Prestressed anchor cable has many construction procedures, high technical content and great concealment, and the construction quality is difficult to control. Therefore, the supervision engineer is required to supervise strictly and carefully to ensure the realization of the design protection goal.

(1), general requirements

(1), steel strand, steel bar and anchoring fixture used in construction must comply with the design requirements, and have factory certificate, warranty and signs. They can be used in construction only after they are sent to CMA qualification testing unit or the central laboratory of the director's office for inspection according to the specified frequency and requirements. Unlicensed products or untested materials are strictly prohibited in construction;

(2), reinforced after entering the site should be stored overhead, should not be piled up in the open air. In addition to meeting the requirements of general steel storage, the storage of prestressed steel strands should also be equipped with moisture-proof and anti-corrosion facilities;

(3) The mixture ratio of building mortar, cement slurry and its raw materials used for anchorage must be tested in parallel by the director of the central laboratory and meet the requirements of design and construction technical specifications before it can be used for construction;

(4) The selection of drilling, grouting, tensioning and mechanical equipment shall comply with the design requirements and construction conditions. Pneumatic dry drilling shall be adopted for drilling, and random drilling is strictly prohibited. The technical performance index and type selection of tensioning equipment must match, and shall not be used in this project without calibration by CMA qualified testing unit or measurement testing department.

2, prestressed anchor cable construction

(1) test

A、

Before construction, a group of not less than 3 anchor cables must be selected at each high slope construction site for on-site pull-out failure test. In order to obtain reliable anchorage technical parameters, the anchorage length of anchor cable used in the test is 2m, 4m, 6m,

The corresponding drilling depth is the same as the designed anchor hole depth of the slope, and each contract section is required to notify the chief engineer's office, the owner and the design representative 2~3 days in advance after completing the test preparation conditions.

B fill in the "anchor cable test record form" for anchor cable test. The principle of the test is to pull or break the anchor cable. The test results are for the dynamic design of the design representative, and the failure criteria of the anchor cable are as follows:

Ⅰ. Long-term instability or non-convergence of anchor cable displacement;

Ⅱ. The displacement of the anchor head caused by the latter load is twice that of the former load, that is, there is an obvious inflection point on the tension-displacement (P-S) curve.

② Drilling holes

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After completing the slope brushing of a slope according to the requirements of the construction drawing design, the contractor shall check the construction scope of the anchor cable together with the supervision engineer or designer (if necessary). If the geological conditions of the slope are basically consistent with the construction drawing design, that is,

It can be used for lofting survey of anchor cable construction. Fill in the "Anchor Cable Drilling Construction Record Form" for anchor cable drilling. The hole depth and aperture of drilling should not be less than the design value, and the inclination and azimuth of drilling should meet the design requirements, which should be adopted after drilling.

High pressure air cleans the hole. The allowable deviation of drilling, the design has been clearly implemented according to the design, and the design has not been clearly implemented according to the following standards:

The effective design depth of ultra-deep hole should not be greater than 50 cm; ;

B hole coordinate error shall not be greater than 65438±00cm；;

C drilling deviation error shall not be greater than 3%;

D. During drilling, the inclination and orientation of drilling tools shall be strictly checked, and the design inclination shall not be modified;

E. During drilling, we should strengthen the guiding role of drilling tools, find the deviation error in time, and take reasonable corrective measures according to the drilling needs;

F, geological observation should be strengthened in the process of drilling, and if it is found that it is obviously inconsistent with the design, it should be reported to the owner and the director's office in time.

(3), anchor cable production and placement

First, the anchor cable production

A, anchor cable should be made in a specially built processing shed. In the production process, the "Prestressed Steel Strand Checklist" should be filled in. After the production is completed, it should be neatly arranged according to different types and hung with signs. The mark shall indicate the number of bundles, bundle length, anchorage length, free length, number of holes, hole depth and aperture.

Ⅱ prestressed steel strand blanking must adopt mechanical cutting, arc cutting is strictly prohibited; ⅲ prestressed anchor cable braided steel strand should be arranged neatly, smoothly and firmly, and there should be no twisting or winding phenomenon. The surface should be derusted and decontaminated, and the expansion ring, tightening ring and grouting pipe used for anchor cable production must be arranged and installed according to the design requirements;

Ⅳ Anchor cable must be coated with anticorrosive coating according to design requirements, and the free section should be covered with polyethylene plastic pipe or PVC pipe. Before sheathing, both ends of the casing should be filled with butter within the length range of 10~20cm, and sealed with engineering tape to ensure that cement slurry does not enter the steel strand in the free section.

ⅴ The anchorage length, free length and tension length of the anchor cable should not be less than the design requirements;

B, anchor cable transportation and placement

ⅰ anchor cable transportation, hoisting process should be careful operation, shall not damage the anchor cable structure and its protective coating;

Two. Fill in the "Anchor Cable Installation Inspection Record Form" for anchor cable placement, and the following inspections must be carried out before the anchor cable enters the hole:

A, sundry around the anchor hole and orifice must be removed;

B, anchor hole number plate and anchor hole number must be the same, and should check the hole depth and anchor cable length;

C, anchor cable should be no obvious bending and torsion phenomenon, into the slurry in the anchor cable, exhaust pipe must be smooth;

D, anchor cable protective layer without damage, any damage must be repaired;

(4), anchor hole grouting

Grouting should be carried out as soon as possible according to the design requirements after anchor cable pouring. If it is found that there is a large amount of groundwater in the anchor section and the formation is muddy during drilling, it should be reported to the owner and the director's office in time.

Whether to adopt secondary split grouting will be decided with the design representative on site. Fill in "Anchor Hole Grouting Construction Record Form (B8)" for anchor hole grouting.

B the quality control requirements of anchor hole grouting are as follows:

A, cement mortar strength is not less than 30Mpa, sand particle size should be less than or equal to 2 mm, grouting should be injected through the grouting pipe from bottom to top, and fresh slurry can be returned to the orifice. Water cement ratio and grouting pressure should meet the design requirements of construction drawing.

B, slurry strength specimen every 30 anchor hole not less than a group, less than 30 holes to take a group;

C, after the completion of anchor hole grouting, the orifice section will be vacated due to bleeding contraction and must be filled, otherwise the ground beam or frame beam shall not be constructed. If the ground beam is constructed first and then the anchor cable is constructed, it shall not be tensioned and locked before the empty hole section is filled.

⑤ Tension locking of anchor cable

A, the tension of anchor cable must be carried out after the grouting strength of anchor cable, the concrete strength of ground beam or the concrete strength of frame reach the design strength, and the "Prestressed Anchor Cable Tension Inspection Record Form" shall be filled in;

B, tensioning equipment must be calibrated, and draw the pressure gauge reading-tensioning curve, to guide the field tensioning operation. Tension equipment should be calibrated once every six months, and tension equipment or pressure gauges that are strongly impacted after disassembly and maintenance must be recalibrated immediately;

C design tension load, over-tension load and locking load shall be consistent with the design. Tension should be controlled by stress and checked by elongation value. When the actual elongation value is greater than 10% or less than 5% of the calculated elongation value, the tensioning shall be suspended until the reason is found out and measures are taken to adjust it.