Construction Quality Control of Reinforced Retaining Walls
Abstract
The construction technology of reinforced retaining walls in highway construction and the problems that may easily occur during construction are analyzed. problem, how to strengthen the construction quality control of reinforced retaining walls was discussed.
Keywords
Quality control of reinforced retaining wall construction process
With the rapid development of highway construction in our province, reinforced retaining walls have become The technical and economic benefits are increasingly being promoted and applied in high-grade highway projects. In the contract section of the Shugang Connection Line in Rizhao Section of Tongsan Expressway, two typical sections adopt the roadbed protection type of reinforced retaining walls. Based on the actual construction, this article discusses how to control the construction quality of reinforced retaining walls.
1 Design of reinforced retaining wall
1.1 Adoption of reinforced retaining wall
The port connection line is an important link between the Tongsan Line and Rizhao Port The road section is an important part of the Rizhao Section project of the Tongsan Line. It is designed in accordance with the first-class highway standards. Two sections adopt the roadbed protection type of reinforced retaining wall. One is the retaining wall of the central separation zone on the inside of the K3 030-K3 920 section. This section is located in the Beijing Road interchange area, and the average roadbed height is 4.5 meters. Because this road section overlaps with urban roads, various pipes and pipelines have been placed in the central separation zone of the original road. For the convenience of protection and maintenance, no more earth can be filled above the central zone, so a reinforced retaining wall is used; in addition, a reinforced retaining wall is used; One is the foot of the slope of section K6 010 to K6 250. This section is located on the edge of a large pond. This pond is about 20 meters deep and accumulates water all year round. The design unit finally decided after analyzing the aspects of cost, stability, and aesthetics. A reinforced retaining wall is used to protect the foot of the roadbed slope near the pond. The average height of the retaining wall is 13 meters.
1.2 Structural type and calculation index
The retaining wall adopts a shoulder-type reinforced soil structure, cast-in-place C30 concrete strip foundation, prefabricated and installed C30 reinforced concrete panels, and the reinforced belt adopts CAT30020C The technical indicators of steel-plastic composite tie bars are the basis for calculation, and the upper part of the filling retaining wall is made of gravel soil (the technical indicators should meet r=19.5KN/M3, фgt; 35o). For the filling of the water-logged retaining wall, it is required to use permeable filling such as gravel soil or gravel (its technical index should meet фgt; 37o).
2 Construction of reinforced soil retaining walls
The construction of reinforced soil retaining walls should strictly comply with the "Technical Specifications for the Construction of Highway Reinforced Earth Engineering", "Technical Specifications for the Construction of Highway Subgrade" and design requirements. Before construction, technical personnel should fully understand the design intent, be familiar with the design drawings, and construct in strict accordance with the drawings.
2.1 The general construction process flow chart of reinforced retaining walls is as follows:
2.2 Construction operation and quality control
2.2.1 Foundation construction
Before construction, surface planting soil and high liquid limit clay should be excavated, and the bearing layer should be weathered sandstone or a stratum that meets the design bearing capacity. The foundation excavation depth is greater than 50cm. If significant changes in geological conditions are found during construction, the design unit should be contacted promptly so that corresponding measures can be taken. The foundation pit should be tidied up and compacted after excavation. If it does not meet the design bearing capacity, it should be dealt with.
2.2.2 Panel prefabrication
Steel formwork must be used for wall panel prefabrication. The steel formwork and base plate must be inspected and repaired frequently, and the concrete residue on the formwork must be removed every time. Apply release agent before prefabrication to ensure that the prefabricated panels are smooth and smooth and meet the design accuracy requirements. The reserved rib holes on the panel must be smooth.
In order to ensure the quality of concrete, mechanical vibration should be used. If the surface is rough and slurry-free, cement mortar with the same lime-sand ratio can be used to polish the surface to make it smooth and beautiful.
The inspection standards for panels are: qualified strength; side length error is not greater than ±5mm or 0.5 of the side length; two diagonal errors are not greater than 10mm or 0.7 of the maximum diagonal length; thickness error is within 5mm ~-3 mm; the surface flatness error shall not be greater than 4mm or 0.3 of the length (width). There is no obvious deviation in the reinforcement holes and the reinforcement is easy to penetrate. Panels that do not meet the above standards are strictly prohibited.
2.2.3 Installation of panels
1) Before installing the first layer of panels, the outer edge line of the panel should be accurately drawn on the top surface of the clean strip foundation, and the curved section should be Encrypt control points appropriately. Then fix a point on the determined outer edge line and conduct a horizontal measurement, and divide and level the base of the slab according to the length of the slab.
2) The installation panel can be started from the wall end and both sides of the settlement joint, using appropriate lifting equipment or manual lifting, and the hanging wires are installed in place. During installation, the inclination of a single panel can generally be about 1, which is used as the deformation value of the panel under lateral pressure when the filler is compacted. It is strictly prohibited to tilt the panel outward under any circumstances.
3) Use M5 cement mortar for leveling when installing panels. Except for drainage joints, the insides of horizontal and vertical joints are all seamed, and the outside of the board should be simply seamed and kept clean. Drainage joints are generally set every 3 meters and replaced with dry-laid vertical joints. The horizontal error between adjacent panels on the same layer should not be greater than 10mm. When the gap width is large, it should be filled with asphalt cork. The installation seams should be even, smooth and beautiful. And it is not allowed to install the upper layer of panels on the panels that have not completed the filling operation. It is strictly prohibited to adjust the horizontal error by placing gravel or iron sheets under the panel to avoid stress concentration and damage to the panel.
4) After the filler rolling of each layer of panels is stable, the horizontal and vertical directions of the panels should be checked with a pendant ball or hanging wire to facilitate timely correction and prevent the accumulation of deviations. Every time 2 to 3 layers of panels are installed, the installation quality should be comprehensively inspected. If the quality exceeds the requirements, it must be corrected in time. Inspection items include axis deviation, sag or slope, flatness, panel damage, height difference between adjacent panels, panel gap width and maximum width, etc.
2.2.4 Laying of tie bars
1) Selection of tie bars. The tie bars should be made of CAT30020C steel-plastic composite tie bars. The surface of the tie bars should have rough patterns. The breaking tension of a single wire should be not less than 9KN, the breaking elongation should not be greater than 2, and the length per ton is about 12000m. The product should be accompanied by an inspection report from the manufacturer, and its breaking tensile strength and elongation should meet the design requirements. At the same time, the product should have good anti-aging properties, and its anti-aging properties should be tested by a nationally mandated testing unit and have a test report.
Stretching straps should be inspected according to regulations, and the inspection results must meet the design standards.
2) Unloading the stretch band. Arrangements should be made in advance based on the packaging specifications and the design length of each cross-section reinforcement at the entire work site, and the materials should be cut reasonably and avoid cutting materials while laying, so as to avoid waste of reinforcement materials or dimensional errors caused by human randomness.
The reinforcement strip is laid in the form of one reinforcement strip passing through the reinforcement hole and divided into two strands of equal length. Therefore, the cutting length of each reinforcement strip should be multiplied by the design length of the reinforcement strip at the node. 2 plus 300~500mm margin (as the length occupied by the tie bars when passing through the holes).
3) Laying of tie bars. The ribs should be laid according to the designed length and number of roots on flat, compacted fill soil with 3 transverse side slopes (make the rib end 5 to 10cm higher than the front end). The tendons should be straightened and tightened, and should not be curled or kinked. The ribs should be as perpendicular to the wall as possible and open evenly in a fan-shaped and radial shape. They should be evenly distributed as much as possible, and at least 2/3 of the length should not overlap.
When laying the reinforced strips, use filler to fix the laying position while laying. First, use filler to form several longitudinal rows in the middle and rear of the ribs to press the reinforcement material. The amount and density of the filler should be enough to fix the position of the ribs. Then check each root to ensure that it is straightened and tightened. Then spread the fill as designed.
After each layer of ribs is laid, inspection and acceptance must be carried out. The inspection includes the length, number, uniformity, flatness, connection method, and tightness of the connection with the panel, etc.
2.2.5 Paving of filler
1) Collection of filler. Reinforced filler should be collected at a collection site where all performance and technical indicators of the soil meet the design requirements (фgt; 35°). In any case, geotechnical tests must be conducted on the filler to be collected to ensure its internal friction angle, specific gravity All indicators meet the design requirements. The filler should be evenly graded, the maximum particle size should not be greater than 15cm, and the total content of the largest particle size blocks should not be greater than 15cm.
2) Paving of filler. Filling can be spread mechanically and manually. When mechanical paving of reinforcement is used, it must be supplemented by manual work. Manual work is to use people to transport and spread the filler on the stretch belt. When using a bulldozer to spread filler, the thickness of the filler on the tie belt shall not be less than 20cm. Transport vehicles are generally not allowed to drive on uncompacted reinforcements; if temporary driving is required, the filler thickness shall not be less than 30cm, and the vehicle speed shall not be greater than 5km/h. Sudden braking is not allowed to avoid damage to the tie belts. dislocation.
The paving thickness of each layer of filler can be determined according to the type of filler, compaction equipment, etc., and shall not be greater than 30cm.
2.2.6 Rolling
The road roller should be a vibrating roller or a smooth wheel roller, and it is strictly forbidden to use one foot for rolling. It is strictly forbidden to use heavy machinery for rolling within 1.0mm from the panel and at the corners. It is advisable to use light machinery such as a roller under 5 tons or a vibrating rammer.
When rolling the filler, you should start from half the length of the ribs, roll towards the end of the ribs, and then roll from half the length towards the wall. During rolling, the running direction of the roller should be perpendicular to the ribs, and the width of the overlap between the wheel mark of the next rolling and the wheel mark of the previous rolling should not be less than 1/3 of the wheel advance. The first pass should be done slowly and lightly to prevent the soil from pushing up or dislocating the tendons. After the second pass, you can press slightly faster and harder. Each time, the entire transverse rolling range should be rolled, and then the next rolling should be carried out. The number of rolling passes should be subject to reaching the specified compaction degree. The roller shall not make sudden changes in direction of operation or sudden braking on uncompacted fill.
After each layer of the reinforced body is rolled, the compaction degree is checked. The number of detection points should be no less than 3 points per 500 m2 or per 50m long engineering section. The detection points should be staggered from each other and selected randomly. There should be at least one detection point within 1 meter behind the panel (every 500m2 or every 50m long). The compaction degree requirements are: the compaction degree within 1.0 meters from the panel is not less than 90, and the compaction degree within the remaining range is not less than 95.
3 Several issues that should be paid attention to
3.1 Tension straps should be protected from sunlight as much as possible during transportation, storage, and processing. When laying the straps, the exposure time should be shortened as much as possible, and fillers should be used in time. Cover, the total exposure time during construction shall not exceed 8 hours.
3.2 The foundation, wall and roof should be divided into sections of about 10 meters, with a seam width of 20mm at the sections, and asphalt wood wool boards should be used to fill the seams. The top surface of each segmented foundation shall be on the same horizontal plane.
3.3 Water filtering geotextiles (specification: 300g/m2) should be hung at the drainage joints of the panels. On the strip basis, they should be laid flat at least 50mm into the wall and gradually hung upward as the panels rise. When hanging the sticker, it must be close to the panel.
3.4 The backfilling after the reinforced body is carried out simultaneously with the reinforced body, and the compaction degree is not less than 95.
3.5 Do a good job in drainage at the construction site. In case of rainfall, appropriate measures should be taken to drain the water quickly or cover the construction site.
3.6 Each process must be accepted by the relevant departments before the next process can be constructed, and the construction acceptance records must be kept.