Box-type roadbed composite foundation structure and construction method

Abstract

The invention relates to the field of composite foundation structures, in particular 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 comprises a cushion layer, a microorganism solidification hard shell layer and pile bodies from top to bottom, the upper ends of the pile bodies are located in the microorganism solidification hard shell layer, and the pile bodies are CFG piles and discrete piles. The frame box type roadbed structure and the combined composite foundation structure are combined, the structural characteristics of the frame box type roadbed structure and the combined composite foundation structure are brought into full play, the roadbed stability is guaranteed, meanwhile, the roadbed slope land and the foundation treatment range are reduced, the overall roadbed manufacturing cost is saved, and meanwhile the defects existing in treatment of a single pile type foundation in an ultra-deep covering type karst stratum are overcome; the foundation bearing capacity can be remarkably improved, the foundation soil liquefaction condition is eliminated, the construction cost of a karst roadbed can be reduced, and super-long cast-in-situ bored pile construction is avoided.

Description

Technical Field

[0001] The invention relates to the field of composite foundation structures, and in particular to a box-type roadbed composite foundation structure and a construction method. Background Art

[0002] At present, the filling slope of 1:1.25 to 1:2 is usually used on both sides of the railway subgrade structure, which is the most widely used subgrade structure type at home and abroad. However, the width of this subgrade structure is several times the width of the subgrade surface, which requires a lot of land resources such as cultivated land and forest land, and the scope of foundation treatment is also much larger than the scope of the subgrade surface. In plain areas, due to the lack of qualified fillers, fillers often need to be transported from a distance, and the foundation soil layer is generally deep and soft, requiring foundation treatment. The cost of subgrade fillers and foundation treatment is huge. The above factors combined lead to a long construction time and high construction costs for railway subgrade projects.

[0003] In the case of thick and soft foundation soil in plain areas, when it cannot meet the bearing capacity or deformation requirements, foundation treatment measures will be adopted to form a composite foundation. Commonly used composite foundation treatment methods include CFG piles, loose piles, etc. At the same time, for the subgrade structure of the foundation in the ultra-deep overburden strong karst development area, it is generally necessary to use an ultra-long end-bearing pile-plate structure to reinforce the ultra-deep overburden karst.

[0004] CFG pile is the abbreviation of cement fly ash gravel pile, which is a pile formed by mixing gravel, stone chips, sand, fly ash, cement and water. It can make full use of the bearing capacity of the soil between the piles and transfer the load to the deep foundation, thereby improving the bearing capacity of the foundation and reducing deformation. CFG piles are not reinforced, and industrial waste fly ash is used as an admixture, which greatly reduces the project cost. The CFG pile method is suitable for treating clay, silt, sand and relatively hard soil layers at the pile end. However, its disadvantage is that it cannot eliminate foundation liquefaction, and quality problems such as broken piles and necking are prone to occur during construction.

[0005] Bulk material piles refer to piles composed of bulk materials such as sand, gravel or crushed stone. Among them, crushed stone sand piles (compacted sand piles) are a typical representative of bulk piles and one of the commonly used pile types. Bulk piles such as sand piles, slag piles, and crushed stone piles mixed with steel slag are also used at home and abroad. Bulk piles, especially crushed stone piles, are mainly suitable for the reinforcement of saturated soil foundations such as general clay, silt, and sand. The advantages are: they have obvious effects of eliminating liquefaction and reducing upper settlement for foundations with low bearing capacity and the presence of liquefied layers. The disadvantage is: the effect of improving the bearing capacity of the foundation is not obvious, and the maximum bearing capacity of the treated foundation can only reach 1.5 times the bearing capacity of the original foundation.

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

[0007] The box-type roadbed composite foundation structure has a broad application market and application scenarios for the reinforcement of soft soils such as general clay, silt sand and other soft soils in plain areas and ultra-deep covered strong karst development areas. Based on this, a box-type roadbed composite foundation structure is proposed, which can effectively reduce the construction land and procedures, shorten the construction period, save the overall cost of the roadbed, and solve the shortcomings of special strata and single pile foundation treatment, so as to meet the green, low-carbon and high-quality construction requirements of railway projects. Summary of the invention

[0008] The purpose of the present invention is to solve the shortcomings existing in the treatment of special strata and single pile type foundation, and to propose a box-type roadbed composite foundation structure and construction method.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A 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 hard shell layer and a pile body from top to bottom. The upper end of the pile body is located inside the microbial solidified hard shell layer. The pile body adopts two types: CFG pile and loose pile.

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

[0012] Preferably, a plurality of CFG piles and loose piles are arranged alternately in the shape of plum blossom piles.

[0013] Preferably, the granular pile is a gravel pile and the length of the gravel pile is longer than that of the CFG pile. The specific size should be calculated and determined according to the on-site conditions.

[0014] Preferably, the cushion layer is composed of a crushed stone layer and a medium-coarse sand layer and has several layers of geogrids sandwiched therein.

[0015] Preferably, the frame box type roadbed comprises a bottom plate, two vertical web plates and a top plate from bottom to top, wherein the two vertical web plates are perpendicular to and connected to the top plate and the bottom plate. The width and thickness of each plate can be calculated according to the specific conditions of the project.

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

[0017] Preferably, a drain pipe is arranged on the upper side of the top plate, a plurality of ventilation holes are arranged on the web plate, drain pipes are arranged transversely along the line direction from the center of the upper side of the bottom plate to both sides, and cross-shaped reinforcing steel bars are used around the drain pipes.

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

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

[0020] S2, drilling grouting holes;

[0021] S3, preparing a microbial solidifying agent, injecting the microbial solidifying agent into the soil body to be consolidated from the grouting hole through a grouting pump, ensuring that the slurry is evenly distributed during grouting to induce calcium carbonate precipitation and achieve mud consolidation;

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

[0023] S5, firstly carry out the construction of the bulk piles, and then carry out the construction of the CFG piles;

[0024] S6, pile cap is arranged on the top of bulk pile and CFG pile;

[0025] S7, after the pile body is fully constructed, the upper cushion layer is applied;

[0026] S8, after the combined composite foundation is constructed, the upper frame box roadbed is constructed, and the frame box roadbed is cast from bottom to top.

[0027] Preferably, the grouting in S3 maintains a pressure of 0.5 to 2.5 MPa and a flow rate of 10 to 50 L / min, and in S4, the soil is left to stand for 24 to 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 floor area and masonry index per linear meter. It can eliminate traditional roadbed fillers, reduce loads, and greatly reduce the number of foundation reinforcements. It can also be designed in an integrated manner with culverts, which can effectively reduce the cost per kilometer of roadbed in plain areas and karst development areas, better solve the problems of land use limitations in developed areas and lack of fillers in plain areas, and reduce the "bridge-tunnel ratio".

[0030] (2) The combined composite foundation used in the present invention is a composite foundation structure composed of a shallow microbial solidified hard crust layer + CFG piles + loose piles. The use of this structure and its construction method can overcome the deficiencies in the prior art to a certain extent. In plain areas with thick and soft foundation soil layers and ultra-deep covered karst development areas, it can significantly improve the foundation bearing capacity and eliminate the liquefaction of the foundation soil. It can also reduce the cost of karst roadbed engineering and avoid the construction of ultra-long bored piles;

[0031] (3) The construction method of the present invention first completes the construction of the microbial solidified hard shell layer, and then the loose piles are constructed. After the loose piles are constructed, the intermediate CFG piles are constructed. The surface of the foundation soil layer is first solidified, and then the loose piles are used to effectively eliminate the liquefaction characteristics of the foundation, eliminate the liquefaction of the foundation soil, and reduce the problems of broken piles and necking during the subsequent CFG pile construction. Finally, the bearing capacity of the foundation is improved by the CFG piles.

[0032] In summary, the present invention combines the frame box-type roadbed structure and the combined composite foundation structure to give full play to their respective structural characteristics, ensure the stability of the roadbed, reduce the land used for roadbed slopes and the scope of foundation treatment, save the overall cost of the roadbed, and solve the shortcomings of single pile-type foundation treatment in ultra-deep covering karst strata. It can not only significantly improve the bearing capacity of the foundation and eliminate the liquefaction of the foundation soil, but also reduce the cost of the karst roadbed project, avoid the construction of ultra-long bored piles, and meet the green, low-carbon, and high-quality construction requirements of railway projects. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0035] Figure 3 It is a cross-sectional schematic diagram of a box-type roadbed composite foundation structure of the present invention;

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

[0037] In the figure: 1-bottom plate; 2-web plate; 3-top plate; 4-microorganism solidified hard shell layer; 5-cushion layer; 6-pile cap; 7-CFG pile, 8-gravel pile, 9-waterproof layer, 10-protective layer, 11-drain pipe, 12-ventilation hole. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] In the description of the present invention, it is necessary to understand that the terms "upper", "lower", "lower end", "bottom", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0040] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0042] Example

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

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

[0045] This embodiment provides a double-track railway size, the frame box-type roadbed structure height H is 6.5-7.0m; the bottom plate 1 is 10.0m wide and 1.0m thick; the net distance between the two webs 2 is 5.35m, the thickness is 0.65m, and the top plate 3 is 0.5m thick.

[0046] Among them, waterproof layer 9 and protective layer 10 are arranged on the upper side of top plate 3 and bottom plate 1. The thickness of concrete protective layer on the inner side of ballasted track retaining wall can be designed to be 60mm, and the thickness of protective layer on the upper side of bottom plate 1 can be designed to be 40mm. A certain slope should be retained during construction to facilitate drainage.

[0047] A PVC drainage pipe 11 is arranged on the upper side of the top plate 3 . A PVC drainage pipe 11 with an outer diameter of 160 mm is arranged on the inner side of the slag retaining wall every 5 m along the line direction. A cross-shaped reinforcement steel bar is used around the drainage pipe 11 .

[0048] In order to ensure the internal environment of the frame box-type roadbed structure, ventilation holes 12 are arranged on the web 2. The size of the ventilation holes 12 needs to be calculated according to the project conditions. In this embodiment, two rows of ventilation holes 12 with a diameter of 100 mm are arranged on the webs 2 on both sides. The spacing between the ventilation holes 1 is 2m, the top ventilation hole 1 is 30.5m away from the top plate, and the bottom ventilation hole 12 is 11.0m away from the bottom plate. If the ventilation hole 12 collides with the stressed steel bars, the position should be adjusted flexibly and appropriately.

[0049] In order to enhance drainage, PVC drainage pipes 11 with an outer diameter of 100 mm are horizontally arranged at intervals of 2 m from the center of the upper side of the bottom plate 1 to both sides along the line direction.

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

[0051] The cushion layer 5 is connected to the bottom plate 1 of the upper frame box-type roadbed. The thickness of the cushion layer 5 is generally 0.6m, and it is composed of 0.4m crushed stone + 0.2m medium-coarse sand. Two layers of geogrid are sandwiched inside the cushion layer 5.

[0052] A pile cap 6 is arranged on the top of the pile body. Generally, a C35 concrete pile cap 6 is used. The specific size of the pile cap 6 is determined by calculation. The pile body is composed of CFG piles 7 and gravel piles 8. To achieve a better reinforcement effect, the gravel piles 8 are longer than the CFG piles 7. The specific size should be determined by calculation according to the on-site conditions. Figure 3 As shown, in the cross section, the CFG piles 7 and the gravel piles 8 are arranged crosswise; Figure 4 As shown, in the plan view, the CFG piles 7 and the gravel piles 8 are arranged alternately in the shape of plum blossom piles.

[0053] The pile spacing of the pile body is determined by design calculation. The gravel pile 8 can be replaced with other loose piles with better properties according to the specific conditions of the project.

[0054] In this embodiment, a construction method of a box-type roadbed composite foundation structure includes the following steps:

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

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

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

[0058] S4, after the 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 crust layer 4 with a thickness of less than 5.0 m;

[0059] S5, firstly construct the gravel pile 8, and then construct the CFG pile 7;

[0060] S6, pile cap 6 is arranged on the top of gravel pile 8 and CFG pile 7;

[0061] S7, after the pile body is fully constructed, the upper cushion layer 5 is applied;

[0062] S8, after the combined composite foundation is constructed, the upper frame box-type roadbed is constructed, and the frame box-type roadbed is constructed by pouring the entire box body from bottom to top.

[0063] In this embodiment, the microbial solidification hard shell layer 4 is first applied during construction, and then the gravel pile 8 is applied. After the gravel pile 8 is applied, the middle CFG pile 7 is applied. The surface of the foundation soil layer is first solidified, and then the gravel pile 8 is used to effectively eliminate the liquefaction characteristics of the foundation and eliminate the liquefaction of the foundation soil, reduce the problems of broken piles and necking during the subsequent construction of the CFG pile 7, and finally improve the bearing capacity of the foundation through the CFG pile 7.

[0064] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A box-type roadbed composite foundation structure, characterized in that: It consists of an upper frame box-type roadbed and a lower combined composite foundation. The combined composite foundation includes a cushion layer, a microbial solidified hard shell layer and a pile body from top to bottom. The upper end of the pile body is located inside the microbial solidified hard shell layer. The pile body adopts two types: CFG pile and loose pile.

2. 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, and the pile cap is located at the upper end of the pile body and connected thereto.

3. The box-type roadbed composite foundation structure according to claim 1, characterized in that: Multiple CFG piles and loose piles are arranged alternately in the shape of plum blossom piles.

4. The box-type roadbed composite foundation structure according to claim 1, characterized in that: The dispersed pile is a gravel pile and the length of the gravel pile is longer than that of the CFG pile.

5. The box-type roadbed composite foundation structure according to claim 1, characterized in that: The cushion layer is composed of a crushed stone layer and a medium-coarse sand layer, and a plurality of geogrid layers are sandwiched therein.

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

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

8. The box-type roadbed composite foundation structure according to claim 6, characterized in that: A drain pipe is arranged on the upper side of the top plate, a plurality of ventilation holes are arranged on the web plate, and a drain pipe is arranged transversely along the line direction from the center of the upper side of the bottom plate to both sides, and the drain pipe is surrounded by a criss-cross reinforced steel bar.

9. A construction method for a box-type roadbed composite foundation structure according to claims 1-8, characterized in that: The following steps are involved: S1. Before construction, the ground should be drained and leveled; S2, drilling grouting holes; S3, preparing a microbial solidifying agent, injecting the microbial solidifying agent into the soil body to be consolidated from the grouting hole through a grouting pump, ensuring that the slurry is evenly distributed during grouting to induce calcium carbonate precipitation and achieve mud consolidation; S4, after the grouting is completed, the soil is left to stand for a period of time to ensure that the microorganisms complete the MICP reaction to form a microbial solidified hard crust layer; S5, firstly carry out the construction of the bulk piles, and then carry out the construction of the CFG piles; S6, pile cap is arranged on the top of bulk pile and CFG pile; S7, after the pile body is fully constructed, the upper cushion layer is applied; S8, after the combined composite foundation is constructed, the upper frame box roadbed is constructed, and the frame box roadbed is cast from bottom to top.

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

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