Calculation and prediction of the uplift capacity of squeezed branch piles (SBP) are still immature. This study develops a method to predict the load-displacement relationship and ultimate capacity of SBP under pullup load by using a hyperbolic model to describe the nonlinear load transfer between pile-soil and plate-soil. The uplift bearing behaviors of SBP are analyzed through six sets of indoor model tests in homogeneous soils. The results, along with field tests of single-plate piles in layered soils and the indoor tests, confirm the high accuracy of the theoretical prediction method. The effects of three factors, including the pile side soil damage ratio (Rf), the horizontal earth pressure coefficient (k) and the damage angles of the soil under plate (psi), on the prediction results are analyzed. The results show that these factors significantly affect the second half of the loaddisplacement curve of SBP. Furthermore, as the Rf rises, the anticipated ultimate uplift capacity of SBP decreases linearly; as the k rises, it increases linearly; and as the psi rises, it increases nonlinearly.

Suction caisson, characterized by convenient installation and precise positioning, is becoming increasingly prevalent. Over prolonged service, a significant seepage field forms around the caisson, particularly in sandy seabed, altering the contact stress at the caisson-soil interface and causing change in the interface shear strength. Given these interface contact properties, a series of cyclic shear tests are performed, incorporating the effect of pore water pressure. Test results indicate that the interface shear strength depends on normal stress, while the interface friction angle is only minimally influenced. Drawing from the findings of the cyclic shear tests, a cyclic t-z model is established to simulate the seepage-influenced caisson-soil interface shear behavior, which is also validated at the soil unit scale through interface shear tests and at the suction caisson model scale by centrifuge tests. It is further employed to forecast the evolution of skirt wall friction for a cyclic uplifting suction caisson, showcasing the capability in capturing the foundation failure under high-amplitude cyclic loading.

This paper presents coupled thermo-hydro-mechanical finite element analyses (FEAs) of undrained uplift capacity for buried offshore pipelines operating at elevated temperature. An anisotropic thermoplastic soil constitutive model was employed to simulate mechanical behaviour of seabed soil under the combined actions of thermal and mechanical loading. FEAs investigated the influences of different parameters, e.g., pipeline embedment depth, pipe-soil interface roughness, duration of pipeline operation, and operating temperature, on pipeline uplift capacity. Time-dependent evolutions of temperature and excess pore water pressure were also tracked in soil surrounding the pipeline. For different durations of pipeline operation, FEA results revealed an improvement in normalized uplift capacity Nu of pipelines operating under elevated temperature. However, such an increase in Nu was diminished by a maximum of 7 % with increase in the ratio RTH of thermal diffusivity to coefficient of consolidation of surrounding soil. For different normalized pipeline embedment, 20-30 % enhancement of Nu was observed after six months of pipeline operation at 60 degrees C. However, after six months of operation, further improvement in Nu was negligible. Based on FEA results, this paper proposes an equation to estimate pipeline uplift capacity as a function of operating temperature, depth of embedment, and duration of pipeline operation.

After sand liquefaction, buried underground structures may float, leading to structural damage. Therefore, implementing effective reinforcement measures to control sand liquefaction and soil deformation is crucial. Stone columns are widely used to reinforce liquefiable sites, enhancing their resistance to liquefaction. In this study, we investigated the mitigation effect of stone columns on the uplift of a shield tunnel induced by soil liquefaction using a high-fidelity numerical method. The liquefiable sand was modeled using a plastic model for large postliquefaction shear deformation of sand (CycLiq). A dynamic centrifuge model test on stone column-improved liquefiable ground was simulated using this model. The results demonstrate that the constitutive model and analysis method effectively reproduce the liquefaction behavior of stone column-reinforced ground under seismic loading, accurately reflecting the time histories of excess pore pressure ratio and acceleration. Subsequently, numerical simulations were employed to analyze the liquefaction resistance of saturated sand strata and the response of a shield tunnel before and after reinforcement with stone columns. Additionally, the effects of densification and drainage of the stone columns were separately studied. The results show that, after installing stone columns, the excess pore pressure ratio at each measurement point significantly decreased, eliminating liquefaction and mitigating the uplift of the tunnel. The drainage effect of the stone columns emerged as the primary mechanism for dissipating excess pore pressure and reducing tunnel uplift. Furthermore, the densification effect of stone columns effectively reduces soil settlement, particularly pronounced around the stone columns, i.e., at a distance of three times the diameter of the stone column.

The objective of this research is to perform seismic analysis for column supported tanks, focusing on the performance assessment under multi-dimensional earthquakes and considering fluid-structure interaction (FSI), soilstructure interaction (SSI), and the uplift effect. A finite element model (FEM) capable of integrating the above complicated factors is generated to study the seismic response of two types of tanks, including anchored and resilient tanks. The FEM of tanks considering these effects is first verified by using experimental and numerical results, and then the FSI and SSI effects on the natural frequencies of tanks are investigated. Subsequently, their seismic responses, i.e., structural displacements, member stresses, base shear and overturning moments, are obtained, and the influences of multi-dimensional excitations, SSI and uplift effects on them are further studied. The results show that the inclusion of multi-dimensional seismic components causes significantly increase in structural responses in perpendicular direction, making column supported tanks more susceptible to damage. The SSI effect leads to larger displacement, but smaller stress level especially for softer soil type. Resilient tanks do not suffer plastic failure of their walls and columns, and outperform anchored tanks regardless of soil conditions even under severe multi-dimensional earthquakes. In addition, resilient tanks have quick resilience capability, which provides favorable references to seismic design of column supported tanks.

Rocking isolation is an effective method for reducing structural damage during earthquakes and aligns with a seismic design approach that aims to minimize damage to bridges. The seismic responses of rocking structures are significantly influenced by the soil-structure interaction and the soil characteristics. In this research, a shaking table test was conducted on a single-pier rigid-frame bridge model with an uplifting footing, considering soil-structure interaction. This test was used to validate a finite element model (FEM) developed using ABAQUS software. Subsequently, the seismic responses of the rigid- frame bridge with a pile foundation capable of rocking at the pier base were analyzed in detail. Four soil types, including silt, silt clay, sand, and clay, were examined, and two foundation types were considered: a fixed pile foundation and a rocking pile foundation. The results indicate that uplifting the footing can reduce the deck's acceleration and the pier's bending moment, while increasing the bridge's displacement, compared to a bridge with a fixed pile foundation.

Historical earthquake-induced damage and studies have shown that the impact of vertical earthquake motions on sand liquefaction cannot be ignored in liquefiable sites with underground structures. Therefore, this study performed a finite element-finite difference (FE-FD) coupling numerical method to compare the influence of different seismic component excitations (vertical, horizontal, and bidirectional) on sand liquefaction with and without subway stations and to further explore the uplift mechanism of the subway station under vertical earthquake motion. The results revealed that the liquefaction response of the foundation soil is much different in the model with and without the subway station. In a liquefiable site with a subway station, the vertical seismic component may also trigger soil liquefaction due to soil structure interaction, while in the unstructured site, it cannot trigger liquefaction. The vertical seismic component will aggravate the degree of liquefaction and horizontal acceleration response of soil near subway stations, and the extent of this influence decreases with the increase of horizontal distance between the soil and the side wall of the subway station. In addition, the influence of vertical earthquake motions on the uplift of subway stations is related to seismic wave characteristics and the value of Arias intensity. The mechanism of the effect of vertical earthquake motion on the uplift of subway stations is to reduce friction between structure and soil and increase the flow deformation of the soil.

Tunnels located in liquefiable soils are prone to flotation following earthquakes. When the shaking-induced pore water pressure buildup continues, saturated soil surrounding the tunnels liquefies, flotation occurs and the soil loses its shear resistance against the uplift force from the buoyancy of the tunnel. Mitigation of liquefaction-induced uplift of tunnels is one of the concerns of geotechnical engineers. This article aims to investigate the efficacy of the available mitigation techniques using a finite element program with an emphasis on the prediction of excess pore water pressures in the surrounding soil and the uplift of the tunnel. In addition to the conventional techniques, a newly developed technique Partial Saturation was modeled to examine its effect on the reduction of the tunnel uplift. A parametric study was done to compare the effectiveness of partial saturation with other mitigation techniques. Results showed that the partial saturation technique would effectively dissipate the excess pore water pressure in the soil around the tunnels. It also performs well in the reduction of the uplift of the tunnel. The most appealing advantage of this technique against the other available mitigation techniques is that it can be employed easily without disturbing the soil around the tunnels. A new methodology to numerically simulate the partially saturated sands was described in this paper.

The bending and damage suffered by the pipelines during the upward movement depend largely on the displacement of the pipe and the damage degree of the surrounding soil. According to the failure mechanism of the surrounding soil caused by the upward movement of pipelines, this paper described the shear plane development of the uplifting load-displacement curve (LDC) across varying phases. However, the existing LDC model is not able to accurately calculate the change in overlying load during pipeline upward. Hence, to precisely determine the uplifting load of the pipeline, a composite power-exponential function (CPEF) is proposed. Additionally, modifications have been made to the calculation formula for the residual uplifting load. The proposed CPEF comprises four parameters: a , b , c , and d . To verify the validity of the proposed CPEF model, the experimental results are compared with the calculated results of the proposed CPEF, which show that the proposed CPEF model can well predict the entire process of uplifting load changes on the pipeline during the upward movement process. Finally, the influence of parameters on the LDC calculated by CPEF under the same conditions was analyzed by varying the parameters of CPEF.

As underground structures' burial depth increases, buoyancy resistance due to groundwater becomes more pronounced. This study, through numerical simulation, analysis of field measurement data, and theoretical analysis, explores the impact of changes in groundwater level on the failure mode and uplift resistance of expanded base piles and proposes a new method for calculating the ultimate uplift capacity of expanded base piles considering the effect of groundwater. The research shows that the rise in groundwater level significantly affects the uplift performance of expanded base piles by altering the physical and mechanical properties of the soil and the morphology of the pile-soil failure surface, thereby affecting the pile's load-bearing capacity. The study identifies a three-segment failure mode for expanded base piles and notes that as the groundwater level rises, the extent of the failure surface gradually expands. Additionally, the paper underscores the importance of considering groundwater levels in practical engineering design and suggests re-evaluating the measured uplift capacity using the calculation method proposed in this study to ensure engineering safety. This research provides a theoretical basis and computational tools for designing belled uplift piles under the influence of groundwater, offering significant reference value for engineering practice.