Piles In Cohesionless Soils Research Articles

Lateral capacity of group helical piles in sand: an experimental and numerical study for sustainable infrastructures

ABSTRACT Helical piles are integral to support resilient infrastructures subjected to axial and lateral loads. This study explored model-scale testing of group helical piles in cohesionless soil in a rigid box. Initially, a total load of 5000 N is applied to the pile raft model, followed by a lateral load of 1600 N. Nine model tests are performed with a configuration of four, six, and nine, having conventional, single helical, and double helical piles. The data logger facilitated data collection using MATLAB software, and the load was increased at rate of approximately 4.9N/sec. The computed average reduction in the displacement of Single and Double Helical Pile Rafts is observed as 36.43% and 55.71%, respectively, compared to Conventional Pile Rafts. The addition of a second helix further reduced lateral displacement by 19.27%. Numerical analysis on Plaxis-3d showed that the experimental and numerical results are in good agreement.

Using geopolymer coated and uncoated geotextile as a hybrid method to improve uplift capacity of screw piles in cohesionless soil

In this research, experimental studies and numerical analyses were carried out to investigate how the usage of geotextile and geopolymer coated geotextile as a hybrid method changes the uplift behavior of the screw piles in cohesionless soil. In this context, traditional pile behavior, the effect of different number of helixes and embedment depths on screw piles, the mechanism of geotextile and the effects of geopolymer coating process were investigated. In addition, experimental studies were modeled by using Plaxis 3D and parametric studies were carried out after verification between the results of experimental study and numerical analysis. In the numerical analysis, a segmented helix model consisting of four 90-degree slices was developed instead of the planar helixes commonly used in the literature. For further investigation of the effectiveness of hybrid method, parameters such as improvement ratios and breakout factors were calculated. When the results obtained within the scope of the study were evaluated, the geopolymer coating process increased the bearing capacity of the geotextile by 24 % at 27 % less elongation. It was also seen that uncoated and geopolymer coated geotextile increased the screw pile performance in terms of improvement ratios by 294 % and 364 %, respectively.

Analysis of the Variability of Axial Bearing Capacity Piles in Cohesionless Soil in the Development of Meyerhof Formula

Analysis of the Variability of Axial Bearing Capacity Piles in Cohesionless Soil in the Development of Meyerhof Formula

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.

Nonlinear response of laterally cyclic loaded pile in cohesionless soil based on conical strain wedge model

The response to environmental lateral cyclic loads is an important design consideration for offshore piles installed in sand. This paper proposes a novel conical strain wedge (CSW) model to simulate the pile-cohesionless soil interaction under lateral cyclic loads. The CSW model enhances the depiction of passive compression soil zone resistance and failure pattern compared to the conventional strain wedge (SW). The developed model is incorporated in a simplified and efficient method to calculate the nonlinear pile response to lateral cyclic loads. The performance of the developed theoretical model is validated by comparing its predictions with observations from several experimental studies reported in the literature. The validated CSW model and its solutions are then employed to elucidate the performance characteristics of the pile-soil system under cyclic loading. The results revealed that: (1) the degradation of soil stiffness is more pronounced at the onset of cyclic loading and the rate of increase in pile response due to degradation diminishes with the increase in the number of loading cycles; (2) as the cyclic load amplitude increases, the increase in pile displacement becomes increasingly severe; (3) the number of loading cycles has greater influence on the response of piles with lower flexural stiffness; and (4) the effect of soil shear strength on the pile displacement becomes significant as the number of loading cycles increases, whereas its effect on the pile maximum bending moment diminishes gradually.

Experimental and analytical assessment of the pullout capacity of axially loaded under-reamed pile in cohesionless soil

Experimental and analytical assessment of the pullout capacity of axially loaded under-reamed pile in cohesionless soil

Performance-Based Design Method for Multiple Helices of Helical Pile in Cohesionless Soil

Multiple helices are being used frequently in helical pile applications nowadays. This paper presents multiple helices on simplified field design charts for small diameter helical piles that relate service compressive load and soil parameters as a group with the pile parameters. This study conducts an extensive three-dimensional nonlinear finite element analysis (FEA) study on multiple helices piles using the FEA program PLAXIS to evaluate helices’ performance subjected to axial compressive loads. A calibrated and verified numerical model uses full-scale load testing data of multiple helices from practical experience. This paper compiled numerical results from 495 models to propose an extension of the chart-based design. Here, the optimized combination of multiple helices will be the output of the design chart for soil type, service load, and allowable displacement as input. At the end of this paper, the design charts for double and triple helices are validated for cohesionless soil. The correlation square, R2, ranges from 0.69 to 0.86 for cohesionless soil. The mean Qc/ Qm is 0.90 for double helices and 1.04 for triple helices. Preliminary evaluation suggests that the method performs well. The authors believe that this study will permit engineers and state agencies to better understand the behavior of multiple helices, resulting in a more resilient approach in designing small diameter helical piles for a compressive load.

Numerical evaluation of slope effect on soil–pile interaction in seismic analysis

This study aims to evaluate the slope effect on the behavior of soil–pile interface in the lateral direction, which is a factor governing the seismic response of pile-supported structures. A series of numerical simulations of a single pile in cohesionless soil subjected to lateral loading were performed by considering various slope configurations, soil densities, and loading directions. The lateral and confining forces acting at the soil–pile interface increased at a comparable rate under increasingly lateral loading. The ratio of the ultimate lateral force to the ultimate confining force was defined as a lateral interface-force ratio, which was introduced to quantify the slope effect on the strength parameter of the lateral soil–pile interface. The lateral interface–force ratio increased together with embedment depth and maintained a constant value below a certain depth corresponding to the change in failure mechanism from the wedge mode to the flow mode. In addition, an interface model of the soil–pile separation due to the slope failure was developed for the numerical analysis of piles in the cohesionless soil. Finally, the proposed lateral soil–pile interface was implemented via a three-dimensional numerical simulation of a dynamic centrifuge test for the validation work. The good agreement between the numerical simulation and experimental data indicates the reasonable applicability of the proposed interface properties.

Full-Scale Axial Load Response of Jetted and Grouted Precast Piles in Cohesionless Soils

Full-Scale Axial Load Response of Jetted and Grouted Precast Piles in Cohesionless Soils

Single pile in cohesionless soil in sloping ground under lateral loading

Pile foundations are adopted if a soil of low bearing capacity extends to a considerable depth or if the structure is heavy or the settlement due to the structure is large. It transfers the load to a strong, stable stratum of soil. The behaviour of soil in slope and piles embedded in it is an elaborated soil-structure interaction problem. This paper presents the results of experimental investigations on a single pile subjected to lateral load by varying relative density of soil in the horizontal and sloping ground with three different slopes of 1V: 2H, 1V: 2.5H and 1V: 3H. The lateral load carrying capacity of the pile is considerably decreased when the lateral load is applied in the direction of the slope. It is found that the lateral load carrying capacity of the pile is increased for higher relative density of sand and the lateral capacity of the pile is greater in flatter slope than in steeper slope. The effect of different slopes on normalized lateral load versus displacement for the lateral load applied in the direction along and against slope is quantified. A set of empirical equations are formulated to determine the deflection, fixity depth and moment for the pile in sloping ground.

Numerical Analysis of Laterally Loaded Long Piles in Cohesionless Soil

The capability of piles to withstand horizontal loads is a major design issue. The current research work aims to investigate numerically the responses of laterally loaded piles at working load employing the concept of a beam-on-Winkler-foundation model. The governing differential equation for a laterally loaded pile on elastic subgrade is derived. Based on Legendre-Galerkin method and Runge-Kutta formulas of order four and five, the flexural equation of long piles embedded in homogeneous sandy soils with modulus of subgrade reaction linearly variable with depth is solved for both free- and fixed-headed piles. Mathematica, as one of the world's leading computational software, was employed for the implementation of solutions. The proposed numerical techniques provide the responses for the entire pile length under the applied lateral load. The utilized numerical approaches are validated against experimental and analytical results of previously published works showing a more accurate estimation of the response of laterally loaded piles. Therefore, the proposed approaches can maintain both mathematical simplicity and comparable accuracy with the experimental results.

Evaluation of the Static Design Procedure in the Canadian Foundation Engineering Manual for Piles in Cohesionless Soil

Piles provide a convenient solution for heavy structures, where the foundation soil bearing capacity, or the tolerable settlement may be exceeded due to the applied loads. In cohesionless soils, the two frequently used pile installation methods are driving and drilling (or boring). This paper reviews the results of a large database of pile load tests of driven and drilled piles in cohesionless soils at various locations worldwide. The load test results are compared with the static analysis design method for single piles recommended in the Canadian Foundation Engineering Manual (CFEM) and other codes and standards such as the American Association of State Highway and Transportation Officials, Federal Highway Administration, American Petroleum Institute, Eurocode, and the Naval Facilities Engineering Command. An improved pile design procedure is proposed linking the pile design coefficients (β) and (Nt) to the friction angle of the soil, rather than employing the generalized soil type grouping scheme previously used in the CFEM. This improvement included in the new version of the CFEM 2021 produces a more unified value of the pile capacity calculated by different designers, reducing the obtained design capacity discrepancies.

Seismic response of end-bearing fibre-reinforced polymer (FRP) piles in cohesionless soils

Seismic response of end-bearing fibre-reinforced polymer (FRP) piles in cohesionless soils

Ultimate lateral capacity of single piles in cohesionless soils

Ultimate lateral capacity of single piles in cohesionless soils

Lateral soil resistance of rigid pile in cohesionless soil on slope

A modified method is proposed in this paper to evaluate the ultimate lateral soil resistance of rigid piles in cohesionless soil on slopes, which is based on wedge-equilibrium analysis. The method assumes that the soil resistance in front of the pile is compressed under the lateral load and that a wedge is formed without damage. The frontal soil resistance and side shear resistance are mainly considered and the response of the lateral resistance rigid pile in the cohesionless soil slope is described by hyperbola p-y curves. To validate the modified theoretical solution, the model is compared with the test results of the field pile and numerical simulation results. Combined with numerical simulation, the effect of slope angles on the lateral resistance around the pile is discussed. The results show that the modified theoretical solution is feasible for rigid piles in cohesionless soil on slopes.

Uplift Capacity Prediction of Continuous Helix Piles in Cohesionless Soils Using Cone Penetrometer Tests

Full-scale tests were performed on continuous helix piles in cohesionless soils. An investigation on the failure mechanisms is presented in this article. Prediction methods are also used for the estimation of the piles uplift capacity using CPT tests. For all tested piles, a cylindrical failure surface was found. The load–displacement curves highlighted that both the inter-helix spacing ratio S/Dh and the helix diameter Dh influence the uplift capacity. Using a statistical analysis, a new prediction method based on the CPT tests is proposed. This method permits to obtain the ultimate uplift capacity of continuous helix piles according to their geometrical parameters such as: inter-helix spacing ratio S/Dh, helix diameter Dh and shaft diameter d. The applicability of the proposed method was evaluated using four statistical criteria: (1) the best-fit line, (2) the arithmetic mean and standard deviation, (3) the cumulative probabilities, and (4) the log-normal and histogram distributions. Based on these criteria, the following conclusion can be made. The proposed method: (1) tends to underestimate the measured capacity of less than 1%, (2) the prediction probability of the ultimate load capacity within a 20% accuracy level is close to $$96\%$$ .

Non - prismatic model for laterally loaded pile in granular soil resisted by ultimate lateral reaction

ABSTRACT This paper introduces a non-prismatic model for laterally loaded piles in cohesionless soil. The response of the laterally loaded pile may not be accurate by modelling the pile as a prismatic member, especially when the soil lateral resistance is considered linear at the heavy lateral loads. The governing differential equation for the new non-prismatic model is derived considering the ultimate lateral soil reaction and it is solved using the differential quadrature method. Formulas, which determine the geometry of the non-prismatic model, are introduced for both driven and bored piles considering both free head and fixed head conditions. The proposed model is verified by field experimental results and theoretical results for both bored and driven piles which show a good agreement. The new model becomes more effective than the traditional prismatic model after lateral load reaches 41.6667% of the lateral load capacity of both bored and driven piles.

Optimal Plastic Analysis and Design of Pile Foundations Under Reliable Conditions

In this research, in order to evaluate the plastic limit load and also plastic design parameters of the long pile foundations subjected to horizontal loads, shakedown method is applied. In carrying out shakedown analysis and design methods, large plastic deformations and residual displacements could develop in the pile foundation which might lead to the failure of the structure. For this reason, complementary strain energy of residual forces proposed as a limit condition to control the plastic deformation of the pile structure. Furthermore, considering the uncertainties (strength, manufacturing, geometry) the limit conditions on the complementary strain energy of residual forces are assumed randomly and the reliability condition was formed by the use of the strict reliability index. The influence of the limit conditions on the plastic limit load and design parameters of the long pile in cohesionless soil subjected to lateral load were investigated and limit curves for shakedown load factors are presented. The numerical results show that the probabilistic given limit conditions on the complementary strain energy of residual forces have significant influence on the load bearing limit and the design parameters of pile foundations. The formulations of the reliability based problems lead to mathematical programming which were carried out by the use of non-linear algorithm.

Frequency- and intensity-dependent impedance functions of laterally loaded single piles in cohesionless soil

This paper investigates the frequency-dependent pile-head impedance characteristics of a model soil-pile foundation system under large amplitude loads, inducing soil yielding. Testing was conducted on a scaled single pile embedded in sand under a 1g condition. A laminar shear box mounted on a unidirectional shaking table was used to house the soil-pile foundation system. Quasi-static loads and dynamic loads were applied to obtain the force–displacement relationships and pile-head impedance functions, respectively, through the pile head connected to a loading actuator providing fixity to the pile head in all directions, except horizontal. In the quasi-static case, loads with three different velocities were applied to study the rate-dependent characteristics of the lateral bearing capacity of the pile. The Stereo-PIV system was employed to measure the surface soil displacement around the pile. The lateral bearing capacity changed with the loading velocity, but the soil near the pile showed a consistent failure pattern despite a significant change in velocity. Lateral pile-head dynamic impedance functions were obtained for low-to-high amplitude harmonic loading for a wide range of frequencies. The dynamic stiffness was seen to converge to that of the secant static stiffness with an increase in the amplitude of the dynamic loading for all the excitation frequencies.

A p–y Model for Large Diameter Monopiles in Sands Subjected to Lateral Loading under Static and Long-Term Cyclic Conditions

The design of large diameter monopiles subjected to cyclic lateral loading is of interest in many applications, such as, for example, in the offshore wind energy industry. Engineering design methods to estimate the deflection of these structures are required for this purpose. In the present work, a p–y model for large diameter monopiles subjected to lateral loading is proposed. The model considers a pile in cohesionless soil subjected to static and long-term cyclic loading. Its formulation features the consideration of nonlinear relations for the ultimate soil resistance pu and the initial subgrade modulus Epy0 among the soil depth and a cyclic factor that accounts for the effect of the soil density and loading amplitude. A relation is also proposed to account for a base shear force at the tip of the monopile. The proposed relations were employed and solved under the beam on nonlinear Winkler foundation (BNWF) approach and were adjusted to simulate a number of three-dimensional (3D) finite-element (FE) models accurately, accounting for variations on pile geometry, soil properties, and loading conditions. In the end, the performance of the proposed relations was evaluated through the comparison with a field test and a centrifuge test.