Well periphery reinforcement construction method for pavement inspection well

Abstract

The invention discloses a pavement inspection well periphery reinforcement construction method which comprises the following steps: S1, manual reverse excavation: after road bed construction is completed, performing reverse excavation around a built inspection well body in a manual mode to form an annular well periphery operation area; s2, layered backfilling is conducted, specifically, in the well periphery operation area, graded sand gravel is adopted for layered backfilling; and S3, layered tamping is conducted, specifically, the graded sand gravel backfilled in each layer is symmetrically tamped until backfilling is conducted to the designed elevation and the preset compaction degree is achieved, and a dense well periphery backfilling body is formed. The construction method provided by the invention not only systematically overcomes the stubborn quality problem of the pavement inspection well periphery from the technical level, but also shows comprehensive advantages in the aspects of efficiency, cost, controllability and social benefits, and has good popularization and application values.

Description

Technical Field

[0001] This invention relates to the field of municipal road construction technology, specifically to a method for reinforcing the perimeter of road manholes. Background Technology

[0002] In urban municipal road construction, the area around manholes on asphalt pavements is a common weak point in terms of quality. Traditional construction methods typically involve backfilling the area around the manhole with undisturbed soil or ordinary filler after its construction, followed by simultaneous compaction with the road structure layer. This method has significant drawbacks:

[0003] First, the narrow space around manholes makes it difficult for large compaction machinery to operate, while small tools often fail to compact the material properly, resulting in insufficient backfill density. Second, the large difference in stiffness between the manhole body (usually brick) and the surrounding flexible roadbed material easily leads to uneven settlement under repeated vehicle loads. Third, the installation elevation of manhole covers is often poorly controlled, easily creating a height difference with the final road surface. These problems cause "navel-like" defects such as road surface subsidence, cracking, and damaged manhole rings to appear shortly after the road is opened to traffic, seriously affecting driving safety, comfort, and road aesthetics, and incurring high costs for repeated repairs and traffic disruptions.

[0004] To address this, the industry has made some attempts to improve the process, such as using manual replacement and local reinforcement. However, these are mostly scattered measures and have not formed a systematic and efficient construction method. There are still shortcomings in ensuring the long-term quality of backfilling, improving work efficiency, and controlling costs. Summary of the Invention

[0005] This invention aims to overcome the aforementioned deficiencies of existing technologies and provide a systematic and effective method for reinforcing the perimeter of road manholes. The core of this invention lies in fundamentally solving the technical problems of inadequate backfilling, easy settlement, and uneven manhole covers through a set of optimized procedures and specific structural reinforcement measures.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for reinforcing the perimeter of road manholes includes the following steps:

[0008] S1. Manual reverse excavation: After the roadbed construction is completed, manual reverse excavation is carried out around the constructed manhole body to form a ring-shaped manhole perimeter work area.

[0009] S2. Layered backfilling: In the well perimeter work area, graded gravel is used for layered backfilling;

[0010] S3. Layered compaction: Each layer of graded sand and gravel is symmetrically compacted until it reaches the design elevation and the preset compaction degree, forming a dense well perimeter backfill.

[0011] In some embodiments, before performing step S1, it is ensured that the strength of the mortar or concrete foundation of the manhole body has reached the design strength requirement.

[0012] In some embodiments, in step S2, the particle size distribution, moisture content and water stability of the graded gravel must meet the requirements of relevant road engineering specifications for base course backfill materials.

[0013] In some embodiments, in step S3, a frog-type rammer or a vertical impact rammer is used to perform the layered compaction; and when the subsequent road structure layer is compacted by a road roller, the backfill area around the well is simultaneously compacted.

[0014] In some embodiments, before step S1, step S0 is further included: prefabricating a reinforced concrete well shaft, wherein a cold-drawn round steel lifting ring for hoisting is pre-embedded in the prefabricated reinforced concrete well shaft.

[0015] In some embodiments, after step S3, step S4 is further included: installing the precast manhole, specifically, during the construction of the road water-stabilized base course, the precast reinforced concrete manhole is hoisted and installed onto the top of the inspection well body.

[0016] In some embodiments, after step S4, step S5 is further included: pouring reinforced concrete reinforcement structural layer, specifically, on the periphery of the well backfill and precast reinforced concrete well cylinder, steel bars are tied on site and formwork is erected, and then concrete is poured to form a cast-in-place reinforced concrete ring beam or reinforced concrete slab, so that it is integrated with the well backfill and precast well cylinder as a whole.

[0017] In some embodiments, after step S5, step S6 is further included: installing and leveling the manhole cover, specifically including:

[0018] S61. After the construction of the lower asphalt layer of the road is completed, the asphalt material around the well is removed to expose the top surface of the precast reinforced concrete well cylinder or the reinforced structure layer.

[0019] S62. Determine the design elevation of the top surface of the manhole cover based on the longitudinal and transverse slopes of the road design;

[0020] S63. Place the manhole cover in place and use multiple iron wedge plugs to provide multi-point support and fine-tune the bottom of the manhole cover until the top surface elevation of the manhole cover reaches the design value.

[0021] S64. Fill and fix the gap between the bottom of the manhole cover and the supporting surface below by injecting high-grade mortar.

[0022] S65. After the mortar reaches its strength, remove the wedge plug.

[0023] In some embodiments, after step S6, step S7 is further included: spreading and compacting the asphalt surface layer around the well. Specifically, after the well cover is installed and fixed, the asphalt mixture around the well is backfilled and spread in layers. Each layer is spread symmetrically around the well cover and compacted in layers using a small compactor to ensure that the asphalt surface layer around the well is dense and smoothly connected to the well cover.

[0024] In some embodiments, the layered backfilling in step S2 and the layered compaction in step S3 are both carried out symmetrically around the center of the inspection well.

[0025] The beneficial effects that the road manhole perimeter reinforcement construction method disclosed in this application may bring include, but are not limited to:

[0026] 1. Fundamentally improve project quality and effectively solve persistent problems.

[0027] Core technological benefits: By employing the core process of "manual reverse excavation after roadbed formation → layered backfilling with graded gravel → symmetrical layered compaction," the problem of "weak interlayers" caused by limited working space, poor materials, and uneven compaction in the backfill area around manholes is fundamentally solved. The resulting dense, uniform, and water-stable backfill body around the manholes provides a solid and reliable foundation for the entire reinforcement system, curbing post-construction settlement at its source.

[0028] Structural reinforcement effect: The added cast-in-place reinforced concrete reinforcement structure layer (ring beam or slab) actively strengthens the rigidity of the area around the manhole. This structure acts like a "load-bearing tray" or "reinforcing hoop," strongly combining the manhole, compacted backfill, and road structure layer into a whole. This greatly improves the overall rigidity and load-bearing capacity of the area, effectively resisting stress concentration and fatigue damage caused by repeated vehicle traffic, thereby significantly reducing the risk of cracking and breakage of the pavement around the manhole.

[0029] Precision control effect: The manhole cover installation process, which uses "wedge plug fine-tuning + high-grade mortar anchoring," achieves millimeter-level precision matching between the manhole cover elevation and the road's design slope. This not only ensures a smooth and bump-free ride for vehicles, improving comfort, but also prevents rainwater accumulation and impact caused by elevation errors, protecting the manhole perimeter interface.

[0030] 2. Significantly improves construction efficiency and economic benefits

[0031] Process optimization and acceleration: Precast reinforced concrete manholes were used and installed simultaneously during the water-stabilized base construction phase, enabling parallel operation of factory prefabrication and on-site main construction. This transformed traditional on-site masonry and curing processes into assembly-line operations, significantly reducing the time that the manhole construction itself occupied on the critical path and accelerating the overall project progress.

[0032] Cost Reduction and Resource Conservation: By fundamentally preventing common quality defects such as wellbore subsidence and cracking, this method significantly reduces the need for frequent rework and maintenance. As described in the background section, reworking a single inspection well is costly (involving machinery, labor, materials, and traffic disruptions). This method achieves long-term quality stability with a one-time investment, avoiding the direct economic costs, social transportation costs, and material waste caused by repeated excavation and repair, resulting in a significant life-cycle cost advantage.

[0033] Reduce deviations and waste: The principle of symmetrical construction and standardized process control reduce quality deviations during construction and reduce the additional labor, machinery and material losses caused by deviations and rework.

[0034] 3. Enhance construction controllability and quality reliability

[0035] Standardization of materials and processes: Clear regulations on the performance of backfill materials (graded sand and gravel), compaction equipment and processes make construction parameters quantifiable, detectable and traceable, freeing them from excessive reliance on "experience" in traditional processes and improving the homogeneity and controllability of construction quality.

[0036] Prioritizing structural safety: Emphasizing that the excavation and backfilling of the perimeter should only be carried out after the structural strength of the well body meets the standards, ensuring the safety of the construction process and avoiding quality defects in the well body itself caused by disturbance.

[0037] 4. Improve social and environmental benefits

[0038] Ensuring public safety and comfort: After the construction method was implemented, the road inspection wells were integrated with the road, effectively eliminating safety hazards such as vehicle bumps and jumps caused by "belly button" defects, significantly improving the safety and comfort of driving on the road, and demonstrating outstanding public benefits.

[0039] Reduced construction disruption: Improved quality reduces the frequency of post-construction maintenance, which means less repeated excavation and road closures after the road is put into use, thus reducing long-term disruption to citizens' travel and the environment along the route.

[0040] Meets environmental protection and energy-saving requirements: This construction method emphasizes achieving high quality in one go, reducing the repeated consumption and waste of building materials due to quality problems, as well as the energy consumption of repeated entry of construction machinery, which is in line with the concept of green construction and sustainable development. Attached Figure Description

[0041] Figure 1 This is a flowchart of the road inspection well perimeter reinforcement construction method provided in the embodiments of the present invention. Detailed Implementation

[0042] Various exemplary embodiments, features, and aspects of this application will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0043] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, an indirect connection through an intermediate medium, or the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0044] like Figure 1 As shown, a method for reinforcing the perimeter of a road manhole includes the following steps: S1, manual back excavation: after the roadbed construction is completed, manual back excavation is carried out around the constructed manhole body to form a ring-shaped manhole perimeter work area; S2, layered backfilling: within the manhole perimeter work area, graded sand and gravel are used for layered backfilling; S3, layered compaction: each layer of graded sand and gravel is symmetrically compacted until the backfill reaches the design elevation and achieves the preset compaction degree, forming a dense manhole perimeter backfill body.

[0045] This scheme forms the core framework of the entire construction method. First, "reverse excavation" is carried out on a stable subgrade foundation to create a controllable working face for subsequent high-quality backfilling. Then, graded gravel, a water-stable and easily compacted material, is selected for layered backfilling, and specialized layered compaction is used to ensure the density of each layer. The entire process revolves around the existing manhole, ultimately forming a high-density "backfill" reinforcement zone around the manhole, composed of high-quality materials.

[0046] To address the fundamental problem of insufficient density and weak interlayers caused by compaction difficulties in the backfill area around manholes, this invention sets the backfilling process as "reverse excavation after subgrade formation → application of graded gravel → layered symmetrical compaction." This approach firstly avoids interference with subgrade filling, ensuring a stable working surface; the good permeability and friction of the graded gravel allow it to achieve high density even with small machinery; and the layered symmetrical compaction eliminates compaction dead zones, ensuring the backfill is uniform and robust overall. This provides a reliable foundation for the entire manhole reinforcement system.

[0047] To avoid potential displacement or structural damage to the manhole due to insufficient structural strength during circumferential excavation and compaction, the strength of the manhole's masonry mortar or concrete foundation must meet design requirements before proceeding to step S1. This step limits the start time of the core process to ensure structural safety.

[0048] This invention presupposes that the manhole itself meets the required strength standards for manual reverse excavation. This ensures that the reinforcement construction will not damage the manhole body, which is a prerequisite for ensuring the overall project quality.

[0049] In step S2, the particle size distribution, moisture content and water stability of the graded gravel must meet the requirements of relevant road engineering specifications for base course backfill materials.

[0050] To ensure that the backfill material has the expected mechanical properties and water stability, and to prevent the reinforcement effect from decreasing due to unqualified materials, this invention sets the specific parameters of the backfill material to comply with relevant engineering specifications.

[0051] To address the issue of large rollers being unable to effectively compact narrow areas around manholes, while small-scale equipment may still suffer from poor integration with the overall road surface compaction, step S3 employs a frog-type rammer or a vertical impact rammer for the layered compaction. Furthermore, when subsequent road structure layers are compacted with rollers, the backfill area around the manholes is simultaneously compacted. This clarifies the specific equipment used for layered compaction and adds a collaborative process with the overall road compaction.

[0052] This invention specifies the compaction process as follows: first, a frog-type rammer or a vertical impact rammer is used to compact the backfill material at the project site, and then "supplementary compaction" is carried out during overall rolling. "Supplementary compaction" effectively eliminates the compaction difference zone between the backfill material around the well and the large-area roadbed, allowing them to better integrate and avoiding weak points at the interface.

[0053] Before step S1, step S0 is included: prefabricating a reinforced concrete shaft, in which cold-drawn round steel lifting rings for hoisting are pre-embedded. This step prepares for subsequent installation. The prefabricated shaft is pre-cast on site, and the pre-embedded lifting rings inside serve as hoisting connection points.

[0054] To expedite on-site construction, ensure uniform quality of shaft components, and facilitate subsequent installation, this invention employs factory-prefabrication or on-site centralized prefabrication of the upper shaft, and pre-embeds cold-drawn round steel lifting rings for it. Prefabrication ensures concrete strength and dimensional accuracy; the pre-embedded lifting rings provide standardized and safe lifting points, greatly improving efficiency and safety during the installation phase.

[0055] After step S3, step S4 is also included: installing the precast manhole, specifically, during the construction of the road water-stabilized base course, the precast reinforced concrete manhole is hoisted and installed to the top of the inspection well body.

[0056] The precast manhole is lifted by its pre-embedded lifting ring and precisely positioned on top of the completed manhole body. Mortar is usually laid at the joint surface of the two to level and connect them.

[0057] To organically integrate the installation of precast manholes into the overall road construction process and avoid separate construction occupying the roadway, this invention schedules the installation during the construction of the water-stabilized base course. This allows for parallel operation of the road structure layer construction and the manhole ancillary structure construction, effectively saving construction time and utilizing the working surface and environment of the water-stabilized layer construction to facilitate installation positioning and adjustment.

[0058] After step S4, step S5 is also included: pouring reinforced concrete reinforcement structural layer, specifically, on the periphery of the well backfill and precast reinforced concrete well cylinder, steel bars are tied on site and formwork is erected, and then concrete is poured to form a cast-in-place reinforced concrete ring beam or reinforced concrete slab, so that it is integrated with the well backfill and precast well cylinder as a whole.

[0059] This is an additional rigid reinforcement structure added outside of the compacted backfill and precast manhole. A steel mesh is tied to the surface of the backfill around the manhole, formwork is erected around the steel reinforcement, and poured concrete encloses the lower part of the manhole and anchors it within the backfill. The form of the ring beam or approach slab is selected based on the design load-bearing requirements.

[0060] To overcome the problem of stress concentration and fatigue failure caused by abrupt changes in stiffness around manhole covers, this invention incorporates a cast-in-place reinforced concrete reinforcement layer around the manhole. This layer acts like a rigid hoop or load-bearing plate, strongly integrating the underlying dense backfill, the manhole body, and the precast manhole casing into a unified whole. It significantly disperses and transfers wheel loads from the road surface, greatly improving the overall load-bearing capacity and deformation resistance of the manhole perimeter area, effectively preventing cracking and subsidence.

[0061] After step S5, step S6 is also included: installing and leveling the manhole cover, specifically including: S61, removing the asphalt material around the manhole; S62, determining the design elevation; S63, fine-tuning the wedge plug; S64, injecting mortar to fix it; S65, removing the wedge plug.

[0062] The manhole cover is placed on top of the reinforced structural layer or precast manhole casing. Fine-tuning and leveling in three dimensions are achieved using multiple adjustable iron wedge plugs. After leveling, high-grade mortar is poured into the bottom gaps to form a stable support and bond. The wedge plugs, serving as temporary supports and adjustment tools, are removed after the mortar has cured.

[0063] To address the common problem of manhole cover installation elevation being difficult to control precisely, leading to height differences with the road surface, this invention employs a precision leveling process combining mechanical fine-tuning and chemical anchoring. Millimeter-level precise leveling is achieved using iron wedge plugs, followed by permanent fixing with high-grade mortar. This ensures that the top surface elevation of the manhole cover perfectly matches the road's designed slope, thereby guaranteeing smooth driving.

[0064] After step S6, step S7 is also included: spreading and compacting the asphalt surface layer around the well. Specifically, after the well cover is installed and fixed, the asphalt mixture around the well is backfilled and spread in layers. Each layer is spread symmetrically around the well cover and compacted in layers using a small compactor.

[0065] Around the already leveled and fixed manhole cover, hot asphalt mixture is spread and compacted using the same "symmetrical, layered" principle as the leveling time.

[0066] To prevent hollow areas, settlement, or poor joints between the asphalt surface layer around the manhole from occurring due to uneven paving and compaction, this invention specifies that the final layer of asphalt surface layer around the manhole should also be symmetrically layered and compacted using small machinery. This ensures that the interface area between the manhole cover and the asphalt road surface is equally dense and flat, achieving a seamless connection, effectively sealing against water, and extending the life of the interface.

[0067] The layered backfilling in step S2 and the layered compaction in step S3 are both carried out symmetrically around the center of the inspection well.

[0068] To fundamentally avoid uneven pressure on the backfill material around the well due to uneven construction stress, which could lead to well tilting or uneven settlement later, this invention defines the key operational principle of backfilling and compaction as "symmetrical about the center." This principle is consistently applied and is the fundamental guarantee for ensuring uniform stress and coordinated operation of the reinforcement material around the well, thus improving the universality and reliability of the solution.

[0069] The invention will be further described in detail below with reference to a specific engineering example. This implementation case takes the Hutang West Road project in Xiangtan City as an example.

[0070] First, construction preparation: develop a special plan, communicate with the design team to determine that reinforced concrete ring beams will be used as the reinforcement structural layer, and select a prefabrication site.

[0071] Step 1: After the manhole is constructed and the mortar strength meets the standard, use a custom steel mold at the prefabrication site to pour C30 concrete prefabricated manhole cylinder, and pre-embed Φ10 cold-drawn round steel lifting rings, and cure to the specified strength.

[0072] Step 2: After the roadbed is compacted in layers, a circular working pit with a diameter of approximately 1.5 meters is manually excavated, centered on the manhole. The pit is filled with graded gravel that meets specifications, in three layers (approximately 20cm each). For each layer, two workers simultaneously fill the material from symmetrical directions. A vertical impact rammer is then used to compact the material symmetrically from both sides towards the center in a spiral motion, ensuring a compaction degree of ≥96%. When the entire roadbed is compacted with a road roller, the area around the manhole is compacted several times additionally.

[0073] Step 3: On the day the road water-stabilized base course is laid, a truck crane is used with a soft cable to pass through the precast manhole ring and lift it to the installation position. The grout is placed on the manhole body and initially checked with a spirit level.

[0074] Step 4: After the precast well casing is installed and before the asphalt base course is constructed, a ring beam frame made of Φ12 steel bars is tied in the trench around the well, wooden formwork is erected, and C30 concrete is poured to form a reinforced concrete ring beam that is 40cm wide and 20cm thick. This ring beam covers the lower part of the well casing and is combined with the lower backfill. Water is then sprinkled for curing.

[0075] Step 5: After the asphalt base layer is laid and compacted, the asphalt material above the manhole cover is manually and precisely removed. The surveyor calculates the center and four sides elevation of the manhole cover based on the road's designed slope. The heavy-duty ductile iron manhole cover is installed, with four iron wedge-shaped plugs placed at the four corners of the cover base. Adjustments are made by gently tapping with a small hammer, ensuring the elevation of each point on the top surface of the cover deviates from the design value by within ±2mm. M30 high-strength cement mortar is poured into the pre-drilled holes under the manhole cover base to fill the gaps. After 24 hours of curing, the wedge-shaped plugs are gently removed, and the small holes are filled with mortar.

[0076] Step 6: Lay the asphalt surface layer. When the paver approaches the manhole cover, workers carefully backfill the area around the manhole cover with hot asphalt mixture, filling in thin layers, each layer not exceeding 5cm in thickness. Immediately use a hot tamping hammer to symmetrically compact the mixture around the manhole cover until it is flush and dense with the overall road surface.

[0077] Through the implementation of the above steps, the road inspection wells in the Hutan West Road project have remained flat for a long time after the road was opened to traffic, without any obvious subsidence or cracking, which verifies the effectiveness of this construction method.

[0078] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for reinforcing the perimeter of road manholes, characterized in that, Includes the following steps: S1. Manual reverse excavation: After the roadbed construction is completed, manual reverse excavation is carried out around the constructed manhole body to form a ring-shaped manhole perimeter work area. S2. Layered backfilling: In the well perimeter work area, graded gravel is used for layered backfilling; S3. Layered compaction: Each layer of graded sand and gravel is symmetrically compacted until it reaches the design elevation and the preset compaction degree, forming a dense well perimeter backfill.

2. The method for reinforcing the perimeter of road manholes according to claim 1, characterized in that, Before performing step S1, ensure that the strength of the mortar or concrete foundation of the manhole body has reached the design strength requirements.

3. The method for reinforcing the perimeter of road manholes according to claim 1, characterized in that, In step S2, the particle size distribution, moisture content and water stability of the graded gravel must meet the requirements of relevant road engineering specifications for base course backfill materials.

4. The method for reinforcing the perimeter of road manholes according to claim 1, characterized in that, In step S3, a frog-type rammer or a vertical impact rammer is used to compact the layers; and when the subsequent road structure layers are compacted with a road roller, the backfill area around the well is simultaneously compacted.

5. The method for reinforcing the perimeter of road manholes according to claim 1, characterized in that, Before step S1, step S0 is also included: prefabricating a reinforced concrete well shaft, wherein a cold-drawn round steel lifting ring for hoisting is pre-embedded in the prefabricated reinforced concrete well shaft.

6. The method for reinforcing the perimeter of road manholes according to claim 5, characterized in that, After step S3, step S4 is also included: installing the precast manhole, specifically, during the construction of the road water-stabilized base course, the precast reinforced concrete manhole is hoisted and installed to the top of the inspection well body.

7. The method for reinforcing the perimeter of road manholes according to claim 6, characterized in that, After step S4, step S5 is also included: pouring reinforced concrete reinforcement structural layer, specifically, on the periphery of the well backfill and precast reinforced concrete well cylinder, steel bars are tied on site and formwork is erected, and then concrete is poured to form a cast-in-place reinforced concrete ring beam or reinforced concrete slab, so that it is integrated with the well backfill and precast well cylinder as a whole.

8. The method for reinforcing the perimeter of road manholes according to claim 7, characterized in that, Following step S5, step S6 is also included: installing and leveling the manhole cover, specifically including: S61. After the construction of the lower asphalt layer of the road is completed, the asphalt material around the well is removed to expose the top surface of the precast reinforced concrete well cylinder or the reinforced structure layer. S62. Determine the design elevation of the top surface of the manhole cover based on the longitudinal and transverse slopes of the road design; S63. Place the manhole cover in place and use multiple iron wedge plugs to provide multi-point support and fine-tune the bottom of the manhole cover until the top surface elevation of the manhole cover reaches the design value. S64. Fill and fix the gap between the bottom of the manhole cover and the supporting surface below by injecting high-grade mortar. S65. After the mortar reaches its strength, remove the wedge plug.

9. The method for reinforcing the perimeter of road manholes according to claim 8, characterized in that, After step S6, step S7 is also included: spreading and compacting the asphalt surface layer around the well. Specifically, after the well cover is installed and fixed, the asphalt mixture around the well is backfilled and spread in layers. Each layer is spread symmetrically around the well cover and compacted in layers using a small compactor to ensure that the asphalt surface layer around the well is dense and smoothly connected to the well cover.

10. The method for reinforcing the perimeter of road manholes according to any one of claims 1 to 9, characterized in that, The layered backfilling in step S2 and the layered compaction in step S3 are both carried out symmetrically around the center of the inspection well.

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