Pile Soil Research Articles

FIELD INVESTIGATION OF THE INITIAL SETTLEMENTS OF PILE NOT CONNECTED TO THE RAFT IN A COMBINED RAFT-PILE FOUNDATION

Problem statement. The patented useful model for the design of the combined raft-pile foundation (CRPF), consisting of a raft part and piles, with a gap of height Δ is made between the raft part and the piles. That is, the distribution of settlements (resistances) of the soil base under the raft and then under the piles (after the hinged connection of the piles with the raft) is assumed, based on the condition of not exceeding the maximum allowable settlement su of the building or structure. The initial settlement of the piles, which arises from the effect of the additional loading (negative) friction force acting on their lateral surface within the compressible layer during the pressure loading of the soil base raft part, must additionally be taken into account to correct the value of the gap Δ. The purpose of the article is to conduct field investigation of the piles initial settlements under the action of additional loading (negative) friction forces acting along their lateral surface in a large-scale combined raft-pile foundation to identify new dependencies and generalize them. Conclusions. On the basis of field studies, a qualitatively new dependence of the pile deformation on the action of additional ground friction forces has been revealed, which shows the "pile up-slip effect" due to the excess of resistance forces on its lateral surface with manifestation of inverse (elastic) deformations of the ground base of the pile. On the basis of field investigation, a qualitatively new dependence of the pile deformation on the effect of soil additional loading (negative) friction forces was revealed, which shows the “effect of the pile slipping upwards” due to exceeding the negative friction forces the resistance forces on its lateral surface with the manifestation of reverse (elastic) deformations of the pile soil base, which indicates the need to take this phenomenon into account when determining the gap between the raft part and the piles in projects of similar CRPF.

Numerical and Experimental Analysis of Seismic Soil Pile Structure Interaction

The fundamental design of the piles is finished by static analysis, but particularly in seismically dynamic locales, the last configuration requires dynamic study. Dynamic soil-pile-structure interaction analyses require the stress-strain conduct of soils under dynamic loading conditions. The material nonlinearity can be addressed by comparable linear or completely nonlinear strategies. The correlation of these methodologies in the free-field site reaction analyses has been concentrated in recent years. In any case, the impacts on the soil-pile-structure interaction analyses have not been illustrated. In this study, a well-known centrifuge test was demonstrated and analyzed in the frequency domain (ACS SASSI) and in the time-domain (FLAC 3D) for equivalent-linear and fully nonlinear methods, respectively. The soil space was displayed with solid components in the projects, while the structural beam elements were utilized for the pile and the superstructure. The scaled speed acceleration time history of the Kobe earthquake was applied to the lower part of the soil-pile-structure model, and the acceleration-time histories were acquired at the ground surface and the superstructure. The outcomes obtained from the ACS SASSI and the FLAC 3D were compared with the centrifuge test. As per the outcomes, the peak ground and the superstructure accelerations were close to the experimental outcomes; however, the periods at the peak spectral accelerations were slightly different from the test results. The difference is more pronounced in SASSI than in FLAC, which may be attributed to the solution methods. Apart from the solution methods, the difference might be the inability to fully simulate the complex centrifuge test.

Effect of Relative Stiffness of Pile and Soil on Pile Group Effect

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.

Gentle Driving of Piles (GDP) at a sandy site combining axial and torsional vibrations: Part II - cyclic/dynamic lateral loading tests

Gentle Driving of Piles (GDP) is a new technology for the vibratory installation of tubular (mono)piles. Its founding principle is that both efficient installation and low noise emission can be achieved by applying to the pile a combination of axial and torsional vibrations. Preliminary development and demonstration of the proposed technology are the main objectives of the GDP research programme. To this end, onshore medium-scale tests in sand have been performed on piles installed using both impact and vibratory driving methods (including GDP). While the results of the installation tests are presented by Tsetas et al. (2023), this work focuses on the post-installation performance of GDP-driven piles under a sequence of slow/large-amplitude (cyclic) and faster/low-amplitude (dynamic) load parcels. The field data point out the influence of onshore unsaturated soil conditions, which result in complex cyclic pile stiffness trends due to the interplay of pile–soil gapping and soil’s fabric changes. The pile stiffness under small-amplitude vibrations is strongly correlated with the previous response to large load cycles, and noticeably frequency-dependent for load cycles with a period lower than 1 s. Overall, the post-installation performance of GDP-driven piles appears to be satisfactory, which encourages further development and demonstration at full scale.

An extension of Broms’ theory to unsaturated soils

This paper presents an analytical method to predict the horizontal capacity of piles in unsaturated soils. The method extends the well-known Broms approach to account for the combined effect of the groundwater table and the apparent cohesion of the unsaturated soil above it. Similar to the original formulation of Broms, the present method calculates the maximum horizontal force and bending moment that can be sustained by the pile for two different head fixities (i.e. free-head and restrained-head) as a function of non-dimensional parameters that depend on the geometry and flexural resistance of the pile (i.e. yielding moment), the soil resistance and the type of failure mechanism (i.e. short, intermediate or long pile). Compared to Broms’ solution, the method introduces additional non-dimensional parameters that relate the water retention behaviour of the soil to the geometry of the pile. The proposed formulation accurately predicts the lateral capacity of piles as experimentally measured in previous works. Results confirm that consideration of the partially saturated state of the soil above the groundwater table is essential for a reliable estimate of the horizontal capacity of piles.

Monopile installation in clay and subsequent response to millions of lateral load cycles

The installation-induced changes in the state of clayey soils caused by pile driving processes are investigated numerically. Hydro-mechanically coupled Coupled-Eulerian–Lagrangian analyses are carried out for this purpose. After installation, the piles are subjected to one million lateral loading cycles using a novel high-cycle accumulation (HCA) model for clay implemented in an in-house code, modelling loading conditions to which piles are subjected in the offshore environment. Consistent with the results of field tests, it is found that higher values of initial overconsolidation ratio result in a greater increase in radial effective stress during the installation process. Compared to simulations neglecting the installation process, jacked piles show less accumulation of deformations when subjected to lateral cyclic loading, especially for a larger number of load cycles and for initially overconsolidated soil. It is concluded that the assumption of wished-in-place conditions is conservative in terms of pile rotation in most cases, while the stiffness of the soil–pile system at small rotations is comparable for jacked and wished-in-place piles.

An analytical method to evaluate the capacity of laterally loaded piles in unsaturated soils

The growing pressures of climate change, increased usage and unprecedented geo-hazards impose a modification in the way civil engineering structures are designed and constructed. This isparticularly true for geotechnical works, which are very sensitive to changes of environmental conditions. For instance, the response of a pile under lateral loading is strongly influenced by the stiffness and strength of the first few metres of soil below the surface, which are often partly saturated. To consider this effect, the present paper describes an analytical method, which extends the well-known Broms approach to predict thelateral capacity of piles in unsaturated soils. More specifically, the proposed method considers the combined effects of the position of the ground water table and the extra strength of the partially saturated soil above it. Compared to Broms approach, the solution introduces four additional non-dimensional parameters that relate the soil-water retention behaviour to the geometry of the pile. The method provides a direct evaluation of the lateral pile capacity in partly saturated soils, which can be used as a basis for more accurate design.

Localized shear strength mobilization at geosynthetic interfaces caused by spreading soil upslope

Localized interface shear strength failures have occurred during placement and spreading of cover soils on top of geosynthetic layers on slopes using construction equipment, typically bulldozers (‘dozers’). The mechanisms of these types of failures are rarely considered and evaluated in design reports and calculations. The present paper intends to improve upon the analyses presented in previous literature references by providing straightforward equations of static equilibrium that the user can easily input into a spreadsheet to model various dozer sizes, geometries, and shear strengths. The present paper analyzes the shear forces below the soil pile being pushed, as well as below the dozer tracks, which has not been previously considered in the available literature. The equations provided in the present paper should be useful for design engineers to avoid slippage on slopes where dozers are spreading soil materials over geosynthetics, or for forensic experts who evaluate why slippage may have occurred.

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

Dynamic Behavior of Helical Piles in Dry and Liquefiable Soils using Scaled Shake Table Tests

The dynamic behavior of helical piles with different numbers of helices as well as a single slender shaft was examined through a series of scaled shake table tests. Multiple shakings were applied during each test series to evaluate the seismic behavior of the helical piles and the slender shaft considering different response parameters. A considerable ground settlement was observed during the first shaking in each test series, whereas negligible helical pile and slender shaft settlements were measured during all tests. The dynamic response of the helical piles was evaluated based on their bending moment variation along the depth and various measured response parameters at the model superstructure level. The bending moment variation indicated a similar trend along the depth for the helical piles and the slender shaft: the maximum moment was consistently observed at the boundary between dense and liquefiable layers. The observed bending moments along the depth increased with increases in input motion amplitude and superstructure weight. Densification of the liquefiable layer during different test series reduced the maximum bending moment along the depth for each pile due to increased relative density. Increasing the number of helices enhanced the dynamic performance of the helical piles compared to the slender shaft in terms of maximum bending moment, maximum horizontal displacement, residual horizontal displacement, and superstructure acceleration in different ground conditions.

Impact of Suction on the Near Surface Lateral Soil Response using Centrifuge Modeling

Recent studies have shown that unsaturated soils lead to greater lateral pile capacity. This study aims to experimentally assess how suction stress affects the lateral response of piles in unsaturated cohesionless soil. Two centrifuge tests were performed at 50 g to evaluate the effect of suction stress in the soil. Lateral loads were applied monotonically on a single free-head pile in a displacement-controlledmanner to a maximum pile head displacement of 0.44 m. The first test was conducted on fully saturated cohesionless soil, while the second test was performed in an unsaturated state with a mixed unsaturatedsaturated soil layer. The water table was lowered to about 0.12 times the embedded pile depth to ensure an unsaturated condition in the zone closer to the surface of the soil. Lateral response assessment indicates that the unsaturated soil influenced the pile head response, leading to larger applied lateral loads for similar pile displacements in comparison to the fully saturated soil test. Experimental findings reveal that suction stress played a meaningful role in magnitudes of pile bending moments and lateral resistances for unsaturated cohesionless soils.

Numerical study on vertical bearing behavior of pedestal pile’s embedded in fine grained soils

The aim here is to investigate the behavior of pedestal/belled piles present in soft clay soil through numerical analysis using Plaxis 2D software. The method used here was based on finite element analysis to simulate pile-soil interactionandtoanalyzethepile’sbehaviorunderdifferentloadsbyvaryingparameterssuchaslengthembedded inthesoilandalsothediameteroftheshaft.Theresultsindicatethatincreaseinlengthaswellastheshaftdiameter of the pile enhances the pile’s load-bearing capacity. The study also shows that the pedestal/bell pile can improve the pile’s performance in soft clay soil by reducing the soil’s displacement and increasing the pile’s axial capacity in comparison to conventional straight pile. The study concludes that the pedestal/belled pile is a promising option for the foundation of structures in soft clay soil, and the numerical analysis using Plaxis 2D software can provide quick and reliable predictions of the pile’s behavior. The study’s findings can be useful for optimizing the design of pedestal/belled piles in soft clay soil and improving the efficiency and safety of foundation systems in similar geotechnical conditions.

The performance of laterally loaded piles in layered sandy soils under variable degree of saturation

This paper investigates the capacity of a single laterally loaded pile in single- and multi-layered sandy soils under dry, unsaturated and saturated conditions for a wide range of void ratios. Two Linear ariable Differential Transformers (LVDT) were employed to measure lateral displacements. For unsaturated tests, on one layer and two layered sandy soils, suction was controlled using the hanging column technique. Two different suction levels were applied to the soils. The results demonstrated that, the capacity of a single laterally loaded pile in single- and multi-layered sandy soils, under unsaturated conditions, were greater than those in dry and saturated conditions for loose, medium and dense states. Comparison between experimental data for unsaturated tests and several proposed mathematical expressions in the literature for calculating the capacity of a single laterally loaded pile in sandy soils showed a significantly good fit between measured and predicted values of the capacity of the piles where Bishop’s stress is used in the expressions instead of effective stress, confirming the importance of inclusion of suction and degree of saturation in mathematical models when unsaturated conditions of soils were investigated.

Evaluation of the Bearing Capacity of the Board Pile in Collapsible Soil using A Laboratory Model

The pile’s ultimate capacity or failure load must be computed by some criteria using load-settlement curve data gathered during the pile load test. Many scholars have proposed several approaches for evaluating the pile’s ultimate capacity in the past. This study compared different failure criteria to predict the ultimate load capacity for piles with two different lengths-to-diameter ratios embedded in gypseous soil with gypsum content of 60% under soaked and unsoaked conditions. Two types of piles were used. Floating pile and end-bearing pile. Davisson, Brinch Hansen’s 80 percent, Chin-Kondner, Mazurkiewicz’s, and Brinch Hansen’s 90 methods that were used in this study predict a higher value of the ultimate pile capacity, whereas the Decourt Extrapolation method gave fluctuated value. Fuller and Hoy’s, Butler and Hoy’s methods give far away value from realistic. On the other hand, Shen’s, ASTM, Terzaghi, and DeBeer’s methods predicted an acceptable and realistic value. The failure criterion of (15%D) where (D) is pile diameter according to(ASTM D-1143) was adopted in this type of soil.

Horizontally loaded piles in saline soils

The influence of the aggressiveness of the environment and the variability of the saline soil properties on the operation of horizontally loaded piles is studied. The design scheme is taken in the form of a multi-span beam with a variable cross-section formed due to concrete corrosion (Winkler model) and stiffness coefficients. The calculated value of the variable modulus of deformation and the stiffness coefficients of the pile are determined based on the conditions of the construction area and the properties of saline soils.

Displacement analysis of single pile in soft soil with ground load

The pile will have a large lateral displacement in soft soil under the role of heaped load. Based on Biot consolidation theory, combined with a certain highway project, a three-dimensional FEM model was established, the process that the soil lateral load deformation lead to the pile side displacement was simulated. On the ground of the former result, the influence factors for the displacement of pile top and the pile displacement field distribution are analysed. The results shows that, the building load area, load grade and the distance from loading area to pile have a major influence on the pile side displacement. On the other hand, the load on pile top have a very small contribution for stability of anti-side displacement. The buildings nearby the area of pile foundation should be given attention in practical engineering.

Geotechnical performance of combined stone columns and piles capped with reinforced concrete raft foundation in soft clay soil

Stone columns consist of granular material compacted in long cylindrical holes. They are used for improving the strength and consolidation characteristics of compressible soils. However, they are still less effective at supporting heavy loads, since they still cannot transfer applied stresses to deeper layers of soil. The main objective of this numerical study was to investigate the geotechnical performance of a combined foundation system composed of stone columns and piles grouped together under a rigid raft foundation in compressible soil. The failure mechanism of this hybrid foundation system was examined, and configurations optimizing the performance of the combined foundation system were explored. An analytical model was developed for predicting the ultimate carrying capacity of the combined system in compressible soils. It was deduced that combining stone columns and piles in one foundation system improved considerably the system’s carrying capacity. Moreover, the uppermost improvement was observed when the piles were installed on the periphery or edge of the raft foundation, while stones columns were placed at the center area of the raft. The failure of the combined foundation system started from the center of the raft and noticeably extended to its edges. Due to the presence of stone columns in the combined foundation system, the piles did not interact. The areas affected or influenced by the soil–pile interaction also did not overlap.

2ZXS-2 哈密瓜移栽机的关键部件设计与试验

Aiming at the trouble of low survival rate of cantaloupe seedling in hyperthermia, drought and dry land in Turpan region of China, the existing transplanting machine is the key to mechanized and non-destructive transportation and planting of large plants of young tender melon seedlings, root water injection, and precise soil piling in planting holes，and other technical difficulties. The design of mulch film planting cantaloupe transplanter for laying pipes belts and membranes, watering and transplanting, which can complete rotary tillage, spreading drip irrigation belts, laying mulch and covering the soil around the membrane, transplanting pot seedlings on the membrane, and water injection at the bottom. This machine puts the water injection pipeline under the inner side of the transplanter, and through the multi-point linkage electric control, the seedling preservation water is injected into the bottom of the seedlings pot while the seedlings are transferred, which not only ensures the survival rate of the melon seedlings, but also an accurate piling of the planting hole is realized. The technology of transplanting with water and piled soil for planting holes effectively solved the technical problems of mechanized transplanting of cantaloupe under high temperature and arid climate conditions in Turpan. After the cantaloupe seedlings were transplanted in dry land, the probability of survival was more than 96.9% after seven point five hours of drip irrigation. Operating efficiency can reach 0.067 hectares per hour, eight times as much as manual transplanting. The speed of transplanting machine is about 1.1 m/s, the quality of transplanting rate was 93.26 percent. The operating standards of these transplanters meet the agronomic requirements for transplanting cantaloupe.

Nonlinear Stochastic Seismic Response Analysis of Three-Dimensional Reinforced Concrete Piles

A reliable assessment and design of engineering structures requires appropriate estimation and consideration of different sources of uncertainty. The randomness of seismic ground motion is one major uncertainty that needs to be considered from the perspective of performance-based earthquake engineering. To properly account for this uncertainty and its corresponding effect on pile foundations, a stochastic seismic response analytical framework based on a probability density evolution method and a stochastic ground motion model is proposed for the nonlinear stochastic seismic response analysis of pile foundations. A three-dimensional finite element model of a reinforced concrete pile with a large diameter embedded in the soil foundation is firstly established and calibrated using the full-scale lateral load test results from the literature, in which the nonlinear behavior of soil, the soil–pile interaction, the concrete damaged plasticity, and the steel yielding of the pile are properly modeled. Then, the calibrated three-dimensional numerical model is employed as an illustrative example for the stochastic seismic response analysis using the proposed framework. The mean, standard deviation, and probability density function of pile settlement and the dynamic reliabilities of the pile concerning various performance requirements are obtained in the present study. The settlements of the pile show great variability under the excitation of various stochastic ground motions, and the maximum mean value of the pile settlements is about 8 mm. The changing shape of the settlement probability density functions in every moment demonstrates that it is unreasonable to use assumed probabilistic distribution models to characterize the seismic responses of pile foundations during a seismic reliability analysis. Based on the proposed method, it is found that the dynamic reliabilities of the selected reinforced concrete pile concerning four different performance levels are 0, 0.1293, 0.8247, and 1, respectively. The proposed stochastic seismic response analytical method in the present study can provide a proper and comprehensive way to quantify various uncertainties and their corresponding effects on the seismic performance of pile foundations. It can also be used to estimate the actual reliability level of pile foundations that are designed by the current codes when they are subjected to seismic loads.

Field and numerical studies on bearing capacity of helical screw piles in Caspian Sea coast soil

Field and numerical studies on bearing capacity of helical screw piles in Caspian Sea coast soil