Template system optimization and construction method for improving appearance quality of exposed surface of underground excavation square pile

Abstract

The invention discloses a template system optimization and construction method for improving the appearance quality of an exposed surface of an underground excavation square pile. In the invention, a standard brushing process of the water-based release agent special for the steel template is adopted, and mineral admixtures such as fly ash are scientifically doped in a concrete mixing ratio, so that the gloss uniformity of the concrete surface is effectively improved. The release agent forms a uniform protective film on the surface of the template, so that the cohesive force between the concrete and the template is reduced, and the surface rust residue is avoided; the mineral admixture optimizes the microstructure of the concrete, so that the hardened surface color is more uniform and consistent, the overall appearance texture is remarkably improved, a layered pouring process is implemented, the pouring height of each layer is strictly controlled, and meanwhile, an exhaust guide pipe is pre-buried in a reinforcing steel bar dense area, so that an efficient concrete compactness guarantee system is formed. And the exhaust guide pipe timely exhausts air and moisture in the concrete, so that the defects of voids and pitted surfaces caused by bubble accumulation or insufficient vibration are fundamentally reduced, and the surface of the pile body is more compact and smoother.

Description

Technical Field

[0001] This invention belongs to the field of building engineering technology, specifically an optimization of the template system and a construction method for improving the appearance quality of the exposed surface of a square pile in a tunnel. Background Technology

[0002] In modern construction engineering, cut-and-cover square piles are widely used for the support and foundation construction of underground structures. Cut-and-cover square piles are square-section pile foundations constructed using the cut-and-cover method, suitable for densely populated urban areas, complex geological conditions, and projects sensitive to the surrounding environment, such as subways, tunnels, and foundation pit support. This type of pile involves manually or mechanically excavating a square hole underground, then placing a reinforcing cage and pouring concrete to form the pile body. It features high bearing capacity, small deformation, and high construction precision. The construction process of cut-and-cover square piles does not require large-area excavation, reducing interference with surface traffic and adjacent buildings, while also reducing noise and vibration pollution, making it suitable for areas with limited space or high environmental protection requirements. The cross-sectional dimensions of the pile can be adjusted according to design requirements, with common side lengths ranging from 0.8 meters to 2.0 meters, and pile lengths reaching tens of meters, possessing strong bending and shear resistance. During construction, strict control of groundwater treatment, borehole wall stability, and concrete pouring quality is required to ensure the integrity of the pile body and structural safety. Due to its flexible construction and wide adaptability, this type of pile is widely used in deep foundation pit support, foundation replacement, and underground structure engineering.

[0003] However, traditional construction methods often result in quality problems on the exposed surface of the piles, such as uneven surfaces, cracks, and honeycombing defects. These not only affect the aesthetics but may also compromise the durability and safety of the structure. Therefore, improving the appearance quality of the exposed surface of square piles excavated in tunnels has become a key focus for engineering technicians. Summary of the Invention

[0004] The purpose of this invention is to provide an optimized template system and construction method for improving the appearance quality of exposed surfaces of square piles excavated in underground tunnels, in order to solve the problems mentioned above.

[0005] The technical solution adopted in this invention is as follows: an optimization of the formwork system and a construction method for improving the appearance quality of exposed surfaces of square piles excavated in underground tunnels, the method comprising the following steps:

[0006] S1: Determine the control line and mark the pile position according to the foundation axis, fix the wooden pile with concrete, and carry out construction after acceptance; S2: Manually excavate the soil of the first section of the pile hole at a height of 0.9 to 1.2m, and transport it to 1.5 meters outside the pile hole;

[0007] S3: Install the fixed steel formwork, add sealing strips to the joints and apply release agent, pour low heat of hydration concrete, and demold within 8 hours;

[0008] S4: Set the cross axis and elevation to the top of the protective wall, check the verticality and flatness of the hole wall, and control the deviation within the specified range;

[0009] S5: Erect gantry cranes and vertical transportation equipment, and equip them with low-voltage lighting, ventilation fans and safety railings to ensure operational safety;

[0010] S6: Use lifting equipment to excavate and hoist the soil for subsequent pile holes, pour the retaining concrete section by section and calibrate the axis elevation until the design depth is reached;

[0011] S7: After the retaining wall construction is completed, install the Baoli board formwork to ensure the surface quality of the piles after demolding;

[0012] S8: Fabricate the steel cage, hoist and weld it in sections, correct the verticality after lowering it into the hole, and fix the thickness of the protective layer.

[0013] S9: Four mixers and pumping equipment are used to pour concrete, and the pumping process and pipeline cleaning are controlled to ensure the quality of the pouring.

[0014] S10: Install temperature and humidity sensors, automatically spray curing for ≥14 days, cover with insulation blankets to control temperature in winter, and manually remove formwork to protect the pile body;

[0015] S11: Use a 3D laser scanner to check surface flatness and ultrasonic testing to check for internal voids and defects.

[0016] In a preferred embodiment, in step S3, the retaining wall formwork uses standardized steel formwork with a rigidity ≥3mm / m. Sealing strips are added at the joints to prevent grout leakage. A special release agent is applied to the surface of the formwork to ensure a uniform gloss after demolding. After the formwork is installed, the formwork is aligned with the center pile point and then reinforced with reinforcing steel bars. Concrete should be poured immediately after each section of the pile hole retaining wall is excavated. Low-heat cement and high-quality admixtures are used to reduce the risk of shrinkage cracks. The coarse aggregate is 5-40mm graded crushed stone with a mud content ≤1%. To speed up the process, an appropriate amount of early-strength agent can be added to ensure demolding within 8 hours.

[0017] In a preferred embodiment, in step S4, the allowable vertical deviation of the test pile shall not exceed 3%, and the allowable deviation of the pile diameter and pile position shall not exceed 50 mm.

[0018] In a preferred embodiment, in step S5, after the first pile hole is formed, a vertical transport frame is erected at the top of the pile hole. The lighting at the bottom of the well must use low-voltage power supply and waterproof safety lamps with covers. A guardrail is set up at the pile opening. When the pile hole depth exceeds 8m, ventilation should be provided to the bottom of the well to enhance air convection.

[0019] In a preferred embodiment, in step S6, the excavation and hoisting of the second section of the pile hole is carried out. Starting from the second section, the soil is transported using lifting equipment. Personnel inside the pile should wear safety helmets, and personnel on the ground should wear safety belts. After the pile hole is excavated to the specified depth, the diameter of the pile hole and the curvature of the well wall are checked with a support rod. The top and bottom should be vertical and smooth, and the hole wall is repaired.

[0020] Pouring the second section of retaining wall concrete: The concrete is delivered by a tremie pipe, poured manually, and compacted manually; an early-strength agent may be added to the concrete to accelerate its hardening, as determined by testing.

[0021] Check the center axis and elevation of the pile location, and calibrate section by section based on the positioning line of the pile hole opening; for sections below the third section, continue the cycle from the second section downwards, and excavate the pile hole to the elevation. Please have the supervision and design units check the soil conditions.

[0022] In a preferred embodiment, in step S7, after the retaining wall construction is completed, a polycarbonate board template is installed. The template thickness is selected as 12mm to ensure that the rigidity meets the requirements of the pouring force. The cutting size error is controlled within ±2mm. During installation, tie bolts with a spacing of 500mm are used to fix it to the support system. Special sealing tape with a width of 50mm is pasted at the joints, and the overlap length of the tape is not less than 10mm. The gap between the template and the retaining wall structure is controlled within 3mm, and the overall flatness deviation does not exceed 2mm / m, so as to ensure that the flatness of the square pile surface meets the design standard when the formwork is subsequently removed.

[0023] In a preferred embodiment, in step S8, after the reinforcing bars pass the test, a reinforcing cage is made using an AC welding machine according to the construction specifications and design drawings. The reinforcing bar joints are welded, and the lap length is 10d. Since the reinforcing cage is relatively long, it is made in sections. A crane is used to lift and weld the pile hole. After the cage is lowered into the hole, jacks and pullers are used to straighten the reinforcing cage from top to bottom to ensure the thickness of the protective layer and fix it.

[0024] In a preferred embodiment, in step S9, a concrete pumping device is used in conjunction with the casing method to pour the pile body concrete, with the casing extending into the concrete by at least 300-500 mm;

[0025] ①The pumping process specifically includes:

[0026] a. Before pumping concrete, pump clean water out of the storage hopper through the pipeline to wet and clean the pipeline. Then add cement mortar with the same mix ratio as the concrete into the hopper to lubricate the pipeline before pumping concrete. The cement mortar in the pipe should be evenly spread on the pouring surface as required.

[0027] b. When starting pumping, the pumping speed should be slowed down, and the oil pressure change should be within the allowable range. Once pumping is running smoothly, normal pumping speed can be used.

[0028] c. During pumping, the amount of concrete in the hopper should be kept between 10mm above the cylinder opening and 150mm below the hopper opening to avoid low suction efficiency, easy air intake and pipe blockage, and too much concrete will overflow during back pumping and increase the load on the mixing shaft.

[0029] d. Concrete pumping should be carried out continuously. When the concrete supply is not timely, the pumping speed should be reduced. When pumping is temporarily interrupted, mixing should not be stopped. When the blades are stuck, they need to be reversed to queue up and then forwarded. Reverse for a certain period of time, and pumping can only continue after forward rotation is smooth.

[0030] e. If the pumping stop time exceeds 20 minutes and the pipeline is long, the pump should be started every 5 minutes to pump a small amount of concrete. If the pipeline is short, the pump can be turned forward and reversed 2 to 3 times every 5 minutes to make the concrete in the pipe peristalsis and prevent bleeding and segregation. If the pump is stopped for a long time, the temperature is high and the concrete slump is low, it may cause pipe blockage. It is advisable to remove the concrete from the pump and the delivery pipe.

[0031] f. Pumping should proceed from far to near, with pipes gradually dismantled during pouring;

[0032] g. During the high-temperature season, cover the pipes leading into the hall with wet straw bags to cool them down and reduce the temperature of the material entering the mold.

[0033] h. The total horizontal equivalent distance of the pumping pipeline should be less than the maximum pumping distance of the equipment.

[0034] In a preferred embodiment, step S9, the cleaning process after pumping is completed, specifically includes:

[0035] a. When pumping is about to end, the amount of concrete stored in the concrete pipe and hopper and the amount of concrete required at the pouring site should be estimated in order to determine the required amount of concrete.

[0036] b. When cleaning the pipeline after pumping, use an air compressor to push the cleaning ball. First, install the special cleaning pipe, then start the air compressor and gradually increase the pressure. During the cleaning process, tap the delivery pipe at any time to check if the concrete is close to being emptied. When there is still about 10m of concrete in the delivery pipe, the compressor should be slowly depressurized to prevent large explosions and injuries.

[0037] c. After pumping is completed, the concrete pump, placing boom and pipelines should be cleaned immediately. After the pipelines are disassembled, they should be stacked according to their different specifications.

[0038] In a preferred embodiment, in step S10, intelligent maintenance involves installing temperature and humidity sensors, using an automatic spray system to maintain surface humidity ≥90%, a maintenance cycle ≥14 days, and covering with an electrically heated insulation blanket during winter construction to control the internal and external temperature difference ≤20℃.

[0039] When breaking through the protective wall and formwork of the pile body, the formwork is removed manually to avoid damaging the surface quality of the square pile.

[0040] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0041] 1. In this invention, by employing a standardized application process for a water-based release agent specifically for steel formwork, and scientifically incorporating mineral admixtures such as fly ash into the concrete mix design, the gloss uniformity of the concrete surface is effectively improved. The release agent forms a uniform protective film on the formwork surface, reducing the adhesion between the concrete and the formwork and preventing surface rust residue; the mineral admixtures optimize the microstructure of the concrete, resulting in a more uniform and consistent surface color after hardening, and a significant improvement in overall appearance and texture.

[0042] 2. In this invention, a layered pouring process is implemented with strict control over the pouring height of each layer. Simultaneously, venting pipes are pre-embedded in areas with dense reinforcement, forming a highly efficient concrete compaction guarantee system. Layered pouring ensures that the concrete can fully flow and fill the formwork space during vibration, while the venting pipes promptly remove air and moisture from the concrete, fundamentally reducing honeycomb and pitted surface defects caused by air bubble accumulation or insufficient vibration, resulting in a denser and smoother pile surface.

[0043] 3. In this invention, high-strength steel formwork is selected to ensure its rigidity meets construction requirements. Combined with the refined process of mechanical milling to process the pile end face, the tightness of the formwork joints and the accuracy of the pile shape are significantly improved. The high rigidity of the steel formwork effectively resists the lateral pressure during concrete pouring, avoiding formwork deformation; the mechanical milling process ensures the flatness of the pile end face, effectively controlling the misalignment error at the joint. Laser scanning test results show that the overall line smoothness and surface flatness both meet the design standards.

[0044] 4. In this invention, by using a special sealing strip at the joints of the formwork and implementing a standardized vibration process, the common formwork joint marks in traditional construction are successfully eliminated. The sealing strip forms an elastic sealing layer during formwork splicing, preventing the leakage of concrete grout; standardized vibration ensures the full bonding of concrete at the joint, making the transition between layers natural and smooth, without obvious joint marks, thus improving the overall appearance of the pile.

[0045] 5. In this invention, low-heat-of-hydration cement is used to prepare the concrete, and combined with the application of an intelligent temperature-controlled curing system, the temperature stress and shrinkage stress during the concrete hardening process are effectively reduced. The intelligent curing system avoids surface shrinkage cracks caused by insufficient humidity or excessive temperature difference by precisely controlling the ambient humidity and internal and external temperature differences; the low-heat-of-hydration cement reduces the peak heat of hydration, controlling the possibility of crack formation from the source, and reliably ensuring the integrity of the pile surface.

[0046] 6. In this invention, after repairing local defects with epoxy-based repair mortar, a concrete protective agent is then used for full surface treatment, forming a dual protection system. The epoxy-based repair mortar has excellent adhesion and impermeability, ensuring a tight bond between the repaired area and the original concrete; the concrete protective agent forms a dense protective film on the surface, effectively resisting the penetration and adhesion of external pollutants and extending the cleanliness period of the pile body. Attached Figure Description

[0047] Figure 1 This is a schematic diagram illustrating the process principle of the present invention. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0049] Reference Figure 1 ,

[0050] Example:

[0051] An optimization and construction method for a formwork system to improve the appearance quality of exposed surfaces of square piles in underground excavation, the method comprising the following steps:

[0052] S1: Determine the control line and mark the pile position according to the foundation axis, fix the wooden pile with concrete, and carry out construction after acceptance; S2: Manually excavate the soil of the first section of the pile hole at a height of 0.9 to 1.2m, and transport it to 1.5 meters outside the pile hole;

[0053] S3: Install the fixed steel formwork, add sealing strips to the joints and apply release agent, pour low heat of hydration concrete, and demold within 8 hours;

[0054] S4: Set the cross axis and elevation to the top of the protective wall, check the verticality and flatness of the hole wall, and control the deviation within the specified range;

[0055] S5: Erect gantry cranes and vertical transportation equipment, and equip them with low-voltage lighting, ventilation fans and safety railings to ensure operational safety;

[0056] S6: Use lifting equipment to excavate and hoist the soil for subsequent pile holes, pour the retaining concrete section by section and calibrate the axis elevation until the design depth is reached;

[0057] S7: After the retaining wall construction is completed, install the Baoli board formwork to ensure the surface quality of the piles after demolding;

[0058] S8: Fabricate the steel cage, hoist and weld it in sections, correct the verticality after lowering it into the hole, and fix the thickness of the protective layer.

[0059] S9: Four mixers and pumping equipment are used to pour concrete, and the pumping process and pipeline cleaning are controlled to ensure the quality of the pouring.

[0060] S10: Install temperature and humidity sensors, automatically spray curing for ≥14 days, cover with insulation blankets to control temperature in winter, and manually remove formwork to protect the pile body;

[0061] S11: Use a 3D laser scanner to check surface flatness and ultrasonic testing to inspect internal holes and defects.

[0062] In step S3, the retaining wall formwork uses standardized steel formwork with a rigidity ≥3mm / m. Sealing strips are added at the joints to prevent grout leakage. A special release agent (such as water-based release agent) is applied to the surface of the formwork to ensure a uniform gloss after demolding. After the formwork is installed, the formwork is aligned with the center pile points and then the retaining wall reinforcement is tied. Concrete should be poured immediately after each section of the pile hole retaining wall is excavated. Low-heat cement and high-quality admixtures are used to reduce the risk of shrinkage cracks. The coarse aggregate is 5-40mm graded crushed stone with a mud content ≤1%. To speed up the process, an appropriate amount of early-strength agent can be added to ensure demolding within 8 hours.

[0063] In step S4, the allowable vertical deviation of the test pile shall not exceed 3%, and the allowable deviation of the pile diameter and pile position shall not exceed 50mm.

[0064] In step S5, after the first pile hole is formed, a vertical transport frame is erected at the top of the pile hole. The lighting at the bottom of the well must use a low-voltage power supply (12V, 100W) and a waterproof safety lamp with a cover. A guardrail is set up at the pile opening. When the pile hole depth exceeds 8m, ventilation should be provided to the bottom of the well to enhance air convection.

[0065] In step S6, the excavation and hoisting of the second section of the pile hole is carried out. Starting from the second section, the soil is transported using lifting equipment. Personnel inside the pile should wear safety helmets, and personnel on the ground should wear safety belts. After the pile hole is excavated to the specified depth, the diameter of the pile hole and the curvature of the well wall are checked with a support rod. The top and bottom should be vertical and smooth, and the hole wall is repaired.

[0066] Pouring the second section of retaining wall concrete: The concrete is delivered by a tremie pipe, poured manually, and compacted manually; the addition of an early-strength agent to the concrete can be determined by testing to accelerate the hardening of the concrete;

[0067] Check the center axis and elevation of the pile location, and calibrate section by section based on the positioning line of the pile hole opening; for the third section and below, continue the operation from the second section downwards, and excavate the pile hole to the elevation. Please ask the supervision and design units to check the soil conditions.

[0068] In step S7, after the retaining wall construction is completed, install the Baoli board formwork. The formwork thickness is selected as 12mm to ensure that the rigidity meets the requirements of the pouring force. The cutting size error is controlled within ±2mm. During installation, tie bolts with a spacing of 500mm are used to fix it to the support system. Special sealing tape with a width of 50mm is pasted at the joints, and the overlap length of the tape is not less than 10mm. The gap between the formwork and the retaining wall structure is controlled within 3mm, and the overall flatness deviation does not exceed 2mm / m, so as to ensure that the surface flatness of the square pile meets the design standard when the formwork is removed later.

[0069] In step S8, after the reinforcing bars pass the test, the reinforcing cage is made using an AC welding machine according to the construction specifications and design drawings. The reinforcing bar joints are welded with a lap length of 10d. Since the reinforcing cage is long, it is made in sections. A crane is used to lift and weld the pile hole. After the cage is lowered into the hole, jacks and pullers are used to straighten the reinforcing cage from top to bottom to ensure the thickness of the protective layer and fix it.

[0070] In step S9, a concrete pumping device is used in conjunction with the casing method to pour the pile body concrete, with the casing extending into the concrete by at least 300-500mm.

[0071] ①The pumping process specifically includes:

[0072] a. Before pumping concrete, pump the clean water in the storage hopper out of the pipeline to wet and clean the pipeline. Then add cement mortar (or 1:2 cement mortar) with the same mix ratio as the concrete into the hopper to lubricate the pipeline before pumping concrete. The cement mortar in the pipe should be evenly spread on the pouring surface as required.

[0073] b. When starting pumping, the pumping speed should be slowed down, and the oil pressure change should be within the allowable range. Once pumping is running smoothly, normal pumping speed can be used.

[0074] c. During pumping, the amount of concrete in the hopper should be kept between 10mm above the cylinder opening and 150mm below the hopper opening to avoid low suction efficiency, easy air intake and pipe blockage, and too much concrete will overflow during back pumping and increase the load on the mixing shaft.

[0075] d. Concrete pumping should be carried out continuously. When the concrete supply is not timely, the pumping speed should be reduced. When pumping is temporarily interrupted, mixing should not be stopped. When the blades are stuck, they need to be reversed to queue up and then forwarded. Reverse for a certain period of time, and pumping can only continue after forward rotation is smooth.

[0076] e. If the pumping stoppage time exceeds 20 minutes and the pipeline is long, the pump should be started every 5 minutes to pump a small amount of concrete. If the pipeline is short, the pump can be rotated 2 to 3 times in both directions every 5 minutes to make the concrete in the pipe peristalsis and prevent bleeding and segregation. If the pump is stopped for a long time (more than 45 minutes), the temperature is high and the concrete slump is low, it may cause pipe blockage. In this case, the concrete should be removed from the pump and the delivery pipe.

[0077] f. Pumping should proceed from far to near, with pipes gradually dismantled during pouring;

[0078] g. During the high-temperature season, it is advisable to cover the pipes entering the hall with wet straw bags to cool them down and reduce the temperature of the material entering the mold.

[0079] h. The total horizontal equivalent distance of the pumping pipeline should be less than the maximum pumping distance of the equipment;

[0080] In step S9, the cleaning work after pumping is completed specifically includes:

[0081] a. When pumping is about to end, the amount of concrete stored in the concrete pipe and hopper and the amount of concrete needed at the pouring site should be estimated in order to determine the amount of concrete required.

[0082] b. When cleaning the pipeline after pumping, use an air compressor to push the cleaning ball. First, install the special cleaning pipe, then start the air compressor and gradually increase the pressure. During the cleaning process, tap the delivery pipe at any time to check if the concrete is close to being emptied. When there is still about 10m of concrete in the delivery pipe, the compressor should be slowly depressurized to prevent large explosions and injuries.

[0083] c. After pumping is completed, the concrete pump, placing boom and pipelines should be cleaned immediately. After the pipelines are disassembled, they should be stacked according to their different specifications.

[0084] In step S10, intelligent maintenance involves installing temperature and humidity sensors, using an automatic spray system to maintain surface humidity ≥90%, and a maintenance cycle ≥14 days. During winter construction, an electrically heated insulation blanket is used to control the internal and external temperature difference to ≤20℃.

[0085] When breaking through the protective wall and formwork of the pile body, the formwork is removed manually to avoid damaging the surface quality of the square pile.

[0086] Comparative example:

[0087] Method for measuring surface flatness error:

[0088] Before optimization, traditional hot-rolled steel formwork was used for construction. The formwork thickness was 6mm, and ordinary bolts were used for joints without dedicated locating pins. Before installation, the axis was calibrated manually using a ruler. The formwork support system consisted of a single row of steel pipe frames spaced 1.2m apart, without diagonal scissor bracing. Before concrete pouring, the formwork surface was not mechanically milled; it was only manually sanded. During measurement, a 2m straightedge and feeler gauge were used, with a measurement area selected every 5m. Three points were measured in each area, and the maximum value was used as the judgment criterion. Data recording accuracy was retained to 1mm.

[0089] Method for determining the percentage of honeycomb-like pitted surface area:

[0090] No mineral admixtures were added to the concrete mix design. 42.5 grade ordinary Portland cement was used, and 5-25mm continuously graded crushed stone was selected as coarse aggregate, with a sand ratio controlled at 35%. A tremie pipe was used for pouring, achieving a single pour height of 1.2m. A φ50mm immersion vibrator was used for compaction, with a vibration interval of 600mm and a vibration time of 15-20 seconds per point. No sealing strips were applied to the formwork joints; only double-sided tape was used for temporary sealing. Honeycombing and pitting were detected using a combination of visual inspection and steel ruler measurement, with individual defects exceeding 5cm² being excluded. 2 The area is included in the statistics, and the final result is the ratio of the total defect area to the surface area of ​​the pile.

[0091] Method for determining the proportion of color difference area:

[0092] The release agent used was an oil-based mixture of waste engine oil and diesel oil in a 1:1 ratio, applied manually with a brush. The amount applied was not precisely controlled, resulting in some areas being missed or piling up. After concrete pouring, it was not covered for curing and was left to cure naturally. During summer construction, it was exposed to sunlight for more than 4 hours, and during winter construction, no insulation measures were taken. Color difference was detected using a standard color chart comparison method. Observations were made at a distance of 2m from the pile under natural light conditions. Areas with a ΔE value exceeding 3 compared to the reference color chart were marked as color difference areas, and their area percentage was calculated.

[0093] Methods for determining the crack occurrence rate:

[0094] Concrete is prepared using ordinary Portland cement, with a cement content of 450 kg / m³. 3 No fly ash or mineral powder was added; municipal tap water was used for mixing, and the water temperature was not controlled. Curing measures consisted of manual watering twice daily for 10 minutes each time, without monitoring of ambient temperature and humidity. Formwork removal was scheduled for 72 hours after pouring, after which the pile was directly exposed to the atmosphere. Crack detection was performed visually combined with a 5x magnifying glass, counting the number of cracks ≥50mm in length and ≥0.2mm in width, and calculating the crack incidence rate based on the pile surface area, accurate to 0.1 cracks / m. 2 .

[0095] The experimental results are shown in the table below:

[0096] Indicator Item Comparative Example Example Increase Surface flatness error ≤8mm / m ≤3mm / m 62.5％↑ Honeycomb texture area percentage ≥2％ ≤0.5％ 75％↓ Percentage of color difference area ≥5％ ≤1％ 80％↓ Crack incidence <![CDATA[0.5 pieces / m 2 > <![CDATA[0.1 pieces / m 2 > 80％↓

[0097] From the above, we can conclude that:

[0098] In this invention, a standardized application process for a water-based release agent specifically for steel formwork, combined with the scientific incorporation of mineral admixtures such as fly ash into the concrete mix design, effectively improves the gloss uniformity of the concrete surface. The release agent forms a uniform protective film on the formwork surface, reducing the adhesion between the concrete and the formwork and preventing surface rust residue; the mineral admixtures optimize the microstructure of the concrete, resulting in a more uniform and consistent surface color after hardening, and a significant improvement in overall appearance and texture.

[0099] In this invention, a layered pouring process is implemented with strict control over the pouring height of each layer. Simultaneously, venting pipes are pre-embedded in areas with dense reinforcement, forming a highly efficient concrete compaction guarantee system. Layered pouring ensures that the concrete can fully flow and fill the formwork space during vibration, while the venting pipes promptly remove air and moisture from the concrete, fundamentally reducing honeycomb and pitted surface defects caused by air bubble accumulation or insufficient vibration, resulting in a denser and smoother pile surface.

[0100] In this invention, high-strength steel formwork is selected to ensure its rigidity meets construction requirements. Combined with the refined process of mechanical milling to process the pile end face, the tightness of the formwork joints and the accuracy of the pile shape are significantly improved. The high rigidity of the steel formwork effectively resists the lateral pressure during concrete pouring, preventing formwork deformation; the mechanical milling process ensures the flatness of the pile end face, effectively controlling the misalignment error at the joint. Laser scanning test results show that the overall line smoothness and surface flatness both meet the design standards.

[0101] In this invention, by using a special sealing strip at the joints of the formwork and implementing a standardized vibration process, the common formwork joint marks in traditional construction are successfully eliminated. The sealing strip forms an elastic sealing layer during formwork splicing, preventing the leakage of concrete grout; standardized vibration ensures the full bonding of the concrete at the joint, making the transition between layers natural and smooth, without obvious joint marks, thus improving the overall appearance of the pile.

[0102] In this invention, low-heat-of-hydration cement is used to prepare the concrete, and combined with the application of an intelligent temperature-controlled curing system, the temperature stress and shrinkage stress during the concrete hardening process are effectively reduced. The intelligent curing system avoids surface shrinkage cracks caused by insufficient humidity or excessive temperature difference by precisely controlling the ambient humidity and the internal and external temperature difference; the low-heat-of-hydration cement reduces the peak heat of hydration, controlling the possibility of crack formation from the source, and reliably ensuring the integrity of the pile surface.

[0103] In this invention, after repairing local defects with epoxy-based repair mortar, a concrete protective agent is applied for full surface treatment, forming a dual protection system. The epoxy-based repair mortar has excellent adhesion and impermeability, ensuring a tight bond between the repaired area and the original concrete; the concrete protective agent forms a dense protective film on the surface, effectively resisting the penetration and adhesion of external pollutants and extending the cleanliness period of the pile's appearance.

[0104] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the term "comprising" or any other variations thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0105] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An optimization of the formwork system and a construction method for improving the appearance quality of exposed surfaces of square piles excavated in underground tunnels, characterized in that: The method includes the following steps: S1: Determine the control line and mark the pile positions according to the foundation axis, fix the wooden piles with concrete, and carry out construction after acceptance; S2: Manually excavate the soil in the first section of the pile hole at a height of 0.9 to 1.2 meters, and transport it to a position 1.5 meters outside the pile hole; S3: Install the fixed steel formwork, add sealing strips to the joints and apply release agent, pour low heat of hydration concrete, and demold within 8 hours; S4: Set the cross axis and elevation to the top of the protective wall, check the verticality and flatness of the hole wall, and control the deviation within the specified range; S5: Erect gantry cranes and vertical transportation equipment, and equip them with low-voltage lighting, ventilation fans and safety railings to ensure operational safety; S6: Use lifting equipment to excavate and hoist the soil for subsequent pile holes, pour the retaining concrete section by section and calibrate the axis elevation until the design depth is reached; S7: After the retaining wall construction is completed, install the Baoli board formwork to ensure the surface quality of the piles after demolding; S8: Fabricate the steel cage, hoist and weld it in sections, correct the verticality after lowering it into the hole, and fix the thickness of the protective layer. S9: Four mixers and pumping equipment are used to pour concrete, and the pumping process and pipeline cleaning are controlled to ensure the quality of the pouring. S10: Install temperature and humidity sensors, automatically spray curing for ≥14 days, cover with insulation blankets to control temperature in winter, and manually remove formwork to protect the pile body. S11: Use a 3D laser scanner to check surface flatness and ultrasonic testing to inspect internal voids and defects.

2. The template system optimization and construction method for improving the appearance quality of exposed surfaces of square piles excavated in tunnels as described in claim 1, characterized in that: In step S3, the retaining wall formwork uses standardized steel formwork with a rigidity ≥3mm / m. Sealing strips are added at the joints to prevent grout leakage. A special release agent is applied to the surface of the formwork to ensure a uniform gloss after demolding. After the formwork is installed, the formwork is aligned with the center pile point and then the retaining wall reinforcement is tied. Concrete should be poured immediately after each section of the pile hole retaining wall is excavated. Low-heat cement and high-quality admixtures are used to reduce the risk of shrinkage cracks. The coarse aggregate is 5-40mm graded crushed stone with a mud content ≤1%. To speed up the process, an appropriate amount of early-strength agent can be added to ensure demolding within 8 hours.

3. The template system optimization and construction method for improving the appearance quality of exposed surfaces of square piles excavated in tunnels as described in claim 1, characterized in that: In step S4, the allowable vertical deviation of the test pile shall not exceed 3%, and the allowable deviation of the pile diameter and pile position shall not exceed 50mm.

4. The template system optimization and construction method for improving the appearance quality of exposed surfaces of square piles excavated in tunnels as described in claim 1, characterized in that: In step S5, after the first pile hole is formed, a vertical transport frame is erected at the top of the pile hole. The lighting at the bottom of the well must use low-voltage power and waterproof safety lamps with covers. A guardrail is set up at the pile opening. When the pile hole depth exceeds 8m, ventilation should be provided to the bottom of the well to enhance air convection.

5. The template system optimization and construction method for improving the appearance quality of exposed surfaces of square piles excavated in tunnels as described in claim 1, characterized in that: In step S6, the excavation and hoisting of the second section of the pile hole is carried out. Starting from the second section, the soil is transported using lifting equipment. Personnel inside the pile should wear safety helmets, and personnel on the ground should wear safety belts. After the pile hole is excavated to the specified depth, the diameter of the pile hole and the arc of the well wall are checked with a support rod. The top and bottom should be vertical and smooth, and the hole wall is repaired. Pouring the second section of retaining wall concrete: The concrete is delivered by a tremie pipe, poured manually, and compacted manually; an early-strength agent may be added to the concrete to accelerate its hardening, as determined by testing. Check the center axis and elevation of the pile location, and calibrate section by section based on the positioning line of the pile hole. The work for the third section and below will proceed in the same cycle as the second section, excavating the pile holes to the required elevation. Please have the supervisor and design unit check the soil conditions.

6. The template system optimization and construction method for improving the appearance quality of exposed surfaces of square piles excavated in tunnels as described in claim 1, characterized in that: In step S7, after the retaining wall construction is completed, the Baoli board template is installed. The template thickness is selected as 12mm to ensure that the rigidity meets the requirements of the pouring force. The cutting size error is controlled within ±2mm. During installation, tie bolts with a spacing of 500mm are used to fix it to the support system. Special sealing tape with a width of 50mm is pasted at the joints, and the overlap length of the tape is not less than 10mm. The gap between the template and the retaining wall structure is controlled within 3mm, and the overall flatness deviation does not exceed 2mm / m, so as to ensure that the flatness of the square pile surface meets the design standard when the formwork is removed later.

7. The template system optimization and construction method for improving the appearance quality of exposed surfaces of square piles excavated in tunnels as described in claim 1, characterized in that: In step S8, after the reinforcing bars pass the test, the reinforcing cage is made using an AC welding machine according to the construction specifications and design drawings. The reinforcing bar joints are welded with a lap length of 10d. Since the reinforcing cage is long, it is made in sections. A crane is used to lift and weld the pile hole. After the cage is lowered into the hole, jacks and pullers are used to straighten the reinforcing cage from top to bottom to ensure the thickness of the protective layer and fix it.

8. The template system optimization and construction method for improving the appearance quality of exposed surfaces of square piles excavated in tunnels as described in claim 1, characterized in that: In step S9, a concrete pumping device is used in conjunction with the casing method to pour the pile body concrete, with the casing extending into the concrete by at least 300-500mm. ①The pumping process specifically includes: a. Before pumping concrete, pump clean water out of the storage hopper through the pipeline to wet and clean the pipeline. Then add cement mortar with the same mix ratio as the concrete into the hopper to lubricate the pipeline before pumping concrete. The cement mortar in the pipe should be evenly spread on the pouring surface as required. b. When starting pumping, the pumping speed should be slowed down, and the oil pressure change should be within the allowable range. Once pumping is running smoothly, normal pumping speed can be used. c. During pumping, the amount of concrete in the hopper should be kept between 10mm above the cylinder opening and 150mm below the hopper opening to avoid low suction efficiency, easy air intake and pipe blockage, and too much concrete will overflow during back pumping and increase the load on the mixing shaft. d. Concrete pumping should be carried out continuously. When the concrete supply is not timely, the pumping speed should be reduced. When pumping is temporarily interrupted, mixing should not be stopped. When the blades are stuck, they need to be reversed to queue up and then forwarded. Reverse for a certain period of time, and pumping can only continue after forward rotation is smooth. e. If the pumping stop time exceeds 20 minutes and the pipeline is long, the pump should be started every 5 minutes to pump a small amount of concrete. If the pipeline is short, the pump can be turned forward and reversed 2 to 3 times every 5 minutes to make the concrete in the pipe peristalsis and prevent bleeding and segregation. If the pump is stopped for a long time, the temperature is high and the concrete slump is low, it may cause pipe blockage. It is advisable to remove the concrete from the pump and the delivery pipe. f. Pumping should proceed from far to near, with pipes gradually dismantled during pouring; g. During the high-temperature season, cover the pipes leading into the hall with wet straw bags to cool them down and reduce the temperature of the material entering the mold. h. The total horizontal equivalent distance of the pumping pipeline should be less than the maximum pumping distance of the equipment.

9. The template system optimization and construction method for improving the appearance quality of exposed surfaces of square piles excavated in tunnels as described in claim 1, characterized in that: In step S9, the cleaning work after pumping is completed specifically includes: a. When pumping is about to end, the amount of concrete stored in the concrete pipe and hopper and the amount of concrete required at the pouring site should be estimated in order to determine the required amount of concrete. b. When cleaning the pipeline after pumping, use an air compressor to push the cleaning ball. First, install the special cleaning pipe, then start the air compressor and gradually increase the pressure. During the cleaning process, tap the delivery pipe at any time to check if the concrete is close to being emptied. When there is still about 10m of concrete in the delivery pipe, the compressor should be slowly depressurized to prevent large explosions and injuries. c. After pumping is completed, the concrete pump, placing boom and pipelines should be cleaned immediately. After the pipelines are disassembled, they should be stacked according to their different specifications.

10. The template system optimization and construction method for improving the appearance quality of exposed surfaces of square piles excavated in tunnels as described in claim 1, characterized in that: In step S10, intelligent maintenance involves installing temperature and humidity sensors, using an automatic spraying system to maintain surface humidity ≥90%, and maintaining a maintenance cycle ≥14 days. During winter construction, an electric heating insulation blanket is used to cover the pile and control the internal and external temperature difference ≤20℃. In terms of finished product protection measures, when breaking the protective wall and formwork of the pile, the formwork is broken manually to avoid damaging the surface quality of the square pile.

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