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International Journal of Civil Engineering and Technology (IJCIET)Volume 9, Issue 11, November 201

Available online at http://www.iaeme.com/ijciet/issues.

ISSN Print: 0976-6308 and ISSN Online: 0976

©IAEME Publication

BEHAVIOR OF PILED

UNDER EARTHQUAKE LOA

Q. S. Mohammed Shafiqu and R. H.

Department of Civil Engineering, College of Engineering,

Al

ABSTRACT

In this research, the seismic piled raft foundation behavior is investigated via

finite element method. Analyses of the numerical model of multi

applied under the acceleration time history for the Ha

soil types of Iraq. And a parametric study is carried out for investigating the influence

of earthquake acceleration characteristics on the bending moment values along the

piles and settlements of raft foundation. The

one of the most effective dynamic parameter that affected on piles bending moment

and raft settlements. The bending moment values in all piles and raft settlements are

obtained to be higher in cohesive soils than in coh

also coherent with the fact that the shear wave velocities of the clayey soils had higher

values than the shear wave velocities of the sandy soils analysed in this study. The

higher values for bending moments along piles

occurs at soil profiles consisting of soft cohesive soils with large thickness reaching to

about half piles length underlain by layers of medium to loose cohesionless soils.

While the lowest moments and settlements appe

of rock or very dense silty sand. The maximum values of the bending moments has

been obtained at head of piles or at depth of about 5

from the top.

Keywords: Piled-Raft, Earthquake, Dy

Cite this Article: Q. S. Mohammed Shafiqu and R. H. Sa'ur, Behavior of Piled

Foundation Under Earthquake Loading In Various Types of Soil

Journal of Civil Engineering and Technology (IJCIET)

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=9&IType=11

1. INTRODUCTION

The foundation of high-rise building is usually piled foundation subjected to a combined of

normal, horizontal and overturning loads. Foundation of piled

buildings as the raft provides a bearing capacity estimated based on each element stiffness.

IJCIET/index.asp 2770 [email protected]

International Journal of Civil Engineering and Technology (IJCIET) 2018, pp. 2770–2781, Article ID: IJCIET_09_11_277

http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=

and ISSN Online: 0976-6316

Scopus Indexed

BEHAVIOR OF PILED-RAFT FOUNDATION

UNDER EARTHQUAKE LOADING IN VARIOUS

TYPES OF SOIL

Q. S. Mohammed Shafiqu and R. H. Sa'ur


Al-Nahrain University, Baghdad, Iraq


nalyses of the numerical model of multi-storey building were

applied under the acceleration time history for the Hallabjah earthquake in differe

parametric study is carried out for investigating the influence


piles and settlements of raft foundation. The results indicate the shear wave velocity as



obtained to be higher in cohesive soils than in cohesionless soils. This conclusion is



higher values for bending moments along piles and raft settlements were generally



While the lowest moments and settlements appeared in soil profiles consisting mostly


been obtained at head of piles or at depth of about 5-15% of the pile length measured

Raft, Earthquake, Dynamic Behavior, Various Soils.

Q. S. Mohammed Shafiqu and R. H. Sa'ur, Behavior of Piled

Foundation Under Earthquake Loading In Various Types of Soil

Journal of Civil Engineering and Technology (IJCIET) 9(11), 2018, pp.


rise building is usually piled foundation subjected to a combined of

normal, horizontal and overturning loads. Foundation of piled-raft type may be used for such


[email protected]

IJCIET_09_11_277

asp?JType=IJCIET&VType=9&IType=11

RAFT FOUNDATION

DING IN VARIOUS



storey building were

llabjah earthquake in different

parametric study is carried out for investigating the influence


indicate the shear wave velocity as



esionless soils. This conclusion is



and raft settlements were generally



ared in soil profiles consisting mostly


15% of the pile length measured

Q. S. Mohammed Shafiqu and R. H. Sa'ur, Behavior of Piled-Raft

Foundation Under Earthquake Loading In Various Types of Soil, International

p. 2770-2781.


rise building is usually piled foundation subjected to a combined of

t type may be used for such


Behavior of Piled-Raft Foundation Under Earthquake Loading In Various Types of Soil

http://www.iaeme.com/IJCIET/index.asp 2771 [email protected]

Piled raft foundation behavior under earthquake loads is considered very significant and can

influence the stability of structure, and its performance. In liquefiable or soft soil conditions

the consequences can be severe. Davis and Poulos [3] introduced the idea for utilizing piled

raft foundation, and then many researchers described the performance of such foundation

system. Recently various methods for piled raft analysis are presented due to increase of using

such foundations for high-rise buildings instead of relying only on the capacity of the piles.

Many researchers have extensively studied the normal load bearing mechanism by using the

elasticity theory [10] and by applying the finite element method [12]. Piled rafts are designed

in practical use, depending on these results. Studies on the piled raft foundation response

under lateral loads or when subjected to seismic action, however, are rare [4;6]. The

complexity of the behavior during earthquakes due to dynamic interaction among a raft, piles

and a soil necessitates that the design method should include the influence of this mechanism

in an appropriate manner.

The behavior of the raft built on piles in clayey soil subjected to seismic loads is a

problem that attracts the interest of many researchers recently [13]. However, the researches

on the behavior of piled raft under lateral and earthquake loadings in soft clayey soil are

relatively very limited. Furthermore the influence of using piled raft as foundation for a tall

building considering interaction of soil-structure was investigated [2]. In this study where a

Finite Element Code ANSYS was used to model the behavior, it was concluded that soil-

structure interaction was effectively influencing the structure behavior. In another study, the

dynamic response of a 25-storey building resting on piled raft foundation was examined [11]

using SAP 2000 software. It was found that the piled raft in subsoil of dense sand was a

perfect combination for good bearing behavior of the building.

In the current study, procedure for modeling piled raft in various types of soil under

seismic load using PLAXIS software is presented. A parametric study is done dealing with

effect of subsoil types on the behavior of piled raft as foundation for tall building under the

effect of Halabjah earthquake.

2. MODELLING AND ANALYSIS

By finite element technique with using PLAXIS program the piled raft is modelled as solid

elements with finite meshing and the frame system is modelled as a 3D frame. Moreover, up

to a sufficient depth, the soil is taken into consideration knowing that from all four sides the

boundaries are restricted to appropriate distance from the frame structure. The soil mass is

modelled by Mohr-Coulomb and the piles are assumed as a slender beam elements, which are

virtually connected to soil by skin and base interfaces. These structural elements can have

arbitrary cross and inclination through the soil elements at arbitrary positions. The interaction

of the soil and pile at the base is modelled by considering point to volume interface elements,

while the interaction at the skin interface is modelled by line to volume interface elements.

3. NUMERICAL MODELLING OF PILED RAFT FOUNDATION

UNDER EARTHQUAKE LOADING

In this numerical analysis, a 10 storey square building with the same structural system for the

problem of a 15-storeybuilding tested under static force[1] is selected. The raft is at 2.0 m depth

under the ground surface. The dimensions of raft are 25 m × 25 m × 1.5 m with an overhang

of 2.5 m. A 0.75 m diameter concrete circular pile with depth of 15m and a total number of

25 is used below the raft. The parameters for structural, soil and pile elements are as in Table

2.



Table 1Structural, pile and soil parameters[1]

Material

Unsaturated

weight

(γunsat), kN/m3

Saturated

weight

(γsat),kN/m3

Modulus of

elasticity

(E ), kN/m2

Poisson’s

ratio

(ν)

Dilatancy

(ψ),

degree

Friction

angle

(φ),

degree

Cohesion

(c),

kN/m2

Concrete 25 - 3.4 × 107 0.2 - - -

Pile 25 - 2.35 × 107 0.2 - - -

Loose Sand 17 20 20000 0.2 2 32 0.1

Dense Sand 19 21 60000 0.2 8 38 0.1

The PLAXIS 3D program is used for the analysis of the 10-storey building structure

having piled-raft foundation in various soil layers for different sites in Iraq area. The columns

and piles are modelled as frame elements while the floor slab and raft are modelled using

triangular plate elements. Also wedge triangular continuum type elements are modelled soil

layers. The linear elastic and non-linear Mohr-Coulomb models are considered for structural

and soil elements respectively. Figure (1) show connectivity plot and finite element mesh

plots for the piled raft in a typical site.

Figure 1 Connectivity plot and Finite Element Mesh for the piled raft in S10 site

3.1. Soil Properties used in the Analyses

In this study, the database prepared by Mohammed Shafiqu and Abdulrasool [7] with respect

to static and dynamic parameters of most Iraqi soils is used. This database was collected from

many sources and based on different reports for geophysical and geotechnical investigation

works of forty seven projects site. The sites consisted of various layers of rock, cohesionless

and cohesive soils and represents projects for stadiums, pumping stations, oil refinery, multi-

story buildings, electrical substations, plants for water treatment, etc. with locations given in

Figure (2). Nine zones were created according to the Iraqi governorates boundaries, namely

North (N), South (S), Eastern North (EN), Western North (WN), Middle (M), East (E), West

(W), Western and Eastern South (WS and ES respectively)as shown inFigure (2). The sites

symbols in these zones are as listed in Table 2. All the data necessary for Mohr-Coulomb

model were available. The parameters with standard units are as listed below [9]:

E : Young’s Modulus (kN/m2), c : Cohesion (kN/m

2), ϕ : Angle of internal friction (°), υ :

Poisson's ratio (-), ψ : Angle of dilatancy (°), γsat, γunsat : Saturated and unsaturated unit

weight respectively (kN/m3),

The dynamic parameters are [9]: Vs and Vp: Shear and Pressure wave velocities

respectively (m/s), Ed: Dynamic Young's modulus (kN/m2), Gd: Dynamic shear modulus

(kN/m2).



The soil parameters c, ϕ, Vs and Vp are given in Table 4, and the data set for all other

soils parameters together with the layers depth used in this study are given in Mohammed

Shafiqu and Abdulrasool [7].

Figure 2.Projects locations and seismic zones[7]

Table 2Strength and seismic wave velocities values [7]

Site

Symb.

c

(kPa)

ϕ

(°)

Vp

(m/s)

Vs

(m/s)

Site

Symb.

c

(kPa)

ϕ

(°)

Vp

(m/s)

Vs

(m/s)

Site

Symb.

c

(kPa)

ϕ

(°)

Vp

(m/s)

Vs

(m/s)

N1 32 17 992 302

M4

180 0 761 298 ES3

80 0 696 179

0 42 1445 468 68 16 1113 428 60 0 1167 380

N2 0 39 1623 832 0 34 1351 507

ES4

80 0 500 176

N3 49 28 807 354 M5 0 38 1191 430 0 29 600 200

N4 43 21 988 296

M6

28.7 0 322 140 60 8 600 250

35 34 1460 462 31.5 0 776 219

S1

42 8 685 225

EN1 94 0 1745 262 0 38 1504 408 0 33 814 243

0 44 2606 576

M7

50 0 641 189 65 0 1224 333

EN2 81 3 1485 233 100 0 675 248

S2

94 0 625 188

4 42 2313 384 0 37 750 225 0 30 909 185

EN3

55 0 535 219 M8

65 10 841 165 60 5 909 200

21 33 679 301 0 38 1025 279 S3

78 0 646 185

0 42 1384 733 M10

144 0 306 111 0 40 1094 321

EN4

5 37 360 145 0 38 450 183

S4

90 3 434 110

80 0 514 212 E1 83 0 976 372 0 41 500 145

21 39 1065 323 E2 76 0 1076 398 191 0 600 166

EN5

0 32 1125 225 W2

120 0 730 257 S5

34 0 600 200

227 0 1250 321 0 33 1513 379 112 0 750 240

0 42 2500 476

WS1

77 0 688 198 S7

5.33 39 566 230

EN6 120 0 1541 304 0 33 948 265 8.4 40 1404 365

EN7 130 0 1250 312 0 36 1370 497 S8

60 0 434 166

WN1 65 0 1330 459 WS2 0 38 986 417 0 37 510 194

WN2 0 37 773 319 WS3 100 0 1416 312

S9 80 0 294 117

0 42 1113 348

WS4

0 37 1433 284 60 0 381 198

WN3 0 38 1057 362 0 35 1733 550

S10

40 0 550 138

WN4

0 36 714 292 0 35 1650 563 0 37 334 103

46 34 1055 346 WS5 0 41 1613 618 48 0 450 102

0 43 1335 606

WS6

0 43 805 268

WN5

0 37 942 451 0 40 1450 557

0 41 1373 701 0 39 1812 659

M1 76 12 544 186

ES1

53 4 451 111

0 36 736 258 0 36 605 152

M2 125 0 820 265 63 0 690 211

0 36 1150 395

ES2

65 0 377 131

M3 52 12 443 153 60 0 604 250

0 39 769 215 60 8 1362 420



3.2. Earthquake Modelling

To study the effects of acceleration characteristics on the piled raft response, a real

acceleration history for Halabjah, the strongest earthquake in Iraq hit Halabjah city in

Sulaymaniah Province on November 12, 2017 with a magnitude of 7.3 MWwas utilized as

shown in Figure (3). In the numerical analysis, the model bottom boundary is subjected to the

acceleration-time records given in the figure through the x-axis. A 80 seconds section was

applied to the model at intervals of 0.1 seconds.

Figure 3.Halabjah earthquake acceleration time data

3.3. Influence of Dynamic Soil Parameters on the Bending Moment

The results of bending moments along piles A, B, C and D shown in Figure (4) are given in

Figure (5). The results show minimum bending moments for soil profiles consisting generally

of rock or very dense silty sand where the piles working as end bearing piles and the

maximum bending moments appears in soil profiles consisting of lower layers of medium to

loose cohesionless soils where the tip of piles are resting overlaid by large thickness of soft

cohesive soils reaching to about half piles length. With respect to the zones, the highest

bending moments along piles length are predicted at N3, M10, WN2, WS3, E2, EN7, ES4 and

S10 zones. It is observed that generally the bending moment is large at the upper part of the

pile near the ground/the base of the foundation. It is important to note that the pile head is

fixed to the cap and values of moments in between the tip and top of piles are varied from

positive to negative or both according to type, depth and number of soil layers. It is also

indicated that the bending moment is influenced mostly to a depth over length ratio of about

50% in most of the sites. And maximum bending moment calculated is about 500 (kN.m) at

the head of pile for S10 site in south of Iraq which has a soil profile consisting mostly of

layers of cohesive soils with lowest values for shear wave velocities. While the lower values

of bending moments appears in N2 site in north of Iraq with values about 2.0% for that of S10

site.The soil profile for N2 site consisting of rock fragment of limestone with silty sand of

highest shear wave velocities. Thus the shear wave velocity can be considered one of the most

effective dynamic properties that influenced the values of bending moments along the piles.

The bending moment values in all piles are obtained to be higher in cohesive soils than in

cohesionless soils as the velocities of pressure and shear are higher in sandy soils. The pile is

influenced by differential forces as the waves reaching the layers of soils. In homogeneous

soils kinematic pile bending occurs because seismic waves may have different strengths

owing on thickness of soil layers and the structures around that cause a non-uniform damping

in the wave [6]. Therefore, the bending moment may shows sudden changes in value typically

at the two soil layers interface because of the various wave velocity of soils strata.

Results of bending moments in Figure (5) indicates that pile A at centre of raft foundation

has been insignificantly influenced by the earthquake acceleration, piles B and D at centre of

edges for raft foundation are generally the most effected by the earthquake acceleration where

the higher bending moments are appeared mostly along pile B in front of seismic waves.

While generally pile A at the edge of raft foundation is less influenced by the earthquake



comparing to that at B and D. In a lot of soil profiles and generally as the depth increased the

seismic wave velocities increased. The strength of sand soil depends on the frictional

parameters and on the effective stresses. As the depth increased the soil strength will be

higher thus the wave velocities being larger in values. Subsequent bending with curvatures via

strong waves from earthquake has been identified [8] as kinematic bending and liquefaction

induced bending.

For the current study, embedding pile tip through sand or gravel overlaid with clayey soil

predicts lower bending moments at pile tip being higher at the top layers but the bending

moments are mostly influenced through the pile length. For soil profiles consisting of sandy

or clayey soil layer and/or multiple sandy or clayey soil layers, bending moment values are

mostly appeared to be influenced for depth to length ratio of about 50%.

Figure 4.Piles A, B, C and D in the piled raft foundation

Figure 5.Bending moments along the piles A, B, C and D at the various sites



Figure 5.Continue



Figure 5.Continue



3.4. Influence of dynamic soil parameters on the foundation vertical settlement

In this section the evaluation of the maximum vertical settlement and differential settlement

for the raft foundation is carried out. It has been observed that the maximum settlements

appeared in soil profiles where a layers of soft clayey soils are top layers reaching about half

piles length underlaid by layers of medium to loose sand or loose sand followed by soft

clayey soil. While the minimum settlements indicated in soil profiles consisting generally of

rock or very dense silty sand. The large values of settlements are predicted in N3 site in North

zone, M3 in Middle zone, WS1 in South-West zone, WN3 in North-West zone, E2 in East

zone, EN4 in North- East zone, ES1 in South-East zone and S10 in South zone. Figure (6)

presents the total settlement contours for these zones at the raft level 2m below the ground

level for the PLAXIS3D model with structural elements. The PLAXIS3D model with solid

elements for S10 site resulted in higher predicted maximum settlement (smax=5.2 mm) and

differential settlement between the centre and corner of raft (0.357smax) compared to the

other sites. Knowing that the eight times high shear wave velocity site N2 which consist

mainly of rock fragment of limestone with silty sand is recognized by lower maximum

settlement and differential settlement with a values lesser by about 98% than S10 site

consisting mainly of layers of soft and loose cohesion and cohesionless soils respectively. The

foundation overall stability is usually not ensured by piles but it can be indicate that for

minimizing settlements, differential settlements and reducing the tilting of building, piles can

be used for that together with ensuring the good performance of foundation system.

Piles in Piled raft foundations employ for support or control of vertical displacements and

they applying most of the stiffness at serviceability forces, while the raft provides extra

bearing capacity at maximum loading. Consequently, it is mostly possible to minimize the

required piles number when the raft element provides such additional capacity.

From results it can be said that the raft may apply redundancy to piles, such that if there

are one or more weaker or defective piles, or if a number of piles suffered from karstic

conditions in the subsoil. Also the stress applied by piled rafts to the soil cause an increase in

the lateral stress in the soil between the underlying piles, and thus may increase the ultimate

load capacity of a pile as compared to freestanding piles [5]. The obtained results indicates

that soil profiles made up of relatively dense sands or stiff clays, the raft element can provide

a considerable proportion of the stiffness and required load capacity, with the piles working to

boost the action of the foundation, rather than being the major support means.

Thus it can be understand that the utilize of piled raft foundation is an effective procedure

for limiting both total and differential settlements under the dynamic loads provided by the

earthquake, enhancing the bearing capacity of a shallow foundation, and effectively reducing

the internal stress levels and bending moments within a pile.



Figure 6.Continue

4. CONCLUSION

The following conclusions can be drawn based on the results of this study.

• The results of the parametric Finite Element study indicated the most influential dynamic

property of soils that affected the bending moments along the piles and vertical settlements of

the raft is the shear wave velocity. The bending moment values in all piles and raft settlements

[×10-



are obtained to be higher in cohesive soils than in cohesionless soils. This conclusion is also

coherent with the fact that the shear wave velocities of the clayey soils had higher values than

the shear wave velocities of the sandy soils analysed in this study.

• The higher values for bending moments along piles generally occurs at soil profiles consisting

of soft cohesive soils with large thickness reaching to about half piles length underlaid by

layers of medium to loose cohesionless soils. While the lowest moments appeared in soil

profiles consisting mostly of rock or very dense silty sand with a values of about 98% lower

than that for higher values. The maximum values of the bending moments has been obtained

at head of piles or at depth of about 5-15% of the pile length measured from the top.

• The piles at the edges of the foundation experienced the highest bending moments during the

earthquakes acceleration. It was also observed that the highest bending moments occurred

mostly along the piles in front of the seismic waves. And pile at the corner of the edge of raft

foundation is less influenced by the earthquake comparing to the pile at center of the edge.

Also the piles at center of raft foundation can be considered as being insignificantly influenced

by the earthquake acceleration.

• The raft settlements are highest in soil profiles of soft clayey soils with large thickness

reaching about 10m or 50% piles length underlaid by layers of medium to loose sand or loose

sand followed by soft clayey soil. The lowest settlements appeared in soil profiles consisting

mostly of rock or very dense silty sand. The lower vertical and differential settlements values

in these soil profiles are about 2-5% the higher values where the shear wave velocity are

higher in these soils by about 3-8 times.

• It appears also that the settlements will be about 30-40% the higher values when soft or loose

to medium soils overlaid stiff or dense cohesive and cohesionless soils respectively. And the

percentages will be 20-30% when medium to stiff cohesive soils overlaid loose to medium

cohesionless soils layers decreased as the soils consistency being stiffer or denser where the

shear and compression wave velocities becomes lower.

• The piled raft foundation may be an effective way for minimizing total and differential

vertical settlements when subjected to earthquake loadings, enhancing the bearing capacity for

shallow foundation, and significantly minimizing the levels of internal stress and the bending

moments within a pile.

REFERENCES

[1] Ahmed, M., Mohamed, M.H., Mallick, J. andAbulHasan, M. 3D-Analysis of Soil-

Foundation-structure Interaction in Layered Soil.Open Journal of Civil Engineering, 4,

2014,pp. 373-385.

[2] Chaudhari R.R. andKadam, K.N. Effect of Piled Raft Design on High-Rise Building

Considering Soil Structure interaction.International Journal of Scientific and Technology

Research, 2(6), 2013.

[3] Davis, E. and Poulos, H. The Analysis of Piled Raft Systems.Australia Geotechnique

Journal, 2(1), 1972, pp. 21-27.

[4] Hamada, J. Shigeno, Y. Nakamura, N. Onimaru, S. Tanikawa T. and Yamashita, K.

Seismic numerical analysis of piled raft foundation with grid-form deep mixing walls

supporting a base isolated building based on seismic observation records.Journal of

Structural and Construction Engineering(Transactions of AIJ),79(701), 2014, pp. 941-950.

[5] Katzenbach, R., Arslan, U., Moormann, C. andReul, O., Piled raft foundation interaction

between piles and raft.Darmstadt Geotechnics, Darmstadt University of Technology, 4,

1998, pp. 279-296.

[6] Mano, H. andNakai, S. An Approximate Analysis for Stress of Piles in a Laterally

Loaded Piled Raft Foundation.Journal of Structural Engineering, 46B, 2000, pp. 43-50.



[7] Mohammed Shafiqu, Q. S. andAbdulrasool, M. A., Database of Dynamic Soil Properties

for Most Iraq Soils.American Scientific Research Journal for Engineering, Technology,

and Sciences (ASRJETS), 37(1), 2017, pp. 230-254.

[8] Mylonakis, G. and Nikolaou, S. Design Methods for Earthquake-Induced Pile Bending.

Proc. Int. Conf. and Exposition, Deep Foundations Institute, 2002, pp. 1-9.

[9] PLAXIS 3D Manual, Delt University of Technology & PLAXIS, Netherland, 2013.

[10] Poulos, H. An Approximate Numerical Analysis of Pile Raft Interaction.International

Journal for Numerical and Analytical Methods in Geomechanics, 18(2), 1994, pp. 73-92.

[11] Shukla, S.J., Desai, A.K. andSolanki, C. H. A Dynamic Behavioral Study of 25 Storey

Building with Piled Raft Foundation with Variable Subsoils.Int. J. of Structural and Civil

Engineering Research, 2(1), 2013, pp. 119-130.

[12] Yamashita, K., Analyses of Piled raft Model Provided by ISSMGE TC-18 Part2 :

Estimation by three-dimensional finite analysis, ISSMGE TC18 JGS member’s meeting

on Piled rafts, 1998.

[13] Zhang, L. Goh S. and Liu, H. Seismic response of pile-raft-clay system subjected to a

long-duration earthquake: centrifuge test and finite element analysis.Soil Dynamics and

Earthquake Engineering, 92, 2017, pp.488-502.

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BEHAVIOR OF PILED -RAFT FOUNDATION UNDER EARTHQUAKE …iaeme.com/MasterAdmin/uploadfolder/IJCIET_09_11_277/IJCIET_09_11_277.pdf · dynamic response of a 25-storey building resting