Notes on the construction of prestressed anchor cables:
Due to the many construction processes, high technical content, and high concealment of prestressed anchor cables, the construction quality is difficult to control. For this reason, supervision engineers are required to conduct strict supervision carefully and meticulously to ensure the realization of the design protection objectives.
⑴. General requirements
①. Steel strands, steel bars, and anchor clamps used for construction must meet the design requirements and have factory certificates, warranty certificates, and signs. According to regulations Frequency and requirements must be submitted to the CMA qualification testing unit or the central laboratory of the general manager's office before they are approved for construction. It is strictly prohibited to use unlicensed products or materials for construction without inspection after entering the site;
②, Steel must be stored overhead after entering the site and shall not be stacked in the open. In addition to the general steel storage requirements, the storage of prestressed steel strands should also be equipped with moisture-proof and anti-corrosion facilities;
③ Used for anchoring construction The mortar, cement slurry mix ratio and raw materials must be tested in parallel by the central laboratory of the general manager's office and meet the design and construction technical specifications before they can be used for construction;
④, drilling, grouting, tensioning, machinery The selection of equipment should comply with the design requirements and construction conditions. All drilling should use pneumatic dry drilling, and water drilling is strictly prohibited. The technical performance indicators and selection of tensioning equipment must be matched, and it shall not be used in this project without calibration by a CMA qualified testing unit or measurement and testing department;
⑵, Prestressed anchor cable construction
①. Test
A.
Before construction, a group of no less than 3 anchor cables must be selected for on-site pullout failure testing at each high slope construction point. In order to obtain reliable anchoring technical parameters, the lengths of the anchor cable anchoring sections used for the test were 2m, 4m, and 6m respectively.
The corresponding drilling depth is the same as the design anchor hole depth of the slope. Each contract section is required After completing the test preparation conditions, notify the general manager office, owner and design representative 2 to 3 days in advance.
B. Fill in the "Anchor Cable Test Record Form" for the anchor cable test. The test is based on the principle of pulling or breaking the anchor cable. The test results are used by the design representative for dynamic design. The criteria for determining the damage of the anchor cable are:
ⅰ The displacement of the anchor cable is unstable for a long time or the displacement does not converge;
ⅱ The displacement of the anchor head caused by the subsequent load is twice the displacement of the previous load, that is, the tensile force ~The displacement (P-S) curve has an obvious inflection point.
②. Drilling
Contractor
After completing a certain level of slope brushing according to the design requirements of the construction drawing, the contractor should work with the supervising engineer or designer (If necessary) Inspect the area within the anchor cable construction range. If the geological conditions of the slope are basically consistent with the design of the construction drawing, then the anchor cable construction stakeout measurement can be carried out. Fill out the "Anchor Cable Drilling Construction Record Form" for anchor cable drilling. The depth and diameter of the drilled hole shall not be less than the design value. The inclination angle and azimuth angle of the drilled hole shall meet the design requirements. High-pressure air cleaning holes shall be used after drilling. The allowable deviation of drilling shall be carried out according to the design if the design is clear, and the following standards shall be carried out if the design is not clear:
A The super depth of the effective design hole depth shall not be greater than 50cm;
B The hole coordinate error shall not be greater than ±10cm;
C The hole inclination error shall not be greater than 3%;
D The inclination and azimuth angle of the drilling tool should be strictly checked when opening the hole, and the inclination angle and azimuth angle of the drilling tool must not be corrected. Any modification to the designed inclination angle;
E During the drilling process, the guiding role of the drilling tool should be strengthened, the hole inclination error should be detected in a timely manner, and corrective measures should be taken reasonably according to the drilling needs;
F Geological observation should be strengthened during the drilling process. If any obvious discrepancy with the design is found, the owner and the general manager should be reported in a timely manner.
③. Anchor cable production and placement
A. Anchor cable production
ⅰ The anchor cable production should be carried out in a specially set up processing shed. Fill in the production process "Prestressed Steel Strand Wire Bundle Inspection Sheet" is prepared and placed neatly into different types, and a sign is hung. The sign should indicate the bundle number, bundle length, anchoring section length, free section length, and hole number to be placed. , hole depth and aperture;
ⅱ Mechanical cutting must be used when cutting the prestressed steel strands, and arc cutting is strictly prohibited; ⅲ The steel strands braided by the prestressed anchor cables should be arranged neatly, smoothly, and tied It is firm and there should be no twisting or twisting. The surface should be rusted and decontaminated. The expansion ring, tight hoop ring and grouting pipe used in the production of anchor cables must be laid out and installed according to the design requirements;
ⅳ Anchor The cable must be coated with anti-corrosion coating according to the design requirements, and the free section should be covered with polyethylene plastic pipe or PVC pipe. Before inserting, the 10~20cm length range of both ends of the casing should be filled with butter, and the outside should be wrapped with engineering tape to fix and seal to ensure that the cement slurry is not Enter the free section strand.
ⅴ The length of the anchoring section, free section and tension section of the anchor cable shall not be less than the design requirements;
B. Transportation and placement of anchor cables
ⅰ Anchor Care should be taken during the transportation and hoisting of the cable, and the structure of the anchor cable and its protective coating must not be damaged;
ⅱ. When placing the anchor cable, fill in the "Anchor Cable Installation Inspection Record Form", which must be carried out before entering the hole. The following inspections:
a. Debris in the anchor hole and around the hole must be removed;
b. The hole number plate of the anchor rope and the anchor hole number must be the same, and should be Check the depth of the hole and the length of the anchor cable;
c. The anchor cable should have no obvious bending or twisting, and the grout and exhaust pipes in the anchor cable must be smooth;
d. The anchor cable There is no damage to the protective layer, and any damage must be repaired;
④. Grouting of anchor cable holes
A After the anchor cable is installed, grouting should be done as soon as possible according to the design requirements. If during the drilling process it is found that the amount of groundwater in the anchoring section is large and the rock strata are muddy, the owner and the general manager's office should be reported promptly so that the design representative can decide on-site whether to use secondary splitting grouting. Fill out the "Anchor Cable Hole Grouting Construction Record Form (B8)" for anchor cable hole grouting;
B The anchor cable hole grouting quality control requirements are as follows:
a. Cement mortar strength Not less than 30Mpa, the particle size of the sand should be less than or equal to 2mm, the grouting should be injected counter-currently from the bottom of the hole through the grouting pipe, until fresh slurry returns from the hole, the water-cement ratio and grouting pressure It should comply with the design requirements of the construction drawings.
b. There should be no less than one set of 30 anchor cable holes in the slurry strength test piece, and one set should be taken if there are less than 30 holes;
c. After the grouting of the anchor cable hole is completed, holes will appear in the hole section due to the shrinkage of the slurry bleeding, which must be filled up, otherwise the ground beam or frame beam construction is not allowed. If the ground beam is constructed first and the anchor cable is constructed later, Tension locking is not allowed before the empty hole section is filled.
⑤. Tension locking of anchor cables
A Anchor cable tensioning can only be carried out after the anchor cable grouting strength, ground beam concrete strength or frame concrete strength reaches the design strength. , fill in the "Prestressed Anchor Cable Tensioning Inspection Record Form" for anchor cable tensioning;
B The tensioning equipment must be calibrated, and the pressure gauge reading-tensioning force relationship curve should be drawn to guide on-site tensioning operations. . Tensioning equipment is calibrated every 6 months. Tensioning equipment that has been dismantled and repaired or pressure gauges that have experienced strong impact must be recalibrated immediately;
C Design tension load, super tension load, Locking loads should be consistent with the design. Tensioning adopts the stress control and elongation value verification operation method. When the actual elongation value is greater than 10% or less than 5% of the calculated elongation value, the tensioning should be suspended until the cause is identified and measures are taken to adjust before the tensioning can be continued. ;