Foundation structure and construction method of building with high backfill and weak expansive soil in strong karst area

Abstract

The present invention discloses a high-backfill weak expansive soil building foundation structure in a strong karst area, comprising: a karst layer; a backfill layer disposed above the karst layer, with multiple groups of cast-in-place pile assemblies spaced apart within the backfill layer, each group of cast-in-place pile assemblies comprising: porous pipe piles embedded within the backfill layer, with multiple groups of through holes extending vertically through the sidewalls of the porous pipe piles, the porous pipe piles being hollow within the interior; cast-in-place piles with gaps extending through the porous pipe piles, with elastic portions disposed within the gaps between the cast-in-place piles and the porous pipe piles; and a concrete layer cast above the backfill layer, wherein the upper and lower ends of the cast-in-place piles are respectively located within the karst layer and the backfill layer. The present invention achieves the beneficial effects of reducing foundation structure settlement and deformation and increasing foundation bearing capacity by sequentially connecting the concrete layer, backfill layer, and karst layer from top to bottom through the cast-in-place pile assembly consisting of the porous pipe piles and cast-in-place piles.

Description

Technical Field

[0001] The present invention relates to the technical field of building construction, and more particularly to a high-backfill weak expansive soil building foundation structure and a construction method in a strong karst area. Background Art

[0002] In mountainous areas of karst regions, high backfill and strong karst areas are bound to be formed due to the flatness of the site and the balance of excavation and filling of earth and stone.

[0003] Expansive soil is a highly plastic clay with characteristics such as high water absorption, strong plasticity, shrinkage due to water loss, and softening upon immersion. These characteristics pose significant safety challenges to buildings constructed on expansive soil foundations. Based on their free expansion rate, standard moisture content, and plasticity index, soils are classified as non-expansive, weakly expansive, moderately expansive, and strongly expansive. Weakly expansive soils have an expansion rate of 40% to 60%. Based on economic and practical principles, weakly expansive soils are often treated and used as backfill in karst areas to create expansive soil karst foundations. Buildings constructed on expansive soil karst foundations are prone to problems such as uneven foundation settlement, insufficient bearing capacity, and collapse or sliding. Foundation treatment is essential to ensure the long-term stability of the structure.

[0004] In areas with high backfill and strong karst rock, foundation treatment technologies such as CFG piles, reinforced concrete piles, and prestressed pipe piles are often used to form pile-type foundation structures to increase the stability and bearing capacity of high-backfill, weak expansive soil foundations in strong karst regions. For example, patent application number 201710258547.5 discloses an end-bearing rigid pile composite foundation and its construction method. By adjusting the pile top cushion layer, the single pile load mode is end-bearing, which is used to adjust the settlement and deformation of the raft foundation to facilitate construction and save time and cost. However, this foundation structure is mainly used in strong karst regions with high groundwater levels and is not suitable for high backfill and strong karst rock regions using weak expansive soil backfill. Therefore, how to design a high-backfill, weak expansive soil building foundation structure in strong karst regions to achieve the beneficial effects of stable foundation structure, reduced foundation deformation, and sufficient bearing capacity is worthy of careful consideration. Summary of the Invention

[0005] An object of the present invention is to solve at least the above problems and to provide at least the advantages which will be described hereinafter.

[0006] In order to achieve these purposes and other advantages according to the present invention, a high-backfill weak expansive soil building foundation structure in a strong karst area is provided, comprising:

[0007] karst layer;

[0008] A backfill layer is provided above the karst layer, wherein a plurality of groups of cast-in-place pile assemblies are provided at intervals in the backfill layer, and each group of cast-in-place pile assemblies includes:

[0009] A porous pipe pile is buried in the backfill layer, wherein the side wall of the porous pipe pile is provided with a plurality of through holes extending vertically therethrough, and the interior of the porous pipe pile is hollow;

[0010] A cast-in-place pile, the gap of which is provided through the porous pipe pile, and an elastic portion is provided in the gap between the cast-in-place pile and the porous pipe pile;

[0011] a concrete layer, which is poured above the backfill layer;

[0012] Wherein, the upper and lower ends of the cast-in-place pile are respectively located in the karst layer and the backfill layer.

[0013] Preferably, the cast-in-place pile assembly further comprises a plurality of side grouting pipes, which are located between the porous pipe piles and the karst layer and arranged around the lower end of the cast-in-place piles, and are filled with concrete.

[0014] Preferably, the elastic portion includes a plurality of arc-shaped spring plates, the arc-shaped opening ends of the arc-shaped spring plates are provided on the side walls of the cast-in-place piles, and the arc surfaces of the arc-shaped spring plates face the porous pipe piles and abut against the through holes.

[0015] Preferably, the arc-shaped cavity formed between the arc-shaped spring plate and the cast-in-place pile is filled with rubber particles.

[0016] Preferably, the backfill soil in the backfill layer is modified weak expansive soil, and the modified weak expansive soil contains lime and weak expansive soil in a mass ratio of 3:7-10.

[0017] Preferably, the porous pipe piles are buried in the backfill soil to a depth exceeding the atmospheric influence depth.

[0018] Provided is a construction method for a high-backfill weak expansive soil building foundation structure in a strong karst area, comprising the following steps:

[0019] Step 1: Prefabricate the porous pipe piles with hollow interior in a prefabrication plant;

[0020] Step 2: inserting a steel hollow tube into the porous pipe pile, and then casting and sealing the upper and lower ends of the porous pipe pile, wherein a curved spring plate is provided between the porous pipe pile and the steel hollow tube, and the curved spring plate abuts against the through hole of the porous pipe pile;

[0021] Step 3: Pre-drilling holes in the karst layer to form pilot holes, and then hanging porous pipe piles until the hollow steel pipe is inserted into the pilot hole;

[0022] Step 4: After backfilling the backfill soil to a certain height, pour concrete multiple times on the upper end of the steel hollow tube. The concrete forms a hard soil layer with the backfill soil through the side pouring pipe. The steel hollow tube is poured to form the cast-in-place pile. Continue backfilling and compacting to form the backfill layer.

[0023] Step 5: pouring concrete on the backfill layer until the cast-in-place piles are covered to form the concrete layer.

[0024] The present invention has at least the following beneficial effects:

[0025] First, the present invention achieves the beneficial effects of reducing the settlement and deformation of the foundation structure and increasing the bearing capacity of the foundation by connecting the concrete layer, backfill layer and karst layer from top to bottom through a cast-in-place assembly composed of porous pipe piles and cast-in-place piles.

[0026] Second, the present invention provides a curved spring plate between the bored pile and the porous pipe pile to resist the lateral deformation caused by water immersion or water loss in the expansive soil, thereby reducing the settlement deformation of the foundation structure. In addition, the curved cavity of the curved spring plate is filled with rubber particles, thereby increasing the structural stability of the elastic part without affecting its compression deformation or rebound deformation performance.

[0027] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A side sectional view of the building foundation structure according to one of the technical solutions of the present invention;

[0029] Figure 2 A side sectional view of the cast-in-place pile assembly according to one of the technical solutions of the present invention;

[0030] Figure 3 This is a side view of the cast-in-place pile assembly according to one of the technical solutions of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be described in further detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0032] It should be noted that the experimental methods described in the following embodiments are conventional methods unless otherwise specified, and the reagents and materials are commercially available unless otherwise specified; in the description of the present invention, the orientation or positional relationship indicated by the terms is based on the orientation or positional relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply 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.

[0033] like Figures 1 to 3 As shown, the present invention provides a high backfill weak expansive soil building foundation structure in a strong karst area, comprising:

[0034] Karst layer 1; the karst layer 1 is soluble rock above the cave, which includes carbonate rocks such as limestone, gypsum, etc., and the karst layer 1 may contain caves;

[0035] A backfill layer 2 is provided above the karst layer 1. A plurality of groups of cast-in-place pile assemblies 3 are provided in the backfill layer 2 at intervals. Each group of cast-in-place pile assemblies 3 includes:

[0036] The porous pipe piles 31 are buried in the backfill layer 2. The side walls of the porous pipe piles 31 are provided with a plurality of through holes 33 extending vertically therethrough. The interior of the porous pipe piles 31 is hollow. Specifically, the backfill soil of the backfill layer 2 may be weak expansive soil or modified weak expansive soil. The porous pipe piles 31 may be prefabricated by pouring C30 concrete. During prefabrication, the prefabricated porous pipe piles 31 are buried in the backfill layer 2 backfilled with weak expansive soil. A plurality of through holes 33 are provided from top to bottom on the side walls of the porous pipe piles 31. Two adjacent groups of through holes 33 are interconnected and communicate with the interior of the porous pipe piles 31, so as to leave a certain space for accommodating the increased volume of the backfill soil when it is immersed in water and for resisting the lateral deformation of the backfill layer 2 when it is immersed in water and expands.

[0037] A bored pile 32 is provided with a gap through the porous pipe pile 31, and an elastic portion 34 is provided in the gap between the bored pile 32 and the porous pipe pile 31. Specifically, the bored pile 32 can be formed by pouring concrete multiple times through a steel hollow pipe. After a guide hole is drilled in the karst layer 1 by a drilling machine, the steel hollow pipe is placed in the guide hole and concrete is poured to form the bored pile 32. The porous pipe pile 31 is sleeved on the bored pile 32, and an elastic portion 34 is provided in the gap. The elastic portion 34 is laterally abutted against the through hole 33, and two adjacent elastic portions 34 abut against each other in upper and lower directions, so as to resist lateral deformation of the backfill layer 2 caused by water immersion or water loss in the expansive soil.

[0038] A concrete layer 4 is cast above the backfill layer 2; the concrete layer 4 is formed by casting C30-C35 concrete and has a certain strength so that a building can be constructed on the foundation structure and the concrete layer 4;

[0039] Among them, the upper and lower ends of the cast-in-place piles 32 are respectively located in the karst layer 1 and the backfill layer 2; specifically, the karst layer 1 and the backfill layer 2 are fixedly connected by the cast-in-place piles 32 to jointly bear the dynamic and static loads from the upper layer of the foundation structure, so as to achieve the beneficial effect of stabilizing the foundation structure.

[0040] In the above technical solution, a plurality of guide holes are obtained by drilling holes on the top surface of the karst layer 1 where a karst cave exists, and a plurality of prefabricated cast-in-place piles 32 of porous pipe piles 31 are fixed in the plurality of guide holes respectively. Then, backfill soil is backfilled on the karst layer 1 and compacted to obtain the backfill layer 2, and concrete is poured on the backfill layer 2 to form the concrete layer 4. The concrete layer 4, the backfill layer 2, and the karst layer 1 are fixedly connected to form the pile-type foundation structure, which has the advantages of large bearing capacity. The backfill soil can be expansive soil or weak expansive soil, and the height of the backfill layer 2 is located at the bottom of the porous pipe pile. The height of the pile 31 is between that of the cast-in-place pile 32, and when the backfill layer 2 filled with expansive soil expands when it is soaked in water, the through holes 33 and the elastic part 34 provided on the porous pipe pile 31 can resist the lateral expansion and deformation problem caused by the immersion of the expansive soil, thereby reducing the expansion, extrusion and uplift deformation of the backfill layer 2, and further reducing the deformation of the foundation structure; when the backfill layer 2 loses water and shrinks, the compressed elastic part 34 produces rebound deformation, which is laterally transmitted through the radial through holes 33 on the porous pipe pile 31, so that the lateral expansion deformation caused by the expansive soil can be restored, thereby reducing the settlement deformation of the foundation structure.

[0041] In another technical solution, the bored pile assembly 3 further comprises a plurality of side grouting pipes 35, which are located between the porous pipe piles 31 and the karst layer 1 and are arranged on the circumferential side of the lower end of the bored piles 32, and the side grouting pipes 35 are poured with concrete; wherein the side grouting pipes 35 are located between the karst layer 1 and the lower end of the porous pipe piles 31, and the side grouting pipes 35 are poured with concrete together with the bored piles 32, and the concrete is poured by the side grouting pipes 35 and is combined and fixed with the backfill soil at the bottom of the backfill layer 2 to form a hard soil layer on the karst layer 1, so that the backfill soil in contact with the karst layer 1 becomes more compacted and the gaps are reduced, and the backfill soil and the rock of the karst layer 1 form a whole, thereby increasing the surrounding extrusion and solidification friction, thereby reducing the settlement of the foundation structure.

[0042] In another technical solution, the elastic portion 34 includes a plurality of arc-shaped spring plates, the arc-shaped open ends of the arc-shaped spring plates are arranged on the side walls of the cast-in-place piles 32, and the arc surfaces of the arc-shaped spring plates face the porous pipe piles 31 and abut against the through holes 33; the material of the arc-shaped spring plates can be spring steel, rubber or latex, and the arc-shaped setting of the arc-shaped spring plates can abut against the pressure of the expansive soil on the porous pipe piles 31 after it is soaked in water and expanded.

[0043] In another technical solution, the arc-shaped cavity formed between the arc-shaped spring plate and the cast-in-place pile 32 is filled with rubber particles; specifically, the rubber particles are mainly produced by processing various waste rubbers including waste rubber, tourist shoe soles, scraps, cable skins, rubber scraps, automobile pads, automobile tires and other waste rubber raw materials, and have a certain elasticity. The rubber particles fill the arc-shaped cavity to form the elastic part 34, which increases its structural stability without affecting its compression deformation or rebound deformation performance.

[0044] In another technical solution, the backfill soil in the backfill layer 2 is modified weak expansive soil, and the modified weak expansive soil contains lime and weak expansive soil in a mass ratio of 3:7 to 10; specifically, lime and common weak expansive soil or expansive soil are stirred and mixed evenly in a mass ratio of 3:8 to obtain modified weak expansive soil, wherein the lime can effectively inhibit the expansion and contraction tendency of the weak expansive soil and increase the soil strength to reduce the settlement deformation of the backfill layer 2.

[0045] In another technical solution, the depth at which the porous pipe piles 31 are buried in the backfill soil exceeds the atmospheric influence depth; wherein, the atmospheric influence depth refers to the effective depth of the soil's ups and downs deformation caused by factors such as precipitation, evaporation, and ground temperature under the action of natural climate. Its value should be determined by deep deformation observations or water content observations and ground temperature observations of soil in various climate zones. If there is no data, the value can be taken according to the provisions of relevant specifications. The common atmospheric influence depth range is 3m to 5m. The depth at which the porous pipe piles 31 are buried in the backfill soil is greater than the atmospheric influence depth, which further ensures that the backfill layer 2 can bear the static load transmitted by the building in the case of water loss and shrinkage, and transmit it to below the atmospheric influence depth.

[0046] Provided is a construction method for a high-backfill weak expansive soil building foundation structure in a strong karst area, comprising the following steps:

[0047] Step 1: Prefabricate the hollow porous pipe pile 31 in a prefabrication plant; specifically, use C30 concrete formwork to cast and prefabricate the hollow porous pipe pile 31;

[0048] Step 2: Insert a hollow steel pipe into the porous pipe pile 31, and then cast and seal the upper and lower ends of the porous pipe pile 31. A curved spring plate is provided between the porous pipe pile and the hollow steel pipe, and the curved spring plate abuts against the through-hole of the porous pipe pile. Specifically, the upper and lower ends of the porous pipe pile 31 are cast and sealed by a supporting formwork, and the top of the curved spring plate abuts against the through-hole of the porous pipe pile 31 so as to abut against the lateral expansion deformation caused by water immersion of the expansive soil. The curved spring plate also has a certain elasticity to generate rebound deformation when the backfill layer 2 loses water and shrinks, thereby recovering the expansion deformation of the expansive soil.

[0049] Step 3: Pre-drill holes on the karst layer 1 to form guide holes, and then hang the porous pipe piles 31 until the steel hollow pipes are inserted into the guide holes. Specifically, a drilling machine is used to drill multiple guide holes in the karst layer 1, and the prefabricated steel hollow pipes made of porous pipe piles 31 are hung until they are inserted into the guide holes. A tamping machine is used to firmly tamp the steel hollow pipes into the guide holes, wherein multiple side perfusion pipes 35 are welded and connected between the steel hollow pipes and the karst layer 1.

[0050] Step 4: After backfilling the backfill soil to a certain height, pour concrete multiple times on the upper end of the steel hollow tube, and the concrete forms a hard soil layer with the backfill soil through the side grouting pipe 35. After the steel hollow tube is grouting to form the cast-in-place pile 32, continue backfilling and compacting to form the backfill layer 2; wherein, the backfill soil is weak expansive soil modified by lime. After backfilling the backfill soil to cover the side grouting pipe 35, pour concrete multiple times on the upper end of the steel hollow tube, and the concrete flows into the fluffy backfill soil through the side grouting pipe 35, and is fixed with it to form a hard soil layer, so that the backfill soil in contact with the karst layer 1 becomes more compacted and the gap is reduced, and forms a whole with the backfill soil and the rock of the karst layer 1, thereby increasing the surrounding extrusion and solidification friction, thereby reducing the settlement of the foundation structure, and after the steel hollow tube is grouting to obtain the cast-in-place pile 32, continue backfilling and compacting until it covers the porous pipe pile 31 to obtain the backfill layer 2;

[0051] Step 5: pour concrete on the backfill layer 2 until it covers the bored piles 32 to form the concrete layer 4. Specifically, support the formwork on the backfill layer 2 and pour C30 concrete until it covers the upper ends of the bored piles 32. After the curing meets the requirements, the concrete layer 4 is formed.

[0052] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. High backfill weak expansive soil building foundation structure in strong karst areas, characterized by: include: karst layer; A backfill layer is provided above the karst layer, wherein a plurality of groups of cast-in-place pile assemblies are provided at intervals in the backfill layer, and each group of cast-in-place pile assemblies includes: A porous pipe pile is buried in the backfill layer, wherein the side wall of the porous pipe pile is provided with a plurality of through holes penetrating the side wall, and the interior of the porous pipe pile is hollow; A cast-in-place pile is inserted into the porous pipe pile and has a gap with the porous pipe pile, and an elastic part is provided in the gap between the cast-in-place pile and the porous pipe pile; a concrete layer poured above the backfill layer; Wherein, the upper and lower ends of the cast-in-place pile are respectively located in the karst layer and the backfill layer.

2. The high backfill weak expansive soil building foundation structure in strong karst areas according to claim 1, characterized in that: The cast-in-place pile assembly further comprises a plurality of side cast-in-place pipes, which are located between the porous pipe pile and the karst layer and arranged around the lower end of the cast-in-place pile. Concrete is cast in the side cast-in-place pipes.

3. The high backfill weak expansive soil building foundation structure in a strong karst area according to claim 1, characterized in that: The elastic part includes a plurality of arc-shaped spring plates, the arc-shaped opening ends of the arc-shaped spring plates are arranged on the side walls of the cast-in-place piles, the arc surfaces of the arc-shaped spring plates face the porous pipe piles and abut against the through holes.

4. The high backfill weak expansive soil building foundation structure in a strong karst area according to claim 3, characterized in that: The arc-shaped cavity formed between the arc-shaped spring plate and the cast-in-place pile is filled with rubber particles.

5. The high backfill weak expansive soil building foundation structure in strong karst areas according to claim 1, characterized in that: The backfill soil in the backfill layer is modified weak expansive soil, and the modified weak expansive soil contains lime and weak expansive soil in a mass ratio of 3:7-10.

6. The high backfill weak expansive soil building foundation structure in strong karst areas according to claim 5, characterized in that: The depth at which the porous pipe piles are buried in the backfill soil exceeds the atmospheric influence depth.

7. The construction method of the high backfill weak expansive soil building foundation structure in a strong karst area as claimed in claim 2, characterized in that: The following steps are involved: Step 1: Prefabricate the porous pipe piles with hollow interior in a prefabrication plant; Step 2: inserting a steel hollow tube into the porous pipe pile, and then casting and sealing the upper and lower ends of the porous pipe pile, wherein a curved spring plate is provided between the porous pipe pile and the steel hollow tube, and the curved spring plate abuts against the through hole of the porous pipe pile; Step 3: Pre-drilling a hole in the karst layer to form a guide hole, and then hanging a porous pipe pile until the hollow steel pipe is inserted into the guide hole; Step 4: After backfilling the backfill soil to a height that covers the side grouting pipes, pour concrete multiple times on the upper end of the steel hollow pipe. The concrete forms a hard soil layer with the backfill soil through the side grouting pipes. The steel hollow pipe is poured to form the cast-in-place pile. Continue backfilling and compacting to form the backfill layer. Step 5: pouring concrete on the backfill layer until the cast-in-place piles are covered to form the concrete layer.

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