Behavior Of Pile Groups Research Articles

Numerical study on the lateral behavior of pile groups in Toyoura sand using the hypoplastic constitutive model

A pile group under lateral loading is a complex pile‒soil-pile interaction problem. In this study, numerical analysis was used to investigate the lateral behavior of pile groups arranged in a 3 × 3 configuration with varying piles spacings. The hypoplastic constitutive model embedded into ABAQUS software through the UMAT subroutine was used to characterize the stress‒strain relationship of Toyoura sand. The effects of the pile spacing on the load‒displacement relationship of the pile group, the bending moment-depth relationship of each pile in the pile group, the deflection-depth relationship, and the soil resistance distribution were investigated. The results indicate that the lateral bearing capacity of the pile group decreases by more than 50% when the pile spacing is reduced from 7D to 3D. When the pile spacing is greater than 5D, the “edge effect” of the laterally loaded pile group gradually decreases, and when the pile spacing is greater than 7D, the “shadowing effect” can be negligible, and the wedge-shaped failure zone of the pile group occurs within a depth of 5D below the mud surface.

Development of improved finite element formulations for pile group behavior analysis under cyclic loading

AbstractThe effect of cyclic loading is an essential factor leading to progressive soil strength degradation. Therefore, a comprehensive analysis of the pile‐soil system behavior under cyclic loading is required to ensure the stability of pile group. There is room for improvement in the inherent constraint of the conventional numerical model in terms of approximating the soil resistance distribution along the pile by point loads at element nodes, necessitating a specific element that integrates considerations of pile group effect and cyclic loading within a unified framework. This study aims to develop a newly specific type of element for efficiently predicting nonlinear behavior within the pile‐soil system, addressing simulations involving nonlinear pile‐soil interaction, pile group effect, and cyclic loading. Modified element formulations based on soil stiffness matrices and soil resistance vectors specifically address pile group effect and consider parameters that influence pile behavior under cyclic lateral loading. The numerical solution procedure with Newton‐Raphson iteration allows the calculation of pile responses in geometric and material nonlinear analyses. The validation of the proposed method includes several examples, comparing it with existing numerical solutions and experimental tests of single piles and pile groups under cyclic loading. These comparisons further support the consistency of the proposed method with measured data and validate its accuracy in considering group effect and cyclic loading. The parametric study illustrates the ability of the proposed method to capture cyclic loading parameters while considering the influence of the number and magnitude of load cycles, the cyclic load direction, and the installation methods.

Response of group piles subjected to coupled vertical-eccentric lateral-seismic loads

In seismic prone regions, analyzing loaded pile groups can be challenging because of limitations in conventional design methods and the inability of small-scale laboratory tests to accurately replicate the real behavior. Studying how pile group response is affected by the combined impact of vertical, concentric, and seismic loads is challenging. One of the limitations pertains to the intricacy of scaling up experiments, particularly in creating large-scale laboratory models. Thus, a numerical analysis may be appropriate for capturing the response. This study aimed to understand the pile group response in dense sand subjected to vertical, eccentric lateral, and seismic loadings via a large-scale 3D nonlinear finite element model. The validation results indicate that the numerical approach accurately predicts the behavior of pile groups in dense sand. Then, two different layouts of pile groups are analyzed under various loading scenarios on the basis of the recorded data from the El Centro earthquake. The results revealed that the number and arrangement of piles significantly affect the induced settlement. Compared with the 5-pile groups, the 3-pile groups presented higher maximum bending moments under vertical loading. However, the response of the 5-pile groups varied, as they experienced higher bending moment values without vertical loading. The peak lateral soil pressures were higher in the 3-pile groups. Some significant variations appeared in the induced torque resistances when the 5-pile groups were compared with the 3-pile groups. This study demonstrated the reliability of the used numerical approach for analyzing the response of pile groups in dense sand, as an alternative to laboratory test models.

Thermo‒mechanical behavior of energy pile group in dry sand subjected to a horizontal load

The energy pile is an innovative structure element designed to utilize geothermal energy while simultaneously supporting building loads by means of integrating heat exchange tubes into the pile foundation. Despite the intricate thermodynamic characteristics of energy pile groups, research on them remains limited. This study investigated the horizontal load transfer mechanism of an energy pile group in dry sand by conducting a model test on a 2 × 2 energy pile group subjected to horizontal loads. Specifically, the impact of heating or cooling a single pile within the energy pile group was examined. The results showed that the bending moment was significantly larger on a single pile subjected to a thermal load than that of the other piles, with the majority of this variation occurring in its upper part. Additionally, the horizontal load had a strong influence on the rotational angle and horizontal displacement of the energy pile group. The rotational angle and horizontal displacement decreased with increasing depth. With rising temperature, the interaction between the pile and the soil intensified, and the soil pressure on the upper part of the pile increased while that in the lower part decreased.

Finite Element Simulation Analysis of the Influence of Pile Spacing on the Uplift Bearing Performance of Concrete Expanding-Plate Pile Groups

Concrete expanding-plate piles (CEP piles) represent a novel type of variable cross-section concrete cast-in-place pile, wherein one or more bearing plates are added to the pile body to enhance its load-bearing capacity. Compared to traditional uniform-diameter uplift piles, the bearing plates of CEP uplift piles provide additional resistance against uplift, substantially increasing the pile’s uplift bearing capacity. CEP piles exhibit a wide range of application potential in structures such as high-rise buildings, cable-stayed bridges, and offshore platforms. However, due to changes in the load-bearing mechanism, the pile–soil interaction of CEP piles significantly differs from that of straight-shaft piles. Theories applicable to the group effect of straight-shaft piles cannot be directly applied to CEP piles, which has led to imperfections in the theoretical framework for designing CEP piles in practical engineering applications, hindering their broader adoption. Therefore, this paper employs a finite element simulation analysis to study the failure modes of three groups of symmetrically arranged CEP pile groups. The effects of pile spacing on the uplift bearing capacity of CEP pile groups are investigated, leading to a revision of the formula for calculating the uplift bearing capacity of CEP pile groups. This study enhances the theoretical understanding of the load-bearing behavior of CEP pile groups, providing a theoretical basis for their practical engineering applications.

Analytical investigations on thermomechanical behavior of energy pile groups resting on stiff soil strata

Energy piles are increasingly being exploited worldwide because of their dual role of exchanging heat with the ground and providing structural support for buildings. Despite the existing studies, simplified but reasonable methods for estimating the vertical displacement of end-bearing energy pile groups subjected to thermal loads are lacking. To address this challenge, an analytical approach was proposed to analyze the thermomechanical behavior of energy pile groups bearing stiff soil strata. To consider the reduction in soil displacement caused by the presence of a bearing layer, an approximate method where the energy piles comprising solid and mirror-image elements was introduced. The proposed approach was implemented using a self-developed program and validated against the results of existing numerical studies. The results indicated that the thermally induced displacement interaction between the predominant end-bearing piles was more pronounced than that between the floating piles. The displacement interaction decreases with decreasing shaft and base soil stiffness, increasing pile spacing, and decreasing pile slenderness ratio. In addition, a simplified method for estimating the displacement of energy pile groups resting on stiff soil strata was established by superimposing the interaction factor.

Numerical Evaluation of Pile Group Behavior Subject to Earthquake Loads

The seismic design of pile foundations mainly relies on analyzing the seismic response of layered, liquefiable locations. Two design scenarios are taken into consideration from the case histories; the first is how pile foundations react to the stresses and lateral displacements brought on by the lateral dispersion of liquefied soil. The second is how to piles reaction to seismic activity that occurs with the development of high pore water pressures. The PLAXIS 3D software is utilized in this research with a non-linear soil constitutive model (hypoplastic model) for both dry and saturated loose sandy soils under the impact of two earthquakes and the motion of different features to give a complete understanding of the dynamic piled foundation response. The findings from this study show that the site profile, pile diameter, pile length, and excitation of ground motion significantly affect the dynamic response of the layered liquefied site. So, in the saturated case, the increase in the piles length to (L/D = 55) in comparison to the original length (L/D = 35) decreased the peak acceleration at the raft foundation by about (24.4 and 41.9) % under the effect of Kobe and Upland earthquake motion, respectively, while in the dry case, the reduction in peak acceleration was about (22.8 and 40.9) % under the effect of Kobe and Upland earthquake motion, respectively.

Machine induced dynamic field responses of group pile with different pile arrangements

AbstractThe main objective of the current investigation is to study the dynamic behaviour of a 3-pile group with different loading direction under coupled (horizontal and rocking) excitations. To accomplish this objective, machine-induced field excitation tests are conducted on small-scale hollow steel piles. The 3-pile group is driven into the ground in a triangular arrangement with 3d spacing. Two different soil-pile setups, i.e., Pile Group-I and Pile Group-II, are created based on dynamic force directions. In the case of Pile Group-I, the forces are applied to the direction of the median of the triangle, and for Pile Group-II, the forces are applied to other directional loads. From the test results, it is found that the resonant peaks of horizontal and rocking amplitudes for Pile Group-I are lower than Pile Group-II. In the case of resonant frequencies, the values of Pile Group-I are observed to be the same or a little bit higher as compared to Pile Group-II. It is found that the dynamic soil-pile-soil interaction effect is more prominent for Pile Group-II than for Pile Group-I. For numerical investigation, the continuum approach method is utilised with the inclusion of a dynamic group interaction factor to predict the dynamic coupled responses in terms of frequency and amplitude for these two soil-pile setups. To understand the behaviour of pile groups, boundary zone parameters and variations of impedance parameters (stiffness and damping) with operating frequencies are also measured using this theoretical approach.

A two-stage based model for partially-buried pile group response in cross-anisotropic saturated media adjacent to moving harmonic loads

The pile foundations are frequently affected by adjacent traffic loads except for general active loads. However, the dynamic responses of the pile groups under moving loads have been rarely reported before. In addition, the influence of material anisotropy is often neglected. In this paper, a three-dimensional (3D) analytical model for the dynamic analysis of partially buried pile groups in stratified saturated cross-anisotropic media under adjacent moving harmonic loadings is developed. Specifically, a 3D Bernoulli–Euler beam theory is adopted to simulate the monopile and then superimposed into the finite element (FE) formulation for the partially embedded pile groups. Subsequently, the basic solutions of layered saturated cross-anisotropic soils are derived by the analytical layer-element approach (ALEA). By combination with ALEA, the two-stage based boundary element (BE) equations for the pile-soil interface are obtained. Finally, by coupling the FE and BE formulations, the dynamical response equation of pile-soil is established. Based on the verification of the accuracy of the proposed methodology by comparisons with existing solutions and FE results from ABAQUS, the impacts of material anisotropy, pile buried length, loading velocity, and pile stiffness on the time-domain dynamic behavior of pile groups are analyzed. The results show that increasing the pile-buried ratio or pile stiffness reduces the magnitude of the dynamic response. Moreover, with the increase of material anisotropic parameters, the peak pile response decreases. And the peak dynamic response first increases and then reduces as the loading velocity increases.

Study on the behavior of short pile groups on soft soil with sand leveling using a smallscale physical model with schneebeli analog material

This paper examines the effectiveness of short piles on soft ground with leveling sand, using a 2D small model. The study focuses on the geology of the Mekong Delta, which consists of a thick layer of soft soil and a layer of leveling sand with a thickness of 2-5m. The use of small and short piles (less than 30x30 cm and 5m or less) is a viable option for low-rise buildings in such conditions. The model replaces the sandy soil with a Schneebeli analog material and the weak clay with EPS foam, while short reinforced concrete piles are replaced by steel bars of the square cross-section. The vertical load tests were conducted on groups of piles, with variable parameters such as pile spacing, s, and the distance from the pile tip to the boundary of two soil layers, H. The results show that when the pile spacing, s, is constant and the distance from the pile tip to the boundary of two soil layers, H, decreases, as well as the deformed soil area under the pile tip. Conversely, when the pile spacing, s, increases, the failure of the soil under the pile tip becomes more localized. The use of a footing increases the bearing capacity of the pile group but also increases the vertical strain of the foam layer in both vertical and horizontal directions. Overall, the study shows that reinforcing soil with short piles significantly improves bearing capacity, increasing it by 2.3 to 3.5 times compared to unreinforced soil.

Heat transfer performance of large energy pile group in a hybrid system subjected to imbalanced thermal load - A numerical investigation

Introduction
 When a energy pile system is coupled with other heating or/and cooling systems, determining the share of thermal demand that energy piles can meet is crucial in designing the size of each system. In the long term, imbalance in thermal load can affect the heat transfer performance of energy piles, and may also lead to annual accumulation of ground temperature over the years, ultimately causing system failure. Furthermore, the mechanical responses of energy piles are also affected by the temperature changes in the pile body and surrounding soil during operation. While Current researches have predominantly focused on mechanical response under temperature load, understanding the heat transfer performance of energy pile groups is equally necessary. Existing studies on heat transfer largely draw from ground source heat pump (GSHP) systems, despite differences in depth and diameter between energy piles and borehole heat exchangers (BHEs), particularly for closely spaced piles. To address this gap, we conducted a series of numerical experiments based on the Tsinghua Science Museum project to investigate the thermal behavior of energy pile group under annual, imbalanced load and the influence of pile spacing. Based on simulation results, we provide design recommendations on how to determine the proportion of heat load that can be carried by energy piles in hybrid systems.
 Method
 We utilized COMSOL software to conduct three-dimensional modeling of a single pile, and developed a two-dimensional model of a pile group using a self-programmed Matlab program. The accuracy of the model was evaluated by comparing it with the results obtained from energy pile field tests (thermal response tests and thermal performance tests) conducted in Shunyi, Beijing. Subsequently, we established two-dimensional and three-dimensional numerical models for the Tsinghua Science Museum project in Beijing. We performed a series of numerical experiments to investigate the behavior of energy piles under balanced and imbalanced temperature loads for one year. Furthermore, we simulated the thermal responses of energy pile groups with different pile spacings of 2m, 2.85m, and 4m.
 Results
 The cooling load surpasses the heating load causing an imbalanced load. The soil temperature rises noticeably by 2.6 °C compared to the initial state after an operation period of 1 year, indicating an undesirable phenomenon of soil heat accumulation. With continuous running over years, the system will fail due to the excessive soil temperature. Moreover, the heat exchange liquid temperature ranges from -4.35 ℃ to +39.65 ℃, which exceeds the acceptable range of 2 ℃ to 33 ℃. To address this concern, a hybrid system can be utilized where the energy pile system bears a balanced portion of the thermal load, and the auxiliary system bears the remaining load. Simulation under various thermal load proportions reveals a linear relationship between the maximum/minimum outlet temperature and the total heat exchange volume. An energy pile system undertaking 60% heating load and 40% cooling load can run stably for long periods. The soil temperature varies in a range of 8.5 ℃ to 17.9 ℃, while the pile body temperature has a variation range of 4.0 ℃ to 22.8 ℃ (Figure 1).
 The study results for various pile spacings are presented in Table 1. Pile spacing plays a significant role in soil heat accumulation and heat exchange fluid temperature. Despite an invariable pattern in the inflow and outflow temperature curves for varied pile
 spacing, the flow temperature range is significantly influenced. The smaller the spacing, the more prominent is the thermal accumulation in the soil, leading to larger changes in soil temperature and the flow temperature. During design simulation, if the range of flow temperature exceeds the limits of the energy pile system, it may present a safety risk during system operation. In such cases, increasing the pile spacing can render the system more reliable and safe.
 Conclusions
 (1) Whether the system can operate normally can be judged by whether the simulation result of the heat exchange liquid temperature exceeds the limit value. There is a linear relationship between the flow temperature and the total heat exchange. Therefore, the proportion of the load that the energy pile system can bear in the hybrid system can be determined. For the Tsinghua project, the energy pile system can bear 60% of the heating load and 40% of the cooling load.
 (2) The pile spacing affects the magnitude of variation in heat exchange fluid temperature by influencing the degree of heat accumulation in soil. If the range of flow temperature exceeds acceptable limits, it is advised to increase the pile spacing during the design phase to ensure the energy pile system can operate effectively.

Effects of Soil Crust on Seismic Failure Behavior of Pile Group–Bridge System during Liquefaction-Induced Lateral Spreading: Large-Scale Shake Table Experiments

Effects of Soil Crust on Seismic Failure Behavior of Pile Group–Bridge System during Liquefaction-Induced Lateral Spreading: Large-Scale Shake Table Experiments

Cyclic Degradation Parameters of Flow-Controlled Geomaterial for Pile Group Subjected to Torsional Loads

The pile groups support large foundation structures which often experience cyclic torsional loads. Several theoretical and experimental investigations were carried out on pile groups under axial and lateral cyclic loads; however, the study of the response of cyclic torsional loads on pile foundation groups remains elusive. This paper proposes a numerical scheme to capture the behavior of the symmetrical pile group in the flow-controlled geomaterial under cyclic torsional loading. Based on the numerical scheme, three-dimensional finite element analysis was performed to capture the nonlinear response of the pile group using a computational program. The results from the numerical analysis have been compared with the experimental observations. The peak twist and peak shear stress logarithmically decrease and then become asymptotic after a number of cycles of loading for a pile group (2,2) in a flow-controlled geomaterial. A set of cyclic degradation parameters of flow-controlled geomaterial is identified for the pile group and presented as a function of dilation.

Experimental Investigation for Group Efficiency of Driven Piles Embedded in Cohesionless Soil

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.

Experimental investigation of inclined compressive loading on a piled raft foundation

Transmission towers, skyscrapers, and offshore buildings have inclined compressive and uplift loads on their foundations. In addition to vertical loads, storage tanks and bridges face large horizontal loads. Pile and raft footings are used to increase the foundation system's load-carrying capacity and reduce vertical and lateral deflections. The behavior of piles and pile groups under inclined loads was investigated experimentally considering square raft, taking into account factors like pile length, soil density, and pile spacing. The results show that increasing pile length, pile spacing, and soil density enhance bearing capacity and decrease settlement. Piled rafts with L/d ratios of 10, 15, and 20 carry 39.62%, 43.62%, and 63.29% more than raft foundations. Load-bearing capacity increases 21% from 4d to 5d and 32% from 3d to 5d. The analysis of this model demonstrates that an improved pile and raft design in the pile-raft system enhances its efficiency. This foundation system offers a viable alternative for large constructions, potentially making it a more cost-effective option.

Thermo-visco-elastic analysis of thermomechanical behavior of energy pile groups considering time-dependent deformation characteristics of soils

Energy piles are increasingly being exploited worldwide for their dual functions of bearing structural loads and utilizing geothermal energy. However, scarce knowledge is available on the time-dependent thermomechanical behavior of energy pile groups constructed in soft soils. In this paper, an analytical approach was proposed for the thermomechanical analysis of energy pile groups considering the time-dependent deformation of viscoelastic soils and validated against field test data. The impact of the soil creep behavior on the axial load–displacement response and pile-soil-pile interaction of the energy piles was further investigated. Finally, a simplified method and design charts were provided for displacement estimation and design of energy pile groups in soft soils. The results indicated that the displacement of energy piles would change with time until stabilization because of the viscous properties of the soil. The interaction between energy piles was directly related to the pile-soil stiffness ratio, the soil viscosity coefficient, the pile slenderness ratio, the pile spacing, and the number of piles. The soil creep behavior would result in a decrease in the displacement ratio of energy pile groups under thermal loading and an increase under mechanical loading.

Numerical investigations on effects of mechanical and geometrical characteristics on thermally induced group behavior of field-scale energy piles

Energy pile groups generally exhibit different thermomechanical behavior from single energy piles. Aiming to investigate the group behavior of energy piles, three-dimensional numerical models were developed and validated against field test data for a 2 × 2 energy pile-raft foundation. The validated models were subsequently adopted to comparatively analyze the thermomechanical behavior of pile groups operating either partially or fully. The results highlighted that the group action effects would induce lower thermal stress and greater head displacement imposed upon piles. Partially operating grouped piles exhibited differential displacement, thus inducing group tilt in the raft. Besides, parametric studies were made to evaluate the effects of mechanical and geometrical parameters on the group behavior of energy piles. The effects of soil thermal expansion were directly correlated with the heating extent of the soil. Under geological conditions with high soil thermal expansion coefficients, heating-induced tensile stresses and excessive head displacements could occur during the long-term operation of multiple piles. Higher soil elastic modulus resulted in higher restrictions on the thermal movement of piles, thus reducing the head displacement and group tilt, which was considered beneficial in practice. Special attention should be paid to the group action effects for closely-spaced energy pile-raft foundations.

Lateral response of a pile group embedded in the transversely isotropic saturated soil due to surcharge loads

This paper investigates the behavior of pile groups in the transversely isotropic saturated soil under an adjacent surcharge load using a coupling method. The analytical layer-element theory is utilized to the transversely isotropic saturated soil model, and the fundamental solutions of the soil are applied to derive the soil flexibility matrices. And the FEM is used for the piles modeled as Bernoulli–Euler beams considering pile–pile interaction. Then, the dynamic response equations of pile groups are derived by using the FEM–BEM coupled method and considering pile-soil boundary coordination condition. The results of the present model compared well with those in existing solutions. Numerical examples are presented to examine the influences of the soils’ transverse isotropy, the magnitude of the surcharge load, the pile's physical properties and the distance between the load and the pile on the behavior of pile groups. It is observed that as the surcharge load grows, the position of the pile maximum displacement response changes from the middle of the soft soil layer to the top of the pile. The impact of the surcharge load is not significant when the loading action distance is greater than twice the thickness of soft soil layer. Furthermore, relatively large bending moments appear in the middle of the soft soil layer and at the interface of the soil layers.

Numerical evaluations on the effects of different factors on thermo- mechanical behaviour of an energy pile group

Energy pile is a kind of economical and efficient underground energy structure. Obtaining the effects of different factors on the performance of energy pile help to improve the working efficiency of the energy pile. However, the thermo-mechanical behaviour of energy pile groups are more complex than that in single energy pile due to the mutual interference of energy pile groups. In this paper, the energy pile group with the layout of 3 × 3 was simulated by a 3-D numerical model. The influences of soil type, pile spacing, pile material performance and pile arrangement form on the thermo-mechanical behaviour of the energy pile group were investigated. The results show that increasing pile spacing can not only improve the thermal performance of energy pile group but also reduce the pile displacement, but it will lead to the increase of pile axial force because of the weakening of pile group effect. The thermal performance of energy pile group is the highest under the rock-soil condition, followed by sand and clay. However, the pile displacement is the largest when the soil type is sand, followed by clay, and the rock-soil is the smallest, and the influence of soil type on pile axial force is just opposite to pile displacement. At the same time, the increase of thermal conductivity of pile material benefits to heat transfer performance of energy pile group, but it also aggravates the heat accumulation and results in a larger top displacement and axial force of pile. As for concrete compression modulus, increasing the concrete compression modulus can increase the axial force of pile, but the change of concrete compression modulus has no effect on the pile displacement. In terms of layout of energy pile group, the per unit soil volume heat exchange rate of energy pile group in the cross arrangement form is larger than that in sequential arrangement form. However, the variation range of soil temperature in the cross arrangement form is larger than that in the sequential arrangement form, thus increasing pile displacement and reducing pile axial force.

Effect of Allowable Vertical Load and Length/Diameter Ratio (L/D) on Behavior of Pile Group Subjected to Torsion

Some structures such as tall buildings, offshore platforms, and bridge bents are subjected to lateral loads of considerable magnitude due to wind and wave actions, ship impacts, or high-speed vehicles. Significant torsional forces can be transferred to the foundation piles by virtue of eccentric lateral loading. The testing program of this study includes one group consists of 3 piles, four percentages of allowable vertical load were used (0%, 25%, 50%, and 100%) with two L/D ratios 20 and 30, vertical allowable load 110 N for L/D = 20 and 156 N for L/D = 30. The results obtained indicate that the torsional capacity for pile group increases with increasing the percentage of allowable vertical load, when the percentage of allowable vertical load was 100% and L/D ratio (20) the torsional capacity for pile group increases about 42% if compared with the torsional capacity when the percentage of allowable vertical load was 0% for the same L/D ratio. Also increasing L/D ratio leads to increasing the torsional capacity of pile group, when the percentage of allowable vertical load is 100% and L/D ratio (30), the torsional capacity for pile group increased about 51% if compared with torsional capacity when L/D ratio was (20) for the same groups and the same percentage of allowable vertical load. At failure the twist angle for pile group remain constant 3° when the percentage of allowable load change from 0% to 100 and L/D ratio 20, while it decreases from 2.9° to 2.7° when the percentage of allowable load change from 0% to 100% respectively and L/D ratio 30.