Urban road collapsible loess roadbed trenchless reinforcement structure and method

Abstract

This invention discloses a trenchless reinforcement structure and method for collapsible loess subgrades in urban roads, belonging to the field of urban road engineering. It solves the problem of pavement settlement, cracking, and collapse caused by subgrade instability due to water immersion in existing urban road collapsible loess subgrades. The invention features seepage-proof curtains on both sides of the subgrade defect area, with jet grouting piles and powder jet grouting piles installed between the two curtains. These are arranged alternately, with the jet grouting piles located below the wheel tracks of the carriageway. The reinforcement method involves: identifying the subgrade defect area requiring reinforcement; arranging the boreholes for the jet grouting and powder jet grouting piles; constructing the jet grouting piles while simultaneously constructing the seepage-proof curtains; and then, after 7 days, constructing the powder jet grouting piles. This invention, through a combined prevention and treatment reinforcement structure and method, completely solves the problem of collapsible loess subgrade defects in existing urban roads, avoiding road excavation and minimizing traffic disruption.

Description

Technical Field

[0001] This invention belongs to the field of urban road engineering, specifically relating to a non-excavation reinforcement structure and method for collapsible loess subgrade in urban roads. Background Technology

[0002] Collapsible loess is characterized by its porous structure and large internal pores. When exposed to water, its internal structure is easily damaged, its strength decreases, and it becomes prone to collapsing deformation. Collapsible loess is considered an unfavorable geological condition. Roads built in collapsible loess areas are susceptible to subsidence and deformation after water immersion, severely impacting road quality and service life. Subsidence and deformation are more prevalent and severe in urban roads built in collapsible loess areas during their operational period. Firstly, green belts are often located within the roadbed area of ​​urban roads, and irrigation water can easily seep into the roadbed, causing subsidence and deformation. Secondly, urban roads experience more severe rainwater accumulation compared to highways. Rainwater is primarily discharged through underground rainwater pipes, and damage to these pipes or cracked joints can easily cause rainwater to erode the roadbed, leading to subsidence and even collapse. Collapsible loess subgrade defects in existing urban roads not only affect driving comfort and road service life, but also seriously affect driving safety due to subgrade instability, deformation and collapse. It is necessary to propose an effective maintenance measure for collapsible loess subgrade defects in existing urban roads to ensure road safety, comfort and durability.

[0003] Treatment methods for collapsible loess subgrades mainly include: replacement, impact compaction, dynamic tamping, compaction piles, and chemical reinforcement. Most current methods are primarily for newly constructed subgrades. Impact compaction and dynamic tamping can easily disturb and damage underground pipelines. Replacement subgrades require large-scale excavation of the road surface and prolonged traffic interruptions, making them unsuitable for existing urban road construction. Chemical grouting can effectively fill and reinforce localized defects such as sinkholes and cavities in collapsible loess, but it cannot achieve overall subgrade reinforcement. Furthermore, its reinforcement depth is limited and cannot completely eliminate subgrade defects. Summary of the Invention

[0004] The purpose of this invention is to provide a non-excavation reinforcement structure for collapsible loess subgrade of urban roads, so as to solve the problems of road surface settlement, cracking and collapse caused by water immersion and instability of existing urban road collapsible loess subgrade.

[0005] Another objective of this invention is to provide a non-excavation reinforcement method for collapsible loess roadbeds in urban areas.

[0006] The technical solution of the present invention is: a non-excavation reinforcement structure for collapsible loess subgrade of urban roads, wherein seepage prevention curtains are provided on both sides of the subgrade disease area, and jet grouting pile reinforcement bodies and powder jet grouting pile reinforcement bodies are provided between the two seepage prevention curtains. The jet grouting pile reinforcement bodies and powder jet grouting pile reinforcement bodies are arranged alternately, and the jet grouting pile reinforcement bodies are located below the wheel track line of the carriageway.

[0007] As a further improvement of the present invention, the jet grouting pile reinforcement extends from the existing road surface to the bearing layer of the subgrade.

[0008] As a further improvement of the present invention, the seepage-proof curtain is set below the curbstone.

[0009] A non-excavation reinforcement method for collapsible loess subgrade of urban roads includes the following steps:

[0010] A. First, conduct a survey of the existing road surface to identify the roadbed disease areas that need reinforcement; conduct a survey of the pipelines laid under the existing road surface to determine the horizontal position and depth of the pipelines; determine the physical and mechanical parameters of the roadbed soil in the roadbed disease area, such as moisture content and porosity, as well as the roadbed bearing layer.

[0011] B. Arrange the hole positions of jet grouting piles and powder jet grouting piles, and avoid and optimize the arrangement of piles that conflict with pipelines based on geophysical pipeline data.

[0012] C. When carrying out jet grouting reinforcement construction, the construction should proceed from the middle of the roadbed defect area to the outer perimeter.

[0013] D. The seepage prevention curtain is constructed simultaneously with the jet grouting pile reinforcement construction.

[0014] E. The powder jet grouting pile reinforcement is carried out 7 days after the completion of the jet grouting pile reinforcement and the seepage prevention curtain construction. After drilling to the design depth, the drill rod is lifted and powder is sprayed and mixed to form the reinforcement.

[0015] As a further improvement of the present invention, in step C, the jet grouting pile reinforcement body is formed by cutting the soil in the roadbed disease area with cement grout to reinforce the pile, and the cement used is 42.5 ordinary Portland cement with a water-cement ratio of 0.8 to 1.2.

[0016] As a further improvement of the present invention, in step D, the grout for the seepage prevention curtain construction is prepared by improving and mixing the waste grout generated from the jet grouting pile reinforcement construction, and the mass ratio of cement:soil particles:water in the improved grout is 0.45~0.5:0.1:0.45~0.4.

[0017] As a further improvement of the present invention, in step D, an anti-seepage agent, a water-reducing agent, and a retarder are added to the improved grout used for anti-seepage curtain construction to improve the grout setting time, fluidity, pile strength, and impermeability. The admixtures are calculated as a percentage of the grout mass, with the anti-seepage agent dosage being 0.5% to 1%, the water-reducing agent dosage being 0.75% to 1%, and the retarder dosage being 0.075% to 0.15%.

[0018] As a further improvement of the present invention, in step E, after the mixing is completed, the drill rod is lowered to the designed depth and then re-mixed and lifted to the road surface.

[0019] As a further improvement of the present invention, in step E, the powder spraying material for the powder jet pile reinforcement construction is composed of cement, lime, water-absorbing resin and soil from the roadbed disease area. According to the percentage of the reinforced soil mass, the cement content is 15% to 20%, the lime content is 5% to 10%, and the water-absorbing resin content is 1.5% to 2%.

[0020] The beneficial effects of this invention are as follows: This invention addresses the characteristics of road defects in collapsible loess subgrades and the traffic characteristics of urban roads. Through a reinforcement structure and method that combines prevention and treatment, it completely solves the problem of road defects in existing urban roads caused by collapsible loess subgrades. By reinforcing the subgrade with jet grouting piles and powder jet grouting piles, excavation is avoided, minimizing traffic disruption. Jet grouting piles are placed at the wheel tracks of the carriageway to bear the road traffic load and prevent road settlement. High-pressure grout fills the loess cavities and depressions around the piles, eliminating hidden roadbed defects and improving subgrade strength. A powder jet grouting pile is set at the center of the adjacent jet grouting pile reinforcement body. The powder jet grouting pile reinforcement body and the jet grouting pile reinforcement body form a composite foundation, which improves the overall strength and bearing capacity of the roadbed. By adding water-absorbing resin, the internal moisture of the roadbed in the diseased area is continuously absorbed, so as to achieve the purpose of draining moisture and eliminating the weak layer of the roadbed. After absorbing water, the highly absorbent resin continues to lose water according to the moisture change of cement and lime in the pile body after hydration, so as to maintain the internal humidity of the pile body, achieve internal curing of the pile body and improve the strength of the pile body.

[0021] This invention collects the waste slurry generated during jet grouting pile reinforcement construction, and improves it by adding cement, water-reducing agents, and retarders. This improved slurry is then used in anti-seepage curtain construction, forming an anti-seepage curtain below the curb to separate the green belt from the roadway, thus preventing irrigation water from seeping into the roadbed at its source. This invention uses a trenchless roadbed reinforcement method to treat uneven settlement, deformation, and sinkholes in collapsible loess roadbeds in urban roads. The roadbed reinforcement effect is significant, and the construction has minimal impact on traffic. Attached Figure Description

[0022] Figure 1 This is a cross-sectional schematic diagram of a non-excavation reinforcement structure for collapsible loess roadbeds in urban areas, according to the present invention.

[0023] Figure 2 This is a plan view of a non-excavation reinforcement structure for collapsible loess roadbeds in urban areas, according to the present invention.

[0024] In the diagram: 1-Ground jet grouting pile reinforced body; 2-Powder jet grouting pile reinforced body; 3-Impact curtain; 4-Subgrade diseased area; 5-Subgrade bearing layer; 6-Existing road surface; 7-Green belt; 8-Wheel track line of carriageway; 9-Curve stone. Detailed Implementation

[0025] like Figure 1 , Figure 2As shown, a non-excavation reinforcement structure for collapsible loess subgrade of urban roads is provided. An anti-seepage curtain 3 is provided on both sides of the subgrade disease area 4. A jet grouting pile reinforcement body 1 and a powder jet grouting pile reinforcement body 2 are provided between the two anti-seepage curtains 3. The jet grouting pile reinforcement body 1 and the powder jet grouting pile reinforcement body 2 are arranged alternately. The jet grouting pile reinforcement body 1 is located below the wheel track line 8 of the carriageway.

[0026] The jet grouting pile reinforcement 1 extends from the existing road surface 6 to the roadbed bearing layer 5.

[0027] The seepage-proof curtain 3 is set below the curb stone 9 between the existing road surface 6 and the green belt 7.

[0028] A non-excavation reinforcement method for collapsible loess subgrade of urban roads includes the following steps:

[0029] A. First, the existing road surface 6 is surveyed. A falling weight deflectometer and ground penetrating radar are used to detect the road, detect the extent and depth of collapsible loess subgrade voids and subsidence, and determine the subgrade disease area 4 that needs to be reinforced. A geophysical instrument is used to detect the pipelines laid under the existing road surface 6 to determine the horizontal position and depth of the pipelines. The water content, porosity and other physical and mechanical parameters of the subgrade soil in the subgrade disease area 4 and the bearing layer 5 of the subgrade are determined by geological drilling.

[0030] B. Arrange the borehole locations for jet grouting pile reinforcement body 1 and powder jet grouting pile reinforcement body 2. Based on geophysical pipeline data, avoid and optimize the arrangement of piles that conflict with pipelines. The principle for piles to avoid pipelines is as follows: for flexible pipelines such as corrugated pipes and PE pipes, the edge of the reinforcement body should be no less than 1m away from the edge of the pipeline; for rigid pipelines such as reinforced concrete pipes and ductile iron pipes, the edge of the reinforcement body should be no less than 0.5m away from the edge of the pipeline.

[0031] C. After optimizing the layout of the jet grouting pile reinforcement body 1 and verifying the designed borehole positions, the single-pipe method is used for the construction of the jet grouting pile reinforcement body 1, proceeding from the center of the subgrade distress area 4 outwards. The jet grouting pile reinforcement body 1 uses cement grout to cut and reinforce the soil in the subgrade distress area 4, using 42.5 ordinary Portland cement with a water-cement ratio (mass ratio) of 0.8–1.2. Before construction, test piles should be conducted to determine the construction process. A grouting pressure greater than 20 MPa and a lifting speed of 0.2 m / min–0.3 m / min are recommended. When the diameter of the jet grouting pile reinforcement body 1 needs to be enlarged, the pile head is enlarged by increasing the grouting pressure and decreasing the speed. A grouting pressure greater than 30 MPa and a lifting speed of 0.1 m / min–0.2 m / min are recommended.

[0032] D. The seepage barrier 3 is constructed simultaneously with the jet grouting pile reinforcement 1. The recommended grouting pressure for the seepage barrier 3 is 20 MPa, and the lifting speed is 0.3 m / min to 0.4 m / min. The grout used for the seepage barrier 3 is prepared by modifying the waste grout generated from the jet grouting pile reinforcement 1. The mass ratio of cement:soil particles:water in the modified grout is 0.45–0.5:0.1:0.45–0.4. Before construction, the waste grout generated from the jet grouting pile reinforcement 1 is tested to determine its composition, and the cement and water dosages are determined according to the designed grout ratio. Anti-seepage agents, water-reducing agents, and retarders are added to the modified grout used for the seepage barrier 3 to improve the grout setting time, fluidity, pile strength, and impermeability. The admixtures are calculated as a percentage of the grout mass: anti-seepage agent dosage is 0.5%–1%, water-reducing agent dosage is 0.75%–1%, and retarder dosage is 0.075%–0.15%. The improved slurry has an initial setting time of >5h and a final setting time of <10h.

[0033] E. The powder jet grouting reinforcement body 2 is constructed 7 days after the completion of the jet grouting reinforcement body 1 and the anti-seepage curtain 3. After the layout of the powder jet grouting reinforcement body 2 is optimized and the design hole positions are checked, and if there are no errors, a drilling rig is used to drill to the design depth. The drill rod is then lifted and powder is sprayed and mixed to form the reinforcement body. To ensure uniform mixing of the pile body, after mixing, the drill rod is lowered to the design depth, and then re-mixed and lifted to the road surface. The powder spraying material for the powder jet grouting reinforcement body 2 is composed of cement, lime, water-absorbing resin, and soil from the subgrade disease area 4. According to the percentage of the reinforced soil mass, the cement content is 15% to 20%, the lime content is 5% to 10%, and the water-absorbing resin content is 1.5% to 2%. During the powder spraying construction of the powder jet grouting reinforcement body 2, the ash delivery pressure is 0.4 to 0.5 MPa, and the lifting speed is 0.8 m / min to 1 m / min. When the pile length exceeds 5 m, the ash delivery pressure is 0.5 MPa, and the lifting speed is 0.8 m / min.

[0034] Seven days after the completion of the jet grouting pile reinforcement body 1 and the powder jet grouting pile reinforcement body 2, the excess pile body 20cm below the road surface is removed. The holes of the jet grouting pile reinforcement body 1 and the powder jet grouting pile reinforcement body 2 are sealed with concrete. After milling a 4cm layer of the existing road surface 6, a 4cm layer of rubber asphalt concrete is applied for overlay repair. The overlay structure is made of 4cm rubber asphalt concrete. Fiberglass grid is installed between the overlay layer and the existing road surface. Then, the curbstone 9 is installed and the road is opened to traffic.

[0035] The jet grouting pile reinforcement 1 is located at the wheel track line 8 of the carriageway in a rectangular arrangement; the powder jet grouting pile reinforcement 2 is arranged at the center of the rectangle formed by four adjacent jet grouting pile reinforcement 1s, and is distributed in a quincunx pattern with the adjacent jet grouting pile reinforcement 1s; the seepage prevention curtain 3 is located below the curb stone 9 and is formed by multiple jet grouting piles overlapping each other. The center line of the pile body coincides with the edge line of the carriageway, separating the subgrade disease area 4 from the green belt 7.

[0036] The diameter of the jet grouting pile reinforcement body 1 is 0.4m to 0.8m. The transverse pile spacing along the road is the same as the wheel track spacing 8 of the carriageway (1.6 to 1.8m), and the longitudinal pile spacing along the road is 2 to 3 times the pile diameter. The size of the pile diameter and longitudinal pile spacing of the jet grouting pile reinforcement body 1 is determined according to the traffic load. For heavy traffic, the pile diameter is larger and the pile spacing is smaller, and vice versa for light traffic. When the cumulative equivalent axle frequency Ne during the road design reference period is less than 4 million times / lane, the pile diameter is 0.4m, the transverse pile spacing is 1.8m, and the longitudinal pile diameter is 3 times the pile diameter. When the cumulative equivalent axle frequency Ne during the road design reference period is greater than 25 million times / lane, the pile diameter is 0.8m, the transverse pile spacing is 1.6m, and the longitudinal pile spacing is 2 times the pile diameter. When the cumulative equivalent axle frequency Ne during the road design reference period is less than 10,000 times / lane and less than 25 million times / lane, the pile diameter and pile spacing are determined by interpolation according to the above principles based on the actual situation. The length of the jet grouting pile reinforcement 1 is based on penetrating the bearing layer 5 of the roadbed to a depth of 1m; when the pile length exceeds 15m, 15m is sufficient, but the pile head needs to be enlarged for the last 5m, and the pile diameter is enlarged to twice the normal pile diameter.

[0037] The diameter of the jet grouting pile reinforcement body 2 is 0.4–0.6 m, and the pile spacing is determined based on the location of the rotary jet grouting pile reinforcement body 1. The diameter of the jet grouting pile reinforcement body 2 is determined based on the road traffic load. When the cumulative equivalent axle load Ne during the road design reference period is less than 4 million times / lane, the diameter of the jet grouting pile reinforcement body 2 is 0.4 m; when the cumulative equivalent axle load Ne during the road design reference period is greater than 25 million times / lane, the diameter of the jet grouting pile reinforcement body 2 is 0.6 m; when the cumulative equivalent axle load Ne during the road design reference period is less than 4 million times / lane and less than 25 million times / lane, the diameter of the jet grouting pile reinforcement body 2 is 0.5 m. The length of the jet grouting pile reinforcement body 2 is 5–10 m, determined based on the soil moisture content of the collapsible loess subgrade disease zone 4, with the goal of penetrating a soil layer with a moisture content of less than 20%.

[0038] The seepage prevention curtain 3 is formed by the overlapping of multiple jet grouting piles. The seepage prevention curtain 3 uses jet grouting piles with a diameter of 0.5m. The overlap length between the jet grouting piles is 15cm. The pile length of the seepage prevention curtain 3 is 2 to 7m, which is determined according to the soil moisture content of the collapsible loess roadbed disease area 4. The standard is to enter the soil layer with a moisture content of less than 20%. When the depth exceeds 7m, the pile length is 7m.

[0039] The jet grouting pile reinforcement 1 uses cement grout to cut the soil in the roadbed disease area 4 to reinforce the pile. The 28-day strength of the pile should be ≥10MPa.

[0040] Waste slurry generated during the construction of jet grouting pile reinforcement 1 is collected through a recycling device. After being diluted with water, the waste slurry is pumped to a filtration and sedimentation tank. The sedimentation tank filters and settles particles larger than 0.1mm in the waste slurry. The waste slurry is then transported to a mortar mixing plant where cement, anti-seepage agent, water-reducing agent, and retarder are added to improve and mix the mixture, forming a reusable slurry, which is used as the slurry for the seepage barrier 3. The pile body of the seepage barrier 3 has a 28-day lateral strength ≥2MPa and an impermeability ≤1×10⁻⁶. -6 cm / s.

[0041] The jet grouting pile reinforcement body 2 is formed by mixing cement, lime, superabsorbent resin, and soil from the subgrade distress area 4. The cement and lime are added to improve the soil in the subgrade distress area 4, increasing the subgrade strength and bearing capacity. The superabsorbent resin continuously absorbs moisture from the soil in the subgrade distress area 4, draining excess water, improving subgrade humidity, and eliminating weak subgrade. The 28-day lateral strength of the jet grouting pile reinforcement body 2 is ≥5 MPa.

[0042] This invention employs a non-excavation roadbed reinforcement method to address uneven settlement, deformation, sinkholes, and other defects in urban road collapsible loess roadbeds. The roadbed reinforcement effect is significant, and the construction has minimal impact on traffic.

Claims

1. A non-excavation reinforcement structure for collapsible loess subgrade of urban roads, characterized in that: On both sides of the roadbed disease area (4), seepage prevention curtains (3) are provided. Between the two seepage prevention curtains (3), jet grouting pile reinforcement (1) and powder jet grouting pile reinforcement (2) are provided. The jet grouting pile reinforcement (1) and powder jet grouting pile reinforcement (2) are arranged alternately. The jet grouting pile reinforcement (1) is located below the wheel track line (8) of the carriageway. The powder spraying material used in the construction of the powder spraying pile reinforcement (2) is a mixture of cement, lime, water-absorbing resin and soil from the roadbed disease area (4).

2. The trenchless reinforcement structure for collapsible loess subgrade of urban roads according to claim 1, characterized in that: The jet grouting pile reinforcement (1) extends from the existing road surface (6) to the roadbed bearing layer (5).

3. A non-excavation reinforcement structure for collapsible loess subgrade of urban roads according to claim 1 or 2, characterized in that: The seepage-proof curtain (3) is set below the curbstone (9).

4. A method for reinforcing collapsible loess subgrade of urban roads using a non-excavation reinforcement structure according to claim 1, characterized in that... Includes the following steps: A. First, conduct a survey of the existing road surface (6) to determine the subgrade disease area (4) that needs to be reinforced; conduct a survey of the pipelines laid under the existing road surface (6) to determine the horizontal position and depth of the pipelines; determine the physical and mechanical parameters such as the water content and porosity of the subgrade soil in the subgrade disease area (4) and the subgrade bearing layer (5). B. Arrange the hole positions of jet grouting pile reinforcement body (1) and powder jet grouting pile reinforcement body (2), and avoid and optimize the arrangement of piles that conflict with the pipelines based on geophysical pipeline data. C. Carry out jet grouting pile reinforcement (1) construction, adopting the construction sequence from the middle of the roadbed disease area (4) to the outer periphery; D. While the jet grouting pile reinforcement (1) is being constructed, the seepage prevention curtain (3) is also being constructed. The grout used for the construction of the seepage prevention curtain (3) is modified and mixed from the waste grout generated during the construction of the jet grouting pile reinforcement (1). The mass ratio of cement: soil particles: water in the modified grout is 0.45~0.5:0.1:0.45~0.

4. E. Jet Grouting Reinforced Body (2) is constructed 7 days after the completion of the jet grouting reinforced body (1) and the seepage prevention curtain (3). After drilling to the design depth, the drill rod is lifted and powder is sprayed and mixed to form the reinforced body.

5. A non-excavation reinforcement method for collapsible loess subgrade of urban roads according to claim 4, characterized in that: In step C, the jet grouting pile reinforcement (1) uses cement grout to cut the soil in the roadbed disease area (4) to reinforce the pile. The cement used is 42.5 ordinary Portland cement with a water-cement ratio of 0.8 to 1.

2.

6. A non-excavation reinforcement method for collapsible loess subgrade of urban roads according to claim 4 or 5, characterized in that: In step D, anti-seepage agent, water-reducing agent and retarder are added to the improved grout used for the construction of the seepage prevention curtain (3) to improve the grout setting time, fluidity and pile strength and impermeability. The admixtures are calculated according to the mass percentage of the grout, with the anti-seepage agent dosage being 0.5% to 1%, the water-reducing agent dosage being 0.75% to 1%, and the retarder dosage being 0.075% to 0.15%.

7. A non-excavation reinforcement method for collapsible loess subgrade of urban roads according to claim 6, characterized in that: In step E, after mixing is completed, the drill rod is lowered to the designed depth and then remixed and lifted to the road surface.

8. A non-excavation reinforcement method for collapsible loess subgrade of urban roads according to claim 7, characterized in that: In step E, the powder spraying material used in the construction of the powder spraying pile reinforcement (2) is calculated as follows based on the mass percentage of the reinforced soil: cement content is 15% to 20%, lime content is 5% to 10%, and water-absorbing resin content is 1.5% to 2%.

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