Numerical Study of Anchored Piles Using Geostudio

Sigma/W Modeling

Tiorivaldi

and Bangun Marpaung

Department of Civil Engineering, Universitas 17 Agustus 1945 Jakarta, Jakarta, Indonesia

Keywords: Anchored Sheet Piles, Anchored Bored Piles, Santiago Gravel, Retaining Walls, Displacement Versus Depth.

Abstract: This study describes the analysis of machine drilled piles that are anchored and placed discontinuously. The main

advantage of this method is its faster and safer execution compared to hand-dug piles (rectangular cross-

section), which is the most widely used method for retaining walls on gravel soils in Santiago. This paper

shows the results of displacement versus height obtained using numerical modeling (Geostudio Sigma/W

software). In the case of the anchored machine drilled pile used for the construction of the Faculty of Physical

and Mathematical Sciences, Universidad de Chile. The modeling results carried out using Geostudio Sigma/W

were compared with the modeling results carried out by previous researchers on other software as well as the

measured field values. In stage 2 the results obtained were not much different from the results of previous

research. There are quite significant differences in stages 6 and 8 between Geostudio Sigma/W modeling and

other modeling due to the lack of more detailed information regarding available research data.

INTRODUCTION

In urban areas it is usually not possible to use non-

vertical slopes to support excavations due to limited

space (Abramson et al., 2001), so vertical supports are

required. For discontinuous or discontinuous bored

piles, the clearance between the piles is three times

the width (for hand-dug piles) or diameter (for

machine-drilled piles). Retaining walls between piles

is possible due to the arc effect.

Retaining wall is a structure that supports soil on

steep slopes, which can be vertical (Terzaghi et al.,

1996). Among the types of retaining walls, we can

distinguish between anchored piles and unanchored

piles or hand-dug piles.

Piles are built by digging a hole in the ground

(Candoğan, 2008), installing a reinforcing frame in it,

and pouring concrete from the surface. During

excavation, steel casing can be used to avoid wall

collapse in the hole, and is also used as a guide in the

drilling process (Weissenbach et al., 2003).

One of the advantages of using drilled piles

compared to driven piles is that there is no significant

vibration (Weissenbach, Hettler, & Simpson, 2003)

https://orcid.org/0000-0002-9816-573X

https://orcid.org/0009-0004-0914-2678

Corresponding email

and greater excavation depths can be achieved.

Drilling of hand-dug piles is done manually, taking

workers into holes, which can be so deep that they are

frequently exposed to excavation wall collapse caused

by local instability, surface vibrations, or earthquakes.

In the case of using piles, all processes are carried out

from the surface (Raddatz & Taiba, 2017).

The method most widely used in Santiago to

support deep and temporary excavations is hand-dug

piles anchored and placed discontinuously (Sáez &

Ledezma, 2012). In recent years, the use of anchored

piles has been incorporated to fulfill the same

function as hand-dug piles.

This study takes reference from previous research

(Raddatz & Taiba, 2017), describing the anchored

pile method as a soil retaining system, and the

characteristics of a newly constructed engineering

building at the Universidad de Chile. A study of the

geotechnical and structural parameters of the project

located in downtown Santiago was conducted, in

order to build a numerical analysis model through

software. Raddatz and Taiba (2017) used Plaxis 2D,

GGU-Retain and CYPE software: Embedded

Retaining Walls.

422

Tiorivaldi, . and Marpaung, B.

Numerical Study of Anchored Piles Using Geostudio Sigma/W Modeling.

DOI: 10.5220/0012583900003821

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 4th International Seminar and Call for Paper (ISCP UTA ’45 JAKARTA 2023), pages 422-426

ISBN: 978-989-758-691-0; ISSN: 2828-853X

In the research carried out by the author, research

data by Raddatz and Taiba (2017) were input into

GeoStudio software: Sigma/W in numerical analysis.

METHODS

The new building of the Faculty of Physical and

Mathematical Sciences at the Universidad de

Chile, is located between Beauchef, Club Hipico,

Blanco Encalada and Tupper Streets in the

commune of Santiago, Metropolitan area (Pilotes

Terratest, 2021b). This building has seven floors

and six underground floors, with a building

foundation height of 27.5 m or a depth of 29 m

from the zero line, which is located close to the

natural ground level in this sector.

2.1 Anchored Retaining Walls

The sheet piles are considered to be 1 m in diameter

around the perimeter where there is sufficient space

for installation. The sheet pile piles are located at

the factory every 2.5 m between the pile axes (the

building foundation is at a depth of 29 m) or 2.95

m between the pile axes (the building foundation is

at a depth of 27.5 m). On the northern boundary

there is an existing University building, so there is

not enough space for installing piles because the

pile machine does not fit into the existing building.

So rectangular piles are placed under the existing

foundation of the building as supporting piles.

Figure 1: Plan of a retaining wall project with instrumented

piles (Pilotes Terratest, 2021b).

The pile is considered to be embedded at 2.5

meters so that the end of the pile is -30 meters or -

31.5 meters. The pile head is considered to be at an

elevation of -1.5 m to comply with various city

regulations, using a small slope from the pile head to

the ground level. Anchors on steel cables are used as

lateral strengthening elements, each cable has a yield

force of 235 kN and a diameter of 15 mm. The

number of cables depends on the anchor service load.

Inclinometers were installed on two piles to

measure displacement at different stages (Manterola

& Carlos, 2012). The piles installed with

inclinometers are positioned in an area with a gap

between the piles of 2.95 meters between the pile axes

and the building foundation elevation of -27.5 meters.

Measurements are carried out at the second stage

(before installing the first anchor), fourth stage

(before installing the second anchor), sixth stage

(before installing the third anchor) and eighth stage

(final stage of excavation). For the fixed anchor

length, soil is used to pull the grout with a reduced

resistance of 250 kN/m. This value is usually used on

all projects where Santiago gravel is located.

Table 1: Properties of Piles.

Properties Value

Length (m) 28,5

Diameter (m)

Elastic modulus (kN/m

)

23875200

Cross-sectional area (m

) 0,7854

Moment of inertia (m

) 0,049

Axial stiffness (kN) 18751540

Flexural stiffness (kN.m

) 1169884

Source: Raddatz and Taiba, 2017

Table 2: Characteristics of Angkur.

Sifat-sifat Pertama

Kedua Ketiga

Depth (m) -5,00 -13,00 -21,00

Free length (m)

Fixed len

th (m)

16,1

4,1

12,8

5,2

7,9

5,4

Service load (kN) 1004 1297 1331

Free-length

stiffness (kN)

191100 245700 245700

Fixed-length

stiffness (kN)

307500 390000

Source: Raddatz and Taiba, 2017

The project is placed on the typical Santiago

gravel, which has been studied in depth. The high

cohesion values for gravel were confirmed in

previous analysis of triaxial results on this soil

Numerical Study of Anchored Piles Using Geostudio Sigma/W Modeling

423

(Ortigosa & Hidalgo, 1997). The two fine soil layers

identified in the soil mechanics report were

considered in the model created by Pilotes Terratest

for pile design (Pilotes Terratest, 2021). Fine soil

layers have been considered in all numerical models

carried out for this research project.

Table 3: Soil Properties.

Layer 1 (Depth of 0 to 6,5 m)

Fluvial gravel: second deposit

Friction angle = 45

Cohesion = 23,0 kN/m

Unit weigh

= 22,0 kN/m

Layer 2 (From a depth of 6,5 m)

Fluvial gravel: first deposit

Friction angle = 45

Cohesion = 35,0 kN/m

Unit weigh

= 23,0 kN/m

Interlayer (From a depth of 21

m to 22 m and 26 m to 27 m

Fine soil: interlayer

Friction angle = 26

Cohesion = 55,0 kN/m

)

Unit weigh

= 18,0 kN/m

Source: (Raddatz & Taiba, 2017)

A background review for the Santiago gravel has

been carried out, and for deformation increases with

depth, where depth “z” is in meters.

𝐸 = 45000

√

𝑧



𝑘𝑁/𝑚





This equation is similar to that used by many experts

in Santiago based on the research results of (Ortigosa

& Kort, 1997) which stated that the relationship

between deformation modulus and depth was found

through plate load tests at different depths.

2.2 Numeric Analysis

In previous research conducted by Raddatz and Taiba

(2017), numerical analysis was carried out using the

Plaxis 2D, GGU-Retain and CYPE computer

programs. Research carried out by the author added

numerical analysis using the Geostudio Sigma/W

computer program. The analysis is carried out in

stages to represent the problem well.

Geostudio is software that uses numerical analysis

developed by Geoslope International for geo-

engineers and earth-scientists. Geostudio consists of

several applications, specifically TEMP/W, SEEP/W,

SLOPE/W, AIR/W, CTRAN/W, Sigma/W and

QUAKE/W. In this research, the application used is

Sigma/W.

Geostudio Sigma/W is a program based on the

finite element method. The function of this program

is to calculate displacement, resistance, etc. based on

material coating conditions. This program

automatically determines the center of moment by

looking for the minimum point. Then, the anchored

retaining wall is modeled and it is determined

whether the anchored retaining wall is appropriate to

the existing soil conditions.

Figure 2: Geostudio Sigma/W model. Source: Prepared by

the author, 2023.

RESULTS AND DISCUSSION

The following figures show graphically the compa-

rison between field measurements and numerical

modeling results. The numerical modeling results by

previous researchers are included and compared with

the modeling results performed by the author. The

graphs correspond to the fourth (before installation of

the second anchor), sixth (before installation of the

third anchor), and eighth (final stage of excavation)

stages. The first data recorded in the field is the second

data, hence all model results consider the displacement

reduction of the second stage.

ISCP UTA ’45 JAKARTA 2023 - THE INTERNATIONAL SEMINAR AND CALL FOR PAPER (ISCP) UTA ’45 JAKARTA

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Figure 3: Comparison between measurement and modeling

for stage 4 (before installing the second anchor).

Figure 4: Comparison between measurement and modeling

for stage 6 (before installing the third anchor).

Figure 5: Comparison between measurement and modeling

for stage 8 (final excavation stage).

The graph shows that the results obtained from the

modeling are of the same order as the field data, but

the field measurements have a larger displacement at

the top of the pile, which develops significantly in the

early stages of excavation (fourth stage).

The graph obtained from Geostudio Sigma/W in

stage 4 is similar to the graph obtained in modeling

using other software. However, at stage 6 and stage 8,

the Geostudio Sigma/W graph at a depth of -15

meters to -25 meters experienced a horizontal

displacement that was quite significantly larger than

the displacement that occurred in other software. This

significant difference could occur due to a lack of

more detailed information regarding previous

research data, especially anchor data. Thus, the

difference is getting bigger, where at stages 6 and 8

the second and third anchors have been installed.

CONCLUSIONS

The measurements obtained from the inclinometer

are unusual, as high displacements in the early stages

are not expected to occur because the pile stiffness

and anchor working loads are designed for the higher-

pressure conditions that will occur in the final stages.

That is what happened in the Geostudio Sigma/W

results which showed high displacement in the early

stages. There are quite significant differences in

stages 6 and 8 between Geostudio Sigma/W modeling

Numerical Study of Anchored Piles Using Geostudio Sigma/W Modeling

425

and other modeling due to the lack of more detailed

information regarding available research data. In

other design codes such as EAB (German

Geotechnical Society, 2013), various pressure

redistributions are provided depending on the type of

wall, the number of anchor levels and their location.

In the case of three levels of anchorage, the

redistribution is triangular in the length of the pile top.

Therefore, the results will be very different for the top

of the wall depending on the type of design code to be

used (pressure distribution used).

As a recommendation for further research, it can

complement the data that is still missing in this paper

so that better results can be obtained. In addition,

other analysis applications can be used to compare

with existing results.

REFERENCES

Abramson, L. W., Lee, T. S., Sharma, S., & Boyce, G. M.

(2001). Slope Stability and Stabilization Methods, 2nd

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Candoğan, A. (2008). The art and practice of foundation

engineering. Ali Candoğan.

German Geotechnical Society. (2013). Recommendations

on Excavations EAB. John Wiley & Sons.

Manterola, R., & Carlos, M. (2012). Modelación e

instrumentación de las pilas de entibación del proyecto

Beauchef Poniente. Universidad De Chile.

Ortigosa, P., & Hidalgo, E. (1997). Estabilidad de

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