Prestressed Anchorage Cable

Construction Key Point

一、The slope excavation of anchorage engineering is designed and qualified.

二、Before the construction operation, the basic test of prestressed anchor cable (rod) should be carried out, and the construction operation can be carried out after the anchorage parameters are determined.

三、Measurement lofting,?the anchor hole position was accurately measured on the slope and clearly identified.

四、Making Holes

1.?Drilling equipment is selected according to the type of anchorage stratum, aperture, depth, and construction site. Drilling with a geological drilling rig is strictly prohibited; in formations that are easy to collapse, stuck, or buried, the following drilling technique should be used.

2. drilling rigs in place: drilling rig in place vertical and horizontal error≤±50mm, elevation error≤±100mm, drilling angle error≤0.5 °, azimuth error≤±1.0 °.

3. Dry holes without water should be used in drilling to prevent the deterioration of geological conditions caused by drilling.

4. In the process of drilling, geological changes, drilling state (weight on bit, drilling speed), groundwater, etc.

5. After drilling to the design depth, it must be stable drilling for 1~2 minutes. After the drilling is completed, in principle, high-pressure air (0.2a~0.4Mpa) is required to remove all the rock powder and water in the hole.

6. Can use the drilling inclinometer control and detection of drilling inclination.

五、Anchor Cable (rod) Production and Installation

1. Anchor body assembly must set up a height of not less than 50cm assembly platform.

2. Bolt joint using special bolt connection joint, shall not use welding technology. The steel bar of the bolt body should be straight, and free of oil and corrosion. The free section should be sleeved with a plastic casing according to the design requirements, and the connection with the anchorage section should be firmly tied with lead wire and treated with anticorrosion.

3. The anchor cable should be bundled. The steel strand should be mechanically cut, and arc cutting is strictly prohibited. The surface has no oil pollution, no corrosion, no bending, and strict anti-corrosion treatment.

4. After the cable body completes the assembly of the isolating frame and the fastening ring, the guiding cap should be connected at the bottom end. Guide cap size error≤±5mm, joint positioning error≤±20mm, the use of wire binding firm, should not use welding

5. When the anchorage body with secondary supplementary grouting is assembled, the secondary grouting pipe and the sealing device should be installed at the same time; when high pressure splitting grouting is adopted, the initial splitting time should be controlled by slurry strength (the first slurry strength is 5Mpa), and the anchorage section of the secondary grouting pipe should be provided with flower holes and plugs.

6. Pressure dispersion type (tension and compression composite) anchor rope anchorage section between the steel bearing plate and the extrusion sleeve requires the use of bolted fixed, all steel materials exposed part of the surface to be coated with anti-rust paint to protect. Extrusion sleeve to carry out on-site extrusion sampling test, the sampling frequency is generally 3%~5%. Pressure dispersion type (tension-compression composite type) anchor cable, each unit anchor cable should be clearly and firmly marked, so as to adopt differential step tension.

7. In strict accordance with the design requirements of the anchor body free section of the corrosion and isolation, anti-corrosion should be used unbonded prestressed tendons and pressure dispersed anchor head technology, in order to improve the free section of the anti-corrosion level and improve the working state of the anchorage section.

8. Anchor body length: the length of the anchorage section of the allowable error is ±50mm, free section length in addition to meet the design requirements, but also give full consideration to the requirements of tensioning equipment and construction technology, generally reserved long 1.0~1.5m.

六、Grouting

1. After the completion of the anchor hole, the anchor should be installed in time, and grouting, in principle should not exceed 24 hours.

2. According to the grouting material, grouting method, and grouting pressure, combined with the actual situation of anchorage strata, the corresponding grouting equipment should be selected.

3 should be used ordinary Portland cement, high alumina cement should not be used. Fine aggregate should select medium sand with particle size less than 2 mm; the mud content shall not be more than 3 %. In addition to secondary high-pressure grouting (split grouting) and free section secondary grouting (supplementary grouting), it is generally not suitable to use an expansive agent.

4. Grouting slurry should be mixed evenly, with the stir with, and should be completed before the initial setting of the slurry. The strength of the grouting body should not be less than 20Mpa.

5. Generally should be used at the bottom of the hole grouting, until the anchor hole orifice overflow slurry or exhaust pipe to stop exhaust, can stop grouting.

6. Grouting grouting should be recorded.

7. One-time normal pressure grouting is generally used as full-section one-time grouting; the secondary supplementary grouting is suitable for the grouting of the first normal pressure anchorage section, that is after the prestressed tension locking process is completed, the free section of the anchorage body is supplemented by filling grouting. According to the design requirements, in order to improve the uplift resistance of the anchorage section, secondary high-pressure grouting ( splitting grouting) should be adopted.

七、Tension Locking and Sealing Anchor

1. Anchor tension, the bearing surface of the anchor bracket should be flat, and perpendicular to the axis of the anchor.

2. Anchor installation should be closely aligned with the anchor plate and jack, jack axis and anchor hole, and anchor bar axis in the same straight line shall not bend or deflect the anchor head, to ensure uniform bearing coaxial, when necessary, available steel gasket adjustment.

3. When the strength of the anchorage body and abutment concrete reaches more than 80% of the design strength, tension can be carried out.

4. Anchor before the formal tension, should take the design tension value of 10 % to 20% of the anchor for 1 to 2 times pre-tensioned to ensure that all parts of the anchor close contact and the anchor is straight.

5. Permanent anchor tension control stress should not exceed 60 % of its ultimate stress value, and temporary anchor tension control stress should not exceed 65% of its ultimate stress value.

6. Tensioning operations are carried out in strict accordance with the design requirements. After the anchor bar is tensioned to the set maximum tension load value, it should be held for 10 to 15 minutes, and then unloaded and locked. If obvious prestress loss is found, compensation tension should be carried out in time.

7. After the anchor bar is locked, the residual anchor bar is mechanically cut, and arc cutting is strictly prohibited. The length of the anchor bar should be 5 ~ 10cm to prevent dragging and slipping. Filling with cement paste anchor plate and anchor head of each part of the gap, with an anti-rust paint brush, and according to the design requirements for sealing anchor treatment, sealing anchor concrete strength is not less than 20Mpa.