Submarine landslides are a geological hazard that may cause significant damage, and are among the most serious problems in offshore geotechnics. Understanding the mechanism of submarine landslide/offshore structure interaction is essential for risk assessment, but it is challenging due to its complexities. In this study, ten centrifuge tests were conducted to determine how offshore wind turbines founded on four piles respond to consecutive submarine landslides. The tests highlighted two mechanisms of soil deformation and foundation settlement associated with the landslide cycle: (1) deformations of the clay were associated with induced excess pore water pressure, and increased with the number of landslides; and (2) by contrast, foundation settlements largely depended on the dynamic impact of the first cycle and remained unchanged for the remaining events. The settlements were 0.5 m for the 10 m pile foundation and about 0.1 m for the 20 m pile foundation, both in clay and in sand. It was also found that increasing pile length reduces the excess pore water pressure, soil deformation and foundation settlement.

Granite residual soil exhibits a tendency to collapse and disintegrate upon exposure to water, displaying highly unstable mechanical properties. This makes it susceptible to landslides, mudslides, and other geological hazards. In this study, three common biopolymers, i.e., xanthan gum (XG), locust bean gum (LBG), and guar gum (GG), are employed to improve the strength and stability of granite residual soil. A series of experiments were conducted on biopolymer-modified granite residual soil, varying the types of biopolymers, their concentrations, and curing times, to examine their effects on the soil's strength properties and failure characteristics. The microscopic structure and interaction mechanisms between the soil and biopolymers were analyzed using scanning electron microscopy and X-ray diffraction. The results indicate that guar gum-treated granite residual soil exhibited the highest unconfined compressive strength and shear strength. After adding 2.0% guar gum, the unconfined compressive strength and shear strength of the modified soil are 1.6 times and 1.58 times that of the untreated granite residual soil, respectively. Optimal strength improvements were observed when the biopolymer concentration ranged from 1.5% to 2%, with a curing time of 14 days. After treatment with xanthan gum, locust bean gum, and guar gum, the cohesion of the soil is 1.36 times, 1.34 times, and 1.55 times that of the untreated soil, respectively. The biopolymers enhanced soil bonding through cross-linking, thereby improving the soil's mechanical properties. The gel-like substances formed by the reaction of biopolymers with water adhered to encapsulated soil particles, significantly altering the soil's deformation behavior, toughness, and failure modes. Furthermore, interactions between soil minerals and functional groups of the biopolymers contributed to further enhancement of the soil's mechanical properties. This study demonstrates the feasibility of using biopolymers to improve granite residual soil, offering theoretical insights into the underlying microscopic mechanisms that govern this improvement.

To study the effect of increased rainfall on the heat and mass transfer and deformation characteristics of sulfate saline soil, a geometric similarity ratio model (1:6) of the natural site was created inside the self-developed indoor baseplate-atmospheric dual-temperature control model box. For the first time, combined with the characteristics of the surface energy change, the characteristics of water-heat-salt-mechanical coupling changes within sulfate saline soil under normal rainfall and twice the increase in rainfall were studied. The results show that the increased rainfall leads to a more significant decrease in upward shortwave radiation and downward longwave radiation, as well as a more significant increase in the surface net radiation and surface evaporation rate. Additionally, the increase in rainfall leads to an obvious cooling trend in the surface temperature. Compared with normal rainfall, an increase in rainfall leads to a significant increase in soil water content and conductivity, while soil heat flux and temperature significantly decrease. The increased rainfall caused a temperature drop of 1.6 degrees C at 5 cm of saline soil. Moreover, the increased rainfall leads to an increase in the heat release time of sulfate saline soil. Meanwhile, the impact of increased rainfall on the soil water content, conductivity, and temperature gradually weakens with increasing depth. The increased rainfall can exacerbate thawing settlement deformation and alleviate salt frost heave deformation. Compared with normal rainfall, twice the increase in rainfall results in a 0.9 mm increase in thawing settlement deformation and a 2.5 mm decrease in salt frost heave deformation.

In recent years, prestressed pipe piles have been widely used in the reinforcement of soft soil foundation, and there will be obvious soil squeezing effect in the construction of pipe piles. However, the research on the soil squeezing effect of pipe piles under various influencing factors is not clear, and it is difficult to guide the actual construction on site. In this paper, the evolution mechanism of soil squeezing effect, pile-soil deformation characteristics and bearing characteristics in the process of pile sinking are analyzed in depth by means of field monitoring and laboratory test. Combined with visual model test, the distribution law of soil displacement field is clarified, and the effects of various influencing factors such as changing pile spacing and pile sinking sequence are revealed. The results show that the soil deformation caused by pile sinking increases first and then decreases in depth, and the soil deformation decreases exponentially in the horizontal direction. The width of the shear strain zone does not change with the increase of penetration, that is, the influence of the squeezing effect on the adjacent pile is mainly rotation and translation. For double piles, the expansion trend of the inner side of the two piles is smaller than that of the outer side of the pile. The squeezing effect will cause the adjacent pile to move and rotate. When the subsequent pile penetration is completed, the displacement field is no longer a basically symmetrical state, and the influence range in the depth area increases. When the pile spacing is set to more than 4 times the pile diameter, the synergistic bearing capacity of the pile group can be better played; The construction sequence from near to far is preferentially selected during construction, which can effectively reduce the impact on adjacent structures. The research results of this paper can provide a reference for further solving the disposal problem of composite foundation reinforced by pipe pile group.

Calcareous sand has been widely used as a construction material for offshore projects; however, the problem of foundation settlement caused by particle crushing cannot be ignored. Although many methods for reinforcing calcareous sands have been proposed, they are difficult to apply on-site. In this study, a permeable polyurethane polymer adhesive (PPA) was used to reinforce calcareous sands, and its mechanical properties after reinforcement were investigated through compression creep, direct shear, and triaxial shear tests. The reinforcement mechanism was analyzed using optical microscopy, CT tomography, and mercury intrusion porosimetry. The experimental results indicate that there is a critical time during the compression creep process. Once the critical time is surpassed, creep accelerates again, causing failure of the traditional Burgers and Murayama models. The direct shear strength of the fiber- and geogrid-reinforced calcareous sand reinforced by PPA was approximately nine times greater than that without PPA. The influence of normal stress was not significant when the moisture content was less than 10%, but when the moisture content was more than 10%, the shear strength increased with an increase in vertical normal stress. Strain-softening features can be observed in triaxial shear tests under conditions of low confining pressure, and the relationship between the deviatoric stress and strain can be described using the Duncan-Chang model before softening occurs. The moisture content also has a significant influence on the peak strength and cohesive force but has little influence on the internal friction angle and Poisson's ratio. This influence is caused by the different PPA structures among the particles. The higher the moisture content, the greater the number of pores left after grouting PPA.

Integral bridges have been proposed as a jointless design alternative to the traditional counterparts, possessing copious potential economic and structural advantages. However, due to the monolithic connection at the girder- abutment interface, longitudinal deformations from the superstructure must now be accommodated by the stiffness of the approach backfill and soil surrounding the foundation. Consequently, in addition to traffic loads, integral bridge approaches are subjected to long-term, cyclic loading due to diurnal and seasonal thermal variations. This has resulted in two progressive geotechnical phenomena: an escalation of lateral passive pressures at the abutment-soil interface and accumulated deformations near the bridge approach. Over the last two decades, several investigations on the approach backfill-abutment interaction have been carried out. However, previous reviews on integral bridges have not comprehensively discussed the theoretical aspects of these two complex geotechnical issues. Hence, this paper presents a discussion on the long-term response of stress ratcheting observed from controlled analyses, along with a comparison to that from field monitoring data. Subsequently, the occurrence of accumulated deformations, along with a correlation to the mechanism of the cyclic interaction is explored. The effects of foundation design choice and skew angle on the passive pressure accumulation and soil deformation behavior are then presented. Subsequently, approaches used to mitigate the effects of the backfillabutment interaction are compared. From this review, it is apparent that outcomes based on available experimental and field investigations are yet inadequate to develop analytical models required to predict the long-term response of integral bridge approach backfills under various loading conditions.

The theoretical and experimental studies have been carried out on the water and salt migration and deformation characteristics of sulfate saline soil during freeze-thaw cycles. Based on the theory of unsaturated soil mechanics and the thermoelastic continuum and considering the influence of phase change within the pore on thermodynamic and hydrodynamic parameters, the multi-physical fields coupled model of hydro-thermal-salt-mechanical in unsaturated sulfate saline soil has been established. The variation processes of the temperature field, water field, salt field, and stress field of the soil during freeze-thaw cycles were analyzed, and the validity of the theoretical model was verified by indoor experiments. The results show that there are significant attenuation and hysteresis effects when heat is transferred in the soil during freeze-thaw cycles. The water content of migration in the soil increases with the height of the soil column, while the increment of migration water content decreases with the number of freeze-thaw cycles. The formation and dissolution of salt crystals from top to bottom and the sudden increase in the salt crystallization rate are mainly caused by variations in the solubility of the salt solutions due to temperature changes. The formation and dissolution of ice and salt crystals in the soil induce expansion and contraction, and the freeze-thaw cycle conditions have a significant effect on the expansion and residual deformation of the soil.

This paper investigates the impact dynamics of pile-soil interactions, focusing on the mechanisms of kinetic energy dissipation within these systems during vehicular impacts. The study aimed to quantitatively evaluate the force-displacement and energy-displacement responses of piles embedded in crushed limestone material through dynamic bogie testing. A three-dimensional, large-deformation, nonlinear finite element model was developed to enhance the analysis. The computational model integrated a damage-based, elastoviscoplastic soil model with an elastoplastic steel pile model, incorporating strain rate effects. A continuum, damage-based element-erosion algorithm is also employed to accurately simulate large soil deformations, representing a significant advancement in simulation capabilities. The proposed model was validated against physical impact test data, demonstrating a strong correlation with measured force-displacement and energy-displacement results. This model was subsequently utilized to investigate the effects of impact velocity and soil strength on the energy dissipation capacity of pile-soil systems during lateral vehicular impacts. Additionally, this study critically examined the limitations of conventional simulation methods, such as the Updated Lagrangian Finite Element Method (UL-FEM), in capturing the dynamic pile-soil interactions and large soil deformations involved in laterally-impacted pile-soil systems. The research provided fundamental insights into the mechanics of dynamic soil-structure interactions under impact loading, contributing significantly to the geotechnical design and analysis of soil-embedded vehicle barrier systems.

Soil arching is a critical mechanism in understanding the soil-pile interaction of pile-reinforced soil slopes. Previous research primarily focuses on evaluating the arching behavior under static loading conditions, whereas the seismic response of soil arching under earthquake loading remains unclear. This paper aims to investigate the seismic arching behavior in pile-reinforced soil slopes through a series of reduced-scale shaking table tests. The soil deformation characteristics, distribution of dynamic earth pressures, and internal forces of piles were systematically analyzed to evaluate the geometry characteristics and load-transfer ability of soil arching with varying input peak ground acceleration (PGA), pile spacing, and relative density of soils. The results indicate that soil arching that grew in either a wider pile spacing or loose sand tended to fully develop under low input PGAs and exhibited a higher arching height. Following this, a practical model was proposed to predict the stable arching height. With increasing the input PGAs, the seismic arching behavior involved four stages, termed stable, transitional, meta-stable, and failure. The load-transfer ability and seismic response of piles under earthquake loading were dependent on the pile spacing and relative density of soils. A wider pile spacing gave rise to a greater load-transfer ability which was enhanced in the stable arching stage and then diminished in the subsequent stages, showing a different trend from closer pile spacings. Compared to medium dense sand, loose sand reduced the load-transfer ability, but it promoted the occurrence of stable arching and elevated the point of dynamic load application. Furthermore, in the arching failure stage, arching footholds played a crucial role in maintaining slope stability as their instability directly resulted in overall slope failure. These findings are of practical significance for the design and construction of soil slopes reinforced with piles.

The development of land subsidence has seriously affected the safe operation of Beijing-Tianjin high-speed railway. The South-to-North Water Diversion Project Central Route (SNWDP-CR) was officially put into operation in December 2014. It has changed the water supply pattern in Beijing and provided conditions for reducing groundwater exploitation and controlling land subsidence. In this paper, the time-series interferometric data, in situ monitoring data of recent 20 years and the basic geological datasets are combined to compare and analyze the changes of groundwater level, land subsidence and the main subsidence layers along the Beijing-Tianjin high-speed railway before and after the SNWDP-CR. The effects of the environment of Quaternary sedimentary, groundwater exploitation and soil deformation of different lithology on land subsidence along the high-speed railway under the background of new water conditions are revealed. The main conclusions are as follows: 1) The serious land subsidence area along the Beijing-Tianjin high-speed railway always concentrated in the of DK11-DK23. After the operation of SNWDP-CR, the land subsidence along the railway generally showed a slowing trend. The maximum subsidence rate was reduced from 80 mm/yr to 49 mm/yr. The length of subsidence rate that more than 50 mm/yr of the was reduced from 8.0 km to 0 km. 2) The groundwater level of different aquifer groups along the Beijing-Tianjin high-speed railway rose and declined before and after the SNWDP-CR. in eastern part of the plain, the groundwater level of each aquifer group has changed from a continuous decline (range 0.13-1.82 m) to a gradual rise (range 0.45-1.87 m) since 2017. However, in the southeast of the plain, the groundwater level still showed a continuous decline trend, with an average annual decline of 1.2-1.8 m. 3) From 2006 to 2019, the subsidence of the first, second and third compression layer group along the railway accounted for 2.71%, 28.29% and 69%, respectively. The third compression layer group (monitoring layer 94-182 m) had the largest subsidence proportion and was the main subsidence layer. 4) The land subsidence along the Beijing-Tianjin high-speed railway is controlled by the basement structure. The difference of groundwater exploitation intensity led to differences in the spatial distribution of land subsidence along the railway. The subsidence of the soil layer below the bearing layer (about 50 m) of the high-speed railway pile foundation exhibited the characteristics of viscoplastic or viscoelastic plasticity deformation. This of strata is a key layer that needs to be considered for land subsidence control along the Beijing-Tianjin high-speed railway in the future.