A construction method of synchronous dynamic drainage consolidation of soft soil foundation by vacuum preloading

Abstract

This invention discloses a method for vacuum preloading and synchronous dynamic drainage consolidation construction of soft soil foundations, comprising: backfilling a soil cushion layer and laying a sand cushion layer on the target soft soil foundation, and laying drainage pipes and a vacuum system; starting the vacuum system; after the vacuum degree in the target soft soil foundation reaches a stable level, stacking a soil layer of a predetermined thickness on the sand cushion layer; starting to unload the soil layer until the thickness of the soil layer is reduced to the predetermined thickness; after the soil layer is reduced to the predetermined thickness, maintaining the vacuum degree of the target soft soil foundation and simultaneously carrying out two rounds of full compaction on the soil layer; after the full compaction is completed, shutting off the vacuum system, and then carrying out two rounds of spot compaction; after the spot compaction is completed, unloading the remaining thickness of the soil layer; then impact compacting the exposed sand cushion layer and leveling the sand cushion layer. This invention provides faster drainage, reduces consolidation time, and improves consolidation effect.

Description

Technical Field

[0001] This invention relates to the field of soft soil foundation reinforcement technology, specifically a construction method for vacuum preloading and synchronous dynamic drainage consolidation of soft soil foundations. Background Technology

[0002] Most major domestic and international engineering projects and industrial facilities need to be built on soft soil foundations. These foundations require reinforcement to increase their strength before they can be put into use. Existing methods for drainage consolidation of soft soil foundations often employ vacuum preloading. However, when treating deep soft soil foundations, vacuum preloading alone has significant limitations. Settlement develops rapidly in the early stages, but later settlement almost stops, requiring a considerable time overall, and the reinforcement effect is not satisfactory, with high costs. Dynamic consolidation is a method for rapidly increasing foundation strength and reducing compressibility. Some technical solutions propose implementing dynamic consolidation after vacuum preloading, using the impact force generated by the powerful energy of the impact to compress the pores in the soil, creating excess pore water pressure to promote drainage. However, this method has certain drawbacks. After vacuum preloading, the drainage path of the soft soil foundation is greatly reduced, and the excess pore pressure generated by dynamic consolidation is difficult to dissipate, easily forming "rubber soil." This not only fails to achieve rapid reinforcement but also easily leads to foundation instability.

[0003] In summary, there is a need for a method that can combine the advantages of vacuum preloading and dynamic consolidation to achieve faster drainage, thereby reducing consolidation time and improving consolidation effect, i.e., achieving higher consolidation strength. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a construction method for vacuum preloading and synchronous dynamic drainage consolidation of soft soil foundations, which can solve the problems described in the background art.

[0005] The technical solution to achieve the objective of this invention is: a method for constructing vacuum preloading synchronous dynamic drainage consolidation on soft soil foundations, comprising the following steps: A soil cushion layer was backfilled on the target soft soil foundation. After the soil cushion layer was backfilled, drainage pipes were laid, a sand cushion layer was laid on top of the soil cushion layer, and a vacuum system was installed on top of the sand cushion layer. Activate the vacuum system and, once the vacuum level within the target soft soil foundation has stabilized, load a soil layer of a predetermined thickness onto the sand cushion layer. When the consolidation degree and water discharge of the target soft soil foundation reach the corresponding preset thresholds, the earthwork layer is unloaded until its thickness is reduced to the preset thickness. Once the earthwork layer has been reduced to the preset thickness, maintain the vacuum degree of the target soft soil foundation ≥ the preset vacuum pressure, and simultaneously carry out two rounds of full compaction on the earthwork layer. The compaction energy of the first round of full compaction should be < the compaction energy of the second round of full compaction. After the full compaction is completed, the vacuum system is shut off, followed by two rounds of spot compaction and one round of full compaction. The impact energy of the two rounds of spot compaction is the same and greater than that of the final round of full compaction. After the point compaction is completed, the remaining thickness of the earthwork layer is unloaded, and then the exposed sand cushion layer is impact-compacted and leveled until the target soft soil foundation reaches the handover elevation and the drainage operation is completed.

[0006] Furthermore, the drainage pipeline is laid, including: Drainage boards are inserted into the sand cushion layer at preset intervals and inserted to a specified depth. A main water pipe and several collection pipes are laid on the sand cushion layer. The collection pipes are distributed at intervals along the sand cushion layer. Each drainage board is connected to the corresponding collection pipe. The collection pipes are connected end to end and then connected to the main water pipe. One end of the main water pipe extends out of the sand cushion layer. The main water pipe is used to drain the water in the collection pipes.

[0007] Furthermore, a vacuum system is installed, including: A vacuum pump is installed around the sand cushion layer and the soil cushion layer. The vacuum pump is connected to the main water pipe. A sealing wall is built at the boundary of the target soft soil foundation. The sealing wall penetrates at least 50cm through the permeable layer of the target soft soil foundation. Then, a sealing membrane is laid on the surface of the sand cushion layer. Next, the vacuum pump is started. After the vacuum degree in the target soft soil foundation below the sealing membrane reaches a stable level, geotextile is laid on the sealing membrane.

[0008] Furthermore, the vacuum system is activated and the sealing membrane is laid after several days of vacuum pre-compression.

[0009] Furthermore, a soil layer of a predetermined thickness is stacked on the geotextile.

[0010] Furthermore, a graded loading method is adopted to complete the loading of earthwork layers of a predetermined thickness.

[0011] Furthermore, the earthwork layers are loaded in n stages, where n≥2. The thickness of the first stage is 0.5 m, and the first stage uses silt and sand with a maximum particle size of ≤5 cm. The thickness of the second to nth stages is 1 m, and the maximum particle size of the soil used is ≤20 cm. The sum of the thicknesses of all loaded earthwork layers is the preset thickness.

[0012] Furthermore, with n=3, the thickness of the earthwork layer produced by the first stage of loading is 0.5 m, the thickness of the earthwork layer produced by the second stage of loading is 1.5 m, and the thickness of the earthwork layer produced by the third stage of loading is 1.5 m. After the first stage of loading is completed, the second stage of loading begins after several days of vacuum preloading. After the second stage of loading is completed, the third stage of loading begins after several days of vacuum preloading.

[0013] Furthermore, the preset threshold for the degree of consolidation is 80%, and the preset threshold for the effluent flow rate is 3 L·m³. -2 / d, with a preset vacuum pressure of 85 kPa.

[0014] Furthermore, the impact energy of the first full compaction is 500 kN·m, the impact energy of the second full compaction is 800 kN·m, the impact energy of the two spot compaction is 1500 kN·m, and the impact energy of the last spot compaction is 1000 kN·m.

[0015] The beneficial effects of this invention are: faster drainage, reduced consolidation time, avoidance of the "rubber soil" phenomenon, ensuring project safety, and improved consolidation effect. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the drainage system constructed to achieve rapid drainage according to the present invention; Figure 2 This is a schematic diagram of a double-row single-pipe connection; Figure 3 This is a schematic diagram illustrating the changes in staged loading and unloading over time. Figure 4 This is a schematic flowchart of the method of the present invention; In the diagram, 1-target soft soil foundation, 2-drainage board, 3-soil cushion layer, 4-sand cushion layer, 5-vacuum pump, 6-main pipe, 7-earthwork layer, 8-dynamic compaction machine, 9-water collection pipe. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and specific embodiments: like Figures 1-3 As shown, a method for constructing a vacuum preloading synchronous dynamic drainage consolidation system for soft soil foundations includes the following steps: Step 1: Backfill a soil cushion layer on the target soft soil foundation. After backfilling the soil cushion layer, lay a sand cushion layer on top of the soil cushion layer. Insert drainage boards into the sand cushion layer at preset intervals and insert them to a specified depth. Lay a main water pipe and several collection pipes on the sand cushion layer. The collection pipes are distributed at intervals along the sand cushion layer. Each drainage board is connected to the corresponding collection pipe. The collection pipes are connected end to end and then connected to the main water pipe. One end of the main water pipe extends out of the sand cushion layer. The main water pipe is used to drain the water collected in the collection pipes.

[0018] Understandably, a board insertion machine can be used to insert plastic drainage boards to a specified depth, completing the task of inserting the drainage boards into soft soil foundations. Board insertion machines are existing technology, capable of inserting drainage boards at uniform intervals. Drainage boards are generally made of plastic, balancing durability with the smooth flow of water through the channels within the board.

[0019] One of the purposes of backfilling the soil cushion layer is to provide a working surface with a certain bearing capacity for the subsequent insertion machine of the drainage board, so that the insertion machine can perform the drainage board insertion operation on the soil cushion layer.

[0020] For example, the drainage boards and water collection pipes are connected in a double-row single-pipe manner, that is, two drainage boards are connected to both sides of each water collection pipe, and two adjacent rows of drainage boards are connected to the same water collection pipe.

[0021] refer to Figure 2 , Figure 2 Any two adjacent drainage boards are connected to a central water collection pipe to achieve a double-row single-pipe connection.

[0022] The purpose of adopting the double-row single-pipe method is to reserve working space for the construction of the dynamic compaction machine when the dynamic consolidation is carried out simultaneously, and to reduce the impact of consolidation energy transfer on the drainage pipeline (the drainage pipeline formed by the drainage board, the water collection pipe and the main water pipe).

[0023] The upper ends of two adjacent drainage boards are slightly brought together towards the center and connected to the water collection pipe placed in the middle position, which can be fixed by binding.

[0024] The upper parts of all water collection pipes, main water pipes and drainage boards are buried in the sand cushion layer. The burial depth can be set as needed, for example, the burial depth needs to be greater than 15 cm.

[0025] For example, the soil cushion layer is backfilled using a staged backfilling method.

[0026] In this embodiment, at least two-stage backfilling is used for the soil cushion layer. The thickness of the first-stage backfill soil cushion layer is 0.5 m, and the thickness of the second-stage backfill soil cushion layer is 1.5 m. The total thickness of the soil cushion layer obtained by the two-stage backfilling is 2 m, that is, the second-stage backfilling is to continue backfilling the soil cushion layer on the surface of the already backfilled soil cushion layer.

[0027] Understandably, the ring stiffness of the main water pipe is slightly lower than that of a conventional vacuum preloaded main pipe, but the toughness and plastic deformation capacity of the main water pipe are significantly higher than those of a conventional vacuum preloaded main pipe.

[0028] Corrugated pipes can be used for both the water collection pipe and the main water pipe. The advantage of using corrugated pipes is that they ensure good water flow performance of the vacuum pipeline during synchronous dynamic consolidation, and prevent pipeline rupture or breakage during the energy transfer process of dynamic consolidation, thereby avoiding the loss of drainage performance of the vacuum system.

[0029] Step 2: Deploy the vacuum pump, located around the sand cushion layer and soil cushion layer, and connect it to the main water pipe. Then, construct a sealing wall at the boundary of the target soft soil foundation. The height of the sealing wall should be lower than the height of the sand cushion layer, and the sealing wall should penetrate at least 50cm into the permeable layer of the target soft soil foundation. Next, lay a sealing membrane on the surface of the sand cushion layer. Then, start the vacuum pump. After the vacuum level in the target soft soil foundation below the sealing membrane stabilizes, lay geotextile on the sealing membrane, and then pile a pre-set thickness of soil layer on top of the geotextile.

[0030] For example, a staged loading method is used to complete the loading of earthwork layers of a preset thickness.

[0031] For example, the earthwork layer adopts n-level graded loading, n≥2, the thickness of the first level loading is 0.5 m, the first level loading uses silt and sand, and the maximum particle size of the silt and sand is ≤5 cm; the thickness of the second to nth level loading is 1 m, and the maximum particle size of the soil used is ≤20 cm. The sum of the thicknesses of all loaded earthwork layers is the preset thickness a.

[0032] Understandably, the first-stage loading thickness is limited to 0.5 m, and the maximum particle size of the silt and sand used is limited to no more than 5 cm. The purpose is to provide a working support surface for the subsequent dynamic compaction machine by surcharged earth layers, while preventing damage to the sealing membrane caused by excavators and other construction equipment, thus avoiding vacuum loss. It also prevents the soft soil foundation from experiencing punching and shear failure due to excessively thick earth layers. Furthermore, it prevents soil particles from tearing the sealing membrane due to force transmission from excessively thick earth layers.

[0033] Step 3: Monitor the consolidation degree of the target soft soil foundation to reach the preset consolidation degree threshold (e.g., 80%) or the outflow rate to be less than the preset outflow rate threshold (e.g., 3 L·m). -2 When / d), the thickness of the earthwork layer is adjusted to 2 m by unloading or backfilling.

[0034] That is, if the original preset thickness a < 2 m, the backfilling method is used to increase the thickness of the earthwork layer to 2 m; if the preset thickness a > 2 m, the unloading method is used to reduce the thickness of the earthwork layer to 2 m.

[0035] When the degree of consolidation reaches the preset consolidation threshold, it means that after vacuum preloading reinforces the target soft soil foundation to this degree of consolidation, the settlement rate and drainage rate of the target soft soil foundation begin to slow down significantly, and the reinforcement effect is limited at this point. Therefore, it is necessary to arrange dynamic consolidation and vacuum preloading simultaneously to achieve rapid consolidation through synergy. The installation of an energy dissipation system enables the current target soft soil foundation to accommodate large construction equipment (such as dynamic compaction machines) and can also transfer dynamic loads to the deep layers of the soft soil foundation. This compresses the voids in the soil layer that clogs drainage channels, causes localized soil liquefaction, and generates cracks in the clogged layer around the compaction point, forming good drainage channels and further improving the reinforcement effect.

[0036] Adjusting the thickness of the earthwork layer to 2 m maximizes the effect of synchronous dynamic load consolidation construction. Under the premise of ensuring that the sealing membrane is not damaged during the energy transfer process during the dynamic load consolidation stage, the energy can be transferred to a deeper layer of the target soft soil foundation.

[0037] Step 4: Maintain the vacuum degree of the target soft soil foundation to be greater than or equal to 85 kPa, and simultaneously carry out two full compaction operations on the soil layer. The compaction energy of the first full compaction operation is 500 kN·m, and the compaction energy of the second full compaction operation is 800 kN·m.

[0038] After the two full compaction operations are completed, the vacuum pump is turned off simultaneously. After the vacuum pump is turned off, two rounds of spot compaction and one round of full compaction are carried out in sequence. The impact energy of the two rounds of spot compaction is 1500 kN·m, and the impact energy of the final round of full compaction is 1000 kN·m.

[0039] For full-compaction construction, the purpose of starting with low-energy compaction and gradually increasing the energy is to first compact the energy dissipation system composed of the earthwork layer, sand cushion layer, and soil cushion layer through low-energy full-compaction, which significantly improves the bearing capacity and deformation performance, and compresses the large pores on the surface of the target soft soil foundation. Then, high-energy dynamic compaction is used, and the already compacted energy dissipation system and the surface of the target soft soil foundation further transfer energy to the depth of the soft foundation. The soil pores are compressed, local liquefaction occurs, and cracks are generated around the compaction point to improve drainage performance. The energy dissipation system with improved bearing capacity and deformation performance and the soft foundation surface can also deform in coordination, avoiding large differential settlement and damage to the sealing membrane.

[0040] The spacing of the tamping construction is 2 m. The tamping points must avoid the main water pipe and the collection pipe of the sand cushion layer to ensure the drainage performance of the pipeline.

[0041] Step 5: Unload the remaining thickness of the earthwork layer, then impact-compact the exposed sand cushion layer and level it until the target soft soil foundation reaches the handover elevation and the drainage operation is completed.

[0042] refer to Figure 3After 15 days of vacuum preloading (constant load), a sealing membrane is laid, and then the earthwork layer is surcharged in three stages. The first stage of surcharge is represented by line segment ab, with a surcharged earthwork layer thickness of 0.5 m. After several more days of vacuum preloading, the second stage of surcharge begins (represented by line segment cd), with a surcharged earthwork layer thickness of 1.5 m. After several more days of vacuum preloading, the third stage of surcharge begins (represented by line segment ef), with a surcharged earthwork layer thickness of 1.5 m. The vacuum level is maintained at 85 kPa for at least 150 days, and the simultaneous surcharge of vacuum preloading and surcharge preloading lasts for at least 120 days. When the consolidation degree of the target soft soil foundation reaches 80%, the earthwork layer is unloaded, reducing its thickness to the height of point h. Line segment gh represents the unloading amount of the earthwork layer in this stage. After unloading, two rounds of full compaction are carried out, compressing the earthwork layer thickness to the height of point k. The compression amount of the two rounds of full compaction is represented by line segment jk. Then, the target soft soil foundation is left to stand for a certain period of time until the excess pore pressure begins to dissipate. Two rounds of spot compaction and one round of full compaction are then carried out to compress the soil layer to the height of point n, with the compression amount being line segment mn. After the excess pore pressure dissipates, unloading continues, compressing the soil layer to the height of point q, with the compression amount being line segment pq.

[0043] During the vacuum preloading process, the impact construction technology of the dynamic compaction machine must strictly control the impact energy and number of impacts at each compaction point to ensure that the stress is effectively transferred to the reinforced area without damaging pipelines and other facilities.

[0044] For example, after the spot compaction is completed, the surface soil can be consolidated by using an impact roller. The number of impact compaction passes is 18, and the settlement of the last 5 impact compaction passes is required to be no more than 1 cm, and the compaction degree is not less than 95%.

[0045] The embodiments disclosed in this specification are merely illustrative of one aspect of the invention, and the scope of protection of the invention is not limited to these embodiments. Any other functionally equivalent embodiments fall within the scope of protection of the invention. Those skilled in the art can make various other corresponding changes and modifications based on the technical solutions and concepts described above, and all such changes and modifications should fall within the scope of protection of the claims of this invention.

Claims

1. A method for constructing a vacuum preloading synchronous dynamic drainage consolidation system for soft soil foundations, characterized in that, Includes the following steps: A soil cushion layer was backfilled on the target soft soil foundation. After the soil cushion layer was backfilled, drainage pipes were laid, a sand cushion layer was laid on top of the soil cushion layer, and a vacuum system was installed on top of the sand cushion layer. Activate the vacuum system and, once the vacuum level within the target soft soil foundation has stabilized, load a soil layer of a predetermined thickness onto the sand cushion layer. When the consolidation degree and water discharge of the target soft soil foundation reach the corresponding preset thresholds, the earthwork layer is unloaded until its thickness is reduced to the preset thickness. Once the earthwork layer has been reduced to the preset thickness, maintain the vacuum degree of the target soft soil foundation ≥ the preset vacuum pressure, and simultaneously carry out two rounds of full compaction on the earthwork layer. The compaction energy of the first round of full compaction should be < the compaction energy of the second round of full compaction. After the full compaction is completed, the vacuum system is shut off, followed by two rounds of spot compaction and one round of full compaction. The impact energy of the two rounds of spot compaction is the same and greater than that of the final round of full compaction. After the point compaction is completed, the remaining thickness of the earthwork layer is unloaded, and then the exposed sand cushion layer is impact-compacted and leveled until the target soft soil foundation reaches the handover elevation and the drainage operation is completed.

2. The method for constructing vacuum preloading and synchronous dynamic drainage consolidation on soft soil foundations according to claim 1, characterized in that, Laying drainage pipes, including: Drainage boards are inserted into the sand cushion layer at preset intervals and inserted to a specified depth. A main water pipe and several collection pipes are laid on the sand cushion layer. The collection pipes are distributed at intervals along the sand cushion layer. Each drainage board is connected to the corresponding collection pipe. The collection pipes are connected end to end and then connected to the main water pipe. One end of the main water pipe extends out of the sand cushion layer. The main water pipe is used to drain the water in the collection pipes.

3. The method for constructing vacuum preloading and synchronous dynamic drainage consolidation on soft soil foundations according to claim 1 or 2, characterized in that, Laying out a vacuum system includes: A vacuum pump is installed around the sand cushion layer and the soil cushion layer. The vacuum pump is connected to the main water pipe. A sealing wall is built at the boundary of the target soft soil foundation. The sealing wall extends at least 50cm into the permeable layer of the target soft soil foundation. Then, a sealing membrane is laid on the surface of the sand cushion layer. Next, the vacuum pump is started. After the vacuum degree in the target soft soil foundation below the sealing membrane reaches a stable level, geotextile is laid on the sealing membrane.

4. The method for constructing vacuum preloading and synchronous dynamic drainage consolidation on soft soil foundations according to claim 3, characterized in that, Start the vacuum system and, after several days of vacuum pre-compression, lay the sealing membrane.

5. The method for constructing vacuum preloading and synchronous dynamic drainage consolidation on soft soil foundations according to claim 4, characterized in that, A soil layer of a predetermined thickness is piled on the geotextile.

6. The method for constructing vacuum preloading and synchronous dynamic drainage consolidation on soft soil foundations according to claim 1, characterized in that, The earthwork layers of the preset thickness are completed by using a graded loading method.

7. The method for constructing vacuum preloading and synchronous dynamic drainage consolidation on soft soil foundations according to claim 6, characterized in that, The earthwork layers are loaded in n stages, where n≥2. The thickness of the first stage is 0.5 m, and the first stage uses silt and sand with a maximum particle size of ≤5 cm. The thickness of the second to nth stages is 1 m, and the maximum particle size of the soil used is ≤20 cm. The sum of the thicknesses of all loaded earthwork layers is the preset thickness.

8. The method for constructing vacuum preloading and synchronous dynamic drainage consolidation on soft soil foundation according to claim 7, characterized in that, With n=3, the thickness of the earthwork layer produced by the first stage of loading is 0.5 m, the thickness of the earthwork layer produced by the second stage of loading is 1.5 m, and the thickness of the earthwork layer produced by the third stage of loading is 1.5 m. After the first stage of loading is completed, the second stage of loading begins after several days of vacuum preloading. After the second stage of loading is completed, the third stage of loading begins after several days of vacuum preloading.

9. The method for constructing vacuum preloading and synchronous dynamic drainage consolidation on soft soil foundation according to claim 1, characterized in that, The preset threshold for the degree of consolidation is 80%, and the preset threshold for the effluent flow rate is 3 L·m³. -2 / d, with a preset vacuum pressure of 85 kPa.

10. The method for constructing vacuum preloading and synchronous dynamic drainage consolidation on soft soil foundations according to claim 1, characterized in that, The impact energy of the first full compaction is 500 kN·m, the impact energy of the second full compaction is 800 kN·m, the impact energy of the two spot compaction is 1500 kN·m, and the impact energy of the final spot compaction is 1000 kN·m.

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