Deep foundation pit construction method based on environment-sensitive polymorphic support system

Abstract

The invention provides a deep foundation pit construction method based on an environment-sensitive polymorphic support system, which comprises the following steps: step 1, before formal construction of a deep foundation pit project, determining a preliminary support strategy and environmental protection measures adaptive to the environment; step 2, dynamically selecting one or combination of multiple most suitable supporting forms from multiple supporting forms of rectangular supporting, circular supporting, special-shaped supporting and shotcrete-anchor supporting, wherein the multiple most suitable supporting forms are selected from multiple supporting forms of rectangular supporting, circular supporting, special-shaped supporting and shotcrete-anchor supporting; thirdly, according to the supporting mode finally selected in the second step, a corresponding, mature and reliable construction technology is adopted to complete construction of the foundation pit outer envelope structure; and 4, in combination with the selected external envelope support form and the real-time excavation depth of the foundation pit, an internal support system is arranged in a layered and segmented mode. According to the method, by dynamically selecting a proper supporting structure and a mixed supporting system, the negative influence of excavation of the working well on surrounding buildings, roads and underground pipelines is remarkably reduced, meanwhile, the construction efficiency is greatly improved, and the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of foundation pit construction, and in particular to a deep foundation pit construction method based on an environment-sensitive multi-form support system. Background Art

[0002] With the rapid development and utilization of urban underground space in my country, especially as urban integrated pipeline corridor construction enters its peak phase, working shafts, a crucial node in the corridor system, face increasingly complex technical challenges. According to industry statistics (such as the "China Urban Integrated Pipeline Corridor Development Report (2023)"), rectangular working shafts account for approximately 62% of currently under construction and completed integrated pipeline corridors, circular working shafts account for 28%, and irregular-shaped working shafts (such as T-shaped, L-shaped, and cross-shaped to accommodate complex site conditions) account for 10%.

[0003] Traditional deep foundation pit engineering practices, especially during working pit construction, tend to rely on a single, standardized support structure. For example, rectangular concrete retaining structures (such as underground continuous walls and bored cast-in-place piles) are commonly used in conjunction with internal horizontal supports. This traditional single support structure often exhibits poor adaptability when faced with diverse and demanding environmental conditions. For example, in complex environments such as urban renewal, busy road intersections, and those adjacent to important buildings or sensitive underground pipelines, a single support structure struggles to simultaneously meet multiple functional requirements, including structural stress, pipeline routing and avoidance, traffic diversion, and environmental protection, as well as refined design requirements. This can lead to significant construction disturbances (such as excessive vibration and noise, or excessive deformation of adjacent soil and buildings) and low construction efficiency (such as cumbersome procedures and difficult site turnover). Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies of the prior art and provide a deep foundation pit construction method based on an environmentally sensitive multi-form support system.

[0005] The specific technical solutions are as follows: A deep foundation pit construction method based on an environmentally sensitive multi-form support system comprises the following steps: Step 1: Before the formal construction of the deep foundation pit project, a comprehensive survey of the surrounding environment, underground pipeline distribution and detailed geological and hydrological conditions of the project site is carried out, and preliminary support strategies and environmental protection measures that are suitable for the environment are determined; Step 2: Taking into account the excavation depth, plan dimensions, functional requirements, specific environmental sensitivity factors of the project site, detailed geological conditions, and specific project requirements, dynamically select one or a combination of the most appropriate support forms from a variety of support types, including rectangular support, circular support, special-shaped support, and shotcrete support. Step 3: Based on the support form finally selected in Step 2, use the corresponding mature and reliable construction technology to complete the construction of the foundation pit perimeter protection structure; Step 4: Based on the selected external protection support form and the actual excavation depth of the foundation pit, lay out the internal support system in layers and sections.

[0006] Optionally, the special-shaped support includes L-shaped, T-shaped, cross-shaped or irregular polygonal support.

[0007] Optionally, the outer protective structure includes but is not limited to a bored interlocking pile system consisting of meat piles and plain piles interlocking with each other, or a sprayed anchor surface support system consisting of anchor rods (or soil nails), steel mesh and sprayed concrete, or an underground continuous wall, or SMW method piles.

[0008] Optionally, the internal support system includes a combination of one or more components selected from the group consisting of crown beams, waist beams, horizontal frame beams, support beams, concrete plate supports, and steel plate supports.

[0009] Optionally, the reinforced concrete support is arranged at the first support position in the upper part of the foundation pit, and the steel support is arranged at the remaining support positions in the middle and lower part of the foundation pit.

[0010] Optionally, the support beam is made of steel bars and concrete, and is connected to supports on both sides inside the foundation pit to form a support for maintaining the stability of the foundation pit.

[0011] Optionally, the concrete slab is supported at an angle formed along the edge of the foundation pit support.

[0012] Optionally, in step three of the support structure construction, if bored interlocking piles are chosen as the outer protective structure, the construction process includes sequentially or alternately constructing raw piles and plain piles.

[0013] Optionally, in the fourth step of constructing the internal support system, for foundation pits of different geometric shapes, the internal support system is arranged as follows: For circular working shafts, the internal support system is mainly composed of multiple reinforced concrete horizontal frame beams or steel ring beams evenly arranged along the shaft circumference; For rectangular working pits, the internal support system can be a support system composed entirely of reinforced concrete components, including waist beams, braced support beams, and corner concrete slab supports. Alternatively, in some sections or under specific conditions, a hybrid support system combining reinforced concrete supports and steel supports can be used. For special-shaped working pits, due to the complex stress caused by their irregular plane shapes, concrete slab supports should be installed at all internal angles formed by supporting piles for special reinforcement, and each internal support should preferably use reinforced concrete supports with good integrity and high rigidity to ensure the overall stability and corner safety of the foundation pit under complex stress conditions.

[0014] Optionally, the waist beam in the internal support system is a reinforced concrete waist beam or a steel waist beam.

[0015] Compared with the prior art, the present invention has the following beneficial effects: Multi-type support collaborative design: This invention proposes for the first time a dynamic support type selection method based on environmental sensitivity. This method can cover a variety of scenarios, including densely populated urban areas, traffic flow, and complex spaces. This innovation not only improves construction adaptability but also provides more possibilities for engineering design. The use of a steel-concrete hybrid support system improves support efficiency by optimizing stress transfer between steel pipes and concrete and facilitating the easy installation and removal of steel supports. This innovative support system not only increases construction speed but also reduces material costs, resulting in significant economic benefits. Compared with traditional methods, this invention can reduce surface subsidence, shorten construction periods, and effectively lower the risk of secondary disasters. It not only achieves a technological breakthrough but also makes significant contributions to environmental protection and construction safety, providing new ideas and methods for urban underground space development. This technology can flexibly use rectangular, circular, special-shaped or sprayed anchor support structures according to different surrounding environmental conditions, and cleverly combines the dual advantages of steel support and concrete support. By dynamically selecting appropriate support structures and mixed support systems, it significantly reduces the negative impact of working pit excavation on surrounding buildings, roads and underground pipelines, while greatly improving construction efficiency, reducing costs, and breaking the inherent thinking of a unified foundation pit support form. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic structural diagram of the shotcrete support in the deep foundation pit construction method based on the environment-sensitive multi-form support system of the present invention; Figure 2 Schematic diagram of the structure of the steel mesh of the present invention; Figure 3 This is a schematic diagram of the position structure of the anchor rod of the present invention; Figure 4 This is a structural diagram of the circular working shaft support diagram of the present invention; Figure 5 This is a schematic diagram of the concrete support structure of the rectangular working pit of the present invention; Figure 6 This is a schematic diagram of the structure of the steel and concrete supports of the rectangular working pit according to the present invention; Figure 7 This is a schematic diagram of the construction structure of the steel and concrete support diagram of the rectangular working pit of the present invention; Figure 8 This is a structural schematic diagram of the special-shaped working shaft support diagram described in the present invention.

[0017] In the figure: 1. Support piles; 11. Steel piles; 12. Plain piles; 2. Crown beam; 3. Waist beam; 4. Support beam; 5. Steel support; 6. Concrete slab support; 7. Horizontal frame beam; 8. Anchor rod; 9. Sprayed concrete surface layer; 10. Steel mesh; 11. Interlocking piles. DETAILED DESCRIPTION

[0018] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0019] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0021] The present invention provides a deep foundation pit construction method based on an environmentally sensitive multi-form support system, referring to Figures 1-8 , including the following steps: Step 1: Before the formal construction of the deep foundation pit project, a comprehensive survey of the surrounding environment of the project site (including sensitive objects such as adjacent buildings, structures, and vegetation), the distribution of underground pipelines, and detailed geological and hydrological conditions should be conducted, and preliminary support strategies and environmental protection measures that are suitable for the environment should be determined; Step 2: Comprehensively consider the excavation depth, plan dimensions, functional use of the foundation pit, specific environmental sensitivity factors of the project site (including but not limited to the type, structure, foundation form, distance from the foundation pit edge and protection level requirements of adjacent buildings / structures, traffic volume and traffic control requirements of surrounding roads, protection requirements of important vegetation, etc.), detailed geological conditions (such as soil properties and groundwater conditions), and specific project requirements (such as the function as a launch shaft or receiving shaft for tunneling equipment). Dynamically select one or a combination of the most appropriate support forms from a variety of support forms, including rectangular support, circular support, special-shaped support, and shotcrete support. Step 3: Based on the support form finally selected in Step 2, use the corresponding mature and reliable construction technology to complete the construction of the foundation pit perimeter protection structure; Step 4: Based on the selected external protection support form and the actual excavation depth of the foundation pit, lay out the internal support system in layers and sections.

[0022] Among them, special-shaped supports include L-shaped, T-shaped, cross-shaped or irregular polygonal supports.

[0023] The external protective structure includes but is not limited to a bored interlocking pile 11 system consisting of a meat pile 11 and a plain pile 12 interlocked with each other, or a sprayed anchor surface support system consisting of anchor rods 8 (or soil nails), a steel mesh 10 and sprayed concrete, or an underground continuous wall, or an SMW method pile, etc.

[0024] The internal support system includes a combination of one or more components: crown beams 2, waist beams 3, horizontal frame beams 7, braced support beams 4, concrete slab supports 6, and steel plate supports. Furthermore, a hybrid support system combining reinforced concrete and steel supports 5 may be employed in some or all sections, depending on the specific project design requirements and economic and technical comparisons. Reinforced concrete supports are installed at the first support position in the upper part of the foundation pit, while steel supports 5 are installed at the remaining support positions in the middle and lower parts of the foundation pit. Support beams 4, composed of steel bars and concrete, connect the supports on both sides of the foundation pit to form a support structure, maintaining its stability. Concrete slab supports 6 are installed at the angle formed along the edges of the foundation pit supports.

[0025] In step 2, support options include: When the designed excavation depth of the foundation pit exceeds 10 meters and there are existing buildings or important structures nearby whose deformation needs to be strictly controlled, a rectangular support form with good integrity and high rigidity is preferred (such as using bored interlocking piles11 or underground continuous walls as the enclosure structure, combined with multiple internal supports); When the excavation depth of the foundation pit exceeds 10 meters, or the foundation pit needs to pass through relatively hard rock formations, and the main function of the working shaft is to serve as the starting shaft or receiving shaft for tunneling equipment (such as shield machines and pipe jacking machines), circular support is preferred, considering the characteristics of circular structures with uniform force and good integrity. When the site where the working pit is located has an irregular shape and limited space, or in order to minimize the interference and impact on surrounding existing buildings, important underground pipelines, and important immovable green plants, or when construction needs to adapt to busy traffic conditions, it is preferred to use a special-shaped support form that can flexibly adapt to the site boundary conditions; When the geological conditions are relatively good (such as the soil has strong self-stabilizing ability), the surrounding environment is relatively simple and open (no important protection objects), the requirements for foundation pit deformation control are not high, and the project takes economy as one of the main considerations, the spray anchor support form can be selected. In the third step of the support structure construction, if bored interlocking piles 11 are selected as the outer protective structure, the construction process includes sequentially or alternately constructing the steel piles 11 and the plain piles 12, wherein the steel piles 11 are formed by hanging the steel cage after the pile hole is formed and then pouring underwater concrete, while the plain piles 12 are formed by directly pouring underwater concrete or minimally reinforced concrete after the pile hole is formed. The steel piles 11 and the plain piles 12 overlap each other in the plane layout, and some pile materials are cut and interlocked with each other, thereby forming a continuous underground retaining wall with good water-stopping effect and overall rigidity. Excavation is carried out at a slope ratio of 1:1.5. After excavation reaches the elevation, anchor holes are drilled on the slope surface, anchor rods 8 are inserted, and M30 cement mortar is continuously poured from bottom to top. Grouting can be stopped when slurry overflows from the hole or the exhaust pipe stops exhausting and the grouting requirements are met. Then, 10 pieces of steel mesh with a spacing of 200x200 are installed on the slope surface and sealed with a 100mm thick C20 sprayed concrete surface layer 9, thereby forming support for the foundation pit.

[0026] After the construction of the supporting pile 1 is completed, the top of the pile is chiseled out to remove the concrete containing impurities, at least 0.5m above. After the chiseling is completed, the steel bars are tied, the formwork is set up and fixed. At the same time, steel bars need to be reserved at the position of the connecting support beam 4, and then concrete is poured to form a crown beam 2 that is completely in fit with the supporting pile 1; similarly, concrete slab support 6, the first support beam 4 or horizontal frame beam 7 are constructed at the reserved steel bar position of the crown beam 2, so that the foundation pit supporting pile 1, crown beam 2 or horizontal frame beam 7, concrete slab support 6, and the first support form a whole to support the foundation pit.

[0027] In the fourth step of the internal support system construction, the typical arrangement of the internal support system for foundation pits of different geometric shapes is as follows: For a circular working shaft, its internal support system is mainly composed of multiple reinforced concrete horizontal frame beams 7 or steel ring beams evenly arranged along the shaft circumference; For rectangular working pits, the internal support system can be a support system composed entirely of reinforced concrete components, including waist beams 3, bracing beams 4, and corner concrete slab supports 6. Alternatively, in some sections or under specific conditions, a hybrid support system combining reinforced concrete supports and steel supports 5 can be used to optimize construction efficiency and cost. For special-shaped working pits, due to the complex stress caused by their irregular plane shapes, concrete slab supports 6 should be set at all the inner angles formed by the support piles 1 for special reinforcement, and each internal support should preferably use reinforced concrete supports with good integrity and high rigidity to ensure the overall stability and corner safety of the foundation pit under complex stress conditions.

[0028] After the construction of the first horizontal frame beam 7 is completed in the circular working pit, continue to excavate the earth to the bottom elevation of the second horizontal frame beam 7, tie the steel bars, set up the formwork and fix it, pour concrete to form the horizontal frame beam 7, and then cycle through the next horizontal frame beam 7 until the bottom plate is excavated.

[0029] For rectangular working wells, one method is to use reinforced concrete to make a waist beam 3. When tying the steel bars, support beam 4 and concrete slab support 6 steel bars are reserved and tied. The formwork is set up and fixed, and concrete is poured to form waist beam 3, support beam 4 and concrete slab support 6. The next waist beam 3, support beam 4 and concrete slab support 6 are implemented in a cycle until excavation and the bottom plate; the other method is to use 2-work 45C steel to make waist beam 3, hoist and weld pipes to the waist beam 3 to fix them to form steel support 5, and weld and install steel plate supports at the four corners. This method combines reinforced concrete support beam 4 with steel support 5, and completes each support according to the pre-design until excavation to the bottom plate.

[0030] After the first support of the special-shaped working pit is completed, continue to excavate the earth to the bottom elevation of the second support beam 4, tie the waist beam 3, concrete slab support 6, and support beam 4 steel bars, set up the formwork and fix it, pour concrete to form waist beam 3, concrete slab support 6, and support beam 4, and cycle in sequence to implement the next waist beam 3, concrete slab support 6, and support beam 4 until the bottom plate is excavated.

[0031] The waist beam 3 in the internal support system can be selected as a reinforced concrete waist beam 3 or a steel waist beam 3 according to the engineering design requirements and material supply conditions; the steel support 5 usually adopts a standard length of welded steel pipe or steel, which is reliably connected to the waist beam 3 through a special adjustable joint or welding method, and can apply a certain amount of prestress.

[0032] During the entire process of foundation pit excavation and support construction, the deformation of the foundation pit itself (such as pit wall displacement, pit bottom uplift, support axial force changes, etc.) and the environment around the foundation pit (such as settlement and inclination of adjacent buildings, surface displacement, groundwater level changes, pipeline deformation, etc.) are systematically and continuously monitored dynamically, and the monitoring data are promptly fed back to the design and construction management personnel; based on the analysis results of the monitoring data, the subsequent support parameters (such as support spacing, pre-axial force size), excavation methods or construction procedures are dynamically adjusted and optimized when necessary to ensure the project safety and environmental protection goals.

[0033] The above are only preferred embodiments of the present invention and do not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A deep foundation pit construction method based on an environmentally sensitive multi-form support system, characterized in that: The following steps are involved: Step 1: Before the formal construction of the deep foundation pit project, a comprehensive survey of the surrounding environment, underground pipeline distribution and detailed geological and hydrological conditions of the project site is carried out, and preliminary support strategies and environmental protection measures that are suitable for the environment are determined; Step 2: Taking into account the excavation depth, plan dimensions, functional requirements, specific environmental sensitivity factors of the project site, detailed geological conditions, and specific project requirements, dynamically select one or a combination of the most appropriate support forms from a variety of support types, including rectangular support, circular support, special-shaped support, and shotcrete support. Step 3: Based on the support form finally selected in Step 2, use the corresponding mature and reliable construction technology to complete the construction of the foundation pit perimeter protection structure; Step 4: Based on the selected external protection support form and the actual excavation depth of the foundation pit, lay out the internal support system in layers and sections.

2. The deep foundation pit construction method based on the environmentally sensitive multi-form support system according to claim 1 is characterized in that: The special-shaped supports include L-shaped, T-shaped, cross-shaped or irregular polygonal supports.

3. The deep foundation pit construction method based on the environmentally sensitive multi-form support system according to claim 1 is characterized in that: The external protective structure includes but is not limited to a bored interlocking pile system consisting of meat piles and plain piles interlocking with each other, or a sprayed anchor surface support system consisting of anchor rods, steel mesh and sprayed concrete, or an underground continuous wall, or SMW method piles.

4. The deep foundation pit construction method based on the environmentally sensitive multi-form support system according to claim 1 is characterized in that: The internal support system includes a combination of one or more components selected from the group consisting of crown beams, waist beams, horizontal frame beams, support beams, concrete plate supports, and steel plate supports.

5. The deep foundation pit construction method based on the environment-sensitive multi-form support system according to claim 4 is characterized in that: The reinforced concrete support is arranged at the first support position at the upper part of the foundation pit, and the steel support is arranged at the remaining support positions in the middle and lower part of the foundation pit.

6. The deep foundation pit construction method based on the environment-sensitive multi-form support system according to claim 4 is characterized in that: The support beam is composed of steel bars and concrete, and is connected to the supports on both sides inside the foundation pit to form a support for maintaining the stability of the foundation pit.

7. The deep foundation pit construction method based on the environment-sensitive multi-form support system according to claim 4 is characterized in that: The concrete slab is supported at an angle formed along the edge of the foundation pit support.

8. The deep foundation pit construction method based on the environment-sensitive multi-form support system according to claim 1 is characterized in that: In the third step of the support structure construction, if bored interlocking piles are selected as the outer protective structure, the construction process includes sequentially or alternately constructing raw piles and plain piles.

9. The deep foundation pit construction method based on the environment-sensitive multi-form support system according to claim 1 is characterized in that: In the fourth step of the internal support system construction, for foundation pits of different geometric shapes, the internal support system is arranged as follows: For circular working shafts, the internal support system is mainly composed of multiple reinforced concrete horizontal frame beams or steel ring beams evenly arranged along the shaft circumference; For rectangular working pits, the internal support system can be a support system composed entirely of reinforced concrete components, including waist beams, braced support beams, and corner concrete slab supports. Alternatively, in some sections or under specific conditions, a hybrid support system combining reinforced concrete supports and steel supports can be used. For special-shaped working pits, due to the complex stress caused by their irregular plane shapes, concrete slab supports should be installed at all internal angles formed by supporting piles for special reinforcement, and each internal support should preferably use reinforced concrete supports with good integrity and high rigidity to ensure the overall stability and corner safety of the foundation pit under complex stress conditions.

10. The deep foundation pit construction method based on the environment-sensitive multi-form support system according to claim 4, characterized in that: The waist beam in the internal support system is made of reinforced concrete waist beam or steel waist beam.

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