Ultra-high spherical air film structure for deep foundation pit construction

Abstract

The application belongs to the technical field of civil engineering construction, and specifically provides an ultrahigh spherical air film structure for deep foundation pit construction, which comprises: a spherical ultrahigh air film made of flexible film material, the edge of which is sealingly connected to the girder foundation at the top of the foundation pit through an anchoring system, and forms a closed working space after being inflated; a cable net system arranged on the outer surface of the spherical ultrahigh air film and formed by a plurality of ropes connected through connectors, and tightly attached to the surface of the spherical ultrahigh air film; and an air inflation and pressure maintaining system in communication with the inside of the spherical ultrahigh air film and used for maintaining the internal working air pressure of the spherical ultrahigh air film; the air film facility utilization rate is improved, and the comprehensive construction cost is reduced. The existing foundation pit air film is only used for several months to half a year in the earthwork stage and then is removed, and the facility utilization rate is low. The application enables the air film structure to serve the entire foundation pit construction period (usually 1-2 years), greatly improves the utilization efficiency of the air film facility, and significantly reduces the comprehensive amortization cost.

Description

Technical Field

[0001] This invention belongs to the field of civil engineering construction technology, and in particular relates to an ultra-high spherical air-supported membrane structure for deep foundation pit construction. Background Technology

[0002] Foundation pit construction is a systematic project encompassing multiple stages, typically including earthwork excavation, internal support construction, basement floor slab construction, main structure construction, and waterproofing and backfilling. In recent years, foundation pit air-supported membrane technology, as an innovative means of controlling construction dust and noise, has been applied in several major projects in China. However, the aforementioned existing technologies have the following shortcomings: To meet the spatial requirements of the entire construction process, some engineering projects have attempted to increase the height of the air-supported membrane structure to a higher level (sag-to-span ratio exceeding 0.5), but the following common technical bottlenecks exist: Uneven stress distribution on membrane surface: Under normal air pressure, the stress on the surface of ultra-high-pressure membrane is concentrated in the area with greater curvature at the top, which leads to excessive local stress, accelerates membrane fatigue, and shortens service life.

[0003] Since the existing air-supported membrane is removed after the earthwork stage, dust and noise pollution during the main structure construction stage cannot be effectively isolated. The environmental benefits of "green construction" can only cover a part of the construction cycle and cannot run through the entire foundation pit construction process.

[0004] To address the aforementioned issues, existing patents such as CN109853974B disclose an air-supported membrane system for foundation pit operations, which uses a hemispherical air-supported membrane and is equipped with a steel cable net. However, this patent still uses a conventional sag-to-span ratio and conventional air pressure, and the cable net is arranged in a conventional manner. It does not solve the structural stability problem under ultra-high conditions, nor can it cover the main structure construction stage.

[0005] Furthermore, CN119615917A discloses a prefabricated air-supported membrane foundation for a foundation pit, which only involves improvements to the foundation structure and does not involve innovations in the spherical ultra-high air-supported membrane morphology or cable net system. Although the Harbin Institute of Technology A21 student dormitory project achieved an ultra-high air-supported membrane with a near 1:1 span-to-span ratio, its cable net is a conventional oblique orthogonal cable net, which does not adopt the specially designed full cable net system with adjustable tension and locking components described in this invention. Moreover, the working air pressure is still within the conventional air pressure range, and a double-pressure operation mechanism is not adopted, resulting in insufficient structural safety redundancy. Summary of the Invention

[0006] In view of this, the purpose of one or more embodiments of this specification is to propose an ultra-high spherical air-supported membrane structure for deep foundation pit construction, which solves the technical problems of existing foundation pit air-supported membrane structures, such as limited use stages, insufficient space height, insufficient structural stability under ultra-high shape, and lack of green construction continuity.

[0007] The core objective of this invention is to enable the air-supported membrane structure to adapt to the requirements of internal working space height and structural stability during the entire construction process of the foundation pit (from earthwork excavation, internal support construction, basement floor slab construction to main structure construction), thereby achieving green construction throughout the entire process with a single membrane.

[0008] For the purposes described above, one or more embodiments of this specification provide an ultra-high spherical air-supported membrane structure for deep foundation pit construction, including: The spherical ultra-high air-supported membrane is made of flexible membrane material. Its edges are sealed to the ground beam foundation at the top of the pit through an anchoring system. After being inflated, it forms a closed working space. The cable net system is set on the outer surface of the spherical ultra-high air membrane and is composed of multiple ropes that are connected by connectors and tightly attached to the surface of the spherical ultra-high air membrane. An inflation and pressure-maintaining system is connected to the interior of the spherical ultra-high-pressure air film and is used to maintain the internal working air pressure of the spherical ultra-high-pressure air film. Wherein: the sag-to-span ratio of the spherical ultra-high air film, that is, the ratio of the net height of the air film to the short span of the foundation pit, is 0.8 to 1.2; The internal working air pressure maintained by the inflation and pressure holding system is 200Pa to 600Pa; The cable net system weaves cable net units in the form of geodesics according to the curvature changes of the spherical ultra-high air film surface, forming a non-uniform grid structure covering the spherical ultra-high air film surface. The grid density is greater in areas with large curvature than in areas with small curvature. The ropes of the cable net system include a main rope and auxiliary ropes, wherein the diameter of the main rope is larger than the diameter of the auxiliary rope; The connector is equipped with an adjustment unit and a locking component. The adjustment unit is used to adjust the tension of the connected rope, and the locking component is used to lock the position of the adjustment unit.

[0009] Furthermore, the adjustment unit includes an independent adjustment component and an overall adjustment component. The independent adjustment component is used to adjust the tension of a single rope individually, and the overall adjustment component is used to simultaneously tension or release all ropes connected to the connector.

[0010] Furthermore, the locking component is a locking nut, an anti-loosening washer, or a cotter pin, forming a dual anti-loosening mechanism with the adjusting unit.

[0011] Furthermore, the diameter of the main cable is 26mm to 32mm, and the diameter of the auxiliary cable is 16mm to 22mm.

[0012] Furthermore, the anchoring system includes pre-embedded anchors embedded in the ground beam foundation, angle steel strips set along the edge of the air film, and EPDM sealing strips set between the angle steel strips and the film material.

[0013] Furthermore, the inflation and pressure holding system includes a real-time air pressure monitoring module and an automatic pressure replenishment module, which automatically starts pressure replenishment when the air pressure is lower than a set threshold.

[0014] Furthermore, the spherical ultra-high air membrane is made of PVDF double-coated polyester fiber membrane material.

[0015] Furthermore, the ultra-high spherical air-supported membrane structure for deep foundation pit construction also includes an airtight door system and a forced ventilation system. The airtight door system is installed on the spherical ultra-high air-supported membrane to allow personnel and construction machinery to enter and exit.

[0016] As another technical solution, a construction method for ultra-high spherical air-supported membrane structures for deep foundation pits is proposed, applicable to the aforementioned ultra-high spherical air-supported membrane structures for deep foundation pits, including the following steps: S1. Foundation Pit Preparation and Anchoring System Installation: Install pre-embedded anchors and angle steel strips on the ground beam at the top of the foundation pit; S2. Spherical ultra-high air-supported membrane installation: The flexible membrane material is laid above the foundation pit, and the edges of the membrane material are sealed and connected to the ground beam foundation through an anchoring system; S3. Cable net system installation: Based on the curvature distribution of the spherical ultra-high air film membrane surface, a non-uniform grid cable net is installed on the outer surface of the spherical ultra-high air film membrane. In areas with large curvature, a denser grid arrangement and a larger diameter main cable are used, while in areas with small curvature, a sparser grid arrangement and a smaller diameter secondary cable are used. S4. Inflation and Adjustment: Inflate the spherical ultra-high air film to 200Pa~600Pa using the inflation and pressure holding system, gradually increase the pressure and check the sealing performance and structural stability; S5. Full-process operation and maintenance: During each stage of foundation pit excavation, internal support construction, basement floor slab construction and main structure construction, the working air pressure shall be continuously maintained, and the cable net tension shall be adjusted periodically through the adjustment unit, and the position of the adjustment unit shall be locked through the locking component.

[0017] In step S3, a special conversion component is set at the point where the curvature of the spherical ultra-high air film membrane changes abruptly, so that the cable net matches the shape of the membrane surface.

[0018] Beneficial effects: Achieve green enclosure throughout the entire foundation pit construction process. Through an ultra-high shape design with a rise-to-span ratio of 0.8-1.2, the height of the internal working space of the air-supported membrane reaches more than half of the short span of the foundation pit, which can accommodate large construction machinery such as tower cranes to carry out the main structure construction work inside the membrane. This allows the air-supported membrane structure to be used from the earthwork excavation stage to the completion of the main structure construction, realizing green construction throughout the entire process of "one membrane to the end".

[0019] This invention improves the utilization rate of air-supported membrane structures and reduces overall construction costs. Existing air-supported membrane structures for foundation pits are only used for a few months to six months during the earthwork phase before being dismantled, resulting in low utilization rates. This invention enables the air-supported membrane structure to serve the entire foundation pit construction cycle (typically 1-2 years), significantly improving the utilization efficiency of the air-supported membrane structure and substantially reducing overall amortization costs. Furthermore, it provides a larger working space during operations, meeting the needs of complex internal operations.

[0020] Ensuring structural safety throughout the entire construction process. The combined effect of double-pressure operation (200Pa-600Pa) and a specially designed cable net system ensures the air-supported membrane maintains sufficient structural rigidity even at extremely high altitudes, resisting extreme wind and snow weather. The high-pressure self-balancing mechanism allows the structure to maintain its stable shape even during pressure fluctuations, providing reliable safety assurance throughout the entire construction process.

[0021] Improving the construction environment and enhancing social benefits. By implementing fully enclosed construction throughout the entire process, the impact of foundation pit construction on the surrounding atmospheric and acoustic environment is significantly reduced, dust and noise complaints are decreased, and the level of civilized construction in the city is improved. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in one or more embodiments of this specification or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only one or more embodiments of this specification. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 : A schematic diagram of the overall structure of the ultra-high air film structure of this invention; Figure 2 : A schematic diagram comparing the sag-span ratio of the ultra-high air-supported membrane structure of this invention with that of a conventional foundation pit air-supported membrane structure; Figure 3 : A schematic diagram of the non-uniform grid division of the cable net system of the present invention; Figure 4 : A schematic diagram of the anchoring and sealing system of the present invention; Figure 5 This invention provides a schematic diagram of the utilization of work space at each stage of the entire construction process. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments.

[0025] Example 1: Application in a deep foundation pit project for a high-rise building in a cold northern region This embodiment takes a deep foundation pit project of a high-rise building in a cold northern region as an example to illustrate the implementation process and practical application effects of the present invention in detail.

[0026] I. Project Overview and Construction Environment The project is located within a deep foundation pit for a high-rise building in a cold northern region. The pit is roughly rectangular in plan, with some twists and turns, including several protrusions at the southwest corner, forming concave and acute-angled areas. The pit has a short span of 44m and a long span of approximately 147m, with a capping beam centerline area of ​​6468㎡ and a perimeter of 386.8m. The pit is designed to be approximately 22m deep, and the proposed building is an 18-story high-rise with 3 stories underground.

[0027] The project site is located in the core area of ​​the university, bordered by teaching buildings and student dormitories on the east, south, and north sides, with the closest point only 12 meters away from existing buildings. Construction coincides with the university's normal teaching operations, necessitating extremely strict requirements for noise and dust control. The local climate is typical of northern continental climate, with winter lows reaching -15℃ and summer highs reaching 38℃. Spring and autumn are windy, with gusts exceeding level 8. Annual precipitation is approximately 600mm, mainly concentrated in summer.

[0028] If designed using conventional air-supported membrane structures for foundation pits, the sag-to-span ratio can only reach 0.3-0.5, and the maximum height of the air-supported membrane is 22m. This only covers the earthwork excavation stage, with a service life of less than one month. During the main structure construction stage, tower cranes (which generally require 30-40m of clearance) cannot operate inside the membrane, forcing the air-supported membrane to be dismantled prematurely.

[0029] II. Air-supported membrane structure installation stage After construction preparations are completed, the anchoring system for the ground beam at the top of the foundation pit is installed first. During the concrete pouring of the ground beam, high-strength chemical anchors are pre-embedded along the centerline of the cap beam at 1.5m intervals, with an anchoring depth of not less than 600mm. M20 anchors are selected to ensure that the anchoring force meets the design requirements for pull-out bearing capacity. After the ground beam concrete has cured to the design strength, EPDM sealing strips are laid along the edge of the air membrane. The strips are 8mm thick and 100mm wide, possessing excellent aging resistance and airtightness.

[0030] The spherical ultra-high-density air-supported membrane uses high-strength Class G PVDF membrane material with a tensile strength of 10,000 N / 5 cm and a membrane thickness of approximately 0.9 mm. It employs a double-sided coating process, possessing self-cleaning properties, fire resistance (B1 grade), and weather resistance. The membrane material is cut and heat-sealed according to the contour of the foundation pit to form an integral air-supported membrane structure. The edges of the air-supported membrane are connected to pre-embedded anchor bolts via angle steel strips. The angle steel strips have an L-shaped cross-section of 100×8 mm and are secured to the angle steel with pre-embedded anchor bolts, forming a continuous and uniform sealing and clamping force.

[0031] After the installation is completed, start the air inflation and pressure maintaining system for the first inflation. The inflation system is equipped with 4 high-power fans (with a single air volume of 45000m³ / h), and the pressure is gradually increased in stages — first inflate at a low pressure of 100Pa to make the membrane material initially unfold, and check whether there are wrinkles, damages on the membrane surface and the sealing condition of the anchorage edge; after confirming that there is no error, gradually increase the pressure to 200Pa, 300Pa, and finally reach the designed working air pressure of 200Pa. The whole process lasts for about 6 hours, during which the intelligent monitoring system records the air pressure change curve, membrane surface displacement and anchorage point force data in real time.

[0032] III. Installation and Tensioning Stage of Cable Net System After the spherical ultra-high air membrane is inflated and formed, the special cable net system is installed. According to the curvature distribution of the spherical air membrane, the cable net units are woven in the form of geodesics. In the area with the largest curvature at the top of the air membrane (where the rise is about 42m), the grid unit size is encrypted to 2.5m×2.5m; in the areas with small curvature at the bottom and side, the grid unit size is relaxed to 3.5m×3.5m. The main cables adopt φ28mm steel core wire ropes, which are arranged diagonally along the main stress direction of the membrane surface to form the basic load-bearing grid; the auxiliary cables adopt φ20mm steel core wire ropes to connect the main cables and distribute loads.

[0033] Special steel adapters are set at the four corners of the foundation pit and the curvature mutation positions of the plane concave-convex changes for transitional connection. The adapter is a multi-directional connection node, which can connect 4 to 6 cables in different directions at the same time, ensuring that the cable forces in all directions are effectively integrated and evenly transmitted at the node. The end of each cable is provided with a connecting ring, which is sleeved on the adapter and fixed by a pin shaft.

[0034] After the cable net is installed, the system is tensioned through the adjusting unit on the connecting piece. First, use the independent adjusting assembly to perform initial adjustment on each cable — use a torque wrench to adjust the threaded adjusting rod one by one, so that the initial tension of each cable reaches 80% of the designed value. The independent adjusting assembly consists of an adjusting screw rod and a locking nut, which changes the effective length of the cable by rotating the screw rod, so as to precisely control the tension of a single cable. After the initial adjustment is completed, use the integral adjusting assembly to synchronously tension all the cables connected to the connecting piece — by rotating the integral adjusting ring, the cable forces in all directions at the same node are synchronously increased to 100% of the designed value according to the design ratio, ensuring the balance of cable forces in all directions and avoiding the uneven tension problem caused by adjusting one by one.

[0035] After the tensioning is in place, tighten the locking assembly (locking nut + anti-loosening gasket) to lock the position of the adjusting unit to form a double anti-loosening mechanism. After locking, use a tension detector to sample and inspect no less than 30% of the cable tension, and it is qualified when the deviation is controlled within ±5%. The whole process of cable net installation and tensioning takes about 7 days.

[0036] IV. Earthwork Excavation Stage After the air-supported membrane and cable net system are installed, the excavation of the foundation pit begins. At this time, the working air pressure inside the air-supported membrane is maintained at 200 Pa, which is automatically controlled by the inflation and pressure maintenance system. The temperature inside the membrane is maintained at 15-25℃ by an intelligent temperature control system, and the relative humidity is controlled below 60%.

[0037] Earthwork excavation is carried out using small excavators in conjunction with dump trucks. The dump trucks enter and exit through an airlock vehicle access tunnel—this tunnel has two airtight doors. The first door closes after the vehicle enters, and the second door opens only after the air pressure has equalized, ensuring that the air pressure fluctuation within the membrane does not exceed ±20Pa during vehicle entry and exit. Personnel enter and exit through a rotating airtight door, allowing only one person to pass at a time. The door is made of transparent PC board, which also allows light to pass through.

[0038] Although the clearance height requirement is not high during the earthwork excavation stage (approximately 10-15m is sufficient), the spherical air-supported membrane of this invention has been fully deployed to the designed height of 42m, providing ample internal space. The main function of the air-supported membrane at this stage is to isolate dust and noise. An intelligent monitoring system monitors the PM2.5 and PM10 concentrations inside the membrane and the noise level outside the membrane in real time. Data shows that although the PM10 concentration inside the membrane reached as high as 800-1200 μg / m³ during earthwork excavation (due to the large amount of dust generated by the earthwork operation), the PM10 concentration outside the membrane was consistently controlled below 50 μg / m³, achieving a dust blocking rate of over 95%. The noise level outside the membrane decreased from 85 dB(A) before construction to below 45 dB(A), demonstrating a significant noise reduction effect.

[0039] During this phase, the air-supported membrane structure operated stably. During two instances of level 6 gales, the inflation and pressure-maintaining system automatically increased the air pressure from 200 Pa to 420 Pa to withstand the wind load. The maximum displacement of the membrane surface was less than 1 / 200 of the span, and the cable net system functioned normally without any abnormal fluctuations in cable tension. After rain, the membrane surface naturally cleaned itself thanks to the self-cleaning properties of the PVDF coating, requiring no manual maintenance.

[0040] V. Construction Stage of Internal Supports and Basement Floor Slab After the earthwork is excavated to the foundation, the construction of internal supports and the basement floor slab will begin. This stage requires the installation of reinforced concrete internal supports (three in total) and the pouring of a large-volume concrete floor slab (approximately 2.5m thick, with a concrete volume of approximately 16,000 m³).

[0041] The construction of internal supports requires the use of large-scale steel bar processing equipment and concrete pumping equipment, further increasing the requirements for working space. The spherical air-supported membrane expands outward at its edges, increasing the effective clearance height at the edge of the foundation pit from less than 5m with conventional air-supported membranes to over 25m, and improving space utilization from the conventional 50% to over 90%. Steel bar processing areas and formwork stacking areas can be located at the edge of the foundation pit without requiring additional space outside the membrane.

[0042] The large-volume concrete pouring for the foundation slab continued uninterrupted for 72 hours. During the pouring, multiple concrete pump trucks operated simultaneously, and the heat of cement hydration raised the temperature inside the membrane to 32°C. An intelligent ventilation system automatically activated forced ventilation—expelling the hot air from inside the membrane through four exhaust valves, while a fresh air system replenished the system with cooled fresh air, controlling the temperature inside the membrane below 28°C and the relative humidity below 70%, ensuring a comfortable working environment for construction personnel. During concrete curing, the insulation effect of the air-supported membrane kept the temperature inside 8-10°C higher than outside, effectively preventing the adverse effects of low winter temperatures on the concrete hydration reaction.

[0043] During this stage, the internal pressure of the air-supported membrane is maintained at 420Pa (slightly higher than the earthwork stage, to cope with the vibration load generated by the concrete pumping equipment). After three months of continuous load-bearing, the cable net system was found to have a slight decrease in tension (about 3-5%) in some ropes through regular inspections. Fine-tuning and tension replenishment were performed using the independent adjustment components on the connectors. Each adjustment took about 2 hours and did not require machine downtime.

[0044] VI. Main Structure Construction Stage (Months 8-14) The construction of the main structure is the core application scenario of the technical solution of this invention, and it is also a key stage that cannot be covered by existing foundation pit air membrane technology.

[0045] The main structure of this project is a cast-in-place reinforced concrete frame-shear wall structure, with a standard floor height of 3.6m, a total of 18 floors, and a total height of approximately 65m (including the part above ground). Construction will utilize two tower cranes (QTZ125 type, independent height 40m, maximum slewing radius 55m) for the hoisting of large components, while a truck crane will be used in conjunction with the hoisting of the reinforcing cage and the installation and dismantling of the formwork.

[0046] The installation of the tower crane is the key technical challenge at this stage. This invention provides ample operating space for the tower crane through its ultra-high spherical shape (span-to-rise ratio of 0.95, clear height of 42m)—the standard tower crane section has an installation height of 40m, allowing it to be fully erected and rotated within the air-supported membrane. The tower crane foundation is set on the bottom slab of the pit. The location where the tower crane boom passes through the top of the air-supported membrane is handled using a "tower crane through air-supported membrane" technique: an opening is pre-drilled at the top of the air-supported membrane corresponding to the tower crane's position. After the tower crane is installed, the edges of the opening are sealed a second time, using a specially designed flexible sealing sleeve to seal the annular gap between the membrane material and the standard tower crane section, ensuring that airtightness is not compromised.

[0047] During the construction of the main structure, components such as steel reinforcement cages (up to 12m long) and large formwork (up to 3m × 6m) are transported vertically and horizontally within the membrane using tower cranes. The bulging shape of the spherical air-supported membrane edge allows the tower crane to maintain a sufficient turning radius at the edge of the foundation pit—conventional flat air-supported membranes have an effective clearance of less than 5m at the edge, causing the tower crane arm to interfere with the membrane surface when rotating to the edge; however, the spherical air-supported membrane edge of this invention expands outward, increasing the edge clearance height to over 25m, allowing the tower crane to achieve 360° full-range rotation without any dead angles.

[0048] During this stage, the working air pressure of the air-supported membrane is dynamically adjusted according to the construction load. During peak tower crane operation periods in the daytime (when frequent changes in lifting load cause pressure fluctuations within the membrane), the air pressure is set at 480Pa; during nighttime shutdowns, it is reduced to 400Pa to save energy. The intelligent monitoring module of the inflation and pressure-maintaining system collects air pressure data once per second, and automatically initiates pressure replenishment when the air pressure fluctuation exceeds ±30Pa, with a response time of less than 2 seconds.

[0049] When the main structure reached the fifth floor (approximately 20m high), there was still a 22m clearance inside the air-supported membrane, completely unaffected by tower crane operations. As the main structure rose layer by layer, the air-supported membrane consistently covered the entire construction work area, effectively containing dust and noise generated during concrete pouring, rebar tying, and formwork installation and removal. Environmental monitoring data outside the membrane showed that the PM10 concentration outside the membrane remained consistently below the Class II standard limit of the "Ambient Air Quality Standard" during the main structure construction period, and noise levels were below 55dB(A) during the day and below 45dB(A) at night, meeting the acoustic environment requirements for residential areas.

[0050] VII. Winter Construction Phase The construction period for this project spans two winters. In northern regions, winter temperatures are low, requiring complex insulation measures for concrete pouring during conventional open-air construction, and significantly reducing the effective working time.

[0051] The spherical air-supported membrane structure of this invention offers significant advantages for winter construction. Similar to a greenhouse, the air-supported membrane effectively blocks cold air intrusion and reduces heat loss. Actual measurement data shows that when the outside temperature is -12℃, the inside temperature can be maintained at 5-8℃, which is 17-20℃ higher than the outside temperature. This temperature difference allows concrete pouring and curing to be carried out under normal temperature conditions, avoiding the inhibition of concrete hydration by low temperatures, reducing the amount of antifreeze and insulation measures required, and ensuring higher construction quality in winter.

[0052] During winter construction, the internal pressure of the air-supported membrane decreases due to the drop in temperature (due to the thermal expansion and contraction effect of gases). The inflation and pressure-maintaining system automatically compensates—when the internal air pressure drops below 320 Pa, the system automatically activates to replenish the pressure to 200 Pa, ensuring that the membrane stiffness does not decrease due to low temperatures. After snowfall in winter, the snow naturally slides off the spherical curved surface of the membrane, eliminating the need for manual snow removal. The linear expansion coefficient of the cable net system at low temperatures matches that of the membrane material. Adjustment units on the connectors allow for seasonal overall tension replenishment as temperatures rise, ensuring that the cable net tension remains within the design range.

[0053] VIII. Rainy Season Construction Phase The project area experiences heavy rainfall in summer, with July and August being the peak rainy season, often characterized by torrential rains. Conventional open-air construction must be completely halted during heavy rains, and the foundation pit is prone to water accumulation, affecting construction progress and safety.

[0054] The fully enclosed air-supported membrane structure of this invention effectively resists rainwater infiltration. The membrane material undergoes three layers of special coating spraying, providing excellent waterproof performance. Heavy rain falls on the membrane surface and flows rapidly down the spherical curved surface, collected in the drainage ditches at the membrane base, and discharged into the municipal stormwater pipe network. Actual measurements showed no leakage under heavy rain conditions with a daily rainfall of 100mm, and construction operations continued as normal. During the rainy season, the humidity inside the air-supported membrane slightly increases (approximately 75-80%), and the ventilation system automatically increases the exhaust volume to control the humidity within an acceptable range.

[0055] Furthermore, the air-supported membrane structure exhibits superior load-bearing performance compared to conventional structures during heavy rain. Its spherical shape ensures even distribution of rainwater load, minimizing stress concentration points on the membrane surface. The cable net system effectively transfers the rainwater load to the foundation anchorage. The air-pressurization system maintains pressure up to 500 Pa during heavy rain to cope with the combined effects of rainwater impact loads and increased wind speed, providing ample structural safety redundancy.

[0056] IX. Extreme Weather Response During its nearly 14-month operation, the air-supported membrane structure withstood numerous extreme weather tests.

[0057] High winds: The project area experienced multiple gale-force winds (level 8 or higher) during spring and autumn, with maximum instantaneous wind speeds reaching 25 m / s (approximately level 10). The air-pressurization system automatically increased the air pressure to 550 Pa (close to the design limit of 600 Pa) when wind speeds exceeded 15 m / s, giving the membrane surface higher stiffness to withstand wind loads. The cable net system evenly distributed wind pressure to the foundation anchor points, controlling the maximum displacement of the membrane surface to within 1 / 150 of the span, far below the allowable value specified in the standards. Post-storm inspections revealed no damage to the membrane surface, no slack in the cable net, and no displacement of the anchor points.

[0058] Blizzard Weather: A single blizzard in winter can accumulate up to 15cm of snowfall. Due to the steep slope of the spherical curved surface (the top tangent angle is close to 90°), the snow naturally slides off the membrane surface under gravity, with only a small amount accumulating near the base of the membrane, which can be cleared manually. The internal pressure of the air-supported membrane slightly decreases due to the increased snow load (the snow load compresses the membrane surface, causing a slight reduction in volume), and the inflation and pressure-maintaining system automatically replenishes the pressure to 450Pa to offset the effects of the snow load. Throughout the blizzard, the air-supported membrane structure remained safe, showing no signs of collapse.

[0059] High temperatures: In summer, the outside temperature of the membrane can reach 38℃. The PVDF coating of the membrane material can block more than 90% of ultraviolet rays, with a light transmittance of only 7%, effectively avoiding indoor high temperatures caused by direct sunlight. The temperature inside the membrane is maintained below 28℃ through an intelligent temperature control system and forced ventilation. In addition, the spray dust suppression system (which also has a cooling function) installed inside the membrane provides a comfortable working environment for construction personnel.

[0060] 10. Full-process operation and maintenance During the entire 14-month operation period, the routine maintenance and management of the air-supported membrane includes the following: Air pressure monitoring: The intelligent monitoring system continuously records the air pressure, temperature, and humidity data inside the membrane 24 hours a day, generating a data report every 10 minutes. When the air pressure fluctuates abnormally (exceeding ±15% of the set threshold), the system automatically alarms and initiates pressure replenishment.

[0061] Cable net inspection: A visual inspection is conducted weekly to check for broken wires, rust, and loose connections in the ropes; a tension check is conducted monthly, using a tension meter to measure the cable tension at no fewer than 20 nodes. If the tension decreases by more than 8%, tension is replenished via the adjustment unit. A total of 3 tension replenishment operations were performed during operation, each taking approximately 4 hours.

[0062] Membrane surface inspection: A comprehensive inspection of the membrane surface should be conducted monthly, focusing on scratches, abrasions, and whether the heat-sealed seams have come detached. The self-cleaning properties of PVDF membrane materials keep the membrane surface clean, requiring only natural rinsing after heavy rain during operation; no manual cleaning is necessary.

[0063] Equipment maintenance: The air blower, intelligent control system, and ventilation equipment shall be maintained monthly, including replacing filters, checking circuits, and calibrating sensors. The backup diesel generator shall be test-run monthly to ensure it can be started at any time in an emergency.

[0064] XI. Dismantling and Recycling Phase After the main structure reaches the third floor above ground (approximately 12m above ground), the air-supported membrane structure in the foundation pit will have completed its mission. Before dismantling, the air pressure inside the membrane will be slowly released through emergency vents (the rate will be controlled at 50Pa / min to avoid rapid depressurization that could cause the membrane to collapse uncontrollably). Once the air pressure drops below 50Pa, the cable net system (first loosening the secondary cables, then removing the main cables), membrane material, and anchoring system will be dismantled sequentially. The membrane material can be folded for storage, and the cable net and connectors can be recycled. The entire dismantling process will take approximately 5 days.

[0065] XII. Implementation Effect Analysis In this embodiment, the air-supported membrane structure begins service from the earthwork excavation stage and continuously covers the construction of internal support, basement floor slab, and main structure (up to the 3rd floor above ground). The total service period is about 14 months, which is 2 to 7 times that of conventional foundation pit air-supported membrane structures (2 to 6 months).

[0066] The 42m internal clearance of the air-supported membrane structure fully meets the full-range rotation requirements of a 40m high tower crane, achieving a completely green construction process with a single membrane throughout. Comprehensive economic analysis shows that, after amortizing the initial investment of the air-supported membrane structure over a 14-month construction period, the unit-time amortization cost is approximately 70% lower than that of a conventional air-supported membrane structure (used for only 2 months). Furthermore, by avoiding work stoppages during the rainy season, winter low temperatures, and dust and noise complaints, the construction period for the main structure is shortened by approximately 20% compared to conventional methods.

[0067] Comparative Example 1: The swimming pool foundation pit air-supported membrane project adopts the conventional foundation pit air-supported membrane technology route. The foundation pit span is 73.3m, the air-supported membrane height is 23m, the rise-to-span ratio is 0.31, the working air pressure is taken as the conventional value of 200Pa, the cable net adopts a uniform grid (spacing 3.5m, φ18mm), and the membrane material is PVDF membrane material.

[0068] Implementation Results: The air-supported membrane structure can only meet the needs of the excavation stage, with a construction period of approximately 2 months. When construction enters the main structure stage, the internal clearance of 23m is insufficient to accommodate tower cranes for lifting large components (tower cranes generally require 30-40m clearance), necessitating the premature dismantling of the air-supported membrane structure. Dust and noise during the main structure construction stage cannot be isolated, and the initial investment in the air-supported membrane structure is only amortized over 2 months, resulting in a comprehensive amortization cost approximately 6 times that of the proposed solution.

[0069] Comparative Example 2: The foundation pit of a certain water conservancy building project has a span of 46.4m, an air membrane height of 25m, and a rise-to-span ratio of 0.54, which is higher than that of a typical air membrane. However, the cable net system adopts the common existing technology of uniform grid (3.5m spacing, φ16mm), without using non-uniform grids and transition components.

[0070] Implementation Results: Significant deformation of the air-supported membrane on the windward side was observed. Under winds of force 8 and severe convective weather, the cable net exhibited noticeable slippage, resulting in weak overall constraint on the air-supported membrane. Deformation was also evident in the uncabled areas on the sides and corners. Uneven stress on the cable net occurred under variable wind directions, with some cables being overly taut and others relatively slack. This demonstrates that conventional longitudinal and transverse cable nets are unsuitable for air-supported membrane structures with high span-to-span ratios, and the stability of the air-supported membrane structure cannot be effectively guaranteed. The air-supported membrane experienced multiple emergency depressurizations during operation, impacting the construction progress.

[0071] Comparative Example 3: A 45m high air-supported membrane structure (span-to-span ratio of approximately 0.6) collapsed during actual operation. Although the structure had been raised to a certain height, the working air pressure remained at the conventional value of 200Pa, and the double-pressure operation mechanism was not employed. The cable net system was also arranged in a conventional manner. During strong winds, insufficient membrane stiffness led to localized instability and depression, triggering a chain reaction—stress concentration in the depressed areas, membrane tearing, a sudden drop in air pressure, and ultimately, overall collapse.

[0072] This case fully illustrates that without high-pressure support, an air-supported membrane structure will become structurally unstable under extreme conditions due to insufficient stiffness. The double-pressure operating mechanism (200-600 Pa) of this invention fundamentally solves this problem—the high pressure keeps the membrane surface taut at all times, and even under external loads, the deformation of the membrane surface is controlled within the elastic range, preventing instability and depression.

[0073] Comparative Example 4: A foundation pit air-supported membrane project attempted to increase the working air pressure to 400 Pa to achieve higher structural stiffness, but the cable net still used a conventional uniform grid. During operation, it was found that although the high pressure tightened the membrane surface overall, under strong winds, the stress distribution on the membrane surface was extremely uneven—local stress exceeded the standard on the windward side, while the membrane surface on the leeward side was loose and undulating. The cable net only provided effective restraint in the flat area at the top; the sides and corners lacked cable net support, resulting in significant vibrations under wind force and accelerating fatigue damage to the membrane material.

[0074] This case demonstrates that high pressure alone, without a specially designed cable net adapted to the stress distribution characteristics of a spherical curved surface, will lead to stress concentration, accelerating membrane material fatigue and shortening the service life of the air-supported membrane. The specially designed cable net system of this invention arranges the grid and cable diameter differently according to curvature variations, and, in conjunction with a conversion component, achieves a smooth transition of cable force at points of abrupt curvature change, resulting in uniform stress distribution on the membrane surface and fundamentally solving the stress concentration problem.

[0075] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this disclosure (including the claims) is limited to these examples; within the framework of this disclosure, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of this specification as described above, which are not provided in detail for the sake of brevity.

[0076] Although this disclosure has been described in conjunction with specific embodiments thereof, many substitutions, modifications and variations of these embodiments will be apparent to those skilled in the art from the foregoing description.

[0077] One or more embodiments of this specification are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments of this specification should be included within the scope of protection of this disclosure.

Claims

1. An ultra-high spherical air-supported membrane structure for deep foundation pit construction, characterized in that, include: The spherical ultra-high air-supported membrane is made of flexible membrane material. Its edges are sealed to the ground beam foundation at the top of the pit through an anchoring system. After being inflated, it forms a closed working space. The cable net system is set on the outer surface of the spherical ultra-high air membrane and is composed of multiple ropes that are connected by connectors and tightly attached to the surface of the spherical ultra-high air membrane. An inflation and pressure-maintaining system is connected to the interior of the spherical ultra-high-pressure air film and is used to maintain the internal working air pressure of the spherical ultra-high-pressure air film. Wherein: the sag-to-span ratio of the spherical ultra-high air film, that is, the ratio of the net height of the air film to the short span of the foundation pit, is 0.8 to 1.2; The internal working air pressure maintained by the inflation and pressure holding system is 200Pa to 600Pa; The cable net system weaves cable net units in the form of geodesics according to the curvature changes of the spherical ultra-high air film surface, forming a non-uniform grid structure covering the spherical ultra-high air film surface. The grid density is greater in areas with large curvature than in areas with small curvature. The ropes of the cable net system include a main rope and auxiliary ropes, wherein the diameter of the main rope is larger than the diameter of the auxiliary rope; The connector is equipped with an adjustment unit and a locking component. The adjustment unit is used to adjust the tension of the connected rope, and the locking component is used to lock the position of the adjustment unit.

2. The ultra-high spherical air-supported membrane structure for deep foundation pit construction according to claim 1, characterized in that: The adjustment unit includes an independent adjustment component and an overall adjustment component. The independent adjustment component is used to adjust the tension of a single rope individually, while the overall adjustment component is used to simultaneously tension or release all ropes connected to the connector.

3. The ultra-high spherical air-supported membrane structure for deep foundation pit construction according to claim 1, characterized in that: The locking component is a lock nut, anti-loosening washer, or cotter pin, which together with the adjusting unit forms a dual anti-loosening mechanism.

4. The ultra-high spherical air-supported membrane structure for deep foundation pit construction according to claim 1, characterized in that: The diameter of the main cable is 26mm to 32mm, and the diameter of the auxiliary cable is 16mm to 22mm.

5. The ultra-high spherical air-supported membrane structure for deep foundation pit construction according to claim 1, characterized in that: The anchoring system includes pre-embedded anchors embedded in the ground beam foundation, angle steel strips set along the edge of the air film, and EPDM sealing strips set between the angle steel strips and the film material.

6. The ultra-high spherical air-supported membrane structure for deep foundation pit construction according to claim 1, characterized in that: The inflation and pressure holding system includes a real-time air pressure monitoring module and an automatic pressure replenishment module, which automatically starts pressure replenishment when the air pressure is lower than a set threshold.

7. The ultra-high spherical air-supported membrane structure for deep foundation pit construction according to claim 1, characterized in that: The spherical ultra-high air membrane is made of PVDF double-coated polyester fiber membrane material.

8. The ultra-high spherical air-supported membrane structure for deep foundation pit construction according to claim 1, characterized in that: It also includes an airtight door system and a forced ventilation system, wherein the airtight door system is installed on the spherical ultra-high air membrane for personnel and construction machinery to enter and exit.

9. A construction method for ultra-high spherical air-supported membrane structures in deep foundation pits, applicable to the ultra-high spherical air-supported membrane structures according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Foundation Pit Preparation and Anchoring System Installation: Install pre-embedded anchors and angle steel strips on the ground beam at the top of the foundation pit; S2. Spherical ultra-high air-supported membrane installation: The flexible membrane material is laid above the foundation pit, and the edges of the membrane material are sealed and connected to the ground beam foundation through an anchoring system; S3. Cable net system installation: Based on the curvature distribution of the spherical ultra-high air film membrane surface, a non-uniform grid cable net is installed on the outer surface of the spherical ultra-high air film membrane. In areas with large curvature, a denser grid arrangement and a larger diameter main cable are used, while in areas with small curvature, a sparser grid arrangement and a smaller diameter secondary cable are used. S4. Inflation and Adjustment: Inflate the spherical ultra-high air film to 200Pa~600Pa using the inflation and pressure holding system, gradually increase the pressure and check the sealing performance and structural stability; S5. Full-process operation and maintenance: During each stage of foundation pit excavation, internal support construction, basement floor slab construction and main structure construction, the working air pressure shall be continuously maintained, and the cable net tension shall be adjusted periodically through the adjustment unit, and the position of the adjustment unit shall be locked through the locking component.

10. The construction method according to claim 9, characterized in that: In step S3, a special conversion component is set at the point where the curvature of the spherical ultra-high air film membrane changes abruptly, so that the cable net matches the shape of the membrane surface.

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