Search Results (12)

The excavation of upper shallow foundation pits may cause the uneven deformation of existing tunnels buried below a shallow depth. Improper control measures may lead to a series of diseases, such as local cracking or breakage of the tunnel lining, which threaten the safety of tunnel operations. Regarding the safety of the existing tunnel affected by the construction of the foundation pit, cases of the application of portal frame anti-heave structures in upper foundation pit projects of existing tunnels in Shenzhen have been documented, and the main influencing factors have been analyzed and summarized. Taking the Qianhai Ring Water Corridor Project as an example, numerical orthogonal experiments were conducted to analyze the deformation response patterns in the depth of existing tunnels and the effectiveness of control measures in the upper shallow of foundation pit engineering. The roles of portal frame anti-heave structures are analyzed in detail using measured data. Studies indicate that the deformation of the existing tunnels mainly occurs during the top and immediately adjacent block excavation stages, and stabilizes after the uplift-resisting piles and anti-floating slabs form an effective frame structure. The portal frame anti-heave structures, combined with measures such as block excavation, jet grouting interlocking reinforcement, backfilling, and surcharge loading, have extremely strong deformation control capabilities. However, the construction costs are relatively high, leaving room for optimization. Full article

In coastal regions with thick, soft soil deposits, bridge pile foundations are susceptible to lateral displacements induced by the construction of adjacent seawalls. This study employs a three-dimensional nonlinear finite element framework to investigate the lateral deformation mechanisms of rock-socketed bridge piles under seawall surcharge loading in soft soils, considering the effects of both immediate construction and long-term consolidation. A parametric analysis is performed to evaluate the effectiveness of deep cement mixing (DCM) piles in mitigating pile displacements, focusing on key design parameters, including DCM pile length, area replacement ratio, and elastic modulus. The results reveal that horizontal pile displacements peak at the pile head post-construction (25 days: 25 mm) and progressively decrease during consolidation, shifting the critical displacement zone to mid-pile depths (20 years: 12 mm). Bending moment analysis identifies persistent positive moments at the rock-socketed interface. Increasing pile stiffness marginally reduces displacements (a < 1 mm reduction for a 22% diameter increase), while expanding the seawall–pile distance to 110 m decreases displacements by 72–84%. DCM pile implementation significantly mitigates short-term (48% reduction) and long-term (54% reduction) displacements, with optimal thresholds at a 30% area replacement ratio and a 40.5 MPa elastic modulus. This study provides critical insights into time-dependent soil–pile interaction mechanisms and practical guidelines for optimizing coastal infrastructure design to minimize surcharge-induced impacts on adjacent pile foundations. Full article

Situated within the context of a soft ground foundation at an iron ore mining site, this study investigates the impact of substantial surcharges on the settlement of such foundations and the adjacent infrastructure. By employing the finite-difference numerical software FLAC3D 6.0, a series of three-dimensional simulations were conducted to assess the stress response and deformation of gallery pile foundations, shallow foundations, and mine shed pile foundations to step loading. This study integrates the analysis of soil strength augmentation under considerable stress and its attenuation characteristics under significant deformation. Various reinforcement measures, such as the implementation of stone columns, prefabricated vertical drain, and surcharge preloading techniques, were examined for their capacity to consolidate the foundation, reduce settlement, and mitigate impacts on adjacent structures. The results reveal that horizontal displacements in the pile and shallow foundations escalate progressively with additional surcharge throughout the operational period. The most pronounced horizontal deviation in the pile foundations is observed at the juncture between sand and silt strata. Stone columns act effectively as a barrier to the sliding surface, consequently reducing the influence of surcharge on the movement of the foundation. Full article

Excessive lateral forces and the deformation of pile groups caused by adjacent surcharge loading and excavation can potentially lead to the failure or collapse of nearby pile foundations. This paper presents a simplified analytical method to investigate the lateral displacement of passive pile groups caused by combined surcharge-induced and excavation-induced horizontal soil loading and validates it by utilizing two published centrifuge tests and numerical modeling. Firstly, the passive load resulting from surcharge-induced horizontal soil loading is determined using the improved formula of Boussinesq and the theory of local plastic deformation. The additional horizontal force exerted on the pile axis subjected to excavation-induced horizontal soil loading is also taken into account using the Mindlin solution. Furthermore, the shielding effect between pile groups is also proposed to analyze the response of a laterally loaded pile group due to excavation unloading. Secondly, according to the Pasternak foundation model of soil–pile interaction, the equilibrium differential equations are solved by the finite difference method. Finally, parametric analyses are undertaken to evaluate the behavior of different constraints on the pile head and surcharge procedure. The results demonstrate that the capped-head pile groups can provide greater restraint compared to the free-head groups for the lateral displacement of pile groups. The front pile experiences greater forces than the rear one in passive pile groups as a result of the smaller soil pressure on the rear pile. Additionally, increasing the horizontal stiffness of the capped head with fully fixed ends can significantly decrease the horizontal deformation of the pile groups. Full article

The performance of passive battered piles resisting the embankment-induced lateral soil movements may differ from that of the active battered pile and axially loaded existing vertical piles adjacent to embankment constructions. This study was part of a preliminary feasibility investigation for a reinforcement plan of an actual embankment project, aiming to experimentally investigate the performance of passive battered piles under embankment-induced lateral soil movement. To this end, a sequence of reduced-scale model tests of battered piles near the surcharges was first designed in sandy soil with a similarity ratio of 1:30. The effects of pile inclinations (β = −20°, −10°, 0°, +10°, and +20°), surcharge magnitudes, and constraint conditions at the pile tip (free-tip and fixed-tip) on the responses of passive battered piles were explored. Finally, the response characteristics of battered piles resisting the embankment-induced lateral soil movement were analyzed to clarify the working mechanism of these battered piles. Full article

With the increasing development of civil engineering in large cities, more and more excavations and surcharge loadings are being constructed or planned adjacent to existing building piles in crowded urban areas. Previous study on pile deformation has primarily focused on surcharge loading or foundation excavation and given little concern to the combined action of surcharge loading and foundation excavation. The article develops a two-stage process to assess the lateral displacement of nearby pile foundations induced by the combined action of surcharge loading and excavation. Firstly, the local plastic deformation theory and Boussinesq solution are used to accurately predict the passive loading of adjacent pile foundations caused by surcharge loading; Mindlin formulas are adopted to predict the passive pile’s additional lateral stress applied by excavation. Secondly, Pasternak models are adopted and the finite difference method is used to establish the deflection differential formula of the single passive pile. Last but not least, a parametric study is conducted to investigate the influence of the loading dimensions, loading magnitudes, and three-dimensional excavation dimensions. The findings of the calculations reveal that the loading magnitudes have a more significant impact on the lateral displacement of the pile compared to the loading dimensions. Therefore, a concentrated surcharge loading should be avoided. Additionally, the excavation depth has a greater influence on the lateral displacement of the pile compared to the excavation area. In order to mitigate this situation, a step excavation should be implemented for each layer of soil, with the soil excavated away from the pile foundation first. Full article

Due to the complexity of pile–soil interaction, there is little research on active–passive piles that bear the pile-top load transmitted from the superstructure and the pile shaft load caused by the lateral soil movement around the pile simultaneously. The purpose of this study is to analyze the displacement and internal force of active–passive piles. Most of the pile design codes in China use the elastic resistance method to describe the relationship between the lateral soil resistance and the horizontal displacement of the pile, but this is not accurate enough to analyze the internal force and deformation of the pile when the pile displacement is large. For this case, the passive load on the pile shaft caused by the adjacent surcharge load can be described in stages, and the p–y curve method can be used to express the relationship between the lateral soil resistance and the horizontal displacement of the pile. Additionally, taking both the active load (vertical force, horizontal force, and bending moment on the pile top) and the passive load into account, the deflection differential equation of the pile shaft is herein established, and a corresponding finite difference method program is implemented to obtain the calculations pursuant to the equation. The correctness of the analysis method and program was verified by two test cases. The results show that our calculation method can effectively judge the flow state of the soil around piles and accurately reflect the nonlinear characteristics of pile-soil interaction. Moreover, the influence depth of the pile displacement under the passive pile condition caused by the adjacent load is significantly greater than that under active pile condition, and the maximum pile-bending moment appears near the interface of soft and hard soil layer. Full article

Processing of extracted oil sands generates substantial volumes of tailings slurries. Due to the scale and inherent variability of the tailings properties, consolidation settlement is expected to occur at different rates and magnitudes across the tailings deposit. Estimating potential differential settlement of the consolidated deposit surface is an essential input for closure design. This paper presents a three-step methodology that generates multiple realizations of quasi-three-dimensional (3D) surfaces of the consolidated deposit based on the adjacent points. Each point is based on a stochastic one-dimensional (1D) large strain consolidation model developed with Monte Carlo techniques in GoldSim. The simulated surfaces provide early estimates of differential settlement based on the variability of consolidation properties expected in the tailings deposit. Comprehensive sensitivity analyses are performed for differently treated tailings material through 28 distinct scenarios to evaluate the sensitivity of the developed 1D and 3D models to consolidation input parameters over a 40-year time period. The analysis demonstrated that differential settlement is highly sensitive to tailings compressibility and hydraulic conductivity governed by the constitutive relationship parameters, and less sensitive to the solids content, specific gravity or thickness of a surcharge load. Tailings that underwent steady continuous settlement exhibited the largest degree of differential settlement. Full article

In this study, a self-developed adaptive finite element limit analysis (AFELA) code was adopted to explore the stability of dual tunnels in cohesive–frictional soil subjected to surcharge loading and seismic action. Parametric studies of different influential factors, including the depth of tunnels, horizontal distance between tunnels, seismic acceleration coefficient, unit weight, cohesion and internal friction angle of soils, were conducted using the AFELA code. An adaptive meshing technique was adopted for optimal accuracy and efficiency, and a pseudostatic method was used to simulate the seismic action. Strict upper bound (UB) and lower bound (LB) results with relative errors of less than 7% were acquired. Detailed design tables were presented to facilitate the engineering design, and three typical failure patterns, including single side-wall failure, half-cross-shaped failure and cross-shaped failure, corresponding to different stable levels, were summarized for a deeper insight into how the failure mechanism evolved under different conditions. The results indicated that the variations in soil unit weight and void depth affected the seismic bearing capacity almost linearly. Furthermore, the dual tunnel system is vulnerable to seismic actions, and the stability of tunnels was further undermined by the adverse effects of additional seismic-caused interactions between two adjacent tunnels. Full article

Numerous factors affect the soil pressure distributions around buried pipes, including the shape, size, and stiffness of the pipe, burial depth, and the stiffness of the surrounding soil. Additionally, to some extent, a pipe can benefit from the soil arching effect, where the overburden and surcharge pressure at the crown can be supported by the adjacent soil. As a result, a buried pipe only needs to support the portion of the load that is not transferred to the adjacent soil. This paper presents numerical investigations of the soil pressure distributions around buried concrete pipes and crack propagation under different environmental conditions, such as loading, saturation level, and the presence of voids. To this end, a nonlinear elastoplastic model for backfill materials was implemented using finite element software and a user-defined subroutine. Three different backfill materials and two different native soils were selected to examine the material-specific behaviors of concrete pipes, including soil pressure distributions and crack propagation. For each backfill material, the effects of the loading type, groundwater, and voids were investigated. These simulation results provide helpful information regarding pressure redistribution and buried concrete pipe behavior under various environmental conditions. Full article

Surface surcharge changes the existing equilibrium stress field of the stratum and adversely affects the existing tunnel. This paper presents a simplified analytical solution for calculating the longitudinal displacement of existing tunnels that are subjected to adjacent surcharge loading. Based on the Boussinesq solution, the distribution of the additional load matrix caused by the surface surcharge on the existing tunnel was obtained. A Euler–Bernoulli beam with a Pasternak foundation was used as a simplified model for tunnel stress analysis. Using the corrected reaction coefficient of the foundation bed, the differential equation of tunnel deformation was established, and the solution matrix of the longitudinal displacement of the tunnel was obtained by using the finite difference method. The reliability and applicability of the proposed method were verified by comparing the results with finite element simulation results, field test data, and the calculation results of three simplified elastic analysis methods with different foundation bed coefficients. On this basis, the parameters of the load–tunnel model were analyzed, and the effects of the buried depth, the size of the load, the relative positions of the load and the tunnel, and the relative stiffness of the tunnel soil on the maximum displacement of the existing tunnel were calculated. An empirical formula is proposed for calculating the maximum longitudinal displacement of the existing tunnel subjected to surface surcharge. The findings of this research can provide a basis for the theoretical verification of the deformation response of an existing tunnel subjected to adjacent surface surcharge. Full article

In this study, for the establishment of a safety evaluation method, non-destructive tests were performed by developing a full-scale model pier and simulating scour on the ground adjacent to a field pier. The surcharge load (0–250 kN) was applied to the full-scale model pier to analyze the load’s effect on the stability. For analyzing the pier’s behavior according to the impact direction, an impact was applied in the bridge axis direction, pier length direction, and pier’s outside direction. The impact height corresponded to the top of the pier. A 1-m deep scour was simulated along one side of the ground, which was adjacent to the pier foundation. The acceleration was measured using accelerometers when an impact was applied. The natural frequency, according to the impact direction and surcharge load, was calculated using a fast Fourier transform (FFT). In addition, the first mode (vibratory), second mode (vibratory), and third modes (torsion) were analyzed according to the pier behavior using the phase difference, and the effect of the scour occurrence on the natural frequency was analyzed. The first mode was most affected by the surcharge load and scour. The stability of the pier can be determined using the second mode, and the direction of the scour can be determined using the third mode. Full article