THE GROUT LINE
The Grout Line
Paolo Gazzarrini
Overture
Third appointment with the Grout Line,
and unfortunately, without material
from you.
As I threatened in the conclusion of
the September issue I am now obliged
to bother you with one of my recent papers.
The Paper
The paper was published at the 58th.
CGS Conference held in Saskatoon in
September ‘05, and I would like to
thank the organizers for giving me permission to publish this paper in
Geotechnical News. It is, I believe, but I
will let you decide, an interesting case
history of the first application in British
Columbia of Jet-Grouting used for underpinning of an existing old CN tunnel.
Case History of Jet-Grouting in
British Columbia.
Underpinning of CN Rail Tunnel in
North Vancouver
Paolo Gazzarrini
Matt Kokan
Stephen Jungaro
Introduction
A new re-development on North Vancouver’s waterfront east of Lonsdale is
under construction. The development
includes the construction of up to 1,100
residential units in low rise to high rise
buildings as well as a hotel and other
commercial space. The subject site, a
historic ship building facility is being
developed by Pinnacle International of
Vancouver, B.C.
One of the lots, Parcel5, is located on
the Southeast corner of the intersection
of Lonsdale and Esplanade. (See Figure
1 and 2) This lot presented challenging
shoring problems due to the proximity
of Parcel 5 to an existing rail tunnel,
which has a history of previous
movements and repair.
Excavation and shoring was needed
to facilitate the construction of an underground parkade for the future hotel
and convention center to be located immediately adjacent to and below the
present elevation of the historic rail tunnel, which bounds the north end of the
development. The subject site is located
at the southern terminus of Lonsdale
Avenue, which is aligned parallel to a
long post glacial bench located south of
the Coast Plutonic bedrock range that
forms the North Shore mountains.
Previous projects in the area have
identified very difficult soil and groundwater conditions in the area, particularly the presence of high artesian water
pressure within sand and sand and
gravel layers present in the pre-glacial
deposits that underlie the site.
Due to the very high degree of consolidation and high strength of these deposits, driven cut off barriers are not
possible. As a result the conventional
approach to excavation and shoring has
been to used conventional anchored
shotcrete shoring in conjunction with
dewatering wells or suction well points.
Unfortunately this approach has been
only marginally successful as the
pre-glacial deposits in the area are
highly stratified.
Jet-Grouting, a new technology for
BC, was used to underpin the tunnel and
maintain its stability during the excavation, and also to create a groundwater
cut-off wall in order to prevent internal
erosion (piping) of fine to medium
grained sand.
Geotechnical News,
December 2005
47
THE GROUT LINE
Figure 1. Site map
Brief Description of the
Technology
Jet-Grouting is one of the numerous
technologies used to improve the soil or
soft rock.
It is a technique that, utilizing special
tools (Drill bits, monitor and nozzles)
and Equipment (Grout Plant and Grout
Pump), produces soil-cement circular
columns by pumping very fluid grout
mixes at very high speed (800- 900
Km/hours) at high pressures varying
between 30 and 50 MPa (4,300 to 7,200
psi).
Historically the technology was developed in Japan in the middle 70’s and
exported into Europe, in the late 70’s
and early 80’s.
In Europe, specifically in northern
Italy, due to the optimal soil conditions,
which are particularly suitable (alluvial
with sand and gravel), the technology
became more and more popular. In recent years in North America the use of
Jet-Grouting has become more frequent. It is more frequent to the point
Figure 3. How JG works
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Geotechnical News,
December 2005
Figure 2. Final proposed development
that in the last Grouting Conference in
2003 in New Orleans, a conference held
every 5 years, the papers relating to
Jet-G r o u tin g w ere th e mo st
represented.
How Jet-Grouting Works
Contrary to other types of grouting, permeation, compaction or soil-mixing,
Jet-Grouting uses, as mentioned before,
very high speeds of grout mix achievable with very high pressures. The jet,
created at the bottom of the drilling
rods, erodes the original structure of the
soil, and at the same time introduces a
water cement mix into the soil. The result is a soil-cement column that can
achieve different variable diameters and
characteristics depending on: the soil,
the methodology of Jet-Grouting selected and the parameters used for the
jetting.
After the completion of the drilling
to the required depth, the jetting begins.
The rods are withdrawn at a constant
speed (from the bottom upwards) and
rotation. See Fig. 3.
Types of Jet-Grouting
Three main types of Jet-Grouting are
normally used:
• Single-Fluid: The disaggregation of
the soil and its mixing with the grout
mix is done directly by the same
grout mix.
• Double-Fluids: The disaggregation
of the soil and its mixing with the
grout mix is done directly by the
same grout mix and a coaxial air jetting to increase the energy.
• Triple-Fluids: The disaggregation of
the soil is done directly by high
speed (pressure) of water and a coaxial air jetting. The mixing with the
grout mix is created by a lower pressure jet of grout mix, from a nozzle
below the air/water nozzles that encounters the already destroyed soil.
Parameters
The parameters to be considered in the
Figure 4. JG applications
THE GROUT LINE
design phase, generally defined by the
experience of the contractor, are the following:
• Grout mix pressure.
• Air and water pressure, in case of
double and/or triple jetting.
• Diameter and number of the nozzle(s).
• Grout mix composition.
The above three mentioned parameters are related to the consequent flow
reachable.
• Withdrawal speed of the rods. This
parameter and the flow give us the
total quantity of grout mix used for
the treatment of 1 column.
• Rotation speed of the rods/nozzle(s).
Equipment
Medium size equipment is required for
the execution of Jet-Grouting.
• A high pressure grout pump, typically 350HP.
• A grout plant, with silo for cement,
able to produce typically 9 to 12 m3
of grout mix in order to continuously
feed the pump.
• A drill rig specially equipped for
Jet-Grouting. Usually the mast is between 15 and 18 m high to permit the
execution of the columns without the
need to add rods.
• Compressor, in the case of the use of
Double or Triple Jet-Grouting.
• Accessories such as a high pressure
grout hose, special swivel, special
single or double or triple rods, monitor, nozzles etc.
Quality Control
As in all grouting projects carried out
underground the control of the results is
neither obvious nor direct. Thus production quality control is an essential
element of the technology.
The state-of-the-art of Jet-Grouting
requires the installation of sophisticated
sensors and computers at the pump and
at the drill rig to maintain all of the parameters described above under control
in real time during the drilling and jetting operations.
Sensors are installed at the pump to
evaluate in real time, pressure and flow;
sensors are installed at the drill rig to
evaluate the: depth, flow, pressure,
withdraw speed and rotation.
A computer on the drill rig is able to
record and store all these parameters
and allows for control of each phase
during drilling and jetting. The data is
further available and stored automatically either on computer disk, CD rom
or printout.
General Application of Jet-Grouting
Case histories of the application of
Jet-Grouting are available in the literature for numerous purposes, from a simple water cut-off wall to more complicated structural applications, such as
underpinning of structures. (See Fig 4).
Here is a general list:
• Cut-off wall
• Shoring
• Shaft
• General foundation of structures
• Single pile with the possibility of installing reinforced steel (casing or
bar) in the column
• Slabs
• Underpinng of structures
• Tunneling (umbrella treatment). Installation of a steel element (casing
or bar) is usually adopted.
Depending on the application, the
geometry of the jet-grouting treatment
can be:
• Secant (overlapped) columns,
• Tangent columns,
• Scattered columns,
• Monodirectional columns (panels)
Field Tests
Usually, and as a good practice, with the
scope of defining the optimal parameters of jetting, a preliminary field test is
carried out before the start of the production work. Four or five columns
with different parameters, based on the
soil conditions and the contractor’s experience, are drilled and jetted. The columns are further excavated in order to
allow for further visual inspection of the
diameter reached.
Unconfined Compressive Strength
(UCS) and permeability tests can be
carried out for a better understanding of
the final result of the soil-cement
columns.
Advantages and disadvantages of
Jet-Grouting
The advantages of using Jet-Grouted
columns for soil improvement are usually the following:
• No vibrations to the surrounding soil
during the execution of the work,
and consequent reduction in risk of
settlement around the structure.
• Use of relatively small equipment
(case histories of jetting in the basements are available).
• Possibility of easily drilling through
obstructions, as boulders or cobbles
using pre-drilled holes.
• It can be considered as a permanent
soil improvement solution considering that binder is used.
• Flexibility in changing the pattern of
the columns or parameters during
the execution of the work, and adapting the Jet-Grouting in case of unexpected soil conditions.
The main disadvantage is the spoil
that re-flows from the hole during the
jetting of a column. This can be easily
managed with special containment
tanks.
Jet-Grouting Application in
North Vancouver
The principal scope of the work was the
underpinning of the tunnel to allow the
excavation of the underground parking.
Soil Conditions
The soil conditions in the North Vancouver area are generally characterized
by a near surface cap of very dense
lodgement till, comprised of silty sand
with gravel underlain by pre-glacial
sand of the Quadra Formation. The till
is well graded, very dense and therefore
impermeable. It extends to a depth of
about 5 to 6 meters below pre-development grades. The Quadra Formation
underlies the till and contains highly
stratified silts-sands and sands and
gravels. In general the sands are very
fine to fine, though occasional zones of
medium to coarse sand and sand and
gravel occur, particularly as relic channels within the deposit. Groundwater
pressures increase nonlinearly with
depth and high artesian pressures occur
at depths in excess of 10 meters. The
characteristic SPT blow count for the
till is less than ¼ inch penetration for 50
Geotechnical News,
December 2005
49
THE GROUT LINE
Figure 5. JG design (general)
blows in the till and less than ½ inch
penetration for 50 blows in the Quadra
Formation.
Test monitoring wells drilled at the
north end of Parcel 5 were flowing at the
ground surface prior to commencement
of excavation and the final excavation
depth was in excess of 10 meters.
At the Parcel 5 site, the specific case
described in this paper, the pre-glacial
Quadra Formation was approximately
coincident with the base of the tunnel. It
was know prior to construction that the
base of the tunnel contained numerous
voids and was flowing water and sand
on a continuous basis. The shoring designer was concerned that normal well
and well point de-watering would not
create sufficient draw down to permit
conventional underpinning to proceed
and jet grouting was selected as the
most reliable technology for stabilizing
the soil beneath the tunnel.
Design
The scope of the Jet-grouting in the
Photo 1. General site overview
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Geotechnical News,
December 2005
Figure 6. JG design (detail)
North wall was double:
a) A vertical wall was created with the
aid of the reinforcing steel (# 18 bars
and 2.5 foot centers with a reinforced horizontal shotcrete waler).
b) An impervious cut-off was created
to avoid potential loss of sand at the
base of the tunnel and to create a
perfect contact between the bottom
of the concrete box of the tunnel and
the jet-grouted columns. To achieve
this contact, the jet grouting was not
terminated at the bottom of the
tunnel but continued 50 cm above it.
The jet grout wall was extended
south at the east and west ends of Parcel
5 for the purpose of providing a groundwater cut-off.
The design was carried out with a required minimum diameter of the columns of 0.8 meters and a UCS at 28
days of 10 MPa.
Overturning of the tunnel governed
design and thus the top of the tunnel was
restrained using tie backs connected to a
“dead man” located on the north side of
Esplanade Avenue. The calculations indicated that the tunnel could potentially
undergo rotational (raking) failure if it
were not restrained prior to exposing
the base. The base was exposed in controlled panels (15 meters in width) to
maintain passive resistance at the base
of the tunnel prior to the waler being
fully installed. Thus the waler was installed in Sections. The bulk of the horizontal restraint provided for the tunnel
was from the single row of tie back
anchors drilled through the waler.
Since there was an expectation of
high water flows from beneath the tunnel, the waler was constructed prior to
drilling tie backs. While this slowed the
process down slightly it proved to be
highly beneficial as very high groundwater flows were encountered from
some of the tie back holes.
The tie backs consisted of TITAN
30/11 hollow core injection anchors
grouted with Microsil Anchor Grout.
Photo 2. Bar installation
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Photo 3. Spoil
TITAN anchors were used as they
proved to be more economical than
cased installation of conventional bar
for tie backs. The performance of
Microsil Anchor Grout was quite impressive. After drilling the tie backs in,
using a 75 mm diameter bit, groundwater flow from the tie back sockets was
very heavy, in some instances up to 100
litres/minute per 75 mm socket. The
flows were very clean and no grout flow
was observed after completion of the installation. A total of 183 tie backs were
Photo 4. Computer at the grout plant
Figure 7. Drilling log
installed with no failures during testing.
Microsil anchor grout has hydrophobic
properties that allow it to remain stable
under high groundwater flows which
normal Portland cement grout is not capable of.
See Fig 5 and 6 with the design of the
Jet-Grouting wall and Photo 1 with a
general overview of the job site during
the execution of the work.
Quantities and sequence of the
execution of the columns
181 columns, with structural steel, in
the North Wall, 18 columns in the East
wall and 32 columns in the West wall
were carried out totaling 2,250 meters
of drilling and 1,600 meters of jet grouting.
The columns at the North wall were
spaced 0.75 m, the columns at the West
and East wall were spaced 1m.
The average depth of drilling was
9.65 meters and of Jet-grouted columns
Photo 5. Computer at the drill rig
Geotechnical News,
December 2005
51
THE GROUT LINE
Figure 8. Jetting log
6.9 meters. The working platform was
approx. 3 meters above the top of the
jet-grouted columns.
The sequence applied, was a normal
Space Split Method with Primary (P),
Secondary (S) and Tertiary (T) holes.
This sequence was preferred to the wet
on wet sequence due to the small spacing between the columns, and to have
better control of the spoil as described
below.
System and Parameters Used
The double Jet-Grouting system was
Photo 8. Excavation completed at north/west wall
used in this particular application. The
reason for this is twofold: firstly, to have
a better control of the spoil of the jetting
in o r d e r to avo id u n d e s ir e d
overpressure under the tunnel and to
avoid consequent uplifting, secondly, to
have more energy during the Jet-Grouting and to obtain diameter columns of
bigger diameter.
The parameters used, after the results of a field test, in which the diameter of the columns were evaluated in 1
meter, were:
Photo 6. Contact tunnel/jet-grouted columns
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Geotechnical News,
December 2005
• Grout mix composition: W/C=1
• Grout mix pressure= 40 MPa ( 5,715
psi)
• Air pressure= 0.7 MPa (10 psi)
• Rotation = 5 rpm
The #18 bar, 6.5 meters long, was
wet set into the jet grout columns using
a conventional back-hoe. See photo 2.
Quality control during the
execution of the work
1) At the Grout Plant
With the aid of a simple mud balance
the grout mix composition was kept un-
Photo 7. Excavation completed (80%)
THE GROUT LINE
Figure 9- Tunnel monitoring
der control to verify the constancy of
the product produced by the automatic
plant.
2) Spoil Control
With the same mud balance, the spoil
during the jetting was frequently analyzed. The constant measurement of the
density of the spoil helps in evaluating
the behavior of the Jet-Grouting treatment. See photo 3.
The sequence of the columns was
chosen also to analyze whether reduction in the density of the spoil was detectable.
The results we obtained were:
Density of the Grout mix produced at
the plant =
1.50 t/m3
Density (average) of the spoil in the Primary columns=
1.88 t/m3
Density (average) of the spoil in the
Secondary columns=
1.87 t/m3
Density (average) of the spoil in the Tertiary columns=
1.73 t/m3
First of all we can observe that the
value of the density of the spoil in all the
columns was well above the density of
the basic grout mix. This helps us to understand, during the execution of the
work, that the mixing in-situ was
effective.
Additionally we can observe that between the Primary and Secondary (together) and Tertiary columns, a drastic
reduction in density is evident, 1.88 vs.
1.73 t/m3.
This can be explained considering
that between the Primary and Secondary columns the spacing was 1.5 meters
and during the execution of two adjacent columns (P and S) there was no
overlap of jetting in a column already
formed; the jet was acting in virgin
sand.
The situation is different in the case
of the jetting of a Tertiary column,
spaced only 0.75 meters between a P
and a S. The jet was acting between two
columns already formed and the reduction of density of the spoil was a clear
sign of perfect overlapping of columns,
as detected at the end of the work during
the excavation.
Parameters Data
All the parameters, column by column,
both for drilling and grouting, were recorded with the aid of computers installed at the drill rig and pump. See
photos 4 and 5 with the computer installed at the grout plant and drill rig.
See figures 7 and 8 with the printout
samples for drilling and jetting.
Monitoring of the tunnel
Two methods were used to monitor
movement of the tunnel. The base monitoring was completed using a total distance station, which provided move-
ments in three dimensions. The owners
of the tunnel had a requirement for near
full time measurement, which was not
practical for the survey method. As a result tilt beam sensors were offered,
which recorded movements every two
hours. These sensors have a sensitivity
of better than 0.1 mm. Figure10 shows
the tilt beam record as well as the survey
records for one of the monitoring stations. The AC ripple on the tilt meter
output has a period of 24 hours indicating that the system was capable of recording thermal expansion and contraction of the tunnel.
Additionally, visual monitoring of
the interior of the tunnel adjacent to
where Jet-Grouting was carried out, using a camera to observe potential leakage of grout mix in the tunnel during the
jetting.
No movement or major leakages of
grout in the tunnel were observed.
Results
The first visual result was observed after the excavation of the wall. The contact between the base slab of the tunnel
and the Jet-Grouted columns was perfect; there was no leakage of water at the
wall, as well at its bottom.
The diameter of the columns was
approx 1 meter in till and 1.1 meters in
sand. See photos 6 ,7, 8 and 9.
Some coring was carried out after
the completion of the work in some columns, to analyze the characteristics of
the soil/cement columns. The laboratory results obtained, were:
• UCS at 56 days = 14.8 Mpa
-8
• Permeability = 7.6 10 m/s
Conclusions
The technique of jet grouting for
Underpinng was utilized for the first
time in British Columbia on this very
challenging project. The results were
very positive confirming the technique
is suitable for the local soil and groundwater conditions. It is expected that this
experience could encourage the use of
this technique for other difficult projects in the Lower Mainland.
British Columbia is expecting rapid
population growth over the next 10
years and since many of the straightforward sites have already been developed,
Geotechnical News,
December 2005
53
THE GROUT LINE
it is likely that remaining development
sites will require more sophisticated
geotechnical solutions. Jet-Grouting is
expected to be one of many newer techniques introduced into the lower mainland to assist in the development of
these remaining challenging sites. The
technique holds particular promise in
environmental and reservoir applications where a highly controlled
groundwater cut off solution is
required.
Acknowledgment
We would like to thank the owner, Pinnacle International, for the authorization given to the authors for the publication o f this p aper as well as
Con-Tech-Systems and Obermann KG,
pumps and jet-grouting material suppliers, for the assistance supplied during the
execution of the Jet-grouting work.
Paolo Gazzarrini P.Eng., Sea To Sky
Geotech Inc., 12 – 2242 Folkestone Way,
West Vancouver, BC V7S 2X7,
Tel: 604-913-1022,
Fax: 604-913-0106,
email: [email protected]
M a tt Ko k a n , P. E n g. , Pr in c ip a l,
Geopacific Consultants, 102 - 6968 Russell Avenue, Burnaby, BC V5J 4R9,
Tel: 604-439-0922, Fax: 604-439-9189
Stephen Jungaro, Principal, Matcon
Excavation & Shoring, 2208 Hartley
Avenue, Coquitlam, BC, V3K 6X3,
Tel: 604-520-5909,
Fax: 604-520-5957
Conclusion
I hope you enjoy the paper and I
would like, again, as was done in the
previous appointment, to emphasize
the part related to the use of the computer and the quality control during
the execution of the work.
I look forward to receiving material from you!
Ciao.
Geotechnical Engineer
C-CORE is seeking an Engineer for its geotechnical projects carried out for national and international clients.
C-CORE’s geotechnical expertise includes experimental and full-scale modelling, pipeline testing, ice/seabed
interaction, soil/structure interaction, and risk and numerical analysis. Its world class Centrifuge Facility is used
for geotechnical centrifuge applications including cold regions and offshore work and includes an earthquake
simulator.
Applicants should possess an engineering degree; a post-graduate degree is desirable. Five years geotechnical
experience is required and prior involvement in industry related projects would be a valuable asset. Experience
in research and development would also be an asset. The successful applicant will be expected to work in a team
environment, possess excellent communication skills and demonstrate initiative. This role includes assuming
project management responsibilities and client reporting. If you meet these qualifications, we ask that you forward your résumé with the names of three references to the address below.
Salary will commensurate with qualifications and experience. All applications will be treated confidential.
Deadline for submission is January 27, 2006.
C-CORE is a global engineering corporation providing innovative engineering solutions to clients in the natural
resource sectors. We develop and apply advanced technologies to address production and market issues faced by
natural resource sectors such as oil and gas, pipeline, mining, pulp and paper, forestry, fisheries and aquaculture.
We thank all applicants for submitting a résumé; however, only those being interviewed will be contacted.
Mary Booton, Executive Manager, C-CORE, Captain Robert A. Bartlett Building, Morrissey Road, St. John’s,
NL, Canada, A1B 3X5,
Tel: 709 737-8356, Confidential Fax: 709 737-4021, Email: [email protected], http://www.c-core.ca
54
Geotechnical News,
December 2005