Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Numerical Study: Effects of New Piles’ Installation on Adjacent Existing Piles
Dang Tung DANG
Lecturer, Faculty of Civil Engineering, Ho Chi Minh City University of Technology – Vietnam National University, Ho
Chi Minh City, Vietnam
Email: ddtung@hcmut.edu.vn

Manh Tuan NGUYEN
Lecturer, Faculty of Civil Engineering, Ho Chi Minh City University of Technology – Vietnam National University, HoChi Minh City, Vietnam

Khoa M. TRAN
Lecturer, Faculty of Civil Engineering, Saigon Technology University, Ho Chi Minh City, Vietnam

ABSTRACTThe deep foundation technologies that are most applied in Vietnam and other countries are pile driving, static jack-in andpress-in works. Among them, the press-in installation method seems to be the most promising method because of its
mobility and rapid pile installation process with less noise and ground vibration. Piles installed by the press-in method
may cause relatively large displacement of the ground surrounding a pile being pressed-in. Consequently, existing piles,
foundations, underground walls and so on nearby may be significantly influenced. In Mekong River Delta, there weremany cases showing that the existing riverside walls were collapsed when installing new piles next to the old ones. Theseeffects are not considered in construction design. In this paper, the discrete element method (DEM) is proposed to study
the effects of new piles’ installation on adjacent existing piles in granular media. Piles are constructed by using a groupof small particles bonded each other which allow lateral movement at many locations of piles, then it is allowed to moveinto the soil media, during this process, the behaviour of ground and existing piles will be observed.
Key words: Pile Installation, Existing Piles, Ground Displacement, Discrete Element Method

1. Introduction
In Vietnam, the deep foundation technologies that arestructures of harbor were damaged and moved away frommost applied are pile driving and static jacking works

reason for not using the press-in method in pile driving or(Pierre et al., 1989). The installation impact of thesenot considering of new pile installation next to existing

technologies to other buildings around the construction

piles. Besides, there is not any method in Vietnam forsite, especially in narrow area of Hanoi, Ho Chi Minh City

calculation of these problems except for studies ofwhere houses and buildings are built closely or in soft soilmodeling around the world at small-scale laboratories.

land when installing new piles by diesel hammer. This is aarea, is a big problem because it makes structures cracked,

Pile installation has been conducted and modeled

rutted or creates even landslide. In South of Vietnam, therearound the world for investigation of ultimate capacity,were many cases where the existing riverside walls weresoil-pile interaction and also its effect. There are several

collapsed when installing new piles next to the old ones.

methods in evaluating the ultimate uplift capacity of piles

For instance in 2014, there was a harbor on Vam Co Dong

according to the load–displacement curve such as Hanna

river (Long An province) whose width and length are 2.1m

and Afram (1986), Rao and Nasr (2010). Hanna andand 7.4m, respectively; and the harbor was supported by

Afram investigated the pull-out capacity of single rigid

concrete piles which length were about 30m, but all

vertical and batter piles in sand and subjected to axial- 423 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

loading; they found that the pull-out capacity of batter
piles decreases slightly when the pile inclination increased.

2. Simulation from discrete element method
The DEM software, Particle Flow Code in Two

Rao and Nasr conducted small-scale model tests toDimensions (PFC2D version 5.0, Itasca Company, USA)investigate the behavior of vertical single piles embedded

was used in this study. In the following sessions, thein reinforced and non-reinforced cohesionless soil; they

simulation setup and procedures are described in detail.

found that the behavior of piles under uplift loads within

The geometry of the problem being considered in two

geogrid reinforcement involves a complex interaction

dimensions (plane-strain conditions) in which the height

between the surrounding soil, the pile surface and theand width are the same and are 22m. The out-of-plane

geogrid layers. Besides, the tangent intersection method

thickness of the DEM model is 1 m. A pile with a diameterhas been used by Hirany and Kulhawy (1989) for theof 0.4m and an embedded length of 7.1m is used. In thisasymptotic load–displacement curve with a rapid

study, two cases of distances between 2 piles are used fortransition from elastic behavior to failure. Then, in order

evaluation: 3D and 5D with D is the pile diameter. The

to make it simpler, especially in modeling, Fang et al.

chosen distance from existing pile to the closest boundary(2014) defined the uplift load corresponding to the axial

is 9m which is bigger than 20 times of the pile radius. 20

displacement of the pile equal to 10% of the pile diametertimes of pile radius comes from Bolton et al. (1999) whoor they used the 32.5kN of ultimate uplift capacity in view

conducted centrifuge experiments and concluded that theof serviceability based on the idea of Nasr (2013). Thisadditional stresses on the side boundary induced by

32.5kN of ultimate uplift capacity will be used in thispenetration is too small to have any effect on the tip

paper. Furthermore, the installation process of a jacked

resistance when the hard boundary is sufficiently far fromdisplacement pile, and the influence on the soil during

the penetrometer, farther than 20 times of the pile radius.

installation, is still a subject of research such as Lobo-

In this study, the problem was scaled down to 1/20 in

Guerero et al.. (2005, 2007), Jiang et al.. (2006), Yetginer

size of the prototype discrete element method model.

et al. (2006), Tran et al. (2012), and Lee et al. (2012) who

Accordingly, the gravity acceleration used in theused the Discrete Element Method (DEM) for theirsimulation was scaled up in such a way that the scaled

researches instead of the Finite Element Method. Aftermodel provided the same gravity-induced stress field as

Fang et al. (2014), 2D DEM is still useful from thethe prototype. Water was not physically modeled in thegeotechnical engineering viewpoint due to its ability insimulation and the gravity acceleration was justified tofeaturing the strength properties, failure and instability ofaccount for the reduction of effective stresses due

geo-materials with carefully-calibrated contact models.

submergence. As a result, the scaling factor of gravity

2D DEM is an advantageous choice using a current

acceleration (ng) was computed as follows:

conventional computer to investigate large boundaryvalue problems with an extremely large number ofng = ’nd/
(1)
where nd is the scaling factor of geometricparticles.

dimensions and nd=20 used in this study;  is the density

The main objective of this paper is to construct a 2Dof the particles, and ’ is the buoyant density of theDEM framework for simulating pile installation with aparticular emphasis on selecting an appropriate contact

particles, =2.6g/cm3 and ’=1.6g/cm3 is used. Then, thegravity acceleration is 12.31g.

model and parameter of soil and pile particles, and then toThe parameters of soil and pile particles are showedexamine the penetration mechanism. Afterwards, thein Table 1 and Table 2.

simulation results reveal the effects when a new pile was

The simulation procedure of the pile – soil interaction

installed close to an old pile, including vertical andincludes three steps: (1) ground generation; (2) pilehorizontal displacement. In the two survey cases ofinstallation; and (3) pile loading. Firstly, a homogenous

distances between the new pile and the existing pile are

ground was applied based on the expansion method which

three and five times the diameter of the pile.

is used widely (Tran and Lee, 2012) as follows: groundgenerated by creating wall, then generating particle; thenrunning to get balance and applying friction, as well as- 424 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

gravity acceleration of 12.31g; then running until the force

Table 1. Summary of soil parameters

equilibrium was reached; then removing the top wall andParameterValuerunning to get balance. Secondly, pile installation based on
Fang et al. (2014) was initiated by removing the particles

Particle size (mm)6-9where the pile was intended, forming a 20mm wide andInitial planar void ratio

0.21

Particle density (g/cm3)

2.6

with a diameter of 5mm. This pile is regarded as a non-Particle-wall normal stiffness (N/m)

6x108

displacement pile, since it was virtually installed in theParticle-wall tangential stiffness (N/m)

4x108

Local damping coefficient

0.7

point of the surrounding soils. Then, the pile was formed

Viscous damping coefficient

0.0

by regularly arranging identical circular particles in theParticle normal stiffness (N/m)

6x108Particle tangential stiffness (N/m)

4x108Inter-particle frictional coefficient

0.75

400mm high space in the model. This space was then filledwith a pile which was assembled by a total of 320 disks

space left by soils previously removed without disturbing
the surrounding soils or changing the stress state at any

loosest packing with a theoretical planar void ratio of 0.27.
The particle density was chosen in such a way that the pileis comparable to a concrete pile with the bulk unit weight
3equal to 23.5kN/m . The parallel bond contact model wasused here for the contact behavior of the pile particles withTable 2. Summary of parameters of pile particles

model parameters given in Table 2. Extremely large

Parameter

values were assigned to the strength parameters of theparallel bonds in order to avoid failure in the pile itself.

ValueParticle number

320

Particle diameter (mm)5However, a smaller inter-particle friction coefficient equal

Initial planar void ratio

0.27

to 0.75 was used at pile–soil contacts to render theParticle density (g/cm3)

3.06

Inter-particle frictional coefficient

0.75

The inter-particle friction coefficient of pile particles was
set to be 5 to eliminate unwanted particle slippage.

reasonable friction characteristics on the pile–soilinterface. The parameters associated with particle stiffness
and parallel bond stiffness were selected in such a way that

Parallel bond normal tensile strength (Pa)

1.0x10100

the pile resembled a concrete pile made of concrete withParallel bond tangential shear strength (Pa)

1.0x10100

the Young’s modulus of 30GPa according to theParticle normal stiffness (N/m)

6x108cantilever pile with a fixed base was simulated in response

Particle tangential stiffness (N/m)

2.4x108

to a horizontal load at the pile head, and the parameters

Parallel bond normal stiffness (Pa/m)

5.66x1012

Parallel bond tangential stiffness (Pa/m)

2.26x1012

Vietnamese standard. In order to reach this point, a verticalassociated with stiffnesses were justified on a trial-anderror basis until the pile deflection matched the theoreticalvalue based on the Timoshenko beam theory. Finally, pileParallel bond radius ratio r

1loading was simulated by applying 0.5mm/s of velocity on
particles on the top of the pile and running until getting

The procedure of installing new piles next to the olddesired settlement which is measured by tracking location

ones is: Adding the existing pile; using walls to create aof particles on the top of the pile. Force is measured by

new pile with the same diameter of the existing pile, thesumming the vertical component of the contacts between

distance between the new pile and the existing pile is 3D

soil particles and pile particles.

and 5D; applying 30kN of designed load on the existing
pile by applying load on particles on the top of the pile andthe force is 32.35kN as 2.35kN contributes from theweight of pile. All model setups, including penetration- 425 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

process of the new pile by applying velocity of 10cm/s onshows that when the penetrated depth of a new pile isthe walls or the new pile, could be seen on Fig. 1.

about half of existing pile length, two cases of distancesEffects of new installed piles next to the existing pile

are the same in normalized vertical displacement of theare presented from Fig. 2 to Fig. 5 for two types of piles

existing pile. When the penetrated depth of the new pile isdistances.

over half of the existing pile length, the trend of
displacement of two cases are different because of theeffect of distances between old and new pile.
7.1m

22m

22m
Fig. 1 Model setup
Fig. 3 Field velocity when the penetration depth of the newpile below 7.1m (distance of piles is 5D)Fig. 2 Field velocity when the penetration depth of the newpile below 2.1m (distance of piles is 5D)
Fig. 4 Field velocity when the penetration depth of the new

3. Effects of new pile installation on existing pile
Force was measured by summing the vertical

Besides, the effect of a new pile installation on ancomponent of the contacts between soil particles and pile

existing pile can be seen through the horizontal

particles; the vertical and horizontal displacements of thedisplacement of the existing pile during the penetration ofexisting pile were also measured.

new pile. These effects are in Fig. 8 and Fig. 9. As a result,pile below 2.1m (distance of piles is 3D)

The changes of load and vertical displacement on thethe tendency of cures between normalized of the existing

existing pile during the penetration of a new pile are in Fig.

pile and normalized of horizontal displacement are based

6 and Fig. 7. Fig. 6 shows the force or load in the existingon the penetrated depth of installing a new pile.

pile when a new pile was installed. It indicates that the30kN applied load is rather good and there are somescatters for the case of 3D of distance of piles. Fig. 7- 426 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

increased when a new pile was embedded at thelowest level.
In the future, the experiment of two piles should beconducted for checking the agreement between theanalytical and test results.

Fig. 5 Field velocity when the penetration depth of the newpile below 7.1m (distance of piles is 3D)

Fig. 7 Vertical displacement of the existing pile during thepenetration of a new pileFig. 6 Changes of load on existing pile during the penetrationof a new pile

4. Concluding remarks
The paper presents the first stage in consideration of
the effect of a new pile driving on an existing pile by using
the discrete element method in two dimensions. Two piles
with 0.4m of diameter and 7.1m of embedded length wasused. Two cases of distances between 2 piles are used forevaluation: 3 and 5 diameter called the first and the second
case, respectively. The main conclusions are as follows:

Fig. 8 Horizontal displacement of the existing pile during theThe present new pile affects to horizontal andvertical displacement of the existing pile;When the new pile was installed at the middle ofthe existing pile, vertical displacements of twocases have same trend and vice versa;

The horizontal displacements of the existing pile- 427 -penetration of a new pile (distance of piles is 5D)

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

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5. Acknowledgements
The authors would like to acknowledge the support

1989. Construction in Soft Soil for Vietnamby International Press-in Association for this research.

condition. Ho Chi Minh city University ofTechnology publisher, Vietnam.
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