous sand, exhibiting more pronounced accumulation in the initial stage of cyclic loading. Fiber reinforced calcareous sand exhibits reverse shear contraction behavior when liquefaction is imminent. A remarkable finding is the establishment of a unique correlation between pore pressure ratio and shear strain, irrespective of the fiber reinforcement. Consequently, a shear strain-based pore pressure generation model of reinforced calcareous sand is then developed to predict the pore pressure built-up trend under varying fiber content and length conditions. This model is also applicable to various testing conditions and soil types.