A cement-soil construction method for splicing new and old roadbeds in a highway expansion project

Abstract

This application discloses a cement-soil construction method for the splicing of old and new roadbeds in highway expansion projects, comprising the following steps: Using a grader to adjust the scraper angle and employing an oblique scraper operation mode, the scraper cuts into the root of the old roadbed, cutting and turning the cement-soil at the root of the old roadbed to the center of the newly paved area; using a road mixer to perform full-section depth mixing of the entire cement-soil layer, including the turned soil, with the mixing depth penetrating the cement-soil layer; after uniform mixing, the mixture is again spread and backfilled to the root of the old roadbed using a grader, and then finely leveled by the grader; a large road roller is used to perform conventional compaction of the main roadbed; subsequently, for the root edge areas that cannot be effectively compacted by large machinery, manual labor combined with a small rammer is used for supplementary compaction. The beneficial effects of this application are: eliminating bonding blind spots, solving the problem of material segregation at its source; improving compaction degree, completely eliminating edge compaction dead corners; enhancing overall integrity, and significantly reducing the risk of uneven settlement and longitudinal cracks.

Description

Technical Field

[0001] This application belongs to the field of highway engineering construction technology, specifically relating to a cement-soil construction method for the splicing of new and old roadbeds in highway expansion projects. Background Technology

[0002] With the sustained and rapid growth of my country's national economy, highway traffic volume has surged, and many high-grade highways built and opened to traffic in the early stages have entered a period of reconstruction and expansion. In the expansion projects of first-class highways and expressways, widening on both sides is a common method. The quality of the subgrade, as the load-bearing foundation of the pavement structure, directly affects the overall service performance of the expanded road. Cement-soil improvement has become a common technical means for subgrade filling due to its advantages such as controllable cost, mature technology, and significant strength enhancement. For example, in the construction of expressways in collapsible loess areas, to further improve the strength and stability of the subgrade, especially the roadbed structure, the design often uses 4% cement treatment within an 80cm range of the subgrade. In the excavation section and low-fill shallow-cut section of Zhanjiang Avenue, the compaction degree of the fill 30-120cm below the top surface of the subgrade is required to reach 96%, which is difficult to meet with plain soil, thus requiring cement improvement of ordinary soil. However, under the condition of widening on both sides, the root area at the junction of the old and new subgrades faces a series of unique technical challenges due to the narrow space and limited mechanical operation, which has long plagued the engineering community.

[0003] First, the soil quality at the junction of old and new roadbeds differs significantly, making it difficult to guarantee the uniformity of mixing: In highway expansion projects, there are significant material differences at the junction of old and new roadbeds. After years of operation and long-term load, the soil of the old roadbed has become dense and stable, and its physical and mechanical properties are fundamentally different from the newly filled soil of the new roadbed. In the root area at the junction of old and new roadbeds, the mixing rotor of conventional road mixers cannot effectively reach the corners and edges, resulting in insufficient mixing of cement and soil. The construction quality of cement-soil improvement highly depends on the uniform distribution of cement in the soil—after the cement and soil are fully mixed and compacted, the cement begins to set and generate strength, thereby improving the strength of the subgrade and eliminating subgrade subsidence. However, in the root junction area, due to insufficient mixing depth and limited mixing path, the cement dosage is often unevenly distributed, with some areas having excessively high or low cement content. This not only wastes materials but also directly leads to large dispersion in the strength indicators of the improved soil and poor overall integrity. The inability to guarantee the uniformity of cement-stabilized soil solutions has become one of the key factors restricting the quality of roadbed in expansion projects.

[0004] Secondly, large compaction machinery has blind spots, making it difficult to meet edge compaction standards: the compaction quality at the junction of roadbeds plays a crucial role in the joint effect. However, in the root edge area where new and old roadbeds meet, large rollers, limited by their structural dimensions and operating space, cannot effectively compact the edges, easily resulting in under-compaction. Due to difficulties in construction with compaction machinery, the compaction degree at the roadbed edges often cannot be guaranteed, forming under-compacted areas. Especially when the roadbed fill height is large, longitudinal through joints can easily form between the under-compacted area and the normally compacted area due to settlement differences. In existing reconstruction and expansion projects, the settlement control methods for the difference in width between new and old roadbeds are affected by additional stress, often leading to poor control of process settlement depth and edge compaction. To ensure edge stability, the method of over-wide filling followed by slope cutting is often adopted in engineering, but the compaction degree of the root dead corner is still difficult to reach the design target (e.g., ≥96%). The interface between the roadbed and the subgrade is inherently a weak point, and the degree of compaction is difficult to control. If not handled properly, this interface will become the mechanically weak point of the entire subgrade structure.

[0005] Third, uneven settlement is prone to occur at the joint, inducing longitudinal cracks in the pavement. Uneven settlement between new and old roadbeds is one of the most typical and common defects in highway reconstruction and expansion projects. After nearly ten years of operation and long-term load, the settlement of the old roadbed has tended to stabilize, while the new roadbed will inevitably undergo a continuous settlement process after its formation. Due to the difference in consolidation time at the junction of the new and old roadbeds, the degree of consolidation of the foundation and the degree of roadbed compression are different, resulting in differential settlement between the new and old roadbeds. When the additional stress in the pavement structure layer caused by differential settlement exceeds the tensile strength or interfacial strength of the material, longitudinal cracks will occur at the joint between the new and old roadbeds. Once longitudinal cracks form, they not only directly affect driving comfort and safety, but also accelerate water damage and fatigue failure of the pavement structure, significantly shortening the service life of the road. In the existing technology, the treatment of the junction between the new and old roadbeds mostly relies on measures such as step excavation, geogrid laying, and increasing the compaction standard. However, these methods mainly focus on macroscopic structural reinforcement and are still insufficient for the refined treatment of the microscopic area at the root. The quality of splicing relies excessively on crack-resistant materials, while the materials themselves have limited effect on improving the quality of splicing.

[0006] In summary, during the widening projects on both sides of primary highways, the junction area between the old and new roadbeds presents three major technical challenges due to limited space and restricted machinery operation: uneven mixing, difficulty in controlling compaction quality, and a significant risk of uneven settlement. Existing construction methods are insufficient to effectively address these issues, necessitating the development of a new cement-soil construction method specifically for the junction of old and new roadbeds. This method would break down the vertical interface between the old and new roadbeds, improve the uniformity of the mixing at the junction, ensure the quality of edge compaction, and fundamentally eliminate the risk of uneven settlement. Summary of the Invention

[0007] The purpose of this application is to provide a cement-soil construction method for the splicing of new and old roadbeds in highway expansion projects, which solves the problems of uneven cement-soil mixing, numerous blind spots in compaction by large machinery, and poor overall stability of the roadbed in existing highway expansion projects.

[0008] The objective of this application is achieved through the following technical solution: A cement-soil construction method for the joint between new and old roadbeds in a highway expansion project includes the following steps: Step 1, Preparation stage: Clean the edges of the old roadbed; Step 2, slanted blade mixing: Using a grader, adjust the scraper angle and adopt the slanted blade operation mode to cut into the root of the old roadbed, cut and turn the cement soil at the root of the old roadbed to the middle of the newly paved area, break the vertical interface between the old and new roadbeds, and form a transition zone; Step 3, Mechanical mixing: Use a road mixer to mix the entire cement-soil layer, including the soil being turned over, at a full cross-sectional depth. The mixing depth must penetrate the cement-soil layer to ensure that the cement and soil are fully and evenly mixed. Step 4, backfilling and spreading: After mixing evenly, use a grader to spread the mixture back to the base of the old roadbed, and then use a grader to level it. Step 5, conventional compaction: The main roadbed is conventionally compacted using a large road roller; Step 6, reinforcement and compaction: Subsequently, for the root edge areas that cannot be effectively compacted by large machinery, manual labor combined with a small rammer is used to supplement the compaction to ensure that there are no dead corners.

[0009] Furthermore, in step 2, the cement soil within a 20cm wide area at the base of the old roadbed is turned and mixed towards the center.

[0010] Furthermore, in step 2, the cutting angle of the grader's scraper into the root of the old roadbed is 30°~60°, the mixing depth is 20~30cm, and the mixing speed is 1.5~3.0km / h.

[0011] Furthermore, in step 3, the mixing process ensures that the entire cement-soil layer has a uniform color and is free of streaks and clumps of ash.

[0012] Furthermore, in step 3, the mixing rotor speed of the road mixer is 200~300 r / min, the travel speed is 1.0~2.0 km / h, and the road mixer mixes at least twice in both directions, with an overlap width of not less than 20 cm between adjacent mixing tracks.

[0013] Furthermore, in step 4, the loose paving coefficient is controlled by a grader. The loose paving thickness of the mixture after fine leveling by the grader is controlled to be 1.20 to 1.30 times the designed compacted thickness. In addition, a level is used to monitor the elevation in real time during the fine leveling process to ensure that the deviation of the loose paving thickness does not exceed ±5mm.

[0014] Furthermore, in step 5, the road roller follows the principle of compaction from light to heavy and from slow to fast.

[0015] Furthermore, in step 5, the large road roller adopts a vibratory road roller, with the rolling speed controlled at 1.5~2.5km / h, the vibration frequency at 25~30Hz, and the amplitude at 0.8~1.2mm. After static rolling 1~2 times, vibratory rolling is performed 3~4 times.

[0016] Furthermore, in step 6, the operator uses a small impact rammer or plate rammer to compact the area within 20-30cm from the edge until the designed compaction standard is met.

[0017] Furthermore, in step 6, the compaction frequency of the small impact rammer is 400-600 times / min, and the number of compactions at a single point is not less than 8-12. When the small rammer is used in conjunction with manual labor for supplementary compaction, the compaction points are arranged in a quincunx pattern along the edge of the old roadbed root, and the spacing between adjacent compaction points is 15-25cm.

[0018] The beneficial effects of this application are: (1) Eliminating the blind spot in the bonding process and solving the problem of material segregation at its root. Addressing the traditional blind spot in mechanical operations at the junction of old and new roadbeds, a creative approach was taken to utilize the grader's oblique cutting mode to precisely cut and turn the cement-soil within a 20cm wide area at the junction of the old roadbed and transfer it to the center of the newly paved area. This technique breaks the original vertical bonding surface between the old and new roadbeds, allowing the long-consolidated material at the junction of the old and new roadbeds to undergo preliminary physical mixing with the material of the newly constructed roadbed before mixing in the road mixer. Subsequently, through full-section deep mixing in the road mixer, the old and new materials are uniformly mixed a second time under the cementitious bonding system, fundamentally eliminating material segregation at the joint and ensuring a continuous and uniform distribution of cement dosage within the transition zone, providing a homogeneous material foundation for subsequent compaction and molding.

[0019] (2) Improve compaction degree and completely eliminate edge compaction dead corners. Abandoning the traditional compaction approach that relies solely on large road rollers, an innovative graded combined compaction system of "large machinery for main compaction + small rammers for reinforcement" was constructed. Large road rollers perform conventional compaction of the main roadbed with light to heavy and slow to fast speeds to ensure that the compaction degree of the main area meets the standards. Subsequently, for the root edge area (within 20-30cm from the edge) that cannot be effectively reached by large machinery, manual compaction is carried out in combination with small impact rammers or plate rammers in a staggered pattern. Through the complementary advantages of large road rollers and small rammers, full-area and full-depth compaction from the main body of the roadbed to the root edge is achieved, effectively avoiding the compaction degree loss caused by slope cutting after ultra-wide filling, and ensuring that the root edge compaction degree consistently reaches more than 96% of the design specification requirements, fundamentally solving the common quality problem of "under-compaction" at the roadbed edge.

[0020] (3) Enhanced integrity and significantly reduced risk of uneven settlement and longitudinal cracks. Through the synergistic effect of three processes—"oblique mixing, full-depth mixing, and graded compaction"—the junction of the old and new roadbeds is no longer a simple geographical contact surface, but rather forms a well-interlocking transition zone with gradually changing materials and continuous mechanical properties. This transition zone achieves homogenization and fusion of the old and new soils in terms of material composition, and achieves gradeless compaction from the main body to the edge in terms of density, which greatly improves the deformation coordination ability of the old and new roadbeds under load. This technological change effectively eliminates the hidden danger of stress concentration caused by abrupt changes in materials and differences in compaction, significantly reduces the risk of longitudinal cracks and differential settlement during the operation of the expanded highway, effectively ensures the long-term stability and driving comfort of the pavement structure, extends the overall service life of the expanded highway, and has significant economic and social benefits.

[0021] The aforementioned main solution and its various further alternatives can be freely combined to form multiple solutions, all of which are solutions that can be adopted and are claimed in this application; furthermore, the (non-conflicting alternatives) can also be freely combined with each other and with other alternatives. Those skilled in the art, after understanding the solution of this application, will realize from the prior art and common general knowledge that there are many combinations, all of which are technical solutions to be protected by this application, and will not be exhaustively listed here. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the root compaction blind zone treatment in this application.

[0023] Figure 2 This is a schematic diagram of the slanted blade mixing process in this application.

[0024] Figure 3 This is a schematic diagram of the operation of a small rammer at the site of this application.

[0025] Figure 4 This is the final rendering of the on-site operation for this application. Detailed Implementation

[0026] The following non-limiting embodiments are used to illustrate this application.

[0027] Example 1 refer to Figures 1-4 As shown, a cement-soil construction method for the splicing of new and old roadbeds in a highway expansion project includes the following steps: Step 1, preparation stage: When constructing the cement-soil improvement layer, the edge of the old roadbed is first cleaned.

[0028] Step 2, Angled blade mixing: Operate the grader, adjust the blade angle, and use the angled blade operation mode to cut into the root of the old roadbed, cutting and turning the cement soil at the root of the old roadbed to the middle of the newly paved area, breaking the vertical interface between the old and new roadbeds, and forming a transition zone.

[0029] In step 2, the cement-soil within a 20cm wide area at the base of the old roadbed is turned towards the center. The grader's scraper cuts into the base of the old roadbed at an angle of 30°~60°, the turning depth is 20~30cm, and the turning speed is 1.5~3.0km / h.

[0030] Step 3, Mechanical mixing: The road mixer arrives on site and is used to mix the entire cement-soil layer, including the soil being turned over, at a full cross-sectional depth. The mixing depth must penetrate the cement-soil layer to ensure that the cement and soil are fully and evenly mixed.

[0031] In step 3, the mixing process ensures that the entire cement-soil layer has a uniform color and is free of streaks and clumps of ash. The mixing rotor speed of the road mixer is 200~300 r / min, the travel speed is 1.0~2.0 km / h, and the road mixer must make at least two round trips, with an overlap width of not less than 20 cm between adjacent mixing tracks.

[0032] Step 4, backfilling and spreading: After mixing evenly, use a grader to spread the mixture back to the base of the old roadbed, and then use a grader to level it. In step 4, the loose paving coefficient is controlled by a grader. The loose paving thickness of the mixture after fine leveling is controlled to be 1.20 to 1.30 times the designed compacted thickness. In addition, a level is used to monitor the elevation in real time during the fine leveling process to ensure that the deviation of the loose paving thickness does not exceed ±5mm.

[0033] Step 5, conventional compaction: The main roadbed is conventionally compacted using a large road roller; In step 5, the road roller follows the principle of compaction from light to heavy and from slow to fast. Large road rollers use vibratory rollers, with the compaction speed controlled at 1.5~2.5km / h, the vibration frequency at 25~30Hz, and the amplitude at 0.8~1.2mm. After 1~2 static compactions, vibratory compaction is performed 3~4 times.

[0034] Step 6, reinforcement and compaction: Subsequently, for the root edge areas that cannot be effectively compacted by large machinery, manual labor combined with a small rammer is used to supplement the compaction to ensure that there are no dead corners.

[0035] In step 6, the operator uses a small impact rammer or plate rammer to compact the area within 20-30cm of the edge until the design compaction standard is met. The compaction frequency of the small impact rammer is 400-600 times / min, and the number of compactions at a single point is no less than 8-12. When the operator assists the small rammer in supplementary compaction, the compaction points are arranged in a quincunx pattern along the edge of the old roadbed, and the spacing between adjacent compaction points is 15-25cm.

[0036] Example 2 Based on Example 1, this construction method has been applied in a national highway reconstruction project, ensuring the construction period, optimizing the construction method, saving construction costs, and gaining high recognition from the owner.

[0037] The foregoing basic examples and their further alternative examples can be freely combined to form multiple embodiments, all of which are embodiments that can be adopted and claimed in this application. In the scheme of this application, each alternative example can be arbitrarily combined with any other basic example and alternative example.

[0038] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A cement-soil construction method for the joint between new and old roadbeds in a highway expansion project, characterized in that, Includes the following steps: Step 1, Preparation stage: Clean the edges of the old roadbed; Step 2, slanted blade mixing: Using a grader, adjust the scraper angle and adopt the slanted blade operation mode to cut into the root of the old roadbed, cut and turn the cement soil at the root of the old roadbed to the middle of the newly paved area, break the vertical interface between the old and new roadbeds, and form a transition zone; Step 3, Mechanical mixing: Use a road mixer to mix the entire cement-soil layer, including the soil being turned over, at a full cross-sectional depth. The mixing depth must penetrate the cement-soil layer to ensure that the cement and soil are fully and evenly mixed. Step 4, backfilling and spreading: After mixing evenly, use a grader to spread the mixture back to the base of the old roadbed, and then use a grader to level it. Step 5, conventional compaction: The main roadbed is conventionally compacted using a large road roller; Step 6, reinforcement and compaction: Subsequently, for the root edge areas that cannot be effectively compacted by large machinery, manual labor combined with a small rammer is used to supplement the compaction to ensure that there are no dead corners.

2. The cement-soil construction method for the splicing of new and old roadbeds in highway expansion projects according to claim 1, characterized in that: In step 2, the cement soil within a 20cm wide area at the base of the old roadbed is turned and mixed towards the center.

3. The cement-soil construction method for the joint between old and new roadbeds in highway expansion projects according to claim 1 or 2, characterized in that: In step 2, the cutting angle of the grader's scraper into the root of the old roadbed is 30°~60°, the mixing depth is 20~30cm, and the mixing speed is 1.5~3.0km / h.

4. The cement-soil construction method for the joint between old and new roadbeds in highway expansion projects according to claim 1, characterized in that: In step 3, the mixing process ensures that the entire cement-soil layer has a uniform color and is free of streaks and clumps of ash.

5. The cement-soil construction method for the joint between new and old roadbeds in highway expansion projects according to claim 1 or 4, characterized in that: In step 3, the mixing rotor speed of the road mixer is 200~300 r / min, the travel speed is 1.0~2.0 km / h, and the road mixer mixes at least twice in both directions, with an overlap width of not less than 20 cm between adjacent mixing tracks.

6. The cement-soil construction method for the splicing of new and old roadbeds in highway expansion projects according to claim 1, characterized in that: In step 4, the loose paving coefficient is controlled by a grader. The loose paving thickness of the mixture after fine leveling is controlled to be 1.20 to 1.30 times the designed compacted thickness. In addition, a level is used to monitor the elevation in real time during the fine leveling process to ensure that the deviation of the loose paving thickness does not exceed ±5mm.

7. The cement-soil construction method for the splicing of new and old roadbeds in highway expansion projects according to claim 1, characterized in that: In step 5, the road roller follows the principle of compaction from light to heavy and from slow to fast.

8. The cement-soil construction method for the splicing of new and old roadbeds in highway expansion projects according to claim 1 or 7, characterized in that: In step 5, a vibratory roller is used for large road rollers. The rolling speed is controlled at 1.5~2.5km / h, the vibration frequency is 25~30Hz, and the amplitude is 0.8~1.2mm. After static rolling 1~2 times, vibratory rolling is performed 3~4 times.

9. The cement-soil construction method for the splicing of new and old roadbeds in highway expansion projects according to claim 1, characterized in that: In step 6, the operator uses a small impact rammer or plate rammer to compact the area within 20-30cm from the edge until the design compaction standard is met.

10. The cement-soil construction method for the splicing of new and old roadbeds in highway expansion projects according to claim 1 or 9, characterized in that: In step 6, the compaction frequency of the small impact rammer is 400-600 times / min, and the number of compactions at a single point is not less than 8-12. When the small rammer is used in conjunction with manual labor for supplementary compaction, the compaction points are arranged in a quincunx pattern along the edge of the old roadbed root, and the spacing between adjacent compaction points is 15-25cm.

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