Grouting reinforcement and lifting method for building on large thickness collapsible loess foundation

Abstract

The application discloses a method for grouting reinforcement and lifting of a building on a collapsible loess foundation with large thickness, and specifically comprises the following steps: detecting the collapsible loess foundation to determine the collapsible bottom boundary of the collapsible loess foundation; forming a surrounding pile reinforcement layer and a pile end reinforcement layer through low-pressure grouting; and destroying the original structure of deep soil and carrying out splitting grouting lifting through high-pressure grouting. The collapsible bottom boundary is set, the determination condition of the collapsible bottom boundary is proposed according to the parameter value, the boundary line of the collapsible loess soil layer is obtained, and the grouting reinforcement depth is determined. Through the "three-section grouting from top to bottom" mode of the surrounding pile reinforcement layer, the pile end reinforcement layer and the splitting lifting layer, the disturbance to the soil is smaller, and the quality control of the grouting reinforcement and lifting is more favorable. Through the grouting reinforcement of the surrounding soil of the pile, the pile body and the soil are more stably combined together, and the phenomenon that the pile body is damaged during the high-pressure grouting lifting is avoided.

Description

Technical Field

[0001] This invention relates to the field of grouting reinforcement and lifting technology for buildings under adverse geological conditions, and particularly to a grouting reinforcement and lifting method for buildings with thick collapsible loess foundations. Background Technology

[0002] Loess is a unique water-sensitive structure. While relatively dense, it typically exhibits high strength and low compressibility at its natural moisture content. However, when soaked by rainwater or other liquids, its shear strength rapidly decreases, leading to structural damage and significant subsidence, forming collapsible loess. This results in localized tilting and subsidence of buildings, cracking of key components, and compromised functionality. Currently, grouting is a common method for treating collapsible loess foundations. However, the grouting process disturbs the soil, potentially exacerbating collapsibility. Furthermore, there are technical challenges in completely eliminating collapsibility, especially with thick layers of collapsible loess. If collapsibility is not thoroughly eliminated, subsequent contact with water will lead to further subsidence and even more severe consequences. Summary of the Invention

[0003] This invention provides a grouting reinforcement and lifting method for buildings with thick collapsible loess foundations, which solves technical problems such as determining the collapsible bottom boundary of thick collapsible loess, compaction pile reinforcement, and foundation lifting.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A grouting reinforcement and lifting method for buildings with thick collapsible loess foundations, wherein the existing buildings contain collapsible loess foundations, and the collapsible loess foundations are deformed, resulting in uneven settlement of the foundation. The specific steps are as follows: Step 1: Conduct a survey of the collapsible loess foundation. Based on the location of the existing building's foundation, set up survey points around the perimeter of the foundation to measure the soil's cone tip resistance qc, side wall friction fs, and excess pore pressure Δu. Step 2: Determine the collapsibility boundary of the collapsible loess foundation. The collapsibility boundary of collapsible loess refers to the critical depth at which the collapsibility disappears in the strata. The collapsibility boundary is determined based on qc, fs, and Δu from Step 1, and the determination conditions are as follows: S1: When qc suddenly increases to >3MPa, and increases steadily with depth; S2: The modulus resistance Re=fs / qc drops sharply to ≤0.8%; S3: When the excess pore pressure Δu value is close to 0 or slightly positive; The critical depth that simultaneously satisfies the above three criteria is the initial collapsible bottom boundary, with a depth of L. Step 3: Based on the initial sinkhole bottom boundary depth L, take a depth every 0.5m upwards and continue to count and analyze whether there is a critical depth that simultaneously meets the above three judgment conditions, so as to accurately obtain the final sinkhole bottom boundary; use the same method to determine the sinkhole bottom boundary of other detection points. Step 4: Low-pressure grouting is used to reinforce the soil around the compacted piles, so that the soil around the piles and the piles are more firmly bonded together to form an integral pile perimeter reinforcement layer; the soil within 3m to 5m below the pile tip is reinforced to form a pile tip reinforcement layer, thereby protecting the pile body during high-pressure grouting and lifting. Step 5: High-pressure grouting destroys the original structure of the deep soil and splits and lifts it. The loess soil between the elevation of 3-5m below the compaction pile end and the elevation of the collapsible bottom is the deep soil. The deep soil is undisturbed and the soil particles are in the original stable stress state. High-pressure grouting is carried out to destroy its original structure and change the stress state between the loess particles. Step Six: While destroying the original structure of soil particles, split channels are created in the soil. Then, the split and raised layer is reinforced and raised by split grouting. This eliminates the collapsibility of loess and strengthens and raises the soil, thus completing the grouting reinforcement and raising of the thick collapsible loess foundation building.

[0005] Furthermore, the main structure of the existing building is a shear wall structure, and the foundation is a raft foundation; the loess soil beneath the foundation is deformed by rainfall, groundwater recharge, and leakage of water supply and drainage pipes, resulting in uneven deformation of the foundation.

[0006] Furthermore, in step one, with a detection point spacing of 10-15m, a static cone penetration test is used, in which the cone probe is pressed into the soil at the detection point at a uniform speed of 2 cm / s. The cone tip resistance qc, side wall friction fs, and excess pore pressure Δu of the soil are measured.

[0007] Furthermore, in step one, the detection points are set at long-distance intervals along the foundation, and at corners and uneven areas of the foundation.

[0008] Furthermore, in step two, starting from the top of the collapsible loess foundation, the soil layer is taken at a depth of 2m from top to bottom, and the values ​​of qc, fs, Re, and excess pore pressure Δu at different depths are recorded in a table, and the judgment conditions are analyzed in turn.

[0009] Furthermore, during the grouting of the pile perimeter reinforcement layer and the pile tip reinforcement layer, a grouting pressure of 0.15-0.5 MPa is used for grouting.

[0010] Furthermore, during the grouting of the pile perimeter reinforcement layer and the pile end reinforcement layer, grouting holes are arranged around the outer ring of the foundation, with the grouting holes aligned with the longitudinal walls in the main structure. The internal grouting holes are arranged according to the specific indoor conditions. The outer grouting holes are grouted first to form a constraint curtain, and then the internal grouting holes are grouted to prevent cross-grouting and avoid stress superposition.

[0011] Furthermore, the foundation on the side with greater settlement is more prone to collapsibility. To prevent secondary settlement caused by grouting, grouting should begin with the part with less settlement and then gradually proceed to the part with greater settlement.

[0012] Furthermore, in step six, when grouting the split-up layer, the grouting pressure is 1.5~2MPa; the high-pressure grouting changes the stress state between loess soil particles; while destroying the interparticle forces, it creates splitting channels between soil particles.

[0013] Furthermore, in step six, during the lifting process, grouting begins from the side with greater settlement. The grouting holes on this side are densely arranged, and the grouting volume is increased, thereby effectively lifting the side that has settled. When the settlement side is lifted to near the target elevation, appropriate and compensatory grouting is then carried out on the side with smaller or basically stable settlement, thereby ensuring coordinated deformation and lifting of the foundation of the entire building.

[0014] The beneficial effects of this invention are reflected in: 1) This invention establishes a collapsible bottom boundary, measures parameters using a static cone penetration test, and proposes criteria for determining the collapsible bottom boundary based on these parameters. This facilitates the determination of the boundary line of the loess collapsible soil layer and the determination of the grouting reinforcement depth. 2) This invention targets collapsible loess foundations. Through a three-stage grouting approach—comprising a pile perimeter reinforcement layer, a pile end reinforcement layer, and a splitting and lifting layer—it minimizes soil disturbance and facilitates quality control of the grouting reinforcement and lifting process. Specifically, grouting the soil around the pile ensures a more stable bond between the pile and the soil, providing better protection for the pile and preventing damage during high-pressure grouting and lifting. 3) This invention adopts the grouting principle of "outside first, then inside, large first, then small" to reinforce the soil at the pile tip. This can prevent grout leakage, avoid stress superposition, reduce disturbance, and avoid a large amount of secondary settlement during the grouting reinforcement process. At the same time, the pile tip reinforcement formed by grouting plays a good protective role for the pile and avoids the phenomenon of damage to the pile when high-pressure grouting is lifted. 4) This invention destroys the original structure of loess through high-pressure grouting, and then splits and grouts to reinforce and lift the upper foundation. This helps to eliminate the potential collapsibility of deep loess in advance, avoids the phenomenon of loess settling when it encounters water, and prevents problems before they occur. At the same time, it enables the building to be lifted and corrected smoothly, which is safe, economical and efficient. This invention solves the technical problems of determining the collapsible bottom boundary, compaction pile reinforcement, and foundation lifting in thick collapsible loess. Other features and advantages of this invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention; the main objectives and other advantages of this invention can be realized and obtained by means of the methods particularly pointed out in the description. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the grouting reinforcement and lifting profile of a building with a thick collapsible loess foundation; Figure 2 It is a diagram showing the layout of the detection points; Figure 3 This is a schematic diagram of the grouting hole layout; Figure 4 This is a microscopic diagram of soil particles during deep soil grouting reinforcement and lifting. Figure 5 This is the table for determining the initial collapsible bottom boundary at detection point #1; Figure 6 This is the table for determining the final wetland bottom boundary of detection point #1.

[0016] Attached diagram labels: 1-biogas digester, 2-main structure, 3-foundation, 4-compacting pile, 5-pile perimeter reinforcement layer, 6-pile end reinforcement layer, 7-split and uplift layer, 8-detection point, 9-grouting hole location, 10-soil particle, 11-particle gap, 12-interparticle force, 13-grouting pipe, 14-grout. Detailed Implementation

[0017] Taking a residential building project as an example, the building has 11 floors above ground, a shear wall structure, and a raft foundation with a foundation depth of -4.70m. The building is 64.85m long, 11.95m wide, and 32.45m high, comprising three units, with expansion joints in units 2 and 3. The foundation is a raft foundation with a thickness of 600mm, a length of 66.25m, and a width of 11.5m. The top elevation of the raft foundation is -4.100m, the bottom elevation is -4.700m, and ±0.000 corresponds to an absolute elevation of 1744.800. The foundation soil is mainly collapsible loess. Due to a leak in the pipeline of biogas digester 1 located underground on the east side of the building, subsidence has occurred, causing adverse deformation of the foundation soil and uneven settlement of foundation 3. Therefore, it is necessary to reinforce and raise the foundation of the building to further control the impact of uneven settlement on the building.

[0018] Combination Figures 1 to 6 As shown, the grouting reinforcement and lifting method for buildings with thick collapsible loess foundations is further explained. The specific steps are as follows: Step 1: Conduct a survey of the collapsible loess foundation. Based on the location of the existing building's foundation 3, set up survey points 8 around the perimeter of the foundation 3 to measure the soil's cone tip resistance qc, side wall frictional resistance fs, and excess pore pressure Δu. In Step 1, the survey points 8 are spaced 10-15m apart. Using the static cone penetration method, the cone probe is pressed into the soil at survey point 8 at a uniform speed of 2 cm / s. The cone tip resistance qc, side wall frictional resistance fs, and excess pore pressure Δu are then measured.

[0019] In step one, detection points 8 are set at intervals along the longitudinal direction of the foundation 3, and are also set at corners and uneven parts of the foundation 3.

[0020] Step 2: Determine the collapsibility boundary of the collapsible loess foundation. The collapsibility boundary of collapsible loess refers to the critical depth at which the collapsibility disappears in the strata. The collapsibility boundary is determined based on qc, fs, and Δu from Step 1, and the determination conditions are as follows: S1: When qc suddenly increases to >3MPa, and increases steadily with depth; S2: The modulus resistance Re=fs / qc drops sharply to ≤0.8%; S3: When the excess pore pressure Δu is close to 0 or slightly positive, where -5kPa < Δu < +10kPa; The critical depth that simultaneously satisfies the above three criteria is the initial sinkhole boundary, with a depth of L.

[0021] In step two, starting from the top of the collapsible loess foundation, the soil layer is taken at a depth of 2m from top to bottom. The values ​​of qc, fs, Re, and excess pore pressure Δu at different depths are recorded in the table, and the judgment conditions are analyzed in turn.

[0022] Step 3: Based on the initial sinkhole depth L, take a depth every 0.5m upwards and continue to count and analyze whether there is a critical depth that simultaneously meets the above three judgment conditions, so as to accurately obtain the final sinkhole depth.

[0023] by Figure 2 Taking detection point 8 of the middle 1 as an example, according to Figure 5 The data shows that -22m is the initial collapsible bottom boundary, and then depths of 0.5m are taken upwards from -22m for further statistical analysis. Figure 6 This allows for a more precise determination of the final collapsible boundary at -21m. The same method was used to determine the collapsible boundaries at other detection points 8.

[0024] Step 4: Low-pressure grouting is used to reinforce the soil around the compaction pile 4, so that the soil around the pile and the pile are more firmly bonded together to form an integral pile perimeter reinforcement layer 5; the soil within 3m to 5m below the pile tip is reinforced to form a pile tip reinforcement layer 6, thereby protecting the pile body during high-pressure grouting and lifting; when grouting the pile perimeter reinforcement layer 5 and the pile tip reinforcement layer 6, a grouting pressure of 0.15-0.5MPa is used for grouting.

[0025] When grouting the pile perimeter reinforcement layer 5 and the pile tip reinforcement layer 6, grouting holes 9 are arranged around the outer ring of the foundation 3. Figure 3 As shown, the grouting holes 9 are aligned with the longitudinal walls in the main structure 2. The internal grouting holes 9 are arranged according to the specific indoor conditions. Grouting is first performed on the outer grouting holes to form a constraint curtain, and then grouting is performed on the internal grouting holes to prevent cross-grouting and avoid stress superposition. The foundation on the side with greater settlement has greater collapsibility. To prevent secondary settlement caused by grouting, grouting is performed starting from the part with less settlement and then gradually moving towards the part with greater settlement.

[0026] Step 5: High-pressure grouting disrupts the original structure of the deep soil and causes fracturing and uplift, such as... Figure 4 As shown in the figure From left to right, the images show the original state of soil particles 10, the state after grouting failure of grouting pipe 13, and the state after grouting 14 fills the gaps between particles 11. The loess soil between the elevation 3-5m below the end of compaction pile 4 and the boundary elevation of the collapsible bottom is deep soil. The deep soil is undisturbed, and soil particles 10 are in their original stable stress state. High-pressure grouting is performed to destroy their original structure and change the stress state between loess particles 10.

[0027] Step 6: While destroying the original structure of soil particles 10, split channels are created in the soil. Then, split grouting is used to reinforce and lift the split and uplifted layer 7, thereby eliminating the collapsibility of loess and reinforcing and lifting the soil, thus completing the grouting reinforcement and lifting of the thick collapsible loess foundation building.

[0028] In step six, when grouting the split and uplifted layer 7, the grouting pressure is 1.5~2MPa; the high-pressure grouting changes the stress state between loess soil particles 10; while destroying the interparticle force 12, it creates splitting channels between soil particles 10.

[0029] In step six, during the lifting process, grouting begins from the side with greater settlement. The grouting holes on this side are densely arranged, and the grouting volume is increased, thereby effectively lifting the side that has settled. When the settlement side is lifted to near the target elevation, appropriate and compensatory grouting is then carried out on the side with smaller or basically stable settlement, thereby ensuring coordinated deformation and lifting of the foundation of the entire building.

[0030] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A grouting reinforcement and lifting method for buildings with thick collapsible loess foundations, characterized in that, The existing buildings contain collapsible loess foundations, which are deformed and cause uneven settlement of the foundation (3); The specific steps are as follows: Step 1: Conduct a survey of the collapsible loess foundation. Based on the location of the existing building foundation (3), set up survey points (8) around the foundation (3) to measure the cone tip resistance qc, side wall friction fs and excess pore pressure Δu of the soil. Step 2: Determine the collapsibility boundary of the collapsible loess foundation. The collapsibility boundary of collapsible loess refers to the critical depth at which the collapsibility disappears in the strata. The collapsibility boundary is determined based on qc, fs, and Δu from Step 1, and the determination conditions are as follows: S1: When qc suddenly increases to >3MPa, and increases steadily with depth; S2: The modulus resistance Re=fs / qc drops sharply to ≤0.8%; S3: When the excess pore pressure Δu value is close to 0 or slightly positive; The critical depth that simultaneously satisfies the above three criteria is the initial collapsible bottom boundary, with a depth of L. Step 3: Based on the initial sinkhole bottom boundary depth L, take a depth every 0.5m upwards and continue to count and analyze whether there is a critical depth that simultaneously meets the above three judgment conditions, so as to accurately obtain the final sinkhole bottom boundary; use the same method to determine the sinkhole bottom boundary of other detection points (8). Step 4: Low-pressure grouting is used to reinforce the soil around the compaction pile (4) so ​​that the soil around the pile and the pile are more firmly bonded together to form an integral pile reinforcement layer (5); the soil within 3m to 5m below the pile tip is reinforced to form a pile tip reinforcement layer (6) to protect the pile body during high-pressure grouting and lifting. Step 5: High-pressure grouting destroys the original structure of the deep soil and splits and lifts it. The loess soil between the elevation of the compaction pile (4) 3-5m below the end and the elevation of the collapsible bottom is the deep soil. The deep soil is undisturbed and the soil particles (10) are in the original stable stress state. High-pressure grouting destroys its original structure and changes the stress state between the loess particles (10). Step 6: While destroying the original structure of soil particles (10), split channels are created in the soil. Then, the split and raised layer (7) is reinforced and raised by split grouting. This eliminates the collapsibility of loess and reinforces and raises the soil, thus completing the grouting reinforcement and raising of the thick collapsible loess foundation building.

2. The grouting reinforcement and lifting method for a building with a thick collapsible loess foundation as described in claim 1, characterized in that, The main structure (2) of the existing building is a shear wall structure, and the foundation (3) is a raft foundation. The loess soil under the foundation (3) is deformed by rainfall, groundwater recharge and leakage of water supply and drainage pipes, resulting in uneven deformation of the foundation (3).

3. The grouting reinforcement and lifting method for a building with a thick collapsible loess foundation as described in claim 2, characterized in that, In step one, the spacing between the detection points (8) is 10~15m. The static cone penetration method is used to press the cone probe into the soil at the detection point (8) at a uniform speed. The standard speed is 2 cm / s. The cone tip resistance qc, side wall friction fs and excess pore pressure Δu of the soil are measured.

4. The grouting reinforcement and lifting method for a building with a thick collapsible loess foundation as described in claim 3, characterized in that, In step one, the detection points (8) are set at long intervals along the foundation (3), and are also set at corners and uneven parts of the foundation (3).

5. The grouting reinforcement and lifting method for a building with a thick collapsible loess foundation as described in claim 4, characterized in that, In step two, starting from the top of the collapsible loess foundation, the soil layer is taken at a depth of 2m from top to bottom. The values ​​of qc, fs, Re, and excess pore pressure Δu at different depths are recorded in the table, and the judgment conditions are analyzed in turn.

6. The grouting reinforcement and lifting method for a building with a thick collapsible loess foundation as described in claim 5, characterized in that, When grouting the pile perimeter reinforcement layer (5) and the pile end reinforcement layer (6), a grouting pressure of 0.15-0.5MPa is used for grouting.

7. The grouting reinforcement and lifting method for a building with a thick collapsible loess foundation as described in claim 6, characterized in that, When grouting the pile perimeter reinforcement layer (5) and the pile end reinforcement layer (6), grouting holes (9) are arranged on the outer ring of the foundation (3). The grouting holes (9) are aligned with the longitudinal wall in the main structure (2). The internal grouting holes (9) are arranged according to the specific indoor conditions. The outer grouting holes are grouted first to form a constraint curtain, and then the internal grouting holes are grouted to prevent cross-grouting and avoid stress superposition.

8. The grouting reinforcement and lifting method for a building with a thick collapsible loess foundation as described in claim 7, characterized in that, The foundation on the side with greater settlement is more prone to collapsibility. To prevent secondary settlement caused by grouting, grouting should begin with the part with less settlement and then gradually proceed to the part with greater settlement.

9. The grouting reinforcement and lifting method for a building with a thick collapsible loess foundation as described in claim 8, characterized in that, In step six, when grouting the split-lift layer (7), the grouting pressure is 1.5~2MPa; the high-pressure grouting changes the stress state between loess particles (10); while destroying the interparticle force (12), it creates splitting channels in the particle gaps (11).

10. The grouting reinforcement and lifting method for a building with a thick collapsible loess foundation as described in claim 9, characterized in that, In step six, during the lifting process, grouting begins from the side with greater settlement. The grouting holes on this side are densely arranged, and the grouting volume is increased, thereby effectively lifting the side that has settled. When the settlement side is lifted to near the target elevation, appropriate and compensatory grouting is then carried out on the side with smaller or basically stable settlement, thereby ensuring that the foundation of the entire building (3) undergoes coordinated deformation and lifting.

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