Composite foundation pit water-stop retaining structure system under complex geological conditions and construction method of composite foundation pit water-stop retaining structure system

Abstract

The invention relates to the technical field of foundation pit construction, in particular to a composite foundation pit water stopping and supporting structure system under the complex geological condition and a construction method thereof.The water stopping and supporting structure system sequentially comprises a slope protection structure and a foundation pit water stopping and supporting structure from outside to inside, and the slope protection structure comprises a foundation pit cement soil stirring wall, stand columns and a reinforced concrete spraying layer; the foundation pit water retaining supporting structure comprises a front composite wall, a wall heel plate, a wall toe plate and a rear drilling pouring row pile, and the slope protection structure and the foundation pit water retaining supporting structure jointly form a foundation pit support suitable for the complex geological conditions with soft soil and hard soil layers and close to a gentle slope. The strength of the slope protection structure is further improved through stand columns and a reinforced concrete spraying layer, an h-shaped supporting structure is formed by a front composite wall, a wall heel plate, a wall toe plate and rear bored cast-in-place piles, the characteristics of a cantilever retaining wall and cast-in-place piles are combined, the cast-in-place piles permeate into the ground, loads are applied to one side of a soil body through filler, the bending strength is improved, and the slope protection effect is improved. The adaptability to complex geology is greatly improved, and in a complex foundation of soft soil, the protection structure and a soil body are of a synergistic structure, so that the stability and the overall rigidity of the foundation pit and the protection structure are guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of foundation pit construction, and in particular to a composite foundation pit water-stopping retaining structure system and a construction method thereof under complex geological conditions. Background Art

[0002] The soil layer in coastal areas is complex and soft, with high water content, especially in the Yangtze River Delta, the Pearl River Delta and its annex. For complex terrains with gentle slopes near mountains and soft soil layers, such as reclamation plots on tidal flats near mountains, the geology is even more complex, and the requirements for foundation pits are 2-3 times that of general design specifications to meet the requirements. The seismic coefficients and conventional structural designs given in the existing design specifications cannot meet the seismic stability design requirements in special fields and special complex terrains. When designing the foundation pit, it is difficult to meet the requirements for the embedding depth of the piles. If the foundation pit is five meters deep for a basement, a pile length of 50 meters may not meet the design requirements. In actual construction, it is impossible to construct a 50-meter pile length. In some areas, the requirements are that the embedding depth of the piles reaches 2.5 times the excavation depth of the foundation pit. The building pile foundation specification stipulates that the embedding depth of the piles is 4 divided by the horizontal deformation coefficient of the piles, but for soft soil areas, the embedding depth of piles of this depth often cannot meet the requirements. Summary of the invention

[0003] One object of the present invention is to solve at least the above-mentioned problems through a composite foundation pit water-stopping retaining structure system and a construction method thereof under complex geological conditions.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: a composite foundation pit water-stopping and retaining structure system under complex geological conditions, which includes a slope protection structure and a foundation pit water retaining support structure from the outside to the inside, the slope protection structure includes a foundation pit cement soil mixing wall that fits the pit wall soil and columns and reinforced concrete sprayed layers covering the foundation pit cement soil mixing wall, the cross-section of the foundation pit water retaining support structure is H-shaped, the foundation pit water retaining support structure includes a front composite wall, a wall heel plate, a wall toe plate and rear bored and cast-in-place piles, the wall toe plate and the wall heel plate are horizontally arranged on the inner and outer sides of the front composite wall respectively, one end of the wall heel plate is connected to the foundation pit cement soil mixing wall, and the other end is connected to the middle part of the front composite wall, fillers are filled between the front composite wall, the wall heel plate and the reinforced concrete sprayed layer, one end of the wall toe plate is connected to the middle part of the front composite wall, and the other end is connected to the top of the rear bored and cast-in-place piles.

[0005] Preferably, the foundation pit cement soil mixing wall is inclined toward one side of the wall pit soil body, and its angle with the vertical direction is 10-20 degrees.

[0006] Preferably, the slope protection structure also includes prestressed anchor cables extending into the pit wall body.

[0007] Preferably, a flange is provided on the top of the reinforced concrete sprayed layer, and the flange covers the crown beam on the top of the cement-soil mixing wall of the foundation pit and extends 1-2 meters to one side of the pit wall soil.

[0008] Preferably, the front composite wall comprises a front row of bored cast-in-place piles and a front wall body and a rear wall body covering both sides of the front row of bored cast-in-place piles.

[0009] Preferably, the cross-section of the rear wall is trapezoidal, a rear supporting rib is provided on one side of the rear wall, and a front supporting rib is provided on the reinforced concrete sprayed layer.

[0010] Preferably, a vertically arranged slope protection cement soil mixing wall is provided on one side of the foundation pit cement soil mixing wall close to the pit wall soil.

[0011] Preferably, drainage ditches are provided at the end of the flange and the top of the slope protection cement soil mixing wall, and drainage holes are provided at the bottom of the wall heel plate.

[0012] Preferably, the rear-bored cast-in-place pile row is provided with a second layer of concrete wall toward the foundation pit side, and the second layer of concrete wall is also provided with prestressed anchor cables, which pass through the gaps between the front-bored cast-in-place pile rows and penetrate into the pit wall soil.

[0013] The construction method of the composite foundation pit water-stopping retaining structure system under complex geological conditions includes the following steps:

[0014] Step a: level the site;

[0015] Step b, constructing a foundation pit cement soil mixing wall along the oblique direction near the gentle slope, and then constructing a row of piles along the vertical direction;

[0016] Step c: excavating the first layer of foundation pit after the foundation pit cement soil mixing wall reaches the required strength;

[0017] Step d, constructing a reinforced concrete spraying layer on the foundation pit cement soil mixing wall, now a reinforced wall is sandwiched on the foundation pit cement soil mixing wall, and then the concrete spraying layer is carried out;

[0018] Step e: after the reinforced concrete spraying layer reaches a predetermined strength, the prestressed anchor cable is constructed, and then the front support rib is constructed;

[0019] Step f, constructing a wall heel plate and a wall toe plate at the bottom of the pre-drilled cast-in-place pile row;

[0020] Step g, constructing the front wall and the rear wall on both sides of the front bored cast-in-place pile row;

[0021] Step h, constructing rear supporting ribs on the front wall and the wall heel plate;

[0022] Step i, drilling and pouring piles after construction, the positions of the rear drilling and pouring piles are staggered with those of the front drilling and pouring piles;

[0023] Step j: after the post-drilling and grouting piles reach a predetermined strength, excavate the second foundation pit;

[0024] Step k: construct a waterproof wall on the side of the post-drilling and cast-in-place pile row close to the foundation pit, and apply prestressed anchor cables after the waterproof wall reaches a predetermined strength.

[0025] From the above description, it can be seen that the composite foundation pit water-stopping support structure system and its construction method under complex geological conditions provided by the present invention have the following beneficial effects: the slope protection structure and the foundation pit water-stopping support structure together constitute the foundation pit support suitable for complex geological conditions with soft soil and hard soil layers and adjacent gentle slopes. The slope protection structure uses the foundation pit cement soil mixing wall as the first waterproof curtain, the front composite wall and the rear bored cast-in-place pile row as the second and third waterproof curtains, which can effectively prevent groundwater from seeping into the foundation pit, and further improve the protection through the columns and reinforced concrete spraying layer. The strength of the slope structure, the H-type support structure composed of the front composite wall, wall heel plate, wall toe plate and rear bored cast-in-place pile row, combined with the characteristics of the cantilever retaining wall and cast-in-place piles, the cast-in-place piles penetrate into the ground and apply loads on one side of the soil through the filler to improve the bending strength, greatly improving the adaptability to complex geology. In the complex foundation of soft soil, the protective structure and the soil body cooperate with each other, so that the stability and overall stiffness of the foundation pit and the protective structure are guaranteed, and the prestressed anchor cable, concrete spraying, gravity wall and other structures are used to greatly improve the overall stability. The H-type foundation pit water retaining support structure not only improves the structural strength, but also the width of the first layer of the foundation pit is wider than that of the second layer of the pit, which can effectively improve the space utilization rate and ensure the stability of the deep foundation pit excavation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the composite foundation pit water-stopping and retaining structure system of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described below through specific implementation modes.

[0028] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0029] As shown in the figure, the composite foundation pit water-stopping and retaining structure system under complex geological conditions of the present invention includes a slope protection structure and a foundation pit water retaining support structure from the outside to the inside, the slope protection structure includes a foundation pit cement soil mixing wall 11 that fits the pit wall soil and columns and reinforced concrete spraying layer 12 covering the foundation pit cement soil mixing wall 11, the cross-section of the foundation pit water retaining support structure is H-shaped, the foundation pit water retaining support structure includes a front composite wall 21, a wall heel plate 22, a wall toe plate 23 and a rear bored and cast-in-place row of piles 24, the wall toe plate 23 and the wall heel plate 22 are horizontally arranged on the inner and outer sides of the front composite wall 21, one end of the wall heel plate 22 is connected to the foundation pit cement soil mixing wall 11, and the other end is connected to the middle part of the front composite wall 21, fillers are filled between the front composite wall 21, the wall heel plate 22 and the reinforced concrete spraying layer 12, one end of the wall toe plate 23 is connected to the middle part of the front composite wall 21, and the other end is connected to the top of the rear bored and cast-in-place row of piles 24. The slope protection structure and the foundation pit water retaining support structure are jointly composed of foundation pit support suitable for complex geological conditions with soft soil and hard soil layers and adjacent to gentle slopes. The slope protection structure uses the foundation pit cement soil mixing wall 11 as the first waterproof curtain, the front composite wall 21 and the rear bored cast-in-place pile row 24 as the second and third waterproof curtains, which can effectively prevent groundwater from seeping into the foundation pit. The strength of the slope protection structure is further improved by the columns and reinforced concrete spraying layer 12. The H-shaped support structure composed of the front composite wall 21, the wall heel plate 22, the wall toe plate 23 and the rear bored cast-in-place pile row 24 combines the characteristics of the cantilever retaining wall and the bored pile. The bored pile penetrates into the ground and applies a load on one side of the soil through the filler to improve the bending strength, which greatly improves the adaptability to complex geology. In the complex foundation of soft soil, the protective structure and the soil body are coordinated, so that the stability and overall stiffness of the foundation pit and the protective structure are guaranteed, and the prestressed anchor cable, concrete spraying, gravity wall and other structures are used to greatly improve the overall stability. The H-type foundation pit water retaining support structure not only improves the structural strength, but also the width of the first layer of the foundation pit is wider than the second layer of the pit, which can effectively improve the space utilization rate and ensure the stability of large-depth foundation pit excavation.

[0030] The foundation pit cement soil mixing wall 11 is inclined toward one side of the wall pit soil body, and its angle with the vertical direction is 10-20 degrees. The traditional cement soil mixing piles are arranged vertically, and their support force for the slope is insufficient. The present invention innovatively adopts the cement soil mixing piles constructed obliquely to form the foundation protection of the foundation pit, and combined with the columns and the reinforced concrete spray layer 12, it can further improve the strength and stability of the slope protection structure.

[0031] The slope protection structure also includes a prestressed anchor cable extending into the main body of the pit wall. The inclined prestressed anchor cable penetrates deep into the soil, one end of which is connected to the column and the other end is anchored in a stable rock layer or soil layer deep in the hillside. The friction between the reinforcement and the soil is used to improve the deformation condition of the soil and the engineering properties of the soil, thereby achieving the purpose of stabilizing the soil.

[0032] A flange is provided on the top of the reinforced concrete spraying layer 12, and the flange covers the crown beam on the top of the foundation pit cement soil mixing wall 11 and extends 1-2 meters to one side of the pit wall soil.

[0033] The front composite wall 21 includes a front row of bored cast-in-place piles and a front wall body and a rear wall body covering both sides of the front row of bored cast-in-place piles.

[0034] The cross section of the rear wall is a trapezoid, a rear support rib is provided on one side of the rear wall, and a front support rib is provided on the reinforced concrete spray layer 12. The composite wall composed of the front bored cast-in-place pile row, the wall heel plate 22, the wall toe plate 23, the front wall, the rear wall and the rear support rib has better bending strength than the traditional cantilever retaining wall or bored cast-in-place pile row wall. The front bored cast-in-place pile row extends into the ground, and the bending strength is further improved by fillers on the wall heel plate 22, so that the foundation pit has high stability and can adapt to the foundation pit protection of complex terrain including soft soil foundation and close to gentle slope.

[0035] A vertically arranged slope protection cement soil mixing wall is provided on one side of the foundation pit cement soil mixing wall 11 close to the pit wall soil.

[0036] The end of the flange and the top of the slope protection cement soil mixing wall are both provided with drainage ditches. The bottom of the wall heel plate 22 is provided with a design of drainage holes and multiple drainage ditches, which can guide the water flow from the mountain and reduce the risk of landslides. The drainage holes are used to guide the water in the filling area to be discharged.

[0037] The rear bored cast-in-place pile row 24 is provided with a second layer of concrete wall toward the foundation pit side, and the second layer of concrete wall is also provided with a prestressed anchor cable, which passes through the gaps between the front bored cast-in-place pile rows and penetrates into the pit wall soil. The prestressed anchor cable improves the bending strength of the rear bored cast-in-place pile row 24, and the position of the rear bored cast-in-place pile row 24 is staggered with the front bored cast-in-place pile row, so the structure of the front bored cast-in-place pile row will not be damaged when the hole is rotated.

[0038] The construction method of the composite foundation pit water-stopping retaining structure system under complex geological conditions includes the following steps:

[0039] Step a: level the site;

[0040] Step b, constructing the foundation pit cement soil mixing wall 11 along the oblique direction near the gentle slope, and then constructing the front drilling and pouring pile row along the vertical direction;

[0041] Step c: excavating the first layer of foundation pit after the foundation pit cement soil mixing wall 11 reaches a certain strength;

[0042] Step d, constructing a reinforced concrete spraying layer 12 on the foundation pit cement soil mixing wall 11, now a reinforced wall is sandwiched on the foundation pit cement soil mixing wall 11, and then the concrete spraying layer is carried out;

[0043] Step e: After the reinforced concrete sprayed layer 12 reaches a predetermined strength, the prestressed anchor cable is constructed, and then the front support rib is constructed;

[0044] Step f, constructing the wall heel plate 22 and the wall toe plate 23 at the bottom of the front bored cast-in-place pile row;

[0045] Step g, constructing the front wall and the rear wall on both sides of the front bored cast-in-place pile row;

[0046] Step h, constructing rear supporting ribs on the front wall and the wall heel plate 22;

[0047] Step i, constructing rear bored cast-in-place pile rows 24, wherein the positions of the rear bored cast-in-place pile rows 24 are staggered with those of the front bored cast-in-place pile rows;

[0048] Step j: after the post-drilling and grouting piles 24 reach a predetermined strength, excavate the second foundation pit;

[0049] Step k, construct a waterproof wall near the side of the foundation pit after the post-drilling and pouring pile row 24, and apply prestressed anchor cables after the waterproof wall reaches a predetermined strength. There is a certain silt layer in the soft soil foundation pit. When applying the composite spray anchor technology in the silt layer, the following points should be noted: 1) During the well point dewatering process in the foundation pit, the distance from the slope should not be too small, otherwise the slope support surface at the bottom of the base layer will always be at the place with the largest hydraulic slope, which will cause the base silt layer in the foundation pit to be squeezed outward and the slope will be unstable. 2) When setting anchors in the silt layer, the length and direction of the anchors should be appropriately changed so that the anchors are firmly anchored in the non-silt layer and have the required anchoring length. 3) The silt layer at the bottom of the slope in the soft soil foundation pit needs to be reinforced. Steel pipe piles can be selected for reinforcement to avoid the possibility of silt sliding into the foundation pit. Micro crushed stone grouting piles can be selected for the reinforcement of the silt layer, and the construction process is hole forming, diameter steel pipe setting, lower diameter crushed stone and grouting, etc. In the construction of soft soil basement, it is necessary to reasonably control the surrounding temporary loads. The present invention adopts composite support construction technology, so that the horizontal displacement of its slope is relatively small and the stability is good. The composite support structure can actively support the foundation pit soil and work in coordination with the soil. The steel mesh spray layer in the spray anchor support structure has good flexibility and integrity. The H-type foundation pit water retaining support structure has good stability, so that the internal stress distribution of the spray layer and the anchor rod is effectively adjusted. Practice shows that the composite spray anchor technology has good practical application effects in soft soil foundation pits.

[0050] The above are only some specific implementation methods of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial changes to the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. Composite foundation pit water-stopping and retaining structure system under complex geological conditions, characterized by: From the outside to the inside, it includes a slope protection structure and a foundation pit water retaining support structure. The slope protection structure includes a foundation pit cement soil mixing wall that fits the pit wall soil and columns and reinforced concrete spraying layers covering the foundation pit cement soil mixing wall. The cross-section of the foundation pit water retaining support structure is H-shaped. The foundation pit water retaining support structure includes a front composite wall, a wall heel plate, a wall toe plate and rear bored and cast-in-place piles. The wall toe plate and the wall heel plate are horizontally arranged on the inner and outer sides of the front composite wall respectively. One end of the wall heel plate is connected to the foundation pit cement soil mixing wall, and the other end is connected to the middle part of the front composite wall. Filling is filled between the front composite wall, the wall heel plate and the reinforced concrete spraying layer. One end of the wall toe plate is connected to the middle part of the front composite wall, and the other end is connected to the top of the rear bored and cast-in-place piles.

2. The composite foundation pit water-stopping and retaining structure system under complex geological conditions according to claim 1 is characterized by: The foundation pit cement soil mixing wall is inclined toward one side of the foundation pit soil body, and its angle with the vertical direction is 10-20 degrees.

3. The composite foundation pit water-stopping and retaining structure system under complex geological conditions according to claim 1 is characterized by: The slope protection structure also includes a prestressed anchor cable extending into the pit wall body.

4. The composite foundation pit water-stopping and retaining structure system under complex geological conditions according to claim 1 is characterized by: A flange is provided on the top of the reinforced concrete spraying layer, and the flange covers the crown beam on the top of the cement-soil mixing wall of the foundation pit and extends 1-2 meters to one side of the pit wall soil body.

5. The composite foundation pit water-stopping and retaining structure system under complex geological conditions according to claim 1 is characterized by: The front composite wall comprises a front row of bored cast-in-place piles and a front wall body and a rear wall body covering both sides of the front row of bored cast-in-place piles.

6. The composite foundation pit water-stopping and retaining structure system under complex geological conditions according to claim 1 is characterized by: The cross section of the rear wall is trapezoidal, a rear supporting rib is provided on one side of the rear wall, and a front supporting rib is provided on the reinforced concrete sprayed layer.

7. The composite foundation pit water-stopping and retaining structure system under complex geological conditions according to claim 1 is characterized by: A vertically arranged slope protection cement soil mixing wall is provided on one side of the foundation pit cement soil mixing wall close to the pit wall soil body.

8. The composite foundation pit water-stopping and retaining structure system under complex geological conditions according to claim 1 is characterized by: The end of the flange and the top of the slope protection cement soil mixing wall are both provided with drainage ditches, and the bottom of the wall heel plate is provided with drainage holes.

9. The composite foundation pit water-stopping and retaining structure system under complex geological conditions according to claim 1 is characterized by: The rear bored cast-in-place pile row is provided with a second layer of concrete wall toward the foundation pit side, and the second layer of concrete wall is also provided with prestressed anchor cables, which pass through the gaps between the front bored cast-in-place pile rows and penetrate into the pit wall soil.

10. The construction method of the composite foundation pit water-stopping retaining structure system under complex geological conditions according to claims 1-9, characterized in that: The steps include: Step a: level the site; Step b, constructing a foundation pit cement soil mixing wall along the oblique direction near the gentle slope, and then constructing a row of piles along the vertical direction; Step c: excavating the first layer of foundation pit after the foundation pit cement soil mixing wall reaches the required strength; Step d, constructing a reinforced concrete spraying layer on the foundation pit cement soil mixing wall, now a reinforced wall is sandwiched on the foundation pit cement soil mixing wall, and then the concrete spraying layer is carried out; Step e: after the reinforced concrete spraying layer reaches a predetermined strength, the prestressed anchor cable is constructed, and then the front support rib is constructed; Step f, constructing a wall heel plate and a wall toe plate at the bottom of the pre-drilled cast-in-place pile row; Step g, constructing the front wall and the rear wall on both sides of the front bored cast-in-place pile row; Step h, constructing rear supporting ribs on the front wall and the wall heel plate; Step i, drilling and pouring piles after construction, the positions of the rear drilling and pouring piles are staggered with those of the front drilling and pouring piles; Step j: after the post-drilling and grouting piles reach a predetermined strength, excavate the second foundation pit; Step k: construct a waterproof wall on the side of the post-drilling and cast-in-place pile row close to the foundation pit, and apply prestressed anchor cables after the waterproof wall reaches a predetermined strength.

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