Existing line turnout zone light foam concrete micro-disturbance uniform settlement construction method

Abstract

The invention discloses an existing line turnout zone light foam concrete micro-disturbance uniform settlement construction method, and relates to the field of existing line turnout zone construction, and the method comprises the following steps: construction preparation, and determination of a light foam concrete mix proportion and construction power consumption; constructing a cushion layer, pouring a C25 concrete cushion layer on the top surface after filling of the base broken stone cushion layer is completed, expanding the size of the cushion layer, and arranging a first expansion joint; and measuring and setting out, and then setting out a sideline according to the excavation size of the designed step and the filling size of the roadbed. By adopting the existing line turnout area light foam concrete, the additional load on the existing railway can be reduced, the settlement influence on the existing railway is effectively reduced, the light foam concrete is short in period and high in strength, machines are few in the construction process, and the construction cost is reduced. The light foam concrete newly-built line is adopted to reduce disturbance of the adjacent existing line roadbed, the light foam concrete enables the turnout straight strand to be located on the existing line roadbed and the curved strand to be located on the newly-built line roadbed, and roadbed settlement is uniform.

Description

Technical Field

[0001] This invention relates to the field of construction in existing railway turnout areas, and particularly to a method for construction of lightweight foamed concrete with micro-disturbance and uniform settlement in existing railway turnout areas. Background Technology

[0002] To alleviate the transportation pressure on existing lines, a large number of new lines have been built around existing lines. The construction of new lines requires backfilling and the insertion of turnouts on both sides of the existing roadbed. However, the existing railway lines have already been opened and the settlement of the roadbed has become stable. The new lines insert turnouts on the existing lines. After insertion, the straight strand of the turnout is located on the existing roadbed, and the curved strand is located on the new roadbed, which then leads to construction operations.

[0003] Existing construction techniques typically employ traditional filling and improved soil methods, which involve long construction periods, the presence of numerous soft and hard floating objects, close proximity of machinery to existing lines, and complex construction procedures. Furthermore, the construction of new lines can impact the operational status and settlement of existing lines, while the operation of existing lines can restrict the construction techniques of new line subgrades, affecting operational safety and comfort. Therefore, it is necessary to use a lightweight foamed concrete micro-disturbance uniform settlement construction method for turnout areas of existing lines to address these issues. Summary of the Invention

[0004] The purpose of this invention is to provide a method for constructing uniform settlement of lightweight foamed concrete in the turnout area of ​​existing railway lines with micro-disturbance, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for constructing uniform settlement of lightweight foamed concrete in the turnout area of ​​existing railway lines with micro-disturbance, comprising: Step 1: Construction preparation, determine the mix proportion of lightweight foamed concrete and the power supply for construction, select the types and specifications of materials involved in the construction according to the design and relevant construction requirements, and take samples for raw material testing according to the design and relevant specifications; Step 2: Subbase construction. After the base crushed stone subbase is filled, a C25 concrete subbase is poured on top to enlarge the subbase size and set the first expansion joint. Step 3: Measurement and layout. Based on the design dimensions of the step excavation and the roadbed filling, the boundary lines are laid out, the ground elevation is measured, and white lime lines are sprinkled to clarify the filling boundary lines, step excavation boundary lines, and formwork positions. Step 4: Excavation of existing roadbed steps. Steps are excavated on the existing embankment slope, while the existing arched frame slope protection foundation and main frame are preserved. The water-retaining edge of the support frame and the main frame is broken. After the excavation is completed, compaction is carried out. Step 5: Apply a waterproof reinforcement layer to the existing roadbed steps, treat the top surface of the existing slope steps, and then install a waterproof reinforcement layer; Step 6: Lay a layer of impermeable composite geomembrane on the longitudinal steps at the junction of the existing slope and the fill material, as well as on the bottom surface of the lightweight foamed concrete. Step 7: Pour lightweight foamed concrete in layers, using segmented, zoned, and full-layer pouring, and set a second expansion joint, and install lateral and step baffles before pouring; Step 8: Spray the top waterproof layer, lay galvanized steel wire mesh, install back-adhesive waterstop, and then spray the top waterproof layer. Step 9: Lay a layer of impermeable composite geomembrane on the top surface. After the waterproofing construction is completed, lay a layer of impermeable composite geomembrane.

[0006] Preferably, the construction power supply in step one is from the city power grid, and a backup 250kW generator is provided. The construction materials involved in step one specifically include waterproof coatings, composite geomembranes, galvanized steel wire mesh, and high-density foam boards. If the raw materials in step one pass the inspection, they will be delivered to the construction site in stages by the project's material management personnel according to the needs of the project's progress.

[0007] Preferably, the thickness of the C25 concrete cushion layer in step two is 0.1m, the size of the cushion layer in step two is increased to 15cm on each side, the first expansion joint in step two is set every 10m, and the position of the first expansion joint is consistent with the position of the first expansion joint of the lightweight foam concrete. The edge line in step two is marked out by GPS.

[0008] Preferably, the step excavation in step four is carried out in a segmented manner from bottom to top, the water-retaining edge is removed by cutting and demolishing with small crushing equipment, and the demolition and protection are carried out in conjunction with the filling. Step four also includes removing the loose soil in the arch ring, filling and excavating the step with a width of not less than 1.0m, and digging a trench in the middle of the step. The width and depth of the trench are 0.3m and 0.2m, respectively.

[0009] Preferably, the location of the waterproof reinforcement layer in step five is the first transverse expansion joint of the lightweight foamed concrete and the connection between the lightweight foamed concrete and the existing slope. The material of the waterproof reinforcement layer in step five is polyurea waterproof coating, which is applied by spraying. The thickness of the waterproof reinforcement layer is not less than 1.0 mm, and the waterproof reinforcement layer extends beyond the joint by not less than 200 mm on both sides. The treatment of the top surface of the existing slope step in step five is carried out by concrete or mortar to serve as the base layer of the polyurea polymer waterproof layer, and the treatment is carried out before the waterproof layer is sprayed on the top surface of the step excavated on the existing slope.

[0010] Preferably, the composite geomembrane in step six uses polyester filament nonwoven geotextile as its base material and high-density polyethylene geomembrane as its membrane material with a thickness of 0.3 mm. When laying the composite geomembrane in step six, the overlap is achieved by hot welding, and the overlap width is not less than 10 cm. When laying the composite geotextile in step six, it is laid flat and stretched.

[0011] Preferably, the second expansion joint in step seven is specifically set as a transverse second expansion joint every 10m along the route, and the width of the transverse second expansion joint is 3cm, and it is filled with high-density foam board. The installation of the side and step baffles in step seven specifically includes the side and step baffles using 1.5cm thick bamboo plywood, and reinforced with square timber, the size of which is 8cm×8cm. The side baffles are set vertically, and the deviation of the outer plane position does not exceed 1cm.

[0012] Preferably, the lightweight foamed concrete pouring in step seven specifically includes: During the pouring of lightweight foamed concrete, the discharge port is buried 10-20cm below the pouring surface of the lightweight foamed concrete and is constantly turned over. When moving the pouring, taking samples from the discharge port and leveling the surface, the height difference between the discharge port and the current lightweight foamed concrete surface is controlled within 1m. The interval between the completion of slurry preparation and the start of lightweight foamed concrete preparation shall not exceed 45 minutes. Lightweight foamed concrete shall be pumped using a hose. The downtime of the pumping equipment and pipeline shall not exceed 30 minutes. Each pouring layer shall be completed within the initial setting time of the cement slurry. The pouring time shall not exceed 2 hours. When constructing lightweight foamed concrete, water spraying and cooling measures should be taken, and the interval between pouring of adjacent layers should be 10-16 hours, and not less than 8 hours. After the final setting of each layer and before pouring the next layer, water spraying and moisturizing should be carried out. The construction environment temperature for lightweight foamed concrete pouring should be 5℃-35℃. During the pouring process, pouring is carried out from one end to the other along the long axis of the pouring area. If more than one pouring method is used, the pouring can be carried out side by side from one end or diagonally.

[0013] Preferably, in step eight, the galvanized steel wire mesh is laid 0.3m below the top surface and 0.5m above the bottom surface of the lightweight foamed concrete, and 0.2m above the surface of the lightweight foamed concrete and the existing line slope step, and a layer of galvanized steel wire mesh is laid in each location. Furthermore, a layer of galvanized steel wire mesh is laid every 2.0m of lightweight foamed concrete poured. The galvanized steel wire mesh is laid on the top surface of the completed lightweight foamed concrete pouring. The back-attached waterstop in step eight includes a transverse waterstop and a longitudinal waterstop. The transverse waterstop is installed at the second expansion joint of the lightweight foamed concrete and at the slope between the lightweight foamed concrete and the existing roadbed. A drainage ditch is set between the lightweight foamed concrete and the existing road. The longitudinal waterstop is set under the drainage ditch.

[0014] Preferably, the spraying of the top waterproof layer in step eight specifically includes spraying a 5mm thick waterproof layer onto the top surface of lightweight foamed concrete, and the waterproof layer is sprayed with type II polyurea polymer material. The waterproof layer completely covers the outer surface of the lightweight foamed concrete. Before spraying the waterproof layer, a base treatment is performed. If the base does not meet the requirements, grinding, dust removal, and repair are carried out. Holes, cracks, and other defects on the surface of the base are repaired with polymer mortar.

[0015] The technical effects and advantages of this invention are as follows: (1) This invention uses lightweight foamed concrete in the turnout area of ​​existing railway lines. Lightweight foamed concrete is a new type of lightweight filler for roadbed engineering. It has the advantages of light weight, good fluidity, stable performance, strong uprightness, high strength and low environmental impact. At the same time, using lightweight foamed concrete to widen the roadbed can reduce the additional load on the existing railway and effectively reduce the impact on the settlement of the existing railway. Furthermore, lightweight foamed concrete has a short cycle and high strength. There are few machines and simple operation during construction. At the same time, it ensures the safety of railway operation. The use of lightweight foamed concrete in the new line reduces the disturbance to the adjacent existing line subgrade. Lightweight foamed concrete also makes the straight turnout strands located on the existing line subgrade and the curved turnout strands located on the new line subgrade. The roadbed settlement is uniform, which helps to reduce the impact of the new line construction on the operation status and settlement of the existing line. (2) The present invention uses lightweight foamed concrete, which makes construction operation simple, shortens construction time, ensures the construction safety of existing lines and reduces disturbance to the existing line subgrade. Lightweight foamed concrete has low environmental impact and conforms to the low-carbon concept. At the same time, it ensures that the turnout settles evenly on the existing line subgrade and the newly built line subgrade, which increases the safety and comfort of train operation. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the construction process of the lightweight foamed concrete micro-disturbance uniform settlement method for existing railway turnout areas according to the present invention. Figure 2 This is a schematic diagram of the construction of the existing roadbed step excavation according to the present invention; Figure 3 This is a schematic diagram of the construction of the impermeable composite geomembrane according to the present invention; Figure 4 This is a schematic diagram of the back-attached waterstop at the expansion joint of the present invention; Figure 5 This is a schematic diagram of the back-attached waterstop at the groove of the present invention.

[0017] In the diagram: 1. Crushed stone cushion layer; 2. C25 concrete cushion layer; 3. Step excavation edge line; 4. Waterproof reinforcement layer; 5. Composite geomembrane; 6. Galvanized steel wire mesh; 7. Back-attached waterstop. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention provides, for example Figures 1-5 The construction method for uniform settlement of lightweight foamed concrete in the turnout area of ​​existing railway lines, as shown, includes the following specific steps: Step 1: Construction preparation, determine the mix proportion of lightweight foamed concrete and the power supply for construction, select the types and specifications of materials involved in the construction according to the design and relevant construction requirements, and take samples for raw material testing according to the design and relevant specifications; Step 2: Subbase construction. After the base crushed stone subbase 1 is filled, C25 concrete subbase 2 is poured on the top surface to enlarge the subbase size and set the first expansion joint. Step 3: Measurement and layout. Based on the design dimensions of the step excavation and the roadbed filling, the boundary lines are laid out, the ground elevation is measured, and white lime lines are sprinkled to clarify the filling boundary lines, step excavation boundary lines 3, and the formwork position. Step 4: Excavation of existing roadbed steps. Steps are excavated on the existing embankment slope, while the existing arched frame slope protection foundation and main frame are preserved. The water-retaining edge on the support frame and the main frame is broken. After the excavation is completed, compaction is carried out using small machinery. Step 5: Apply waterproof reinforcement layer 4 to the existing roadbed steps. Treat the top surface of the existing slope steps and then install waterproof reinforcement layer 4. Step Six: Lay the impermeable composite geomembrane 5, as shown Figure 4 and Figure 5 As shown, a composite geomembrane 5 is laid on the longitudinal steps at the junction of the existing slope and the fill material, as well as on the bottom surface of the lightweight foamed concrete. Step 7: Pour lightweight foamed concrete in layers, using segmented, zoned, and full-layer pouring, and set a second expansion joint, and install lateral and step baffles before pouring; Step 8: Spray the top waterproof layer, lay galvanized steel wire mesh 6, install back-adhesive waterstop 7, and then spray the top waterproof layer. Step 9: Lay the top impermeable composite geomembrane 5. After the waterproofing construction is completed, the laying of a layer of impermeable composite geomembrane 5 is consistent with step 6.

[0020] Furthermore, the construction power supply in step one will be provided by the city power grid, with a backup 250kW generator. The materials involved in the construction in step one specifically include waterproof coating, composite geomembrane 5, galvanized steel wire mesh 6, and high-density foam board. If the raw materials in step one pass the inspection, they will be delivered to the construction site in stages by the project's material management personnel according to the needs of the project's progress.

[0021] Furthermore, in step two, the thickness of the C25 concrete cushion layer 2 is 0.1m, the size of the cushion layer in step two is increased to 15cm on each side, the first expansion joint in step two is set every 10m, and the position of the first expansion joint is consistent with the position of the first expansion joint of the lightweight foam concrete. The edge line in step two is marked out using GPS.

[0022] Furthermore, in step four, the step excavation is carried out in sections from bottom to top. The water-retaining edge is cut and demolished using small crushing equipment. The demolition and protection are carried out in conjunction with the filling. Step four also includes removing the loose soil in the arch ring, filling and excavating the step with a width of not less than 1.0m, and excavating a trench in the middle of the step. The width and depth of the trench are 0.3m and 0.2m, respectively.

[0023] Specifically, the location of the waterproof reinforcement layer 4 in step five is the first transverse expansion joint of the lightweight foamed concrete and the connection between the lightweight foamed concrete and the existing slope. The material of the waterproof reinforcement layer 4 in step five is polyurea waterproof coating, applied by spraying. The thickness of the waterproof reinforcement layer 4 is not less than 1.0 mm, and the waterproof reinforcement layer 4 extends at least 200 mm beyond the joint on both sides. The treatment of the top surface of the existing slope steps in step five is carried out using concrete or mortar as the base layer for the polyurea polymer waterproof layer. This treatment is performed before spraying the waterproof layer on the top surface of the steps excavated on the existing slope. The spraying process for the waterproof reinforcement layer 4 is as follows: the top surface of the existing slope steps... The surface has been leveled with concrete or mortar, resulting in a smooth surface free of laitance and holes. For the first expansion joint and connections: base layer defects have been repaired with polymer mortar, the surface is free of dust and oil, and there are no loose or loose materials at the joints. A two-component high-pressure airless sprayer was used, equipped with a dedicated static mixing gun. The heating temperature of components A and B was adjusted to 60-70℃, and the pressure to 15-20MPa, ensuring stable material delivery and no leakage. A pre-spray test was conducted: spraying was performed on waste board to check for film uniformity, absence of bubbles and sagging, and confirmation of the correct mixing ratio. Boundary treatment: masking tape was applied along the design boundary of the reinforcement layer to ensure precise spraying coverage and avoid contaminating non-construction areas. The spraying operation steps are as follows: For base layer pre-coating, targeting expansion joints and connection gaps, first apply a single coat of polyurea-specific primer evenly to seal the micropores in the base layer and improve the adhesion between the polyurea and the base layer. Then, apply in layers to form a film. For the first coat (priming): hold the spray gun 30-40cm away from the base surface and use a continuous horizontal spraying method, achieving a thickness of 0.3-0.4mm. Ensure even coverage of the first expansion joint, guaranteeing no missed areas. The corners where lightweight foamed concrete connects to the slope should be rounded to avoid stress concentration caused by sharp angles. For the second coat (thickening): after the first coat has gelled, apply a longitudinal, crisscross spraying method (perpendicular to the direction of the first coat). Apply a 0.4-0.5mm thick coating; ensure the reinforcing layer completely covers 200mm on both sides of the joint, with no exposed substrate, pinholes, bubbles, or other defects. Use a wet film thickness gauge to check the thickness in real time, and promptly reapply the coating to any insufficient areas. Apply a third coat (edge ​​trimming): if the thickness is less than 1.0mm, apply a third coat (0.2-0.3mm thick), focusing on repairing the edges and joints to ensure uniform coating thickness and clear boundaries. After curing and removing the film, keep the construction area well-ventilated to avoid dust contamination. Cure at room temperature for 24 hours until fully cured. After curing, gently peel off the masking tape, clean any excess coating from the edges, and inspect the surface of the reinforcing layer: no cracks, no delamination, and no drips.

[0024] Specifically, in step six, the base material of the composite geomembrane 5 is made of polyester filament nonwoven geotextile, and the membrane material is made of high-density polyethylene geomembrane with a thickness of 0.3mm. When laying the composite geomembrane 5 in step six, the overlap is made by hot welding, and the overlap width is not less than 10cm. When laying the composite geotextile in step six, it is laid flat and tightened to avoid local rolling. If necessary, U-shaped nails can be used for anchoring.

[0025] Specifically, the second expansion joint in step seven is set up as a transverse second expansion joint every 10m along the line direction, with a width of 3cm, and filled with high-density foam board. The second expansion joint must be vertical. The installation of the lateral and step baffles in step seven includes using 1.5cm thick bamboo plywood for the lateral and step baffles. The joints of the templates should be tight to ensure no grout leakage, and reinforced with square timber with dimensions of 8cm×8cm. The lateral baffles are set vertically, and the deviation of the outer plane position does not exceed 1cm. During the pouring process, a special person is assigned to check and strictly prevent displacement.

[0026] More specifically, step seven, the pouring of lightweight foamed concrete, includes: During the pouring of lightweight foamed concrete, the discharge port is buried 10-20cm below the pouring surface of the lightweight foamed concrete and is constantly turned over. When moving the pouring, taking samples from the discharge port and leveling the surface, the height difference between the discharge port and the current lightweight foamed concrete surface is controlled within 1m. The interval between the completion of slurry preparation and the start of lightweight foamed concrete preparation shall not exceed 45 minutes. Lightweight foamed concrete shall be pumped using a hose. The downtime of the pumping equipment and pipeline shall not exceed 30 minutes. Each pouring layer shall be completed within the initial setting time of the cement slurry. The pouring time shall not exceed 2 hours. The pouring time interval should be reasonably adjusted according to the results of process tests when constructing lightweight foamed concrete. Water spraying and cooling measures should be taken during the construction of lightweight foamed concrete. The pouring interval between adjacent layers should be 10-16 hours, and not less than 8 hours. Water spraying should be carried out to keep the layers moist after the final setting of each layer and before the next layer is poured. The construction environment temperature for lightweight foamed concrete pouring should be 5℃-35℃. During the pouring process, pouring is carried out from one end to the other along the long axis of the pouring area. If more than one pouring method is used, the pouring can be carried out side by side from one end or diagonally.

[0027] Furthermore, in step eight, the galvanized steel wire mesh 6 is laid 0.3m below the top surface of the lightweight foamed concrete and 0.5m above the bottom surface, as well as 0.2m above the surface of the lightweight foamed concrete and the existing line slope step. A layer of galvanized steel wire mesh 6 is laid in each of these locations. Additionally, a layer of galvanized steel wire mesh 6 is laid every 2.0m of lightweight foamed concrete poured. The galvanized steel wire mesh 6 is laid on the top surface of the completed lightweight foamed concrete pouring. Furthermore, the back-adhesive waterstop 7 in step eight includes a transverse waterstop and a longitudinal waterstop. The transverse waterstop is installed at the second expansion joint of the lightweight foamed concrete and at the junction of the lightweight foamed concrete and the existing roadbed slope, such as... Figure 4 As shown, a drainage ditch is installed between the lightweight foamed concrete and the existing line, and the longitudinal waterstop is installed below the drainage ditch, as shown. Figure 5 As shown.

[0028] It should be noted that step eight, the spraying of the top waterproof layer, specifically involves spraying a 5mm thick waterproof layer onto the lightweight foamed concrete top surface. This waterproof layer uses Type II polyurea polymer material and completely covers the outer surface of the lightweight foamed concrete. Before spraying the waterproof layer, a substrate treatment is performed to ensure the surface is free of laitance, holes, cracks, dust, and oil. If the substrate does not meet the requirements, it is ground, dusted, and repaired. Holes, cracks, and other defects on the substrate surface are repaired using polymer mortar. The substrate surface is cleaned to remove loose materials, contaminants, and excess deposits that could affect adhesion, creating a clean surface for subsequent inspection and treatment. This is done using a combination of manual sweeping and high-pressure blower cleaning. The procedure involves first removing visible dry impurities such as laitance, loose particles, and dust from the surface. For tightly adhered laitance, a scraper can be used to gently scrape it off, avoiding damage to the substrate. For surface oil stains, a neutral detergent (such as diluted dish soap) is applied to the oily area. After letting it sit for 5-10 minutes, it is repeatedly wiped with a damp cloth, then rinsed with clean water. Finally, it is dried with a hairdryer or allowed to air dry, ensuring that there is no oil residue or detergent traces on the surface. After cleaning, the substrate surface is visually inspected, requiring no obvious accumulation of dust, oil, or laitance, and the surface should not feel sticky to the touch, nor should any loose particles come off. A comprehensive inspection of substrate defects is conducted, accurately identifying various defects on the substrate surface such as holes, cracks, and depressions, and clarifying the location and size of the defects. The depth and distribution of defects provide a basis for targeted treatment. Specific procedures include: a combination of visual inspection, manual inspection, and tool testing; visual inspection of the substrate surface for obvious holes, cracks, pitting, depressions, etc.; manual inspection to check for surface flatness and the presence of raised or recessed areas; for suspected cracks, a crack width detector is used to measure the crack width, and a depth gauge is used to measure the depth of holes or cracks. Detected defects are marked and recorded: the area is marked on the defect edge with chalk, and the defect type (hole / crack / pitting, etc.), size (hole diameter / crack length and width / depression depth, etc.), and location are recorded. This facilitates subsequent treatment according to the order of priority, addressing defects based on their specific characteristics. For each type of defect, a corresponding treatment method should be adopted to ensure complete repair of the defect and that the base surface meets the requirements of being flat, firm, and defect-free. After repair, the base surface should be ground flat to eliminate any protrusions or seam marks that may result from the defect repair, ensuring that the overall surface flatness of the base meets the requirements for waterproofing layer construction. Specific operation: After the polymer mortar repair layer has completely cured, use an electric angle grinder (equipped with diamond grinding discs) to grind the repair area and the surrounding base surface. The grinding should be done by first coarse grinding and then fine grinding: coarse grinding removes burrs, protrusions, and unevenness at the seams on the surface of the repair layer, while fine grinding makes the base surface smooth and flat. During the grinding process, dust generated during grinding should be removed in a timely manner with a vacuum cleaner or blower to avoid secondary pollution.After grinding, check the flatness: Use a 2-meter straightedge against the base surface. The gap between the straightedge and the base should be ≤3mm, and the gap should be evenly distributed without obvious local protrusions or depressions. Final dust removal and acceptance: Remove dust generated during grinding to ensure the base surface is clean. Perform a final acceptance inspection of the base treatment quality. Only after passing the inspection can the waterproof layer be sprayed. Specific operation: Use a high-pressure blower to thoroughly blow the base surface, focusing on the ground areas, corners, and defect repair areas to ensure no dust residue. For corners and other areas difficult to reach with a blower, use a soft brush to gently remove dust. The acceptance criteria are: the base surface is free of laitance, holes, cracks, dust, oil stains, and other defects; the surface is flat and firm, with no loose particles or stickiness to the touch; the repaired area transitions naturally with the surrounding base, without obvious seam marks; the moisture content meets the requirements for waterproof layer construction. Treatment of Hole Defects: Circular or irregular depressions appearing on the base surface may contain loose material, typically ≥3mm deep, affecting the continuity and adhesion of the waterproofing layer. Treatment steps: Hole Cleaning: Gently remove loose particles, laitance, and impurities from the hole using a small chisel or electric hammer, ensuring the hole's inner wall is firm and free of loose material. For deeper holes, layered cleaning is necessary to avoid penetrating the base layer. Moistening Treatment: Spray clean water onto the inner wall of the hole and surrounding base layer using a spray bottle, keeping the base layer moist but not waterlogged. This prevents the base layer from absorbing water from the polymer mortar too quickly, causing the mortar to dry and crack, affecting the repair effect. Polymer Mortar Filling: Select a polymer repair mortar with good compatibility with the lightweight foamed concrete base layer. Add water according to the product instructions and mix thoroughly, ensuring the mortar is free of lumps and has suitable fluidity. Layered Filling Method: For holes ≤20mm deep, fill to the level of the base surface in one go; for holes >20mm deep... For the holes, each layer of mortar should not exceed 10mm in thickness. Wait until the previous layer of mortar has initially set (no obvious indentation when pressed with a finger) before applying the next layer. During filling, repeatedly compact the mortar with a trowel to remove internal air and prevent hollow areas. Surface leveling: After filling, use a trowel to smooth the mortar around the hole and within a 100mm radius, ensuring the repaired surface is level and consistent with the surrounding substrate, without any obvious protrusions. The waterproofing layer spraying procedure involves dust removal and re-inspection of the substrate. One hour before spraying, use a high-pressure blower to perform a final cleaning of the lightweight foamed concrete top surface. Blow away dust generated during construction to ensure the substrate is clean. Apply large-area, layered spraying. First coat (sealing layer): Hold the gun at a distance of 30-35cm and spray horizontally at a constant speed, with a coating thickness of 0.4-0.5mm. Construction sequence: Proceed from the end furthest from the construction entrance towards the entrance, avoiding stepping on already sprayed areas. Coordinate with walkie-talkies during spraying to ensure no missed areas and no drips in overlapping areas. Second coat (main waterproof layer): After the first coat has gelled, apply longitudinally in a cross-hatching manner, with a coating thickness of 0.5-0.6mm.Real-time wet film thickness gauge inspection is used, with one inspection point set every 5 square meters to ensure uniform coating thickness and avoid areas that are too thin or too thick (excessive thickness can lead to incomplete curing, while insufficient thickness can cause pinholes). For edges and special areas, an additional coat of spraying is required at the edges and corners of the lightweight foamed concrete top surface, with a thickness 0.2-0.3 mm thicker than the regular area, to ensure a tight seal. If pinholes or air bubbles appear during spraying, immediately spray the defective areas with a spray gun or smooth them with a scraper to prevent leakage channels after curing.

[0029] By utilizing lightweight foamed concrete in the turnout area of ​​existing lines, the lightweight foamed concrete, with its light weight, good fluidity, and stable performance, achieves the goal of reducing disturbance to the existing track bed when constructing new lines. This ensures that the straight strands of the inserted turnouts are located on the existing track bed, while the curved strands are located on the new track bed, resulting in uniform track bed settlement. At the same time, it shortens the construction period and ensures the safety of construction on existing lines.

[0030] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for constructing lightweight foamed concrete for uniform settlement with minimal disturbance in existing railway turnout areas, characterized by: The specific steps include the following: Step 1: Construction preparation, determine the mix proportion of lightweight foamed concrete and the power supply for construction, select the types and specifications of materials involved in the construction according to the design and relevant construction requirements, and take samples for raw material testing according to the design and relevant specifications; Step 2: Subbase construction. After the base crushed stone subbase (1) is filled, C25 concrete subbase (2) is poured on the top surface to enlarge the subbase size and set the first expansion joint; Step 3: Measurement and layout. Based on the dimensions of the designed step excavation and the dimensions of the roadbed filling, the boundary lines are laid out, and the ground elevation is measured. White lime lines are sprinkled to clarify the filling boundary lines, the step excavation boundary lines (3), and the formwork position. Step 4: Excavation of existing roadbed steps. Steps are excavated on the existing embankment slope, while the existing arched frame slope protection foundation and main frame are preserved. The water-retaining edge of the support frame and the main frame is broken. After the excavation is completed, compaction is carried out. Step 5: Apply a waterproof reinforcement layer to the existing roadbed steps (4). Treat the top surface of the existing slope steps and then install a waterproof reinforcement layer (4). Step 6: Lay a layer of composite geomembrane (5) on the longitudinal steps at the junction of the existing slope and the fill material, and on the bottom surface of the lightweight foamed concrete. Step 7: Pour lightweight foamed concrete in layers, using segmented, zoned, and full-layer pouring, and set a second expansion joint, and install lateral and step baffles before pouring; Step 8: Spray the top waterproof layer, lay galvanized steel wire mesh (6), install back-adhesive waterstop (7), and then spray the top waterproof layer. Step 9: Lay a layer of impermeable composite geomembrane (5) after the waterproofing construction is completed.

2. The construction method for uniform settlement of lightweight foamed concrete in the turnout area of ​​existing railway lines according to claim 1, characterized in that: The construction power supply in step one is the city power grid, and a 250kW generator is on standby. The construction materials involved in step one specifically include waterproof coating, composite geomembrane (5), galvanized steel wire mesh (6) and high-density foam board. If the raw materials in step one pass the inspection, they will be delivered to the construction site in stages by the project department's material management personnel according to the needs of the project progress.

3. The construction method for uniform settlement of lightweight foamed concrete in the turnout area of ​​existing railway lines according to claim 1, characterized in that: The C25 concrete cushion layer (2) in step two has a pouring thickness of 0.1m. The cushion layer size in step two is enlarged to 15cm on each side. The first expansion joint in step two is set every 10m, and the position of the first expansion joint is consistent with the position of the first expansion joint of the lightweight foam concrete. The edge line in step two is marked out using GPS.

4. The construction method for uniform settlement of lightweight foamed concrete in the turnout area of ​​existing railway lines according to claim 1, characterized in that: The step excavation in step four is carried out in sections from bottom to top. The water-retaining edge is cut and demolished using small crushing equipment. Demolition and protection are carried out in conjunction with filling. Step four also includes removing loose soil in the arch ring and filling and excavating the step with a width of not less than 1.0m. A trench is dug in the middle of the step, and the width and depth of the trench are 0.3m and 0.2m, respectively.

5. The construction method for uniform settlement of lightweight foamed concrete in the turnout area of ​​existing railway lines according to claim 1, characterized in that: The waterproof reinforcement layer (4) in step five is set at the first transverse expansion joint of the lightweight foam concrete and the connection between the lightweight foam concrete and the existing line slope. The material of the waterproof reinforcement layer (4) in step five is polyurea waterproof coating, and it is applied by spraying. The thickness of the waterproof reinforcement layer (4) is not less than 1.0 mm, and the waterproof reinforcement layer (4) extends beyond the joint by not less than 200 mm on both sides. The top surface of the existing slope step in step five is treated with concrete or mortar to serve as the base layer of the polyurea polymer waterproof layer. The treatment is carried out before the waterproof layer is sprayed on the top surface of the step excavated on the existing line slope.

6. The construction method for uniform settlement of lightweight foamed concrete in the turnout area of ​​existing railway lines according to claim 1, characterized in that: The composite geomembrane (5) in step six uses polyester filament nonwoven geotextile as its base material and high-density polyethylene geomembrane as its membrane material with a thickness of 0.3 mm. When laying the composite geomembrane (5) in step six, the overlap is achieved by hot welding and the overlap width is not less than 10 cm. When laying the composite geotextile in step six, it is laid flat and tightened.

7. The construction method for uniform settlement of lightweight foamed concrete in the turnout area of ​​existing railway lines according to claim 1, characterized in that: The second expansion joint in step seven is specifically set up as a transverse second expansion joint every 10m along the route, and the width of the transverse second expansion joint is 3cm, and it is filled with high-density foam board. The installation of the side and step baffles in step seven specifically includes the side and step baffles using 1.5cm thick bamboo plywood, and reinforced with square timber, the size of which is 8cm×8cm. The side baffles are set vertically, and the deviation of the outer plane position does not exceed 1cm.

8. The construction method for uniform settlement of lightweight foamed concrete in the turnout area of ​​existing railway lines according to claim 1, characterized in that: The lightweight foamed concrete pouring in step seven specifically includes: During the pouring of lightweight foamed concrete, the discharge port is buried 10-20cm below the pouring surface of the lightweight foamed concrete and is constantly turned over. When moving the pouring, taking samples from the discharge port and leveling the surface, the height difference between the discharge port and the current lightweight foamed concrete surface is controlled within 1m. The interval between the completion of slurry preparation and the start of lightweight foamed concrete preparation shall not exceed 45 minutes. Lightweight foamed concrete shall be pumped using a hose. The downtime of the pumping equipment and pipeline shall not exceed 30 minutes. Each pouring layer shall be completed within the initial setting time of the cement slurry. The pouring time shall not exceed 2 hours. When constructing lightweight foamed concrete, water spraying and cooling measures should be taken, and the interval between pouring of adjacent layers should be 10-16 hours, and not less than 8 hours. After the final setting of each layer and before pouring the next layer, water spraying and moisturizing should be carried out. The construction environment temperature for lightweight foamed concrete pouring should be 5℃-35℃. During the pouring process, pouring is carried out from one end to the other along the long axis of the pouring area. If more than one pouring method is used, the pouring can be carried out side by side from one end or diagonally.

9. The construction method for uniform settlement of lightweight foamed concrete in the turnout area of ​​existing railway lines according to claim 1, characterized in that: The galvanized steel wire mesh (6) in step eight is laid 0.3m below the top surface of the lightweight foamed concrete and 0.5m above the bottom surface, as well as 0.2m above the slope step of the existing line and the lightweight foamed concrete. A galvanized steel wire mesh (6) is laid in each of these locations. A layer of galvanized steel wire mesh (6) is laid every 2.0m of lightweight foamed concrete. The galvanized steel wire mesh (6) is laid on the top surface of the completed lightweight foamed concrete. The back-attached waterstop (7) in step eight includes a transverse waterstop and a longitudinal waterstop. The transverse waterstop is installed at the second expansion joint of the lightweight foam concrete and at the slope between the lightweight foam concrete and the existing roadbed. A drainage ditch is set between the lightweight foam concrete and the existing road. The longitudinal waterstop is set under the drainage ditch.

10. The construction method for uniform settlement of lightweight foamed concrete in the turnout area of ​​existing railway lines according to claim 1, characterized in that: The spraying of the top waterproof layer in step eight specifically includes spraying a 5mm thick waterproof layer onto the top surface of lightweight foamed concrete. The waterproof layer is made of type II polyurea polymer material and completely covers the outer surface of the lightweight foamed concrete. Before spraying the waterproof layer, a base treatment is performed. If the base does not meet the requirements, it is ground, dusted, and repaired. Holes, cracks, and other defects on the surface of the base are repaired with polymer mortar.

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