Proceedings of Indian Geotechnical Conference

December 15-17,2011, Kochi (Paper No. Q-356)

GROUND IMPROVEMENT TREATMENT BY PRELOADING IN THE ENLARGEMENT

OF ALICANTE PORT (SPAIN)

Roberto Rodríguez Escribano. Geological and geotechnical department manager. Prointec, S.A.. rrodriguez@prointec.es

Margarita Díaz-Toledo García. Geological and geotechnical dept project manager. Prointec, S.A.. mdiaz@prointec.es

Javier Escartín García. Ports department manager. Prointec, S.A.. escartin@prointec.es

Marta Estefanía López Sierra. Geological and geotechnical department project manager. Icyfsa. mlopez@icyfsa.com

Claudio Olalla Marañón. Professor, ETSICCP of the Technical University of Madrid (UPM). colalla@caminos.upm.es

ABSTRACT: Port extension works present important challenges, on having possessed compressible materials with

deficient geotechnical characteristics as foundation level. In this respect, the geotechnical case of study is focused on the

compressibility analysis of satured soils under static loads, orienting it to the design of the soil improvement treatment by

preloading in the enlargement of Alicante Port (Spain). The research carried out shows the developed methodology, both

project phase and construction, so that it has been possible on the one hand, to estimate the foreseeable settlements and the

design of the ground improvement treatment by preloading, and on other hand, the most important one, compare the

estimated settlements with the real behaviour of the soil by means of auscultation of the improvement process on the site.

INTRODUCTION

Alicante Port enlargement refers to the construction of three

new terminals for the docks 21, 23 and 25, which will

provide wide use surfaces to satisfy the shipping demand.

To achieve this goal it has been necessary to carry out a

great volume earth filling in order to extend the port surface

towards the sea and therefore carry out the esplanade over

which will be placed the pavement. Fig. 1. (Note: in this

paper the decimal sign used is the comma “,” and the

thousands separator is the full point “.”)

Fig. 1 Aerial photograph of the portuary filling process.

IDENTIFIED PROBLEMATIC

The paved esplanade to execute in the new Alicante Port

East docks, present, same as in other enlargement ports

cases the inconvenient related to the high compresibilty

materials (new fills over sea muds and sands), which

constitute these esplanades foundation.

These kind of materials are usually characterized by

relevant long term settlements. This situation can be

aggravated depending to the percentage of organic matter.

In the case this percentage is relevant the settlement can be

developed in a long time (several years), as the organic

matter. keeps decomposing.

This way, an important settlement is expected to be

generated due to the thickness and geotechnical

characteristics of these kind of compressible materials (sea

sand and muds plus port fills). The magnitude of this

settlement is likely to exceed the limits defined by the

ROM 4.1-94 [1].

This is the reason why the determination of the settlement

magnitude beside the soil consolidation process duration,

function of the use load estimated (30 y 60 kPa) is needed.

METHODOLOGY

To aproach the study for the esplanade geotechnical

viability, it´s necessary to develop several investigation

phases which allow:

The geotechnical characterization of the terrain with

the purpose to estimate the deformability.

Determinate, depending on the use loads, the

settlement magnitude, comparing this to the maximum

stipulated by the ROM 4.1-94 (1994), Guidelines for

the design and construction of port pavements.

In case in which the settlement magnitude exceeds the

service use limits, design an improvement and

reinforcement treatment for the terrain which lets to

reduce the post-constructive settlement.

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R. Rodríguez Escribano, M. Díaz-Toledo García, J. Escartín García, M. E. López Sierra & C. Olalla Marañón

At last, in case in which an improvement treatment will

be needed, auscultate during the process, comparing

the real-field data to the calculated settlement.

To achieve these tasks properly, the project is developed in

to main steps:

Phase 1, Project. Related to the investigation,

characterization, determination and design.

Phase 2, Work; It will allow to control the movements,

compare them to the magnitude estimated in Phase 1

and adjust the soil behavior models.

Each Phase has the same importance, although most of the

times both are totally disconnected and it is not possible to

develop a back-analysis study in order to adjust the

analyzed situation to the real measured settlements.

This study is relevant as it has been possible to reach these

two main points (Phase 1 and Phase 2).

PHASE 1. PROJECT PHASE

Geological-Geotechnical Characterization

Starting from the compilation and analysis, both from the

site available geotechnical information and the field and

laboratory complementary investigation, it was able to

identify the fills and sea sand and muds geotechnical

parameters. There were established the following

geological-geotechnical units, Table 1.

Table 1 Geological-Geotechnical units

Geological-Geotechnical Unit

Thickness (m)

N30 E (MPa)

Cv

(cm2/sg)

Level 1, Anthropic fills

2,8-12,4 12

7,2

Level 2, Muds and silts

0,8-7 5

2,5 3·10-3

Level 3, Sand with gravels

0,4-6,4 50

45

Level 4, Marls, sandstones, conglomerates,

calcarenites

-

R

1.000

Note: N1+N2, Cv = 2·10-2 cm2/sg according to the preload

tests.

Due to the important variability in the stratigraphic profile

and in order to reach the best adjustment for the settlement

estimation, it was decided to identify and to zone areas with

a similar stratigraphy and carry out different stratigraphic

profiles for each area defined, Fig. 2.

Fig. 2 Sectorization related to the geotechnic profile.

Esplanade Viability Analysis

To verify the esplanade viability as foundation level it is

essential to check it is not reached the geotechnical failure

situations, it means sinking, sliding and the use related to an

inadmissible settlement.

These checks have been achieved by applying classic

methodology and also with finite element methods based in

Plaxis code.

According to these results is observed how for the

considered use loads are not reached the requirements

imposed in the guideline for the design and construction of

port pavements, ROM 4.1-94 [1], as the final settlement is

not admissible (superior to 0,10 m along 10 years).

Ground Improvement Methodology Design

Within the wide range of possibilities concerning to the

ground improvement, the treatment which best fits to the

site characteristics and to the technical and economical

requirements, is the embankments preload. According to

the soil grain size and considering the limits proposed by

Queyroi et al (1985) there wont be necessary to combine

preload plus drains.

The improvement treatment by using preloads was designed

for 1,5 times the use loads, therefore the minimum

embankments dimensions (equivalent to an infinite load)

for areas designed for 30 Kpa use load, were 40x80 m and

for areas designed for 60 Kpa use loads, were 60x120 m,

with consolidation periods between 15 and 90 days.

Stability of the Construction Process

For the embankment stability assessment there have been

considered the safety factor values proposed in the ROM

0.5-05 [2] and since it can be considered an accidental and

transitory situation in a short term these values will be

within the following range 1,1<S.F. 1,3. To analyze the

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Ground improvement treatment by preloading in the enlargement of Alicante Port (Spain)

sliding situation it has been used the program Slide

(Rocscience), considering the Mohr-Coulomb lineal failure

criterion, Fig. 3.

Fig. 3 Limit equilibrium stability calculus.

Preload Settlement Assessment

In order to carry out the design of the preload treatment,

calculation has been made of the foreseeable settlements

under the preload stresses and, a posteriori, once the

overburden of earth has been eliminated when the use loads

are applied, with the aim of checking that the regulations on

port pavements ROM 4.1-94 [1] are complied with.

The estimation of the settlements has been done by

comparing classical methods, based on the theory of

elasticity and on one-dimensional consolidation, and finite

element methods by means of Plaxis software, Fig. 4.

Fig. 4 Deformation under the preload embankment.

Also, on the basis of the evolution of the expansion works

on the port, with filled wharfs, others that are partially

filled and others waiting to be filled, and depending on the

moment the preload is located, two settlement calculation

hypotheses have been considered:

Hypothesis A: preload immediately on execution of the

fill. Settlements originated by the fill and compressible

natural ground, due to the effect of the actual weight of

the port fill and due to the effect of the preload.

Hypothesis B: preload a posteriori in time, with fill and

natural ground now consolidated due to the actual

weight of the port fill. Settlements corresponding to the

fill and compressible natural ground due to the effect

of the preload.

Estimation of the Settlements in the Service Phase

It was confirmed that, following the execution of the

preload, the settlements that are going to take place in the

ground when the use overloads are applied will be produced

as a function of the reload modules so long as they do not

exceed loads of 30 and 60 kPa, reducing the settlements to

admissible values.

PHASE 2. WORK PHASE

Auscultation constitutes a valuable tool since it guarantees

the proper and safe evolution of the process, and permits

the real behaviour of the ground to be determined, in

addition to any estimation method in the project.

Test Embankment

In the work, before commencing the improvement

treatment, a preload test embankment has been created,

having a triangular shape in plan view and approximate

dimensions of 45 x 93 m, which has been instrumented with

6 settlement plates and measurements taken periodically,

Fig. 5.

On the basis of the analysis of the settlements produced by

the preload embankment, a retrospective analysis has been

made of the behaviour of the materials by means of various

methods, with the aim of estimating the deformational

parameters of the ground, especially the coefficients of

vertical consolidation (Cv), for the estimation of which

three different methods have been applied: the Casagrande

method or time logarithm method, the Taylor method or

square root of time method, and the Asaoka method [3].

This has allowed the values of the deformation modulus to

be adjusted for the compressible levels (Levels N1+N2).

1

21

28 35

42 48 55 62 69 87 94 108 179

-60,000

-50,000

-40,000

-30,000

-20,000

-10,000

0,000

10,000

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190

SE

TT

LEM

EN

T (

cm

)

TIME (days)

HEIGHT (m) - SETTLEMENTS (cm) - TIME (days)

Base 1. Embankment

Height

Base 1. Settlements

Base 2. Embankment

Height

Base 2. Settlements

Base 3. Embankment

Height

Base 3. Settlements

Base 4. Embankment

Height

Base 4. Settlements

Base 5. Embankment

Height

Base 5. Settlements

Base 6. Embankment

Height

Base 6. Settlements

EM

BA

NK

ME

NT

HE

IGH

T (

m)

NOTE.-Preload settlements plates:- H=4 m: 1 and 3- H=6 m: 2 and 4- H=8 m: 5 and 6

Fig. 5 Graph of height – settlements – time of the preload

test embankment.

Auscultation of Preload Process

The monitoring of the preload has been done by means of

various control devices (settlement plates or inclinometers)

monitoring the vertical and horizontal movements

generated by the preload embankments, increasing safety

and correct evolution.

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R. Rodríguez Escribano, M. Díaz-Toledo García, J. Escartín García, M. E. López Sierra & C. Olalla Marañón

In general, the stabilization of the settlement has been

achieved in advance of the time planned in the project, with

settlement values similar to the estimated ones, considering

hypothesis A, Fig. 6.

Fig. 6 Map of settlement isolines.

In general the settlements have, by a large percentage with

regard to the total, been generated practically

instantaneously and simultaneous with the construction

process (load), with a clear reduction being seen of the

settlement in the plates located around the zones regarded

as already preloaded (zones that have historically supported

overloads of stockpiles, fills, etc.), while the bases located

in the last fill area where a major accumulation of mud

could be seen show settlements clearly greater than the

estimated values.

CONCLUSIONS

The results of the settlements obtained by means of the

auscultation conducted during the preload treatment agree

with the estimates both in the value of the settlement

reached, Fig. 7, and the time of duration of the

consolidation, with the stabilization of the settlements in

general being achieved more rapidly and, in an important

percentage of cases, almost instantaneously with the

loading process.

This reduction in the consolidation times can be produced

by a lesser thickness of the mud layer and, on a

complementary basis, by the displacement of that mud

when the fill is carried out by means of direct pouring,

giving rise to alternating small cohesive layers within the

granular materials being poured, which will facilitate the

drainage or dissipation of the interstitial pressure,

generating a much faster consolidation since the minimum

travel for the drainage of the clay packet becomes reduced.

At the same time, it has to be borne in mind that these

variations can be due to a greater or lesser accuracy in

estimating the coefficient of consolidation.

PT-1.1

PT-1.2

PT-2.1

PT-2.2

PT-2.3PT-2.4

PT-3.1 PT-3.2

0

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20 25 30 35 40 45 50

Re

al S

ett

lem

en

t(c

m)

Estimated Settlement (cm)

CLOSURE AREAOF THE LASTPORT FILLS

HISTORICALPRELOADS AREA

Fig. 7 Adjustment between the estimated settlement values

and those measured on site.

As final conclusions, the following can be stated:

On the basis of the results obtained, the applied

methodology constitutes a valid process for estimating

the compressibility of the ground, in spite of the

limitations caused by the lack of field or laboratory

trials aimed at obtaining the deformational parameters

of the ground which would permit a proper check to be

made of the adopted values.

There exists a good fit between the classical methods

of calculating settlements (theory of on-dimensional

consolidation and the theory of elasticity) and the finite

element method.

The retrospective analysis conducted on the basis of

the auscultation results of the preload test embankment

has allowed a determination to be made of the real

modulus of deformation of the ground (Young’s

modulus) and the coefficient of consolidation, with the

latter showing a certain variation with respect to that

obtained by theoretical methods.

REFERENCES

1. ROM 4.1-94 (1994), Guidelines for the design and

construction of port pavements. State Ports Board.

Ministry of Public Works, Transport and Environment.

Government of Spain.

2. ROM 0.5-05 (2008), Geotechnical Recommendations on Maritime and Port Works. State Ports Board.

Ministry of Public Works, Transport and Environment.

Government of Spain.

3. Asaoka, A. (1978), Observational procedure of

settlement prediction. Soils and Foundations.

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