A method for efficiently treating soft ground of a gas lift combined with a bulk material pile composite foundation

Abstract

This invention discloses a method for efficient treatment of soft soil foundations using a composite foundation of air-lifted and granular material piles, comprising: Step 1) laying a sand cushion layer to form a working surface for the granular material pile construction; Step 2) preparing vertical perforated pipes; Step 3) pre-drilling holes in the foundation soil; Step 4) connecting the air-lift joint to the pneumatic pipe next to the perforated pipe, connecting the top drainage pipe interface to the drainage pipe, and connecting the pneumatic pipe interface to the pneumatic pipe, lowering it into the borehole, and starting to fill the soil; Step 5) compacting the soil until it reaches the surface, completing the entire pile; Step 6) repeating steps 3-5 to complete the driving of the granular material piles; Step 7) connecting the pneumatic pipes to form an air injection pipeline and connecting it to an air compressor, connecting the drainage pipe to form a drainage pipeline leading to the catchment area; Step 8) periodically turning on the air compressor to perform air lifting. This invention has low requirements for equipment and the soil to be treated, is simple and feasible to operate, can achieve efficient consolidation of soft soil foundations, and can be applied to large-area soft soil foundation treatment projects.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering technology, specifically relating to an efficient method for treating soft soil foundations in air-lifted composite material pile foundations. Background Technology

[0002] Soft soil is widely found in the southeastern coastal areas of China. It has the characteristics of high water content, low permeability, and low shear strength. Foundation treatment must be carried out before engineering use to improve its bearing capacity and engineering stability.

[0003] Traditional soft soil foundation treatment methods often require long construction periods, high costs, and complex construction equipment, posing numerous challenges to geotechnical engineering construction and land use. Currently, the surcharge (vacuum) preloading drainage consolidation method (CN112962573B) is a relatively effective soft soil foundation treatment method and is widely used in soft soil foundation treatment projects. However, it also has certain limitations. Water seeping through vertical drainage bodies is difficult to remove from the site, resulting in construction times often exceeding several months. Furthermore, well obstruction and smearing effects further delay the dissipation of excess pore water pressure, extending the foundation construction period and increasing construction costs. Therefore, developing a treatment method to accelerate drainage of soft soil foundations is of great significance.

[0004] In mining and dredging projects, air lift is a common method for vertically lifting solids and liquids, as illustrated in Chinese patents CN110630226A and CN105775752A. The air lift method involves injecting compressed air into the bottom of the lifting channel to reduce the fluid density at the inlet. Under the influence of the pressure difference, the target (e.g., slag or sludge) is lifted vertically upwards. Conventional air lift channels typically have atmospheric pressure at the top outlet, relying solely on the high-pressure gas injected at the bottom of the channel to create the pressure difference and lift large quantities of solids and liquids.

[0005] Precipitated material piles refer to a method of reinforcing foundations by setting precipitated materials (such as gravel and sand) in natural soil to enhance the bearing capacity of the foundation and control post-construction settlement. This method is widely used in soft soil foundation reinforcement. When pore water infiltrates into the precipitated material pile, hydrostatic pressure is generated within the pile, increasing continuously as the water level rises. Once the pores of the precipitated material pile are saturated, the hydrostatic pressure inside the pile equals the pore water pressure outside, and the infiltration of pore water into the soft soil foundation ceases. Water within the pile cannot automatically drain to the surface. Therefore, under its own weight stress alone, the pile can only collect water and cannot continuously drain it. To drive the drainage of water within the pile, additional stress is often created by surcharge on the surface. For example, Chinese patent CN 112962573 B mentions using surcharge preloading combined with vacuum preloading to reinforce soft soil foundations, which involves pre-installing plastic drainage boards, laying sealing membranes, and conducting vacuum preloading. However, it is limited by the extremely low permeability coefficient of soft soil foundation (10).-8 The drainage rate after applying additional stress (on the order of m / s) is extremely low, failing to fully utilize the drainage channel function of the granular material piles. Furthermore, the surcharge method is only applicable to soft soil foundations with a certain bearing capacity. For soft soils with extremely poor engineering properties and almost no bearing capacity, surcharge is practically infeasible, thus limiting the application scope of this method.

[0006] In addition, Chinese patent CN 118187029 A connects the air-lift method with the treatment of soft soil foundations and incorporates jet technology. This method uses jets to cut through the soil layer, creating horizontal drainage channels of a certain depth and width within the soft soil. After pretreatment of the soft soil foundation, drainage boards are laid in the soil. Pore water drawn out of the soil by vacuum pressure collects in the drainage boards and is then pumped upwards along them. However, this method also requires the pre-laying of drainage boards, resulting in high costs and complex construction procedures. Summary of the Invention

[0007] To address the technical problem of limited seepage consolidation when using existing granular material piles to treat soft soil foundations, this invention provides a highly efficient method for treating soft soil foundations using a combination of air lift and granular material piles. Throughout the entire treatment period, this invention allows for periodic air lift operations to continuously drain the water stored within the granular material piles (in the perforated pipes), thereby fully utilizing the drainage channels provided by the granular material piles. Compared to other methods, this invention has lower requirements for equipment and the soil to be treated, is simple and feasible to operate, achieves highly efficient consolidation of soft soil foundations, and can be applied to large-area soft soil foundation treatment projects.

[0008] The technical solution adopted in this invention is:

[0009] A method for efficient treatment of soft soil foundations in air-lifted combined granular material pile composite foundations, characterized by the following implementation steps:

[0010] Step 1) Level the site, remove the surface humus, and lay a sand cushion layer to form a working surface for the construction of loose material piles;

[0011] Step 2) Based on the area of ​​soil to be consolidated, prepare vertical perforated pipes to form the air lift channel;

[0012] Step 3) Pre-drill holes in the foundation soil, and follow the drilling process with the outer casing;

[0013] Step 4) The bottom of the perforated pipe is connected to the pneumatic pipe next to the perforated pipe via an air lift connector, the top drain pipe interface is connected to the drain pipe, and the pneumatic pipe interface is connected to the pneumatic pipe. It is then lowered into the borehole to begin filling.

[0014] Step 5) After the filling material is completed for a section, compaction begins. During the compaction process, the outer casing needs to be removed. Once the soil surface is reached, the entire pile is complete.

[0015] Step 6) Repeat steps 3 to 5 above to complete the installation of loose material piles within the soft soil foundation treatment area. Multiple loose material piles are arranged in multiple rows and columns within the foundation treatment area.

[0016] Step 7) After the granular material pile group is completed, connect the pneumatic pipes to form an air injection pipeline and connect it to an air compressor. Connect the drainage pipes to form a drainage pipeline and lead it to the water collection area.

[0017] Step 8) As pore water enters the perforated pipe, the air compressor is periodically turned on to perform air lift. The water in the perforated pipe enters the water collection area through the drainage pipe, thus completing the application of the air lift method in granular material piles.

[0018] Furthermore, in step 8, after the flower tube is filled, positive pressure gas with a certain pressure and flow rate is introduced until the bottom of the flower tube. After the positive pressure gas is reversed through the air lift joint at the bottom of the flower tube, it pushes the water in the flower tube upward in one go.

[0019] Furthermore, a U-shaped directional tube is provided at the air lift connector at the bottom of the flower tube to change the direction of the injected gas.

[0020] Furthermore, the selection of the airlift time interval is related to the rate of water level rise in the perforated tube, the permeability coefficient of the soft soil, and the changes in pore water pressure in the soft soil.

[0021] Furthermore, the time interval for airlifts is selected as 6 hours / time to 48 hours / time.

[0022] Furthermore, in step 8, the duration of a single air lift and the working air pressure are adjusted according to the site conditions.

[0023] Furthermore, for a 10m long pile, pressurized gas of 100-150kPa can be introduced for 3 minutes or more until no more liquid is discharged from the pipe, in order to empty the pipe.

[0024] Furthermore, the air-lift cycle is determined based on the pile length and the soil drainage rate, and is generally selected in the range of 2-12 hours.

[0025] Furthermore, the pressure of the injected gas is changed by controlling the output pressure of the air compressor.

[0026] Furthermore, insertion tubes are provided on both sides of the upper end face of the air lift connector, and the insertion tubes are inserted into the pneumatic tube.

[0027] The principle of the air lift method is as follows: Compressed air is injected into the bottom of the lifting channel, reducing the fluid density at the inlet. Under the action of pressure difference, the target (e.g., slag or silt) is driven vertically upward. Utilizing the air lift principle, a perforated pipe with a ventilation system can be installed inside the bulk material pile. During the seepage consolidation process, water in the pores of the bulk material seeps into the pipe through the pipe wall. Once the perforated pipe is full, positive pressure gas at a certain pressure and velocity is introduced through the ventilation system until it reaches the bottom of the perforated pipe. After the positive pressure gas is redirected by the air lift joint at the bottom of the perforated pipe, it pushes the water inside the pipe upward in one go, thus forming a composite foundation treatment method combining air lift and bulk material piles. After one air lift (i.e., positive pressure gas venting the water inside the pipe), the hydrostatic pressure of the water inside the perforated pipe disappears, increasing the head difference between the water and the soil, which can effectively accelerate the drainage and consolidation of soft soil. In addition, positive pressure gas can also escape into the surrounding soft soil through the bulk material and introduce splitting cracks in the soft soil to form new drainage channels, further shortening the seepage path of the soft soil and increasing the seepage consolidation rate.

[0028] This invention applies the air lift method to granular material piles. The main mechanism of the combination of the two to improve the foundation strength is as follows: (1) Granular material piles have high permeability. After the pile is formed, the pile body can be used as a drainage channel to guide the pore water of the soft soil foundation to seep into the pile body. Air lift can lift the water in the pile body to the ground surface and promote the seepage and consolidation of the soft soil; (2) Granular material piles replace part of the soil to form a composite foundation. The pile body and the soil between the piles are stressed together, and the bearing capacity is improved in the form of a composite foundation.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. This invention applies the air lift method to granular material piles, providing a new method for reinforcing soft soil foundations. The beneficial effects on promoting soft soil consolidation are mainly as follows: 1) Promoting drainage: The innovative integration of perforated pipes into granular material piles provides an implementation channel for air lift; through the lifting effect of positive pressure gas at the bottom of the perforated pipe, the positive pressure gas carries the water stored in the pipe upwards along the perforated pipe, accelerating the drainage of stored water; 2) Improving the consolidation efficiency of soft soil foundations: After the stored water is drained, the seepage gradient from the soft soil to the pile increases, promoting the active convergence of pore water into the pile, effectively promoting seepage consolidation, and achieving the purpose of improving the bearing capacity of the foundation.

[0031] 2. Compared with the traditional method of using surcharge to provide consolidation driving force, the method of the present invention realizes active seepage of pore water, and the new equipment is low in cost, the construction steps are simple and feasible, and the foundation to be treated has no bearing capacity requirement, which is conducive to its promotion in engineering practice. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the engineering site layout of the present invention;

[0033] Figure 2 This is a schematic diagram of an air-lift flower tube structure;

[0034] Figure 3 This is a cross-sectional view of the air lift connector;

[0035] Figure 4a This is a schematic diagram of the arrangement of the perforated pipe in the loose material pile;

[0036] Figure 4b This is a diagram showing the pressure before and after airlift.

[0037] In the diagram: 1. Air compressor; 2. Drainage pipe; 3. Water collection area; 4. Air injection pipe; 5. Perforated pipe; 6. Bulk material pile; 7. Air lift head; 8. Drainage pipe interface; 9. Pneumatic pipe interface; 10. Perforated pipe wall; 11. Pneumatic pipe; 12. Air lift connector; 13. Pneumatic pipe interface; 14. Steering U-shaped pipe. Detailed Implementation

[0038] The technical solution of this invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0039] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0040] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0041] refer to Figures 1 to 4b The present invention discloses a method for efficient treatment of soft soil foundations in air-lifted combined granular material pile composite foundations, comprising the following implementation steps:

[0042] Step 1) Level the site, remove the surface humus, and lay a sand cushion layer to form a working surface for the construction of loose material piles;

[0043] Step 2) Based on the area of ​​soil to be consolidated, prepare vertical perforated pipes to form the air lift channel;

[0044] Step 3) Pre-drill holes in the foundation soil, and follow the drilling process with the outer casing;

[0045] Step 4) The bottom of the perforated pipe 5 is connected to the pneumatic pipe 11 next to the perforated pipe via the air lift connector 12, the top drain pipe interface 8 is connected to the drain pipe 2, and the pneumatic pipe interface 13 is connected to the pneumatic pipe 11. It is then lowered into the borehole to begin filling.

[0046] Specifically, the filler material is gravel or crushed stone, and its gradation and other parameters need to meet the strength and design requirements of the granular material pile, so that it can increase the bearing capacity of the soft soil foundation to a certain extent, and also provide a radial drainage channel for the deep soft soil to meet the drainage function.

[0047] Step 5) After the filling material is completed for a section, compaction begins. During the compaction process, the outer casing needs to be removed. Once the soil surface is reached, the entire pile is complete.

[0048] Step 6) Repeat steps 3 to 5 above to complete the installation of loose material piles within the soft soil foundation treatment area. Multiple loose material piles 6 are arranged in multiple rows and columns within the foundation treatment area.

[0049] Step 7) After the granular material pile group is completed, connect the pneumatic pipes to form an air injection pipeline 4 and connect it to the air compressor 1. Connect the drainage pipes to form a drainage pipeline 2 and lead to the water collection area 3.

[0050] Step 8) As pore water enters the perforated pipe, the air compressor 1 is periodically turned on to perform air lift. The water in the perforated pipe 5 enters the water collection area 3 through the drainage pipe, thus completing the application of the air lift method in the granular material pile.

[0051] Specifically, after the flower tube 5 is filled, positive pressure gas with a certain pressure and flow rate is introduced until the bottom of the flower tube. After the positive pressure gas is reversed through the air lift joint 12 at the bottom of the flower tube, it pushes the water in the flower tube upward in one go.

[0052] Specifically, the duration and working pressure of a single air lift are adjusted according to the site conditions.

[0053] Specifically, the time interval for air lift is related to the rate of water level rise in the perforated pipe, the permeability coefficient of the soft soil, and the changes in pore water pressure in the soft soil. Preferably, the time interval for air lift is 6 hours / cycle to 48 hours / cycle.

[0054] In one embodiment, a U-shaped 14 tube is provided at the air lift connector 12 at the bottom of the flower tube to change the direction of the injected gas.

[0055] In one embodiment, for a 10m long pile, pressurized gas of 100-150kPa can be introduced for 3 minutes or more until no more liquid is discharged from the perforated pipe, so as to empty the perforated pipe. In order to generate air pressure splitting cracks in the soil and promote soil seepage, the air pressure can be appropriately increased.

[0056] In one embodiment, the air-lift cycle is determined based on the pile length and the soil drainage rate, and is generally selected in the range of 2-12 hours.

[0057] In one embodiment, the pressure of the injected gas is changed by controlling the output pressure of the air compressor 1.

[0058] In one embodiment, insertion tubes are provided on both sides of the upper end face of the air lift connector, and the insertion tubes are inserted into the pneumatic tube.

[0059] The principle of the air lift method is as follows: Compressed air is injected into the bottom of the lifting channel, reducing the fluid density at the inlet. Under the action of pressure difference, the target (e.g., slag or silt) is driven vertically upward. Utilizing the air lift principle, a perforated pipe with a ventilation pipeline can be installed inside the bulk material pile. During the seepage consolidation process, water in the pores of the bulk material seeps into the pipe through the perforated pipe wall 10. Once the perforated pipe is full, positive pressure gas at a certain pressure and flow rate is introduced through the ventilation pipeline until it reaches the bottom of the perforated pipe. After the positive pressure gas is redirected by the air lift joint at the bottom of the perforated pipe, it pushes the water inside the perforated pipe upward in one go, thus forming a composite foundation treatment method combining air lift and bulk material piles. After one air lift (i.e., positive pressure gas venting the water inside the pipe), the hydrostatic pressure of the water inside the perforated pipe disappears, increasing the head difference between the water and the soil, which can effectively accelerate the drainage and consolidation of soft soil. In addition, positive pressure gas can also escape into the surrounding soft soil through the bulk material and introduce splitting cracks in the soft soil to form new drainage channels, further shortening the seepage path of the soft soil and increasing the seepage consolidation rate.

[0060] This invention utilizes an air-lift system multiple times via an air-injection pipeline to facilitate the drainage of water from the perforated pipe. The time interval for the air lift is determined by factors such as the rate of water level rise within the perforated pipe, the permeability coefficient of the soft soil, and changes in the pore water pressure of the soft soil.

[0061] High-pressure air enters the top of the perforated pipe through the air injection pipe 4—pneumatic pipe interface 9—pneumatic pipe 11—pneumatic pipe interface 13—turning U-shaped pipe, exerting the air lift effect to empty the perforated pipe 5. The water in the perforated pipe enters the water collection area 3 through the drainage pipe 2, completing the application of the air lift method in the granular material pile.

[0062] Figure 4a and 4bThe pressure changes before and after airlift are shown. When the perforated pipe is full of water, the hydrostatic pressure inside the pipe is the same as the pressure in the surrounding soil, both increasing linearly with depth. When the perforated pipe is emptied, its hydrostatic pressure returns to zero, creating a pressure difference with the soil. This creates the driving force for water infiltration into the perforated pipe, effectively accelerating the foundation drainage and consolidation process.

[0063] The embodiments described in this specification are merely examples of implementations of the inventive concept. The scope of protection of this invention should not be considered as limited to the specific forms stated in the embodiments. The scope of protection of this invention also includes equivalent technical means that can be conceived by those skilled in the art based on the inventive concept.

Claims

1. A method for efficient treatment of soft soil foundations in air-lifted combined granular material pile composite foundations, characterized in that, The implementation steps include the following: Step 1) Level the site, remove the surface humus, and lay a sand cushion layer to form a working surface for the construction of loose material piles; Step 2) Based on the area of ​​soil to be consolidated, prepare vertical perforated pipes to form the air lift channel; Step 3) Pre-drill holes in the foundation soil, and follow the drilling process with the outer casing; Step 4) The bottom of the perforated pipe is connected to the pneumatic pipe next to the perforated pipe via an air lift connector, the top drain pipe interface is connected to the drain pipe, and the pneumatic pipe interface is connected to the pneumatic pipe. It is then lowered into the borehole to begin filling. Step 5) After the filling material is completed for a section, compaction begins. During the compaction process, the outer casing needs to be removed. Once the soil surface is reached, the entire pile is complete. Step 6) Repeat steps 3 to 5 above to complete the installation of loose material piles within the soft soil foundation treatment area. Multiple loose material piles are arranged in multiple rows and columns within the foundation treatment area. Step 7) After the granular material pile group is completed, connect the pneumatic pipes to form an air injection pipeline and connect it to an air compressor. Connect the drainage pipes to form a drainage pipeline and lead it to the water collection area. Step 8) As pore water enters the perforated pipe, the air compressor is periodically turned on to perform air lift. The water in the perforated pipe enters the water collection area through the drainage pipe. At the same time, the positive pressure gas can also escape into the surrounding soft soil through the granular material and introduce the splitting cracks of the soft soil to form new drainage channels, further shortening the seepage path of the soft soil and increasing the seepage consolidation rate, thus completing the application of the air lift method in granular material piles. In step 8, after the flower tube is full, positive pressure gas with a certain pressure and flow rate is introduced until the bottom of the flower tube. After the positive pressure gas is reversed through the air lift joint at the bottom of the flower tube, it pushes the water in the flower tube upward in one go. A U-shaped directional tube is provided at the air lift connector at the bottom of the flower tube to change the direction of the injected gas.

2. The method for efficient treatment of soft soil foundations in a composite foundation of air-lifted combined granular material piles as described in claim 1, characterized in that, The selection of the airlift time interval is related to the rate of water level rise in the perforated tube, the permeability coefficient of the soft soil, and the changes in pore water pressure in the soft soil.

3. The method for efficient treatment of soft soil foundations in a composite foundation of air-lifted combined granular material piles as described in claim 1, characterized in that, The interval between airlifts is selected from 6 hours / time to 48 hours / time.

4. The method for efficient treatment of soft soil foundations in a composite foundation of air-lifted combined granular material piles as described in claim 1, characterized in that, In step 8, the duration of a single air lift and the working air pressure are adjusted according to the site conditions.

5. The method for efficient treatment of soft soil foundations in a composite foundation of air-lifted combined granular material piles as described in claim 4, characterized in that, For a 10m long pile, pressurized gas of 100-150kPa is introduced and maintained for 3 minutes or more until no more liquid is discharged from the pipe, so as to empty the pipe.

6. The method for efficient treatment of soft soil foundations in a composite foundation of air-lifted combined granular material piles as described in claim 1, characterized in that, The air lift cycle is determined based on the pile length and the soil drainage rate, and is selected within the range of 2-12 hours.

7. The method for efficient treatment of soft soil foundations in a composite foundation of air-lifted combined granular material piles as described in claim 1, characterized in that, The pressure of the injected gas is changed by controlling the output pressure of the air compressor.

8. The method for efficient treatment of soft soil foundations in a composite foundation of air-lifted combined granular material piles as described in claim 1, characterized in that, Insertion tubes are provided on both sides of the upper end face of the air lift connector, and the insertion tubes are inserted into the pneumatic tube.

Images