1. introduction - fenix.tecnico.ulisboa.pt inglês.pdf · water nozzle, mixes with the soil,...

Ground Improvement Technique – Jet Grouting

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Abstract: Ground improvement techniques have been improved over recent years and

have more applicability in soils with weak geotechnical features. This paper focuses on the

ground improvement technique of Jet grouting, referring to its most relevant aspects. In this

context, a brief explanation of the various ground improvement techniques is presented.

References are also made to its various and most common applications. Their systems,

relevant parameters, procedures, equipment used, advantages and disadvantages and quality

control are also addressed. In order to achieve a better understanding of the ground

improvement technique operation - Jet grouting, a case study regarding the construction of

“Cais do Jardim do Tabaco” is presented. This construction was not the only aspect to take into

consideration, as the results of the quality control and instrumentation were also important

elements for a better characterization of the problems that may arise in geotechnical

constructions. The paper continues with a comparative analysis between some possible ground

improvements solutions, taking into consideration the objectives of the case study.

Key words: Ground improvement technique; Jet grouting; quality control; instrumentation.

1. Introduction

1.1. Some of the existing ground improvement techniques

Chapter 1 presents a brief overview of the various ground improvement techniques in

existence as well as an explanation of the importance of the Jet grouting technique, in

particular. In addition, this chapter offers a definition and provides a description of the historical

evolution of the ground improvement technique under study.

The application of ground improvement techniques has become increasingly frequent in

recent times, given that urban areas suffer from a high level of occupation and that, when

available, these same soils tend to be of poor quality for construction. As such, a need to

develop various ground improvement techniques-was perceived.

Some examples of ground improvement techniques include: Preloading; Trench;

Vibrocompaction; Pile-driving; Pudding “in situ”; Dynamics and explosive pudding; Thermical

Treatment; Jet grouting e Deep Mixing; transfer plataforms. Among these drainage ditches,

vibrocompaction, Jet grouting and Deep Mixing are highlighted.

It is possible following an adequate analysis of the situation in question, to chose the most

suitable technique, according to the conditionals, including type of soil, water table, frontier

conditions, among others.

1.2. Definition and Importance of the Technique

The ground improvement technique, known as Jet grouting, aims to improve the

geotechnical characteristics of the soil. This technique takes place solely within the soil without

previous excavation necessary, via the injection of cement grout under high pressure (from 20

to 40 MPa) and high velocity. The injection of cement grout takes place via horizontal jets,


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resulting from the transformation of potential energy from the pumping of the cement grout into

kinetic energy. This energy is able to disaggregate the natural structure of the soil, thereby

mixing the soil particles with the cement grout which, in turn, creates a substance with improved

mechanical characteristics and decreased permeability when compared to the original soil. [1]

It is worth noting that this technique does not require previous excavation and may be

executed in any type of soil (see figure 1), utilizing different directions, and within the soil layers

strictly necessary. This technique offers great potential when compared to other soil techniques,

making Jet grouting a very competitive alternative. [2]

Jet grouting should be used under the following conditions:

When the soil offers insufficient resistance to support a loading change, or shift, in its

respective stress state, via incrementation (cargo capacity) or relief (excavation);

When the soil is excessively permeable, unable to impede undesirable subterranean

water flow. [1]

Figure 1 - Jet Grouting versatility [1]

The Jet grouting techniques offers great versatility in what concerns soil improvement,

given that it can be applied to a wide variety of soil types. It may be used in incoherent soil,

such as sand, gravel, and duly recessed, as well as in cohesive soils such as clay and silt (see

figure 1);

Figure 2 illustrates the various possible applications of this technique.

a) Vertical impervious barrier wall using

overlapping jet grout bodies.

b) Soil improvement underneath

existing buildings.


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Figure 2 - Some Jet Grouting applications [3].

2. Jet grouting

2.1. Jet Systems

The Jet grouting technique has evolved significantly, in order to better suit the diverse

situations in which it has been applied. As such, there was perceived a need to develop various

injection systems, which are as follows:

Jet System 1 or simple;

Jet System 2 or double;

Jet System 3 or triple.

The choice of the injection system should be the most appropriate, taking into consideration

the characteristics of the soil, the objectives of the intervention, the deadline of the construction

and associated costs, thereby achieving the desired characteristics and providing the best

possible column behaviour. With respect to the simple jet system, this system injects only

cement grout at high pressure in coherent soils with a 5 <Nspt <10 and in incoherent soils with

a Nspt <20, (figure 3). Regarding the double jet system, this system provides not only a cement

grout jet but also a second water or compressed air jet. This system is applied in coherent soils

with a Nspt <10 and in incoherent soils with a Nspt <50. The procedure is similar to that used by

the simple jet system. However, various coaxials are utilized, that is to say that during the

injection phase, the cement grout circulates via the interior feed rods at high pressure and the

compressed air, generated by a compressor, passes through the ring space, with the two feed

rods serving as frontiers. At the common exit site, the grout jet is surrounded by compressed air,

thereby increasing its range. This system is used to stabilize soils, impervious panels and to

foundations reinforcement (figure 4). Lastly, the triple jet system likewise possesses two

nozzles. One injects cement grout while the other injects compressed air and water (see figure

5). This method aims to halt the effects of soil erosion and to fill and/or mix the disaggregated

soil. Each jet possesses a different purpose. [5]

The water jet is used to destroy the structure of the soil. Part of the injected water exits

via the hole, bringing with it some of the eroded soil.

c) Underpinning of existing buildings. d) Horizontal canopy for tunneling.


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Air nozzle: Air is injected through the same water nozzle surrounding it and increasing

the disruptive effect. The air jet also causes the emulsion of the mixture water and soil

erosion reducing its density and facilitating their exit to the outside.

Grout nozzle: The grout injected through a second nozzle positioned below the air and

water nozzle, mixes with the soil, resulting in a solidified body.

It can be performed in consistent soil of Nspt <15 and in incoherent soils of Nspt <50. It is

generally used in foundation building, excavations, soil permeability reduce and soil

stabilization. [5]

Figure 3 - Jet System I. [6]

Table 1 depicts the typical values for the different parameters that vary depending on the

system:

Table 1 - Jet Grouting parametrs.

Simple system Doublesystem Triple system

Mín. Máx. Mín. Máx. Mín. Máx.

Grout injection pressure (MPa) 20 60 30 60 3 7

Grout flow (l/min) 40 120 70 150 70 150

Air injection pressure (MPa) - - 0.6 1.2 0.6 1.2

Air flow (l/min) - - 2000 6000 2000 6000

Water injection pressure (MPa) - - - - 20 50

Water flow (l/min) - - - - 70 150

Diameters

Grout injection

(mm) 1.5 3 1.5 3 4 8

Water injection

(mm) - - 1 2 1 2

Air injection (mm) - - - - 1.5 3

Rotation speed (rpm) 10 25 5 10 5 10

Uplifting speed (rpm) 10 50 7 30 5 30

Figure 4 - Jet System II. [6]. Figure 5 - Jet System III. [6]


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2.2. Jet Grouting parameters

To better adapt the technique to the soil it is necessary to perform geotechnical analysis to

determine soil conditions. So through that information can adopt the most appropriate system

Jet to the soil type. The essential characteristics of the geotechnical analysis are aggregate

grading, density, water content, cohesion and soil friction angle. It is through these factors that

the system and the construction process are defined. Knowledge of characteristics is possible

through “in situ” and laboratory tests. [1]

It appears that the larger aggregate grading greater diameters are obtained for the

columns. Soils that have a higher amount of fines – clays and silts resulting in smaller column

diameter since it has greater plasticity and therefore greater consistency and cohesion, thus

increasing the difficult of disintegration the grain and unite them to cement. It cases the

application of higher pressures in grouting. However, the opposite happens with grosser soil –

sands and gravels as it has almost no cohesion, thus facilitating their disintegration. Note that

the initial soil characteristics are one high importance aspect since this technique doesn’t result

from the replacement of soil but a mixture of binder with soil. [1]

When it wants to perform a Jet grouting work is necessary to define a set of parameters in

the project design, such as:

Uplifting speed;

Rotation speed;

Binder fluid pressure;

Grout injection;

Flow injected;

Number of nozzles;

Water/cement ratio.

Jet grouting technique is unique in that it can be applicable in almost any situation, since no

excavation is required for its implementation and equipment are relatively small when compared

with other equipment in civil engineering. The technique can be applied with several geometries

depending on the objective, such as: [1]

Circular columns;

Semi-circular columns;

Circular sector columns;

Simple panel;

Mixed solution with panels and columns.


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2.3. Constructive process and equipment

As mentioned in chapter 1, Jet Grouting technique has the purpose of disintegrateing the

original soil and mix it with cement grout, improving soil qualities.

This process comprises three main phases: [5]

Cut: The initial soil structure is disintegrated and the soil fragments are dispersed by the

action of one or more horizontal jets of high velocity.

Mixing and partial replacement: Some soil particles or soil fragments are replaced and

the others are mixed with the injected grout.

Cementing: The soil particles or soil fragments are bonded together becoming

consolidated body.

However, the building process begins at drilling and, afterwards, the grout is injected as

described above, and finally the column is sealed. [5]

The equipment used in the application technique are the cement silo, central mixer,

injection pump, compressor (Jet 2 and Jet 3) and the drilling/injection machine. [1]

2.4. Quality control

The quality control has a high relevance in a project since it is difficult to ensure that the

parameters described at design, regarding the Jet Grouting technique, correspond to those

obtained.

Thus, it is necessary to perform test-columns in order to define if the adopted parameters

are acceptable. After a test column is executed, the visual geometry is inspected and

subsequently some specimens are collected, in order to perform laboratory test such as the

uniaixal compression test. During the execution of the Jet Grouting technique, the following

parameters are observed, through equipment software: drilling speed; drilling pressure; drilling

depth; cement quantity consumed; injection pressure and pass.

The importance of the occurrence of reflux must be addressed. If there is no reflux, the

information of jet columns may be compromised by the formation of balls instead. Reflux must

submit a soil, thus demonstrating that the soil-cement mixture is developing as desired. [1]

2.5. Advantages and disadvantages

The versatility of this technique must be highlighted, since it can be applied to a wide range

of soil types and is not conditioned by the soil’s permeability in question, as well as work’s

efficiency is greater when compared with traditional solutions.

Jet grouting technique presents a very wide applicability, since it can be used in places of

limited space, such as excavations and tunnels, as well as in places of difficult accessibility. Jet

machines can be small and not very heavy therefore easy to move. Another very important

aspect when building in urban areas are noise and vibration control. The Jet grouting came

improve these effects resulting in reduced noise and vibration. [1]


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However, the limited tensile resistance, as well as the technique’s strict quality control are

needed in order to obtain an element in Jet grouting with the characteristics set out in draft. The

risks of ground lifting, subsoil settlement and subsoil’s chemical aggressiveness are the main

constraints of this technique that should be avoided through a strict quality control. [5]

3. Study case

The main tasks studied in the scope of the present study are related to the closure and fill

of the dock which had undertaken the soil improvement with columns Jet grouting. This contract

was the of a consortium consisting of the following companies: Somague, Seth and OFM.

Hagen was the company responsible for work on Jet grouting.

Regarding geological settings, the results of soil’s classification were obtained through a

site exploration, more specifically through CPTU tests. This categorizes the soil in various

geotechnical areas, as seen in table 2

Table 2 - Soil classification.

Geotechnical

Area Classification

Ø´- Streght

angle (˚)

C´ -Apparenent

Cohesion (KPa)

- Wet Specific

Weight (KN/m3)

E´ (MPa)

- Aterros 30 5 18 10

ZG3 Lodos argilosos 19 8 15 1

ZG2 Lodos arenosos 25 10 17 20

ZG1 Areias Siltosas 30 10 18 10

During execution the project several constraints were taken into consideration, namely the

geological and geotechnical conditions, the surrounding hydrographic and construction

conditions, affected services as well as the execution time.

Foundations’ design was performed taking into consideration of reinforced concrete

structure of the underground Docking. Thus, according to the structure loads, it was expected to

support all the structural piers with tubular steel N80 - API5A Ø244, 5x16, 0 1Ø50mm

(A500/A550) micropiles , sealed inside Ø1800mm Jet grouting columns duly recessed to the

level of sandy silts in the transition to the Miocene substrate so as to allow transmission of loads

primarily by lateral friction.

The docks’ closure was assured through a curtain of sheet piling, resting on a reinforced

concrete structure founded on piles. It also presented the Jet grouting Ø1200 mm / / 1.0 m

curtain implementation along the alignment within the walls of the dock, minimizing the influx of

water inside the dock during the swash hours. Despite this concern, there was a localized top

rupture, which required repair and reinforcement solutions that minimized the risk of recurrence

the identified pathologies. [7]

Taking into account the studied solution for the underground car park indirect foundation

implementation, the following constructive phasing was proposed:


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1- Dock’s closure through a curtain of sheet piling resting on a reinforced concrete structure

founded on piles;

2- Execution of Jet grouting columns test in order to verify the considered parameters;

3- Execution of part of the dock’s fill, including the area along the walls to a height of +4.5

m (ZH), for the execution of Jet grouting columns of the peripheral curtain;

4- Execution of the peripheral curtain of Jet grouting Ø1200 mm / 1.0 m columns in order,

to decrease the permeability of the ground along the underside of the front walls of the dock;

5- Execution of the temporary work platform inside the dock to a height of +1.95 m

(ZH).This platform consists of two biaxial geogrid (SS30 + SS20 geotextile) and two layers of

tout-venant (both approximately 50 cm thick). At the first geogrid placement (geotextile) two

layers with different directions were placed in order to prevent the removal of various pieces of

geogrid when the scraper moves;

6- Execution of Ø1500 mm Jet grouting columns for mud treatment and support of the

temporary weight transfer platform. The columns consists of horizontal alignments or triangles

(zigzag) to improve the stability of the work platform;

7- Throughout the work execution, tests have been made for quality control.

8- Placement of granular material to a height of +4.00. The pudding is performed by

hydraulic compression and, in the last 0.50 meters, by dynamic compression.

In the course of the work several tests were performed in order to verify that the columns

had the correct appearance.

Table 3 - Jet Grouting parametrs.

Column Pressure Jet type Nozzle Cement Lenght [m] Pass

[bar] (1/2) [mm] C/A Kg/m3

Hole Column I [cm] t [seg]

1/1200 340 1 4 0.8 300 4 3.5 4 10

4/1500 380 1 4.5 1.2 600 4 3.5 4 16

Table 4 - Results of uniaxial compression tests.

Sample

E’ [GPa] Stress rupture, σ

[MPa] Reference

Test specimen

age [days]

Date

Coluna 4/1500 – P1 36

18/12/2009

0.67 4.37

Coluna 4/1500 – P2 36 0.70 5.68

Coluna 1/1200 – P1 56 0.52 3.57

Coluna 1/1200 – P2 56 0.50 2.88

Table 3 presents some selected parameters form Ø1200 mm and Ø1500 mm, while table 4

present the results obtained from the uniaxial compression tests performed in order to evaluate

which present the most adequate behavior.


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According to the quality control planning, tests were conducted in several columns and the

results were quite satisfactory (Stress rupture >3.7 MPa and E´>0.5 GPa). All tested parameters

values were higher than those defined in the project, as it can be seen in table 4.

The Instrumentation and Monitoring Plan is a key element in this work and intends to

prevent and manage risk, ensuring that the interventions are performed safely and on budget,

analysis as well the behavior of nearby structures and infrastructure during and after the

execution.

Through the equipment installed at the work site has been possible to obtain results of four

topographical marks. The instrumentation and monitoring plan of the work allowed the

observation of the progress and understanding of the entire operation. The first visit to the work

took place on November 13, 2009 and three columns had been performed although there was a

lot of instability on the fill that was acceptable despite the discomfort.

The visit was aimed at observing the technique since the start of drilling until the grouting

began. The second visit took place on November 20, 2009. The geogrid and the fill had been

extended, a machine was grouting and the Northeast side of the dock hadn’t yet started work on

the Jet grouting. The Grouting parameters remained similar to those observed on the first visit.

In the following visits the evolution of work, on both the Northwest and Northeast, was

observed.

Some stages of the grouting technique, observed in the work visits are present in table 5.

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Work visits Date Fill evolution

1ª Visit November 13, 2009

2ª Visit November 20, 2009

3ª Visit December 4, 2009



6ª Visit January 27, 010


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Table 5 - Stages of the work.

Work visits Date Fill evolution

7ª Visit February 9, 2010

8ª Visit March 9, 2010

9ª Visit May 20, 2010

10ª Visit Augost 12, 2010

11ª Visit September 15 ,

2010

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4. Comparative analysis

This chapter includes a comparative analysis between techniques that can be developed in

the cope of the case study presented. The non-use of gravel columns is explained with more

emphasis.

Based on the calculation models produced by a finite element program and through

analysis, it was found that the phenomena of sludge’s (silt) consolidation induce increases

stresses and significant strain in micropiles of wall’s heading. This phenomenon is due to

displacements when the chosen soil´s treatment technique is vibrocompaction. Thus alternative

soil’s treatment solutions were considered. [8]

After an analysis of the various ground improvement methods, the solutions which are more

compatible with the proposed target are soil-cement panels or columns of Jet grouting and

initially gravel columns which was rules for the reason mentioned earlier. [8]

By examining the hypotheses of Jet grouting and soil-cement panels, it can be concluded

that are very similar although, for “political/administrative” reasons, Columns of Jet grouting

were chosen.

As previously stated in chapter 3, Jet grouting columns are the solution which enables the

flexibility and compatibility with the raised floors structural solution and minimizes risks to

structures and surrounding infrastructures.

5. Conclusions

Jet grouting technique depends on several factors in order to achieve the intended final

result, among which the soil characteristics, the Jet grouting parameters and objective of the

implementation stand out. In order to select the appropriate Jet system and define the ideal

parameters is necessary to gather all the relevant geotechnical information. The test columns

are performed in order to validate the correspondence between the values registered in situ and

what is defined in the project. In this context, quality control in stage procedure is of special

relevance.

The paper provides a first approach to the comprehension of the Jet grouting techniques, in

particular by following a real case study. Throughout the work, strict quality control and rigorous

analysis of the results obtained by the instrumentation installed in the fill of the Dock were

performing.

Thoughout the filling of the Dock, test columns were executed in order to evaluate the

visual aspect and collect the specimens to tested under uniaxial compression in the laboratory,

thus determining the soil-cement tensile strength (3,7 [MPa]) and deformabilidade (0,5 [GPa]).

In addition to the test column performed to measure the diameter and the grouting parameters

was conducted one more test in February. The results of these test showed quite favorable

values.

Through the instrumentation equipment installed in the Dock, the pathologie related to the

closure of the dock´s were evaluated. The method chosen to evaluate undesirable situations in


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this type of work is the analysis of the obtained displacements. Observation and instrumentation

is a simple method to understand the behavior of Jet grouting columns.

The development of Jet grouting technique may be associated with the evolution of drilling

and grouting control software and with instrumentation development. As previously state, the

quality control and the instrumentation are factors of utmost importance so is with the

improvement of these elements that the Jet grouting technique may be perfected.

Comparing different possible solutions with the solution adopted in Study Case it possible

to conclude that the Jet grouting technique is the most adequate taking into account the

proposed objectives. However, if the structural design of raised floors has been finished, the

execution of micropiles incorporated in Jet for medium loads could have been a possible

solution. In the case of high loads the pile-driving would also be a possibility to consider.

References

[1]. Fundações por microestacas e solo-cimento. Pinto, Alexandre. Lisboa : Slides da

disciplina de FOA - Mestrado Integrado em Eng. Civil., 2009;

[2]. Consolidação e reforço de terrenos. Tuneis e obras subterâneas em meio urbano.

Pinto, Alexandre e Falcão. Lisboa : Tuneis e obras subterâneas em meio urbano.Sociedade

portuguesa de getecnia., 2010;

[3]. Bilfinger Berger Foundations. [Online] Bilfinger Berger Foudantions. [Citação: 30 de

Junho de 2010.]

http://www.spezialtiefbau.bilfingerberger.de/C1257130005050D5/vwContentByKey/N276DL8

3645GPEREN/$FILE/Jet%20Grouting.pdf;

[4]. Novatecna. Historial. Novatecna. [Online] Novatecna. [Citação: 20 de Junho de 2010.]

[5]. Jet Grouting. Uma tecnica em desenvolvimento. Carreto, Joana. Porto : VII Congresso

Nacional de Geotecnia - Faculdade de Eng. do Porto, 2000;

[6]. Hayward Baker. [Online] [Citação: 30 de Junho de 2010.];

[7]. Pinto, Alexandre e Tomásio, Rui. Parque de estacionamento subterrâneo - Fundações,

projectode execução. Memória descritiva e justificativa. Lisboa : JetSJ-Geotecnia, 2009;

[8].Pinto, Alexandre e Tomásio, Rui —. Influencia da consolidação forçada dos lodos da

Doca através de execução de colunas de brita, sobre as estruturas e infra-estruturas

adjacentes. Nota tecnica. Lisboa : JetSJ-Geotecnia, 2009;

1. introduction - fenix.tecnico.ulisboa.pt inglês.pdf · water nozzle, mixes with the soil,...

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