Design method of retaining structure for long and narrow foundation pit

Abstract

The application relates to a design method of a retaining type narrow foundation pit supporting structure, which is applied to an underground pipe gallery project adopting premixed fluidized solidified soil trenches, and the design method is as follows: structural design calculation is respectively carried out for different construction stages of the underground pipe gallery, including the following steps: for the process of excavating the foundation pit, the load state calculation of the supporting pile is carried out based on the elastic support point method of the plane bar structure; for the process of adopting the premixed fluidized solidified soil trench, the stress state calculation of the supporting pile and the internal support is carried out based on different elastic resistances provided by the premixed fluidized solidified soil of different ages under different working conditions and acting on the supporting structure. The application provides a design method of the supporting structure adopting the premixed fluidized soil trench on the inner side of the foundation pit, the influence of the premixed fluidized soil on the inner force of the retaining structure is considered, the calculation result of the internal force of the foundation pit supporting pile can be reduced as a whole, the rigidity of the supporting structure design is improved, and the economy of the foundation pit supporting structure is improved.

Description

Technical Field

[0001] This invention relates to the fields of municipal engineering and power engineering construction technology, and specifically to a design method for a support structure for a narrow and elongated foundation pit using a pre-mixed fluidized solidified soil trough. Background Technology

[0002] Underground utility tunnel projects, such as power cable trenches, municipal pipelines, and communication channels, constructed in urban environments often use recyclable support structures, such as steel sheet piles, for support due to geological conditions or constraints imposed by the surrounding environment.

[0003] Taking high-voltage cable lines in the power industry as an example, their implementation requires laying them within certain structures. Based on current technical conditions, common cable structures include cable trenches, cable ducts, cable trenches, cable tunnels, shafts, and cable mezzanines. When multiple circuits of high-voltage power cables with voltage levels above 220kV are laid in a shared trench, tunnel laying is required. Among currently feasible tunneling techniques, open-cut cable tunnels account for the majority. Currently, when designing the foundation pit support, the influence of the foundation pit excavation width is not considered, and various algorithms recommended by JGJ 120 are still used, including horizontal load calculations (including earth pressure calculations, horizontal additional load calculations under top additional loads, etc.), foundation pit support structure calculations (using the elastic support method of planar rod structures), and foundation pit support stability verification (including single-point anchorage stability calculations, circular arc sliding stability calculations, pit bottom heave stability calculations under the foundation bearing capacity model, and circular arc sliding stability calculations with the lowest inner support as the axis).

[0004] Premixed solid fluidized soil is a green, low-carbon, and energy-saving technology developed in recent years, changing the current backfilling methods. Premixed fluidized soil features self-leveling and self-compacting characteristics, a strength exceeding 0.4 MPa, no settlement during backfilling, significant impermeability, fast construction speed, environmental friendliness, and wide applicability. Premixed solid fluidized soil trenching offers advantages such as short construction cycle, low safety risks, a green, environmentally friendly, and pollution-free construction process, stable and controllable quality of the solidified soil after pouring, and fewer process steps. The simultaneous segmented pouring method greatly improves backfilling efficiency. According to the solidified soil backfilling requirements, it reaches the strength required for the next construction step after 12 hours of hardening, exhibiting good forming effect and significantly reducing the unevenness of trench backfilling. Therefore, premixed fluidized soil is also suitable for the aforementioned underground utility tunnel projects.

[0005] However, for underground utility tunnel projects using premixed fluidized bed soil trenches, existing calculation methods, particularly those targeting narrow, elongated foundation pits such as power trenches, municipal utility tunnels, communication pipelines, and municipal pipe networks, still rely on the plane strain and semi-infinite body assumptions of JGJ 120 for building foundation pits. In the calculation of the support structure, the elastic support method is still the primary approach, assuming the internal support is a relatively stiff spring to calculate the pressure on the support structure. Furthermore, the application of premixed fluidized bed soil in trenching only considers its trenching and anti-seepage functions, failing to consider the elastic support effect that the fluidized bed soil can provide between the support structure and the structures within the trench as the curing process progresses. Moreover, its uniaxial compressive strength reaches 0.80 MPa, representing a significant elastic support effect. Its influence on support structures such as recyclable sheet piles also exists, but existing design methods cannot account for this influence. The solidification of fluid soil will have a certain impact on the internal force and deformation of the support piles. If the impact of fluid soil solidification is not considered, problems such as damage to the support structure and internal support may occur due to the timing of the removal of the internal support of recyclable support structures such as sheet piles and the recycling of support piles not being optimal. This will result in a reduction in the number of times recyclable sheet piles or internal supports can be reused, which is not conducive to investment control.

[0006] Therefore, it is necessary to improve the design method for the support structure in underground utility tunnel projects that use premixed fluidized bed soil troughs. Summary of the Invention

[0007] The purpose of this invention is to provide a design method for a retaining structure for narrow foundation pits that takes into account the influence of different ages of premixed fluidized solidified soil.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A design method for a retaining-type narrow foundation pit support structure is applied to an underground utility tunnel project using premixed fluidized solidified soil trenches. The support structure of the underground utility tunnel includes retaining piles, supporting beams, and internal supports. The design method for the retaining-type narrow foundation pit support structure involves performing structural design calculations for different construction stages of the underground utility tunnel. This includes: for the excavation process, calculating the load state of the retaining piles based on the elastic support method of planar rod structures; and for the process using premixed fluidized solidified soil trenches, calculating the stress state of the retaining piles and the internal supports based on the different elastic resistances provided by premixed fluidized solidified soil at different ages under different working conditions.

[0010] The stress state calculation of the support piles and the internal supports includes: calculating the stress state of the support piles and the internal supports based on the lateral pressure exerted on the inner side of the support piles by the fluidized soil of the first support pile (formed by using pre-mixed fluidized solidified soil to fill the first trough below the first internal support) and the solidification process of the fluidized soil of the first trough; and calculating the stress state of the support piles and the internal supports based on the distributed reaction force provided by the fluidized soil of the first trough as soil resistance during the removal of the first internal support. The calculations are as follows: For the flowable soil in the second trough formed by using pre-mixed fluidized solidified soil to reach the second inner support, and for the solidification process of the flowable soil in the second trough, the stress state of the support pile and the inner support is calculated based on the lateral pressure generated by the flowable soil in the second trough acting on the inner side of the support pile. For the process of removing the second inner support, the stress state of the support pile and the inner support is calculated based on the distributed reaction force provided by the flowable soil in the first trough and the flowable soil in the second trough at different ages and heights as soil resistance.

[0011] The distributed reaction force provided by the fluid soil at different ages of the first and second fertilization trenches is calculated.

[0012] The distributed reaction force p provided by the fluid soil s The calculation method is as follows: p s =k s v+p s0 In the formula, k s ρ is the horizontal reaction coefficient of the premixed fluidized solidified soil, v is the horizontal displacement value of the premixed fluidized solidified soil compressed by the support structure at the distributed reaction calculation point, and p is the horizontal displacement value of the support structure at the distributed reaction calculation point. s0 This represents the initial distributed reaction force.

[0013] The initial distributed reaction force p s0 The calculation method is as follows: p s0 =σ pk K a,i In the formula, σ pk K represents the vertical earth pressure value at the inner distribution points of the support structure. a,i Let be the active earth pressure coefficient of the i-th layer.

[0014] The horizontal reaction coefficient k of the premixed fluidized solidified soil s The calculation method is as follows: k s =m(zh), where m is the proportionality coefficient of the horizontal reaction force of the premixed fluidized solidified soil, z is the depth of the calculation point from the ground, and h is the excavation depth of the foundation pit under the calculation condition.

[0015] The method for calculating the proportionality coefficient m of the horizontal reaction force of the premixed fluidized solidified soil is as follows: In the formula, c represents the cohesion of the premixed fluidized solidified soil. The internal friction angle of premixed fluidized solidified soil, v b The horizontal displacement of the support structure at the bottom of the foundation pit, the cohesion c of the premixed fluidized solidified soil, and the internal friction angle of the premixed fluidized solidified soil are given. The height is determined according to the different soil layers of the premixed fluidized solidified soil.

[0016] When the actual horizontal displacement of the support structure at the bottom of the pit is less than or equal to 10 mm, the horizontal displacement v of the support structure at the bottom of the pit is... b Take 10mm.

[0017] The calculation of the load state of the support piles includes the calculation of the force on the support structure, the calculation of the embedded stability, the calculation of the circular arc sliding stability, the calculation of the bottom heave stability, the calculation of the stability of the weak underlying layer, and the calculation of groundwater control.

[0018] The design method for the retaining type narrow foundation pit support structure also includes selecting the support structure, choosing the type of support pile according to the required excavation depth, and determining the width of the foundation pit excavation according to the construction method.

[0019] Due to the application of the above technical solutions, the present invention has the following advantages compared with the prior art: The present invention proposes a design method for a support structure using pre-mixed fluid soil troughs on the inner side of the foundation pit, taking into account the influence of pre-mixed fluid soil on the internal forces of the support structure. In terms of model simplification, the support points on the inner side of the support piles are replaced by a series of elastic support points instead of individual support points at the inner support. Overall, this can reduce the calculation results of the internal forces of the foundation pit support piles, improve the stiffness of the support structure design, and enhance the economy of the foundation pit support structure. Attached Figure Description

[0020] Appendix Figure 1 This is a schematic diagram of the support structure for an underground utility tunnel.

[0021] Appendix Figure 2 This is a cross-sectional view of the underground utility tunnel after backfilling with premixed fluidized solidified soil.

[0022] Appendix Figure 3 This is a construction flowchart for underground utility tunnels.

[0023] Appendix Figure 4 This is a geometric model diagram of the trough leading to the first inner support.

[0024] Appendix Figure 5 This is a mechanical model diagram of the trough leading to the first internal support.

[0025] Appendix Figure 6This is a geometric model diagram of the section from the trough to the second inner support.

[0026] Appendix Figure 7 This is a mechanical model diagram of the section from the trough to the second inner support.

[0027] Appendix Figure 8 This is a geometric model diagram of the top support after it has been removed.

[0028] Appendix Figure 9 This is a mechanical model diagram after the top support has been removed.

[0029] Appendix Figure 10 This is a flowchart illustrating the design method of the support structure for narrow and elongated foundation pits according to the present invention.

[0030] In the attached diagrams: 1. Support piles; 2. Support beams; 3. Internal supports; 4. Foundation pit; 5. Foundation soil inside the pit; 6. Surface restoration layer; 7. Subbase; 8. Cable channel; 9. Cable bracket; 10. Premixed fluidized solidified soil. Detailed Implementation

[0031] The present invention will be further described below with reference to the embodiments shown in the accompanying drawings.

[0032] Example 1: This invention relates to a design method for a retaining structure (retaining structure) for a narrow, elongated foundation pit using premixed fluidized solidified soil troughs. The method comprises three stages: selection of the retaining structure, calculation of the load from the excavation of the foundation pit 4 to the bottom and the retaining piles 1, and calculation of the internal forces after the premixed fluidized soil trough is formed. This invention is characterized by its ability to consider the influence of the unconfined compressive strength of premixed fluidized soil under different age conditions. Specifically, for cable trench projects, municipal pipeline projects, and municipal utility tunnel projects using premixed fluidized soil backfill and recyclable retaining structures such as sheet piles for support, the retaining structure used in the underground utility tunnels includes retaining piles 1, supporting beams 2, and internal supports 3. The retaining piles 1 are arranged in two opposing rows, with the foundation pit 4 excavated between the two rows of retaining piles 1. Below the foundation pit 4 is the foundation soil 5. The supporting beams 2 are arranged along the length of the foundation pit 4 at the top of the retaining piles 1. The internal supports 3 are horizontally installed along the cross-section of the foundation pit 4, and multiple internal supports 3 can be installed longitudinally. A cushion layer 7 is installed at the bottom of the foundation pit 4, and a cable channel 8 with a cable support 9 is installed on the cushion layer 7. The remaining space in the foundation pit 4 is backfilled with pre-mixed fluidized solidified soil 10, and a surface restoration layer 6 can also be installed at the surface.

[0033] The technical solution of this application mainly includes the following aspects:

[0034] 1. Optimize the design of the foundation pit space and the process of replacing the support.

[0035] The design method for a retaining structure for narrow, elongated foundation pits includes selecting the type of retaining structure, choosing the type of retaining pile 1 based on the required excavation depth, and determining the excavation width of the foundation pit 4 according to the construction method. Specifically, the optimization of the internal support 3 arrangement mainly considers that after using pre-mixed fluidized bed troughs, personnel are not required to enter the foundation pit 4 for compaction and backfilling operations. Its width can be reduced from the original general specification requirement of 0.8m~1.2m to 0.6m~1.0m, effectively reducing the excavation width by more than 0.4m. For cable foundation pits using retaining structures as support, the excavation depth varies depending on the type of retaining structure and the stiffness of the retaining pile 1. Generally, sheet piles can be used for excavation depths not exceeding 9m, and cast-in-place piles can be used for excavation depths not exceeding 15m. The retaining structure is attached. Figure 1 As shown in the attached figure, the cross-sectional view of the underground utility tunnel after backfilling with premixed fluidized solidified soil 10 is as follows. Figure 2 As shown.

[0036] The construction process is as follows: (1) Trial mixing of premixed fluidized solidified soil at the construction site; (2) Positioning, clearing, and pipeline re-measurement of support pile 1; (3) Construction and maintenance of support pile 1; (4) Excavation of foundation pit 4, construction of internal support 3, and transportation of excess soil from foundation pit 4 to the fluidized soil processing plant; (5) Construction of power channel structures, including necessary foundation treatment, subbase 7 construction, pipe laying or cable trench construction, and necessary reinforced concrete maintenance; (6) Premixed fluidized solidified soil 10 in foundation pit 4 below internal support 3, and a 7-day curing period; (7) Dismantling of internal support 3, premixed fluidized soil in the upper part of internal support 3, and a 7-day curing period; (8) Recycling of recyclable support pile 1; (9) Restoration of the ground surface of cable channel 8. The construction process of cable trench and power tunnel projects using recyclable steel sheet pile support and premixed fluidized solidified soil 4 in the trench is as follows. Figure 3 As shown.

[0037] As can be seen from the construction process flow chart of the above recyclable retaining structure:

[0038] (1) The premixed fluid soil trough has a certain impact on the construction process of the retaining structure, mainly in the consideration of the removal and replacement of the internal support 3.

[0039] (2) The use of premixed fluidized solidified soil 10 can basically utilize the soil excavated from the foundation pit 4, the soil backfilled on the surface, and the soil replaced by the pipe and its enclosing structure layer, which can be used as external disposal soil.

[0040] (3) The premixed fluidized solidified soil 10 has no effect on the design calculation of recyclable steel sheet piles before the trench is built, but after the tunnel inside the foundation pit 4 is poured, it has a greater impact on the working conditions of the replacement support, especially when the trench is built below the inner support 3. The premixed fluidized solidified soil 10 has a certain impact on the timing of the removal of the inner support 3 and the recycling of steel sheet piles. This impact needs to be considered when designing and optimizing the foundation pit 4.

[0041] (4) When multiple internal supports 3 are set, the influence of the trenching process on the internal force of the support pile 1 should also be considered, and the design should be optimized in combination with the actual project.

[0042] The premixed fluidized solidified soil 10 has no impact on the design calculation of non-recyclable cast-in-place piles before the foundation pit is filled. However, after the tunnel inside the foundation pit 4 is poured, it has a significant impact on the working conditions of the support replacement, especially when the foundation pit is filled below the inner support 3. The premixed fluidized solidified soil 10 has a certain impact on the timing of the removal of the inner support 3. This impact needs to be considered when designing and optimizing the foundation pit 4.

[0043] After the tunnel is poured, a support replacement process is usually required. Using pre-mixed fluidized solidified soil 10, which has high strength, eliminates the need for bottom support replacement. The pre-mixed fluidized solidified soil 10 in the pit can be directly used as a soil spring in the calculation of the support pile 1. The calculation of the recyclable and non-recyclable support pile 1 can include the following two parts:

[0044] (1) According to the provisions of JGJ 120 "Technical Specification for Support of Foundation Pit", the load state of the support pile 1 is calculated according to the elastic support method of planar structure. The load state calculation of the support pile 1 includes the calculation of the force of the support structure, the calculation of the embedded stability, the calculation of the circular arc sliding stability, the calculation of the bottom heave stability, the calculation of the stability of the weak underlying layer, and the calculation of groundwater control.

[0045] (2) When the tunnel construction is completed, the premixed fluid solidified soil trough is adopted. Based on the different ages of the premixed fluid soil, the internal force analysis results of the support structure under the action of "only compression and no tension" springs with different stiffnesses can be considered. The internal force of the support structure can be calculated according to the "elastic support method of planar rod structure".

[0046] A schematic diagram of the trough leading to the bottom of the first inner support 3 is attached. Figure 4 As shown, the corresponding mechanical model diagram is attached. Figure 5 As shown. Where, P ak —External active earth pressure on the retaining structure; b0 —Depth of the retaining pile 1 inserted into the bottom of the pit; b a —Four retaining piles for the foundation pit, 1 meter deep; P s —Soil reaction force distributed on the inner side of foundation pit 4; P r-i—Elastic resistance (early-age strength) of pre-mixed fluid soil acting on retaining structures; b m —Height of the pre-mixed fluidized solidified soil 10 below the lowest inner support 3; F a F b —The reaction force on the support 3 inside the foundation pit 4.

[0047] When a retaining structure is equipped with multiple internal supports 3, as the pre-mixed fluidized soil is continuously backfilled, the internal supports 3 within the pit also need to be continuously removed from bottom to top. The common practice is to backfill the fluidized soil in layers below the internal supports 3, allow it to cure for a certain period, and then remove the internal support 3 structure. At this time, the load of the internal support 3 structure is transferred to the tunnel structure inside the pit 4 or the foundation soil on the opposite side through the deformation of the cast-in-place piles or sheet piles, thereby achieving a balance of loads on the inner and outer sides of the pit 4 support structure. Considering the different stiffnesses of the support structures, the load F of the unloaded portion of the internal support 3... a F b The load change process on the retaining structure is as follows: The pre-mixed fluid soil transferred to the inside of foundation pit 4 or the soil from the undisturbed part is shared by the retaining structure.

[0048] (1) After the premixed fluidized solidified soil 10 is backfilled to the position of the inner support 3 at the bottom of the pit, the premixed fluidized solidified soil 10 gradually changes from fluid to solid with the inner support 3 structure as a model. After curing for a certain period of time (such as 7 days), the premixed fluidized soil gradually hardens into a cement-soil wall with greater rigidity, which can provide greater support rigidity (simplified as a "press-only" spring), and can simulate the greater resistance of the foundation pit 4 inside the foundation pit 4.

[0049] (2) Compared to the case where the fluid soil trough extends to the bottom of the first inner support 3, the fluid soil inside the foundation pit 4 is divided into two layers, namely, the layer at the bottom of the first inner support 3 is P. r-a ·b m The first inner support 3 to the bottom of the crown beam P r-i ·b n , where P r-a P r-i The support stiffness of premixed fluidized solidified soil 10 at different ages.

[0050] A schematic diagram of the trough leading to the bottom of the second inner support 3 (crown beam) is attached. Figure 6 As shown, the corresponding mechanical model diagram is attached. Figure 7 As shown. Where, P ak —External active earth pressure on the retaining structure; b0 —Depth of the retaining pile 1 inserted into the bottom of the pit; b a —Four retaining piles for the foundation pit, 1 meter deep; P s —Soil reaction force distributed on the inner side of foundation pit 4; P r-i —Elastic resistance (early-age strength) of premixed fluid soil acting on retaining structures; Pr-a —Elastic resistance of premixed fluid soil to retaining structures (later-age strength); b m —Height of the premixed fluidized solidified soil 10 below the first internal support 3; b n —The pre-mixed fluidized bed solidifies to the top height of the fluidized soil trough below the lowest inner support 3; F c —The force exerted on the cap beam after the support of foundation pit 4 is removed.

[0051] Cable tunnel (pipe gallery) projects constructed using non-recoverable retaining structures such as cast-in-place piles often require the removal of the cap beam of the cast-in-place piles and the pile body within a certain depth to accommodate other pipelines crossing the tunnel roof. At this point, the pre-mixed fluidized solidified soil has also completed its curing within the specified age range (e.g., 7 days), and its elastic resistance value can be expressed as P. r-a The combined model and mechanical model at this point are shown in the appendix. Figure 8 and attached Figure 9 As shown. When recyclable sheet piles are used for construction, the calculation method for the support pile 1 before recycling is the same.

[0052] The support structure using pre-mixed fluidized solidified soil trenches is designed and calculated in the same way as the existing foundation pit support structure, i.e., according to the provisions of JGJ 120-2012 "Technical Specification for Foundation Pit Support". However, after using pre-mixed fluidized solidified soil trenches, it is not necessary to compact the soil inside the foundation pit, reducing the outward force of the trench on the foundation pit. When the fluidized soil trench is used, it provides lateral force of the fluidized soil in a fluidized state, which is supported at the bottom of the inner support 3. As the strength of the fluidized soil increases with age and solidifies, it becomes a solid that can provide resistance to the soil outside the pit. When the inner support 3 or the top cap beam is removed, the active earth pressure outside the pit will be transferred to the tunnel structure inside the pit or the inner side of the opposite support pile 1 through the fluidized soil due to the deformation of the support structure. The overall stress decomposition can be carried out in the following steps:

[0053] (1) The fluid soil trough extends to the bottom of the first inner support 3. The fluid soil inside the pit 4 is in a fluid plastic state. The lateral pressure generated by its own weight will act on the inner side of the support pile 1 of the pit 4 to balance part of the soil outside the pit.

[0054] (2) As the fluid soil solidifies, it gradually changes from a fluid plastic state to an elastic-plastic body with greater strength. In mechanical modeling, it can be simulated as a spring that is "only compressed and not stretched".

[0055] (3) Remove the first inner support 3. The load on the inner support 3 is transferred to the premixed fluid soil through the pile and the coordinated deformation with the solidified fluid soil. The active earth pressure outside the pit is transferred to the premixed fluid soil. Under normal circumstances, the operation cycle of pipe gallery projects is relatively short, and the curing period is often 7 days. At this time, the age strength of the premixed solidified soil has not reached its maximum value. The strength it provides can be calculated using the m value of an earlier age. The distributed soil reaction force is defined as p. r-i As the deformation beams of the support pile 1 vary, the soil resistance provided by the pre-mixed fluid soil inside the foundation pit 4 also varies, but overall it shows a pattern consistent with the geometric deformation of the pile.

[0056] (4) The premixed fluid soil is placed in the trough to a certain depth below the ground surface. At this time, due to the fluid plastic effect of the premixed fluid soil, the inner side of the support pile 1 is subjected to the lateral pressure generated by its own weight. The active earth pressure on the outer side of the support pile 1 is balanced. As the fluid soil is cured and its strength increases, the second pouring part can provide a larger distributed reaction force when under pressure.

[0057] (5) Remove the second inner support 3 at the top. At this time, the support pile 1 deforms towards the inside of the pit. The deformation causes compression towards the fluidized solidified soil. After being compressed, the fluidized soil can provide counterexamples with different m values ​​in segments, including the fluidized soil poured and cured to a certain age at the top, which can provide distributed reaction force p. r-i At this point, the premixed fluid soil generated in the first fertilizer tank at the bottom further increases, and its distribution reaction force is defined as p. r-a ;

[0058] (6) Calculate the stress on the cast-in-place piles and internal supports 3 under different working conditions, and perform structural calculations and reinforcement.

[0059] Therefore, as attached Figure 10 As shown, a design method for the support structure of a narrow, elongated foundation pit 4 in an underground utility tunnel project using premixed fluidized solidified soil 10 is as follows: Structural design calculations are performed for different construction stages of the underground utility tunnel. Specifically, this includes: for the excavation of the foundation pit 4, the load state calculation of the support piles 1 is performed based on the elastic support method of planar rod structures; for the process of using premixed fluidized solidified soil 10 to fill the trench, the stress state calculation of the support piles 1 and the internal support 3 is performed based on the different elastic resistances provided by premixed fluidized solidified soil 10 at different ages under different working conditions acting on the support structure.

[0060] The stress state calculation for the support pile 1 and the inner support 3 includes: calculating the stress state of the support pile 1 and the inner support 3 based on the lateral pressure generated by the fluid soil in the first trench (formed by using pre-mixed fluidized solidified soil 10 to fill the trench below the first inner support 3) and the solidification process of the fluid soil in the first trench, and the process of removing the first inner support 3; and calculating the stress state of the support pile 1 and the inner support 3 based on the distributed reaction force provided by the fluid soil in the first trench as soil resistance. The calculations are as follows: For the fluid soil in the second trough formed by using pre-mixed fluidized solidified soil 10 to fill the trough below the second inner support 3, and for the solidification process of the fluid soil in the second trough, the stress state of the support pile 1 and the inner support 3 is calculated based on the lateral pressure generated by the fluid soil in the second trough acting on the inner side of the support pile 1; For the process of removing the second inner support 3, the stress state of the support pile 1 and the inner support 3 is calculated based on the distributed reaction force provided by the fluid soil in the first trough and the fluid soil in the second trough at different ages and heights as soil resistance.

[0061] The distributed reaction force provided by the fluid soil at different ages of the first and second fertilization trenches is calculated.

[0062] The distributed reaction force p provided by the fluid soil s The calculation method is as follows:

[0063] p s =k s v+p s0 (1)

[0064] In equation (1), p s The distributed reaction force (kPa) provided to the fluid soil, k s The horizontal reaction coefficient (kN / m) of premixed fluidized solidified soil 10 3 v is the horizontal displacement (m) of the premixed fluidized solidified soil compressed by the support structure at the distribution reaction calculation point, and p is the horizontal displacement value of the premixed fluidized solidified soil compressed by 10. s0 The initial distributed reaction force is (kPa).

[0065] Initial distributed reaction force p s0 The calculation method is as follows:

[0066] p s0 =σ pk K a,i (2)

[0067] In equation (2), σ pk K represents the vertical earth pressure (kPa) at the distribution points on the inner side of the support structure. a,i Let be the active earth pressure coefficient of the i-th layer.

[0068] Horizontal reaction coefficient k of premixed fluidized solidified soil 10 s The calculation method is as follows:

[0069] k s =m(zh) (3)

[0070] In equation (3), m is the proportionality coefficient (kN / m) of the horizontal reaction force of the premixed fluidized solidified soil 10. 4 ), z is the depth of the calculation point from the ground (m), and h is the excavation depth of the foundation pit 4 under the calculation condition (m).

[0071] The method for calculating the proportionality coefficient m of the horizontal reaction force of premixed fluidized solidified soil 10 is as follows:

[0072]

[0073] In equation (4), c is the cohesion (kPa) of the premixed fluidized solidified soil 10. The internal friction angle (°) of the premixed fluidized solidified soil 10, the cohesion c of the premixed fluidized solidified soil 10, and the internal friction angle of the premixed fluidized solidified soil 10 are given. The height values ​​were taken separately for different soil layers of the premixed fluidized solidified soil 10. b Let v be the horizontal displacement (mm) of the support structure at the bottom of pit 4. When the actual horizontal displacement of the support structure at the bottom of pit 4 is less than or equal to 10mm, the horizontal displacement v of the support structure at the bottom of pit 4 is... b Take 10mm.

[0074] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A design method of a retaining type long and narrow foundation pit supporting structure, applied to an underground pipe gallery project using premixed fluidized solidified soil bins, the supporting structure used by the underground pipe gallery comprising supporting piles, support waist beams and internal supports, characterized in that: The design method of the supporting and retaining type long and narrow foundation pit supporting structure is: respectively performing structural design calculation for different construction stages of the underground pipe gallery, including: based on the elastic support point method of the plane bar structure, performing load state calculation of the supporting pile for the process of excavating the foundation pit; based on different elastic resistances provided by the pre-mixed flow state solidified soil of different ages on the supporting structure under different working conditions, performing stress state calculation of the supporting pile and the inner support for the process of using the pre-mixed flow state solidified soil trench; The stress state calculation of the supporting pile and the inner support includes: based on the lateral pressure generated by the flow state soil body of the first flow state soil trench on the inner side of the supporting pile, performing stress state calculation of the supporting pile and the inner support for the process of using the pre-mixed flow state solidified soil trench to form the flow state soil body of the first flow state soil trench under the first inner support and the solidification process of the flow state soil body of the first flow state soil trench; based on the distributed reaction force provided by the flow state soil body of the first flow state soil trench as soil resistance, performing stress state calculation of the supporting pile and the inner support for the process of removing the first inner support; based on the lateral pressure generated by the flow state soil body of the second flow state soil trench on the inner side of the supporting pile, performing stress state calculation of the supporting pile and the inner support for the process of using the pre-mixed flow state solidified soil trench to form the flow state soil body of the second flow state soil trench under the second inner support and the solidification process of the flow state soil body of the second flow state soil trench; based on the distributed reaction force provided by the flow state soil body of the first flow state soil trench and the flow state soil body of the second flow state soil trench according to different ages and heights as soil resistance, performing stress state calculation of the supporting pile and the inner support for the process of removing the second inner support.

2. The method of designing a retaining structure for a long and narrow foundation pit according to claim 1, wherein: The m value of the flow state soil body of the first flow state soil trench and the flow state soil body of the second flow state soil trench is calculated based on different ages to calculate the distributed reaction force provided by the flow state soil body.

3. The method for designing a retaining diaphragm wall pit support structure according to claim 2, wherein: The distributed reaction force p provided by the flowable soil body s The calculation method is as follows: p s = k s v + p s0 , wherein k s is the horizontal reaction force coefficient of the premixed flowable solidified soil, v is the horizontal displacement value of the support structure at the distributed reaction force calculation point to compress the premixed flowable solidified soil, and p s0 is the initial distributed reaction force.

4. The method for designing a retaining diaphragm wall pit support structure according to claim 3, wherein: The initial distribution counterforce p s0 The calculation method is as follows: p s0 = σ pk K a,i , wherein σ pk is the vertical earth pressure value of the inner distribution point of the support structure, and K a,i is the active earth pressure coefficient of the i-th layer.

5. The method for designing a retaining diaphragm wall pit support structure according to claim 3, wherein: The horizontal reaction coefficient k of the premixed fluidized solidified soil s The calculation method is as follows: k s =m(zh), where m is the proportionality coefficient of the horizontal reaction force of the premixed fluidized solidified soil, z is the depth of the calculation point from the ground, and h is the excavation depth of the foundation pit under the calculation condition.

6. The method for designing a retaining diaphragm wall pit support structure according to claim 5, wherein: The calculation method of the proportional coefficient m of the horizontal counterforce of the premixed fluidified solidified soil is: In the formula, c is the cohesion of the premixed fluidified solidified soil, is the internal friction angle of the premixed fluidified solidified soil, v b is the horizontal displacement amount of the support structure at the bottom of the foundation pit, the cohesion c of the premixed fluidified solidified soil, the internal friction angle The different soil layers of the premixed fluidified solidified soil are respectively taken at different heights.

7. The method for designing a retaining diaphragm wall pit support structure according to claim 6, wherein: the actual horizontal displacement amount of the support structure at the bottom of the foundation pit is less than or equal to 10mm b 10mm is taken.

8. The method of designing a retaining structure for a long and narrow foundation pit according to claim 1, wherein: The calculation of the load state of the supporting pile includes the calculation of the stress of the supporting structure, the calculation of the embedded stability, the calculation of the circular sliding stability, the calculation of the anti-heave stability of the pit bottom, the calculation of the stability of the soft underlying layer, and the calculation of the underground water control.

9. The method of designing a retaining structure for a long and narrow foundation pit according to claim 1, wherein: The design method of the supporting and retaining type long and narrow foundation pit supporting structure further includes selecting the supporting structure, selecting the type of the supporting pile according to the required excavation depth, and determining the width of the foundation pit excavation according to the construction method.

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