CA3165878A1 - Combined construction method and system of vacuum pipe well combined with pneumatic fracturing in deep soft soil foundation - Google Patents

Abstract

The invention discloses a combined construction method and system of vacuum pipe well combined with pneumatic fracturing in deep soft soil foundation, the construction method comprising: vacuumizing a sealed pipe well by a vacuum pump so that negative pressure is formed in the pipe well, at the same time delivering the gas extracted by the vacuum pump to a pressurizing tank, then the pressurizing tank injecting the high pressure air into the soft soil between the pipe wells to produce pneumatic fracturing in the soil body; expanding the flow path of groundwater, and accelerate the dewatering rate of the pipe well and thus promote the precipitation consolidation of the soft soil. This method effectively solves the problems that the traditional (vacuum) pipe well dewatering method is not effective to treat the soft clay layer with low permeability and the precipitation rate is not high.

Description

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 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.

2 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

3 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);

4 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 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 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 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 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 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, 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 where K denotes a permeability coefficient of a phreatic layer (mid); C
denotes thickness of 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 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+ ) 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 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.

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, 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 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, 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

Claims (10)

What is claimed is:

1. A combined construction method of vacuum pipe well combined with pneumatic fracturing in deep soft soil foundation, characterized in 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.

2. The combined construction method of vacuum pipe well combined with pneumatic fracturing in deep soft soil foundation according to claim 1, characterized in that, 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.

3. The combined construction method of vacuum pipe well combined with pneumatic fracturing in deep soft soil foundation according to claim 2, comprising the following steps:
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 Date Recue/Date Received 2022-06-29 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 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.

4. The combined construction method of vacuum pipe well combined with pneumatic fracturing in deep soft soil foundation according to claim 3, characterized in that, 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.

5. The combined construction method of vacuum pipe well combined with pneumatic fracturing in deep soft soil foundation according to claim 4, characterized in that, the number of the pipe wells is calculated by the following formula:

Date Recue/Date Received 2022-06-29 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, 2TIC(2C ¨S )S
Q = d d Asdpit In(1+ ) where K denotes a permeability coefficient of a phreatic layer (m/d); C
denotes thickness of the confined aquifer (m); Sd denotes the designed precipitation depth (m); R
denotes radius of ro = VA/
influence (m), =d ; r0 denotes equivalent large well radius (m); rt. A denotes site area (m2); t denotes the designed precipitation time (days);
for the depressurization pipe well, /115d Q=21-dc In(l+R/ ) / r where, K denotes a permeability coefficient of the confined aquifer (m/d); M
denotes the thickness of the confined aquifer (m);

6. The combined construction method of vacuum pipe well combined with pneumatic fracturing in deep soft soil foundation according to claim 1, characterized in that, 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.

7. The combined construction method of vacuum pipe well combined with pneumatic fracturing in deep soft soil foundation according to claim 1, characterized in that, 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.

8. The combined construction method of vacuum pipe well combined with pneumatic fracturing in deep soft soil foundation according to claim 1, characterized in further comprising Date Recue/Date Received 2022-06-29 the following steps:
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.

9. A combined construction system of a vacuum pipe well combined with pneumatic fracturing in deep soft soil foundation, characterized in 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 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 Date Recue/Date Received 2022-06-29 communicated with a plurality of gas injection pipes inserted into the earth's surface at different depths.

10. The combined construction system of a vacuum pipe well combined with pneumatic fracturing in deep soft soil foundation, characterized in that, 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.
Date Recue/Date Received 2022-06-29