Suction anchor foundations serve as a critical anchoring solution for submerged floating tunnel (SFT) cable systems. In marine environments, these foundations must endure not only static loads but also long-term oblique cyclic loading caused by wave excitation, which can result in soil weakening and a reduction in bearing capacity. This study systematically examines the oblique cyclic bearing behavior of SFT suction anchors using a combined experimental and numerical approach. The results demonstrate that (1) the cyclic load ratio initially increases with increasing wave periods, then decreases, before rising again; (2) displacement accumulation at the mooring point occurs rapidly during the initial wave loading cycles, gradually stabilizing as cycling progresses; (3) during foundation failure, tension redistribution displays asymmetric characteristics, with connected cables experiencing load reduction while adjacent cables are subjected to amplified forces; (4) numerical analyses quantify key parametric relationships, revealing that the weakening coefficient (alpha) decreases with increasing loading angle, exhibits a positive correlation with zeta b, and shows a negative correlation with zeta c. These findings advance the understanding of cyclic performance in SFT anchors and offer essential insights for SFT safety evaluations.

The widespread distribution of riprap in estuarine mudflats has brought significant challenges to the penetration construction of steel casings. To reveal the effects of casing length, diameter and wall thickness on the stress and deformation, as well as the deformation characteristics and mechanical behaviors of the steel casing during the sinking process, the paper utilizes finite element method to construct a three-dimensional numerical model of the collision between steel casings and riprap in mudflat. The research results indicate that longer steel casing has better crushing effect on the riprap, smoother deflection curve of the casing body and smaller deformation at the casing end under the same casing diameter and wall thickness conditions. Under the same casing length and wall thickness conditions, the steel casing with a larger diameter has a better crushing effect on the riprap and smaller deformation at the casing end. As the casing diameter increases, the stress values of S11 and S33 in the soil at the casing end gradually decrease, and the range of stress concentration gradually increases. This study can provide a theoretical basis for the design and construction of steel casings in the riprap environment of the mudflat near the estuaries.

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.

The mechanical behavior of monopile support systems for offshore wind turbines under current-induced loads was investigated through numerical simulations. Using the Large Eddy turbulence model, the fluid-structure coupling was analyzed in both unidirectional and bidirectional directions. In the unidirectional coupling, the pressure and velocity profiles of the fluid around the pile were determined. While in the bidirectional coupling, the force distribution, pile displacement, and moment distribution were obtained, along with the current-induced load transmitted from the pile to the soil. The coupling analysis revealed that the fluid flow around the pile exhibited cyclic loading behavior due to the interaction between the fluid and the pile, effectively resulting in an oscillating pile within a steady flow. Additionally, the pile's stress distribution remained within the tensile yield limit of the steel, indicating a stable state in the fluid-pile model within the given flow conditions. Furthermore, the soil reaction forces obtained from the fluid-pile-soil coupling model validated the accuracy of the current-induced load calculations. This study introduces a novel approach that considers the fluid-pile-soil coupling, offering valuable insights for pile foundation design. The findings of this research have significant engineering implications and practical value, providing a robust foundation for future offshore wind turbine installations.

The overall reinforcement of soft soil foundation has the disadvantages of large engineering quantity and high cost. When the pile foundation bears horizontal loads in the soil, the mechanical properties of the soil near the surface have a greater impact on it compared to the deep soil. Therefore, studying the influence of shallow soil reinforcement on the horizontal bearing capacity of pile foundations has important engineering significance. Studying the influence of shallow soft soil reinforcement around piles on the horizontal bearing performance of piles is of great significance for improving the economic efficiency of pile foundation reinforcement technology in soft soil areas. In this paper, seven pile-soil finite element models are established based on ABAQUS 2022 software to study the influence of shallow reinforcement on the horizontal bearing capacity of single pile. The models were established on the basis of a field test and its validity was verified. The influence of different reinforcement degrees on the horizontal bearing capacity of piles is analyzed by taking the reinforcement width and reinforcement depth as variables. The results indicate that shallow ground improvement significantly enhances the horizontal bearing capacity of the pile. The horizontal bearing capacity of the pile is increased by 83.0%, 104.3%, and 224.4%, respectively, corresponding to a reinforcement width of 2 times, 3 times, and 4 times the diameter of the pile, respectively. With the increase of the reinforcement width, the bending moment and deformation of the pile under the same horizontal load decrease significantly, while it has no significant effect on the location of the maximum bending moment of the pile. The bearing capacity of the pile foundation gradually increases with the increase of the reinforcement depth. Compared with the unreinforced situation, the horizontal bearing capacity of the pile body is increased by 224.4%, 361.3%, and 456.8%, respectively, corresponding to a reinforcement depth of 0.1 times, 0.2 times, and 0.3 times the pile length. As the reinforcement depth increases, the corresponding increase in bearing capacity does not increase linearly, but gradually decreases. This indicates that blindly carrying out deep soil reinforcement without comprehensive evaluation is not advisable.

In order to study the thermal characteristics of pre-bored grouted planted energy pile groups in saturated clay foundation under different operation modes, a self-designed model test system is used to examine the thermal response of single pile and pile group. By embedding sensing test elements, data on pile top displacement, pile stress, pile and surrounding soil temperatures, horizontal soil pressure, and pore water pressure are collected. Findings show that the heated pile influences adjacent unheated piles through thermal diffusion, leading to increased pile body temperature and top displacement. Moreover, the overall heat transfer efficiency of energy pile groups is lower than that of single piles. The absolute displacement change at the pile top in energy pile groups is greater under cooling conditions than under heating conditions, necessitating safety considerations. The group effect results in larger pile top displacements and lower additional thermal stresses in energy pile groups compared to single piles. Furthermore, as the number of energy piles in a group increases, the thermal characteristics become more pronounced, accompanied by greater variations in horizontal soil pressure and pore water pressure around the piles.

In response to a series of engineering disasters encountered during the excavation and support construction of loess tunnels, considering the issues of water enrichment in surrounding rock induced by excavation disturbance and system bolt failure, drawing on the concepts of lime pile composite foundation and composite bearing arch, and based on the principle of the New Austrian Tunneling Method (NATM) that fully mobilizes and leverages the self-supporting capacity of surrounding rock, this study comprehensively considers the wetting and stress adjustment processes of the surrounding rock after excavation disturbance in loess tunnels. By adopting the technical principle of water absorption and densification of shallow surrounding rock, suspension and anchoring of deep surrounding rock, and composite arch bearing, a new type of water-absorbing, densifying, and anchoring bolt was developed that can reduce the water content of surrounding rock while enhancing its resistance. To further investigate the water absorption, densification effect, and pull-out bearing characteristics of this new bolt, laboratory model tests were conducted, examining the temperature, pore water pressure, densification stress of the soil around the bolt, as well as the physical properties of the soil in the consolidation zone. The test results indicate that a cylindrical heat source forms around the water-absorbing, densifying, and anchoring bolt, significantly inducing the thermal consolidation of the surrounding soil. The variations in temperature, pore water pressure, and densification stress of the soil around the bolt truly reflect the qualitative patterns of hydro-thermal-mechanical changes during the water absorption, curing, and exothermic reaction processes. The water absorption and densification segment of the bolt effectively enhances the density of the soil in the water absorption, densification, and consolidation zone, improving soil strength parameters. Compared to traditional mortar-bonded bolts, the water-absorbing, densifying, and anchoring bolt exhibits a greater pull-out bearing capacity. The research findings provide important guidance for the theoretical design and engineering application of this new type of bolt.

The bearing and deformation characteristics of embankments with rigid-flexible long-short pile composite foundations (RLPCFs) in thick collapsible loess strata are not yet accurately understood. In this study, a large-scale field experiment was conducted, and screw (long) and compaction (short) piles were employed to reinforce a of the foundation of the Lanzhou-Zhangye high-speed railway in thick collapsible loess. The pile load transfer, foundation settlement, pile-soil stress distribution, and load sharing characteristics were analyzed to reveal the bearing properties of the composite foundation. The results show that negative friction arises along the upper part of the pile, and the neutral points of the short pile and long pile are located at 2/5 and 1/3 down the pile lengths, respectively. The short pile eliminates the collapsibility of the shallow loess and enhances the foundation's bearing capacity. The long pile transfers the load of the shallow foundation and pile top to the deep foundation through lateral friction, which reduces the settlement of the shallow foundation. When the soil arch in the embankment is fully formed, the short pile bears approximately 20% of the load, while the long pile and the soil between piles bear 80%. With the increase in embankment filling height, the load borne by the long pile rises, and the load borne by the soil between piles decreases gradually. The top settlement of the cross- of the composite foundation is distributed in a concave basin shape, and the maximum settlement occurs in the center of the embankment. The parameters of the short pile can be obtained on the basis of the collapsibility grade and bearing capacity of the loess foundation, the length and area replacement rate of the long pile can be obtained based on the settlement control requirements of the superstructure of the composite foundation, and the lateral friction of the long pile can be increased by increasing the roughness of the pile and setting the screw.

This study explores the application effect of the new non-isocyanate polyurethane curing agent on the rapid curing mechanism and bearing characteristics of piles in beach foundations. Through laboratory tests and field tests, the effects of the curing agent on the physical and mechanical properties of sand were systematically analyzed, including compressive strength, shear strength, and elastic modulus, and the effects of water content and cement-sand mass ratio on the properties of sand after curing were investigated. The results show that introducing a curing agent significantly improves the mechanical properties of sand, and the cohesion and internal friction angle increase exponentially with the sand mass ratio. In addition, the increase in water content leads to a decrease in the strength of solidified sand, and the microstructure analysis reveals the change in the bonding effect between the solidified gel and the sand particles. The field static load tests of single piles and pile groups verify the effectiveness of the rapid solidification pile in beach foundations and reveal the significant influence of pile length and pile diameter on the bearing capacity. This study provides a theoretical basis and technical support for the rapid solidification and reinforcement of tidal flat foundations and provides important guidance for related engineering applications.

Offshore wind energy will become one of the important sources of energy in the future, and root piles with good pullout bearing characteristics can be used for the foundation of offshore wind power generation facilities. Through the model test, the pullout bearing characteristics of root piles with different water content states in coral sand foundation are comparatively analyzed, and the pullout bearing deformation law and pile body force transmission characteristic law of root piles is revealed. The results show that when the coral sand foundation is saturated and the water level rises and falls, compared with the dry sand foundation, the pullout bearing capacity of the root pile decreases, and the ability to control the displacement is sharply weakened. The axial force curve at the root is in the shape of a step; after the foundation is affected by water, the maximum value of lateral friction resistance first appears at the bottom root, and the lateral friction resistance at the lower root is always greater than that at the upper root; the water level rise and fall leads to a decrease in the lateral friction resistance in the area of the pile without a root, and the lateral friction resistance in the area of the root is increased. Under saturated and water level rise and fall condition, the total bearing ratio of the root pile increases, and the bearing ratio of the lower root pile is always larger than that of the upper root. After loading, the soil in the upper part of the pile is compacted, and the soil in the lower part is loosened; the maximum value of soil pressure in the compacted area of the dry sand condition gradually moves downward, and the maximum value of soil pressure in the saturated and water level rise and fall condition is always located in the lowermost part of the compacted area; the pore water pressure in the saturated and water level rise and fall condition is basically equal with the hydrostatic pressure, and there is no obvious super pore water pressure generated. The research results provide scientific basis for the application of root piles in coral sand foundation.