Box type roadbed composite foundation structure and construction method

Abstract

The present application relates to the field of composite foundation structure, especially to a box type roadbed composite foundation structure and a construction method. The box type roadbed composite foundation structure is composed of an upper frame box type roadbed and a lower combined composite foundation. The combined composite foundation includes a cushion layer, a microbial solidified crust layer and a pile body from top to bottom. The upper end of the pile body is located inside the microbial solidified crust layer. The pile body adopts two types of CFG pile and bulk pile. The present application combines the frame box type roadbed structure and the combined composite foundation structure, fully utilizes the structural characteristics of each structure, ensures the stability of the roadbed, reduces the land used by the roadbed slope and the foundation treatment range, saves the overall cost of the roadbed, solves the shortcomings of single pile type foundation treatment in the super deep overburden karst stratum, significantly improves the foundation bearing capacity, eliminates the soil liquefaction of the foundation, reduces the cost of the karst roadbed engineering, and avoids the construction of the super long cast-in-place pile.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of composite foundation structure, in particular to a box type roadbed composite foundation structure and a construction method. BACKGROUND

[0002] At present, the slope ratio of 1:1.25~1:2 is usually used on both sides of the railway roadbed structure, which is the most widely used roadbed structure type at home and abroad. However, the land occupation width of this roadbed structure type is several times the width of the roadbed surface, which requires a large amount of land resources such as farmland and forest land, and the foundation treatment range is much larger than the roadbed surface range. In the plain area, due to the lack of qualified fillers, the fillers need to be transported from a long distance, and the foundation soil layer is generally deep and soft, which needs to be treated. The cost of roadbed filler and foundation treatment is huge. The above factors comprehensively lead to a longer construction time and higher construction cost of railway roadbed engineering.

[0003] For the case that the foundation soil layer in the plain area is deep and soft, when it cannot meet the bearing capacity or deformation requirements, foundation treatment measures are used to form a composite foundation. The commonly used composite foundation treatment methods include CFG pile and bulk material pile.

[0004] CFG pile is a short name for cement fly ash gravel pile, which is a pile formed by mixing gravel, stone chips, sand, fly ash with cement and water. It can fully utilize the bearing capacity of the soil between the piles to transfer the load to the deep foundation, thereby improving the bearing capacity of the foundation and reducing the deformation. CFG pile does not need reinforcement, and uses industrial waste fly ash as an admixture, which greatly reduces the engineering cost. CFG pile method is suitable for treating cohesive soil, silt, sand and relatively hard soil layer at the pile end. However, its disadvantage is that it cannot eliminate foundation liquefaction, and quality problems such as broken pile and necking may occur during construction.

[0005] Bulk material pile refers to a pile composed of bulk materials such as sand, sandstone or gravel. Among them, gravel sand pile (compacted sand pile) is a typical representative of bulk material pile, and is one of the commonly used pile types. Currently, bulk material piles such as sand pile, slag pile and steel slag mixed gravel pile are also used at home and abroad. Bulk material pile, especially gravel pile, is mainly suitable for reinforcing general clay, silt, sand and other saturated foundations. Its advantages are: for treating foundations with low bearing capacity and existing liquefaction layer, it has obvious effects of eliminating liquefaction and reducing upper settlement. The disadvantage is: for improving the bearing capacity of the foundation, the treated foundation bearing capacity can only reach 1.5 times of the original foundation bearing capacity.

[0006] Ultra-deep covered karst generally refers to covered karst with a burial depth greater than 30m, or even greater than 100m. At present, ultra-deep covered karst is reinforced with ultra-long end-bearing pile-slab structures, which has the disadvantages and difficulties of high cost and great construction difficulty.

[0007] For the reinforcement of subgrade structures in plains areas with deep and weak soft soils such as general clay, silt, and sand, as well as in ultra-deep, strongly karst-developed areas, box-type subgrade composite foundation structures have a broad application market and application scenarios. Based on this, a box-type subgrade composite foundation structure is proposed, which effectively reduces construction land use and procedures, shortens the construction period, and saves the overall cost of the subgrade. At the same time, it solves the shortcomings of special strata and single pile foundation treatment, and meets the requirements of green, low-carbon, and high-quality construction of railway engineering. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of treating special strata and single-pile foundations, and to propose a box-type roadbed composite foundation structure and construction method.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A box-type roadbed composite foundation structure consists of an upper frame box-type roadbed and a lower combined composite foundation. The combined composite foundation includes, from top to bottom, a cushion layer, a microbial solidification hard shell layer, and piles. The upper end of the piles is located inside the microbial solidification hard shell layer. The piles are of two types: CFG piles and loose piles.

[0011] Preferably, the combined composite foundation further includes a pile cap located inside the microbial solidified hard shell layer, the pile cap being located at the upper end of the pile body and connected to it.

[0012] Preferably, multiple CFG piles and loose piles are arranged in a staggered pattern.

[0013] Preferably, the loose-body piles are crushed stone piles, and the length of the crushed stone piles is longer than that of the CFG piles. Specific dimensions should be calculated and determined based on site conditions.

[0014] Preferably, the cushion layer consists of a crushed stone layer and a medium-coarse sand layer, with several layers of geogrid sandwiched inside.

[0015] Preferably, the frame-box roadbed includes a bottom slab, two vertical web plates, and a top slab, from bottom to top. The two vertical web plates are perpendicular to and connected to the top and bottom slabs. The width and thickness of each slab can be calculated according to the specific project requirements.

[0016] Preferably, a waterproof layer and a protective layer are provided on the upper side of the top plate and the bottom plate.

[0017] Preferably, a drain pipe is provided on the upper side of the top plate, a number of ventilation holes are provided on the web plate, and a drain pipe is provided laterally from the center of the upper side of the bottom plate along the direction of the line. The drain pipe is surrounded by a grid-shaped reinforcing steel bar.

[0018] This invention also provides a construction method for a box-type roadbed composite foundation structure, comprising the following steps:

[0019] S1. Before construction, the ground surface should be drained and leveled.

[0020] S2, Drill grouting holes;

[0021] S3, prepare microbial solidifying agent, inject the microbial solidifying agent into the soil to be consolidated through the grouting hole using a grouting pump. During grouting, it is necessary to ensure that the grout is evenly distributed, induce calcium carbonate precipitation, and achieve mud consolidation.

[0022] S4. After grouting is completed, the soil is left to stand for a period of time to ensure that the microorganisms complete the MICP reaction and form a microbial solidified hard shell layer.

[0023] S5, first carry out the construction of loose piles, and then carry out the construction of CFG piles after the loose piles are completed.

[0024] S6, pile caps are installed on the top of the loose-body piles and CFG piles;

[0025] S7. After all the piles are constructed, the upper cushion layer is applied.

[0026] S8. After the composite foundation is completed, the upper frame box roadbed is constructed. The frame box roadbed is poured from bottom to top.

[0027] Preferably, in S3, the grouting maintains a pressure of 0.5–2.5 MPa and a flow rate of 10–50 L / min, and in S4, the soil is left to stand for 24–48 hours.

[0028] Compared with the prior art, the present invention provides a box-type roadbed composite foundation structure and construction method, which has the following beneficial effects:

[0029] (1) The present invention adopts a box-type roadbed composite foundation structure. Compared with the traditional roadbed structure, it has a lower land area and masonry index per meter. It can eliminate the traditional roadbed filler, reduce the load, greatly reduce the amount of foundation reinforcement, and can be integrated with culvert design. It can effectively reduce the cost per kilometer of roadbed in plain areas and karst development areas, and better solve the problems of land use limitations in developed areas and lack of filler in plain areas, and reduce the "bridge-tunnel ratio".

[0030] (2) The composite foundation adopted in this invention is a composite foundation structure consisting of a shallow microbial solidified hard shell layer, CFG piles, and loose piles. Using this structure and its construction method can overcome the shortcomings of the existing technology to a certain extent. In the plains, in areas with deep, soft, and ultra-deep karst development, it can significantly improve the bearing capacity of the foundation, eliminate soil liquefaction, reduce the cost of karst roadbed engineering, and avoid the construction of ultra-long bored piles.

[0031] (3) The construction method of this invention first completes the construction of the microbial solidification hard shell layer, then the granular piles are constructed, and after the granular piles are completed, the intermediate CFG piles are constructed. The surface of the foundation soil layer is first solidified, and then the granular piles are used to effectively eliminate the liquefaction characteristics of the foundation soil, thereby reducing the occurrence of problems such as pile breakage and necking during the subsequent CFG pile construction. Finally, the bearing capacity of the foundation is improved through the CFG piles.

[0032] In summary, this invention combines a frame-box subgrade structure and a composite foundation structure, giving full play to the characteristics of each structure. While ensuring the stability of the subgrade, it reduces the land use for subgrade slopes and the scope of foundation treatment, saving the overall cost of the subgrade. At the same time, it solves the shortcomings of single-pile foundation treatment in ultra-deep karst strata. It can significantly improve the bearing capacity of the foundation, eliminate soil liquefaction, reduce the cost of karst subgrade projects, avoid the construction of ultra-long bored piles, and meet the requirements of green, low-carbon, and high-quality construction of railway projects. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the frame-box roadbed structure of the present invention;

[0034] Figure 2 This is a longitudinal section schematic diagram of a box-type roadbed composite foundation structure according to the present invention;

[0035] Figure 3 This is a schematic cross-sectional view of a box-type roadbed composite foundation structure according to the present invention;

[0036] Figure 4 This is a schematic diagram of the combined composite foundation planar structure of the present invention;

[0037] In the diagram: 1-bottom plate; 2-web plate; 3-top plate; 4-microbial solidified hard shell layer; 5-cushion layer; 6-pile cap; 7-CFG pile; 8-gravel pile; 9-waterproof layer; 10-protective layer; 11-drainage pipe; 12-ventilation hole. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0039] In the description of this invention, it should be understood that the terms "upper", "lower", "lower end", "bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0040] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0041] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0042] Example

[0043] A box-type roadbed composite foundation structure, consisting of an upper frame box-type roadbed and a lower composite foundation.

[0044] like Figure 1 As shown, the frame-box roadbed includes a bottom slab 1, two vertical web plates 2, and a top slab 3 from bottom to top. The two vertical web plates 2 are perpendicular to and connected to the top slab 3 and the bottom slab 1. Ballast and other supporting facilities are constructed above the top slab 3, and a composite foundation is constructed below the bottom slab 1. The width and thickness of each slab can be calculated according to the specific project requirements.

[0045] This embodiment provides a double-track railway structure with a frame box subgrade structure height H of 6.5-7.0m; a bottom plate 1 width of 10.0m and a thickness of 1.0m; a net distance of 5.35m between two web plates 2 and a thickness of 0.65m; and a top plate 3 thickness of 0.5m.

[0046] Waterproof layer 9 and protective layer 10 are provided on the upper side of the top slab 3 and the bottom slab 1, respectively. The thickness of the concrete protective layer on the inner side of the ballast track retaining wall can be designed to be 60mm, and the thickness of the protective layer on the upper side of the bottom slab 1 can be designed to be 40mm. A certain slope should be maintained during construction to facilitate drainage.

[0047] A PVC drainage pipe 11 is installed on the upper side of the top slab 3. Every 5m along the line, a PVC drainage pipe 11 with an outer diameter of 160mm is installed on the inner side of the retaining wall. The drainage pipe 11 is surrounded by a grid-shaped reinforcing steel bar.

[0048] To ensure the internal environment of the frame box subgrade structure, ventilation holes 12 are arranged on the web plate 2. The size of the ventilation holes 12 needs to be calculated according to the specific project conditions. In this embodiment, two rows of ventilation holes 12 with a diameter of 100mm are set on the two sides of the web plate 2, with a spacing of 2m between the ventilation holes 1. The uppermost ventilation hole 1 is 30.5m away from the top plate, and the lowermost ventilation hole 12 is 11.0m away from the bottom plate. If the ventilation hole 12 collides with the reinforcing steel, its position should be adjusted appropriately.

[0049] To enhance drainage, PVC drainage pipes 11 with an outer diameter of 100mm are laid horizontally every 2m along the line direction from the center of the upper side of the base plate 1 to both sides.

[0050] As attached Figure 2 As shown, the lower composite foundation includes, from top to bottom, a cushion layer 5, a microbial solidified hard shell layer 4, and a pile body, with the upper end of the pile body located inside the microbial solidified hard shell layer 4.

[0051] The subbase 5 is connected to the bottom plate 1 of the upper frame box subgrade. The thickness of the subbase 5 is generally 0.6m, consisting of 0.4m of crushed stone + 0.2m of medium and coarse sand. The subbase 5 has two layers of geogrid sandwiched inside.

[0052] A pile cap 6 is installed on top of the pile body, generally made of C35 concrete. The specific dimensions of the pile cap 6 are determined by calculation. The pile body consists of two types of piles: CFG piles 7 and crushed stone piles 8. To achieve a better reinforcement effect, the crushed stone piles 8 are longer than the CFG piles 7; their specific dimensions should be calculated and determined based on site conditions. Figure 3 As shown, in the cross-section, CFG piles 7 and crushed stone piles 8 are arranged alternately; as Figure 4 As shown in the plan, CFG piles 7 and gravel piles 8 are arranged in an alternating quincunx pattern.

[0053] The spacing between the piles is determined by design calculations. The crushed stone piles (8) can be replaced with other loose-grain piles of better quality, depending on the specific project requirements.

[0054] This embodiment describes a construction method for a box-type roadbed composite foundation structure, including the following steps:

[0055] S1. Before construction, the ground surface should be drained and leveled.

[0056] S2, Drill grouting holes, using a square or equilateral triangle shape to drill grouting holes with a depth of less than 5.0m;

[0057] S3, prepare microbial solidifying agent, inject the microbial solidifying agent into the soil to be consolidated through the grouting hole using a grouting pump, maintain a pressure of 0.5-2.5 MPa and a flow rate of 10-50 L / min during grouting to ensure uniform distribution of grout, induce calcium carbonate precipitation, and achieve mud consolidation;

[0058] S4. After grouting is completed, the soil is left to stand for 24 to 48 hours to ensure that the microorganisms complete the MICP reaction and form a microbial solidified hard shell layer with a thickness of less than 5.0m.

[0059] S5, first construct the 8 crushed stone piles, and after the 8 crushed stone piles are constructed, construct the 7 CFG piles.

[0060] S6, pile caps 6 are installed on the top of the crushed stone piles 8 and CFG piles 7;

[0061] S7. After all the piles are constructed, the upper cushion layer 5 is applied.

[0062] S8. After the composite foundation is completed, the upper frame box roadbed is constructed. The frame box roadbed is formed by pouring the entire box from bottom to top.

[0063] In this embodiment, the microbial solidification hard shell layer 4 is first constructed, followed by the construction of the crushed stone piles 8. After the crushed stone piles 8 are completed, the intermediate CFG piles 7 are constructed. First, the surface of the foundation soil is solidified, and then the crushed stone piles 8 effectively eliminate the liquefaction characteristics of the foundation soil, reducing the likelihood of pile breakage and necking during the subsequent construction of the CFG piles 7. Finally, the CFG piles 7 improve the bearing capacity of the foundation.

[0064] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A construction method for a box-type roadbed composite foundation structure, characterized in that: Includes the following steps: S1. Before construction, the ground surface should be drained and leveled. S2, Drill grouting holes; S3, prepare microbial solidifying agent, inject the microbial solidifying agent into the soil to be consolidated through the grouting hole using a grouting pump. During grouting, it is necessary to ensure that the grout is evenly distributed, induce calcium carbonate precipitation, and achieve mud consolidation. S4. After grouting is completed, the soil is left to stand for a period of time to ensure that the microorganisms complete the MICP reaction and form a microbial solidified hard shell layer. S5, first carry out the construction of loose piles, and then carry out the construction of CFG piles after the loose piles are completed. S6, pile caps are installed on the top of the loose-body piles and CFG piles; S7. After all the piles are constructed, the upper cushion layer is applied. S8. After the combined composite foundation is completed, the upper frame box roadbed is constructed. The frame box roadbed is poured from bottom to top. One method for constructing a box-type roadbed composite foundation structure is used to form a box-type roadbed composite foundation structure, which consists of an upper frame box-type roadbed and a lower composite foundation. The composite foundation includes a cushion layer, a microbial solidification hard shell layer and piles from top to bottom. The upper end of the piles is located inside the microbial solidification hard shell layer. The piles are of two types: CFG piles and loose piles.

2. The construction method of a box-type roadbed composite foundation structure according to claim 1, characterized in that: The combined composite foundation also includes a pile cap located inside the microbial solidified hard shell layer, the pile cap being located at the upper end of the pile body and connected to it.

3. The construction method of a box-type roadbed composite foundation structure according to claim 1, characterized in that: Multiple CFG piles and loose piles are arranged in a staggered pattern.

4. The construction method of a box-type roadbed composite foundation structure according to claim 1, characterized in that: The loose-body piles are made of crushed stone and the length of the crushed stone piles is longer than that of the CFG piles.

5. The construction method of a box-type roadbed composite foundation structure according to claim 1, characterized in that: The cushion layer consists of a layer of crushed stone and a layer of medium-coarse sand, with several layers of geogrid sandwiched inside.

6. The construction method of a box-type roadbed composite foundation structure according to claim 1, characterized in that: The frame box-type roadbed includes a bottom plate, two vertical web plates, and a top plate from bottom to top. The two vertical web plates are perpendicular to and connected to the top plate and the bottom plate.

7. The construction method of a box-type roadbed composite foundation structure according to claim 6, characterized in that: The top plate and the bottom plate are provided with a waterproof layer and a protective layer on their upper sides.

8. The construction method of a box-type roadbed composite foundation structure according to claim 6, characterized in that: The top plate is provided with a drain pipe on its upper side, the web plate is provided with several ventilation holes, and the bottom plate is provided with a drain pipe on its upper side from the center to both sides along the line direction. The drain pipe is surrounded by a grid-shaped reinforcing steel bar.

9. The construction method of a box-type roadbed composite foundation structure according to claim 1, characterized in that: In S3, the grouting pressure is maintained at 0.5~2.5 MPa and the flow rate is 10~50 L / min. In S4, the soil is left to stand for 24~48 hours.

Images