Debris flows are a type of natural disaster induced by vegetation-water-soil coupling under external dynamic conditions. Research on the mechanism by which underground plant roots affect the initiation of gulley debris flows is currently limited. To explore this mechanism, we designed 14 groups of controlled field-based simulation experiments. Through monitoring, analysis, calculation, and simulation of the changes in physical parameters, such as volumetric water content, pore-water pressure, and matric suction, during the debris flow initiation process, we revealed that underground plant roots change the pore structure of soil masses. This affects the response time of pore-water pressure to volumetric water content, as well as hydrological processes within soil masses before the initiation of gully debris flows. Underground plant roots increase the peak volumetric water content of rock and soil masses, reduce the rates of increase of volumetric water content and pore-water pressure, and increase the dissipation rate of pore-water pressure. Our results clarify the influence of underground roots on the initiation of gulley debris flows, and also provide support for the initiation warning of gully debris flow. When the peak value of stable volumetric water content is taken as the early warning value, the early warning time of soil with underground plant roots is delayed by 534 to 1253 s. When the stable peak value of pore-water pressure is taken as the early warning value, the early warning time of soil with underground plant roots is delayed by 193 to 1082 s. This study provides a basis for disaster prevention and early warning of gully debris flows in GLP, and also provides ideas and theoretical basis under different vegetation-cover conditions area similar to GLP.

The presence of desiccation cracks can affect rainfall-induced slope stability through both hydraulic and mechanical ways. Despite the valuable insights gained from physical tests in literature, there still lacks understanding how crack characteristics impact water flow dynamics and slope stability, especially considering the coexistence of vegetation. In this study, new analytical solutions were derived for calculating pore-water pressure and slope stability for an infinite unsaturated slope with cracks and vegetation. Both enhanced infiltration from water-filled cracks and water uptake by plant roots are considered. Using the newly developed solutions, two series of parametric analyses were carried out to improve understanding of the factors affecting crack water infiltration and hence the stability of vegetated slope. The calculated results show that slope failure at shallow depths is governed by the surface crack ratio, whereas deeper failures typically occur with greater crack depths. The surface crack ratio primarily influences the hydraulic response at shallow depths not exceeding 1.5 m, hence affecting the factor of safety for slip surfaces within the crack zone. Moreover, increasing the crack-to-root depth ratio from 0.5 to 1.5 results in a 25% reduction in suction at 1.5 m, threatening slope safety in deeper depth after 10-year rainfall.

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.

This paper experimentally investigates the wave pressure and pore pressure within a sandy seabed around two pipelines under the action of random waves (currents). The experiments revealed that when the random wave plus current cases are compared with the random wave-only case, the forward current promotes wave propagation, whereas the reversed backward current inhibits wave propagation. Furthermore, the wave pressure on the downstream pipeline decreases as the relative spacing ratio increases and increases as the diameter increases. However, alterations in the relative spacing ratio or dimensions of the downstream pipeline exert a negligible influence on the wave pressure of the upstream pipeline. Moreover, the relative spacing ratio between the pipelines and the dimensions of the pipelines considerably influence the pore pressure in the sand bed. When the relative spacing ratio remains constant, increasing the downstream pipeline diameter will increase the pore-water pressure of the soil below the downstream pipeline.

Although; over-saturation of pore-water has been known as potential stress agent, there hasn't been attention to subgrades behavior under extreme dry state. For improved design and construction to mitigate cracks, the two extreme states were considered at Cargo Airport site around fractured Abakaliki anticlinoria, Nigeria. Dynamic tests (remote sensing, electrical-resistivity) and static tests (Atterberg limit, Standard Penetration, Dynamic Cone Penetrometer) produced results that formed basis of modeled solutions, and revealed potential shear planes. Such planes typically reflected low friction angle between 11 degrees and 13 degrees, as well as cohesion ranging from 13 to 23 kPa; indicating isolated silty clay with Plasticity index (PI) = 1.5, and verified through stress-curves behavior in response to pore-pressure status. Such responses created various spaces between the curves. Comparing the space relations in ratios showed novel mathematical demonstration for pavements stability prediction.

Residual liquefaction, a significant issue in marine engineering, results from accumulated pore-water pressure in the seabed due to cyclic shear stresses, which compromises soil stability. This study aims to investigate residual liquefaction around gravity-based marine structures by means of a 2D numerical model. The model employs a two-step procedure: First, the stresses in the soil domain are determined via solving Biot equations, and subsequently the generation and diffusion of accumulated pore pressure in the soil is simulated by means of a pressure diffusion equation with a source term. The model was first validated against analytical solution for pore pressure buildup in the seabed under progressive waves, and against experimental data for residual liquefaction around a buried submarine pipeline. The results showed that the model can satisfactorily capture pore pressure buildup and residual liquefaction in the seabed around structures. Once validated, the model was utilized to model the pore-water pressure buildup and residual liquefaction potential around a caisson breakwater under the action of standing waves and the wave-induced rocking motion of the caisson, separately and in combination. Spatial distribution of liquefaction potential was determined in the seabed soil around the caisson with and without a bedding layer on the seabed. The model results revealed the critical role of the bedding layer in reducing liquefaction susceptibility under standing waves and rocking motion, and highlighted that the rocking motion alone poses a significant risk of inducing residual liquefaction in the seabed around the caisson.

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.

Freeze-thaw cycles (FTC) cause significant changes in the physical and mechanical properties of soil, leading to structural alterations that can seriously threaten the safety and longevity of engineering structures. To investigate the consolidation characteristics of soils subjected to FTC, 18 sets of consolidation compression tests were carried out with saturated clay. Using a modified consolidation apparatus, the changes in pore-water pressure (PWP) and strain during consolidation were measured, with a focus on the effects of dry density and the number of FTC. The results show that although the overall patterns of PWP and strain during consolidation are similar before and after FTC, variations in dry density and the number of FTC lead to significant differences in the measured values. Specifically, PWP decreases while soil deformation increases with an increasing number of FTC cycles, even across different dry density conditions. The most pronounced changes in PWP and strain occur during the first 1-3 FTC cycles, with some samples showing continued significant changes up to 3-5 cycles. However, beyond five FTC, the increments in PWP and strain become considerably smaller. Meanwhile, an approximate linear relationship was observed between the peak PWP and steady-state strain values during graded loading, with this linearity decreasing as dry density increases. In addition, the Burgers model was modified based on the measured dissipation pattern of PWP to overcome the shortcomings of the traditional Burgers model. The modified Burgers model provides a more accurate representation of the soil's deformation process following FTC compared to the traditional model. This study can provide theoretical guidance for predicting the deformation of soils after freeze-thaw cycles.

Earthquakes and groundwater are pivotal factors affecting slope stability. However, the majority of previous studies have focused on these factors individually, neglecting their combined effects. Hence, this paper aims to develop a framework using the kinematic approach of limit analysis to investigate the stability of slopes in partially saturated soils under the combined effects of seismic force and pore-water pressure. The pseudodynamic method (PDM) was employed to capture the temporal-spatial effect of horizontal and vertical seismic waves. Variations in suction and effective unit weight profiles with moisture content under steady-state unsaturated flow were considered. External rates arising from both static pore-water pressure and earthquake-induced excess pore-water pressure were incorporated into the energy-balance equation. With the aid of gravity increase method (GIM), an explicit expression of safety factor (FS) was derived and optimized using a genetic algorithm (GA). The validity of this approach was verified through a comparison with existing solutions. Parametric analyses were conducted to explore the influence of varying groundwater level, seismic coefficients, suction, threedimensional effects, excess pore water pressure, unsaturated flow types, and pseudo-dynamic parameters, on the FS and critical sliding surface of slopes in partially saturated slopes. This framework can provide a good reference for the safety design of reservoir slope under the combined effects of earthquakes and groundwater.

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.