Reinforcement structure and construction method of collapsible loess foundation in underground chamber

Abstract

The present invention discloses a collapsible loess foundation reinforcement structure and construction method for an underground chamber, comprising a chamber, initial support and advance support applied to the chamber, wherein locking anchor rods are driven into the feet of the initial support; the initial support is provided with a grid steel frame, and micropiles are arranged between the grid steel frames, wherein the micropiles pass through the collapsible loess layer and penetrate into the non-collapsed loess layer. The present invention achieves the treatment of the collapsible loess foundation within a dark excavated chamber, which can effectively reduce the amount of loess collapse and reduce safety risks during its service life. It has the advantages of strong structural integrity, easy to ensure construction quality, and little impact on the surrounding environment, effectively expanding the conditions for constructing underground chambers in self-weight collapsible loess areas.

Description

Technical Field

[0001] The invention belongs to the technical field of underground tunnel foundation construction, in particular to an underground chamber collapsible loess foundation reinforcement structure and a construction method. Background Art

[0002] Collapsible loess is an unsaturated, undercompacted soil with large pores and vertical joints. Under natural moisture, it has low compressibility and high strength. However, when soaked in water under a certain pressure, the soil structure rapidly deteriorates and produces significant additional subsidence, posing a significant hazard to buildings and structures. In recent years, with the development of urban subway construction in my country, an increasing number of subway lines have been built, and many subway tunnels inevitably need to pass through collapsible loess sites. Construction of subway tunnels in non-self-weight collapsible loess sites is generally not treated. However, for self-weight collapsible loess sites, when the stratum is soaked in water, the structural foundation will collapse and deform under the action of its own weight. If left untreated, this will pose a significant risk to the tunnel structure and operational safety.

[0003] When it comes to collapsible loess foundations, commonly used treatment methods include cushioning, dynamic compaction, compaction, grouting, and pre-soaking. These methods were developed in engineering practices other than underground tunnels and have been widely used. However, there is still a lack of relevant research results on the treatment of collapsible loess in underground tunnels.

[0004] The present invention proposes an underground chamber collapsible loess foundation reinforcement structure and construction method, which provides a method for treating the base self-weight collapsible loess in a dark-excavated chamber. The structure has the advantages of strong structural integrity, easy to ensure construction quality, and little impact on the surrounding environment. The structure can effectively reduce the collapsible deformation of the self-weight collapsible loess, enhance the safety of the structure, and effectively expand the conditions for constructing underground chambers in self-weight collapsible loess areas. Summary of the Invention

[0005] In response to the above-mentioned problems, the present invention proposes a collapsible loess foundation reinforcement structure and construction method for an underground chamber. The specific scheme is as follows:

[0006] An underground cavern collapsible loess foundation reinforcement structure, characterized in that: it comprises a cavern, initial support and advance support are applied on the cavern, and locking anchor rods are driven at the feet of the initial support;

[0007] The initial support is provided with a grid steel frame, micro piles are arranged between the grid steel frames, and the micro piles pass through the collapsible loess layer and penetrate into the non-collapsed loess layer.

[0008] Preferably, the micro pile has pile foundation main reinforcement, and the pile foundation main reinforcement is welded to the grid steel frame as a whole.

[0009] Preferably, the initial support is provided with steel mesh on the soil-facing side and the soil-repelling side of the grid steel frame.

[0010] Further preferably, the grid steel frame includes a plurality of grid main bars and a plurality of grid U-shaped bars, the grid main bars are welded to each other via the grid U-shaped bars, and the grid main bars and the pile foundation main bars are welded to each other.

[0011] Further preferably, a secondary lining is applied on the initial support to further reinforce the chamber and meet its functional requirements.

[0012] The second purpose of the present invention is:

[0013] A construction method for reinforcing a collapsible loess foundation of an underground chamber, a collapsible loess foundation reinforcement structure of an underground chamber, wherein the chamber is divided into four parts, namely, part I, part II, part III and part IV, for construction, and comprises the following steps:

[0014] Step 1: Carry out advance support of part I, excavate part I of the soil, and carry out initial support and temporary intermediate partition wall;

[0015] Specifically, the advanced support of Part I was carried out, grouting was carried out to reinforce the ground, core soil was reserved, the soil of Part I was excavated, the initial support and temporary intermediate partition wall of Part I were carried out, and locking anchors were installed at the foot of the initial support.

[0016] Step 2: Excavate the soil of Part II, construct initial support and temporary partition walls, and reinforce the foundation with micro piles inside the chamber;

[0017] Specifically, the soil of Part II was excavated, initial support and temporary partition walls were constructed for Part II, and micropiles were constructed between the initial support grid steel frames for foundation treatment.

[0018] Step 3: Carry out advanced support for Section III, excavate the soil for Section III, and carry out initial support and temporary intermediate partition walls;

[0019] Specifically, the advanced support of Section III was implemented, grouting was used to reinforce the ground, core soil was reserved, the soil of Section III was excavated, the initial support and temporary intermediate partition wall of Section III were implemented, and locking anchors were installed at the foot of the initial support.

[0020] Step 4: Excavate the soil of Part IV, construct initial support and temporary partition wall, and reinforce the foundation with micro piles inside the chamber;

[0021] Specifically, the soil of Section IV will be excavated, initial support and temporary partition walls will be constructed for Section IV, and micropiles will be constructed between the initial support grid steel frames for foundation treatment.

[0022] Step 5: Remove the temporary partition wall in sections and apply secondary lining concrete;

[0023] Specifically, the temporary partition wall is dismantled in sections from top to bottom and secondary lining is applied.

[0024] Preferably, the feature is that when the chamber is excavated, the front and rear offset of parts I, II, III and IV of the chamber should be no less than 15m. After parts II and IV are respectively connected, micro piles are constructed inside the chambers of parts II and IV.

[0025] Preferably, when performing initial support, holes are reserved at the micropile positions for constructing micropiles. After the initial support reaches the design strength, the micropiles are constructed and then the reserved holes on the initial support are sealed.

[0026] Preferably, the micropiles are constructed using a dry drilling process and a skip-driving method. The spacing of the micropiles along the width of the chamber is 700 mm. In order to avoid hole collapse, casing is used to protect the holes. The casing mouth is 10 cm above the ground. The allowable deviation of the pile position plane does not exceed 20 mm, and the verticality deviation of the pile body does not exceed 1%.

[0027] The beneficial effects of the present invention are:

[0028] 1. Steel mesh is set on both the soil-facing side and the soil-receiving side of the initial support of the cavern, and the steel bars of the micro piles are welded to the grid steel frame of the initial support of the cavern, which enhances the integrity of the structure and effectively improves its ability to resist uneven settlement and deformation.

[0029] 2. During the initial support construction of the cavern, holes are reserved at the pile positions of the micropiles. The micropiles are implemented after the initial support of the cavern sections is connected. The construction process is simple, there is no cross-operation, and the construction quality is easy to ensure, which effectively expands the conditions for constructing underground caverns in loess areas prone to self-weight collapse.

[0030] This method allows for the treatment of collapsible loess foundations within a concealed excavation chamber, resulting in low noise and vibration during construction and minimal impact on the surrounding environment. This method effectively reduces the amount of collapsible loess, improves the bearing capacity of the foundation, and thus reduces safety risks during its service life. Furthermore, the method offers flexibility and requires a small construction site, with a plan size of 0.8m x 1.8m and a clearance height of 2.2m meeting construction requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that these drawings are designed for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless otherwise specified, these drawings are intended only to conceptually illustrate the structures described herein and are not necessarily drawn to scale.

[0032] Figure 1 This is a cross-sectional view of the initial support of the foundation reinforcement treatment solution of the present invention;

[0033] Figure 2 It is a longitudinal section diagram of the foundation reinforcement treatment scheme of the present invention;

[0034] Figure 3 This is a cross-sectional view of the underground chamber of the present invention after it is penetrated;

[0035] Figure 4 It is a plan view of the connection between the micro pile and the primary support grid of the underground chamber;

[0036] Figure 5 This is a cross-sectional view of the connection between the micro pile and the primary support grid of the underground chamber;

[0037] Figure 6 It is a flow chart of the construction method of the present invention.

[0038] In the picture:

[0039] 1- Initial support; 2- Advanced support; 3- Locking anchor rod; 4- Temporary intermediate partition wall; 5- Micro pile; 6- Secondary lining; 7- Grille main reinforcement; 8- Grille U-shaped reinforcement; 9- Pile foundation main reinforcement. DETAILED DESCRIPTION

[0040] First of all, it should be noted that the specific structure, features and advantages of the present invention will be described in detail below by way of example. However, all descriptions are for illustration only and should not be understood as limiting the present invention. In addition, any single technical feature described or implied in the embodiments mentioned herein, or any single technical feature shown or implied in the drawings, can still be combined or deleted between these technical features to obtain more other embodiments of the present invention that may not be directly mentioned herein. In addition, in order to simplify the drawings, the same or similar technical features may be marked in only one place in the same drawing.

[0041] In the present invention, unless otherwise clearly stipulated and limited, the terms "install", "set", "connect", "fix", "screw" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, ordinary technicians in this field can understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0042] The following is combined with Figure 1 -Attached Figure 6 The present invention will be described in detail. Example 1

[0043] An underground cavern collapsible loess foundation reinforcement structure is characterized by comprising a cavern, an initial support 1 and an advance support 2 being applied on the cavern, and a locking anchor rod 3 being driven at the foot of the initial support 1;

[0044] The initial support 1 is provided with a grid steel frame, and micro piles 5 are arranged between the grid steel frames. The micro piles 5 pass through the collapsible loess layer and penetrate into the non-collapsed loess layer.

[0045] Furthermore, in the embodiment, it can also be considered that the micro pile 5 has pile foundation main reinforcement 9, and the pile foundation main reinforcement 9 is welded to the grid steel frame as a whole.

[0046] Furthermore, in the embodiment, it can also be considered that the initial support 1 is provided with steel meshes on the soil-facing side and the soil-removing side of the grid steel frame.

[0047] Furthermore, in the embodiment, it can also be considered that the grid steel frame includes multiple grid main bars 7 and multiple grid U-shaped bars 8, the grid main bars 7 are welded to each other through the grid U-shaped bars 8, and the grid main bars 7 and the pile foundation main bars 9 are welded to each other.

[0048] Furthermore, in the embodiment, it can also be considered that a secondary lining 6 is applied on the initial support 1 to further reinforce the chamber and meet its functional requirements.

[0049] Working principle:

[0050] Micropiles 5 are bored, 300mm in diameter, and are positioned between the grid steel frames of the primary support 1. They must penetrate the collapsible loess layer and penetrate at least 1m into the non-collapsed loess layer. This ensures both the feasibility of the micropiles and their effectiveness in treating collapsible soil layers. Furthermore, steel mesh is installed on both the soil-facing and soil-removing sides of the grid steel frames in the primary support 1. Multiple grid main bars 7 and multiple grid U-shaped bars 8 are welded to each other, and the grid main bars 7 are welded to the pile foundation main bars 9, improving the structural integrity and enhancing its resistance to uneven settlement. Example 2

[0051] A construction method for reinforcing a collapsible loess foundation of an underground chamber, a collapsible loess foundation reinforcement structure of an underground chamber, wherein the chamber is divided into four parts, namely, part I, part II, part III and part IV, for construction, and comprises the following steps:

[0052] Step 1: Carry out advance support 2 of part I, excavate soil of part I, and carry out initial support 1 and temporary intermediate partition wall 4;

[0053] Specifically, the advanced support 2 of Part I is constructed, the ground is reinforced by grouting, core soil is reserved, the soil of Part I is excavated, the initial support 1 and temporary intermediate partition wall 4 of Part I are constructed, and locking anchor rods 3 are driven at the foot of the initial support 1;

[0054] Step 2: Excavate part II of the soil, construct initial support 1 and temporary intermediate partition wall 4, and reinforce the foundation with micro piles 5 inside the chamber;

[0055] Specifically, the soil of Part II is excavated, the initial support 1 and temporary intermediate partition wall 4 of Part II are constructed, and micro piles 5 are constructed between the grid steel frames of the initial support 1 for foundation treatment;

[0056] Step 3: Carry out advanced support 2 of Section III, excavate soil of Section III, and carry out initial support 1 and temporary intermediate partition wall 4;

[0057] Specifically, the advanced support 2 of Section III is constructed, the ground is reinforced by grouting, core soil is reserved, the soil of Section III is excavated, the initial support 1 and temporary intermediate partition wall 4 of Section III are constructed, and locking anchor bolts 3 are driven at the foot of the initial support 1;

[0058] Step 4: Excavate the soil of Part IV, construct the initial support 1 and temporary intermediate partition wall 4, and construct micro piles 5 inside the chamber to reinforce the foundation;

[0059] Specifically, the soil of Section IV is excavated, the initial support 1 and temporary intermediate partition wall 4 of Section IV are constructed, and micro piles 5 are constructed between the grid steel frames of the initial support 1 for foundation treatment;

[0060] Step 5: Remove the temporary partition wall 4 in sections and apply secondary lining 6 concrete;

[0061] Specifically, the temporary middle partition wall 4 is dismantled in sections from top to bottom, and the secondary lining 6 concrete is applied.

[0062] In this embodiment, Section II of the chamber is staggered at least 15 meters from Section I, Section III is staggered at least 15 meters from Section II, and Section IV is staggered at least 15 meters from Section III. Furthermore, the temporary intermediate partition wall 4 supports and reinforces the geological mass surrounding the chamber during the excavation process, preventing displacement and deformation of the rock or soil, and maintaining the safety and stability of the chamber. After all micropiles 5 are installed, the temporary intermediate partition wall 4 is removed and the secondary lining 6 is installed to ensure the stability of the chamber and meet its functional requirements.

[0063] Furthermore, it can also be considered in the embodiment, which is characterized in that: when the cavern is excavated, the front and rear offset of parts I, II, III and IV of the cavern should be no less than 15m, and after parts II and IV are respectively connected, micro piles 5 are installed inside the caverns of parts II and IV.

[0064] Furthermore, in the embodiment, it can also be considered that when the initial support 1 is applied, holes need to be reserved at the pile positions of the micropiles 5 for the construction of the micropiles 5. After the initial support 1 reaches the design strength, the micropiles 5 are constructed, and then the reserved holes on the initial support 1 are sealed.

[0065] Furthermore, in the embodiment, it can also be considered that the micro piles 5 adopt a dry operation hole-forming process and a skip-driving method for construction. The spacing between the micro piles 5 along the width direction of the chamber is 700 mm. In order to avoid hole collapse, casing is used to protect the holes. The casing mouth is 10 cm above the ground. The allowable deviation of the pile position plane does not exceed 20 mm, and the verticality deviation of the pile body does not exceed 1%.

[0066] In this embodiment, in steps 2 and 4, the micropiles 5 are bored using a dry drilling process, and the spacing of the micropiles 5 along the width of the chamber is 700 mm to ensure that the collapsible deformation after foundation treatment is controlled below 20 mm and the characteristic value of the composite foundation bearing capacity is not less than 200 kPa.

[0067] This invention treats collapsible loess foundations within a concealed excavation chamber, effectively reducing the amount of loess collapse and lowering safety risks during its service life. It boasts strong structural integrity, easily guaranteed construction quality, and minimal impact on the surrounding environment, effectively expanding the conditions for constructing underground chambers in areas prone to self-weight collapsible loess.

[0068] The above embodiments describe the present invention in detail, but the contents described are only preferred embodiments of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A construction method for reinforcing a collapsible loess foundation of an underground chamber, comprising a collapsible loess foundation reinforcement structure of an underground chamber, characterized in that: The invention comprises a chamber, wherein an initial support (1) and an advance support (2) are applied on the chamber, wherein a locking anchor rod (3) is driven at the foot of the initial support (1); the initial support (1) is provided with a grid steel frame, and micro piles (5) are arranged between the grid steel frames, and the micro piles (5) pass through the collapsible loess layer and penetrate into the non-collapsed loess layer; The micro pile (5) has a pile foundation main reinforcement (9), and the pile foundation main reinforcement (9) is welded to the grid steel frame as a whole; The initial support (1) is provided with steel mesh on the soil facing side and the soil facing side of the grid steel frame; The grid steel frame comprises a plurality of grid main bars (7) and a plurality of grid U-shaped bars (8), the grid main bars (7) are welded to each other via the grid U-shaped bars (8), and the grid main bars (7) and the pile foundation main bars (9) are welded to each other; The construction method for reinforcing the collapsible loess foundation of an underground chamber is to divide the chamber into four parts: Part I, Part II, Part III, and Part IV for construction, and includes the following steps: Step 1: Carry out advance support (2) of part I, excavate soil of part I, and carry out initial support (1) and temporary intermediate partition wall (4); Specifically, the advance support (2) of Part I is implemented, the ground is reinforced by grouting, the core soil is reserved, the soil of Part I is excavated, the initial support (1) and temporary intermediate partition wall (4) of Part I are implemented, and locking anchor rods (3) are installed at the foot of the initial support (1); Step 2: Excavate the soil of Part II, construct the initial support (1) and temporary intermediate partition wall (4), and construct micro piles (5) inside the chamber to reinforce the foundation; Specifically, the soil of Part II is excavated, the initial support (1) and temporary intermediate partition wall (4) of Part II are constructed, and micro piles (5) are constructed between the grid steel frames of the initial support (1) for foundation treatment; Step 3: Carry out advance support (2) of Section III, excavate the soil of Section III, and carry out initial support (1) and temporary intermediate wall (4); specifically, carry out advance support (2) of Section III, reinforce the stratum by grouting, reserve core soil, excavate the soil of Section III, carry out initial support (1) and temporary intermediate wall (4) of Section III, and install locking anchor rods (3) at the foot of the initial support (1); Step 4: Excavate the soil of Part IV, construct the initial support (1) and temporary intermediate partition wall (4), and construct micro piles (5) inside the chamber to reinforce the foundation; Specifically, the soil of Part IV is excavated, the initial support (1) and temporary intermediate partition wall (4) of Part IV are constructed, and micro piles (5) are constructed between the grid steel frames of the initial support (1) for foundation treatment; Step 5: Remove the temporary middle partition wall (4) in sections and apply the secondary lining (6) concrete; Specifically, the temporary middle partition wall (4) is dismantled in sections from top to bottom, and the secondary lining (6) concrete is applied.

2. The method for reinforcing the collapsible loess foundation of an underground chamber according to claim 1, characterized in that: A secondary lining (6) is applied on the initial support (1) to further reinforce the chamber and meet its functional requirements.

3. The method for reinforcing the collapsible loess foundation of an underground chamber according to claim 1 is characterized in that: When the cavern is excavated, the front-to-back offset of parts I, II, III and IV of the cavern should be no less than 15m. After parts II and IV are respectively penetrated, micro piles (5) are then installed inside the caverns of parts II and IV.

4. The method for reinforcing the collapsible loess foundation of an underground chamber according to claim 1, characterized in that: When constructing the initial support (1), holes need to be reserved at the pile positions of the micro piles (5) for constructing the micro piles (5). After the initial support (1) reaches the design strength, the micro piles (5) are constructed, and then the reserved holes on the initial support (1) are sealed.

5. The method for reinforcing the collapsible loess foundation of an underground chamber according to claim 1, characterized in that: The micro piles (5) are constructed by dry drilling technology and skip-driving method. The spacing of the micro piles (5) along the width direction of the chamber is 700 mm. In order to avoid hole collapse, casing is used to protect the hole. The casing mouth is 10 cm above the ground. The allowable deviation of the pile position plane does not exceed 20 mm, and the verticality deviation of the pile body does not exceed 1%.

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