A, the construction technology and flow chart is as follows:
1. drill
Drilling is the key process to control the construction period in anchor cable construction. In order to ensure the drilling efficiency and quality, a down-the-hole percussion drill is used. When drilling with a drilling rig, the drill pipes required for drilling should be arranged neatly according to the designed length of anchor cable, and the drill pipes are used up and the hole depth is just in place. The drilling depth should exceed the design length of anchor cable by about 0.5m
After drilling, pull out the drill pipe and drilling tool one by one, and clean the impactor for later use. Check the hole depth with polyethylene pipe and blow the hole with high pressure wind. When the dust in the hole is blown clean and the hole depth is not less than the designed length of the anchor cable, pull out the polyethylene pipe and block the orifice.
Handling of two special cases:
Treatment of water seepage. During or after drilling, small stones and gray or yellow aggregate are blown out of the hole without dust, indicating that there is water seepage in the hole and more rock powder is attached to the hole wall. At this time, if the hole depth is enough, clean water is injected and blown out with high-pressure wind until clean water is blown out. If the hole depth is not enough, even if the impactor is working and the footage is still there, stop drilling immediately, pull out the drilling tool, wash the well and continue drilling, and so on until the end. Sometimes there is a lot of water seepage in the cave, water accumulation, mud and gravel blowing out. In this case, the rock powder will not stick to the hole wall, and drilling can continue as long as the impactor works. If the water seepage is too large to submerge the impactor, the impactor will automatically stop working, and the drilling tool should be pulled out for pressure grouting.
Treatment of well collapse and sticking. Hole collapse often occurs when drilling holes through strongly weathered rocks or rock fracture zones. The main sign of hole collapse is that yellow rock powder is blown out of the hole, mixed with some undisturbed (non-bit broken, non-fresh and dull) stones. At this time, regardless of the drilling depth, stop drilling immediately, pull out the drilling tools, and carry out solid wall grouting. The grouting pressure is 0.4 MPa, and the slurry is a mixture of cement mortar and water glass. After 24 hours, drill again. In rainy season, mud often seeps into holes along the fractured zone of rock mass. Before wall-fixing grouting, the mud must be washed clean with water and wind (the stones collapsed into the borehole do not need to be removed), otherwise, not only the wall-fixing grouting effect is poor, but also the illusion is easily caused.
2. The production of anchor cable
The anchor cable is braided while drilling in the field, and the inner anchor section is corrugated and the tension section is straight. The blanking length of the steel grain line is the sum of the design length of the anchor cable, the height of the anchor head, the length of the jack, the thickness of the tool anchor and the working anchor, and the tension allowance. Under normal circumstances, the cutting allowance of steel strand is 50 mm, put the cut steel strand on the workbench smoothly, measure the design length of internal anchor segment and anchor cable, and mark them respectively; Within the scope of the internal anchorage section, penetrate into the centering isolation bracket 60- 100 cm, and tie the fastening ring between two pairs of centering brackets; Tie a fastening ring every meter in the tensioning section, put a plastic pipe on the ring and coat it with butter; Finally, install a guide cap on the end cover of the anchor cable.
3. Anchor cable installation
Before installing the anchor cable hole, check whether the anchor cable number is consistent with the hole number. After confirmation, clean the hole with high-pressure air again, and then start to install the anchor cable.
The installation of downward inclined anchor cable is relatively simple, and there are no more technical problems. Pay attention to the following four points when installing upward inclined and horizontal anchor cables: check and locate the position of slurry stop ring and slurry limit ring, and replace them according to technical requirements if they are damaged; Check the position and smoothness of the exhaust pipe; Send the anchor cable into the hole, stop pushing when the positioning grout stop ring reaches the orifice, and install the grouting pipe and the one-way valve; After the anchor cable is in place, check whether the exhaust pipe is unblocked again. If it is not clear, pull out the anchor cable and send the cable after troubleshooting.
4. Anchoring grouting
The anchor grouting adopts exhaust grouting construction. For the downward inclined hole, insert grouting pipe into the bottom of the hole, inject mortar from the bottom of the hole, and exhaust air from the anchor hole; Updip and horizontal holes, mortar is injected from the orifice, air is pressed to the bottom of the hole, and enters the exhaust pipe from the bottom of the hole (horizontal anchor cable, air enters the exhaust pipe through the slurry limiting ring).
In the grouting process of upward inclined and horizontal anchor holes, when the exhaust pipe is no longer exhausted and the dilute cement slurry is pressed out of the exhaust pipe, the grouting is full; For downward inclined anchor cable grouting, mortar position indicator is used to control grouting position.
Grouting machine shall be used for anchor hole grouting, and the grouting pressure shall be kept at 0.3-0.6 MPa.
5. Anchor pier
The function of the anchor pier is to transfer the concentrated load of the anchorage to the rock surface and adjust the stress direction of the rock surface. In order to make the upper surface of the anchor pier perpendicular to the axis of the anchor cable, the thin-walled steel pipe with the same outer diameter as the drill bit is welded orthogonally with the backing plate in advance, and the other end of the steel pipe is inserted into the drilling hole before pouring the anchor pier.
6. Anchor cable tension
The tensioning equipment shall be calibrated before tensioning the anchor cable. During calibration, connect the jack, tubing, pressure gauge and high-pressure oil pump, repeat the test for three times by using the method of jack actively outputting on the pressure machine, take the average value, and draw the curve of jack output (KN) and pressure (MPa) indicated by the pressure gauge as the basis for tensioning the anchor cable. Because the initial starting pressure of domestic pressure gauges is not exactly the same, the calibration curve must indicate the number of the pressure gauge during calibration and cannot be changed during use. After the pressure gauge is damaged or the jack is removed, it should be recalibrated.
If the anchor cable is composed of several steel wires, the whole step-by-step tensioning procedure can be adopted, and the stability time of each step is 2 ~ 3 minutes; If the anchor cable is composed of multiple steel wires, the assembly length will not be exactly the same. In order to improve the stress uniformity of each steel strand of anchor cable, the procedure of single tension first and overall compensation tension after 3 days is adopted.
7. Hole sealing and grouting
After compensation tensioning, hole sealing and grouting shall be carried out immediately. For the downward inclined anchor cable, insert the grouting pipe from the reserved hole until the nozzle enters the top surface of the anchorage section about 50cm；; For upward inclined and horizontal anchor cables, grouting pipe is reserved for grouting. The air in the hole is exhausted through the exhaust pipe arranged on the positioning slurry stop ring.
8. External protection
After hole sealing and grouting, leave 50mm steel strand from the anchorage, cut off the rest, and paint a protective layer of cement mortar with a thickness of not less than 50mm outside.
In order to complete the construction task on schedule with good quality and quantity, QC hours must be set up at the construction site, scientific working methods should be adopted at every stage from beginning to end, a series of countermeasures and implementation methods should be formulated, the anchor cable structure should be improved in time, the construction technology should be actively improved, the advanced network technology should be adopted to organize the construction, and the production should be balanced as much as possible, so that the drilling, grouting, tensioning and anchor sealing processes will not be delayed or crossed, and the construction records should be made in a unified form.
Second, the quality control
1. anchor point lofting, the allowable error in all directions is 65438±0cm.
2. Scaffolding must be stable, and the fastening of fasteners must be checked.
3. According to the design orifice coordinates, install the special steel pipe for drilling rig on the scaffold, put the drilling rig on the special steel pipe, use theodolite to release the baseline along the slope direction, then use directional frame to release the azimuth angle of anchor cable, and use goniometer to adjust the inclination angle until it meets the design requirements. After fastening the fasteners, check the coordinates, orientation and inclination of the drill hole again. After confirmation, tighten all fasteners again so that the error does not exceed: inclination angle 0.5, azimuth angle 1.
4. The allowable error of anchor hole diameter is 2mm.
5. In case of hole collapse, stop drilling immediately, carry out solid wall grouting, and then sweep the hole after grouting for 24 hours.
6. Rinse the hole thoroughly, and there shall be no stone powder and water left in the hole.
7. The preparation of anchor cable shall ensure that each steel strand is always arranged evenly, and straight, twisted and forked, rust and oil stains shall be removed, and those with dead bends, mechanical damage and rust pits shall be removed.
8. The length of the anchor cable shall be determined according to the actual depth of the borehole, with an allowable error of 2 cm, and the anchor cable shall be numbered accordingly according to the hole number.
9. The positioning guide flower frame and boat-shaped bracket (both unified) of the anchorage section should be installed on the anchor cable in strict accordance with the design requirements, and the binding iron mouth should not only be able to withstand a certain tension, but also ensure the free stretching of the anchor cable.
10. The anchor cable laying shall ensure that the grouting thickness of the anchor cable hole wall is not less than 1cm, the anchor cable laying shall be straight, and the tensioning section shall be placed in the center of the anchor hole.
1 1. Grouting shall be carried out in the inner anchor section, and the cement shall be No.525 ordinary portland cement. The mixed cement mortar shall be uniform, and there shall be no precipitation during use. In order to ensure the performance of the slurry, different additives can be added, and the filling coefficient of grouting is 1. 1- 1.3.
12. Strictly control the water addition and water-cement ratio, and the allowable error of lime-sand ratio is 0.03.
13. The allowable deviation of anchor pier fabrication is 3 cm in all directions. When installing, the orifice positioning steel pipe should be placed first to ensure that the anchor pier is vertical to the anchor hole.
14. The tension of anchor cable must be carried out after the mortar of anchorage section and concrete of anchor pier reach the design strength.
15. Before tensioning, the tensioning equipment shall be calibrated, and the average value shall be taken three times. The uneven tension coefficient of each steel skeleton is between 0.95- 1.05, and the tension difference of each steel skeleton is 5%.
16. Patching shall be carried out 6- 10 days after tensioning is completed, and the tensioning force shall be 20% of the design pretension.
17. Before the grouting stops, when the grouting overflows the orifice, the grouting in the tensioning section must be stable for 1-2 minutes. After 24 hours, grouting is needed to ensure adequate grouting.
Third, safety measures
1, technical safety disclosure before construction, and clear division of labor and unified command during construction.
2, all kinds of machinery and tools should be in good condition and reliable.
3. Do a good job of safety inspection before taking up the post, which shall be the responsibility of the team leader, with responsibility to people and mutual supervision. Construction personnel should wear safety helmets when entering the site, and operators should concentrate on observing relevant safety operation procedures.
4. Mechanical and electrical equipment should be operated by special personnel.
5. Electric (gas) welding operators should hold operation certificates.
6. Drilling for slope reinforcement works is usually carried out on scaffolding. In order to ensure the absolute safety and stability of the scaffold, the double-row method is adopted with the spacing of 1.2- 1.3m, diagonal braces and cross braces are added at the gravity concentration place, and short anchor piles are set to anchor the scaffold on the stable rock wall.
7. Safety protection facilities should be set up for aerial work, and traffic safety protection should be set up for operations near existing lines.
8. Pneumatic drilling rig pipeline connection should be firm, to avoid tripping and throwing people.
9. The grinding wheel cutting machine used for cutting steel strand should have a safety shield to prevent debris from hurting people.
10. The grouting pipeline should be unblocked, and there should be no blockage, so as to avoid sudden gushing of slurry and personal injury. When not in use, the grouting pipeline should be washed with water in time.