Prestressed high slope protection construction scheme

For mountain highways, prestressed anchor cable beams are generally used for the stability of roadbed high slopes. The construction of prestressed anchor cable beam is a special operation with complicated geological conditions, hidden key projects and difficult construction technology. Arrange training and good construction team with rich construction experience to carry out construction. The main construction process is as follows:

1, the anchor hole measurement slope construction while digging reinforcement, that is, a level of excavation and a level of protection, do not allow a excavation to the end. According to the elevation and design requirements of each work site, the anchor hole position should be accurately measured, and the hole position error should not exceed ±50 mm. If the existing slope is uneven or the site is particularly difficult, it should be approved by the design supervision unit, and on the premise of ensuring slope stability and structural stability, the positioning accuracy should be appropriately relaxed or the anchor hole positioning should be adjusted.

2, drilling equipment The selection of drilling equipment should be based on the type of anchor layer, anchor hole aperture, anchor hole depth and construction site conditions. The underground hole is used to form the hole by rock shock. Pipe drilling technology is used in fractured or soft, water-filled strata that are prone to collapse, stuck and buried drilling.

3, the rig is in position to drill the anchor hole into the construction, set up the scaffolding to meet the corresponding bearing capacity and stability conditions, according to the slope measurement hole position, accurately install the fixed rig, strictly adjust the position to ensure that the vertical and horizontal error of the anchor hole is not more than ± elevation error is not more than 50mm±100mm, the drilling Angle and direction meet the design requirements, and the allowable error position of the inclination Angle is ±1.0°. Allowable azimuth error ±2.0°.

4, the drilling method requires dry drilling, the use of rhinestone is prohibited, to ensure that the anchor cable construction will not worsen the engineering geological conditions of the slope rock mass, to ensure the bond performance of the hole wall. Strictly control the drilling speed according to the performance of the drill and the anchorage layer to prevent the drilling distortion and diameter reduction, resulting in anchoring difficulties or other accidents.

5. The formation changes of each hole in the drilling process, the drilling state (drilling pressure, drilling speed), groundwater and some special circumstances should be recorded on site construction. In case of poor drilling phenomena such as collapse and contraction, the drilling should be stopped immediately, and the solid wall grouting treatment (grouting pressure 0.1 ~ 0.2MPa) should be carried out in time, and the cement mortar should be drilled again after the initial setting.

6, drilling hole diameter and hole depth is not less than the design value. In order to ensure the diameter of the anchor hole, the actual diameter of the drill bit is not less than the design aperture. In order to ensure the depth of the anchor hole, the actual drilling depth should be greater than the design depth of 0.2m.

7, anchor hole cleaning drilling to reach the design depth, can not immediately stop drilling, require stable drilling within 1 to 2 minutes, stop the hole bottom sharp, can not reach the design aperture. The drilling wall shall not have sediment and water viscosity, and must be cleaned up. After drilling, high-pressure air (wind pressure 0.2 ~ 0.4MPa) shall be used in addition to all rock powder and water bodies in the hole, so as not to reduce the bond strength of cement mortar and rock and soil in the hole wall. Except for the anchorage of relatively hard and complete rock mass, it should not be washed with high pressure water. The anchorage bar and grouting can be installed only after the water pressure and water amount become smaller when the pressure water flow in the anchorage hole is discharged. If necessary, drainage holes should be set up in appropriate parts around. If the design requires the treatment of water in the anchor hole, the general use of grouting plugging, secondary drilling and other methods.

8. After the anchor hole is drilled, the next process must be inspected by the on-site supervision before it can be carried out. The aperture and hole depth inspection generally adopts the design aperture, drill bit and standard drill pipe, requiring the drill bit to advance smoothly without impact or jitter, the inspection length of the drill tool to meet the depth of the design anchor hole, the drilling requirement is stable, and the high-pressure wind inspection has no obvious splashing slag and water phenomenon. At the same time, the position, inclination and position of the anchor hole are required to be checked. After the sub-work of the anchor hole construction is qualified, it can be regarded as the anchor hole drilling inspection is qualified.

9. The prestressed anchor cable body consists of four parts: anchor beam, free section, anchor section and stable section. The pressure-dispersed anchor cable is composed of three unit anchor cables, each of which is anchored by two unbonded steel strands on the steel carrier. The steel strand is symmetrically anchored to the steel carrier by a special extrusion spring and extrusion sleeve, requiring a single connection strength greater than 200KN. The steel carrier shall be processed with No. 45 steel and its thickness shall not be less than 2cm. The steel strand adopts φj15.24mm and φj12.7mm high strength and low relaxation unbonded prestressed steel strand. Before installation, ensure that each steel strand is straight, without twisting or forks, and evenly arranged. Remove rust and oil, and remove dead bends, mechanical damage, and rust pits. Wire loops are set along the anchor cable body axis every 1.0 to 1.5m to ensure that the thickness of the protective layer of the anchor cable is not less than 20mm. Before installing the anchor cable body, carefully check the anchor hole number to confirm that it is correct, then blow the hole with high pressure air, manually slowly put the anchor cable body into the hole, measure the length of the steel strand exposed in the hole with a steel ruler, calculate the length of the anchor cable in the hole (the error is controlled within 50mm), and ensure the anchoring length.

10. Cement mortar is used for anchoring grouting, and the construction mix is determined after the test and selection. The actual grouting amount is generally greater than the theoretical grouting amount, or the anchor vent no longer exhausts, and the hole grouting overflow is the end of the grouting standard. If the grout is not satisfied or settling, the grout should be added until it is filled. After grout, clean the grout pipe, grout gun and grout casing, and make grout records.

11. The ground beam is poured with C25 concrete. The foundation should be laid with a 2cm mortar leveling layer, and then the production and installation of steel bars. The number of steel bar joints in the same section shall not exceed 1/2 of the total number of steel bars, and the section spacing of welded joints shall not be less than 1m. If the anchor cable interferes with the stirrup of the vertical beam, the stirrup spacing can be adjusted locally. Concrete pouring, especially around the anchor holes, is densely reinforced and must be carefully vibrated to ensure quality.

12. The tension, locking and sealing of the anchor cable are determined by the field tension test. The tensioning and locking of anchor cables are graded in strict accordance with the operating procedures. After the design tension is completed for 6-10D, the tension is compensated, and then locked. After the compensation tension, from the amount of anchor, set aside 5 long ~ 10cm steel strand, the rest of the cutting, must be cut mechanically, strictly prohibit arc cutting. Finally, the gap between the anchor plate and the anchor head is filled with water slurry, and then the anchor head is sealed with no less than 20mpa concrete to prevent corrosion and aesthetics.

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