Behaviour of piles subjected to passive loading due to ...

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ARTICLE Behaviour of piles subjected to passive loading due to embankment construction Can. Geotech. J. Downloaded from www.nrcresearchpress.com by University of New South Wales on 03/26/14 For personal use only.

M.R. Karim, S.-C.R. Lo, and C.T. Gnanendran

Abstract: Behaviour of two embedded piles subjected to passive loading due to construction of an embankment was modelled in this paper. The piles were installed at the berm section of an embankment in a later stage of its construction. The investigation was carried out using a combination of two- and three-dimensional analyses. The analysis results were compared with the field-measured values and they agreed well. Key words: post-construction subsoil movements, soft soil, pile, lateral bending. Résumé : Dans cet article, le comportement de deux pieux enfouis soumis a` des sollicitations passives causées par la construction d’un remblai est modélisé. Les pieux ont été installés dans la section de berme d’un remblai a` un stade avancé de sa construction. L’étude a été réalisée en utilisant une combinaison d’analyses en deux et trois dimensions. Les résultats de l’analyse ont été comparés a` des valeurs mesurées sur le terrain, et correspondent bien. [Traduit par la Rédaction] Mots-clés : mouvements du sol sous la surface post-construction, sol mou, pieu, flexion latérale.

Introduction It is not uncommon to see bridge abutments being supported on pile foundations. These structures and their pile foundations are often subjected to passive forces due to lateral movements of the foundation soils. The safety of the piled foundation may depend on additional stresses induced by passive forces from the soil. So far, there has been limited research – case studies on such embedded structures in a field scale. This paper numerically models the behaviour of two trial piles subjected to lateral subsoil movement due to the construction of Leneghans embankment (details are presented later). The behaviour of a pile and its interaction with surrounding soils is a three-dimensional (3D) problem and a 3D-capable numerical program FLAC3D (fast Lagrangian analysis of continua in three dimensions, developed by Itasca Consulting Group 2005), was used for this analysis. Leneghans embankment is a very large embankment founded on a 16.5 m thick clay layer with a base area of about 20 000 m2. To add to the complexity, it was constructed beside an existing embankment (Lo et al. 2008) and was improved with geosynthetics and also prefabricated vertical drains (PVDs). Three-dimensioanl modelling of such a large volume of soil with complicated features is difficult, time-consuming, and in some cases not practical. To save computational time in the analysis, a simplified approach was taken. A combination of two-dimensional (2D) and 3D consolidation analyses were used. Modelling of some of the more complicated aspects of the problem was avoided or simplified as will be discussed later in the paper in appropriate sections. In essence, the pile–soil interactions were modelled with a displacementbased elastoplastic FLAC3D analysis (of the piles and surrounding soils) and the input displacements were estimated from an appropriate 2D plane strain analysis. The elastoplastic Modified Cam Clay (MCC) model (Roscoe and Burland 1968) was used to model the foundation soil. It should be

noted that the Leneghans embankment foundation soil showed significant creep behaviour (Karim et al. 2010, 2011). However, two things were considered while choosing the constitutive model. Firstly, the investigation was conducted over a relatively shorter period of time (4 months) and secondly, the MCC model has been proven to calculate the lateral displacements with good accuracy for the case of Leneghans embankment foundation soil (Manivannan et al. 2011; Lo et al. 2013). Thus, from the authors’ experience with this particular site, the MCC model was considered adequate.

Leneghans embankment and the piles Details of Leneghans embankment, i.e., its construction sequence, foundation soil profiles, and instrumentation can be found in Lo et al. (2008) and Karim et al. (2010). A brief description is presented here. Leneghans embankment was constructed in the 1990s as a part of the Sydney–Newcastle highway extension project and is located about 150 km north of Sydney, Australia. Figure 1 presents the layout of the northern section of the embankment including location of the piles. The dashed lines represent chainage lengths. The embankment was constructed on top of a 16.5 m thick layer of high-plasticity soft clay that is underlain by a layer of shale bedrock. The reduced level (RL) of the natural ground at the embankment site varies between +0.5 and +0.9 m and the ground water table fluctuates between RL + 0.55 and +1.17 m. The embankment is about 300 m long, 32 m wide at the crest, and about 60 m wide at the foundation level and was constructed in four stages. In the first three stages, the construction reached a specified RL of +5.5 m, which took 366 days. In the fourth stage, which started at 578 days, it was preloaded with 1 m of fill. The preloading fill was subsequently removed at 807 days. The first three stages of the embankment construction sequence are presented in Fig. 2. Two different types of fill materials were used for the embankment construction, i.e., lightweight bottom ash for the core of the

Received 12 December 2012. Accepted 16 December 2013. M.R. Karim, S.-C.R. Lo, and C.T. Gnanendran. School of Engineering and Information Technology, University of New South Wales, Canberra, ACT 2600, Australia. Corresponding author: M.R. Karim (e-mail: [email protected]; [email protected]). Can. Geotech. J. 51: 303–310 (2014) dx.doi.org/10.1139/cgj-2012-0468

Published at www.nrcresearchpress.com/cgj on 16 December 2013.

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Fig. 1. Layout of embankment including location of trial piles and additional inclinometer (not to scale). RL, reduced level.

146820 m *

146 860 m

146 900 m

RL +.75m

N Plane strain modelling axis

RL +3.2m RL +5.5m

Northern Berm

RL +3.2m

Old Leneghans drive Trial pile

Additional inclinometer

*

Ground level at RL 0.75 m (average value)

Fig. 2. Construction sequence of Leneghans embankment (first three stages).

6

RL of embankment top 5

Reduced Level (m)

Can. Geotech. J. Downloaded from www.nrcresearchpress.com by University of New South Wales on 03/26/14 For personal use only.

RL +3.2m

4

3

2

1

0 0

100

200

300

400

Time (days)

embankment and heavier conventional fill materials for the berm sections and surcharging. As mentioned before, PVDs were installed (at 1.5 m triangular spacing) to accelerate consolidation and geosynthetics were used at the foundation level to enhance stability. The embankment was constructed beside an older road embankment (Old Leneghans drive) on the eastern side, which acted as a toe berm. A brief description of the installed piles (after Mak (1996)) is presented here. The locations of the piles are shown in Fig. 1. Both piles

are 22.2 m long driven piles, made of precast concrete and of octagonal shape with 550 mm diameter (with 1% steel reinforcement). Both of them were fitted with inclinometer tubes at their centre. A third inclinometer was installed at the mid distance between the installed piles to monitor soil lateral movements. The centre to centre distance between the piles is 3.5 m. One of the piles was fitted with an oversized casing to isolate its top 3 m from the action of surrounding soils. Hereafter, the pile without a casing will be referred to as pile 1, whereas the pile with a casing will be called pile 2. Published by NRC Research Press

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Fig. 3. Finite element mesh used for the analysis to estimate subsoil movement.


Location of displacement application face (approx)

Location of pile

Geosynthetic and interface (joint) elements

16.5 m

4m

4.5 m

20 m

14.5 m

32.5 m

Table 1. Foundation soil parameters of Leneghans embankment (Lo et al. 2008). Vertical permeability coefficients from one-dimensional consolidation tests and back-estimated multiplier

pc0 (kPa) at top of layer

RL

M

␭

␬

␷

ecs

Ki (m/day)

e0

ck

Multiplier

2D analysis

3D analysis

+0.3 to −2.8 m −2.8 to −7.8 m −7.8 to −10 m −10 to −16 m

1.113 1.113 1.113 1.113

0.33 0.38 0.38 0.33

0.066 0.076 0.076 0.066

0.3 0.3 0.3 0.3

2.70 3.08 3.08 2.70

3.0E−5 1.5E−5 1.5E−5 1.5E−5

1.78 1.78 1.78 1.78

0.83 0.83 0.83 0.83

4.32 4.32 4.32 4.32

152.9 122.48 52.99 57.68*

153 122.5 77.6 84.9*

Note: M, slope of the critical state line; ␭, compression index; ␬, recompression index; ␷, Poisson’s ratio; ecs, critical state void ratio; Ki, reference permeability; e0, reference void ratio; ck, slope of K–e plot; pc0, preconsolidation pressure of in situ soil. *pc0 below RL −10.0 m increases linearly with depth at a rate of 6.05 kPa/m.

The relative stiffness of the piles was found to be 1.12E-4 (calculated using KR = EpIp/(EsL4), where Ep and Ip are the elastic modulus and moment of inertia of the pile, respectively; Es is the average horizontal soil modulus along the pile; L is the length of the pile). The piles can be classified as flexible piles (as the relative stiffness is less than 10−2) (Mayerhoff 1979).

Soil lateral movements using a 2D analysis To estimate the lateral displacements acting on the piles, a plane strain fully coupled MCC consolidation analysis was carried out using the numerical program “A Finite Element Numerical Algorithm” (AFENA) originally developed at the University of Sydney (Carter and Ballam 1995) and further modified at the University of New South Wales, Canberra, Australia. The plane strain section is shown by the arrow in Fig. 1. It should be noted that the lateral foundation displacement may vary on different sections on the east or west side of the considered section in this paper. That means that piles 1 and 2 might have been subjected to different magnitudes of lateral forces. However, as the distance between the two piles was small compared to the length of the east–west face of the embankment, the difference should be minimal and the considered section should produce adequate estimation of the lateral deformation of the foundation soil. The mesh geometry along with the displacement boundary conditions are presented in Fig. 3.

Table 2. Properties of embankment fill materials and interface elements. Parameter

Lightweight bottom ash

Properties of fill material c (kPa) 5.0 ␾ (°) 40 ␺ (°) 7 ␥ (kN/m3) 14.0 ␯ 0.3

Conventional fill 5.0 28 4 20.0 0.3

Duncan and Chang (1970) parameters K 500 500 m 0.5 0.5 Interface elements Cf (kPa) 3 ␾ (°) 35

3 35

Note: c, cohesion; ␾, angle of internal friction; ␺, dilation angle; ␥, bulk unit weight; ␯, Poisson's ratio; K and m, Duncan and Chang (1970) parameters; Cf, cohesion intercept for the joint shear strength.

After trials with a few different cross sections, a 20 m section of the main embankment with the northern berm section of the embankment was considered appropriate. Any extension of the geometry on the left-hand side (Fig. 3), i.e., southward in Fig. 1, Published by NRC Research Press

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5

5

0

0

-5

-5

-10

-10

RL (m)


Fig. 4. Calculated soil lateral displacement during installation of pile and after 90 and 120 days of installation.

-15

at 547 days (pile installation) at 578 days (preloading start date) at 637 days (90 days after pile installation) at 667 days (120 days after pile installation)

-20

-15

-20 0

50

100

150

200

250

Total displacements (mm) Fig. 5. Incremental displacements after installation of pile plotted against RL.

did not significantly alter the calculated lateral displacement profiles. The side and the bottom boundaries of the plane strain mesh were modelled as impermeable and the top of the foundation soil was modelled as permeable, i.e., zero excess pore water pressure (pwp) boundary because of the presence of a sand blanket that was laid during the early stages of construction. The PVDs were modelled as free draining (after Karim et al. (2011)). Subsequently, a “plane strain equivalent horizontal permeability”, Kh#, that could represent the combined effect of smear zone reduced permeability and permeability in the undisturbed

zone was used for the analysis and was calculated using the procedure described in Hird et al. (1992). After a few trials, the plane strain equivalent drain spacing was chosen as 4 m. The permeability of the soil was allowed to vary with void ratio according to the following relationship: (1)

logK ⫽ logKi ⫺

e0 ⫺ e ck

where K is permeability of the soil, Ki is a reference permeability (can be horizontal, vertical or “equivalent”) at the reference void Published by NRC Research Press

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Fig. 6. FLAC3D mesh geometry used for pile analysis: (a) 3D view and (b) top view.

(a) pile 1

pile 2

(b) 16.5m found. soil.


5m 4m Bed rock

3.5m

5m 39 m

3m

36 m

13.5 m

displacement application face

Table 3. Material properties for concrete pile and interface elements. Material properties

Values adapted for analysis

Elastic pile Dry density (kg/m3) Young’s modulus (GPa) Poisson’s ratio Bulk modulus (GPa) Shear modulus (GPa)

2500 25.0 0.2 13.9 10.4

Interface elements Friction angle (°) Cohesion (kPa)

19 25

ratio of e0, e is current void ratio of the soil, and ck is slope of the K–e plot (i.e., a semi-log plot with K plotted in log scale on the vertical axis). The coefficients of eq. (1) was estimated from oedometer tests conducted on Leneghans embankment foundation soil. More details on permeability estimation can be found in Karim et al. (2010, 2011) and Manivannan et al. (2011). As mentioned before, the foundation soil was modelled with the elastoplastic MCC model. All the material parameters, except for the values of in situ preconsolidation stresses, were deduced from a comprehensive set of laboratory tests. The in situ preconsolidation stresses were estimated using the undrained shear strength profiles (Lo et al. 2008). The MCC material parameters are presented in Table 1. The foundation soil – geosynthetic and geosynthetic-embankment fill interaction was modelled using nondilatant nodal compatibility joint elements. The geosynthetic reinforcement (Paralink 200 M) was modelled as linear elastic bar elements with manufacturerprovided material parameters (i.e., axial stiffness of 1760 kN/m at a strain level of 5% and tensile strength of 125 kN/m). Both types of embankment fill materials were modelled as Mohr–Coulomb solids and the Duncan and Chang (1970) equation was used to allow for the change in stiffness of the soil due to change in effective stresses. The properties of the embankment fill materials and the interface elements were reported by Karim et al. (2011) and are presented in Table 2. The shale bedrock, present at the bottom of the foundation soft clay layers, was also

Table 4. Calculated stress and pore-water pressure changes due to pile driving. Pore-water pressure change (kPa) Depth from ground surface (m)

Zone 1

Zone 2

0–1 1–2 2–3 3–4 4–5 5–6 6–7 7–8 8–9 9–10 10–11 11–12 12–13 13–14 14–15 15–16.5

4.539038 18.83708 23.10636 24.70313 26.08616 27.7859 29.16636 30.64014 32.18712 35.36894 38.51033 42.11264 45.70975 49.30257 52.89179 56.47798

0 0 5.813032 6.218944 6.568324 6.995158 7.338718 7.704265 8.087513 8.896589 9.692567 10.60341 11.50905 12.41039 13.30815 14.20286

modelled using the Mohr–Coulomb model, but with higher values of Young’s modulus (1 GPa) and cohesion of 3 MPa. To obtain appropriate input lateral deformations for the 3D analysis, the embankment was analysed from the start of the construction to the day of installation of piles and continued throughout the monitoring period. Four displacement profiles were taken at the location of the maximum displacements (approximately 3 m to the south from the location of the piles) at 547, 578, 637, and 667 days, coinciding with the pile installation date, preloading start date, 90 days after pile installation, and 120 days after pile installation, respectively. The total displacement profiles are presented in Fig. 4. It can be seen in Fig. 4 that there were very little lateral movements occurring in the foundation soil after the installation of the piles and until the start of preloading. Almost all of the lateral movements occurred because of the preloading. The incremental displacement profiles (from the date of pile installation) were Published by NRC Research Press

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Fig. 7. Predicted and recorded lateral deformation profiles for pile 1 at 90 and 120 days after date of installation. 5

RL (m)


0

-5

-10 Field 90 days Field 120 days FLAC 90 days MCC FLAC 120 days MCC

-15

-20 0

0.01

0.02

0.03

0.04

0.05

Displacements (m) calculated from Fig. 4 and were used as input displacements for the subsequent 3D analyses. The incremental profiles are presented in Fig. 5.

Behaviour of piles using 3D analysis This part of the analysis was carried out using FLAC3D (Itasca Consulting Group 2005). The mesh geometry used in the 3D analysis is presented in Fig. 6. The width of the geometry (perpendicular to the plane strain axis) was taken to be 13.5 m. Displacement was applied on the face of the geometry as indicated in the figure. The distance between the pile centres to the face of application of displacement was kept at 3 m. A length of 36 m beyond the location of the piles was modelled to eliminate any boundary effect. All the side boundaries (except for the face of application of the displacement) and the bottom boundary were modelled to have zero displacement in the appropriate directions. Similar to the previous analysis, the foundation soil was modelled using elastoplastic MCC material. Due to the construction of the embankment, the in situ preconsolidation pressure of the soil changed. The updated preconsolidation pressure values were taken from the 2D analysis; and are presented in Table 1. All the other MCC parameters were unchanged. The embankment fill material properties were as shown in Table 2. The geosynthetic was not modelled as its effect could be treated as insignificant during the period under consideration in the 3D analysis (Karim et al. 2012). The piles were modelled as isotropic elastic solids based on the estimated maximum bending moment and the pile bending moment capacity. The maximum bending moment in the pile in this study was estimated to be 190 kN·m (Fleming et al. 2008), which was much less than the yield moment (338 kN·m) of the pile. The material properties of the piles are presented in Table 3. Interface elements were used on the outer perimeter of the pile shaft and hence joined the pile and the adjacent soils. A friction angle of 19° and a cohesion of 25 kPa was considered appropriate as the interface properties (NFEC 1986). To save computational time, PVDs were modelled as their 2D equivalents. The effect of PVDs was represented by creating zero

excess pwp boundary planes at 3 m intervals and the Kh# of the soil was adjusted accordingly using a procedure derived from Hird et al. (1992). Driving of piles induces changes in stresses and pwp in the surrounding soils. A set of simplified solutions was proposed by Randolph et al. (1979) and Randolph and Wroth (1979) for calculating these changes and were used in this study. They were calculated assuming that, under undrained conditions, the mean effective stress remains constant and thus the excess pwp is equal to the change in mean total stress (Randolph and Wroth 1979). The zone of influence was divided into two subzones and average changes were applied for calculation and modelling simplicity. The extents of zones 1 and 2 were considered to be 0.725 and 1.725 m from the outer perimeter of the piles, respectively. The soil outside this range was found not to be significantly affected by the pile driving process. The calculated pwp changes are tabulated in Table 4. After generating the initial stresses in the 3D mesh, the pile zones (elements) were activated and the calculated changes in stresses and pwp due to pile driving were added to the surrounding soil zones. Incremental displacements were applied (in the form of velocity) on each grid point (node) on the face of the geometry as indicated in Fig. 5. As mentioned in a previous section, there was very small subsoil movement occurring after the installation of the piles and until the first day of preloading. Taking this into account, increments of displacements were started only after the start of preloading. To ensure convergence, small incremental time steps were used and the out-of-balance forces were always within acceptable limit.

Results and discussion The field-measured and calculated lateral deformations for pile 1 at 90 and 120 days (from the day of pile installation) are presented in Fig. 7. As can be seen from the figure, the shapes of the displacement profiles have been calculated with very good accuracy along with the location of the maximum displacements. However, the magnitude of the displacements was consistently Published by NRC Research Press

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Fig. 8. Predicted and recorded lateral deformation profiles for pile 2 at 90 and 120 days after date of installation. 5 Field 90 days Field 120 days FLAC 90 days MCC FLAC 120 days MCC

RL (m)

-5

-10

-15

-20 0

0 .02

0 .0 4

0 .06

Displacements (m) Fig. 9. Predicted and recorded lateral deformation profiles at inclinometer location at 90 and 120 days after date of installation. 5

0

RL (m)


0

-5

-10 Field 90 days Field 120 days FLAC 90 days MCC FLAC 120 days MCC

-15

-20 0

0.02

0.04

0.06

Displacements (m) overcalculated throughout the depth for both field measurement dates. The maximum displacement was overcalculated by about 40% and 20% at 90 and 120 days, respectively. This might be attributed to the inherent tendency of the constitutive model used in the 2D analysis to overcalculate the input lateral displacements (Karim et al. 2011; Manivannan et al. 2011). The field profiles show considerable difference in magnitude of displacements occurring during the time period between 90 and 120 days. The calculated profiles on the other hand showed that the displacements were es-

sentially ceasing after 90 days. This was somewhat expected as there was not much difference between the 90 and 120 day input deformation profiles as shown in Fig. 5 and can be attributed to use of the MCC model in calculating the input deformations. Figure 8 presents the field-measured lateral deformations along with the numerical analysis results for pile 2, which was fitted with an oversized casing to isolate its top 3 m from the action of surrounding soils. The shapes of the profiles, also in this case, have been captured with reasonable accuracy. Both calculated Published by NRC Research Press


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profiles (at 90 and 120 days) showed the maximum pile displacement occurring at the top of the pile and it was consistent with the field observation. For the 90 day profile, the 3D analysis calculated the pile displacement on the conservative side and the maximum displacement was calculated almost perfectly. However for the case of the 120 day profile, the maximum lateral displacement was undercalculated. The difference in the shapes of displacement profiles between piles 1 and 2 suggest that the top few metres of soil, which were highly overconsolidated, played a significant role in the lateral bending behaviour of the piles. Figure 9 presents the calculated and recorded lateral deformations at the inclinometer that was installed between the two piles. In this case as well, the locations and magnitude of maximum displacements were captured with very good accuracy at both 90 and 120 days. For the 90 day profile, the maximum deformation was overcalculated by about 20% and it was about 3% for the 120 day profile. It should be noted that the soil deformations recorded in the inclinometer (between the piles) are higher than that for pile 1 on both the dates. This might be due to the higher stiffness of piles, which provided higher resistance against lateral bending. This is also consistent with the field observations.

Conclusion and discussion The effect of passive loading on a pair of abutment piles due to construction activities on a nearby embankment have been modelled in this paper using simplified analysis techniques. Some of the complicated features of the problem such as creep in the foundation soil and dynamic effects of pile installation were not taken into account. The analysis was conducted in two steps. The pile–soil interaction was modelled using a displacement-based 3D analysis and the input deformations were calculated using a simplified plane strain analysis. Despite the simplifications, the analyses captured the lateral deformation behaviour, including the shapes of the profiles, as well as the location of maximum deformation along with its magnitude for both piles with acceptable accuracy. The lateral deformation profile at the inclinometer location (between the two piles) was also calculated with good accuracy. The good agreement with the field-measured value suggests that the simplifications in this paper can be considered as acceptable.

Acknowledgements The generous and kind support provided by the NCI National Facility, Australia, to the third author towards this research project is gratefully acknowledged. Also acknowledged are the generous help and support (with field monitoring data, soil samples,


and laboratory test results) of Transport Roads & Maritime Services (erstwhile RTA), NSW, Australia. The opinions expressed in this paper, however, are solely those of the authors.

References Carter, J.P., and Ballam, N.P. 1995. AFENA users’ manual. Version 5.0 [computer program]. Center for Geotechnical Research, University of Sydney, Sydney, Australia. Duncan, J.M., and Chang, C.-Y. 1970. Nonlinear analysis of stress and strain in soils. Journal of the Soil Mechanics and Foundation Division, ASCE, 96(SM5): 1629–1653. Fleming, K., Weltman, A., Randolph, M., and Elson, K. 2008. Piling engineering. Taylor & Francis, Hoboken, N.J. Hird, C.C., Pyrah, I.C., and Russel, D. 1992. Finite element modelling of vertical drains beneath embankments on soft ground. Géotechnique, 42(3): 499–511. doi:10.1680/geot.1992.42.3.499. Itasca Consulting Group, Inc. 2005. Fast Lagrangian Analysis of Continua in 3 dimensions user’s guide. Itasca Consulting Group, Inc., Minneapolis, Minn. Karim, M.R., Gnanendran, C.T., Lo, S.-C.R., and Mak, J. 2010. Predicting the longterm performance of a wide embankment on soft soil using an elasticviscoplastic model. Canadian Geotechnical Journal, 47(2): 244–257. doi:10. 1139/T09-087. Karim, M.R., Manivannan, G., Gnanendran, C.T., and Lo, S.-C.R. 2011. Predicting the long-term performance of a geogrid-reinforced embankment on soft soil using two-dimensional finite element analysis. Canadian Geotechnical Journal, 48(5): 741–753. doi:10.1139/t10-104. Karim, M.R., Gnanendran, C.T., and Lo, S.-C.R. 2012. Effect of geosynthetic reinforcement creep on the long term performance of an embankment. In State of the Art and Practice in Geotechnical Engineering Geo-Congress 2012, Oakland, Calif. pp. 1330–1339. Lo, S.R., Mak, J., Gnanendran, C.T., Zhang, R., and Manivannan, G. 2008. Longterm performance of a wide embankment on soft clay improved with prefabricated vertical drains. Canadian Geotechnical Journal, 45(8): 1073–1091. doi:10.1139/T08-037. Lo, S.-C.R., Karim, M.R., and Gnanendran, C.T. 2013. Consolidation and creep settlement of embankment on soft clay: prediction vs. observation. In Geotechnical predictions and practices in dealing with geohazards. Edited by J. Chu, J.M. Hoover, S.P.R. Wardani, and A. Iizuka. Springer, Dordrecht. pp. 77–94. Mak, J. 1996. F3 freeway, City of Newcastle, Leneghans Drive, Minimi to Beresfield, Swamp-2, Monitoring report no. 3. Scientific Services Branch, RTA. G2510/4. Manivannan, G., Karim, M.R., Gnanendran, C.T., and Lo, S.-C.R. 2011. Calculated and observed long term performance of Leneghans embankment. Geomechanics and Geoengineering, 6(3): 195–207. doi:10.1080/17486025.2011.578667. Mayerhoff, G.G. 1979. Soil-structure interaction and foundations. In Proceedings of the 6th Panamerican Conference on Soil Mechanics, Lima, Peru. pp. 109–140. NFEC. 1986. Foundation and earth structures, design manual 7.02. Naval Facilities Engineering Command, Washington, D.C. Randolph, M.F., and Wroth, C.P. 1979. An analytical solution for the consolidation around a driven pile. International Journal for Numerical and Analytical Methods in Geomechanics, 3: 217–229. doi:10.1002/nag.1610030302. Randolph, M.F., Carter, J.P., and Wroth, C.P. 1979. Driven piles in clay - the effects of installation and subsequent consolidation. Géotechnique, 29(4): 361–393. doi:10.1680/geot.1979.29.4.361. Roscoe, K.H., and Burland, J.B. 1968. On the generalized stress-strain behaviour of wet clay. Cambridge University Press, Cambridge, UK.

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