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The present research introduces an optimum performance soft computing model by comparing deep (multi-layer perceptron neural network, support vector machine, least square support vector machine, support vector regression, Takagi Sugeno fuzzy model, radial basis function neural network, and feed-forward neural network) and hybrid (relevance vector machine) learning models for estimating the pile group settlement. Six kernel functions have been used to develop the RVM model. For the first time, the single (mentioned by SRVM) and dual (mentioned by DRVM) kernel function-based RVM models have been employed for the reliability analysis of settlement of pile group in clay, optimized by genetic and particle swarm optimization algorithms. For that purpose, a database has been collected from the published article. Sixteen performance metrics have been implemented to record the model's performance. Based on the performance comparison and score analysis, models MS3, MS9, MS17, MS23, and MS25 have been recognized as the better-performing models. Furthermore, the regression error characteristics curve, Uncertainty analysis, cross-validation (k-fold = 10), and Anderson–Darling test reveal that model MS23 is the best architectural model in reliability analysis of pile group settlement. The comparison of model MS23 with published models shows that model MS23 has outperformed with a performance index of 1.9997, a20-index of 100, an agreement index of 0.9971, and a scatter index of 0.0013. The compression index, void ratio, and density influence the pile group settlement prediction. Also, the problematic multicollinearity level (variance inflation for > 10) significantly affects the performance and accuracy of the deep learning model.

This study investigates the performance of helical and straight pipe pile groups in sandy soils, focusing on their compressive axial load-bearing capacities through a series of small-scale model tests. The research highlights comparing two pile types, emphasizing the material efficiency and load-bearing advantages of helical piles. Both types of piles were tested under varying pile spacing and embedment depths. The results reveal that, for both pile types, the contribution of frictional load to the overall capacity is negligible, with most of the load-bearing capacity attributed to end-bearing. The study identified the optimal pile spacing and embedment depth for maximum load-bearing capacity to be 3.5 and eight times the diameter of the straight pipe pile, respectively. Despite straight pipe piles demonstrating up to 26% higher bearing capacity, they required twice the amount of steel compared to helical pile groups. In contrast, helical piles demonstrated up to 23% greater load-bearing capacity at embedment depths less than the optimal value.

Pile groups are designed to sustain complex loads in various engineering. During the design of a pile group, the obvious pile group effect should be considered for closely spaced pile groups. However, the group effect considered by different scholars varies, which makes it hard for engineers to consider the pile group effect for the design of a pile group. In this study, the finite element (FE) method is proposed to advance our understanding of the variations of pile group effects developed by different researchers, based on the concept of soil–pile relative stiffness. The relationship between soil–pile relative stiffness and normalized lateral load–displacement curves and bending moment profile response of the pile group is investigated. The results show that the pile group effect increases with the increase in soil–pile relative stiffness; the pile group effect increases with the decrease in pile spacing, increases with the increase in of number of piles in the group, and is significantly affected by pile group arrangement as well.

In recent years, much of the research in geotechnical earthquake engineering has focused on liquefaction of loose, saturated sands and silts. However, the dynamic behaviour of soft, clayey soils and their interaction with pile foundations during the earthquakes have received relatively little attention. In this study, an attempt is made to investigate the dynamic behaviour of soft clay and its interaction with pile foundations during earthquakes using high gravity centrifuge testing. A model single pile and two sets of 3 × 1 row model pile groups with different pile spacing were embedded in soft kaolin clay and tested under the action of model earthquakes at 50 times the earth’s gravity. The strength and stiffness of clay were evaluated using a T-bar test and an air hammer device respectively. The focus of this research is to investigate the dynamic response of friction piles in soft clay. However, this depends on the dynamic response of the soft clay layer around the pile. To this end, one-dimensional ground response analysis was performed using DEEPSOIL software to emphasise the importance of non-linear analysis in characterising the seismic behaviour of soft clays. It will be shown that clay response depends both on the earthquake intensity and the shear strength and stiffness of the clay layer. This has a direct bearing on the response of single piles and pile groups, with larger amplification occurring for small intensity earthquakes and attenuation occurring for stronger earthquakes.

As a common geohazard, landslides may cause enormous losses of human lives and properties. It is necessary to prevent landslides by effective technical measures. The grouted micro-steel-pipe pile group is a typical composite anti-sliding structure applied in landslide-stabilization engineering, where the micropiles and the surrounding geomaterials interact to resist the landslide thrust. In this study, laboratory experiments were carried out to investigate the anti-sliding performance of a kind of 3 × 3 grouted micro-pipe pile group anchored in bedrock at different row spacing of micropiles. The results indicate that the grouted micro-pipe pile group shows a relatively large anti-sliding capacity at row spacing of 4–8 times the micropile diameter. The active earth pressure on micropiles induced by soil movement shows an approximately triangular distribution. More of the thrust load transfers from the rear pile row to the middle and front pile rows gradually as the thrust load increases, where the ratios of earth thrust among the rear, middle and front pile rows can reach up to 1:0.60:0.44. The maximum bending moment occurs at the anchoring segment close to the bedrock surface. As the thrust loading increases, the maximum bending moment of the rear pile row will first increase to a peak value and then rapidly decrease, implying the micropile group is about to lose its anti-sliding ability. The development of deformation can be characterized as three stages including the slow deformation stage, accelerating deformation stage and unstable deformation stage. It is recommended that the horizontal displacement of pile head should be less than 1% of the loading depth for actual engineering design.

With the rapid development of urbanization and infrastructure construction, the requirements for the foundation design of high-rise buildings and large bridges are increasing. Pile foundations, as important supporting structures, are widely used in weak foundations and high-rise buildings. However, pile groups show significant advantages in bearing capacity, settlement control, and structural stability, while also bringing complex pile–soil interactions and group pile effects. Based on an FLAC3D numerical simulation (version 3.0), this paper constructs a pile group composite foundation model under different pile length conditions and analyzes the influence of pile–soil interaction on the group pile effect. The results show that pile length has a significant impact on the settlement and bearing capacity of the pile group composite foundation. When the pile length exceeds a certain critical value (23.4 m in this study), the interaction between piles is enhanced, the bearing capacity of the soil between piles is improved, the pile–soil stress ratio is reduced, and the overall settlement is effectively controlled. Moreover, there are obvious differences in settlement and stress distribution between pile group composite foundations and single-pile composite foundations, and the group pile effect can lead to greater settlement and more complex stress distribution. Therefore, when designing pile group composite foundations, factors such as pile length, pile spacing, and geological conditions should be fully considered to optimize foundation performance. This study provides a theoretical basis and reference for the design and optimization of pile group composite foundations, highlighting the importance of considering pile length and pile–soil interaction in practical engineering applications.

In cases where stiffness and bearing capacity of soil aren’t sufficient to carry loads of a structure, depth of the foundation of the structure can be increased by using a pile group to transmit the loads to the soil layers with high bearing capacity. The behaviour of the pile group is discrepant with the response of a single pile due to the pile-pile and the pile-soil interactions. Therefore, extensive experimental and numerical studies have been performed for reliable and economical design of the pile groups. Even so, group efficiency ( η ) received no attention from researchers. Therefore, it is intended to investigate experimentally the group efficiency in this study. The pile groups with different pile spacings were tested in sandy soil with loading tests. The tests were performed at various relative densities and L/D ratios with the pile groups. After the small-scale tests, the determined group efficiency was compared with the existing methods. As a result, the influences of the pile length, diameter, spacing, and relative density on the group efficiency are investigated. From the results of the tests, it was found that although the conventional empirical formulas on pile group behaviour is that group efficiency is smaller than 1, the group efficiency for driven piles in cohesionless soils ranged between about 1.31 and 1.66 in this study.

Shield tunneling adjacent to existing piles is common occurrence in subway construction. This study proposes a novel tunnel model capable of simultaneously simulating ground loss, unloading effects, and void grouting under in-flight conditions. Several three-dimensional (3D) centrifugal scale model tests are implemented in a silty-silty clay composite to investigate the response of a single pile (Test SP) and pile group (Test GP) with a sinking low cap subject to adjacent tunneling. The results indicate a critical influence area, i.e., 0.75D in front and 0.25D behind the centerline of the existing piles, is observed for the pile head settlement, in each test, and the induced bending moment in the piles above the tunnel spring line is more sensitive to tunneling than that below it. A decreasing trend in axial force along the pile shaft is observed in Test SP, whereas Test GP shows the opposite behavior. The maximum variations in axial force and bending moment occur near the tunnel invert and crown in Test SP, respectively, however, they all appear near the tunnel spring line in Test GP. There is a law of load transfer for downward migration in Test SP. In Test GP, however, the load on the upper part of pile P1 decreases and shifts to the lower section of pile P1 and the whole pile P2. Subsequently, the load on the upper part of pile P2 reduces and transfers to the lower part of pile P2 and the whole pile P1. A significant increment in the earth pressure near the pile toe is observed. The pore water pressure increases slightly at first and then dissipates. Digital image correlation (DIC) has been preliminarily demonstrated as a valuable tool for visually capturing the progressive behavior of pile-soil interactions during in-flight tunneling, proving advantageous for analyzing tunnel-soil-pile interaction issues under centrifugation conditions.

Inclined pile foundations with high inclination angles, subjected to both vertical and horizontal load, are increasingly used due to the advancement in installation technology. This study aimed to characterize the bearing capacities and deformation behavior of inclined pile foundations subjected to vertical and horizontal loads in laboratory-scaled testing. In a series of pile-modeled tests, the stainless-steel pile as a model pile, the single pile and the symmetrical 2 × 1 pile group were installed in dense sand at 0°, 10°, 20°, and 30° of inclination angles. The experiment in an inclined single pile subjected to vertical load aimed to minimize the eccentricity effect. The results showed that the optimal pile inclinations for vertical load were 10° and 20° for single pile and pile group, respectively. For optimal pile inclinations of horizontal load, they were between −10° to −20° and 20° for single pile and pile group, respectively. The ratios of the ultimate horizontal load to the ultimate vertical load ( Q uh / Q uv ) ranged from 0.02 to 0.19 and 0.15 to 0.23 for the single pile and the pile group tests, respectively. The group efficiencies for vertically loaded pile groups ranged from 58%–139% and 107%–130% for horizontal loading.

Constructing offshore wind turbines on artificial islands is considered a viable option, but negative skin friction (NSF) is a significant adverse factor that cannot be ignored. The NSF adversely affects the bearing capacity of pile foundations. Currently, design methods for studying the impact of NSF group effects mainly rely on empirical approaches. Moreover, existing experimental studies do not simulate the NSF experienced by offshore wind turbine pile groups on artificial islands. In order to further explore the impact of pile group effects on NSF experienced by offshore wind turbine pile foundations on artificial islands, this study conducted indoor model tests on single piles and 3 × 3 rectangular pile groups in sandy soil under uniformly distributed loading on surrounding soil. The experiment measured the settlement of piles at various positions within single piles and rectangular pile groups, as well as the settlement of the soil surrounding the piles and the NSF. Through calculations, the experiment determined the neutral points and NSF group effect coefficients for each pile. The results indicate that densely spaced pile groups are advantageous in reducing settlement of the surrounding soil, thereby mitigating the adverse effects of NSF. Due to the influence of pile group effects, different positions within the group experience varying degrees of NSF. Consequently, in practical engineering applications, settlement of both the pile groups and the surrounding soil should be calculated separately. Furthermore, design considerations for the uplift forces and neutral points of piles at different positions within the pile group should adhere to distinct standards.