To address the issues of significant deformation and susceptibility to liquefaction of silt under traffic loads, while also promoting the reuse of waste lignin, lignin was used to reinforce silt. A series of laboratory experiments were conducted to investigate the effects of different lignin contents and curing periods on the compressive strength of the soil. Additionally, the study analyzed the cumulative plastic deformation and excess pore-water pressure under various conditions. Using scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy, the microstructural characteristics of silt before and after lignin modification were qualitatively and quantitatively described. The experimental results indicate that lignin can significantly enhance the compressive strength of soil, and the optimal effect was observed at an 8% lignin content. At a curing age of 28 days, the strength of the treated soil was 2.65 times that of the untreated soil. The treated soil exhibited greater shear strength than the untreated soil. The addition of lignin significantly reduced the cumulative plastic deformation and excess pore-water pressure of the soil, mitigating various risks in the subgrade, such as insufficient bearing capacity and liquefaction. Lignin binds soil particles and undergoes a cementation reaction without the formation of new minerals. The cementitious material fills the voids in the soil, gradually transforming large pores into medium and small pores. Combined with the particle pores and cracks analysis system, quantitative analysis indicates that as the lignin content increased, the soil porosity gradually decreased, reaching a maximum soil compactness at an 8% admixture. The research findings can provide theoretical references for the engineering application of lignin.

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.

The reverse-consolidation caused by excavation inevitably affects the bearing capacity of basal soil to resist water pressure in confined aquifers, posing a risk to excavation stability. However, there is still a lack of efficient solutions to incorporate the layered heterogeneity into the analysis of the reverse-consolidation. This study proposes a practical approach where the spectral Galerkin method is used to capture the variation of soil properties with depth. The boundaries are characterized by time-dependent drainage boundary conditions to simulate the excavation process. The excess pore-water pressure profile is described by a single expression calculated by common matrix operations. The rationality and accuracy of the practical approach are verified by existing analytical models and field data. Subsequently, the permeability coefficient variability, relatively impervious interlayer, and sand interlayer are analyzed to illustrate their effects on the reverse-consolidation behavior of basal soil. Results indicate that the distribution of excess pore-water pressure is significantly influenced by the variability and distribution form of the permeability coefficient. The relatively impervious interlayer delays the dissipation of excess pore-water pressure and bears a large hydraulic gradient, while the sand interlayer is the opposite. These above influences become more significant as the excavation progresses due to the time effect.

To consider the influence of the interaction of each clayey layer in the interbedded soils of a foundation on the soil consolidation, a two-dimensional calculation model based on the overall analysis is proposed and the controlling equations of each layer are established. A semianalytic solution for the excess pore-water pressure in the frequency domain is derived by combining the Laplace transform with the Fourier cosine transform and introducing the boundary transformation method. The theoretical solution is compared with numerical simulations for verification, and the relevant parameters are also analyzed to further explore the consolidation characteristics of the foundation. The results show that the proposed theoretical solution can effectively reflect the distribution of excess pore-water pressure in each soil layer under the given foundation conditions; the deviation of the average degree of consolidation from the numerical results is less than 2.0%. When only one sandy layer is laid out in the foundation, it is most conducive to the consolidation to arrange the sandy layer in the middle-lower part of the soil layer. When the total thickness of the sandy layer is the same, the maximum consolidation rate that can be achieved by arranging two sandy layers in the lower part of the foundation is slightly faster than that achieved by arranging a single sandy layer. When the ratio of the horizontal permeability coefficient of the sand to the permeability coefficient of the adjacent clay is greater than or equal to 20, the excess pore-water pressure in the sandy layer can be considered to be evenly distributed along the vertical direction.

The pore-water pressure response during vibratory pile driving considerably affects the piling process and environment. With the applications of high-frequency technology in upgrading the vibratory hammer, the pore-water pressure variation under high-frequency driving conditions becomes more complicated. However, there is a lack of relevant detailed investigations. This paper conducts an in situ experiment with a comprehensive monitoring and measuring system to examine the pore-water pressure response in the complete process of high-frequency vibratory pile driving. The real-time variations of pore-water pressure at the pile-soil interface and surrounding soil are evaluated, respectively. Furthermore, the excess pore-water pressure distributions and evolutions are analyzed in-depth. Then, the mechanism analysis and affected zone range determination are performed based on the development of excess pore-water pressure. The analysis results indicate that vibratory pile driving with high frequency leads to an increase of excess pore-water pressure and consequently soil quasi-liquefaction at the pile-soil interface. The apparent accumulation of excess pore-water pressure concentrates in the local range of soil around the pile tip and decays rapidly in the radial direction. According to the field observations, the increase of the pore-water pressure in the surrounding soil is attributed to the frictional penetration of the pile tip and the frictional vibration of the pile shaft. Furthermore, the maximum radial radii of the fully and partially quasi-liquefied zones are approximately 2.9 and 3.6 times the pile diameter, respectively.