A cooperative compression-tension telescopic support pipe connector for a subway foundation pit, and application thereof in supporting the subway foundation pit and a subway foundation pit supporting method

Abstract

The application relates to the field of building, in particular to support during subway foundation pit excavation. The application provides a cooperative compression and tension telescopic support pipe connector for a subway foundation pit, application of the cooperative compression and tension telescopic support pipe connector in supporting the subway foundation pit and a subway foundation pit supporting method. A rigid box body with distributed screw holes is anchored to an underground continuous wall through expansion bolts, and a dynamic bearing system with an external gear and internal thread which is specially adapted to the subway foundation pit is creatively adopted, so that the stress of the soil outside the pit is directly converted into structural pre-tightening force; an electric drive control technology is adopted to realize millimeter-level precision adjustment, and the traditional loose joint structure is completely replaced, so that the problems of the prior art, such as that the shear / bending strength is insufficient to support 30% of the body, and the stress concentration exceeds the standard, are solved, and a breakthrough innovative protection mechanism is provided for deep foundation pit engineering.

Description

Technical Field

[0001] This invention relates to the field of construction, and in particular to support during the excavation of subway foundation pits. Background Technology

[0002] Since the beginning of the 21st century, China's economy has developed rapidly, and cities have entered a stage of rapid development. Urban underground engineering is one of the effective ways to solve traffic congestion and urban land shortage.

[0003] Subway construction is inseparable from foundation pit excavation. To ensure the smooth construction of the subway foundation pit and the safety of surrounding buildings, a support structure is usually installed between the subway foundation pit and its side walls. This structure is mostly supported by internal bracing. Traditional internal bracing systems are mostly made of steel and concrete.

[0004] The limitations of concrete supports are as follows: Concrete supports require demolition by blasting or mechanical crushing, generating noise, vibration, and dust, significantly impacting the surrounding environment. For example, if a foundation pit in a city center uses concrete supports, demolition by blasting would require closing surrounding roads, causing traffic congestion and resident complaints; it also has a high density (approximately 2.4 t / m³). 3 The additional load generated by the self-weight of the support may exacerbate the deformation of the retaining structure, especially in soft soil foundations where additional reinforcement is required; the rigid joint between the support and the retaining structure (such as continuous walls and piles) requires pre-embedded steel bars and on-site welding, which is prone to stress concentration or cracking due to construction errors. For example, in one project, the concrete at the end of the support was spalled due to a 5cm misalignment of the steel bars at the joint, forcing grouting reinforcement; concrete supports are rigid structures and cannot be adjusted in length or prestressed like steel supports, making it difficult to adapt to soil deformation after excavation; concrete supports are disposable structures and cannot be recycled, resulting in serious material waste and failing to meet the requirements of green construction.

[0005] The limitations of steel supports are that the shear and bending resistance of the steel support connectors is weaker than that of the support body itself, and they cannot withstand tensile forces, which can easily lead to overall instability. Replacing the connectors attached to the diaphragm wall with steel supports could very likely have reduced or even prevented this accident.

[0006] Comparative mechanical tests conducted according to the standard "Steel Structure Joints for Buildings" (JG / T 476-2015) revealed that the shear and bending strength limits of traditional flexible joints are only about 70% of the strength limits of the supporting pipe body, with a strength gap of up to 30%. This quantitative result accurately reveals its nature as a weak link in the structure.

[0007] In recent years, some scholars and engineers have proposed using a double-threaded structure, such as patent (CN213390163U). However, adjustment relies on manually rotating the hexagonal rod with a wrench, which is laborious in deep foundation pit operations and lacks fine-tuning precision. The extension rod requires manual assembly of the connecting seat, resulting in low modular assembly efficiency. (CN222413045U) The four telescopic components require independent adjustment of the drive ring, leading to poor synchronization and a tendency to tilt and become unstable. When the bidirectional screw extends the support plate, the screw is exposed to the soil environment, making it prone to jamming and failure. There is no load-bearing protection, and the screw may bend and deform under overload. (CN222332723U) The threaded rod and sleeve are manually rotated and connected, making hole positioning difficult (aligning the slider and the fixing seat is required). The extension plate relies on spring limit blocks, which can easily trigger unexpected contraction due to foundation pit vibration. The quick-release design sacrifices structural rigidity, posing a risk of instability under high load conditions. The above three patents are limited to the first layer and cannot be applied to other layers of multi-layer deep foundation pits. Furthermore, the effective bearing area is small, failing to meet the high-pressure requirements of subway foundation pits, resulting in poor practicality.

[0008] In addition, unlike ordinary foundation pits, subway foundation pits have the following characteristics:

[0009] I. Differences in Control Standards: A Dimensional Leap from "Centimeter-Level Tolerance" to "Millimeter-Level Sensitivity"

[0010] 1. Control Paradigm for Ordinary Excavation Pits: The surrounding environment of ordinary building excavation pits is usually relatively relaxed, possibly adjacent to roads or municipal pipelines, or at a certain distance from existing buildings. Their deformation control targets are relatively lenient, falling within the "centimeter-level tolerance" range. In industry standards and practice, the allowable horizontal displacement of the top of the retaining structure is usually in the range of 30-50 mm, and the allowable ground settlement is mostly between 20-40 mm. Within this range, slight deformation of the support system and losses of prestress due to material relaxation or temperature changes are within acceptable safety margins and will not immediately lead to catastrophic consequences. 2. Control Paradigm for Subway Excavation Pits: Subway excavation pits are always located in the core area of ​​cities, often adjacent to operating subway tunnels, high-speed rail lines, important historical buildings, and dense integrated utility tunnels—"lifeline" projects crucial to urban operational safety. These structures are extremely sensitive to foundation deformation, and their control standards are "millimeter-level sensitive." For example, to ensure the safe and stable operation of subway trains, the settlement or horizontal displacement control standards for adjacent tunnels are usually extremely stringent, requiring strict control within a range of +1mm / -3mm or even smaller. Under such extreme requirements, any slight deformation, uncontrollable prestress relaxation, or axial force attenuation in ordinary support devices can be the "last straw that breaks the camel's back," causing the protected object to deform beyond the limit and leading to serious consequences.

[0011] Typical Case: A Crossing Project in the Shanghai Metro

[0012] The subway station was constructed using the open-cut method, with the minimum clearance between the sidewall of its ultra-deep excavation pit and the operating subway tunnel being only 3.5 meters. The subway operator's protection requirement was that the settlement of the operating tunnel must be strictly controlled within +1mm / -3mm. In this case, the retaining structure of the excavation pit (diaphragm wall) will deform inward under soil pressure. This deformation will disturb the soil around the tunnel, leading to tunnel settlement. If ordinary steel supports and their hydraulic actuators are used, the error in applying prestress in a single instance may exceed 10%, and due to the unreliable locking mechanism, the axial force may decrease by more than 15% within 24 hours due to material creep and temperature changes. This kind of support system, lacking precision and stability, provides a constantly changing support stiffness, failing to provide a constant, rigid constraint on the retaining structure. This results in the inability to accurately predict and control the deformation of the retaining structure, inevitably causing disturbance to the soil around the tunnel and leading to excessive tunnel settlement. The consequences will be: shutdown of the existing line, costly tunnel lifting and reinforcement, huge social impact, and exorbitant compensation. Therefore, in foundation pits located close to lifeline projects, ordinary support devices are excluded from the design and selection stage due to their inherent low precision and easy loosening, and are absolutely unusable.

[0013] II. Differences in Environmental Boundaries and Load Conditions: From "Static Compression" to "Dynamic Alternating Tension and Compression"

[0014] 1. Load characteristics of ordinary foundation pits:

[0015] The load conditions of ordinary foundation pits are relatively simple and stable. The support system mainly considers static earth pressure and water pressure, and the support components mainly function as axially compressed members. The design of traditional hydraulic hinges is based on this assumption, and its "wedge block" locking mechanism is only effective when under pressure.

[0016] 2. The complexity of the load on the subway foundation pit:

[0017] The working conditions of subway foundation pits are extremely complex, and the support system often needs to withstand complex dynamic and alternating tensile and compressive loads. For example, during the excavation of deep foundation pits, due to excavation unloading, changes in groundwater, or disturbances from surrounding loads, the retaining structure (diaphragm wall) may bulge outwards from the pit, causing a change in the deformation mode of the diaphragm wall. This deformation will force the installed support system to elongate, thus changing the support components from the expected compressive state to a tensile state. In addition, large-span steel supports are significantly affected by diurnal and seasonal temperature differences, and thermal expansion and contraction will generate complex additional stresses within the system.

[0018] Under such working conditions, traditional hydraulic swivel joints have a fatal flaw: once the support is subjected to tension, the wedge blocks inside will instantly lose their restraint, resulting in the complete loss of prestress and support failure.

[0019] Typical Case: A subway foundation pit project in Shenzhen adjacent to an operating line

[0020] A 23-meter-deep foundation pit for a subway transfer station in Shenzhen required excavation adjacent to an existing subway tunnel, with a minimum clearance of less than 5 meters between the two. When the pit reached its lowest level, the combined effects of dewatering and unloading caused displacement of the retaining structure (diaphragm wall) outwards. This deformation forced multiple installed steel supports to elongate, transforming them from compression members to tension members. The project utilized traditional hydraulic swivel joint supports. At the moment the supports began to bear tension, the wedge-shaped blocks inside the swivel joints failed to maintain their locking position under the tension, popping out of their pins and causing several supports to simultaneously detach and fail. The load borne by these supports instantly transferred to the remaining support system, triggering a chain reaction that ultimately led to a sudden alarm for the retaining structure displacement, causing a rapid deterioration in the safety situation of the foundation pit and nearly resulting in a major engineering accident. This case fully exposes the fatal flaw of ordinary support devices: they can only withstand compression, not tension. In the complex and dynamic load environment of a subway foundation pit, this defect is like a time bomb. Once the deformation mode of the retaining structure changes unexpectedly, it will instantly trigger a dangerous situation.

[0021] III. Differences in Construction Philosophy and Efficiency: From "Strength First" to "Stiffness and Spatiotemporal Effects First"

[0022] 1. Construction logic of ordinary foundation pits:

[0023] The design of ordinary foundation pits is mostly controlled by strength, that is, ensuring that the support and retaining structures are strong enough to avoid being crushed. The construction pace allows for some flexibility, and the relatively long time for support installation, curing, and dismantling has a relatively controllable impact on the overall construction period.

[0024] 2. The Ironclad Rules of Subway Excavation Construction:

[0025] The design of subway foundation pits is dominated by stiffness and spatiotemporal effects. Rapid excavation and rapid support are indisputable principles. After excavation, stress is released, and deformation continues to develop with increasing exposure time (spatiotemporal effect). Therefore, the exposure time of the foundation pit is directly proportional to the risk. The installation speed of each support is crucial; the interval between excavation and support effectiveness must be minimized. The slow installation speed, low prestressing efficiency, and insufficient joint stiffness of ordinary supports directly prolong the high-risk operation time and cannot meet the requirement of rapidly forming a high-rigidity support system.

[0026] Typical Case: An ultra-deep and ultra-large foundation pit in the core area of ​​Beijing CBD

[0027] Located in the core area near Guomao Bridge in Beijing, the foundation pit is deep and large, and its impact on surrounding top-tier office buildings, hotels, and transportation hubs must be strictly controlled. In this project, "time is risk, efficiency is safety." If cast-in-place concrete supports are used, each support requires at least 7-10 days of exposure time in the foundation pit, from earthwork excavation, rebar binding, formwork erection to concrete pouring and curing to reach design strength. Deformation will continue to develop, accumulating risks and causing significant anxiety. If ordinary prefabricated steel supports are used, relying on manual hydraulic jacks for pre-jacking and locking requires 4-5 workers operating for several hours, which is inefficient and cannot meet the requirement of quickly forming hundreds of support systems in a foundation pit of tens of thousands of square meters. This slow-paced construction mode would artificially prolong the high-risk period, fundamentally contradicting the core safety requirement of "rapid completion" for subway foundation pits.

[0028] IV. Differences in Construction Environment

[0029] Subway foundation pits need to traverse complex geological strata (such as soft soil, sand layers, and alternating layers of rock), requiring special attention to quicksand and piping; groundwater control is stringent: the water level must be lowered to 1-2 meters below the bottom of the pit, and the impact of long-term precipitation on surrounding settlement must be considered. Ordinary foundation pits are mostly located in shallow urban built-up areas with relatively homogeneous strata (such as clay and silty clay); groundwater control is simple: short-term precipitation is sufficient, with a small impact on the surrounding water level.

[0030] Furthermore, the surrounding environmental constraints differ. Subway foundation pits are adjacent to sensitive facilities: they are often located in the city's core area, with existing buildings (residential / commercial buildings), underground pipelines (gas pipes / water supply pipes), and existing subway lines within 3-5 meters (the minimum clearance is only 2-3 meters); settlement control is extremely strict: the surrounding ground settlement limit is ≤30mm, pipeline settlement is ≤10mm, and the settlement of existing subway structures is ≤5mm. Ordinary foundation pits are mostly surrounded by open land or low-rise buildings, and the distance to the foundation pit is often >10 meters; settlement control is more lenient: the ground settlement limit is ≤50mm, and the requirements for the impact on pipelines and buildings are low.

[0031] Therefore, the area poses a high risk of quicksand and piping, requires strict dewatering measures, and is concerned about potential subsidence in the surrounding area. Furthermore, due to its extremely close proximity to sensitive facilities, subsidence control must be implemented at the millimeter level (≤5mm).

[0032] Traditional support systems are slow to install, resulting in prolonged exposure of the excavated soil and increased risks of quicksand and piping. There is an urgent need to provide stable and reliable support to ensure the stability of the retaining structure during precipitation. Currently, no publicly available subway excavation support device can overcome these problems. Summary of the Invention

[0033] This invention provides a collaborative compressive-tensile telescopic support pipe connector and a support method for subway foundation pits. A rigid box with distributed threaded holes is anchored to a continuous underground wall using expansion bolts. It also features a unique "external gear-internal thread" dynamic load-bearing system adapted to subway foundation pits, directly converting the stress of the external soil into structural preload. Utilizing electric drive control technology, it achieves millimeter-level precision adjustment, completely replacing the traditional flexible head structure. This invention offers a breakthrough solution to the persistent problems of insufficient shear / bending strength (less than 30% of the main support) and excessive stress concentration in existing technologies, providing a groundbreaking and innovative protection mechanism for deep foundation pit engineering.

[0034] To achieve the above objectives, the present invention provides the following specific solutions for a compressive-tensile synergistic telescopic pipe connector for internal support in foundation pits and a foundation pit support method:

[0035] This invention provides a collaborative compressive and tensile telescopic support pipe connector for subway foundation pits, comprising a box-type structure and a pipe structure;

[0036] The first side of the box-shaped structure is provided with distributed screw holes, which are used to anchor the box-shaped structure to the underground continuous wall by expansion bolts. The first side is provided with multiple round-ended rectangular grooves inside the box-shaped structure to avoid the protrusions of the screw holes.

[0037] A circular hole is provided at the center of the second side of the box-shaped structure opposite to the first side. Multiple grooves are arranged in the circular hole, and threaded rollers are installed in each of the multiple grooves for relative movement between the pipe structure and the circular hole of the box-shaped structure.

[0038] A small gear is installed on the second outer surface of the box-shaped structure next to the circular hole. The small gear rotates independently of the box-shaped structure.

[0039] The first end of the pipeline structure is provided with a flange, which is used to connect with the supporting pipeline in the foundation pit. The flange is located outside the box-shaped structure.

[0040] The second end of the pipe structure, opposite to the first end, is provided with multiple rounded rectangular protrusions. These protrusions pass through circular holes and fit into multiple rounded rectangular grooves of the box-shaped structure. Therefore, the second end of the pipe structure is located inside the box-shaped structure. The outer surface of the pipe structure is provided with a spiral thread, and two external gear internal thread components are fitted around the pipe structure. The internal threads of the external gear internal thread components mesh with the spiral thread, and the pinion meshes with the external gear of the external gear internal thread components to drive the external gear internal thread components to move axially along the spiral thread.

[0041] The number of internal threaded components of the external gear is 2, and the diameter of each component is larger than that of the circular hole. They are located on both sides of the circular hole of the box-shaped structure and abut against the box-shaped structure. The number of small gears that match them is also 2.

[0042] Preferably, the round-end rectangular groove has a certain height so that when the relative positions of the box-type structure and the pipe structure in the supporting pipe connector change, the round-end rectangular protrusion of the pipe structure can be inserted into the round-end rectangular groove of the box-type structure to avoid the supporting pipe rotating in the foundation pit.

[0043] Preferably, a gap is provided between the rounded rectangular protrusion of the pipe structure and the bottom of the rounded rectangular groove of the box structure, and the gap is used to insert a wedge to improve the compressive strength.

[0044] Preferably, one end of the pinion has a protruding cylinder with a diameter of 25-35mm and a length of 45-55mm, and a bearing is fitted on the cylinder; the other end of the pinion has a hexagonal groove, which is used to connect with an electric drill to drive the pinion to rotate.

[0045] Preferably, the meshing contact surface between the threaded wire and the internal threaded component of the external gear, and the contact surface between the threaded roller and the threaded wire, are all filled with a graphene lubricating layer.

[0046] Preferably, the height of the threaded roller is 15-25mm, and each side of the threaded roller is provided with a cylinder with a diameter of 3-6mm and a length of 15-25mm; a cover block is also provided in the groove of the circular hole, and the cover block is fixed to the box-shaped structure by screws to limit the threaded roller.

[0047] Preferably, the number of distributed screw holes on the first side of the box-shaped structure is 8, and the diameter of the circular hole is 600mm.

[0048] Preferably, the engagement length of the outer thread of the pipe structure is 400mm, the coverage diameter is 600mm, and the pitch is 8mm; the internal thread specification of the external gear internal thread component is consistent with the thread. Preferably, the pipe structure is machined from a pipe body and has a flange on one side and three protruding round-ended rectangles on the other side, with a thread on the outer side having an engagement length of 400mm, a coverage diameter of 600mm, and a coverage pitch of 8mm. Preferably, the pipe structure is equipped with two external gear internal thread components, with the same internal thread specification as above. Preferably, the housing has eight evenly distributed bolt holes on the side with bolt holes, and three grooves on the same side, avoiding the bolt holes, correspond one-to-one with the three protrusions of the pipe structure. The center of the opposite side has a circular hole with a diameter of 600mm, and the lower half of the circular hole has seven evenly arranged grooves. A small gear that matches the specification of the external gear internal thread component is installed on the upper right side of the circular hole. Preferably, the groove in the lower half of the circular hole is fitted with a threaded roller that matches the specifications of the internal threaded component of the external gear. The roller has a height of 20mm and two protruding cylinders with a diameter of 6mm and a length of 20mm on each side.

[0049] Preferably, one end of the pinion has a protruding cylinder with a diameter of 30mm and a length of 50mm, and a corresponding bearing is installed on the cylinder to reduce friction; and the other end of the pinion has a hexagonal groove for driving the electric drill.

[0050] The present invention also provides the application of the above-mentioned synergistic compressive and tensile telescopic support pipe connector in supporting subway foundation pits.

[0051] The present invention also provides a method for installing and using the above-mentioned cooperative compressive and tensile telescopic support pipe connector, comprising the following steps:

[0052] S1, the box-shaped structure with distributed screw holes is anchored to the underground continuous wall by bolts, and an external gear internal thread component is installed on the outside of the circular hole of the box-shaped structure;

[0053] S2, place the jack into the box-shaped structure, use a crane to move the pipeline structure to a suitable position, and apply a certain load to its flange to make it enter the box-shaped structure supported by the jack;

[0054] S3, the second external gear internal thread component is installed on the inner side of the circular hole of the box structure. After moving to the appropriate position, the applied force is unloaded and the jack is removed.

[0055] S4. After connecting the support pipe in the pit to one side of the flange, insert the two small gears into the corresponding holes of the box structure. Use a hexagonal interface direct-connect electric drill to rotate the small gear on one side, thereby driving the internal threaded part of the external gear to mesh and apply bolt preload at the same time. The same applies to the other side.

[0056] S5, after installation, the pinion gear can be uninstalled for use during the next adjustment;

[0057] S6. After the rest of the parts are installed, insert the wedge into the gap to improve its compressive strength, and the installation is complete.

[0058] In summary, the present invention has the following beneficial effects:

[0059] This invention provides a collaborative compressive-tensile telescopic support pipe connector for subway foundation pits. It uses expansion bolts to fix the housing with bolted holes to a continuous underground wall, and utilizes an external gear and internal thread component to fix the flanged pipe, enabling it to withstand soil stress outside the pit. This invention features a groundbreaking integrated composite structure of "external gear drive - internal thread engagement" adapted to the subway foundation pit construction environment. The leverage effect of the external gear doubles the installation torque, significantly reducing operational intensity by over 60% and increasing construction efficiency by 3 times. Its precision internal thread system actively compensates for ±5mm structural gaps, simultaneously increasing axial tensile bearing capacity to 2.2 times that of traditional hinged connectors. Furthermore, a gradient graphene lubricating layer is composite-filled on the key contact surfaces of the threaded pair, resulting in a 42.7% reduction in wear rate verified by ASTM G133 standards. Combined with a modular and detachable design, the component recycling rate reaches 98%. This comprehensive approach achieves a revolutionary breakthrough in construction convenience, structural safety, long-term durability, and circular economy, providing a disruptive alternative solution for the field of building steel structures.

[0060] Specifically:

[0061] 1. Possessing "dual strength in tension and compression," it eliminates catastrophic failures caused by unexpected working conditions. The rigid self-locking connection mechanism, consisting of an "external gear-internal thread" transmission pair and a "wedge block," provides a connection node similar to a "high-strength bolt." This node has excellent tensile strength, providing equally reliable and robust constraint force whether subjected to compression or tension. This fundamentally eliminates the risk of support failure and detachment due to pit bottom heave, vibration, etc., providing crucial safety redundancy for subway foundation pits to cope with complex load conditions. The spiral construction of this invention allows for free adjustment of its length, enabling the component to be used under different clearance conditions, thereby improving the accuracy and applicability of the support pipe connector in subway foundation pits.

[0062] In deep foundation pit projects for subways located only 2-3 meters from existing subway tunnels, the failure of any internal support could lead to catastrophic consequences. The rigid node of this invention, through its innovative threaded drive design, endows the support system with superior tensile strength. When the underground continuous wall deforms outwards due to changes in soil pressure, the support members may transition from a compressive state to a tensile state. At this time, this invention not only maintains structural integrity but also continuously provides constraint force through threaded engagement, effectively inhibiting further deformation of the retaining structure. This "dual strength in tension and compression" characteristic forms a crucial safety redundancy. Its external gear drive system can generate an initial preload of 800kN, actively controlling deformation development and efficiently converting external soil stress into the structure's own resistance, providing a safety guarantee for foundation pit construction adjacent to lifeline projects that traditional support technologies cannot achieve. 2. Precise control of axial force, achieving "millimeter-level" deformation control. The core of controlling settlement lies in controlling the deformation of the retaining structure, and the core of deformation control lies in precisely controlling the axial force of each support. This invention, through electric tensioning, can control the axial force accuracy to ±2% and maintain this accuracy over a long period (the external gear-internal thread structure allows for flexible expansion and contraction, meeting axial displacement requirements under various uncertainties). This means that designers can more accurately predict and control the deformation of the foundation pit, thus enabling them to meet the almost stringent settlement requirement of ≤5mm.

[0063] 3. It achieves true "prefabrication" and "electrification." All components are prefabricated in the factory and assembled on site. The electric tensioning and fastening of a single support can be completed within 30 minutes. This is more than three times more efficient than the traditional manual hydraulic jacking method, which can greatly shorten the exposure time of the foundation pit and quickly suppress the deformation caused by time and space effects, perfectly meeting the core safety requirements of "quick and decisive action, and stability in exchange for rigidity" for subway foundation pits. Attached Figure Description

[0064] Figure 1 It is a simplified cross-sectional structural diagram of the foundation pit containing supporting pipe connectors.

[0065] Figure 2 This is a simplified diagram of the supporting pipe connector structure.

[0066] Figure 3 This is a simplified top view of the supporting pipe connector.

[0067] Figure 4 This is a simplified top view of the pinion and bearing.

[0068] Figure 5 This is a simplified structural diagram of a pinion and bearing.

[0069] Figure 6 This is a simplified cross-sectional view of the right side of the supporting pipe connector.

[0070] Figure 7 This is a simplified structural diagram of a threaded gear system.

[0071] Figure 8 This is a top view of a threaded gear system.

[0072] Figure 9 It is a threaded gear system Figure 8 A simplified cross-sectional diagram.

[0073] Figure 10 This is a Von Mises stress contour plot.

[0074] Figure 11 This is a URES displacement contour plot.

[0075] Figure 12 This is a URES displacement scaled-up contour plot.

[0076] Figure 13 It is an ESTRN strain cloud map.

[0077] Figure 14 This is a Mises stress contour plot of the connector.

[0078] Figure 15 This is a stress-strain curve diagram showing the point of maximum stress on the connector gear.

[0079] Figure 16 This is a Mises stress cloud diagram of a wedge block.

[0080] Figure 17 This is a stress-strain curve diagram at the point of maximum stress in the wedge block.

[0081] In the diagram: 101—support pipe connector, 102—4m steel support, 103—6m steel support, 1—box structure, 2—pipe structure, 3—flange, 4—external gear internal thread component, 5—threaded wire, 6—pinion, 7—clearance, 8—threaded roller, 9—cover block, 10—screw, 11—bearing. Detailed Implementation

[0082] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments.

[0083] Before installing ordinary steel supports, this invention measures the width of the foundation pit and uses steel supports at reasonable intervals, without requiring precise values. The pipe connectors supporting the foundation pit will compensate for the errors of traditional flexible joints.

[0084] Example 1

[0085] like Figure 1The diagram shown is a schematic of the application scenario of the pipe connector of the present invention in a subway foundation pit. This embodiment provides a case study of the actual application process of the product of the present invention in a subway foundation pit.

[0086] During the excavation phase, the excavation strictly follows the principle of layered and segmented excavation. After the first layer of soil is excavated to the design elevation of the first support (e.g., 1.5m below the ground surface), the bottom is manually cleared and the support axis is measured and marked. The pipe connector 101 is fixed to the diaphragm wall with expansion bolts. Then, the pre-assembled 4m steel support 102 or 6m steel support 103 is hoisted to the axis position and directly connected to the adjacent support with flanges through the pipe connector 101. Finally, threaded prestress is applied, and the pipe connector 101 replaces the hinged joint at both ends of the support. After the axial force of the upper support stabilizes (deformation ≤2mm after 24 hours of monitoring), the lower layer of soil continues to be excavated down to 3.5m, and the above process is repeated to erect the second support. At this time, the threaded structure of the pipe connector 101 (allowing ±5mm axial displacement) automatically compensates for uneven deformation of the foundation pit and avoids support expansion and contraction. The connector is only used at the support docking nodes throughout the process, which is 3 times more efficient than the traditional hinged joint installation.

[0087] like Figure 2 As shown, a collaborative compressive tensile telescopic support pipe connector for subway foundation pits includes a box-type structure 1 and a pipe structure 2.

[0088] The first side of the box-type structure 1 is provided with distributed screw holes, which are used to anchor the box-type structure 1 to the underground continuous wall by expansion bolts. The first side is provided with multiple round-ended rectangular grooves inside the box-type structure 1 to avoid the protrusions of the screw holes.

[0089] A circular hole is provided at the center of the second side opposite to the first side of the box-shaped structure 1. Multiple grooves are arranged in the circular hole, and threaded rollers 8 are installed in each of the multiple grooves for relative movement between the pipe structure 2 and the circular hole of the box-shaped structure 1.

[0090] A small gear 6 is installed on the outer surface of the second side of the box-shaped structure 1 next to the circular hole. The small gear 6 rotates independently of the box-shaped structure 1.

[0091] The first end of the pipe structure 2 is provided with a flange 3, which is used to connect with the supporting pipe in the foundation pit. The flange 3 is located outside the box structure 1.

[0092] The second end of the pipe structure 2, opposite to the first end, is a solid circle and has multiple round-ended rectangular protrusions. These protrusions pass through circular holes and fit into multiple round-ended rectangular grooves of the box-shaped structure 1. Therefore, the second end of the pipe structure 2 is located inside the box-shaped structure 1. The outer surface of the pipe structure 2 is provided with a surrounding thread 5, and two external gear internal thread components 4 are fitted around the pipe structure 2. The internal threads of the external gear internal thread components 4 mesh with the thread 5, and the pinion 6 meshes with the external gear of the external gear internal thread components 4 to drive the external gear internal thread components 4 to move axially along the thread 5.

[0093] The number of the external gear internal thread components 4 is 2, and the diameter of each component is larger than that of the circular hole. They are located on both sides of the circular hole of the box-type structure 1 and abut against the box-type structure 1. The number of the matching pinions 6 is also 2.

[0094] The rectangular groove at the round end has a certain height so that when the relative positions of the box structure 1 and the pipe structure 2 in the support pipe connector change, the rectangular protrusion at the round end of the pipe structure 2 can be inserted into the rectangular groove at the round end of the box structure 1 to avoid the support pipe rotating in the pit.

[0095] The meshing contact surfaces of the threaded wire 5 and the internal threaded component 4 of the external gear, as well as the contact surfaces of the threaded roller 8 and the threaded wire 5, are all filled with a graphene lubricating layer.

[0096] In this embodiment, the box-shaped structure 1 has eight evenly distributed bolt holes on one side with holes, and three rounded rectangular grooves on the same side, avoiding the bolt holes. The box-shaped structure 1 has a circular hole with a diameter of 600mm at its center on the opposite side with holes. The lower half of the circular hole has seven evenly arranged grooves, and a small gear 6 is installed on the upper right side of the circular hole. The pipe structure 2 has a flange 3 on one side and three protruding rounded rectangular pieces on the other side that fit perfectly with the three grooves of the box-shaped structure. It has a threaded line 5 on the outer side, and two external gear internal thread components are arranged in the middle section, with thread specifications consistent with the threaded line 5.

[0097] like Figure 3 As shown, the rectangular concave-convex part at the round end contains a gap 7, into which a corresponding wedge can be inserted to improve the compressive strength.

[0098] like Figure 4 and Figure 5 As shown, one end of the pinion 6 has a protruding cylinder with a diameter of 30mm and a length of 50mm, and a bearing 11 is fitted on the cylinder; the other end of the pinion 6 has a hexagonal groove, which is used to connect with an electric drill to drive the pinion 6 to rotate.

[0099] like Figures 7 to 9As shown, the lower half of the circular hole has a groove evenly arranged, and a threaded roller 8 is installed in the groove. The roller 8 has two cover blocks 9 corresponding to the protruding part. The cover blocks 9 are fixed to the lower half of the circular hole by four screws 10.

[0100] The length of housing structure 1 accounts for approximately 61.4% of the total connector length, and the length of pipe structure 2 accounts for approximately 73.55% of the total connector length. The interaction length between housing structure 1 and pipe structure 2 accounts for approximately 45.16% of the total connector length and approximately 61.4% of the length of pipe structure 2. The area ratio of the side of housing structure 1 with distributed screw holes to the corresponding side of the second side is approximately (1.85-2.11):1, and the area ratio of the second side of housing structure 1 to the area of ​​the circular hole is approximately (2.95-3.28):1. The ratio of the first end flange 3 of pipe structure 2 to the outer diameter of pipe structure 2 is approximately (1.27-1.56):1.

[0101] Example 2

[0102] This embodiment provides an installation method for a collaborative compressive-tensile telescopic support pipe connector for subway foundation pits, related to Embodiment 1 above. During installation, a graphite lubricant layer is first sprayed onto each threaded portion to improve its service life.

[0103] S1, the box-shaped structure 1 with distributed screw holes is anchored to the underground continuous wall by bolts, and an external gear internal thread component 4 is installed on the outside of the circular hole of the box-shaped structure 1 on the pipe structure 2.

[0104] S2, place the jack into the box structure 1, use a crane to move the pipe structure 2 to a suitable position, apply a certain load to its flange 3 to make it enter the box structure 1 supported by the jack;

[0105] S3, the second external gear internal thread component 4 is installed on the inner side of the circular hole of the box structure 1 on the pipe structure 2. After moving to the appropriate position, the applied force is unloaded and the jack is removed.

[0106] S4, after the flange 3 is connected to the support pipe in the pit, insert the two small gears 6 into the corresponding holes of the box structure 1 respectively, use the hexagonal interface direct-connect electric drill to rotate the small gear 6 on one side, thereby driving the external gear internal thread component 4 to mesh and apply bolt preload at the same time, the same applies to the other side;

[0107] S5, after installation, the pinion 6 can be uninstalled for use during the next adjustment;

[0108] S6. After the rest of the parts are installed, insert the wedge into the gap 7 to improve its compressive strength and complete the installation.

[0109] In the structure of this application, the internal threaded component of the external gear is equivalent to the nut in the bolt structure. Rotating the small gear drives the large gear, causing the internal threaded component (nut) of the external gear to move to one side of the housing. The same applies to the other side. Finally, the internal threaded components of the external gears on both sides move towards the outer wall of the housing, making the pipe structure completely fixed. In the final stage of rotation, a preload force similar to that of a bolt structure is applied to it.

[0110] Example 3

[0111] The performance of the collaborative compressive-tensile telescopic support pipe connector for subway foundation pits described in Example 1 was tested. The experimental process and conclusions are as follows:

[0112] 3.1. The wear rate was reduced by 42.7%, determined according to the internationally recognized ASTM G133 standard linear reciprocating wear test method. Under the same working conditions, the volumetric wear of the threaded pair specimen with a gradient graphene lubricating layer and the unlubricated reference specimen were compared. The precise percentage was obtained after rigorous calculation, proving that its wear resistance was significantly improved.

[0113] 3.2. The 60% reduction in operational intensity and the 3-fold increase in construction efficiency are derived from rigorous on-site comparative tests. Actual measurements using a torque sensor show that the operating force required to drive the product using a designated electric drill is only 40% of that required for traditional manual wrench operation. Furthermore, statistical analysis using time measurement methods shows that the total time to complete the installation of a single node is reduced from 45 minutes using traditional methods to 15 minutes, increasing efficiency by 300%.

[0114] 3.3. Tensile bearing capacity increased to 2.2 times. Destructive testing on a universal testing machine according to "Metallic materials, tensile testing - Part 1: Test method at room temperature" (GB / T 228.1) confirmed that its ultimate bearing capacity is 2.2 times that of the traditional hinge.

[0115] 3.4. The ±5mm gap compensation capability is a theoretical calculation based on the product's core design parameters (400mm engagement length, 8mm pitch), and has been verified by actual size measurement to confirm its ability to compensate for installation errors and adapt to deformation.

[0116] 3.5. The component recycling rate reaches 98%, a figure derived from statistical analysis of a simulation test involving hundreds of disassembly and assembly cycles. The test results show that the vast majority of major structural components can be disassembled and reused without damage, with only a few seals requiring replacement, fully verifying the recyclability of its modular design.

[0117] Example 4

[0118] For the deep foundation pit environment of subways, tensile and shear load calculations and the conversion between axial displacement and angle were performed. The parameters involved in the device are as follows:

[0119] 4.1. Calculation of tensile and shear loads:

[0120] The material for the collaborative compressive tensile telescopic support pipe connector used in this application for subway foundation pits can be Q235 steel;

[0121] The contact length between the threaded wire 5 and the internal threaded component 4 of the external gear is 100mm, covering a threaded wire with a diameter of 600mm and a pitch of 8mm, with a safety factor of 2.

[0122] Key parameters: Nominal thread diameter (D): 600 mm (major diameter), thread engagement length (L): 400 mm (thread engagement length), pitch (P): 8 mm; yield strength (σ y ): 250 MPa (conservative value, for design purposes), ultimate tensile strength (σ ult ): 400 MPa, ultimate compressive strength: same as tensile strength, shear strength (τ) ult ): Take 60% of the ultimate tensile strength, i.e., τ ult = 0.6 × 400 = 240 MPa. Thread strength can be affected by two main failure modes: tensile failure, which refers to bolt fracture at the thread root (minor diameter); and shear failure, which refers to the thread teeth being sheared off (depending on the engagement length and pitch).

[0123] Minor diameter (dmin): For metric threads, the formula for calculating the minor diameter is:

[0124] dmin = D - 1.0825 × P In the formula: dmin For a path, D The nominal diameter of the thread. P Pitch;

[0125] Substitute the value: dmin = 600 - 1.0825 × 8 = 591.34 mm

[0126] Core cross-sectional area (Acore): used for tensile strength calculation.

[0127] Acore = π × (dmin / 2) 2 =π×(591.34 / 2) 2 =π×(295.67) 2

[0128] calculate: (295.67) 2 =87420.7489mm 2

[0129] Acore=3.1416×87420.7489≈274641mm 2

[0130] Pitch diameter (dp): Used for shear strength calculation.

[0131] dp=D-0.6495×P=600-0.6495×8=600-5.196=594.804mm

[0132] Number of threads (n): n = L / P = 400 / 8 = 50

[0133] Shear area (As): The shear area of the thread uses the approximate formula As = π×dp×L×K, where K = 0.8 K = 0.8 (empirical coefficient for metric threads).

[0134] As = π×594.804×400×0.8

[0135] Step-by-step calculation:

[0136] π×594.804×400=3.1416×594.804×400≈3.1416×237921.6=747455.5mm 2

[0137] As = 747455.5 × 0.8 = 597964.4 mm 2

[0138] Failure mode analysis

[0139] The thread strength is determined by the smaller value of the following two failure modes:

[0140] Tensile failure load (Ftensile): Ftensile = σult×Acore = 400×274641 = 109856400 N (approx. 109.9 MN)

[0141] Shear failure load (Fshear): Fshear = τult×As = 240×597964.4 = 143511456 N (approx. 143.5 MN)

[0142] Since Ftensile < Fshear, tensile failure is the critical mode (lower tensile strength). This means that the strength of the thread is mainly controlled by the tensile failure of the bolt, rather than thread shear. This is in line with engineering experience: when the engaged length L / D = 400 / 600 ≈ 0.67 < 0.8, tensile failure usually dominates, but here due to the smaller pitch (more threads), the shear strength is higher and tensile is still more critical.

[0143] Generally speaking, the tensile-compressive failure load is 109.9 MN and the shear failure load is 143.5 MN.

[0144] 4.2. Conversion between axial displacement and angle

[0145] The tensile length of the internal thread in the large gear is essentially the axial displacement of the thread, which depends on the pitch of the thread P , when the thread rotates one week (360°), the axial displacement = pitchP Therefore, when the large gear rotates 180°, the axial displacement is: L = P / 2=4mm, rotation ratio i=n 小 / n 大 =z 大 / z 小 (n) 小 =Number of turns of the pinion, n 大 =Number of large gear revolutions, z in this invention 大 =175, z 小 =20).

[0146] Therefore n 小 =n 大 ×z 大 / z 小 =0.5×175 / 20=4.375 laps

[0147] In summary, when the large gear rotates 180°, the axial displacement of the component is 4mm, and the small gear rotates approximately 4.5 revolutions.

[0148] Example 5

[0149] To further enable its application in actual subway deep foundation pit projects, a finite element simulation analysis of the internal support under self-weight and pressure was conducted. The specific analysis is as follows:

[0150] Simulation objectives: ① To verify the mechanical properties of the seven small rollers at the bottom under rated working load, ensuring that their strength, stiffness, and stability meet design requirements. ② To verify the load-bearing capacity of the entire connector under tensile and compressive loads, ensuring that it meets actual engineering conditions.

[0151] Analysis content: ① Static analysis, simulating the distribution of stress, strain, and displacement values ​​of the entire structure under gravity. ② Static analysis, simulating the stress distribution of this steel pipe connector under axial tension and compression.

[0152] Geometric model:

[0153] 1. Use SolidWorks to create accurate 3D geometric models of seven small rollers. Use three 6m steel pipes and pipe connectors protruding 1m on each side, totaling 20m. The parameters of the small roller models are shown below and in Table 1. Furthermore, non-critical parts were simplified by removing the small gear components and adding chamfered corners to improve computational efficiency and removing the connector base plates for easier construction.

[0154] Key parameters of a rack (thread):

[0155] The rack pitch P = 8mm, corresponding to the gear end face module M. t =P / π=2.546mm

[0156] rack tooth profile angle rack = 20°

[0157] Table 1 Gear Parameter Calculation

[0158]

[0159] Material properties: All components are tentatively defined as Q355 steel with an elastic modulus of 206 GPa, a plastic stress of 345 MPa, a Poisson's ratio of 0.3, and a density of 7.85 g / cm³. 3 .

[0160] Connections and interactions: Since the two sides of the box-shaped body are fixed to the surrounding frame, the two sides are set to be completely fixed; the interaction of the remaining parts is completely interactive, that is, it can be matched using SolidWorks.

[0161] Load applied: g = 9.81 kg / m² applied to the entire structure. 3 Gravitational component.

[0162] ① Overall analysis of stress contour plots:

[0163] From the clouds Figure 10 As can be seen from the color distribution, the stress distribution exhibits a clear gradient change. The red and orange areas represent the regions with the highest stress, typically located at support points, constraint points, or mid-span. The blue areas represent regions with lower stress. This distribution pattern conforms to the basic mechanical behavior of simply supported or continuous beams under their own weight: the stress is greatest where the bending moment is the largest (usually at mid-span or fixed end).

[0164] Maximum stress value: The maximum stress (Von Mises stress) shown in the figure is 1.592e+008 N / m. 2 That is, 159.2 MPa.

[0165] ② Overall analysis of displacement contour plots:

[0166] Deformation: Cloud Figure 11 The results show that the deformation pattern of the support is a smooth, continuous curve, with the maximum displacement occurring in the middle of the structure. This perfectly matches the expected deformation behavior of a simply supported or continuous beam under a uniformly distributed load (self-weight), indicating that the finite element model settings (constraints and loading) are reasonable.

[0167] Maximum displacement: The maximum resultant displacement shown in the figure is 4.451e-004 m, or 0.445 mm. This is a very small deformation.

[0168] Deformation ratio: Figure 12The deformation ratio in the image is 672.464, which means that the software magnifies the actual deformation by 672 times so that we can clearly see the trend and shape of the deformation with our naked eyes.

[0169] ③ Overall analysis of strain cloud diagram

[0170] Strain distribution pattern: Clouds Figure 13 Consistent with the stress contour plot, it exhibits a clear gradient change. The red and orange areas represent regions of highest strain, corresponding to high-stress locations in the previous stress contour plot (such as support points and areas near the mid-span). The blue areas represent low-strain regions. This distribution further validates the rationality of the model's stress distribution.

[0171] Maximum strain value: The maximum strain value shown in the figure is 2.354e-004, which is 235.4 microstrain (με). This is a very small amount of deformation.

[0172] Comparison of total strain simulation results and calculations:

[0173] ① Strength verification and safety assessment, calculation of allowable compressive stress, i.e., allowable contact stress ( The allowable contact stress formula for gear tooth surface contact strength is as follows: (Q355 steel, temporarily taken) =355MPa; In general industrial applications, the load is relatively stable, so S is taken as... H = 1.4. )The simulated maximum stress value is 159.2 MPa.

[0174] Verification comparison: 159.2 MPa < 253.6 MPa

[0175] Conclusion: Under pure self-weight conditions, the maximum stress within the steel pipe support is significantly lower than the allowable stress of Q355 steel. The structural strength fully meets the requirements and has a large safety margin. The safety margin ratio is 253.6 / 159.2 ≈ 1.59.

[0176] ② Stiffness verification and safety assessment

[0177] For supporting structures, in addition to strength, stiffness (the ability to resist deformation) is equally important. Excessive deformation can affect the overall stability of the supporting system and its connection with adjacent components.

[0178] Evaluation criteria: In engineering, stiffness is usually assessed by the ratio of deflection (maximum displacement) to span to determine if it meets requirements. For internal supports in foundation pits, a common control standard is maximum deflection ≤ span / 1000.

[0179] The support span (length) L is 20 meters, consisting of three 6-meter steel pipes and pipe connectors protruding 1 meter on each side. Calculation verification: Actual maximum deflection: δmax = 0.445 mm, Allowable deflection: [δ] = L / 1000 = 20000 mm / 1000 = 20 mm

[0180] Verification and comparison:

[0181] Calculated maximum deflection (δ_max): 0.445 mm

[0182] Permissible deflection ([δ]): 20 mm

[0183] Evaluation result: 0.445 mm << 20 mm

[0184] Conclusion: Under pure self-weight conditions, the maximum deformation of the steel pipe support is far less than the allowable value specified in the code. The structural stiffness fully meets the requirements and has a large margin of safety.

[0185] ③ Correlation analysis between strain value and material behavior

[0186] Strain is the amount of deformation per unit length. It directly reflects the degree of deformation of a material and is closely related to stress through Hooke's Law.

[0187] Hooke's Law verification: For linear elastic materials, stress (σ) = elastic modulus (E) × strain (ε).

[0188] The elastic modulus E of Q355 steel is approximately 2.06 × 10⁻⁶. 5 MPa.

[0189] The previously obtained maximum stress σ_max ≈ 159.2 MPa.

[0190] Therefore, the theoretically calculated maximum strain should be: ε = σ / E = 159.2 / (2.06 × 10⁻⁶) 5 ) ≈ 7.73 × 10 -4 ≈ 773με.

[0191] In summary, the maximum strain value obtained from the simulation is 235.4 με, which differs from the theoretically calculated value (773 με). This is perfectly normal because the contour plot displays nodal stress and strain: the point of maximum stress and the point of maximum strain are not necessarily the same node, and the software selects the maximum value for each when generating the contour plot.

[0192] The values ​​are located at different points in the graph: the 235.4 MPa microstrain in the graph may be the value of a specific node or element, while the previous stress of 159.2 MPa was the value of another node.

[0193] Average vs. Extreme Values: The color smoothing process of cloud maps may display the average value, while the reported values ​​are the extreme values.

[0194] Key conclusion: Both the highest value of 773 με and the highest value of 235.4 με are extremely small, far below the strain corresponding to the yield of steel (the yield strain of Q355 steel is approximately ε_s = 355 / (2.06×10⁻⁶)). 5 ) ≈ 0.00172 ≈1720με).

[0195] 2. Only this steel pipe connector is used as the geometric model. In order to make the data under tension and compression more accurate, the lower semi-circular roller and all threads, including the small gear at the top and some holes that do not affect the results, are removed. The material properties are the same as above.

[0196] Connections and Interactions: Simulations were performed using Abaqus, with one side of the box set as completely fixed. The numerical model employed numerous contact surfaces, all using universal contact methods. A surface-to-surface contact method was used to simulate universal contact, employing hard contact. The coefficient of friction for the tangential friction force applied using the penalty function method was 0.2.

[0197] Load application: In order to accurately simulate the interaction between the loading plate and the specimen end plate, a reference point RP-1 was established at the center of the outer surface of the end plate to apply a concentrated force F. The outer surface and RP-1 are connected by motion coupling. The concentrated force F is set to be applied from 0 to 5000kN in 1% increments.

[0198] This simulation of axial pressure conditions applied an axial pressure of 5000 kN, and all components were made of Q355 steel. The focus was on analyzing the stress distribution, strain characteristics, and mechanical response of the connector, gear transmission components, and wedge block. The specific results are as follows:

[0199] ① Overall analysis of the main body stress cloud diagram:

[0200] from Figure 14 It can be clearly observed that the stress distribution of the connector under axial pressure exhibits the characteristics of "local concentration and overall uniformity." The stress values ​​range from 2.393 × 10⁻⁶. -5 The stress ranges from 217.0 to 260.4 MPa, with high-stress areas (stress values ​​217.0~260.4 MPa) mainly concentrated on the gear meshing contact surface, the connection between the housing and the internal threaded components of the external gear, and the root of the flange stiffening ribs. These areas are key nodes for axial force transmission, where force flows converge, leading to significant stress concentration. In contrast, low-stress areas (stress values ​​21.7~86.8 MPa) are distributed in secondary load-bearing parts such as the side walls of the housing and non-load-bearing sections of the steel pipes, with stress levels significantly lower than the yield strength of Q355 steel.

[0201] Combination Figure 15 It can be seen that under axial pressure, the stress value at the point of maximum stress in the connector gear stabilizes in the range of 151.84~151.93 MPa, corresponding to a strain of 6.45×10⁻⁶. -4 (i.e., 645με). From the curve trend, the stress and strain show a strict linear relationship without any inflection point or fluctuation. This indicates that the gear is always in the pure elastic working stage under this load, and the material does not undergo plastic deformation. The reliability of the gear transmission is effectively verified.

[0202] ② Overall analysis of the stress cloud diagram of the wedge block

[0203] observe Figure 16 As a key bearing component for axial force transmission, the wedge block exhibits a significant gradient in stress distribution along the inclined plane. The stress values ​​range from 7.139 × 10⁻⁶. -2 The stress ranges from 123.7 to 147.0 MPa. The high-stress area (stress value 123.7~147.0 MPa) is concentrated on the contact end face between the wedge block and the groove of the box body and the middle of the inclined surface. This area directly bears the axial pressure and transmits the force to the waler. It is the core stress-bearing part of the wedge block. The low-stress area (stress value 7.14~18.8 MPa) is distributed on the non-contact side and end of the wedge block. The stress level is extremely low and there is no risk of stress.

[0204] from Figure 17 It can be seen that the stress value at the point of maximum stress in the wedge block is stable at 128~148MPa, corresponding to a strain of 2.73×10. -3 ~2.96×10 -3 (i.e., 2730~2960με). Stress and strain also exhibit a linear relationship, conforming to Hooke's Law (Q355 steel elastic modulus E=206GPa, theoretical strain...). The simulated strain is approximately 713με (the slightly higher value is due to the inclusion of local contact deformation), indicating that the wedge block shows no signs of slippage under axial pressure, its self-locking performance is reliable, and it can stably transmit axial force.

[0205] Comparison of simulation results and calculations:

[0206] Based on the "Standard for Design of Steel Structures" (GB 50017-2017) and the simulation results above, and assuming that all components are made of Q355 steel (allowable stress is calculated with a safety factor of 1.25, i.e., [ The simulation results (284 MPa) are compared and analyzed with the theoretical calculation results in terms of the strength of the main structure and the performance of the core components.

[0207] ① Comparison of main structural strength

[0208] Under axial pressure (5000kN), the axial stress σ of the Q355 steel pipe section is theoretically calculated. 理论 =N / A=5000×10 3 / 29810≈167.7MPa, where the steel pipe is a commonly used 609mm diameter steel pipe in engineering, with an outer diameter D=609 mm, wall thickness t=16 mm, and inner diameter d=D-2t=577 mm; the cross-sectional area A=π / 4(D 2 -d 2 ) = π / 4(6092-5772) = 29810 mm 2 The simulation results show that the average stress of the steel pipe section is approximately 150 MPa, with a maximum stress not exceeding 200 MPa. The simulated stress is not only lower than the theoretically calculated value but also significantly lower than the allowable stress of 284 MPa for Q355 steel, with a safety margin of at least 42%, indicating that the strength of the steel pipe section fully meets the design requirements. For the connector housing, which is a welded structure of Q355 steel plate, the allowable stress calculated according to the bending member theory is 284 MPa. The simulation results show that the maximum stress in the housing is approximately 180 MPa, concentrated at the root of the stiffening ribs. This stress value is lower than the allowable stress, eliminating the risk of plastic yielding. Furthermore, the overall stiffness of the housing effectively transmits axial force, with no signs of local instability, further verifying the strength and reliability of the connector housing.

[0209] ② Strength comparison of core components (gears - threads + wedges)

[0210] For an external gear-internal thread structure, based on the mechanical properties of Q355 steel (ultimate tensile strength 470 MPa), its tensile failure load Ftensile = is theoretically calculated. ult ×Acore=470×283064=113225600≈133.0MN, (The area calculation is the same as in Example 4,) dmin = D - 1.0825 × P

[0211] Substitute the value: dmin = 60 - 1.0825 × 8 = 600.34 mm

[0212] Core cross-sectional area (Acore): used for tensile strength calculation. Acore = π × (dmin / 2) 2 =π×(600.34 / 2) 2 =π ×(300.17) 2

[0213] calculate: (300.17) 2 =90102.0289mm 2 ,Acore=3.1416×90102.0289≈283064mm 2The allowable tensile load [Ftensile] = 133.0 / 1.25 ≈ 106.4MN. In the simulation results, the maximum stress in the gear meshing area is approximately 260.4 MPa, corresponding to a load of approximately 7400 kN. This does not reach the theoretical failure threshold, and the stress value is close to but does not exceed the allowable stress of 284 MPa for Q355 steel. However, the fatigue risk during long-term use needs to be considered. Regarding the compressive strength of the wedge blocks, the corrected theoretical calculation results (based on Q355 steel) show that there are three wedge blocks. The first block has a height of 576 mm, a bottom width of 120 mm, a top width of 130.46 mm, and a thickness of approximately 50 mm. The second and third blocks have the same height of 497 mm, a bottom width of 120 mm, a top width of 128.68 mm, and a thickness of 50 mm. Dimensions: Top (a) = 128.68 mm, Bottom (b) = 120 mm, Height (h) = 497 mm, Thickness (t) = 40 mm, Bearing area (Ac): Ac = a × t = 128.68 mm × 50 mm = 6434 mm 2 The compressive bearing capacity Nc of a single wedge block = ×Ac=284×6434≈1827kN, and the total bearing capacity when the three wedge blocks work together to transmit force is approximately 5481kN. When the simulated load is 5000kN, the maximum stress of a single wedge block is approximately 147.0MPa, which is only 51.8% of the allowable stress of Q355 steel, indicating sufficient compressive strength margin. Meanwhile, the stress-strain curve obtained from the simulation is linear and there is no slippage phenomenon. The tilt angle (α) of the wedge block is calculated. The lateral offset c of one side of the wedge block is: c = (a - b) / 2 = (128.68 -120) / 2 = 4.34 mm. Therefore, the tangent of the tilt angle α is: tan(α) = opposite side / adjacent side = c / h = 4.34 / 497 ≈ 0.008732, and the tilt angle α is: α = arctan(0.008732) ≈ 0.5°. Combined with the theoretically calculated tilt angle of the wedge block of 0.5° (less than the friction angle of 8.53°), it shows that the self-locking performance of the wedge block is still reliable and can stably maintain the prestress.

[0214] ③ Theoretical calculations comparing stiffness and deformation show that when the steel pipe support length is 20m and the axial pressure is 5000kN, the axial stiffness EA = E × A = 2.06 × 10 5 ×29810×10 -3 =6140860 kN, axial deformation δ of the steel pipe 理论 =NL / (EA)=5000×20 / (6.14×10 6The simulated deformation is approximately 0.0163m = 16.3mm, while the total axial deformation of the steel pipe support in the simulation results is approximately 15.8mm (the maximum displacement of the connector is 0.54mm). The deviation between the two is less than 3%, which is consistent with the linear elastic deformation law. Furthermore, the simulated deformation value is far lower than the allowable support deformation in the specification (≤L / 1000 = 20mm), indicating that the overall stiffness of the support system can meet the requirements for foundation pit deformation control. Regarding the contact deformation of the wedge block, the theoretically calculated contact deformation δ... 接触 = ×t / E=147×50 / 206×10 3 The maximum deformation at the contact point is approximately 0.04 mm, which is about 0.0357 mm. The deformation is so small that it will not affect the self-locking performance of the wedge block and can ensure the stable transmission of prestress.

[0215] The above examples are only used to illustrate the present invention. The structure and connection method of each component can be varied. All equivalent changes and improvements made on the basis of the technical solution of the present invention should not be excluded from the protection scope of the present invention.

Claims

1. A collaborative compressive-tensile telescopic support pipe connector for subway foundation pits, characterized in that, It includes a box-type structure (1) and a pipe structure (2); The first side of the box structure (1) is provided with distributed screw holes, which are used to anchor the box structure (1) to the underground continuous wall by expansion bolts, and the first side is provided with multiple round-ended rectangular grooves inside the box structure (1) to avoid the screw holes; The box-shaped structure (1) has a circular hole at the center of the second side opposite to the first side. Multiple grooves are arranged in the circular hole, and threaded rollers (8) are installed in the multiple grooves for relative movement between the pipe structure (2) and the circular hole of the box-shaped structure (1). A small gear (6) is installed on the second outer surface of the box structure (1) next to the circular hole. The small gear (6) rotates independently of the box structure (1). The first end of the pipe structure (2) is provided with a flange (3), which is used to connect with the supporting pipe in the foundation pit. The flange (3) is located outside the box structure (1). The second end of the pipe structure (2) opposite to the first end is provided with multiple rounded rectangular protrusions. The multiple rounded rectangular protrusions pass through the circular holes and fit into the multiple rounded rectangular grooves of the box structure (1). Therefore, the second end of the pipe structure (2) is located inside the box structure (1). The outer surface of the pipe structure (2) is provided with a surrounding thread (5), and the pipe structure (2) is fitted with two external gear internal thread components (4). The internal thread of the external gear internal thread component (4) meshes with the thread (5). The pinion (6) meshes with the external gear of the external gear internal thread component (4) to drive the external gear internal thread component (4) to move axially along the thread (5). The number of the external gear internal thread components (4) is 2, and the diameter of each component is larger than that of the circular hole. They are located on both sides of the circular hole of the box-type structure (1) and abut against the box-type structure (1). The number of the matching pinions (6) is also 2. The circular rectangular groove has a certain height so that when the relative positions of the box structure (1) and the pipe structure (2) in the support pipe connector change, the circular rectangular protrusion of the pipe structure (2) can be inserted into the circular rectangular groove of the box structure (1) to avoid the support pipe rotating in the pit. A gap (7) is provided between the rounded rectangular protrusion of the pipe structure (2) and the bottom of the rounded rectangular groove of the box structure (1). The gap (7) is used to insert a wedge to improve the compressive strength.

2. The connector according to claim 1, characterized in that, One end of the pinion (6) is provided with a cylinder with a diameter of 25-35mm and a length of 45-55mm, and a bearing (11) is fitted on the cylinder; the other end of the pinion (6) is provided with a hexagonal groove, which is used to connect with an electric drill to drive the pinion (6) to rotate.

3. The connector according to claim 1, characterized in that, The meshing contact surfaces of the threaded wire (5) and the internal threaded component (4) of the external gear, and the contact surfaces of the threaded roller (8) and the threaded wire (5) are all filled with a graphene lubricating layer.

4. The connector according to claim 1, characterized in that, The height of the threaded roller (8) is 15-25mm, and each side of the threaded roller (8) is provided with a cylinder with a diameter of 3-6mm and a length of 15-25mm; a cover block (9) is also provided in the groove of the circular hole, and the cover block (9) is fixed to the box structure (1) by screws (10) to limit the threaded roller (8).

5. The application of the collaborative compressive and tensile telescopic support pipe connector as described in claim 1 in supporting subway foundation pits.

6. A method for supporting subway foundation pits using the collaborative compressive-tensile telescopic support pipe connector as described in claim 1, characterized in that, Includes the following steps: S1, the box-shaped structure (1) with distributed screw holes is anchored to the underground continuous wall by bolts, and an external gear internal thread component (4) is installed on the outside of the circular hole of the box-shaped structure (1). S2, place the jack into the box structure (1), use a crane to move the pipe structure (2) to a suitable position, apply a certain load to its flange (3) so that it enters the box structure (1) supported by the jack. S3, the inner side of the circular hole of the box structure (1) is equipped with the second external gear internal thread component (4) on the pipe structure (2), and after moving to the appropriate position, the applied force is unloaded and the jack is removed; S4, after connecting the support pipe in the pit to one side of the flange (3), insert the two small gears (6) into the corresponding holes of the box structure (1), use the hexagonal interface direct-connect electric drill to rotate the small gear (6) on one side, thereby driving the external gear internal thread component (4) to mesh and apply bolt preload at the same time, the same applies to the other side; S5, after installation, the pinion gear (6) can be uninstalled for use during the next adjustment; S6. After the rest of the parts are installed, insert the wedge into the gap (7) to improve its compressive strength, and the installation will be completed.

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