Settlement Of Pile Groups Research Articles

Analysis of creep settlement of pile groups in linear viscoelastic soil

SummaryThis paper presents the analysis of creep settlement of pile groups for line pile groups, square pile groups, and rectangular pile groups undergoing creep settlements over a period of time. The soil is treated as a viscoelastic material and is modeled using a three‐parameter viscoelastic model. The damping component (dashpot) takes care of the permanent time‐dependent deformations in three‐parameter viscoelastic model. An approach suggested by Mindlin has been employed to calculate the stress distribution along the pile length in a group. The viscoelastic problem is converted into an elastic problem by the application of Laplace transform. Results in the form of variation of interaction factors for parameters such as pile length to diameter ratio, pile spacing, Poisson's ratio, and modulus ratio have been presented. Comparison has been made between interaction factors for piles groups undergoing immediate settlements and creep settlements. Finally, a typical predictive example has been presented for a 3 × 3 pile group showing creep settlement. The load rearrangement due to creep settlements causes about 5% to 35% increase in base resistance over time. Interaction factors for pile groups (2 × 1, 3 × 1, 2 × 2, and 3 × 2) undergoing creep settlement is about 15% to 55% higher than the interaction factors considering only the immediate settlements for pile group spacing less than or equal to 5d.

Pile group settlement analysis on the basis of Static Load Test

Settlement of large pile groups is most often estimated by the Alternative Foundation Method. However, this method has some limitations related to assumed uniformity of pile loads. A very big problem is also related to estimating the stiffness of subgrade loaded by a group of piles. Similar problems arise when piled foundation is numerically modelled in Finite Element Method or Boundary Element Method programmes. The results obtained are highly dependent on the input data, especially on characteristics describing soil subgrade stiffness and strength and moduli at pile – soil contact. The paper presents an example of using the results of trial static calculations for the pile made using a technology not identical with that ultimately implemented for the project. The subgrade stiffness modulus was determined with Inverse Analysis using bored pile test load. The results attained were used for further calculations (forecast) the settlement of prefabricated driven pile (a single one) and then to estimate of pile group settlement under full load from bridge structure abutment.

On the Applicability of the Influence Function Obtained from Single-Pile Calculations for the Calculation of Pile Groups

The results of FEM calculations of the settlement of individual piles and pile groups are presented. A relation is shown between the additional settlements of unloaded piles and the settlements of the soil around loaded piles. The settlements of loaded and unloaded piles are found to decrease with increasing number of piles in a group (reinforcement effect).

3D Numerical Modeling of Pile Group Responses to Excavation-Induced Stress Release in Silty Clay

Development of underground transportation systems consists of tunnels, basement construction excavations and cut and cover tunnels which may encounter existing pile groups during their construction. Since many previous studies mainly focus on the effects of excavations on single piles, settlement and load transfer mechanism of a pile group subjected to excavation-induced stress release are not well investigated and understood. To address these two issues, three-dimensional coupled-consolidation numerical analysis is conducted by using a hypoplastic model which takes small-strain stiffness into account. A non-linear pile group settlement was induced. This may be attributed to reduction of shaft resistance due to excavation induced stress release, the pile had to settle substantially to further mobilise end-bearing. Compared to the Sp of the pile group, induced settlement of the single pile is larger with similar settlement characteristics. Due to the additional settlement of the pile group, factor of safety for the pile group can be regarded as decreasing from 3.0 to 1.4, based on a displacement-based failure load criterion. Owing to non-uniform stress release, pile group tilted towards the excavation with value of 0.14%. Due to excavation-induced stress release and dragload, head load of rear piles was reduced and transferred to rear piles. This load transfer can increase the axial force in front piles by 94%.

Three - dimensional Numerical Simulation and Validation of Load-settlement Behaviour of a Pile Group under Compressive Loading

Settlement of pile foundation is one of the controlling pile design parameters and its numerical simulation is one of the techniques widely used to predict the settlement behaviour of piles. This study was on the settlement behaviour of a pile group located in silty-sand deposits using the finite element (FE) approach which is based on the static pile load test. Three different types of analyses were investigated: (1) a linear elastic (LE) analysis in which the soil was assumed to be linear elastic, (2) a complete nonlinear analysis in which the soil adjacent to the pile shaft as well as the soil between the piles were modelled using the Mohr Coulomb (MC) or hardening soil (HS) model, and (3) a combined analysis in which the soil close to the pile shaft was modelled using the HS model while the soil in the remaining area was modelled using the LE or MC model. Numerical results obtained for the load-settlement behaviour of the pile group were validated using the popular RATZ analytical approach. The results of the FE analysis suggest that incorporating a nonlinear zone of soil close to the pile shaft as an interface and leaving the soil beyond this zone as linear elastic give a more reasonable estimation and a much better prediction of the pile group settlement. It is also suggested that for a typical pile group, a nonlinear interface of thickness equal to the pile diameter and extending from the pile shaft to the edge of the zone would be sufficient to capture the load transfer mechanism. The group settlement ratio predicted in this study is in good agreement with the findings made in the previous studies.

Settlement and load transfer mechanism of a pile group adjacent to a deep excavation in soft clay

Three-dimensional coupled consolidation analysis is conducted to gain insight into the response of a 2×2 floating pile group adjacent to deep excavation in soft clay. By using a validated finite element model, the influence of the excavation depth, pile length, pile group location from excavation, the supporting system stiffness, soil state and permeability, and working load are systematically studied. The analysis revealed that the maximum settlement occurs when the pile group is founded at the excavation level and at a distance of 0.75-times the excavation depth, although the induced bending moment is minimum. In contrast to pile group settlement, tilting is maximum when it gets closer to the wall and minimum at a distance of 0.75-times the excavation depth. It is also observed that the influence of system stiffness is more pronounced for the flexible wall and when the pile group is located at the excavation level. Applied working load influences pile group settlement but has relatively minor effects on pile group tilting. Excess negative pore water pressures are generated in the soil elements due to excavation. Pile group experiences progressive long term settlement with the dissipation of excess negative pore water pressure.

Model test of the group piles foundation of a high-speed railway bridge in mined-out area

The research on the mechanism of pile-soil-cap-goaf interaction and settlement of high-speed railway bridge located in mined-out area is still relatively rare. By taking the pile group of Guanshandi bridge foundation in Hefei- Fuzhou high-speed railway as the prototype, a model test is carried out. According to the similarity theory, the similar constant is derived and the similar model material is determined. Meanwhile, three types of data including the bearing behavior of piles, and the settlement law, and soil among piles are investigated. It can be found that: the influence of goaf on the bearing capacity of pile is inversely to the loading degree, the larger of loading degree, the smaller impact of goaf on the bearing capacity. There is no negative side friction can been found in pile body and the degree of downward tendency for the barycenter of side friction layout is obvious for piles in goaf. Although the bearing ratio of soil resistance under cap is relatively large, the cap effect is suggested be ignored considering the characteristic of goaf. There is a maximum critical value for the uneven settlement of pile group in goaf, and when the value is reached, the uneven settlement stop growing anymore. In addition, the formula for calculating bearing capacity and settlement of pile group in goaf based on test results, theory analysis and related standard is established.

A theoretical analysis of the bearing performance of vertically loaded large-diameter pipe pile groups

This paper aims to present a theoretical method to study the bearing performance of vertically loaded large-diameter pipe pile groups. The interactions between group piles result in different bearing performance of both a single pile and pile groups. Considering the pile group effect and the skin friction from both outer and inner soils, an analytical solution is developed to calculate the settlement and axial force in large-diameter pipe pile groups. The analytical solution was verified by centrifuge and field testing results. An extensive parametric analysis was performed to study the bearing performance of the pipe pile groups. The results reveal that the axial forces in group piles are not the same. The larger the distance from central pile, the larger the axial force. The axial force in the central pile is the smallest, while that in corner piles is the largest. The axial force on the top of the corner piles decreases while that in the central pile increases with increasing of pile spacing and decreasing of pile length. The axial force in side piles varies little with the variations of pile spacing, pile length, and shear modulus of the soil and is approximately equal to the average load shared by one pile. For a pile group, the larger the pile length is, the larger the influence radius is. As a result, the pile group effect is more apparent for a larger pile length. The settlement of pile groups decreases with increasing of the pile number in the group and the shear modulus of the underlying soil.

Some observations of the influence factors on the response of pile groups

A simplified approach for nonlinear analysis of the load-displacement response of pile groups embedded in multilayered soils is presented in this work. A hyperbolic model is used to capture the relationship between unit skin friction and pile-soil relative displacement developed along the pile-soil interface and the stress-displacement relationship developed at the pile end. Considering interactive effect among piles, the parameters related to the hyperbolic model of an individual pile in a group can be computed. As to the analysis of the response of pile groups, a highly effective iterative computer program is developed using the hyperbolic model of an individual pile in a group. The efficiency and accuracy of the present method is verified using a well-documented field test. Furthermore, a parametric study is conducted to capture the influence of pile spacing and number of piles on the load-settlement response of the pile groups connected to a rigid cap. The pile-group settlement ratio and the pile-group resistance ratio are analyzed to assess the interaction effect among individual piles.

Settlement and load transfer mechanism of pile group due to side-by-side twin tunnelling

Development of underground transportation systems often involve twin tunnels, which may encounter existing pile groups during construction. Since many previous studies mainly focus on the effects of single tunnelling on single piles, settlement and load transfer mechanism of a pile group subjected to twin tunnelling are not well investigated and understood. To address these two issues, two three-dimensional centrifuge tests were carried out in this study to simulate side-by-side twin tunnels (excavated one after the other on both sides of the pile group) at two critical locations relative to the pile group, namely next to (Test TT) and below the toe of the pile group (Test BB). Moreover, numerical back-analyses of the centrifuge tests are conducted by using a hypoplastic model, which takes small-strain stiffness into account. Both measured and computed results show that the induced tilting of the pile group in Test TT is significantly larger than that in Test BB, with a maximum percentage difference of 120%. On the other hand, a slightly smaller (about 13%) settlement of the pile group is induced in Test TT, as compared to that in Test BB. This is because the pile group in Test TT is partially located within the major influence zone of tunnelling-induced ground settlement while the entire pile group in Test BB is bounded by the major influence zone of ground settlement. Two distinct load transfer mechanisms due to twin tunnelling are identified, i.e., the load in the pile group in Test TT transfers downwards from the pile shaft to the pile toe while the load in the pile group in Test BB transfers upwards from the pile toe to the pile shaft. Apart from load transfer along each pile, load re-distribution also occurs among piles during twin tunnelling. In both Tests TT and BB, axial load at pile head only reduces at a pile closet to the advancing tunnel face and the reduction is re-distributed to the other three piles. The load re-distribution among piles results in a maximum increase of axial force of 10% in Test TT.

Prediction of the Settlement for the Vertically Loaded Pile Group Using 3D Finite Element Analyses

The settlement prediction of small pile group at working load using 3D Finite Element (FE) approach was carried out based on the case of Belfast pile load test. Three different types of analysis were investigated: a linear elastic (LE) analysis where all the soil was assumed to be linear elastic, a complete nonlinear (CNL) analysis where both the soil adjacent to the pile shafts and between the piles using the Hardening Soil (HS) model, and a nonlinear and linear elastic analysis (NL-LE) with the soil close to the pile shafts using HS model while the soil in the remaining area is modeled as an elastic material. Then all the FE analyses were compared to the analytical approach (RATZ). The results of FE analysis suggest that incorporating a nonlinear zone of soil close the pile shaft and leaving the soil linear elastic beyond this zone gives more reasonable estimation of interaction factor, thus, a much better prediction of pile group settlement will be observed. It is suggested that a value of half the pile width for the distance from pile shaft to the edge of this nonlinear zone would be sufficient to capture the load transfer mechanism for a typical pile group. While best prediction was given by RATZ approach as the group settlement ratio which reflect the interaction effect between piles in the group obtained from RATZ mostly close to the field measurements.

Pile Group Settlement Estimation: Suitability of Nonlinear Interaction Factors

In this paper, predictions of pile settlement determined by appropriate superposition of two-pile interaction factors are compared with those computed from continuum analysis. A finite-element package is used in conjunction with the nonlinear Hardening Soil model and the pile group sizes studied are larger than in previous research. The study is presented in two phases: (1) examination of the modulus variation within the group allowing the elimination of some variables, and (2) comparison of pile settlement predictions in the context of the significant variables. The research shows that predictions using the former approach match the continuum analyses very closely for friction piles and reasonably well for end-bearing piles, and show potential for reducing computational time and effort in such problems. The paper also distinguishes between alternative definitions of interaction factor and shows that most accurate predictions arise from interaction factors calculated when only one of the two piles is loaded.

Finite Element Analysis for Pile Group Foundation Settlement in Soft Soil

The three-dimensional finite element model for pile group foundation settlement analysis within soft soil pile is developed using ABAQUS. The Cap plasticity model and the elastic model are used to model the soil and the pile respectively. The contact interface elements are installed between the pile and the soil interface. The undrained loading conditions and drainage loading conditions in the soft soil piled raft foundation settlement are analyzed respectively and computation results are compared. The results show that pile group foundation in soft soil settlements increase with load increasing in both the undrained conditions and drainage conditions. The bearing capacity of the pile group under the undrained conditions is larger than that under drained conditions with the same pile group. The pile group settlement under the undrained conditions is smaller than that under drained conditions.

Re-mobilization of pile shaft friction after an earthquake

During strong earthquakes, significant excess pore pressures can develop in saturated soils. After shaking ceases, the dissipation of these pressures can cause significant soil settlement, creating downward-acting frictional loads on piled foundations. Additionally, if the piles do not support the full axial load at the end of shaking, then the proportion of the superstructure’s vertical loading carried by the piles may change as a result of the soil settlement, further altering the axial load distribution on piles as the soil consolidates. In this paper, the effect of hydraulic conductivity and initial post-shaking pile head loading is investigated in terms of the changing axial load distribution and settlement responses. The investigation is carried out by considering the results from four dynamic centrifuge experiments in which a 2 × 2 pile group was embedded in a two-layer profile and subjected to strong shaking. It is found that large contrasts in hydraulic conductivity between the two layers of the soil model affected both the pile group settlements and axial load distribution. Both these results stem from the differences in excess pore pressure dissipation, part of which took place very rapidly when the underlying soil layer had a large hydraulic conductivity.

Theoretical Analysis on Settlement Calculation of Pile Foundation with Minimum Complementary Energy of Elastic Mechanics Based on the Ritz Variational Method

In this paper, based on the model test，numerous deductions and calculations have been done, which was about the settlement of single pile and pile group in homogeneous foundation. With minimum complementary energy of elastic mechanics on the basis of the ritz variational method, through the MATLAB programming, theoretical calculation results were obtained, then comparison and analysis with the model test results were made to verify the feasibility of theoretical calculation.

Simplified Calculation Approach for Settlement of Single Pile and Pile Groups

AbstractThis paper proposes a simple analytical approach for nonlinear analyses of the load-displacement response of single piles and pile groups. Two models were adopted in the proposed approach. One model is based on a hyperbolic nonlinear relationship to simulate the behavior between unit skin friction and pile displacement developed along the pile-soil interface. The other model uses a bilinear hardening model to simulate the load-settlement response developed at the pile base. Based on the two proposed models, a highly effective iterative computer program was developed for nonlinear analysis of the load-settlement behavior of a single pile. Concerning analysis of the response of pile groups, the interaction between two piles was assumed to be composed of two aspects: interaction between pile shafts and interaction between pile bases. Based on this assumption, a reduction coefficient was introduced into the discussion of pile-pile interaction to account for the reinforcing effect between piles. Compar...

Analytical Method for Settlement of Axially Loaded Compressible Pile

In the design of pile foundation, settlement rather than the bearing capacity is often the controlling factor. Therefore, foundation settlement should be assessed as accurately as possible. Empirical methods are generally used to determine the settlement of pile foundation. As per IS code: 8009, for point bearing pile group, the pile group is replaced by a fictitious footing at the top of the bearing layer. For friction pile groups, it is assumed that the fictitious footing is at a depth of Dp/3 above the pile tip. In IS code method, settlements happen to be same for both the rigid friction pile and compressible pile groups, whereas settlements in case of compressible pile are higher than those in rigid friction pile. An alternative analytical method is developed for determining the stresses induced in the soil due to the axially loaded friction and compressible pile. The vertical stress coefficients obtained by the method proposed are used to determine the settlements of the axially loaded group of friction and compressible piles. It is found that settlement of compressible pile group obtained by analytical method is 2.5 times that of rigid friction pile group settlement obtained by IS code 8009 method or empirical method.

Calculation for Settlement of High Cap Extra-Long Large Diameter Pile Groups

The settlement of high cap extra-long large diameter pile groups is made up of pile elastic compression and settlement of soil layers under pile end in theory. Methods to calculate pile compression of high cap extra-long large diameter pile groups was deduced or listed. Six methods to calculate settlement of soil layers under pile end were expounded through extra-long large diameter pile groups under south tower of main bridge of Sutong Yangtse River Highway Bridges. The results show that piles’ elastic compression should be calculated into the settlement of extra-long large diameter pile groups, including that caused by pile’s own weight, and it is little difference between test value and total settlement which is composed of piles’ elastic compression calculated through the formula deduced in the paper and theoretic settlement of soil layers under pile end based on Mindlin’s additional stress solution, only making 0.06% lower.

Field performance of long bored piles within piled rafts

In this study, well-instrumented field tests on bored piles were conducted at two construction sites in Zhejiang, China. At the first site, three bored piles in clay deposits overlying rock were load-tested to investigate the load transfer and deformation behaviour of a single pile. The lengths of the 1·1 m diameter test piles ranged from 88 m to 120 m, allowing particular insight into the in situ performance of long piles. In addition, the load–settlement behaviour of these piles within a piled raft group was observed during and after construction of the building they supported. At the second site, four bored piles 32 m long and 0·6 m in diameter were observed during single-pile static load tests, and during and after construction of the overlying building. The pile-head settlement was observed to be due mainly to the compression of the pile shaft for the long pile at the first site. The threshold of slip displacement for fully mobilising the shaft resistance was found to be 15–20 mm and 10–15 mm in clayey and silty deposits respectively. The measured load–deformation behaviour at the pile base demonstrates that the base resistance of single piles in a piled raft system is greater than that in the single-pile condition, and the pile-group settlement ratio is related to the applied pile-head load. The bearing pressure under the perimeter of the raft was measured and found to be greater than the bearing pressure beneath the central part of the raft, although the ratio between these values was found to vary with the applied structural load. In the cases studied, approximately 80% of the applied structural load was carried by the piles; the remainder was carried by the raft in bearing against the soil.

Settlement of piled foundations using equivalent raft approach

This paper presents a comprehensive study on estimating the settlement of large-scale pile groups using the equivalent raft approach. First, five common methods of analysis are briefly reviewed. The reliability of the methods is then verified by back-analysing six well-documented case studies of large-scale piled foundations, all of which include hundreds of piles. The case studies include three representative footing types, characterised according to the pile cap stiffness as flexible, semi-rigid, and rigid. It was found that the stiffness of the pile cap and the consideration of horizontal stress increments are the key factors affecting the estimation of settlement. It is concluded that, with appropriate consideration of the various factors, several of these methods can reasonably be applied for the estimation of the settlement of pile groups.