【Excerpt】How to construct the slope anchor cable?

1、Internal industry technical preparation

 

        1) Before the start of construction, relevant technical personnel should be organized to carefully study the implementation construction organization design, read and review the construction drawings, clarify relevant technical issues, and be familiar with the specifications and technical standards.

 

        2) According to the requirements of the technical disclosure model, prepare the technical disclosure, and make the technical disclosure to the construction personnel, conduct pre-job technical training for the participating construction personnel, and hold the certificate after passing the examination.

 

        3) Construction safety assurance measures and emergency preplans shall be formulated.

  

 

 2、Field technical preparation

 

        1) According to the material items and quantity in the material plan sheet of the submitted project material department, arrive at the site, and pass the test, supervision sampling inspection and peaceful inspection.

 

        2) The location of mud abandonment and discharge has been implemented, and the procedures have been completed.

 

        3) The tension equipment (jack and oil table) arrived at the site and has been completed.

 

        4) The site construction is 0.5 meters below the anchor cable anchor line, with the anchor cable construction conditions.

 

        5) The land acquisition of the construction site shall be completed, and the site shall be leveled. The living and production houses should be completed, and the living and office facilities should be fully equipped, and can meet the needs of the main management and technical personnel entering the living and office.

 

3、Technical requirements

 

        3.1 Prepare the implementation construction organization design, including the construction sequence of pile hole position, construction process design and main technical measures, safety and quality assurance measures, labor organization and material guarantee, etc.

 

        3.2 Calibrate the jack, high pressure oil pump and pressure gauge, and draw the pressure gauge reading-tension relationship curve to know the strong pull operation on site.

 

        3.3 Prepare sufficient steel strand and anchors according to the quantity of construction drawings, and sample for mechanical properties testing.

 

        3.4 Install air compressor and grouting pump, and lay air supply pipe and grouting pipe.

 

        3.5 Before the construction of anchor cables, the anchorage test shall be conducted on site at 3% of the number of working anchor cables, and no less than 3 pieces.

 

4、Construction procedures and process flow

 

4.1 Drilling

 

        The crane is used to locate the geological drilling rig in the first row of anchor cable operating platform, the drilling position and the drill Angle are adjusted and measured, and the fasteners are fixed to the operating platform and the rock surface, and constructed from bottom to top. With the progress of drilling, a layer of operating platform is erected in time. Process: positioning drilling high pressure air cleaning hole.

 

        The aperture of the anchor cable is 130mm, and mechanical drilling is used to ensure that the drilling hole depth meets the design requirements, and water flushing drilling is strictly prohibited. In case of loose and broken collapsed hole, following pipe drilling technology should be adopted; in case of collapsed hole, stop drilling immediately, use pressure of 0.1—0.2MPa grouting, and resweep drilling after initial setting. After drilling, high pressure air cleaning hole must be used to remove the rock powder and water in the hole. When a polyethylene pipe is used to check the hole depth, the hole depth is not less than the design length of the anchor cable, pull out the polyethylene pipe, and plug the hole with fabric or cement bag paper for use. 

 

4.1.1 Production of anchor cable

 

        According to the design requirements, the anchor cable adopts 1x7 standard steel strand, the nominal diameter is φ15.2mm, its standard strength is 1860 Mpa, When the anchor cable is made, the cutting length of steel strand is: anchor section + free section + 1.5m exposed tension section. The steel strand is cut by toothless saw, and the guide cone, expansion ring and positioning plate are made of φ 45mm steel pipe and φ 8mm steel bar. The anchor cable can be prepared on site while drilling. The internal anchor section is corrugated shape and the tension section is straight shape.

 

        The free section of the anchor cable should be coated with strong anticorrosive coating, the anchor cable should be tied with fine wire every 1m, coated with anti-rust oil, and the bellows should be filled with butter, both ends are closed and fixed with outer engineering tape; a φ 20-22mmPVC plastic protective pipe can be set for each single steel strand, filled with butter within 10-20cm at both ends, and the outer engineering tape can be closed and fixed. The anchor cable anchor end is provided with a center bracket (expansion ring) every 1.0m, made of 20mm thick polyethylene plastic plate, and the anchor cable is tied with fine wire in the middle of each two expansion rings.

 

4.1.2 Installation of the anchor cable

 

        Before installing the cable to the anchor cable hole, check whether the number of the anchor cable is consistent with the hole number. After confirmation, then clear the hole with high pressure air once to install the anchor cable.

       

        The following four points should be noted when installing the anchor cable:

 

① Check the position of the slurry stop ring and the slurry limit ring, damaged, replace according to the technical requirements;

② Check the position and smooth condition of the exhaust pipe;

③ Anchor cable is sent into the hole. When the slurry stop ring reaches the hole, stop pushing and install the grouting pipe and one-way valve;

④ After the anchor cable is in place, check whether the exhaust pipe is unblocked again. If not, pull out the anchor cable and send the cable again after troubleshooting.

Anchor cable structure diagram

 

4.1.3 Grouting

       

        The anchor cable grouting adopts the hole bottom grouting, the mortar is injected from the hole bottom, and the air is discharged from the air outlet. The grouting position indicator is used to control the grouting position.

 

        The anchor cable hole grouting is grouting machine and the grouting material is M40 cement mortar. The mix ratio is determined by the test and the grouting pressure is not less than 0.6—0.8Mpa. The mortar filling must be full and dense. After the first grouting is finished, the grouting.

 

4.1.4 Construction of the anchor beam

        

        The anchor beam is a compression component, which transfers the concentrated load of the anchor to the rock surface. In addition, because the orifice rock surface is generally not perpendicular to the axis of the anchor cable, the anchor beam also has the role of adjusting the force direction of the rock surface. In order to make the upper surface of the anchor beam perpendicular to the axis of the anchor cable, a thin wall steel pipe with the same outer diameter and the diameter of the drill bit is welded in advance, and the other end of the steel pipe can be inserted into the drilling hole before pouring the anchor beam.

 

4.1.5 The tension of the anchor cable

 

        After the anchor cable tension reaches the design strength of 70%, the tension equipment is calibrated before drawing the anchor cable to avoid stress error. During calibration, combine the jack, oil pipe, pressure gauge and high pressure oil pump, repeat the press with the method of active output, take the average, draw the jack output (KN) and the pressure strength (Kpa) curve indicated by the pressure gauge, as the basis of the anchor cable tension. The initial starting pressure of the domestic pressure gauge is not exactly the same, so the pressure gauge number during calibration must be indicated on the calibration curve, and shall not be replaced in use. After the pressure gauge is damaged or the jack is removed or disassembled.

 

        The anchor cable tension is divided into two steps, the first tension is 70% of the total tension, and the interval between the two tension should not be less than 3-5 days. In order to reduce the prestress loss, the total tension should include the overtension value, and the free section is 15% -25%, and the free section is 10% -15% when it is rock layer. Record the elongation of the anchor cable in the tension to verify whether the elongation is consistent with the force. All levels of tension are the design tension increased by 25% multiple, each stage interval time of 2-5 minutes, the last stage interval of 30 minutes. In order to overcome the prestress loss caused by formation creep and other factors, one supplementary tension was made, and then locked to remove the excess steel strands and anchor with concrete.

  

  

4.1.6 Seal hole grouting

 

        The grouting pipe is inserted from the reserved hole until the grouting is about 50cm into the top surface of the anchorage section. The air in the hole is discharged through the exhaust pipe disposed at the positioning slurry stop ring.

 

4.1.7 External protection

 

        After grouting, leave 50mm steel strand from the anchor, cut off the rest, and cover the C30 concrete anchor with external thickness not less than 50mm.

 

4.2 Construction process flow

       

        See the construction process flow chart of the prestressed anchor cable for the construction process flow flow

  

 

5、Construction requirements

 

        The following points must be paid practical attention to during the construction of the prestressed anchor cable:

 

        (1) The hole error must be strictly controlled, the inclination Angle and horizontal Angle error must be controlled below 1 degree, the deviation of the hole slope is less than 1 / 50, try not to disturb the rock layer around the hole, and blow the hole from the bottom of the hole for at least 10 minutes.

 

        (2) When making the anchor cable, the anchor cable should be twisted to minimize the secondary stress; the anticorrosion of the free section of the anchor cable, anticorrosive oil and plastic casing, and the anchor section must be removed to enhance the bonding force between the anchor cable and the mortar.

 

        (3) The anchor beam is the direct stress component of the tension of the anchor cable, so the pressure surface of the pad should be smooth and perpendicular to the axis direction of the anchor cable.

 

——Source: Baidu online library

                                                                                                                                                                

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