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Title
Abstract
Figures
Introduction
Procedure of Analysis
Check of the Procedure Against Known Solutions
Back-Analysis of Some Case Histories
Discussion
References
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Engineering
Civil Engineering

Settlement of piled foundations

Profile image of A. MandoliniA. Mandolini

1997, Géotechnique

https://doi.org/10.1680/GEOT.1997.47.4.791
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26 pages

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Abstract

A numerical code for the prediction of the settlement of pile groups and piled rafts is presented. The code is based on the interaction factors method; the non-linearity is simulated as suggested by Caputo and Viggiani, that is, concentrating it at the pile±soil interface. In the linear range, the accuracy is checked against known benchmark solutions. A standard procedure, based on the results of load tests on single piles, is suggested for the evaluation of soil properties and for the implementation of the analysis in real cases. Nineteen well-documented case histories are then analysed, calculating for each of them a linear elastic, an equivalent linear elastic and a non-linear solution. Five out of the 19 cases are illustrated in some detail, to allow a deeper insight into the procedure. In all but one of the analysed cases the predicted values of the average settlement are within AE20% of the observed values. The maximum differential settlement is predicted with slightly lesser accuracy. For foundations characterized by a relatively high safety factor, linear and non-linear analyses are essentially equivalent. Some evidence suggests that the low-strain shear modulus, obtained by in situ shear wave velocity measurements, can be successfully employed in the prediction of the settlement. When the safety factor is low, the consideration of nonlinearity becomes mandatory.

Figures (25)
Fig. 1. Comparison between results of computations carried out with different codes Figure 1 (Randolph, 1994; Mandolini, 1994b) shows the computed overall pile group stiffness for square groups of piles embedded in an elastic half- space, with L/d=25, E,/G= 1000, v,=0-5, and s/d=2-5 and 5. The group stiffness Ky is defined as the ratio between the total load acting on the pile group and the average settlement of the group. In Fig. 1, the stiffness is normalized as Kp/(sGn°°), where G is the shear modulus of the soil and n the number of piles in the group. The
Fig. 1. Comparison between results of computations carried out with different codes Figure 1 (Randolph, 1994; Mandolini, 1994b) shows the computed overall pile group stiffness for square groups of piles embedded in an elastic half- space, with L/d=25, E,/G= 1000, v,=0-5, and s/d=2-5 and 5. The group stiffness Ky is defined as the ratio between the total load acting on the pile group and the average settlement of the group. In Fig. 1, the stiffness is normalized as Kp/(sGn°°), where G is the shear modulus of the soil and n the number of piles in the group. The
Table 1. Essential features of the analysed case histories
Table 1. Essential features of the analysed case histories
Table 2. Computed and observed average settlement w,, and maximum differential settlement Ona ‘ (a) ‘core’ foundation; (b) ‘dog-leg’ foundation; (c) ‘hammerhead’ foundation; (d) overall.
Table 2. Computed and observed average settlement w,, and maximum differential settlement Ona ‘ (a) ‘core’ foundation; (b) ‘dog-leg’ foundation; (c) ‘hammerhead’ foundation; (d) overall.
Fig. 3. Case history No. 2: typical soil profile and properties at building site; the subsoil model adopted in the analysis is shown on the right-hand side
Fig. 3. Case history No. 2: typical soil profile and properties at building site; the subsoil model adopted in the analysis is shown on the right-hand side
Fig. 2. Case history No. 2: layout of foundations of the building; pile locations are shown as solid circles, pile caps as full lines and columns as filled rectangles; overall dimensions are 33-6 m X 24-4 m
Fig. 2. Case history No. 2: layout of foundations of the building; pile locations are shown as solid circles, pile caps as full lines and columns as filled rectangles; overall dimensions are 33-6 m X 24-4 m
Fig. 5. Case history No. 2: comparison between predicted and observed settlements Fig. 4. Case history No. 2: load—settlement curves of two loading tests on piles
Fig. 5. Case history No. 2: comparison between predicted and observed settlements Fig. 4. Case history No. 2: load—settlement curves of two loading tests on piles
Fig. 6. Case history No. 5: schematic of the molasses tank and subsoil model adopted in the analysis
Fig. 6. Case history No. 5: schematic of the molasses tank and subsoil model adopted in the analysis
Fig. 8. Case history No. 5: comparison between predicted and observed settlements Fig. 7. Case history No. 5: loading test results on single pile
Fig. 8. Case history No. 5: comparison between predicted and observed settlements Fig. 7. Case history No. 5: loading test results on single pile
Fig. 9. Case history No. 8: layout of the test and subsoil profile It may be seen that the LE analysis allows a rather good prediction of the actual settlement up Considering that the predrilled hole disconnects the pile from the upper gravelly layer, a subsoil model with five elastic layers resting on a rigid base has been adopted in the analysis; it is also shown in Fig. 9.
Fig. 9. Case history No. 8: layout of the test and subsoil profile It may be seen that the LE analysis allows a rather good prediction of the actual settlement up Considering that the predrilled hole disconnects the pile from the upper gravelly layer, a subsoil model with five elastic layers resting on a rigid base has been adopted in the analysis; it is also shown in Fig. 9.
Fig. 10. Case history No. 8: comparison between predicted and observed load—settlement curves; the ELE curve has been obtained using at each load level the secant modulus evaluated at the same level from the load test on a single pile
Fig. 10. Case history No. 8: comparison between predicted and observed load—settlement curves; the ELE curve has been obtained using at each load level the secant modulus evaluated at the same level from the load test on a single pile
Fig. 11. Case history No. 9: subsoil profile and subsoil model adopted in the analysis; the geometry of the model and the ratio between the moduli of any | layers are the same as assumed by Poulos (1993)
Fig. 11. Case history No. 9: subsoil profile and subsoil model adopted in the analysis; the geometry of the model and the ratio between the moduli of any | layers are the same as assumed by Poulos (1993)
Fig. 12. Case history No. 9: comparison between predicted and observed settlements
Fig. 12. Case history No. 9: comparison between predicted and observed settlements
Fig. 13. Case histories Nos. 10, 11 and 12: layout of the foundation
Fig. 13. Case histories Nos. 10, 11 and 12: layout of the foundation
Fig. 14. Case histories Nos. 10, 11 and 12: schematic plan and section of the structure
Fig. 14. Case histories Nos. 10, 11 and 12: schematic plan and section of the structure
Fig. 15. Case histories Nos. 10, 11 and 12: subsoil profile and properties, and subsoil model adopted in the analysi:
Fig. 15. Case histories Nos. 10, 11 and 12: subsoil profile and properties, and subsoil model adopted in the analysi:
Fig. 16. Case histories Nos. 10, 11 and 12: load—settlement curves of four load tests on piles (PLC, preloading cell)
Fig. 16. Case histories Nos. 10, 11 and 12: load—settlement curves of four load tests on piles (PLC, preloading cell)
Fig. 17. Case histories Nos. 10, 11 and 12: loading history and settlement observed during and after ‘onstruction
Fig. 17. Case histories Nos. 10, 11 and 12: loading history and settlement observed during and after ‘onstruction
* Pile C underwent a brittle failure at a load of 18 MN. As stated elswhere, the value of Qiim reported in the table is intended only as a geometrical parameter of the hyperbola fitting the initial part of the load—settlement curve. Table 3. Data resulting from the load tests on single piles
* Pile C underwent a brittle failure at a load of 18 MN. As stated elswhere, the value of Qiim reported in the table is intended only as a geometrical parameter of the hyperbola fitting the initial part of the load—settlement curve. Table 3. Data resulting from the load tests on single piles
Table 4. Parameters for the analysis At the site of the bridge over the river Gariglia- no (cases 13 and 17), a set of cross-hole measure- ments of the shear wave velocity were published by Mancuso & Mandolini (1993); they also carried out a number of vibration measurements during the driving of piles, and interpreted them in terms of shear wave velocity. The results they obtained lead to values of the shear modulus Gp equal to 18 MPa in a surface crust, and then increasing with depth from 9 MPa at a depth of 5m to 30 MPa at a depth of 30 m below ground surface.
Table 4. Parameters for the analysis At the site of the bridge over the river Gariglia- no (cases 13 and 17), a set of cross-hole measure- ments of the shear wave velocity were published by Mancuso & Mandolini (1993); they also carried out a number of vibration measurements during the driving of piles, and interpreted them in terms of shear wave velocity. The results they obtained lead to values of the shear modulus Gp equal to 18 MPa in a surface crust, and then increasing with depth from 9 MPa at a depth of 5m to 30 MPa at a depth of 30 m below ground surface.
Fig. 18. Case histories Nos. 10, 11 and 12; comparison between predicted and observed settlements for some alignments shown in Fig. 13 and around the perimeter of the raft
Fig. 18. Case histories Nos. 10, 11 and 12; comparison between predicted and observed settlements for some alignments shown in Fig. 13 and around the perimeter of the raft
Fig. 19. Comparison between predicted and observed settlements: (a) average settlement, LE analysis; (b) average settlement, NL analysis; (c) average settlement, ELE analysis; (d) maximum differential settlement, LE and NL analysis; (e) maximum differential settlement, ELE analysis
Fig. 19. Comparison between predicted and observed settlements: (a) average settlement, LE analysis; (b) average settlement, NL analysis; (c) average settlement, ELE analysis; (d) maximum differential settlement, LE and NL analysis; (e) maximum differential settlement, ELE analysis
Table 5. Values of the small-strain shear modulus of the pyroclastic soils in the eastern Naples area, as deduced by shear wave velocity measurements and back-figured from load tests on single piles at three building sites Fig. 20. Case history No. 18: soil properties and subsoil model assumed in the analysis
Table 5. Values of the small-strain shear modulus of the pyroclastic soils in the eastern Naples area, as deduced by shear wave velocity measurements and back-figured from load tests on single piles at three building sites Fig. 20. Case history No. 18: soil properties and subsoil model assumed in the analysis
Table 6. Comparison between different evaluations of the average settlement of buildings in eastern Naples Area “These analyses refer to a load level lower than that at the end of construction.
Table 6. Comparison between different evaluations of the average settlement of buildings in eastern Naples Area “These analyses refer to a load level lower than that at the end of construction.

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Proposal Mehran Naghizadehrokni Non–Linear Analysis of Soil–Pile–Structure Interaction on Structures with Piled Raft Foundation
Mehran Naghizadeh
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Prediction of elastic settlement of rectangular piled raft foundation
Jagat Jyoti Mandal

Japanese Geotechnical Society Special Publication, 2016

A FE -BE coupling technique is used in the present study for prediction of elastic settlement of rectangular piled raft foundations. The raft is idealised as a thick plate freely resting on soil medium, which is idealised as a semi-infinite, isotropic and homogeneous elastic half -space. The plate and the half-space are two separate models in unilateral and frictional contact at the interface. Pile is idealised as a spring of equivalent stiffness, obtained from simplified approach based on elastic theory assuming it to be a shaft in the half-space. Boundary element method is employed to determine the soil stiffness matrix by inverting the soil flexibility matrix, using Mindlin's solution for a point load in half-space as a fundamental solution. Finite element method is employed to determine the raft stiffness matrix based on Mindlin's plate bending theory, which allows transverse shear deformation. Transformation of the boundary element matrices are carried out to make it compatible for coupling with plate stiffness matrix obtained from finite element method. Combined stiffness matrix of the soil-pile-raft system is obtained by summing up the stiffness of the soil-raft system and the stiffness contribution of the piles at selected locations. A computer programme is developed, based on the procedure describe above, in which discretisation is automatic and requires very nominal data input. Effect of pile parameter on settlement of a piled raft system subjected to uniformly distributed load is studied for different number and configuration of piles to demonstrate the efficacy of piled raft system in reducing settlement.

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Numerical Analysis of Piled-Raft Foundations on Multi-Layer Soil Considering Settlement and Swelling
Dr. Zaheer Ahmed Almani

Buildings, 2022

Numerical modelling can simulate the interaction between structural elements and the soil continuum in a piled-raft foundation. The present work utilized a two-dimensional finite element Plaxis 2D software to investigate the settlement, swelling, and structural behavior of foundations during the settlement and swelling of soil on various soil profiles under various load combinations and geometry conditions. The field and laboratory testing have been performed to determine the behavior soil parameters necessary for numerical modelling. The Mohr–Coulomb model is utilized to simulate the behavior of soil, as this model requires very few input parameters, which is important for the practical geotechnical behavior of soil. From this study, it was observed that, as soil is soft and has less stiffness, the un-piled raft was not sufficient to resists and higher loads and exceeds the limits of settlement. Piled raft increases the load carrying capacity of soil, and the lower soil layer has a...

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Numerical Analysis of Settlement of a Piled Raft Foundation on Coastal Soil
Civil Engineering Journal (civilejournal.org)

Civil Engineering Journal, 2023

There is a growing demand for multi-story buildings for residence and commercial purposes in coastal areas of Sindh, Pakistan. Such types of soils are generally considered more compressible with high groundwater levels, which may cause lower shear strength and higher settlement. The computation of the settlement of foundations requires the use of advanced constitutive models, which are not commonly used due to a lack of field or experimental data. This study is carried out to illustrate the use of an advanced soil model, i.e., Hardening Soil Model for the computation of settlement. For this purpose, numerical modeling was carried out using Finite Element Program PLAXIS 2D. Initially, the MC Model was utilized for the calculation of the settlement of a 10-story building in the coastal soil. In addition, parametric analyses for the effects of modulus of elasticity, permeability, and dilatancy angle were carried out. The results mainly suggest that the settlement of the building constructed on a piled raft foundation, predicted with the MC model, was 40% higher than that of the HS model. For prediction of settlement of the piled raft foundation, the results suggest that the HS model can be given preference as compared to the MC model.

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Numerical analysis of piled raft foundation in sandy and clayey soils
Arumugam Balasubramaniam

This paper presents 2-D and 3-D numerical analysis of un-piled raft and piled raft foundation on two different soil conditions. The numerical analysis was carried out in two case studies with three typical load intensities of the serviceability load. The first case study investigates the raft-pile-soil interaction in sandy soil. The second case study examines the raft-pile-soil interaction in soft clay. Finally, the behaviours of piled raft foundation in two different case studies are assessed and conclusions are made.

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    Sven Hansbo Lecture: Deep foundation design - Issues, procedures and inadequacies
    Harry Poulos

    2019

    This paper reviews the key issues that must be addressed in the design of deep foundations, especially for support of high-rise buildings. Common design criteria are then set out, and a three-stage design process is outlined. The importance of geotechnical site characterization is emphasised. Some of the available design tools are discussed, together with their limitations, and a comparison is made of analysis results from four different programs. Finally, some perceived inadequacies of common design procedures are discussed, including: ignoring foundation interactions, assuming a rigid raft, oversimplification of the ground profile, ignoring external ground movements, and ignoring kinematic seismic effects. Examples of the consequences of these inadequate procedures are illustrated via relevant case histories.

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    Flexible Pile Group Interaction Factors under Arbitrary Lateral Loading in Sand
    Diethard König

    Journal of Marine Science and Engineering, 2020

    Marine and harbor structures, wind turbines, bridges, offshore platforms, industrial chimneys, retaining structures etc. can be subjected to significant lateral loads from various sources. Appropriate assessment of the foundations capacity of these structures is thus necessary, especially when these structures are supported by pile groups. The pile group interaction effects under lateral loading have been investigated intensively in past decades, and the most of the conducted studies have considered lateral loading that acts along one of the two orthogonal directions, parallel to the edge of pile group. However, because of the stochastic nature of its source, the horizontal loading on the pile group may have arbitrary direction. The number of studies dealing with the pile groups under arbitrary loading is very limited. The aim of this paper is to investigate the influence of the arbitrary lateral loading on the pile group response, in order to improve (extend) the current design app...

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    An analytical continuum model for axially loaded end‐bearing piles in inhomogeneous soil
    Aggelos Tsikas

    International Journal for Numerical and Analytical Methods in Geomechanics, 2019

    An approximate static solution is derived for the elastic settlement and load-transfer mechanism in axially loaded end-bearing piles in inhomogeneous soil obeying a power law variation in shear modulus with depth. The proposed generalised formulation can handle different types of soil inhomogeneity by employing pertinent eigen-expansions of the dependent variables over the vertical coordinate, in the form of static soil "modes", analogous to those used in structural dynamics. Contrary to available models for homogeneous soil, the associated Fourier coefficients are coupled, obtained as solutions to a set of simultaneous algebraic equations of equal rank to the number of modes considered. Closed-form solutions are derived for the: (i) pile head stiffness, (ii) pile settlement, axial stress, and side friction profiles leading to actual, depth-dependent, Winkler moduli, (iii) displacement and stress fields in the soil, (iv) average, depth-independent Winkler moduli to match pile head settlement. The predictive power of the model is verified via comparisons against finite-element analyses. The applicability to inhomogeneous soil of an existing regression formula for the average Winkler modulus is explored.

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    A Local Design Method for Pile Foundations
    Alessandro Mandolini

    Advances in Civil Engineering, 2018

    The work at hand attempts to propose a local pile design method based on pile load test results for a reference site. Such LPDM is simply based on the identification of three dimensionless quantities, such as the capacity ratio CR, the stiffness ratio SR, and the group settlement ratio Rs. To prove the LPDM reliability, experimental data collected during years in the Neapolitan area (Italy) have been used to obtain the abovementioned coefficients. Then, LPDM has been applied, as a preliminary design method, to three well-documented case histories applying capacity and settlement-based design (CBD and SBD) approaches. The satisfactory agreement between the geometry in the original design of piles and the one obtained by applying the LPDM proves that the proposed methodology may be very helpful for preliminary design, allowing for reasonable accuracy while requiring few hand calculations.

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    Load-Settlement Behaviour of Model Pile Groups in Sand Under Vertical Load
    Mauricio Sales

    Journal of Civil Engineering and Management, 2017

    Model pile load testing is effective to study the load-settlement behaviour of pile foundations given the con­trolled environment in which the testing is done. This paper reports a testing program in a large calibration chamber involving individual piles and pile groups installed in sand samples of three different densities. Tests on both nondis­placement and driven piles are evaluated to assess the influence of the pile installation process on pile load-settlement response. A method is proposed to predict the load-settlement response of a pile group based on the response of a single pile. The method is shown to produce estimates that are in good agreement with measurements. The influence of pile group configuration, pile spacing, soil density and method of pile installation is discussed.

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