Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Combined Construction Method and System of Vacuum Pipe Well
Combined With Pneumatic Fracturing in Deep Soft Soil Foundation
Technical Field
The invention relates to a foundation treatment technology, in particular to a
combined
construction method and system of vacuum pipe well combined with pneumatic
fracturing in
deep soft soil foundation, belonging to the technical field of a soft soil
foundation treatment
method.
Background
Soft soil is widely distributed in coastal and riverside areas in China. In
addition to high
water content, high compressibility, low shear strength and low permeability,
such soil is usually
deeply buried, and the bottom stratum has hydraulic connection with the
surrounding waters, and
the engineering geological conditions are extremely complicated. With the
increasing of
large-scale development of tidal flat and reclamation projects, the foundation
treatment of such
kind of deep soft soil has also become research difficulty and hotspot in the
engineering field.
At present, a vacuum preloading method is one of the most commonly used
methods to treat
soft clay and dredger fill silt in coastal and riverside areas. However, the
vacuum preloading
method takes a long processing time, and the vacuum degree will gradually
attenuate along with
the processing depth, so that the processing depth is limited. In addition,
the vacuum preloading
method can easily lead to accumulation and clogging of fine soil around the
PVD plate, so that
the treatment effect is lower than what is expected.
The traditional pipe well dewatering method places a submersible pump at the
bottom of the
well, and water is pumped through a pipe to the discharge point. This method
is generally
applicable to the stratum with rich underground aquifer and large soil
permeability, and is mostly
used for foundation pit dewatering. However, for the soft clay layer with a
small permeability
coefficient, the treatment effect is relatively general due to the slow flow
of groundwater.
The patent technology with the patent number ZL201510300457.9, and the title
"Construction Method of Vacuum Pipe Well Dewatering System", mainly provides a
set of
construction methods to solve the problems that the wellhead sealing
construction technology
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Date Recue/Date Received 2022-06-29
and method existing in the existing tube well technology are not perfect, the
vacuum pump
equipment covers a large area and has a large noise, and during construction
in winter, the
circulating water is easy to freeze during the intermittent operation of the
vacuum pump.
However, when this technology is applied to the deep soft soil foundation,
there is still the
problem that the vacuum degree attenuates with the depth of the pipe well,
which leads to the
inconspicuous negative pressure effect and thus the low precipitation
efficiency.
The patent technology with the patent number ZL201510560294.8, and the title
"Vacuum
Pipe Well Dewatering System" mainly introduces a set of vacuum pipe well
dewatering
equipment, including a water collection tank, a centrifugal pump, a vacuum
pump, a water
collection main pipe and so on. However, this technology does not specify the
process flow of
vacuum pipe well dewatering.
Summary of the Invention
In view of the above technical problems, the invention adopts the combined
construction
mode of the vacuum pipe well and pneumatic fracturing, in which the pipe well
is vacuumized,
at the same time high pressure gas is injected into soft soil between pipe
wells to generate
pneumatic fracturing and enlarge the flow channel of the groundwater, and
under the dual action
of vacuum negative pressure and pneumatic fracturing, the flow of groundwater
is accelerated,
which promotes the consolidation of precipitation. This method can be used to
treat deep (deeper
than 20 m) soft soil foundation, and has the beneficial effects of reducing
construction period,
saving construction cost and effectively improving foundation bearing
capacity.
In order to achieve the above technical purpose, the present invention adopts
the following
technical solution:
a combined construction method of vacuum pipe well combined with pneumatic
fracturing
in deep soft soil foundation, comprising: vacuumizing a sealed pipe well by a
vacuum pump so
that negative pressure is formed in the pipe well to accelerate the movement
of groundwater in
the soft soil interlayer into the pipe well, at the same time delivering the
gas extracted by the
vacuum pump to a pressurizing assembly to form high pressure air, then the
pressurizing
assembly injecting the high pressure air into the soft soil between the pipe
wells to produce
pneumatic fracturing in the soil body.
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Date Recue/Date Received 2022-06-29
Preferably, the pipe well comprises a plurality of depressurization pipe wells
and a plurality
of vacuum pipe wells, wherein the plurality of depressurization pipe wells are
evenly distributed
on the outermost side of the site according to the pipe well spacing, the
plurality of vacuum pipe
wells are evenly distributed inside the site and surrounded by the plurality
of depressurization
pipe wells; the depressurization pipe wells are disposed in a confined aquifer
at a depth for
extracting confined water; the vacuum pipe wells are vacuumized and are
disposed in a phreatic
aquifer for extracting phreatic water.
Preferably, the method comprises:
a drilling and well completion process, in which reverse circulation drilling
technology is
used, and the holes are drilled in the site according to a certain interval
between the pipe wells;
wherein the drilling diameter is larger than the diameter of the pipe well by
more than 30 cm, the
drilling depth of the vacuum pipe well is 50 cm to 100 cm above the bottom
surface of the
phreatic aquifer, and the drilling depth of the depressurization pipe well is
50 cm to 100 cm
above the bottom surface of the confined aquifer;
a pipe well placement process, in which the pipe well is put into the borehole
by a
suspension method, and after the pipe well is fixed, the filter material is
backfilled in the pores of
the outer wall of the pipe well and the inner wall of the borehole, and the
filling height of the
filter material is consistent with the thickness of the aquifer; for the
vacuum pipe well, after
plugging treatment with cement slurry above the aquifer, a submersible pump
connected to a
pumping pipe is placed in the pipe well, and an outer end of the pumping pipe
is communicated
to a surface water collecting ditch; for the depressurization pipe well, after
plugging with clay, a
submersible pump connected to a pumping pipe is put in the pipe well, and an
outer end of the
pumping pipe is communicated to the surface water collecting ditch;
a vacuum fracturing process, in which one end of a suction pipe is inserted
into the vacuum
pipe well for at least 0.5 m through a suction hole in the sealed well cover
of the pipe well, the
other end of the suction pipe is connected to a vacuum pump, and an air outlet
of the vacuum
pump is communicated to a pressurizing assembly to compress the air; wherein
an outlet end of
the pressurizing assembly is communicated with a plurality of gas injection
pipes inserted into
the earth's surface at different depths, and the gas injection pipes are
arranged between the pipe
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Date Recue/Date Received 2022-06-29
wells and provided with different depths;
a precipitation consolidation process, in which the submersible pump, the
vacuum pump
and the pressurizing assembly are opened; wherein the pore water in the soft
soil foundation
moves and collects to the pipe well under the dual action of the pneumatic
fracturing outside the
pipe well and the vacuumizing inside the pipe well, after being filtered by
the filter material of
the outer wall of the pipe well, the pore water is pumped to the surface water
collecting ditch by
the submersible pump;
a well sealing treatment process, in which after the dewatering consolidation
reaches the
required degree of consolidation, the dewatering work is finished, the
submersible pump is
raised, and the dewatering well is directly backfilled with sand.
Preferably, the pipe well spacing is determined according to the site area and
the number of
the pipe wells; the gas injection pipes at all depths in the same treatment
area are evenly
distributed, and the gas injection pipes at the same depth are connected in
parallel.
Preferably, the number of the pipe wells is calculated by the following
formula:
n= AQIq
where, n denotes the number of dewatering wells; Q denotes site water inflow
(m3/d); q
denotes water output of a single well (m3/d); X, denotes an adjustment
coefficient, taken as 1.1;
for the vacuum well,
2-X(2C ¨S )S
Q = d d Assit
In(1+ )
ro
where K denotes a permeability coefficient of a phreatic layer (mid); C
denotes thickness of
the confined aquifer (m); Sd denotes the designed precipitation depth (m); R
denotes radius of
ro=
influence (m), R= 10Sd ; r0 denotes equivalent
large well radius (m); A denotes
site area (m2); t denotes the designed precipitation time (days);
for the depressurization pipe well,
/115d
Q 2751c M(1+ )
/ r0
where, K denotes a permeability coefficient of the confined aquifer (mid); M
denotes the
thickness of the confined aquifer (m);
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Date Recue/Date Received 2022-06-29
preferably, the pipe well is a steel pipe with a hole; the steel pipe has an
imperforate section
and a perforated section, the perforated section of the vacuum pipe well has a
consistent
thickness with the phreatic aquifer, and the perforated section of the
depressurization pipe well
has a consistent thickness with the confined aquifer; and the perforated
section is wrapped by a
nylon filter mesh having a mesh number of 60.
Preferably, in the drilling process, the specific gravity of the wall
protection mud is
controlled at 1.10-1.15; after drilling to the designed depth, it is necessary
to clean the hole and
change the mud, and adjust the mud specific gravity to about 1.05.
Preferably, the method further comprises:
a geological survey process for surveying the engineering and hydrogeological
conditions
of the treatment site, wherein the engineering and hydrogeological conditions
include the
permeability coefficient of the soil layer, a water conductivity coefficient,
a radius of influence,
depths of the phreatic layer and the confined aquifer;
a site leveling process for making the site present a basin structure with
both sides being
high and the middle being low; and when the soil moisture content on the
surface of the site is
higher than a certain degree, backfilling a layer of miscellaneous fill or
hard clay with the
thickness of 1 m to 2 m.
A combined construction system of a vacuum pipe well combined with pneumatic
fracturing in deep soft soil foundation, comprising:
a plurality of depressurization pipe wells and a plurality of vacuum pipe
wells; the plurality
of vacuum pipe wells are evenly distributed and surrounded by the plurality of
depressurization
pipe wells; the depressurization pipe well and the vacuum pipe well
respectively include a
perforated section and an imperforate section located above the perforated
section; the perforated
section of the vacuum pipe well has a consistent thickness with the phreatic
aquifer, and the
perforated section of the depressurization pipe well has a consistent
thickness with the confined
aquifer; filter material is arranged in the annulus between the perforated
section and the inner
wall of the borehole, and the filling height of the filter material is
consistent with the thickness of
the aquifer; the vacuum pipe well is provided with cement plugging above the
aquifer; the
depressurization pipe well is provided with clay plugging above the aquifer;
the depressurization
Date Recue/Date Received 2022-06-29
pipe well and the vacuum pipe well are respectively provided with submersible
pumps
communicating with the surface water collecting ditch;
a vacuum fracturing mechanism, comprising a vacuum pump, a pressurizing
assembly and a
plurality of gas injection pipes; the gas injection pipes are arranged between
the pipe wells and
provided with different depths; an air inlet of the vacuum pump is
communicated with a suction
pipe which is inserted into the vacuum pipe well for at least 0.5 m through a
suction hole of the
sealed well cover, and the air outlet of the vacuum pump is communicated to a
pressurizing
assembly to compress the air; wherein an outlet end of the pressurizing
assembly is
communicated with a plurality of gas injection pipes inserted into the earth's
surface at different
depths.
Preferably, the pipe well is a steel pipe with a hole, the pressurizing
assembly is a
pressurizing tank, the perforated section is wrapped by a nylon filter mesh
having a mesh
number of 60; the plurality of vacuum pipe wells are arranged in an array;
each gas injection
pipe is surrounded by at least four of the vacuum pipe wells; a plurality of
depressurization pipe
wells are arranged outside and around the plurality of vacuum pipe wells; the
spacing between
two adjacent depressurization pipe wells is greater than the spacing between
two adjacent
vacuum pipe wells.
The invention has the following beneficial effects:
The combined construction method and system of vacuum pipe well combined with
pneumatic fracturing in deep soft soil foundation provided by the disclosure
has the following
beneficial effects:
firstly, the invention adopts the combined construction mode of the vacuum
pipe well and
pneumatic fracturing, in which the vacuum negative pressure in the pipe well
and pneumatic
fracturing outside the pipe well "work in collusion", which thus can
accelerate the movement of
groundwater into the pipe well, improve the efficiency of dewatering and
consolidation, and save
the construction period.
Secondly, in the present invention, the vacuum action and the pneumatic
fracturing are
based on one set of construction equipment and share one set of air extraction
and air injection
pipeline, and only one pressurizing tank is provided behind the vacuum pump,
which not only
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Date Recue/Date Received 2022-06-29
saves the equipment cost, but also reduces the space for site use.
Thirdly, in the invention, the function of the gas in the soft body is fully
utilized, the
application range of the traditional (vacuum) pipe well dewatering method is
expanded, and the
method can be used for treating deep (deeper than 20 m) soft soil foundation.
Specific embodiment of the invention is disclosed in detail with reference to
the following
description and the accompanying drawings, indicating the manner in which the
principles of the
invention may be employed. It should be understood that the embodiment of the
present
invention is not thus limited in scope.
The features described and/or shown for one embodiment can be used in one or
more other
embodiments in the same or similar manner, can be combined with the features
in other
embodiments or replace the features in other embodiments.
It should be emphasized that, the term "include/contain" refers to, when being
used in the
text, existence of features, parts, steps or assemblies, without exclusion of
existence or
attachment of one or more other features, parts, steps or assemblies.
Brief Description of the Drawin2s
In order to more clearly explain the embodiments of the invention or the
technical solution
in the prior art, drawings that need to be used in the description in
embodiments or the prior art
will be simply introduced below, obviously the drawings in the following
description are merely
some examples of the invention, for persons ordinarily skilled in the art, it
is also possible to
obtain other drawings according to these drawings without making creative
efforts.
FIG. 1 is a structural view showing the combined construction of a vacuum pipe
well
combined with pneumatic fracturing in deep soft soil foundation provided in an
embodiment of
the disclosure;
FIG. 2 is a layout chart of the pipe well of FIG. 1;
FIG. 3 is a simple flow chart of steps of the combined construction method of
vacuum pipe
well combined with pneumatic fracturing in deep soft soil foundation provided
in an
embodiment of the disclosure.
Reference Signs: 1. vacuum pipe well; 2. submersible pump; 3. depressurization
pipe well;
4. steel pipe of perforated section; 5. filter material; 6. clay plugging; 7.
steel pipe of imperforate
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Date Recue/Date Received 2022-06-29
section; 8. cement plugging; 9. vacuum pump; 10. pumping pipe; 11. suction
pipe; 12.
pressurizing tank; 13. gas injection pipe; 14. pneumatic fracturing point; 15.
phreatic aquifer; 16.
confined aquifer; 17. sealed well cover; 18. the earth's surface; 19. water
collecting ditch.
Detailed Description of the Preferred Embodiments
In order to make those skilled in the art better understand the technical
solutions in the
present invention, the technical solutions in the embodiments of the present
invention will be
clearly and completely described in the following with reference to the
accompanying drawings
in the embodiments of the present application. Obviously, the described
embodiments are only a
part of the embodiments of the present invention, but not all of them. Based
on the embodiments
of the present invention, all other embodiments that are obtained by persons
skilled in the art
without making creative efforts shall fall within the protection scope of the
present invention.
It should be noted that when an element is referred to as being "disposed" on
another
element, it may be directly on another element or there may be another element
in the middle.
When one element is considered to be "connected" to another element, it may be
connected
directly to another element or there may be another element in the middle. The
terms "vertical,"
"horizontal," "left," "right" and other similar expressions used herein are
used for illustrative
purposes only and are not meant to be the only embodiment.
Unless otherwise defined, all technical and scientific terms used herein have
the same
meanings as that are generally understood by those skilled in the art
belonging to the technical
field of the present invention. The terms used herein in the description of
the invention are for
purposes of describing specific embodiments only and are not intended to limit
the invention.
The terms "and/or" as used herein include any and all combinations of one or
more related listed
items.
As shown in FIG. 1, an embodiment of the disclosure provides a combined
construction
system of a vacuum pipe well 1 combined with pneumatic fracturing in deep soft
soil foundation,
comprising: a plurality of depressurization pipe wells 3 and a plurality of
vacuum pipe wells, a
vacuum fracturing mechanism.
Wherein the plurality of vacuum pipe wells 1 are evenly distributed and
surrounded by the
plurality of depressurization pipe wells 3. The depressurization pipe well 3
and the vacuum pipe
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Date Recue/Date Received 2022-06-29
well 1 respectively include a perforated section (the section denoted by the
sign 4) and an
imperforate section (the section denoted by the sign 7) located above the
perforated section. The
perforated section of the vacuum pipe well 1 has a consistent thickness with
the phreatic aquifer
15, and the perforated section of the depressurization pipe well 3 has a
consistent thickness with
the confined aquifer 16 (approximately equal). Filter material 5 is arranged
in the annulus
between the perforated section and the inner wall of the borehole, and the
filling height of the
filter material 5 is consistent with the thickness of the aquifer. The vacuum
pipe well 1 is
provided with cement plugging 8 above the aquifer. The depressurization pipe
well 3 is provided
with clay plugging 6 above the aquifer. The depressurization pipe well 3 and
the vacuum pipe
well 1 are respectively provided with submersible pumps 2 communicating with
the surface
water collecting ditch 19.
In the embodiment, the pipe well is a steel pipe 7 with a hole; the steel pipe
7 has an
imperforate section and a perforated section. The pressurizing assembly is a
pressurizing tank 12
such as a sealed storage tank. The perforated section is wrapped by a nylon
filter mesh 4 having
a mesh number of 60. As shown in FIG. 2, the plurality of vacuum pipe wells 1
are arranged in
an array. Each gas injection pipe 13 is surrounded by at least four of the
vacuum pipe wells 1; a
plurality of depressurization pipe wells 3 are arranged outside and around the
plurality of
vacuum pipe wells 1. The spacing between two adjacent depressurization pipe
wells 3 is greater
than the spacing between two adjacent vacuum pipe wells 1.
The vacuum fracturing mechanism includes a vacuum pump 9, a pressurizing
assembly 12
and a plurality of gas injection pipes 13. The gas injection pipes 13 are
arranged between the
pipe wells 1 and provided with different depths. An air inlet of the vacuum
pump 9 is
communicated with a suction pipe 11 which is inserted into the vacuum pipe
well 1 for at least
0.5 m through a suction hole of the sealed well cover 17. The air outlet of
the vacuum pump 9 is
communicated to a pressurizing assembly to compress the air. Wherein an outlet
end of the
pressurizing assembly is communicated with a plurality of gas injection pipes
13 inserted into
the earth's surface at different depths.
It should be noted that the vacuum pump 9 is a suction pump, and in other
embodiments, an
air compressor pump (air compressor) may also be used to suck the gas in the
pipe well and
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Date Recue/Date Received 2022-06-29
simultaneously inject the gas into the gas injection pipe 13 to achieve
pneumatic fracturing.
In a preferred embodiment, the vacuum pump 9 may be communicated to two or
more
pressurizing tanks 12 at the same time, and three or more gas injection pipes
13 communicated to
the two or more pressurizing tanks 12, respectively. The pressurizing tank 12
is provided with a
pressure sensor (a barometric pressure sensor, also referred to as a
barometer) that detects the
internal pressure thereof. The connecting pipe between the gas injection pipe
13 and the
pressurizing tank 12 is configured to be able to individually control
connection and
disconnection between each gas injection pipe 13 and the pressurizing tank 12.
By providing two
or more pressurizing tanks 12 to provide multiple air sources, a steady output
of high-pressure
air is ensured. At the time of gas storage, the high-pressure gas inside the
pressurizing tank 12
provides gas at different injection pressures.
An illustrative example is that the pressurizing assembly comprises a first
pressurizing tank
and a second pressurizing tank. Wherein a gas inlet of the first pressurizing
tank and the vacuum
pump 9 are communicated with each other through a first gas inlet duct. A gas
inlet of the second
pressurizing tank and the vacuum pump 9 are communicated with each other
through a second
gas inlet duct. The first gas inlet duct and the second gas inlet duct do not
interfere with each
other and each of them is provided with a gas inlet control valve.
Three or more gas injection pipes 13 are connected in parallel to each of the
pressurizing
tanks 12, respectively. The gas injection pipes 13 are arranged between the
drainage plates at
different intervals and provided at different depths. The gas injection pipes
13 at all depths in the
same treatment area are evenly distributed, and the gas injection pipes 13 at
the same depth are
connected in parallel. The gas injection pipes 13 include a first gas
injection pipe, a second gas
injection pipe, and a third gas injection pipe at different depths.
Specifically, as shown in FIG. 1,
the length of each of the gas injection pipes 13 is different, and thus the
required buried depth is
also different. In this embodiment, one ends of the three gas injection pipes
13 are buried at
required depths below the ground surface 11, and are 15 m, 18 m, and 21 m,
respectively. It is
worth pointing out that the buried depth of the first gas injection pipe, the
second gas injection
pipe and the third gas injection pipe can be adjusted according to the design
depth of foundation
treatment.
Date Recue/Date Received 2022-06-29
The control module has an automatic mode and a manual mode, and in the manual
mode,
the operator can also manually open the vacuum pump 9, open each valve, check
whether the gas
injection pipe 13 is communicated, determine whether the pipe is communicated
according to the
pressure detected by the pressure sensor, and in case of blockage, the gas
injection pressure can
be raised to the maximum pressure for dredging treatment. When it is
determined that the pipe is
communicated, the control module can switch to the automatic mode to perform
valve control,
so as to realize pressure storage of the pressurizing tank 12 and opening and
closing control of
the valve of each pipe, and to realize pneumatic fracturing gas injection
control of the gas
injection pipe 13, and furthermore, the automatic control of pneumatic
fracturing is realized.
Another embodiment of the present invention provides a combined construction
method of
a vacuum pipe well 1 combined with pneumatic fracturing in deep soft soil
foundation, in which
the above described combined construction system of a vacuum pipe well 1
combined with
pneumatic fracturing in deep soft soil foundation can be adopted, but not
limited thereto.
In this embodiment, the method comprises: vacuumizing a sealed pipe well by a
vacuum
pump 9 so that negative pressure is formed in the pipe well to accelerate the
movement of
groundwater in the soft soil interlayer into the pipe well, at the same time
delivering the gas
extracted by the vacuum pump 9 to a pressurizing assembly to form high
pressure air, then the
pressurizing assembly injecting the high pressure air into the soft soil
between the pipe wells to
produce pneumatic fracturing in the soil body.
The pipe well comprises a plurality of depressurization pipe wells 3 and a
plurality of
vacuum pipe wells 1, wherein the plurality of depressurization pipe wells 3
are evenly distributed
on the outermost side of the site according to the pipe well spacing, the
plurality of vacuum pipe
wells 1 are evenly distributed inside the site and surrounded by the plurality
of depressurization
pipe wells 3; the depressurization pipe wells 3 are disposed in a confined
aquifer 16 at a depth
for extracting confined water; the vacuum pipe wells 1 are vacuumized and are
disposed in a
phreatic aquifer 15 for extracting phreatic water.
The pipe well (the depressurization pipe well 3 and the vacuum pipe well 1) is
a steel pipe 7
with a hole; the steel pipe 7 has an imperforate section and a perforated
section, the perforated
section of the vacuum pipe well 1 has a consistent thickness with the phreatic
aquifer 15, and the
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Date Recue/Date Received 2022-06-29
perforated section of the depressurization pipe well 3 has a consistent
thickness with the
confined aquifer 16; and the perforated section is wrapped by a nylon filter
mesh 4 having a
mesh number of 60.
Specifically, as shown in FIG. 3, the method comprises:
a geological survey process for surveying the engineering and hydrogeological
conditions
of the treatment site, wherein the engineering and hydrogeological conditions
include the
permeability coefficient of the soil layer, a water conductivity coefficient,
a radius of influence,
depths of the phreatic layer and the confined aquifer 16;
a site leveling process for making the site present a basin structure with
both sides being
high and the middle being low; and when the soil moisture content on the
surface of the site is
higher than a certain degree, backfilling a layer of miscellaneous fill or
hard clay with the
thickness of 1 m to 2 m;
a drilling and well completion process, in which reverse circulation drilling
technology is
used, and the holes are drilled in the site according to a certain interval
between the pipe wells;
wherein the drilling diameter is larger than the diameter of the pipe well by
more than 30 cm, the
drilling depth of the vacuum pipe well 1 is 50 cm to 100 cm above the bottom
surface of the
phreatic aquifer 15, and the drilling depth of the depressurization pipe well
3 is 50 cm to 100 cm
above the bottom surface of the confined aquifer 16; in the drilling process,
the specific gravity
of the wall protection mud is controlled at 1.10-1.15; after drilling to the
designed depth, it is
necessary to clean the hole and change the mud, and adjust the mud specific
gravity to about
1.05.
a pipe well placement process, in which the pipe well is put into the borehole
by a
suspension method, and after the pipe well is fixed, the filter material 5 is
backfilled in the pores
of the outer wall of the pipe well and the inner wall of the borehole, and the
filling height of the
filter material 5 is consistent with the thickness of the aquifer; for the
vacuum pipe well 1, after
plugging treatment with cement slurry above the aquifer, a submersible pump 2
connected to a
pumping pipe 10 is placed in the pipe well, and an outer end of the pumping
pipe 10 is
communicated to a surface water collecting ditch 19; for the depressurization
pipe well 3, after
clay plugging 6, a submersible pump 2 connected to a pumping pipe 10 is put in
the pipe well,
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Date Recue/Date Received 2022-06-29
and an outer end of the pumping pipe 10 is communicated to the surface water
collecting ditch
19;
a vacuum fracturing process, in which one end of a suction pipe 11 is inserted
into the
vacuum pipe well 1 for at least 0.5 m through a suction hole in the sealed
well cover 17 of the
pipe well, the other end of the suction pipe 11 is connected to a vacuum pump
9, and an air outlet
of the vacuum pump 9 is communicated to a pressurizing assembly to compress
the air; wherein
an outlet end of the pressurizing assembly is communicated with a plurality of
gas injection
pipes 13 inserted into the earth's surface at different depths, and the gas
injection pipes 13 are
arranged between the pipe wells and provided with different depths;
a precipitation consolidation process, in which the submersible pump 2, the
vacuum pump 9
and the pressurizing assembly are opened; wherein the pore water in the soft
soil foundation
moves and collects to the pipe well under the dual action of the pneumatic
fracturing outside the
pipe well and the vacuumizing inside the pipe well, after being filtered by
the filter material 5 of
the outer wall of the pipe well, the pore water is pumped to the surface water
collecting ditch 19
by the submersible pump 2;
a well sealing treatment process, in which after the dewatering consolidation
reaches the
required degree of consolidation, the dewatering work is finished, the
submersible pump is
raised, and the dewatering well is directly backfilled with sand.
In the vacuum fracturing process, the pipe well spacing can be determined
according to the
site area and the number of the pipe wells; the gas injection pipes 13 at all
depths in the same
treatment area are evenly distributed, and the gas injection pipes 13 at the
same depth are
connected in parallel. The number of the pipe wells is calculated by the
following formula:
n= AQIq
where, n denotes the number of dewatering wells; Q denotes site water inflow
(m3/d); q
denotes water output of a single well (m3/d); X, denotes an adjustment
coefficient, taken as 1.1;
for the vacuum well,
2-X(2C ¨S )S
Q = d d Asdpit
In(1+ )
r
0
where K denotes a permeability coefficient of a phreatic layer (mid); C
denotes thickness of
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Date Recue/Date Received 2022-06-29
the confined aquifer (m); Sd denotes the designed precipitation depth (m); R
denotes radius of
= VA/
influence (m), R= 105d K; r0 denotes equivalent large well radius (m); rt.
; A denotes
site area (m2); t denotes the designed precipitation time (day);
for the depressurization pipe well 3,
/115d
Q = 21-dc M(1+ )
/ r0
where, K denotes a permeability coefficient of the confined aquifer 16 (m/d);
M denotes the
thickness of the confined aquifer 16 (m).
In order to better understand the present invention, the present invention
will be described
in detail below with reference to a specific embodiment.
With reference to FIGs. 1 and 2, a construction site is located near the
Yangtze River in
Nanjing, belongs to the alluvial flood plain and terrace edge of the Yangtze
River, where soft soil
is widely distributed, with a depth of 20 m to 40 m, over 40m locally, low
bearing capacity, large
deformation and long settlement duration, and in order to reduce post-
construction settlement, it
is necessary to treat deep soft soil and accelerate its consolidation
settlement. In addition, the
construction period of the project is short, the conventional vacuum
preloading method take long
time, and the treatment effect of the deep soft soil is effective.
The overall terrain of the project site is relatively flat, and the ground
elevation is between
3.62 m to 8.26 m. According to the engineering geological survey data, there
are many silty sand
silty soil interbeds in the soft soil at the upper part of the site, which are
in the shape of a
thousand-layer cake, and the horizontal thin layer stratification is obvious.
These interbeds
become the horizontal movement channel of groundwater, which is beneficial to
reduce
groundwater level and pore water pressure. However, due to the small thickness
of the interbeds,
the groundwater has certain viscosity and flows slowly under the action of its
own weight, and
negative pressure is formed in the well pipe by vacuumizing the well pipe,
which thus can
accelerate the movement of groundwater in the interbeds to the dewatering
well, at the same
time, high-pressure air is injected into the soil between the pipe wells to
generate pneumatic
fracturing, expand the flow path of pore water pressure, accelerate the flow
of pore water into the
pipe wells, thus promoting the dewatering and consolidation of the soft soil
and improving the
14
Date Recue/Date Received 2022-06-29
work efficiency and save construction period.
The types of groundwater in the site are mainly pore phreatic water and micro-
confined
water in the quaternary loose layer. The phreatic aquifer is included in the
C)-1 and 0,-2 silty
soft soil layers, the 0,-1 layer of silty fine sand interbedded with silty
clay in the site area is
slightly bearing and the underlying bedrock contains fissure water.
The combined construction method of a vacuum pipe well combined with pneumatic
fracturing in deep soft soil foundation in the above embodiment is adopted for
foundation
treatment, mainly comprising the following steps:
a step 1: surveying the engineering and hydrogeological conditions of the
treatment site,
including the permeability coefficient of the soil layer, a water conductivity
coefficient, a radius
of influence, depths of the phreatic layer 15 and the confined aquifer 16, and
so on.
It is surveyed through geological survey that the types of groundwater in the
site are mainly
pore phreatic water and micro-confined water in the quaternary loose layer.
The phreatic aquifer
15 is included in the C)-1 and 0,-2 silty soft soil layers, the 0,-1 layer of
silty fine sand
interbedded with silty clay in the site area is slightly bearing, belonging to
bearing aquifer 16. By
simple pumping test, hydraulic parameters such as a permeability coefficient,
a water conductivity
coefficient and a radius of influence of each soil layer are determined as
shown in Table 1.
Table 1 Hydraulic Parameters of Aquifer
Water
Aquifer Permeability Radius of Single Well
Aquifer Depth Conductivity
Aquifer Type Thickness Coefficient
Influence Flow
Coefficient
h (m) M (m) K (mid) R (m) T (m2/d) q (m3/d)
Phreatic
2.7-23.7 21 11.46 345 50.42 365
Aquifer
Confined
23.7-28.1 4.4 0.86 130 / 51.48
Aquifer
A step 2: leveling the site, for make the site like a "pot" with both sides
slightly higher and
the middle slightly lower. Due to the high water content of the surface soil
of the site, a layer of
Date Recue/Date Received 2022-06-29
miscellaneous fill of 1.5 m thick is backfilled to ensure normal construction
and pumping
sealing.
A step 3: drilling and well completion, in which reverse circulation drilling
technology is
used, and the holes are drilled in the site according to a certain interval
between the pipe wells.
The vacuum pipe well 1 adopts a steel pipe 7 with a pipe diameter of 273 mm
and a wall
thickness of 3 mm, and has a pore-forming diameter of about 450 mm and a well
depth of about
23 m. The filter pipe overwraps a single layer of nylon filter mesh 4 having a
mesh number of
60. The depressurization pipe well 3 adopts a steel pipe 7 with a pipe
diameter of 273 mm and a
wall thickness of 3 mm, and has a pore-forming diameter of about 450 mm and a
well depth of
27 m. The filter pipe is a bridge-type filter pipe and overwraps nylon filter
mesh 4 having a mesh
number of 60.
The pipe well spacing is determined according to the site area and the number
of the pipe
wells. The number of the pipe wells can be calculated by the following
formula:
n= 2Q1q
where, n denotes the number of dewatering wells; Q denotes site water inflow
(m3/d); q
denotes water output of a single well (m3/d); X, denotes an adjustment
coefficient, taken as 1.1.
For the phreatic water,
IrK(2C ¨S )S
Q = d d Assit
In(1+ )
0
where K denotes a permeability coefficient of a phreatic layer (mid); C
denotes thickness of
the confined aquifer (m); Sa denotes the designed precipitation depth (m); R
denotes radius of
R=10S ro= VA/
influence (m), d ; ro denotes equivalent large well radius (m); A
denotes
site area (m2); t denotes the designed precipitation time (days).
For the depressurization pipe well,
/115d
Q=277k In(l+R/ )
r
0
where, K denotes a permeability coefficient of the confined aquifer (mid); M
denotes the
thickness of the confined aquifer (m);
the calculation results are shown in Table 2.
16
Date Recue/Date Received 2022-06-29
Table 2 Calculation of Plane Layout Plan of Pipe Well
Design Equivalent Design Site
Aquifer Radius of Number
Area Precipitation Large Well
Precipitation Water
Thickness Influence of Wells
Pipe Well Type Depth Area Time Inflow
A Q
cim (m) Sd (m) R (m) r0 (m) t (d) n
(m2) (m3/d)
Vacuum Pipe
Well
7056 21 15 130 47.5 20 1493 33
(phreatic water
well)
Depressurization
Pipe Well 7056 4.4 15 345 47.5 20 2248 9
(confined well)
Based on the above calculation results, the site layout design is also
considered. As shown
in FIG. 3, 36 vacuum pipe wells are arranged in the site in a regular
quadrilateral arrangement
with a spacing of 14m, and 12 depressurization pipe wells are arranged in the
outermost
periphery of the site with a spacing of 28m.
A step 4: cleaning the hole and changing the mud. Due to the finer aquifer
particles in the
soft soil layer, in the drilling process, the specific gravity of the wall
protection mud should be
controlled at 1.10-1.15. In order to prevent mud from affecting the water
output of the
dewatering well, natural mud making by stratum is adopted as far as possible.
After drilling to
the designed depth, it is necessary to clean the hole and change the mud, and
adjust the mud
specific gravity to about 1.05.
A step 5: placing the pipe well. The pipe well is slowly put into the borehole
by a
suspension method, and after the pipe well is fixed, the filter material 5 is
backfilled in the pores
of the outer wall of the pipe well and the inner wall of the borehole, and
medium coarse sand
filter material 5 is backfilled. For the vacuum pipe well 1, cement plugging 8
is used for
treatment above the aquifer. For the depressurization pipe well 3, since the
plugging area is large,
17
Date Recue/Date Received 2022-06-29
the clay plugging 6 can be used. Subsequently, a submersible pump is placed in
the pipe well,
and is connected to the upper pumping pipe, and the other end of the pumping
pipe is directly
placed at the water collecting ditch.
A step 7: connecting a vacuumizing-pneumatic fracturing system (vacuum
fracturing
process). One end of the suction pipe 11 is inserted into the pipe well
through the suction hole of
the sealed well cover 17 at a position of about 1 m, and the other end thereof
is connected to the
vacuum pump 9. A gas injection pipe 13 is connected to the air outlet of the
vacuum pump 9, is
connected to the pressurizing tank 12 to compress air, and the other end of
the gas injection pipe
is then inserted into the pneumatic fracturing points 14 at different depths
on the surface of the
earth. The gas injection pipes are arranged between the pipe wells and
provided with different
depths (15 m, 18 m, and 21 m). The gas injection pipes at all depths in the
same treatment area
are evenly distributed, and the gas injection pipes at the same depth are
connected in parallel.
A step 8: precipitation and consolidation. The submersible pump 2, the vacuum
pump 9 and
the pressurizing tank 12 are opened. The control panel on the pressurizing
tank is adjusted and
the gas injection pressure is set to be 1.0 MPa. The pore water in the soft
soil foundation moves
and collects to the pipe well under the dual action of the pneumatic
fracturing outside the pipe
well and the vacuumizing inside the pipe well, after being filtered by the
filter material of the
outer wall of the pipe well, the pore water is pumped to the water collecting
ditch 19 on the
earth's surface by the submersible pump 2. The pore water pressure of soft
soil foundation
decreases and the effective stress increases, which can realize precipitation
consolidation.
A step 9: well sealing treatment. After pumping water for 60 days, the
consolidation degree
of soft soil in the site reaches 94% and meets the design requirements, the
dewatering work is
finished, the submersible pump 2 is raised, and the pipe well is directly
backfilled with sand.
Any numerical value referred to herein includes all values of a lower value
and an upper
value that are incremented by one unit from a lower limit value to an upper
limit value, with an
interval of at least two units between any lower value and any higher value.
For example, if it is
stated that the number of components or process variables such as temperature,
pressure, time,
etc., have a value from 1 to 90, preferably from 20 to 80, more preferably
from 30 to 70, the
purpose is to illustrate that the equivalents such as 15 to 85, 22 to 68, 43
to 51, 30 to 32 are also
18
Date Recue/Date Received 2022-06-29
explicitly recited in the specification. For values smaller than 1, one unit
is suitably considered to
be 0.0001, 0.001, 0.01, 0.1. These are merely intended to be explicitly
expressed examples, and it
may be considered that all possible combinations of numerical values
enumerated between the
lowest value and the highest value are explicitly set forth in a similar
manner in this
specification.
Unless otherwise stated, all ranges include end points and all numbers between
the end
points. The "about" or "approximate" used with the range is suitable for both
end points of the
range. Thus, "about 20 to 30" is intended to cover "about 20 to about 30,"
including at least the
indicated end points.
All articles and references disclosed, including patent applications and
publications, are
incorporated herein by reference for all purposes. The term "consisting
essentially of' to describe
a combination should include the elements, components, parts or steps
determined and other
elements, components, parts or steps that do not substantially affect the
substantially novel
features of the combination. The use of the terms "comprising" or "including"
to describe
combination of the elements, components, parts or steps herein also
contemplates embodiments
that consist essentially of such elements, components, parts or steps. The use
of the term "may"
herein is intended to illustrate that any of the described attributes that may
be included are
optional.
The plurality of elements, components, parts or steps can be provided by a
single integrated
element, component, part or step. Alternatively, the single integrated
element, component, part or
step may be divided into separate multiple elements, components, parts or
steps. A disclosed "a"
or "an" used to describe an element, a component, a part or a step does not
mean to exclude other
elements, components, parts or steps.
It should be understood that the above description is for purposes of
illustration and not for
purposes of limitation. Many embodiments and many applications other than the
examples
provided will be apparent to those skilled in the art from reading the above
description.
Accordingly, the scope of the present teachings should not be determined with
reference to the
above description, but should be determined with reference to the appended
claims and the full
scope of equivalents owned by these claims. The disclosure of all articles and
references,
19
Date Recue/Date Received 2022-06-29
including patent applications and publications, is incorporated herein by
reference for purposes
of completeness. The omission of any aspect of the subject matter disclosed
herein in the
foregoing claims is not intended to waive the subject matter and the inventor
should not be
deemed to have considered the subject matter as a part of the disclosed
subject matter.
Date Recue/Date Received 2022-06-29
