Boring - Trenchless International

Chemically restoring
pipeline position
By Masahi Komura, Koichi Araki, Hideki Shimada, Takashi Sasaoka,
Kikuo Matsui and Takahisa Tomii
Current renewal methods for pipelines and culverts are very effective for pipe function decline and accident
prevention, but offer little in the way of rehabilitating meandering and slacks of pipes. Continually expanding
urbanisation means that restoring pipeline position using open cut methods has become less desirable, and as
such has led to the development of new pipeline position restoration technologies, such as the chemical injection
method.
Figure 5. Sludge discharge.
Comparison between prediction and the result of site investigation
Item Prediction Result
Setting depth of injection pipe Gl-6.1 Metres Gl-6.1 Metres
Number of pipe 14 14
Injection amount 8,147 Litres 8,304 Litres
Industry review
April 2010 - Trenchless International
Pipe renewal methods
One of the main causes of meandering
and slacks is a lack of ground support.
The pipelining renewal methods as shown
in Figure 1 are all unable to repair the
shrunk diameter or slacks of a pipeline as
none of these lining methods were effective
for ground improvement underneath
the pipeline. Figure 2 shows a pipeline
after renewal construction.
Restoring pipeline position
A technique commonly used for the
improvement of subsided constructions is
ground upheaval with injection grouting.
However, it is difficult to define the amount
of the injection grouting material that is
necessary for position restoration of the
pipeline, the shape of the pipe, and the
impact to adjacent structures.
To overcome these problems, a new
method has been developed that involves
making a guide space formed primarily in
the direction that the pipeline needs to be
moved before construction. This process
involves building casing pipes and a feeding
pipe for injection grout. The feeding
pipe is set at the guide space location.
After pressurised slurry is sprayed from
the feeding pipe to disturb the ground, the
pipeline position may be improved.
This technique requires the consideration
of drilling diameter, soil conditions,
and the arrangement of the form and
placement intervals of the feeding pipes.
A suitable injection material requires a
gelling time of around ten seconds with no
change in strength, volume or weight after
the injection. In cases of position restoration
by grouting, a grouting material that
uses two liquids, such as cement and
sodium silicate, may be used. After each
component is injected by a grouting pump
into a guide space, both components
are mixed in the same volume. However
Renewal
Method
Indepenent
Pipe
Compound
Pipe
Bilayer
Structure
Reversal
Formation
Production
Reversal
Formation
Guide Pipe
Figure 1. Classification of the renewal
methods.
there are few materials that satisfy these
requirements of cutting, mixing, and gelling.
Moreover when using a pump, the
injection performance and gelling time of
the grouting material are not satisfied at
the same time.
Thus, a new grouting material that suits
the restoration method of the pipeline
position via grouting was developed along
with a method that enables the selection
of the discharge quantity of different types
of grouting material.
These days the extent of restoration
and injection quantity of grouting materials
is determined in advance, and
optimal length and depth of injection are
determined prior to construction. Figures
3 – 6 show the application procedures
for the restoration method. After adopting
the restoration method, snake-advancing
Figure 3. Guide casing pipe setting.
Figure 2. Illustration of pipeline after
renewal construction.
and slack were rehabilitated with the
underpinning effect and increased ground
strength. Figure 7 shows the image of the
soil condition after restoration.
Measurement of snake-advancing
and slack
When restoring the position of a pipeline,
an accurate survey of the location of
the pipeline is typically required before
developing a detailed layout of the restoration
plan.
The measurement of the existing position
is performed by optical survey and,
where man-entry is possible, by manual
logging with results contributing to
background information for the restoration
plan. However, in the case of gas
Figure 4. Chemical injection for preliminary
soil compaction.
Figure 6. Main injection for restoration.
or small conduit pipes when man-entry
is not possible, two kinds of devices are
used. The first is a camera with a survey
instrument attached which is inserted into
the pipe to measure its depth, as shown
in Figure 8. The second is a device which
directly measures the top positions of
the pipeline as shown in Figure 9. This
top position measurement system has
been developed by the Department of
Earth Resources Engineering at Kyushu
University.
The top position measurement system
involves preparing the casing pipe by
drilling down to the pipe with pressurised
slurry. The sprayed slurry is pumped from
a tank on the surface and excavates and
liquefies the soil, which is then continuously
sucked from the casing pipe. After
the hole has been extended to the top of
the pipe a measuring rod is inserted into
Figure 9. Measurement system for position
of pipeline.
Figure 7. Image of the soil condition after
construction.
the drilled hole and the magnetised tip is
set on top of the pipeline. This ability to
establish existing conditions prior to construction
works has resulted in improved
site execution and management.
Amount calculation of restoration
method construction
When planning restoration and construction
works, it is necessary to calculate
the amount of injection.
Step one: determining the
injection depth
It is necessary to consider upheaval
pressure to ensure appropriate planning
when determining the injection depth for
the restoration constructions. A pulse
injection is adopted because ground
upheaval can be easily monitored and
controlled, making it easier to repair the
damaged pipes.
It is assumed that the effect of the pulse
injection is defined as a cone, the centre
of which is defined as the outflow point of
the injection hole. The height and width of
the cone are the distance from the centre
to the real arrival points of the grouting
material, as shown in Figure 11. It is supposed
that the injection pressure of the
grouting is acting within the range of the
cone as mentioned above. For example, if
the upheaval is measured 0.15 MPa at an
injection depth of 10 metres and the radius
of the cone is 10 metres, the vertical angle
is 60 degrees. If the upheaval pressure is
defined as the pressure required project
from the pipeline, the injection depth is
determined as follows.
D= d 1 + d 2 (1)
Figure 8. Image of the water level
measurement, gauge, and recording
paper.
Where D, d 1 , and d 2 are the injection
depth, sum of overburden of the pipeline
and diameter of the pipeline, and distribution
depth of the pulse of the chemical
grouting, respectively, d 2 is calculated
as follows;
(a) If the effective range of the pressure
is acted in 1/3 of the injection effective
radius,
d 2 = d 1 /2 (2)
(b) If the effective range of the pressure
is acted in 1/4 of the injection effective
radius,
d 2 = d 1 /3 (3)
Step two: calculating the number of
casing pipes
The number of casing pipes that are
used for the injection to repair the pipelines
is determined as follows.
N= 2n (4)
N, L, and L3 are the number of casing
pipes, distance of the restoration, and the
interval of casing pipes respectively. n
is calculated as n= L / L3. The arrangement
of casing pipe differs depending on
whether the pipeline is a concrete pipe
or a pvc pipe. When concrete pipes are
used, casing pipes are set up at the joints
of the each of the pipelines.
Step three: calculating the grouting
material per pipe
The distribution of the grouting materials
resulting from the injection site experiment
is shown in Figure 12. From this result, it
is supposed that the circular cone of the
hatching part of the cylinder in Figure 13 is
the range that grouting materials are uniformly
distributed. It is also assumed
Industry review
April 2010 - Trenchless International
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