Patent Publication Number: US-2023151573-A1

Title: Soft soil foundation porous-depth air compression drainage device and working method thereof

Description:
CROSS REFERENCE TO THE RELATED APPLICATIONS 
     This application is based upon and claims priority to Chinese Patent Application No. 202111361278.8, filed on Nov. 17, 2021, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to the technical field of geotechnical engineering and in particular to a soft soil foundation porous-depth air compression drainage device and a working method thereof. 
     BACKGROUND 
     The soft soil foundations have the features of high natural water content, large void ratio, strong compressibility, low permeability and poor bearing capacity and the like. When structures are built on the soft soil foundations, engineering load may extremely easily cause excessive settlement of the foundation and the consolidation settlement of the foundation may continue for a very long time due to low permeability of the soft soil. Especially under the engineering conditions of large soil layer thickness of the soft soil foundation, since the groundwater in the deep soft soil foundation has to run a long drainage path before flowing out of ground surface, the natural drainage consolidation may continue for several decades or even several hundred years. Excessive post-construction settlement usually affects normal use of engineering, and may even bring engineering disasters. The surcharge pre-loading method and the vacuum pre-loading method and the like currently adopted have good effect on drainage consolidation of shallow soft soils but poor effect on drainage consolidation of deep soft soils, resulting in long time of drainage consolidation treatment of deep soft soils and high engineering costs. The drainage consolidation of deep soft soil layer has become a difficult point in drainage consolidation treatments of soft soil foundation. Especially, for large area bearing of a soil body for a structure, the drainage consolidation of the deep soft soil layer is extremely important. However, the existing deep soft soil consolidation treatment has the defects of long time and high engineering costs. 
     SUMMARY 
     In order to overcome the existing defects in the prior art, the present invention provides a soft soil foundation porous-depth air compression drainage device applicable to large area bearing of a soil body for a structure and a working method thereof, which are used to drain deep groundwater in a soft soil foundation so as to accelerate drainage consolidation of deep soft soil and reduce post-construction foundation settlement and deformation. 
     The purpose of the present invention is achieved by using the following technical solution. The soft soil foundation porous-depth air compression drainage device comprises an air compression pipe and a water drainage pipe. A water drainage cavity body and an air diffusion cavity body are buried respectively in a soft soil foundation. At least two water drainage cavity bodies are disposed around the air diffusion cavity body, and a bottom of the air diffusion cavity body in the soft soil foundation is lower than a bottom of the water drainage cavity body in the soft soil foundation. A connection opening is opened on a top end surface of the air diffusion cavity body and is connected with the air compression pipe, and the air compression pipe protrudes out of ground surface along a vertical direction of the soft soil foundation and communicates with an inflation pump. A connection opening is opened on a top end surface of the water drainage cavity body and is connected with the water drainage pipe, one end of the water drainage pipe protrudes to the bottom of the water drainage cavity body, and the other end of the water drainage pipe protrudes out of the ground surface along the vertical direction of the soft soil foundation. With the disposal of the above drainage device in the soft soil foundation, deep drainage can be achieved for the soft soil foundation and a drainage consolidation time of the deep soft soil foundation is shortened, so as to reduce a saturation degree of the deep soil body and reduce the post-construction settlement and deformation of the soft soil foundation. Further, deep soft soil consolidation treatment is achieved for the large area bearing of the soil body for the structure. 
     Preferably, the air diffusion cavity body has an outer diameter greater than or equal to an outer diameter of the water drainage cavity body, and a vertical distance between the bottom of the air diffusion cavity body in the soft soil foundation and the bottom of the water drainage cavity body in the soft soil foundation is 1 to 2 m. The outer diameter difference of the two cavity bodies enables an air pressure in the air diffusion cavity body to not only satisfy a seepage pressure for driving the soil body but also convey and satisfy a pressure in the water drainage cavity body through the seepage pressure; the distance difference of the two cavity bodies can enable groundwater in a deep soil body under the cavities to be fully seeped into the water drainage cavity body, thus achieving deep soft soil consolidation treatment for large area bearing of the soil body. 
     Preferably, four water drainage cavity bodies are disposed and equidistantly distributed along a radial circumference of the air diffusion cavity body. In this way, an area of deep soft soil consolidation treatment can be increased, and the drainage for an effective area of soil body is more uniform during a soft soil consolidation treatment process. 
     Preferably, a vertical distance between the air diffusion cavity body and a ground surface of the soft soil foundation is greater than 10 m, and a transverse distance between the air diffusion cavity body and the water drainage cavity body is 3 to 5 m. This helps air compression toward the air diffusion cavity body and water drainage out of the ground surface from the water drainage cavity body and the distance may be adjusted to adapt to time control requirements of drainage consolidation and soft soil consolidation with requirements of different depths and areas and better adapt to deep soft soil consolidation treatment for large area bearing of the soil body for different areas of structures. 
     Preferably, a height of the water drainage cavity body is greater than a height of the air diffusion cavity body. Since the air diffusion cavity body is buried deeper, such height difference designing can promote seepage of a soil body between above the air diffusion cavity body and the surrounding of the water drainage cavity body, thus further shortening the time for deep soft soil consolidation treatment. 
     Preferably, the air diffusion cavity body comprises a rigid bracket and a geofabric. The rigid bracket is a cylindrical body which is externally wrapped with the geofabric and buried along a vertical direction of the soft soil foundation. With the disposal of the above structure, the rigidity of the air diffusion cavity body in the soft soil foundation can be guaranteed, and meanwhile, it has air permeability and can prevent soil body from entering the cavity. 
     Preferably, the water drainage cavity body is enclosed by a water-permeable pipe and buried along the vertical direction of the soft soil foundation. In this case, the water drainage cavity body has water permeability and can prevent soil body from entering the cavity. 
     A working method using the soft soil foundation porous-depth air compression drainage device as mentioned above is provided, which includes the following steps. 
     Step S 1 , a deep hole which has a depth of at least 10 m and is used for burying the air diffusion cavity body is drilled in the soft soil foundation, at least two deep holes for burying the water drainage cavity bodies are drilled 3 to 5 m transversely from the above deep hole, then the air diffusion cavity body with the air compression pipe and the water drainage cavity body with the water drainage pipe are put on the bottoms of respective deep holes, and soil body is filled in the respective deep holes until they are flush with the ground surface of the soft soil foundation. 
     Step S 2 , the inflation pump is used to compress air into the air compression pipe such that the air diffusion cavity body forms a high air pressure and maintains this pressure greater than a pore water pressure of surrounding soil body and less than a self-weight pressure of the soil body, and the air in the air diffusion cavity body is squeezed and diffused toward surrounding soil bodies to drive groundwater in the soil bodies to flow along a maximum pressure gradient direction. 
     Step S 3 , during an inflation process of the air diffusion cavity body, a seepage pressure for driving the soil body by the air pressure is conveyed to the surrounding water drainage cavity bodies and causes a pressure in the water drainage cavity bodies to rise. When a pressure head in the water drainage cavity body reaches the ground surface, groundwater seeping into the water drainage cavity body flows out of the ground surface through the water drainage pipe. 
     The present invention has the following beneficial effects: by using the soft soil foundation porous-depth air compression drainage device and in combination with use of an air compression drainage method, the followings can be achieved: 1. deep drainage of the soft soil foundation can be achieved, drainage consolidation time of the deep soft soil can be shortened, and deep soft soil consolidation treatment can be achieved for large area bearing of soil body for the structure; 2. by adjusting the distance between the water drainage cavity body and the air diffusion cavity body, time control requirements of drainage consolidation can be satisfied; 3. during a drainage process, it is only required to compress air into the air diffusion cavity body and drive groundwater by air pressure to flow out of the soil body, resulting in low energy consumption. 
     Preferably, in the steps S 2  and S 3 , when the air compression pipe is pressurized, the air diffusion cavity body is in a high pressure state; by using the high pressure condition of the air diffusion cavity body, groundwater of its surrounding soil bodies is driven to flow to a neighboring water drainage cavity body having lower pressure and then discharged out of ground surface by the water drainage pipe; further, more efficient water drainage can be achieved using air pressure, such that the water seeping efficiency of the water drainage cavity body is greatly increased, causing the deep groundwater to flow out of the ground surface through the water drainage pipe. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         FIG.  1    is a structural schematic diagram illustrating a soft soil foundation porous-depth air compression drainage device according to the present invention. 
         FIG.  2    is a structural schematic diagram taken along A-A in  FIG.  1   . 
         FIG.  3    is a structural schematic diagram illustrating an air diffusion cavity body according to the present invention. 
     
    
    
     The numerals of the drawings are described below:  1 . air compression pipe,  2 . water drainage pipe,  3 . water drainage cavity body,  4 . air diffusion cavity body,  5 . inflation pump,  6 . soft soil foundation,  41 . rigid bracket,  42 . geofabric. 
     DETAILED DESCRIPTIONS OF EMBODIMENTS 
     The present invention will be detailed in combination with accompanying drawings. As shown in  FIGS.  1  and  2   , the present invention comprises an air compression pipe  1  and a water drainage pipe  2 . A water drainage cavity body  3  and an air diffusion cavity body  4  are buried respectively in a soft soil foundation  6 . Four water drainage cavity bodies  3  are disposed and equidistantly distributed along a radial circumference of the air diffusion cavity body  4 , and a bottom of the air diffusion cavity body  4  in the soft soil foundation  6  is lower than a bottom of the water drainage cavity body  3  in the soft soil foundation  6  so as to achieve deep soft soil consolidation treatment for large area bearing of soil body for a structure. A connection opening is opened on a top end surface of the air diffusion cavity body  4  and is connected with the air compression pipe  1 , and the air compression pipe  1  protrudes out of ground surface along a vertical direction of the soft soil foundation  6  and communicates with an inflation pump  5 . A connection opening is opened on a top end surface of the water drainage cavity body  3  and is connected with the water drainage pipe  2 , and one end of the water drainage pipe  2  protrudes to the bottom of the water drainage cavity body  3  such that water seeping into the water drainage cavity body  3  from the soil body can be discharged out of the ground surface through the water drainage pipe  2  as possible and meanwhile unnecessary consumption of drainage drive pressure can be avoided. The other end of the water drainage pipe  2  protrudes out of the ground surface along the vertical direction of the soft soil foundation  6 . The drainage drive pressure of the water drainage cavity body  3  comes from a seepage pressure conveyed by the air pressure. The vertical direction mentioned above refers to a direction perpendicular to the ground surface, such that the air compression of the air compression pipe  1  to the air diffusion cavity body  4  and the air compression and drainage efficiency of the water drainage cavity body  3  to the water drainage pipe  2  are more efficient. In this case, a path for air compression and water drainage is greatly shortened, helping more to shorten the drainage consolation time of the deep soft soil foundation. 
     The air diffusion cavity body  4  has an outer diameter greater than or equal to an outer diameter of the water drainage cavity body  3 , such that an air pressure in the air diffusion cavity body can not only satisfy a seepage pressure for driving the soil body but also convey and satisfy a pressure in the water drainage cavity body through the seepage pressure. A vertical distance between the bottom of the air diffusion cavity body  4  in the soft soil foundation  6  and the bottom of the water drainage cavity body  3  in the soft soil foundation  6  is 1.5 m. The distance difference of the two cavity bodies can enable groundwater in a deep soil body under the cavities to be fully seeped into the water drainage cavity body, thus achieving deep soft soil consolidation treatment for large area bearing of the soil body. 
     As a principle, air and liquid always flow along a maximum pressure gradient direction and a pressure gradient is directly proportional to a pressure difference between two points and inversely proportional to a distance of two points. The vertical distance between the air diffusion cavity body  4  and the ground surface of the soft soil foundation  6  is 12 m, and a transverse distance between the air diffusion cavity body  4  and the water drainage cavity body  3  is 4 m. The larger the distance between the air diffusion cavity body  4  and the water drainage cavity body  3  is, the longer the water drainage takes. But, based on actual requirements, if the deep soft soil drainage consolidation is large in area and depth, it is required to increase the distance between the air diffusion cavity body  4  and the water drainage cavity body  3  while increasing the distance between the air diffusion cavity body  4  and the ground surface of the soft soil foundation  6 , so as to adapt to deep soft soil consolidation treatment for bearing of different areas of soil bodies. 
     A height of the water drainage cavity body  3  is greater than a height of the air diffusion cavity body  4  with their usual height ratio being 1:2. Such height difference designing can promote seepage of a soil body between above the air diffusion cavity body and the surrounding of the water drainage cavity body, thus further shortening the time for deep soft soil consolidation treatment. 
     As shown in  FIG.  3   , the air diffusion cavity body  4  comprises a rigid bracket  41  and a geofabric  42 . The rigid bracket  41  is a cylindrical body which is externally wrapped with the geofabric  42  and buried along a vertical direction of the soft soil foundation  6 . The water drainage cavity body  3  is enclosed by a water-permeable pipe and buried along the vertical direction of the soft soil foundation  6 . The vertical burying mentioned above means that axes of the two cavities are perpendicular to the ground surface. In this way, the spatial arrangement will be more compact and the drainage efficiency will be higher. At the same time, deep soft soil consolidation treatment can be achieved for large area bearing of soil body for the structure. 
     Provided is a working method using the soft soil foundation porous-depth air compression drainage device, which includes the following steps. 
     Step S 1 , a deep hole which has a depth of 12 m and is used for burying the air diffusion cavity body  4  is drilled in the soft soil foundation  6 , at least two deep holes for burying the water drainage cavity bodies  3  are drilled 4 m transversely from the above deep hole, then the air diffusion cavity body  4  with the air compression pipe  1  and the water drainage cavity body  4  with the water drainage pipe  2  are put on the bottoms of respective deep holes, and soil body is filled in the respective deep holes until they are flush with a ground surface of the soft soil foundation  6 . 
     Step S 2 , the inflation pump  5  is used to compress air into the air compression pipe  1  such that the air diffusion cavity body  4  forms a high air pressure and maintains this pressure greater than a pore water pressure of surrounding soil body and less than a self-weight pressure of the soil body, and the air in the air diffusion cavity body  4  is squeezed and diffused toward surrounding soil bodies to drive groundwater in the soil bodies to flow along a maximum pressure gradient direction. 
     Step S 3 , during an inflation process of the air diffusion cavity body  4 , a seepage pressure for driving the soil body by the air pressure is conveyed to the surrounding water drainage cavity bodies  3  and causes a pressure in the water drainage cavity bodies  3  to rise. When a pressure head in the water drainage cavity body  3  reaches the ground surface, groundwater seeping into the water drainage cavity body  3  flows out of ground surface through the water drainage pipe  2 . 
     In the steps S 2  and S 3 , when the air compression pipe  1  is pressurized, the air diffusion cavity body  4  is in a high pressure state; by using the high pressure condition of the air diffusion cavity body  4 , groundwater of its surrounding soil bodies is driven to flow to a neighboring water drainage cavity body  3  having lower pressure and then discharged out of ground surface by the water drainage pipe  2 ; the drainage drive pressure of the water drainage cavity body  3  comes from a seepage pressure conveyed by the air pressure in the air diffusion cavity body  4 . When the transverse distance between the water drainage cavity body  3  and the air diffusion cavity body  4  is small, the compressed air of the air diffusion cavity body  4  enters, through the soil bodies, the water drainage cavity body  3  as the drainage drive pressure, so as to further increase the drainage efficiency and reduce the time for deep soft soil drainage consolidation. 
     The present invention is not limited to the above embodiments, and any changes to its shape or material shall be considered as a variation of the present invention and fall in the scope of protection of the present invention as long as the structural design of the present invention is adopted.