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Prestressed Anchor Bolt + Hanging Net Shotcrete Slope Protection Construction
I. Preparation for construction
(1) Measure and stake out according to the drawing to determine the position of the anchor hole of the anchor cable, the position of the frame and the geometrical dimensions.
(2) Mechanical performance testing and personnel quality assessment and training.
(3) Anchor cable pull test is carried out before the construction of the anchor cable is fully rolled out. The test is performed at a site similar to the geological conditions of the reinforcement project to determine the maximum tension that the anchor cable can withstand, the safety of the anchoring project, and the parameters used. is it right or not.
(4) Before construction, test and inspect the materials and report them to the supervision engineer.
(1) Formation of holes
① The construction scaffold meets the corresponding bearing capacity and stable conditions, and the fixed drilling rig is accurately installed according to the measurement and placement hole position. The vertical and horizontal errors of the drilling must not exceed ± 5cm, and the elevation errors must not exceed ± 10cm.
② Use a down-the-hole drill or an anchor drill to impact the holes. Follow-up drilling technology should be used in strata with broken or soft and saturated water.
③ Adopt anhydrous dry drilling. The drilling speed should be strictly controlled to prevent drilling distortion and diameter reduction. Pay attention to the picking of the core and maximize the core take-up rate. The anchoring section must enter the moderately weathered or harder rock formation.
④ Make on-site construction records. In case of collapsing holes, etc., solid wall grouting treatment should be carried out and then re-drilled.
⑤ After drilling to the designed depth, drill steadily for 1 to 2 minutes to prevent sedimentation at the bottom of the hole. In principle, high-pressure air (wind pressure 0.2 ~ 0.4Mpa) is required to completely remove the rock powder and water body from the hole.
⑥ After the drilling is completed, the anchor reinforcement should be installed and grouted in a timely manner within 24 hours.
(2) Emptying and inspection
Use high-pressure air (wind pressure 0.2 ～ 0.4MPa) to remove all the rock powder and water inside the hole from the hole, so as not to reduce the bonding strength of the cement mortar to the rock and soil body of the hole wall. Except for anchoring of relatively hard and complete rock mass, high pressure water shall not be used for washing. If there is confined water flowing out of the anchor hole, the anchor ribs and grouting can be installed after the water pressure and the amount of water become smaller, and if necessary, a drainage hole should be provided in the surrounding area for treatment. The inspection of the hole diameter and hole depth generally uses the designed hole diameter, drill bit and standard drill pipe to inspect the hole under the conditions of the on-site supervision station. It is required that the drill bit advances smoothly during the hole inspection process without impact or jitter. Depth, smooth back-drilling requirements, no significant splashing dust and water phenomenon with high pressure wind inspection. At the same time, it is required to review the position, inclination and azimuth of the anchor hole. After all the sub-items of the anchor hole construction are qualified, they can enter the next process.
(4) Installation of anchor rod, grouting, pull-out test
Anchor rods are made according to the design requirements. The bolts are made of C32 fine-rolled threaded steel bars. The connection between the anchor bars and steel bars uses standard galvanized connectors provided by the manufacturer and must not be welded. Before construction of the anchor rod, a destructive pull-out test should be carried out at 3% of the number of anchor rods at different positions on the slope. The construction of the anchor rod can only be performed after the test meets the design requirements.
Anchor rod installation A set of reinforcing steel brackets are installed every 2.0m along the axis of the anchor rod to ensure that the thickness of the protective layer of the anchor rod is not less than 25mm. The anti-corrosion of the anchor end is treated with anti-corrosion measures such as painting and oiling. Before installation, make sure that each steel bar is straight, remove rust and oil, check the number of the anchor hole carefully before installing the anchor body, and then blow the hole with high pressure air after confirming that it is correct. Put the anchor body into the hole slowly. , Use a steel ruler to measure the length of the steel rod exposed outside the hole, calculate the length of the anchor rod in the hole (the error is controlled within the range of ± 50mm), and ensure the anchoring length.
Grouting is performed by secondary grouting. The grouting uses cement mortar with a designation not lower than the design strength. A normal pressure grouting operation starts from the bottom of the hole. The actual grouting volume is generally larger than the theoretical grouting volume, or the anchor vent holes are no longer vented and the holes are not vented. Mouth slurry overflows the thick slurry as the standard for the end of grouting. If grouting is unsatisfactory or settlement occurs after grouting, the grouting should be replenished until it is full. The grouting of the same anchor must be completed continuously without stopping in the middle, and the shrinkage part must be replenished before the initial setting of the slurry. After the grouting is finished, clean the grouting pipe, grouting gun and grouting sleeve, and make grouting records at the same time.
Seven days after the grouting of the anchor rods, 1% and no less than 3 anchor rods were selected for the pullout test. Pulling force average> design value, minimum pulling force> 0.9 design value. The design pull-out force is not less than 50KN.
(5) Laying steel mesh and installing anchor pads
After the grouting is completed, the pier construction is performed, and then the reinforcement mesh is laid. The reinforcement mesh is made of A6 steel bars with a distance of 20cm. The reinforcement mesh can be laid with the slope, and the overlap length is 20cm.
The anchor plate is a square steel plate with a size of 200 × 200mm and a thickness of 20mm. After the design strength of the pier reaches 80% or more, tighten the anchor head nut. When the anchor nut is locked, the tightening force is not less than 50KN, and then perform secondary grouting and seal the anchor.
In order to ensure the construction quality, after the construction of the slope anchor is completed, the stress wave nondestructive inspection is performed on 5% of the total number of anchors to ensure that the length and grouting density of the anchor meet the design requirements.
The mixing ratio of shotcrete is cement: sand: fine stone = 1: 2: 2. Shotcrete is used for shotcrete construction. Check the excavation section before spraying concrete, remove slope dust, floating soil, and wet the slope. When spraying, the distance from the nozzle to the slope is controlled within the range of 0.6 to 1.2 m, the wind pressure is controlled to be 0.3 to 0.5 MPa, and the nozzle a = 90 ° is the best. The nozzle makes continuous circular motion and forms a spiral movement. The next circle presses one-third of the previous circle. The spray line should move from bottom to top and present an "S" shape motion. The spraying of the concrete is performed in two stages, the first spraying thickness is 5 cm, and the second spraying to the designed thickness. The spraying of the next layer should be carried out after the concrete of the previous layer has finally set. The wind pressure is strictly controlled during operation, and the concrete that rebounds and splashes is promptly removed after the spraying operation, and the sprayed surface is wet-cured. The thickness of sprayed concrete is tested by the method of embedding steel bars. Two hours after the final setting of the sprayed concrete, water spray should be used for curing, and the curing time should not be less than 7 days.