Friction Piles Research Articles

Numerical study on settlement-dependent variation of raft-soil-pile interactions for large piled raft in clay soil

In a piled raft foundation, the stresses applied on the soil from the raft and piles overlap, which leads to changes in the settlement and bearing capacity of the raft and each individual pile. In this numerical study, settlement-dependent variation of three interaction factors, namely piles-to-piles (P-P), raft-to-piles (R-P), and piles-to-raft (P-R) have been investigated for large piled raft in stiff clay. The unpiled raft is flexible, the piles are friction piles and the effects of pile number, spacing and length on these interaction factors are presented. The P-P factor increases and then tends to become constant at a certain settlement. In contrast, the R-P factor always shows an increasing trend with settlement. However, the P-R interaction factor initially decreases and then increases with settlement. At the final settlement equal to 0.35% of raft width, the P-P, R-P, and P-R interaction factors range from 0.95 to 1.10, 0.86–1.04, and 0.25–0.92, respectively. Predictive equations have been proposed for these interaction factors and thereby determine the load-sharing ratio and mobilized safety factor. Within the allowable settlement range satisfying the serviceability limit, a good agreement between the results obtained from predictive equations and the finite element analyses is demonstrated for different piled raft configurations.

A simple analytical model for bamboo-reinforced slopes using modified Bishop method

Introduction: Embankments are constructed in many places for transportation purposes such as railways and roads. The stability of slopes in embankments has always been a concern, especially in cohesionless soils. There are many methods to increase the safety factor of cohesionless soil slopes using geogrids, geocells, concrete piles, and so on. The conventional material used to stabilize slopes has a huge impact on the environment. Nowadays, researchers are using natural fibers such as bamboo and coir fiber for stabilization purposes.Methods: In this paper, bamboo piles are used to stabilize slopes. The bamboo piles are inserted vertically on the slope face to increase the shear strength and stability against slope failure. A limit equilibrium method has been developed to estimate the stability of a slope improved by friction piles after modifying the Bishop method of slices. The stability of the slope is analyzed for both the reinforced conditions and the unreinforced conditions using the developed analytical formula.Results and Discussion: The analytical equations were developed by considering three modes of slope failure: shear failure of the bamboo piles along the failure surface, movement of the upper part of the soil, leaving the bamboo pile embedded in the base soil, and pulling out of the bamboo along with the upper part of the soil mass. Further validation of the results is carried out with the limit equilibrium method-based software SLOPE/W using a modified Bishop method. The factor of safety increased after reinforcing the slope with bamboo piles for all three modes.

Closed-form dynamic stiffness formulation for modal and dynamic response analysis of pile group foundations

A closed-form dynamic stiffness (DS) formulation is proposed for pile group foundations. This model consists of a rigid cap and an arbitrary number of flexible piles. The rigid cap, connecting to all piles, is modeled as a rigid body resting on an elastic foundation. For each pile, a longitudinal soil–pile model and a preloaded Timoshenko beam on viscoelastic Pasternak foundation are adopted to describe the longitudinal and transverse vibration, respectively. The piles can be either friction piles or end-bearing piles, and pile sections surrounded by different soil layers can be easily modeled by the assembly of pile elements with different parameters. The proposed DS formulations essentially use very few degrees of freedom to, nevertheless, describe the broadband dynamic behaviors of complex pile group foundations in a highly accurate manner. The DS formulation is then used for modal and dynamic response analysis. For modal analysis, the Wittrick–Williams algorithm is applied, with the key issue J0 count problems resolved. The proposed method is verified against some existing results. This research provides an exact and highly efficient modal and response analysis tool for pile group foundations, which can be used for the dynamic analysis of pile foundations subjected to earthquake or traffic excitations.

Model Test Study on the Load-bearing Behaviour of Multi-tooth Piles under Different Bearing Layers

In soft soil or karst areas, several problems exist, such as the poor properties of the pile tip bearing layer or difficulties in cutting the rock. Using multi-tooth piles, end-bearing piles can be turned into friction piles to solve these problems. Through the scale model device, three variables: the bearing layer, tooth length, and tooth number, are designed to experimentally explore the load-bearing behaviour of multi-tooth piles under different bearing layer conditions. The test results show that the model pile has better anti-settlement performance in the sand bearing layer than in the red clay bearing layer. Compared with smooth piles, multi-tooth piles can greatly improve the bearing capacity of pile foundations in bearing layers with poor stiffness. The tooth length and tooth number greatly impact the compressive bearing capacity and the pile-side resistance of the multi-tooth pile, respectively. The concept of roughness is innovatively introduced to quantify the roughness of pile surfaces, which provides an effective method for the subsequent experimental and theoretical research of multi-tooth piles and other similar piles with small cross-section modifications. This study can enrich the research field of small, modified cross-section piles and provide a reference for innovative research on pile foundations.

Analysis of different elevation buildings with heights of 4, 8, 12, 16, 20, and 24 floors on friction piles

Foundation is one of the most important parts of the structure. The design and selection of foundations must be carried out properly to strengthen the structure. Different elevation buildings require more careful foundation design than other structures. The bearing capacity and settlement of the soil acting on the pile foundation will be very important to be taken into consideration in the construction of different elevation buildings, because the different elevation buildings have different heights, so the placement of the foundation depths is also different. There is load data to be used, load data will vary according to the elevation of the building. The difference on structure elevation is four-storey buildings until it reaches 24 storey building. Each floor has a height of three meters. The foundation analyzed by using bored pile. The soil data is from Central Jakarta. The foundation will be analyzed under the following condition. The foundation will be placed at the same pile diameters which is one meter and uses different dephts. In this study, the bearing capacity and soil settlement analysis was carried out using bored piles on the conditions described before. The result of this research will provide information about bearing capacity and settlement that occurs on different elevation building if the foundation uses a friction piles. This research concludes that the use of friction piles in ineffective.

Mathematical Model of an Offshore Friction Pile in Multilayered Saturated Soils

In this paper, an analytical methodology is proposed to study the vibration of an offshore friction pile embedded in multilayered saturated viscoelastic soils by combining Biot’s saturated wave propagation theory, Novak’s plane-strain model, and the fictitious saturated soil pile model. The corresponding semi-analytical solution for the dynamic response of the pile is developed considering the heterogeneity, porosity, and limited thickness of the soils. The approach and relevant solution presented are validated by comparisons with existing solutions. Furthermore, numerical instances are used to investigate the influences of the porosity and heterogeneity of the saturated soils around and beneath the pile on the vibration of the pile. The findings from this paper provide a theoretical reference for a comprehensive understanding of the wave propagation characteristics of a friction pile embedded in heterogeneous saturated soil with limited thickness.

Effect of slope on lateral bearing capacity of nearshore large-diameter monopiles in cohesive soil

This study investigates the effect of slope on the lateral bearing capacity of nearshore large-diameter monopiles in cohesive soil by the finite element limit analysis (FELA) method. The reduction coefficient is introduced to quantify the capacity reduction due to the slope effect, and the critical distance making the slope-induced capacity reduction negligible is normalized for generalization. After the validations by cases of different soils, an alternative way to quickly and straightforwardly assess the pile bearing capacity in sloping stratum for the most frequently-encountered cases in engineering practice is provided by multiplying the reduction coefficients in several design tables with the capacity in level stratum. The subsequent parametric studies indicate that the reduction coefficient and critical dimensionless distance are mainly governed by the internal friction angle, slope angle, and pile embedded length-diameter ratio but are almost insensitive to dimensionless cohesion and slope height-pile embedded length ratio. In addition, the failure mode of the pile-slope system would develop from local failure to transitional failure and global failure with a significant drop in pile bearing capacity while the pile-slope parameters cannot guarantee slope stability.

Evolution of tunnel uplift induced by adjacent long and collinear excavation and an effective protective measure

Tunnel uplift control is an important issue for excavation construction near an existing tunnel, especially for long and collinear excavations. In this study, an effective anti-floating measure combining shaft excavation with the frictional pile slab (FPS) was proposed based on a long and collinear foundation pit above existing metro tunnels. The convergence of the shield segments was carefully measured using automatic total stations over 800 days. Numerical simulation was applied to analyze the effect of the width of the shaft excavation and geometric dimension of the frictional pile on the tunnel uplift. Furthermore, a multiobjective optimization procedure was proposed to optimize anti-floating design considering both safety and economy. A comparison between the FPS method and the high-pressure jet-grouting pile (HJP) method shows that the FPS method is a more effective way to control the heave of the underlying tunnel induced by long and colinear excavation due to its small-scale graded unloading and integral portal anti-floating structure. Combining the FPS method with sectional excavation, all the heaves of the underlying tunnel can be controlled to be less than 9 mm. For granite residual strata, the width of shaft excavation is advised to be lower than 8 m, and the length of the frictional pile is suggested to be longer than the distance between the pit bottom and tunnel invert. The heave of the tunnel crown is suggested as the key index to evaluate the excavation-induced disturbance on the underlying tunnel. The unloading ratio and construction time are the key factors that influence the magnitude of tunnel heave. Compared with the actual design, an optimal design with a lower cost and better anti-floating effect is obtained with the proposed multiobjective optimization procedure. The presented tunnel deformation data, advised anti-floating method and construction sequence can provide useful guidance for similar scenarios.

Seismic evaluation of frictional FRP piles in saturated sands using shaking table tests

This manuscript presents results of two shaking table tests that were used to characterize seismic performance of Fibre-Reinforced Polymers (FRP) pile groups in saturated sand. A laminar shear box with a dimension of 1.0 m × 1.0 m and a depth of 1.0 m was employed to contain the soil medium and allow the soil to respond in the same fashion as the free field. Two types of composite group piles (2 × 2) made of Carbon FRP (CFRP) and Glass FRP (GFRP) along with a series of Aluminum model piles were manufactured and embedded as frictional piles within the soil. The pile-soil models were subjected to acceleration time histories adopted from the 2010 Val-des-Bois Earthquake in Canada and the 1995 Kobe Earthquake. The foundation motions recorded along the model piles showed significantly higher levels of excitation compared to the accelerations recorded within the soil at the same level. This was attributed to strong interaction between the soil and the foundation, and higher flexural stiffness of the model piles. Pile material was also found to influence the seismic response of pile caps and its superstructure through kinematic soil-pile interaction and possible rocking motion. The aluminum pile cap experienced significantly higher acceleration response compared to the FRP piles. Among the FRP piles, GFRP piles were shown to provide slightly better performance and could be an appropriate alternative piling material for frictional traditional piles especially in liquefiable soils.

Early development of the Dutch cone penetrometer test

The cone penetration test (CPT) was developed in the Netherlands in the early 1930s as a deep-sounding apparatus that measured cone resistance and was used to assess the distribution of alluvial soils and peat. It was developed further by increasing the push-down force to provide a method of designing piles. During the 1940s, improvements were made by increasing the push-down force, also improving the probe geometry and test procedure. One of the most important developments of the CPT was made in Indonesia by Dutch engineers in the 1950s, who added the friction sleeve used to measure local friction. The data from this device were used in an empirical design method to determine the bearing capacity of friction piles. The device became known as the ‘mechanical CPT’ and has now been superseded by probes with the same basic dimensions but with loads and pressures measured locally using transducers. The modern ‘electric CPT’ offers significant advantages; however, there are still places where the mechanical CPT is used widely, such as in Indonesia. It should be appreciated that there can be significant differences in the measured parameters, such that awareness of the type of probe being used is important, as are the methods of interpretation.

Study on Vertical Load-Carrying Capacity of Post-Grouting Bored Piles

The relationship between pile side frictional resistance and pile tip resistance and settlement is assumed to be ideal elastic–plastic. The load-transfer method is used to analyze the load-bearing characteristics of bored pile in actual projects, and the results are compared with static load test results to prove the reliability of the analysis method and its parameters, on the basis of which the bored piles are reinforced with grouting, namely, pile tip grouting, pile side grouting, and pile tip pile–side composite grouting, are analyzed. The results show that the pile tip grouting mainly improves pile tip resistance and has almost no effect on pile side frictional resistance; the pile side grouting improves pile tip resistance and pile side frictional resistance more significantly; and pile tip–pile side composite grouting improves pile tip resistance and pile side frictional resistance more significantly than the first two. The ultimate load-carrying capacity of the pile is increased by 19%, 49%, and 53% after the use of pile tip grouting, pile side grouting, and composite grouting respectively.

A Report on the Design and Field Execution Study for Friction Pile Process

A Report on the Design and Field Execution Study for Friction Pile Process

Analysis of Load-Settlement Curve Based on Load Transfer at Pile-Soil Interface

A field pile loading test was carried out on the Peshawar–Karachi Motorway (PKM) project in Pakistan to show the settling mechanism of bored pile foundation in pulverized soil and the force characteristics of frictional resistance at the pile-soil interface. The changes in pile lateral frictional resistance and pile settlement during the loading-unloading process of test piles were measured and analyzed, as well as the load-settlement distribution characteristics of test piles in different soil layers, the distribution of test pile internal forces, and the changes in pile-soil relative displacement. It was established that there was considerable deterioration of pile lateral frictional resistance and residual deformation of pile tip displacement throughout the test pile load-settlement process, and the association between the pile-soil interface frictional resistance and pile-soil relative displacement was addressed. The results reveal that the frictional resistance at the pile-soil interface is directly connected to the nature of the soil layer, with a positive connection between the natural density, specific gravity, compression deformation, and the plastic index under immediate load, and a negative correlation between the natural moisture content, compression coefficient, and settlement variations after unloading. The load-settlement of the pile rose in a non-linear proportion during the loading-unloading operation, with a maximum settlement value at the pile top of 8.14 mm and a residual deformation at the pile bottom of 1.94 mm. The frictional resistance of the pile perimeter was distributed non-linearly throughout the pile depth, and the frictional resistance of the pile-soil interface was severely deteriorated at an embedded depth of 15 m, with the degradation degree of the silty soil layer being significantly smaller than that of the silty clay soil. The relative pile-soil displacement was positively linked with the lateral frictional resistance of the pile under the same load, and the correlation coefficient in silty soil was much greater than that in sandy soil.

Study on Reliability of Friction Pile Foundation with Grouting at Pile Bottom

The reliability calculation model of grouting pile foundation under eccentric load was studied. JC method was used to calculate its single reliability. Considering the correlation of failure modes, the narrow limit of the reliability of grouting pile foundation was obtained.

A Field Study on the Arching Behavior of a Geogrid-Reinforced Floating Pile-Supported Embankment

Geogrid-reinforced floating pile-supported (GRFPS) embankments are widely used in areas with moderately compressed soil. Due to the interaction among foundation soil, suspended piles and geogrids, the characteristics of stress and deformation are very complicated. In this paper, a field filling test of GRFPS embankments with two pile lengths (L = 8 m, 15 m), S1 and S2, was carried out in areas with moderately compressed soil. The evolution of soil arching, deformation of soil, piles and geogrids during the construction and equilibrium stage of embankments were monitored. Results show that with the increasing of filling height, there were three stages for the evolution soil arching: no soil arching, formation of soil arching, and stabilization of soil arching. When the pile-soil settlement ratio η reached its minimum value, soil arching formed, and the differential settlement between pile and soil at the top of pile cap (Δδ) was around 1% of the net pile spacing (s-d, where s is the pile spacing, d is the diameter of pile cap). The corresponding critical filling heights (Hcri) were 1.4 (s - d) and 3(s - d) for S1 and S2, respectively. The strain of geogrid mainly developed during the initial stage of filling with the development of Δδ. When the filling height was larger than 5.2 m, the magnitude of soil arching was larger for the embankment with longer pile length (S2). Meanwhile, for S2, the soil arching coefficient Cc gradually transited from friction piles into the end-bearing piles with the increasing filing height of the embankment. The strain of the geogrid mainly occurs in the initial stage of filling (t < 75 d), mainly due to the differential settlement between the pile and soil. After that, the overall settlement of the composite foundation also slightly caused the strain of the geogrid. Finally, three states of soil arching effects of the GRFPS embankment and the evolution characteristics of each index under different states are proposed. This case study provides an enhanced understanding of the performance GRFPS embankment.

LOAD-BEARING CAPACITY AND RELIABILITY ANALYSIS OF FRICTION PILES ON PULL-OUT LOADS

The article presents new methods for load-bearing capacity evaluation and reliability analysis for friction piles under pull-out loads. The new approach is also proposed for the friction forces description on the pile lateral surface, which arise not as a result of the pile “failure”, but as a result of pile material microdisplacements (deformations). The presented method for reliability analysis is based on the fuzzy sets theory and can be used with incomplete statistical information about the controlled parameters, which will reduce financial and time costs. Numerical examples of the pile load-bearing capacity and reliability calculation are given, as well as a comparison of the results with the standard approach.

Experimental Investigation of the Impact of Necking Position on Pile Capacity Assisted with Transparent Soil Technology

Necking in different positions of a pile body has a significant influence on the bearing performance of a single pile. The transparent soil model experiment was adopted to investigate the impacts of necking positions on the vertical bearing capacity of a single pile and the soil deformation around the pile, and subsequently, the causes of the variation of bearing capacity were analyzed. The results show that the existence of necking does not change the bearing behavior of single pile as pile friction resistance. The bearing capacity of piles decreased by 8.21% and increased by 7.30% when the necking is located in the shallow and middle pile body, respectively, while it did not change significantly when the defects were in the deep part of the pile. The necking position has a significant effect on the deformation and deformation range of soil. The soils at the top, side, and near the end of a pile were mainly influenced by shallow necking, middle necking, and deep necking, respectively. The soils at the location of necking had apparent settlement phenomenon as the piles subsided. The soils at shallow necking’s locations were relatively loose, which reduced the side friction force of piles and finally resulted in a reduction of bearing capacity of a single pile. With the increase of the load, the soil around piles gradually developed penetration phenomenon (large deformation), while the soil at the end of pile moved up against pile settlement, which made the necking soil in the middle denser. The loss of side friction resistance was less than the resistance from the necking, which gave birth to an increase in the bearing capacity of a single pile. It was finally found that the side friction resistance and the resistance caused by necking were the main factors governing the bearing capacity of necking single piles.

Simplified analytical method for static and stability analysis of circular tapered friction piles

This paper presents a new, simplified analytical method to study the static and stability response of circular tapered friction piles in homogeneous or non-homogeneous Pasternak soil. The governing differential equation (GDE) of the proposed element is derived in a classical manner and solved using the Differential Transformation Method (DTM). This complex analysis is reduced to solve a system of two linear algebraic equations, which solution is readily available and easy to code. The proposed formulation is of practical interest for both onshore and offshore structures, and it can be used to conduct: (a) lateral load–deformation, (b) elastic stability, and (c) second-order analysis of prismatic and tapered friction piles. Tapered friction piles with various distributions of end-bearing resistance and skin friction can be investigated. The proposed formulation includes the effect of (i) any end-boundary condition at the ends of the element (i.e., translational and rotational constraints), (ii) a uniform or linear variation of skin friction, and (iii) a uniform or linear variation of the modulus of subgrade reaction. Five examples are presented to validate the accuracy of the proposed approach.

Factors Influencing Pile Friction Bearing Capacity: Proposing a Novel Procedure Based on Gradient Boosted Tree Technique

In geotechnical engineering, there is a need to propose a practical, reliable and accurate way for the estimation of pile bearing capacity. A direct measure of this parameter is difficult and expensive to achieve on-site, and needs a series of machine settings. This study aims to introduce a process for selecting the most important parameters in the area of pile capacity and to propose several tree-based techniques for forecasting the pile bearing capacity, all of which are fully intelligent. In terms of the first objective, pile length, hammer drop height, pile diameter, hammer weight, and N values of the standard penetration test were selected as the most important factors for estimating pile capacity. These were then used as model inputs in different tree-based techniques, i.e., decision tree (DT), random forest (RF), and gradient boosted tree (GBT) in order to predict pile friction bearing capacity. This was implemented with the help of 130 High Strain Dynamic Load tests which were conducted in the Kepong area, Malaysia. The developed tree-based models were assessed using various statistical indices and the best performance with the lowest system error was obtained by the GBT technique. The coefficient of determination (R2) values of 0.901 and 0.816 for the train and test parts of the GBT model, respectively, showed the power and capability of this tree-based model in estimating pile friction bearing capacity. The GBT model and the input selection process proposed in this research can be introduced as a new, powerful, and practical methodology to predict pile capacity in real projects.

The effect of thermal consolidation on bearing characteristics of static drilling rooted energy pile

Static drilling rooted energy pile is a new type of energy pile technology recently developed and promoted in soft soil areas. This technology has the advantages of green, low-carbon and good heat exchange effect. But its related basic theoretical research is still lacking. Therefore, the physical model of the static drilling rooted energy pile is deduced. The thermal consolidation settlement process of the soil around the pile is analyzed firstly based on one-dimensional thermal consolidation theory. And, the load transfer method is combined to derive the pile circumference under the coupling effect of load and temperature variation. The governing equations for frictional resistance and pile deformation are deduced and solved with numerical programs. Then an actual engineering case with static drilling rooted energy pile in soft soil area is calculated and analyzed. The results show that the temperature increase of the surrounding soil increases the relative displacement of pile and soil, which resulting in a decrease in the upper side friction resistance and an increase in the lower side friction resistance; and this effect will be enlarged during the cooling stage. The maximum axial addition stress caused by the temperature variation reaches 75.4% of the stress by load, so the influence of temperature changes on the bearing capacity of the pile foundation cannot be ignored. The research laid a theoretical foundation for the analysis and popularization of the static drilling rooted energy pile in coastal soft area.