Interactive precipitation vacuum combined surcharge preloading reinforcement deep soft foundation system and method thereof

Abstract

This invention employs an interactive precipitation-vacuum combined surcharge preloading system and method for reinforcing deep soft soil foundations. The method involves deploying precipitation wells during vacuum preloading. By periodically switching the vacuum pumps of the precipitation wells on and off and connecting them to the atmosphere, an interactive precipitation effect is created between the precipitation wells and drainage boards. During the process of connecting the precipitation wells to the atmosphere, a vacuum pressure gradient is formed in the soil between the precipitation wells and drainage boards, thereby creating a hydraulic gradient between them. This significantly reduces the clogging effect of the drainage boards and enhances the precipitation efficiency of the precipitation wells. This treatment method offers significant improvements for the reinforcement of deep soft soil foundations, shortening the construction period and reducing construction and maintenance costs. Furthermore, the method is simple, easy to implement, and applicable to practical engineering projects.

Description

Technical Field

[0001] This invention relates to an interactive precipitation vacuum combined with surcharge preloading system and method for reinforcing deep soft foundations, belonging to the field of foundation engineering construction technology. Background Technology

[0002] With the rapid development of coastal cities and the increase in population in my country, land resources are becoming increasingly scarce. Land reclamation is an effective way to solve the shortage problem in coastal areas worldwide, leading to a surge in port construction and tidal flat development projects. In practice, mud dredged from the seabed near the reclamation site is commonly used as the reclamation material. These projects involve soft soils characterized by high water content, deep foundations, and high compressibility. Vacuum preloading, as a commonly used, economical, and reliable drainage consolidation method, has been widely applied. In the reinforcement of shallow soft soil, traditional vacuum preloading combined with surcharge preloading can achieve good results.

[0003] However, the vacuum preloading combined with surcharge scheme still has many drawbacks in the reinforcement of deep soft soil: First, the drainage consolidation time is relatively long, the settlement rate is difficult to stabilize, and post-construction settlement is difficult to assess, increasing construction time; second, the additional stress caused by the preloading load decreases with depth, resulting in an unsatisfactory reinforcement effect on deep soft soil and limited treatment depth. As the reinforcement depth increases, the vacuum degree decreases, and the effective depth is generally limited to about 10m. The underlying soft soil cannot be effectively consolidated, which can easily lead to large-scale vertical settlement and horizontal displacement deformation in the later stages of the project, which is not conducive to the progress of the project and the reduction of construction and maintenance costs.

[0004] In summary, based on the current situation and technical conditions, there is an urgent need to invent a foundation reinforcement method for deep soft soil to reduce construction costs, shorten the construction period, reduce subsequent settlement and deformation damage, and improve the effectiveness of deep soft soil foundation reinforcement. Summary of the Invention

[0005] Technical Problem: The purpose of this invention is to provide an interactive precipitation-vacuum combined surcharge reinforcement scheme for deep soft soil foundations. This method significantly improves the reinforcement effect on deep soft soil foundations (thickness exceeding 10m), shortens the construction period, and reduces construction and maintenance costs. This method is technically sound and can solve problems such as insufficient reinforcement depth, insufficient surcharge material, excessively high surcharge costs, and long construction periods in traditional vacuum-combined surcharge schemes.

[0006] To achieve the above-mentioned technical objectives, the present invention will adopt the following technical solution:

[0007] An interactive precipitation vacuum combined surcharge preloading reinforcement system for deep soft soil foundations is used to reinforce deep soft soil foundations. It includes drainage boards and precipitation wells. The drainage boards and precipitation wells are vertically and uniformly arranged in the deep soft soil foundation. The pipe depth of the drainage board is greater than the pipe depth of the precipitation well, and the pipe diameter of the drainage board is smaller than the pipe diameter of the precipitation well. At the same time, several pipes of the drainage board are uniformly arranged around each precipitation well.

[0008] Each drainage board is connected to either vacuum pump A or the external atmosphere via pumping pipe A, while each dewatering well is connected to vacuum pump B via pumping pipe B. Vacuum pump A and vacuum pump B operate independently.

[0009] Preferably, the lower end of the drain pipe is equipped with a filter screen.

[0010] Preferably, the well wall has perforations, the surface is covered with filter cloth, and the lower end of the well is equipped with a filter screen.

[0011] Preferably, the surface of the deep soft soil foundation is covered with a sealing membrane, and the drainage board, dewatering well, pumping pipe A and pumping pipe B are all covered under the sealing membrane; a load is provided on the outside of the sealing membrane.

[0012] Preferably, water level observation wells are also installed in the deep soft soil foundation; the pumping pipeline A is connected to either the vacuum pump A or the external atmospheric environment via a control switch; the control switch controls the operating conditions based on the water level readings from the water level observation wells.

[0013] Another technical objective of this invention is to provide a method for reinforcing deep soft soil foundations using interactive precipitation-vacuum combined surcharge preloading, based on the aforementioned interactive precipitation-vacuum combined surcharge preloading system for reinforcing deep soft soil foundations, comprising the following steps:

[0014] Step 1: Vertically and evenly lay several drainage boards and dewatering wells in the soft soil foundation according to the set spacing, wherein: the laying depth of the drainage boards is greater than the laying depth of the dewatering wells;

[0015] Step 2: Connect the drainage board's pumping pipe to vacuum pump A and the dewatering well's pumping pipe to vacuum pump B. Vacuum pump A and vacuum pump B operate independently to allow for independent on / off control and control of the dewatering well's connection to the atmosphere.

[0016] Step 3: Vacuum pump A and vacuum pump B are used to evacuate the corresponding drainage boards and dewatering wells respectively;

[0017] Step 4: Perform surcharge preloading on the soft soil foundation;

[0018] Step 5: When the vacuum level in the drainage pipe of the drainage board and the drainage pipe of the dewatering well is stable, and the water and air output of vacuum pump A and vacuum pump B are reduced, turn off vacuum pump B.

[0019] Step Six: Connect the pumping pipe of the rainwater well to the outside atmosphere, so that the air pressure at the location of the rainwater well is atmospheric pressure; while keeping the pumping pipe of the drainage board connected to vacuum pump A, so that the air pressure at the location of the drainage board is - At this time, a vacuum pressure gradient is formed in the soil between the drainage board and the dewatering well, which causes groundwater to accumulate towards the drainage board. Groundwater flows from the dewatering well to the drainage board, and the groundwater level drops.

[0020] Step 7: When the outflow rate and volume of groundwater from the dewatering well to the drainage board decrease, close the connection between the dewatering well's pumping pipe and the outside atmosphere; then turn on vacuum pump B to evacuate the dewatering well until the vacuum level in the dewatering well stabilizes and the outflow of water and air through vacuum pump B decreases, then turn off vacuum pump B; repeat steps 6 and 7 until the preset dewatering level is reached, then unload the pump, and the construction is complete.

[0021] Preferably, water level observation wells are installed at key nodes in the construction site; the switching on and off of the vacuum pump B of the dewatering well and the time for connecting to the atmosphere are controlled by the water level: when the outflow rate of groundwater from the dewatering well to the drainage board decreases, the vacuum pump of the dewatering well is turned off, and the atmosphere is connected, causing groundwater to flow from the dewatering well to the drainage board. At this time, the water level observation well receives atmospheric pressure and the water level drops; as the time of connection between the dewatering well and the atmosphere increases, the area of ​​slow water level rise becomes gradual. When the water level reaches a fixed value, the vacuum pump of the dewatering well is turned on to perform vacuuming. This is one cycle.

[0022] Preferably, the water level observation well adopts sealed sampling to avoid inaccurate water level readings caused by atmospheric pressure connecting the water level well.

[0023] Preferably, the construction is carried out in stages. In the early stage of construction, the drainage boards and dewatering wells are subjected to conventional vacuum pre-pressure and air extraction to achieve a sufficient vacuum environment to promote drainage. In the middle stage of construction, the drainage rate slows down, and the dewatering wells are periodically connected to the atmosphere to increase the vacuum pressure gradient of the soft foundation and accelerate drainage.

[0024] Preferably, the lower end of the drainage board is equipped with a filter screen; the drainage board is 100±2mm wide, 3.5-6.0±0.5mm thick, and has a depth of not less than 20m; the wall of the dewatering well is covered with perforations, the surface is wrapped with filter cloth, and the lower end of the pipe is equipped with a filter screen with a hole diameter of 300mm and a depth of not less than 10m.

[0025] Beneficial effects: Compared with traditional vacuum preloading combined loading technology, the present invention has the following advantages:

[0026] 1. Accelerate the consolidation rate of the upper soft soil layer. This method accelerates the pumping speed by arranging dewatering wells, shortening the consolidation time of the upper soft soil layer and reducing the vacuum preloading cycle;

[0027] 2. Effectively reinforces underlying soft soil, accelerates drainage rate, and enhances consolidation strength. This method connects the dewatering wells to the atmosphere through low-periodicity drainage, increasing the vacuum pressure gradient between the wells and the drainage board, thereby improving the dewatering effect on deep soft soil.

[0028] 3. Short construction period and reduced construction and maintenance costs. Due to the deep burial of the underlying soil layer, traditional vacuum preloading combined with surcharge loading methods cannot effectively consolidate it, often leading to significant settlement during the service life and increased maintenance costs. This method can quickly and effectively improve the construction speed, reduce later settlement and deformation, and lower construction and maintenance costs. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the first stage of the present invention, showing vacuum combined loading preloading.

[0030] Figure 2 This is a schematic diagram of the connection between the precipitation well and the atmosphere, representing the second stage of the present invention.

[0031] Figure 3 This is a schematic diagram of the third stage of the present invention: an interactive precipitation combined with surcharge method for strengthening the foundation.

[0032] Figure 4 This is a flowchart illustrating the process of implementing the present invention;

[0033] Figures 5(a) and (b) show the layout of plastic drainage boards and dewatering wells in Examples 1 and 2, respectively. Detailed Implementation

[0034] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0035] The interactive precipitation-vacuum combined surcharge reinforcement soft soil system described in this invention is as follows: Figure 3 As shown. The system includes: an underwater soil drainage system, a sealing system, a vacuum pumping system, an interactive dewatering system, and a groundwater level monitoring system. Compared with traditional vacuum dewatering preloading, the main addition is the interactive dewatering system, the construction process of which is as follows: Figure 4 As shown, this includes: leveling the construction site. laying geotextile at the construction site Install drainage boards, dewatering wells, and water level monitoring wells. Construction of mixing walls and sealing trenches Lay one layer of geotextile and two layers of sealing film. Vacuum test evacuation for 5-10 days Vacuum pre-compression for one month surcharge construction Alternately implement the connection between precipitation wells and the atmosphere, and shut down the connection between precipitation wells and the atmosphere. Uninstallation complete. The installation process includes the following steps:

[0036] Phase 1: Reference Figure 1 Several plastic drainage boards are vertically installed in the soft soil foundation at predetermined intervals. The installation range, depth, and spacing of the plastic drainage boards should meet the design requirements. Dewatering wells are installed according to the designed range, depth, and spacing, ensuring a uniform distribution between them and the plastic drainage boards. Each dewatering well is equipped with a filter screen at its lower end, and the well pipe surface has filter holes and is wrapped with filter cloth. A drainage sand cushion layer is laid on the soft soil foundation surface, and the suction pipes are installed within the sand cushion layer at a depth of not less than 20cm. A sealing membrane is installed on the sand cushion layer. The drainage boards and the pumping pipes of the dewatering wells are connected to independent vacuum pumps A and B. After a period of vacuuming, preloading is performed.

[0037] Phase Two: Reference Figure 2 Once the vacuum level stabilizes under the vacuum membrane (sealing membrane) and the water and air output from vacuum pump A decreases, shut off vacuum pump B corresponding to the dewatering well, and connect the drainage board pipe to the atmosphere. At this time, the air pressure at the dewatering well location is atmospheric pressure (0 kPa), while the drainage board remains connected to vacuum pump A, with an air pressure of -80 kPa. A vacuum pressure gradient forms in the soil between the drainage board and the dewatering well, causing water to accumulate towards the drainage board. The groundwater level drops near the drainage board, forming a large dewatering funnel. Groundwater flows from the dewatering well location towards the drainage board, the dewatering rate increases rapidly, and the groundwater level drops.

[0038] Phase Three: Reference Figure 3 After a period of time, the water discharge rate from the drainage board decreased, and the water output dropped. Then, the vacuum pump B corresponding to the dewatering well was turned on to evacuate the well. Due to the prolonged vacuuming in the first stage, the foundation returned to a vacuum level of -80 kPa, and the water level recovered. (Reference) Figure 4 The interactive precipitation-vacuum combined loading scheme involves periodically repeating the process between the second and third stages. This involves periodically evacuating the precipitation wells and connecting them to the atmosphere. By periodically and interactively adjusting the underground vacuum pressure gradient, the groundwater level is lowered.

[0039] Example 1:

[0040] 1. SPB-B type plastic drainage boards are selected, with a thickness of 4mm, a width of 100mm, and a permeability coefficient of 5*10-7cm3 / s. They are laid 25m deep on soft soil foundations. The dewatering wells are made of PVC material, with perforated pipe walls, a filter cloth covering the surface, and a filter screen at the lower end of the pipe with a pore size of 300mm and a depth of 15m. The plastic drainage boards are laid out in squares spaced 1m apart, with a dewatering well placed at the center of each square. The layout is shown in Figure 5(a).

[0041] 2. Two vacuum pumps (vacuum pump A and vacuum pump B, respectively) are installed to independently connect the drainage pipe (pumping pipe A) of the drainage board and the drainage pipe (pumping pipe B) of the dewatering well, so as to be used for independent construction;

[0042] 3. When using vacuum preloading to construct a deep soft soil foundation for one month, some of the water in the soft soil foundation is drained. At this time, the drainage effect of vacuum preloading decreases.

[0043] 4. Implement surcharge preloading on soft soil foundation, with a surcharge height of 2m;

[0044] 5. Turn off the vacuum pump of the rainwater well and connect it to the atmosphere to raise the vacuum level inside the rainwater well to atmospheric pressure;

[0045] 6. During this process, by observing the water level in the observation well as it gradually rises and then leveling off, the vacuum pump in the dewatering well is turned on using the water level control method.

[0046] 7. By periodically opening and closing the vacuum pump of the dewatering well and connecting it to the atmosphere, the interactive drainage consolidation between the drainage board and the dewatering well is achieved.

[0047] Example 2:

[0048] 1. SPB-B type plastic drainage boards are selected, with a thickness of 4mm, a width of 100mm, and a permeability coefficient of 5*10-5cm3 / s. They are laid 20m deep on soft soil foundations. The dewatering wells are made of PVC material, with perforated pipe walls, a filter cloth covering the surface, and a filter screen at the lower end of the pipe with a pore size of 300mm and a depth of 10m. The plastic drainage boards are laid out in squares spaced 0.8m apart, with a dewatering well placed at the center of each square. The layout is shown in Figure 5(b).

[0049] 2. Two vacuum pumps are independently connected to the drainage pipes of the drainage board and the drainage pipes of the dewatering well, so as to be used for independent construction;

[0050] 3. By using vacuum preloading to construct deep soft soil foundations for half a month, some of the water in the soft soil foundation is drained. At this time, the drainage effect of vacuum preloading decreases.

[0051] 4. Turn off the vacuum pump of the rainwater well and connect it to the atmosphere to raise the vacuum level inside the rainwater well to atmospheric pressure;

[0052] 5. During this process, by observing the water level in the observation well as it gradually rises and then leveling off, the vacuum pump in the dewatering well is turned on using the water level control method.

[0053] 6. By periodically opening and closing the vacuum pump of the dewatering well and connecting it to the atmosphere, the interactive drainage consolidation between the drainage board and the dewatering well is achieved.

Claims

1. A method for reinforcing deep soft soil foundations using interactive precipitation-vacuum combined surcharge preloading, implemented based on an interactive precipitation-vacuum combined surcharge preloading system for reinforcing deep soft soil foundations, characterized in that... The interactive precipitation-vacuum combined surcharge preloading reinforcement system for deep soft soil foundations includes drainage boards, dewatering wells, water level observation wells, and control switches. The drainage boards and dewatering wells are vertically and uniformly arranged in the deep soft soil foundation. The depth of the drainage board pipes is greater than the depth of the dewatering well pipes, and the diameter of the drainage board pipes is smaller than the diameter of the dewatering well pipes. Several drainage board pipes are uniformly arranged around each dewatering well. Each drainage board is connected to either vacuum pump A or the external atmosphere via a pumping pipe A. Similarly, each dewatering well is connected to either vacuum pump B or the external atmosphere via a control switch via a pumping pipe B. Vacuum pump A and vacuum pump B operate independently. The method for reinforcing deep soft soil foundations using interactive precipitation combined with vacuum loading and preloading includes the following steps: Step 1: Vertically and evenly lay several drainage boards and dewatering wells in the soft soil foundation according to the set spacing, wherein: the laying depth of the drainage boards is greater than the laying depth of the dewatering wells; Step 2: Connect the drainage board's pumping pipe to vacuum pump A and the dewatering well's pumping pipe to vacuum pump B. Vacuum pump A and vacuum pump B operate independently to allow for independent on / off control and control of the dewatering well's connection to the atmosphere. Step 3: Vacuum pump A and vacuum pump B are used to evacuate the corresponding drainage boards and dewatering wells respectively; Step 4: Perform surcharge preloading on the soft soil foundation; Step 5: When the vacuum level in the drainage pipe of the drainage board and the drainage pipe of the dewatering well is stable, and the water and air output of vacuum pump A and vacuum pump B are reduced, turn off vacuum pump B. Step Six: Connect the pumping pipe of the rainwater well to the outside atmosphere, so that the air pressure at the location of the rainwater well is atmospheric pressure; while keeping the pumping pipe of the drainage board connected to vacuum pump A, so that the air pressure at the location of the drainage board is - At this time, a vacuum pressure gradient is formed in the soil between the drainage board and the dewatering well, which causes groundwater to accumulate towards the drainage board. Groundwater flows from the dewatering well to the drainage board, and the groundwater level drops. Step 7: When the outflow rate and volume of groundwater from the dewatering well to the drainage board decrease, close the connection between the dewatering well's pumping pipe and the outside atmosphere; then turn on vacuum pump B to evacuate the dewatering well until the vacuum level in the dewatering well stabilizes and the outflow of water and air through vacuum pump B decreases, then turn off vacuum pump B; repeat steps 6 and 7 until the preset dewatering level is reached, then unload the pump, and the construction is complete.

2. The method for reinforcing deep soft soil foundations using interactive precipitation and vacuum combined loading preloading as described in claim 1, characterized in that: Water level observation wells are set up at key nodes in the construction site; the switching on and off of the vacuum pump B of the dewatering well and the time for connecting to the atmosphere are controlled by the water level: when the outflow rate of groundwater from the dewatering well to the drainage board decreases, the vacuum pump of the dewatering well is turned off, and the atmosphere is connected, causing groundwater to flow from the dewatering well to the drainage board. At this time, the water level observation well is subjected to atmospheric pressure and the water level drops; as the time of connection between the dewatering well and the atmosphere increases, the water level slowly rises and tends to level off. When the water level reaches a fixed value, the vacuum pump of the dewatering well is turned on to perform vacuuming. The above is one cycle.

3. The method for reinforcing deep soft soil foundations using interactive precipitation and vacuum combined loading preloading as described in claim 2, characterized in that: Sealed sampling is used in water level observation wells to prevent atmospheric pressure from connecting the wells and causing inaccurate water level readings.

4. The method for reinforcing deep soft soil foundations using interactive precipitation and vacuum combined loading preloading as described in claim 1, characterized in that: Construction is carried out in stages. In the early stage of construction, conventional vacuum pre-pressure and air extraction are carried out on the drainage boards and dewatering wells to achieve a sufficient vacuum environment to promote drainage. In the middle stage of construction, the drainage rate slows down, and the dewatering wells are periodically connected to the atmosphere to increase the vacuum pressure gradient of the soft foundation and accelerate drainage.

5. The method for reinforcing deep soft soil foundations using interactive precipitation and vacuum combined loading preloading as described in claim 1, characterized in that: The lower end of the drainage board is equipped with a filter screen; the drainage board is 100±2mm wide, 3.5-6.0±0.5mm thick, and has a depth of not less than 20m; the wall of the dewatering well is covered with perforations, the surface is wrapped with filter cloth, and the lower end of the pipe is equipped with a filter screen with a hole diameter of 300mm and a depth of not less than 10m.

6. The method for reinforcing deep soft soil foundations using interactive precipitation and vacuum combined loading preloading as described in claim 1, characterized in that: The surface of the deep soft soil foundation is covered with a sealing membrane, and the drainage board, dewatering well, pumping pipe A and pumping pipe B are all covered under the sealing membrane; a load is set on the outside of the sealing membrane.

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