Load shedding protection structure for reconstruction of road above existing pipe gallery in soft soil area

Abstract

The utility model discloses a load shedding protection structure for reconstruction of a road above an existing pipe gallery in a soft soil area. The load shedding protection structure comprises a light foam soil load shedding layer and a geogrid reinforced layer. The density of the light foam soil deloading layer is far lower than that of common embankment filled soil, the additional load of the lifting embankment above the existing pipe gallery can be reduced, differential settlement deformation of a foundation can be controlled by arranging a step-shaped connecting structure, meanwhile, geogrids are fully laid on the upper portion of the light foam soil, differential settlement of the common filled soil embankment and the light foam soil embankment is further reduced, and the construction efficiency is improved. The pavement structure durability is improved. According to the existing pipe gallery load shedding protection structure combining the light foam soil and the geogrid, settlement deformation of the existing pipe gallery under the embankment load can be reduced, differential settlement of the upper pavement structure can be controlled, large-scale excavation and renovation of the existing pipe gallery can be avoided, and the construction cost is saved.

Description

Technical Field

[0001] This utility model relates to a load-reducing protection structure for the reconstruction of roads above existing utility tunnels in soft soil areas. Background Technology

[0002] Statistics show that my country has cumulatively started construction on 1,647 integrated utility tunnel projects, with a total length of 5,902 kilometers and a tunnel network of 3,997 kilometers. Integrated utility tunnels integrate and unify various underground pipelines and scattered facilities, forming a unified underground network that enables comprehensive management, maintenance, and repair of foundation facilities, while effectively avoiding the chaotic situation of intertwined pipelines on the urban surface. With the continuous advancement of urban modernization in my country, urban roads, existing utility tunnels, and other related infrastructure face problems such as aging and damage, leading to reduced road traffic efficiency and potential traffic safety hazards. To improve the quality of urban road services and ensure public safety, the reconstruction and expansion of urban roads and existing utility tunnels are imperative.

[0003] Because soft soil is widely distributed in coastal areas, plains, inland lake basins, depressions, and riverbanks in my country, it has engineering characteristics such as high water content, high compressibility, high void ratio, and low degree of consolidation. For roadbed reconstruction and elevation with soft soil, construction disturbance and additional loads from embankment filling seriously affect the stress state of existing utility tunnels and the settlement and deformation of pavement structures. This may induce defects such as cracks, torsion and shear, damage, and fissures in existing utility tunnels, causing uneven settlement of pavement structures and resulting in longitudinal and transverse cracks, threatening the long-term operational safety of existing utility tunnels and pavement structures.

[0004] To meet the requirements for controlling embankment settlement and deformation in road reconstruction and expansion projects above existing utility tunnels, ground treatment methods such as surcharge preloading, dynamic compaction, cement mixing piles, and precast pipe piles are generally used to reinforce soft soil foundations. However, these methods all have certain limitations. Surcharge preloading will generate significant additional stress on the existing utility tunnel below due to the surcharge load. Dynamic compaction will cause significant vibration and disturbance during construction, threatening the operational safety of the existing utility tunnel. Cement mixing piles and precast pipe piles are difficult to construct due to the limitations of the underground space of the existing utility tunnel and will affect subsequent underground space development. Therefore, commonly used ground treatment methods cannot simultaneously meet the requirements for controlling embankment settlement and deformation and controlling the stress on the existing utility tunnel structure. Utility Model Content

[0005] Purpose of the utility model: In view of the above-mentioned prior art, this utility model provides a load-reducing protection structure for the reconstruction of roads above existing utility tunnels in soft soil areas, which can meet the dual requirements of controlling embankment settlement and deformation and controlling the stress on existing utility tunnel structures.

[0006] Technical solution: A load-reducing protection structure for road reconstruction above existing utility tunnels in soft soil areas, comprising a lightweight foamed soil load-reducing layer and a geogrid reinforcement layer; the lightweight foamed soil load-reducing layer is located between the road structure and the existing utility tunnel, and the lightweight foamed soil load-reducing layer is connected to the ordinary fill embankment by a stepped connection structure, and the geogrid reinforcement layer is fully laid on top of the lightweight foamed soil load-reducing layer.

[0007] Furthermore, the lightweight foamed soil load-reducing layer requires the lightweight foamed soil to have a wet density range of 500~1100 kg / m³. 3 Furthermore, the wet density of the lightweight foamed soil below the groundwater level is not less than 1000 kg / m³. 3 The subgrade section requires an unconfined compressive strength of 0.8 MPa or higher after 28 days; the embankment section requires an unconfined compressive strength of 0.6 MPa or higher after 28 days; and the replacement subgrade requires an unconfined compressive strength of 0.4 MPa or higher.

[0008] Furthermore, the lightweight foamed soil load-reducing layer is located at a distance from the pavement structural layer. H 1 ≥ 50cm, and the bottom of the lightweight foamed soil layer is 50cm away from the existing utility tunnel. H 2≥100cm; The lightweight foamed soil load-reducing layer is equipped with a stepped connection structure, with a step height-to-width ratio of 1:2 and a step height of not less than 0.3m. The length of the existing pipe gallery on both sides of the lightweight foamed soil is longer than the specified width. L 2≥0.5m.

[0009] Furthermore, the geogrid reinforcement layer uses a bidirectional polypropylene tensile geogrid. The mesh side length within the geogrid should be controlled within the range of 60~150mm, the tensile strength of a single strip should not be less than 80KN / m, the width is approximately 5m, the roll length is 30~50m, the tensile strength of a single strip should be >150MPa, and the ultimate elongation of a single strip should be <10%. The geogrid reinforcement layer is fully laid on top of the lightweight foamed soil load-reducing layer, with extra-wide lengths on both sides. L 1≥2m.

[0010] Compared with the prior art, the structure described in this utility model has significant progress and effects:

[0011] 1. Lightweight foamed soil load-reducing layers are characterized by low self-weight and high stiffness, effectively reducing the additional load on embankment fill, minimizing foundation settlement and deformation, and controlling the stress state of existing utility tunnels. Compared with other foundation treatment methods, lightweight foamed soil construction causes less disturbance, has a lower additional load on the superstructure, and does not require the driving of a bearing layer, thus achieving the dual purpose of reducing pavement settlement and deformation and controlling the stress state of existing utility tunnels. The stepped connection structure of the lightweight foamed soil load-reducing layer enables a smooth transition of additional loads between the lightweight foamed soil embankment and the ordinary fill embankment, reducing differential settlement between the two.

[0012] 2. Based on the tension effect and load transfer principle, geogrid further transfers the self-weight load of the pavement structure to the lightweight foamed soil load-reducing layer, reduces the additional stress on the ordinary fill embankment on both sides, coordinates the settlement deformation of the lightweight foamed soil embankment and the ordinary fill embankment, and controls the differential settlement of the pavement structure. Attached Figure Description

[0013] Figure 1 Schematic diagram of the cross-section of the load reduction protection structure;

[0014] Figure 2 shows a comparison of foundation settlement before and after the implementation of the load reduction protection structure. Figure 2(a) shows the settlement of the foundation before the replacement with lightweight foamed soil, and Figure 2(b) shows the settlement of the lightweight foamed soil.

[0015] Figure 3 Lightweight foamed soil extra wide width L 2. Schematic diagram of the influence of the foundation and existing pipe gallery on settlement and deformation;

[0016] Figure 4 Distance between lightweight foamed soil and existing utility tunnel H 2. The influence of the stress state on the existing utility tunnel is shown in the figure. Detailed Implementation

[0017] To illustrate the technical solution provided by this utility model in detail, further description is provided below with reference to the accompanying drawings.

[0018] This utility model provides a load-reducing protection structure suitable for the reconstruction of roads above existing utility tunnels, such as... Figure 1 As shown, the structure includes a lightweight foamed soil load-reducing layer and a geogrid reinforcement layer. The lightweight foamed soil load-reducing layer is characterized by its low self-weight and high stiffness. It is located between the pavement structure and the existing utility tunnel. A stepped connection structure is provided between the lightweight foamed soil load-reducing layer and the ordinary fill embankment. The geogrid reinforcement layer is characterized by its good ductility and high tensile strength. The geogrid reinforcement layer is fully laid on top of the lightweight foamed soil load-reducing layer. The lightweight foamed soil load-reducing layer, with its low self-weight and high stiffness, can effectively reduce the additional load on the embankment fill, thereby reducing foundation settlement and controlling the stress state of the existing utility tunnel. The stepped connection structure enables a smooth transition of the additional load between the lightweight foamed soil embankment and the ordinary fill embankment, reducing differential settlement between them. Geogrids can further transfer the self-weight load of the pavement structure to lightweight foamed soil through the reinforcement effect, reducing the additional stress on the ordinary fill embankments on both sides, coordinating the settlement and deformation of the lightweight foamed soil embankment and the ordinary fill embankment, and controlling the differential settlement of the pavement structure. The existing pipe gallery load reduction and protection structure of lightweight foamed soil combined with geogrids can not only reduce the settlement and deformation of the existing pipe gallery under the embankment load and control the differential settlement of the upper pavement structure, but also avoid large-scale excavation and repair of the existing pipe gallery, saving project costs.

[0019] In this example, the road surface to be reconstructed will be raised by 1.2m, with a designed pavement structure layer thickness of 0.67m. The existing utility tunnel beneath it is 3.4m wide and 2.5m deep. The lightweight foamed soil is designed to be buried 117cm below the pavement structure design elevation, with a replacement thickness of 1.5m. The distance between the lightweight foamed soil and the top of the existing utility tunnel is 2.2m, the bottom overwidth is 0.6m, and the excavation steps are 1m wide and 0.5m high. The lightweight foamed soil has a wet density of 800kg / m³. 3 The 28-day unconfined compressive strength is 1.0 MPa. The lightweight foamed soil layer is fully covered with geogrid with an extra width of 2m. The geogrid is a bidirectional polypropylene tensile geogrid with a mesh side length of 100mm, a width of 5m, a roll length of 40m, a tensile strength of 100kN / m for a single strip, and an ultimate elongation of 5% for a single strip.

[0020] The implementation method for the above structure includes the following steps:

[0021] S1. Determine the thickness of the lightweight foamed soil replacement based on the road design height and the depth of the existing pipe gallery top.

[0022] S2. Compare the changes in embankment height before and after road reconstruction and expansion, and calculate the wet density of lightweight foam for replacement based on the principle of equal load replacement.

[0023] S3. Based on the design requirements for the density and compressive strength of the replacement layer, the wet density is confirmed to be 800 kg / m³. 3 At that time, 1 cubic meter of lightweight foamed soil requires 550.01 kg of cement, 220.004 kg of water, and 29.983 kg of air bubbles. Lightweight foamed soil is prepared according to the design ratio.

[0024] S4. Backfill the embankment fill material in layers to 117cm below the design elevation of the road surface; excavate to the design depth of the replacement fill, excavate the connection structure with the ordinary embankment, the step width is 100cm, the step height is 50cm, and then backfill the embankment fill material in layers to the top design elevation of the lightweight foamed soil.

[0025] S5. Lightweight foamed soil is kept moist and cured for no less than 7 days. After curing, geogrid is fully laid on top of the lightweight foamed soil load-reducing layer and extended 2m on both sides.

[0026] S6. Backfill soil in layers down to the bottom of the pavement structure layer.

[0027] As shown in Figures 2-4, this utility model, to meet the dual requirements of controlling embankment settlement and deformation and controlling the stress on the existing utility tunnel structure during road reconstruction above the existing utility tunnel, employs a composite structure of a lightweight foamed soil load-reducing layer combined with a geogrid reinforcement layer to reduce foundation settlement and deformation and protect the safety of the existing utility tunnel structure. The lightweight foamed soil load-reducing layer, characterized by its low self-weight and high stiffness, effectively reduces the additional load on the embankment fill, thereby reducing foundation settlement and controlling the stress state of the existing utility tunnel. The stepped connection structure enables a smooth transition of the additional load between the lightweight foamed soil embankment and the ordinary fill embankment, reducing differential settlement between them. The geogrid, through its reinforcing effect, further transfers the self-weight load of the road structure to the lightweight foamed soil embankment, reducing the additional stress on the ordinary fill embankments on both sides, coordinating the settlement and deformation of the lightweight foamed soil embankment and the ordinary fill embankment, and controlling differential settlement of the road structure. The existing pipe gallery load reduction protection structure of lightweight foamed soil combined with geogrid can reduce the settlement and deformation of the existing pipe gallery under the embankment load, control the differential settlement of the upper pavement structure, and avoid large-scale excavation and repair of the existing pipe gallery, thus saving project costs.

[0028] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A load reduction protection structure for reconstruction of an existing pipe gallery overhead road in soft soil area, characterized in that: It comprises a light foam soil unloading layer and a geogrid reinforced layer; the light foam soil unloading layer is located between a pavement structure and an existing pipe gallery, the light foam soil unloading layer is connected with common filling embankment by a stepped connection structure, and the geogrid reinforced layer is fully paved on the top of the light foam soil unloading layer.

2. The load reduction protection structure for reconstruction of an existing pipe gallery overhead road in soft soil area according to claim 1, characterized in that: The light foam soil unloading layer is away from the pavement structure layer by H1≥50 cm, and the bottom of the light foam soil layer is away from the existing pipe gallery by H2≥100 cm; the light foam soil unloading layer is provided with a stepped connection structure, the height-width ratio of the step is 1:2, the step height is not less than 0.3 m, and the length L2 of the overwide part of the light foam soil on both sides of the existing pipe gallery is ≥0.5 m.

3. The load reduction protection structure for reconstruction of an existing pipe gallery overhead road in soft soil area according to claim 1, characterized in that: The wet density of the lightweight foam soil in the lightweight foam soil unloading layer is 500-1100 kg / m 3 , and the wet density of the lightweight foam soil below the underground water level is not less than 1000 kg / m 3 ; the roadbed part requires 28-day unconfined compressive strength of 0.8 MPa or more, the embankment part requires 28-day unconfined compressive strength of 0.6 MPa or more, and the replaced foundation requires unconfined compressive strength of 0.4 MPa or more.

4. The load reduction protection structure for reconstruction of an existing pipe gallery overhead road in soft soil area according to claim 1, characterized in that: The geogrid reinforced layer adopts a bidirectional polypropylene tensile geogrid, the mesh edge length in the geogrid is controlled in the range of 60-150 mm, the tensile strength of a single strip should be not less than 80 KN / m, and the single strip ultimate elongation is <10%; the geogrid reinforced layer is fully paved on the top of the light foam soil unloading layer, and the length L1 of the overwide part on both sides is ≥2 m.

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