A structure and method for preventing and controlling differential settlement of subgrade at the edge of a linear underground structure

Abstract

The present invention provides a structure and method for preventing and controlling differential settlement of subgrade at the edge of a linear underground structure. A reinforced concrete capping beam is arranged on the foundation pit support pile, and a reinforced concrete slab is arranged on the capping beam. One end of the slab is connected to the capping beam through reserved steel bars, and the other end is placed above the subgrade to form a subgrade of a rigid-flexible transition section. Grouting holes are reserved in the underground structure, and the grouting holes are located at the gaps between the support piles. The grouting pipe can extend under the slab for grouting to avoid the bottom of the pipe becoming void due to subgrade settlement and causing slab breakage. A sleeper beam is arranged under the joint between the slabs to prevent the slabs from having longitudinal dislocation. The beneficial effects of the present invention are as follows: through the combination of the reinforced concrete slab and the geogrid, a transition structure is formed, so that the subgrade will not produce sudden differential settlement, avoiding the generation of transverse and longitudinal cracks on the road. The cost is much lower than that of the full cross-section of the road for precast pipe piles, cement mixing piles or high-pressure jet grouting pile composite foundation treatment, and it has good economy and applicability in soft soil areas.

Description

Technical Field

[0001] The present invention relates to the technical fields of urban underground space and soft foundation treatment, and particularly relates to a structure and method for preventing differential settlement of subgrade at the edge of a linear underground structure. Background Art

[0002] The intensive use of underground space is the trend of current urban construction. In the commercial and financial center areas of cities, linear underground structures such as utility tunnels, underground ring roads, and underground commercial streets are often built under roads. These underground structures are relatively sensitive to settlement. If differential settlement occurs, it will lead to diseases such as stepped joints and water leakage, and the cost of their maintenance is very high. To avoid such situations, relatively strong foundation treatment is often carried out under underground ring roads and utility tunnels. Especially in soft soil areas, composite foundations such as precast pipe piles and cast-in-place piles are often set under linear underground structures. In addition, since these underground structures are cavity structures themselves, the earth pressure under them is less than that in other areas. If the transition treatment at the edge of the underground space is not appropriate, it is extremely easy to cause differential settlement at the edge of the structure, resulting in longitudinal cracks on the road. On the one hand, it affects the urban image and driving comfort, and may even cause traffic accidents. On the other hand, it also consumes a large amount of funds for road repair.

[0003] If all the subgrade outside the underground space is treated with composite foundations such as precast pipe piles, cement mixing piles or jet grouting piles to make its stiffness close to that above the underground space, the cost is relatively high, and it is usually only adopted when the road width outside the underground space is narrow.

[0004] At present, there are also some underground projects that set corbels on the side walls of the structure, and then set a transition slab on the corbels, or directly set corbels on the top slab of the structure to form a rigid-flexible transition structure. In addition, if a transition slab is directly set on the corbel on the side wall of the structure or on the top slab, the earth pressure on the transition slab will be directly transmitted to the underground structure, and the structure stress is relatively complex, and generally, additional reinforcement is required. In bridge construction, the transition slab at the bridgehead is also a commonly used device to prevent vehicle bump at the bridgehead, but the bottom of the transition slab often undergoes voiding or even slab breakage due to the settlement of the soft foundation. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a structure and method for preventing differential settlement of subgrade at the edge of a linear underground structure, which can reduce differential settlement and avoid the occurrence of pavement cracks.

[0006] The structure for preventing differential settlement of subgrade at the edge of a linear underground structure includes: foundation pit support piles, capping beams, transition slabs, grouting holes, grouting pipes, geogrids, and a certain linear underground structure;

[0007] At the top of the vertically arranged foundation pit retaining piles, a capping beam is lapped, and a bridging slab is arranged on the capping beam; the bridging slab is arranged on the roadbed, and one end of it is lapped on the top of the capping beam; several layers of geogrids are laid in the fill above the lapping part of the bridging slab and the capping beam.

[0008] In a certain linear underground structure, grouting holes are reserved, and the grouting holes are arranged in the gaps between adjacent foundation pit retaining piles; one end of a grouting pipe is inserted into the grouting hole, and the other end is inserted below the reinforced concrete bridging slab; when the bottom of the reinforced concrete bridging slab is hollowed out, the grouting pipe is used for grouting.

[0009] Furthermore, the bridging slab is connected to the top of the capping beam through reserved steel bars.

[0010] Furthermore, both the capping beam and the bridging slab are made of reinforced concrete.

[0011] Furthermore, the direction of the grouting hole points to the lower part of the bridging slab.

[0012] Furthermore, the structure also includes a bolster beam, and the bolster beam is arranged below the joint seam between the bridging slabs.

[0013] Furthermore, two layers of geogrids are laid within a range of 2m to 4m on both sides above the lapping part of the bridging slab and the capping beam.

[0014] A method for preventing differential settlement of the roadbed at the edge of a linear underground structure, using the above-mentioned structure for preventing differential settlement of the roadbed at the edge of a linear underground structure, includes the following steps:

[0015] S1: Excavate the ground above the bridging slab and a certain linear underground structure to the elevation of the top surface of the capping beam;

[0016] S2: Construct the foundation pit retaining piles, and pour the capping beam and the support structure;

[0017] S3: After the strength of the capping beam and the support structure poured at the top of the foundation pit retaining piles reaches the engineering design value, excavate the foundation pit to the engineering design elevation;

[0018] S4: Construct a certain linear underground structure, and reserve grouting holes at the axils at the top of the side walls of the certain linear underground structure;

[0019] S5: Backfill the foundation pit and construct the bridging slab;

[0020] S6: Backfill the roadbed above the bridging slab and the certain linear underground structure, lay geogrids, and then compact the geogrids to the engineering design compaction degree;

[0021] S7: Construct the pavement structure and ancillary structures above a certain linear underground structure;

[0022] S8: When there is a hollowing at the bottom of the bridging slab, inject grout through the grouting holes reserved on a certain linear underground structure by inserting a grouting pipe to prevent the situation that the bottom of the bridging slab is voided, resulting in the breaking of the bridging slab and causing road surface settlement.

[0023] Further, both the capping beam and the bridging slab are made of reinforced concrete.

[0024] Further, the grouting holes are located at the gaps between adjacent foundation pit support piles and point to the lower part of the bridging slab.

[0025] The beneficial effects brought by the technical solution provided by the present invention are as follows:

[0026] 1. By forming a transition structure with a concrete bridging slab, the settlement difference at the edge of the utility tunnel will not change suddenly, avoiding the generation of longitudinal cracks on the road surface;

[0027] 2. One end of the reinforced concrete bridging slab is placed on the support structure, and the soil pressure on the bridging slab will not be transmitted to the linear underground structure, avoiding the problems that the underground structure is under complex stress and the cost needs to be increased when the bridging slab is placed on the wall corbel or roof slab of the linear underground structure;

[0028] 3. Grouting holes are reserved in the underground space, and the grouting pipe can extend to the lower part of the bridging slab for grouting, which can effectively prevent the bottom of the slab from being voided, avoid road surface settlement caused by the breaking of the bridging slab, and also avoid drilling holes on the road surface for grouting. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be further described below in conjunction with the drawings and embodiments. In the drawings:

[0030] Figure 1 is a schematic structural view of a structure for preventing differential settlement of the roadbed at the edge of a linear underground structure in an embodiment of the present invention;

[0031] Figure 2 is a schematic view of the sleeper beam under the reinforced concrete bridging slab in an embodiment of the present invention;

[0032] Figure 3 is a flowchart of a method for preventing differential settlement of the roadbed at the edge of a linear underground structure in an embodiment of the present invention.

[0033] In each of the drawings, the list of components represented by each reference numeral is as follows:

[0034] 1 - Support pile; 2 - Reinforced concrete capping beam; 3 - Reinforced concrete bridging slab; 4 - Grouting hole; 5 - Grouting pipe; 6 - Geogrid; 7 - Sleeper beam; 8 - A certain linear underground structure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] For a clearer understanding of the technical features, objectives, and effects of the present invention, the specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0036] An embodiment of the present invention provides a structure and method for preventing differential settlement of the subgrade at the edge of a linear underground structure. The linear underground structure refers to a long-strip underground structure, such as an underground loop, an underground utility tunnel, an underground commercial street, etc.

[0037] Please refer to Figures 1 to 3 , Figure 1 which is a schematic diagram of a structure for preventing differential settlement of the subgrade at the edge of a linear underground structure in an embodiment of the present invention, Figure 2 which is a schematic diagram of a sleeper beam under a reinforced concrete slab in an embodiment of the present invention, Figure 3 and which is a flowchart of a method for preventing differential settlement of the subgrade at the edge of a linear underground structure in an embodiment of the present invention; the structure for preventing differential settlement of the subgrade at the edge of a linear underground structure specifically includes: a retaining pile 1, a reinforced concrete capping beam 2, a reinforced concrete slab 3, a grouting hole 4, a grouting pipe 5, a geogrid 6, a sleeper beam 7, and a certain linear underground structure 8.

[0038] As Figure 1 shown, a reinforced concrete capping beam 2 is provided at the top of the retaining pile 1 of a certain linear underground structure 8, and a reinforced concrete slab 3 is provided at the top of the reinforced concrete capping beam 2; the reinforced concrete slab 3 is arranged on the subgrade, and one end of it is lapped on the top of the reinforced concrete capping beam 2 through reserved steel bars; in this part, since the reinforced concrete slab 3 can be closely connected to the reinforced concrete capping beam 2, its displacement is restricted, deformation is reduced, and it is avoided that the reinforced concrete slab 3 falls off from above the reinforced concrete capping beam 2 when the differential settlement is large. Grouting holes 4 are reserved in a certain linear underground structure 8, the grouting holes 4 are arranged at the gaps between adjacent retaining piles, and the direction of the grouting holes 4 points to the bottom of the reinforced concrete slab 3; one end of the grouting pipe 5 is inserted into the grouting hole 4, and the other end can be inserted under the reinforced concrete slab 3; when the bottom of the reinforced concrete slab 3 is hollowed out, the grouting pipe 5 grouts. Geogrids are provided in the area where the reinforced concrete slab is prone to being pulled and cracked above the lap joint with the reinforced concrete capping beam, that is, two layers of geogrids are provided within a range of 2 m to 4 m on both sides 2 above the lap joint of the reinforced concrete slab 3 and the reinforced concrete capping beam 2.

[0039] As Figure 2 shown, the joint between the reinforced concrete slabs 3 is set at the deformation joint of a certain linear underground structure 8, and a sleeper beam 7 is provided under the joint to avoid differential settlement along the longitudinal direction of the reinforced concrete slab.

[0040] As Figure 3As shown in the figure, a method for preventing and controlling differential settlement of subgrade at the edge of a linear underground structure, using the above-mentioned structure for preventing and controlling differential settlement of subgrade at the edge of a linear underground structure, specifically includes the following steps:

[0041] S1: Excavate the ground above the reinforced concrete slab 3 and a certain linear underground structure 8 to the elevation of the top surface of the reinforced concrete crown beam 2;

[0042] S2: Construct the retaining piles 1, and pour the reinforced concrete crown beam 2 and the support structure; this support structure is the internal support of the foundation pit, usually made of materials such as steel pipes, reinforced concrete, and profiled steel, and the support form is mostly cross bracing;

[0043] S3: After the strength of the retaining piles 1, the poured reinforced concrete crown beam 2 and the support structure reaches the design value, excavate the foundation pit to the design elevation;

[0044] S4: During the construction of a certain linear underground structure 8, at the axil angle at the top of its side wall, reserve grouting holes 4. The grouting holes are located in the gaps between the retaining piles 1 and point to the lower part of the slab.

[0045] S5: Backfill the foundation pit and construct the reinforced concrete slab 3;

[0046] S6: Backfill the subgrade above the reinforced concrete slab 3 and the underground structure 8, lay several layers of geogrids 6 and then compact to the design compaction degree.

[0047] S7: Construct the road surface structure and ancillary structures above, etc.

[0048] S8: When the bottom of the reinforced concrete slab 3 is hollowed out, insert a grouting pipe 5 through the reserved grouting hole 4 on a certain linear underground structure 8 for grouting.

[0049] The beneficial effects of the present invention are as follows: By forming a transition structure, sudden differential settlement of the subgrade will not occur, avoiding the generation of transverse and longitudinal cracks on the road. The cost is much lower than that of using precast pipe piles, cement mixing piles or high-pressure jet grouting piles for composite foundation treatment of the entire road section, and it has good economy and applicability in soft soil areas. The specific effects are as follows:

[0050] 1. By combining the concrete slab with the geogrid, a transition structure is formed, so that the settlement difference at the edge of the pipe gallery will not change suddenly, avoiding the generation of longitudinal cracks on the road surface;

[0051] 2. One end of the reinforced concrete slab is placed on the support structure, and the soil pressure on the slab will not be transmitted to the underground structure, avoiding the problems of complex stress on the underground structure and the need to increase the cost when the slab is placed on the side wall corbel or the top slab of the structure;

[0052] 3. Reserve grouting holes in the underground space. The grouting pipe can extend under the slab for grouting, which can effectively prevent the bottom of the slab from becoming hollow, avoid road surface settlement caused by slab breakage, and also avoid grouting by drilling holes on the road surface.

[0053] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preventing and controlling differential settlement of subgrade at the edge of a linear underground structure, adopting a structure for preventing and controlling differential settlement of subgrade at the edge of a linear underground structure, characterized in that: The structure includes: foundation pit retaining piles (1), capping beams (2), reinforced concrete slabs (3), grouting holes (4), grouting pipes (5), geogrids (6) and a certain linear underground structure (8); At the top of the vertically arranged foundation pit retaining piles (1), there is a capping beam (2) lapped, and a reinforced concrete slab (3) is arranged on the capping beam (2); the reinforced concrete slab (3) is arranged on the roadbed, and one end of it is lapped on the top of the capping beam (2); several layers of geogrids (6) are laid in the fill above the lapping part of the reinforced concrete slab (3) and the capping beam (2); Grouting holes (4) are reserved in a certain linear underground structure (8), and the grouting holes (4) are arranged in the gaps between adjacent foundation pit retaining piles (1); one end of a grouting pipe (5) is inserted into the grouting hole (4), and the other end is inserted under the reinforced concrete slab (3); when the bottom of the reinforced concrete slab (3) is hollowed out, the grouting pipe (5) grouts; The reinforced concrete slab (3) is connected to the top of the capping beam (2) through reserved steel bars; The structure also includes a sleeper beam (7), and the sleeper beam (7) is arranged below the joint seam between the reinforced concrete slabs (3); Two layers of geogrids (6) are laid within a range of 2m to 4m on both sides above the lapping part of the reinforced concrete slab (3) and the capping beam; The method includes the following steps: S1: Excavate the ground above the reinforced concrete slab (3) and a certain linear underground structure (8) to the elevation of the top surface of the capping beam (2); S2: Construct the foundation pit retaining piles (1), and pour the capping beam (2) and the support structure; S3: After the strength of the capping beam (2) and the support structure poured at the top of the foundation pit retaining piles (1) reaches the engineering design value, excavate the foundation pit to the engineering design elevation; S4: Construct a certain linear underground structure (8), and reserve grouting holes (4) at the axils at the top of the side walls of the certain linear underground structure (8); S5: Backfill the foundation pit and construct the reinforced concrete slab (3); S6: Backfill the roadbed above the reinforced concrete slab (3) and the certain linear underground structure (8), lay several layers of geogrids (6), and then compact the geogrids (6) to the engineering design compaction degree; S7: Construct the road surface structure and ancillary structures above a certain linear underground structure (8); S8: When the bottom of the reinforced concrete slab (3) is hollowed out, insert a grouting pipe (5) through the reserved grouting holes (4) on the certain linear underground structure (8) to grout, so as to prevent the situation that the bottom of the reinforced concrete slab (3) is separated from the ground, resulting in the slab breakage of the reinforced concrete slab (3) and causing road surface settlement.

2. The method for preventing and controlling differential settlement of subgrade at the edge of a linear underground structure according to claim 1, characterized in that: The direction of the grouting hole (4) points to the lower part of the reinforced concrete slab (3).

3. A method for preventing and controlling differential settlement of subgrade at the edge of a linear underground structure as claimed in claim 1, wherein: The capping beam (2) is made of reinforced concrete.

4. A method for preventing and controlling differential settlement of subgrade at the edge of a linear underground structure according to claim 1, characterized in that: The grouting hole (4) is located at the gap between adjacent foundation pit retaining piles (1) and points to the lower part of the reinforced concrete slab (3).

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