Construction of anchor cable frame beam

First, the working principle of anchor cable

Anchor cable is a special retaining structure, which aims to reduce the excavation amount of undisturbed soil and protect the ecological environment of high excavation area. It mainly solves the stability problem of fractured soil between the fractured surface and the free surface of soil. Its working principle is: depending on the tensile prestress of the anchor cable, the anchor is locked on the pile body, and the reaction force generated by the anchor cable is transmitted to the broken soil through the pile body, so that the broken soil remains stable under the action of external force. One end of the prestressed anchor cable is supported by the frame beam of the anchorage section, the other end is supported by the pile body, and the middle passes through the broken soil.

Second, the arrangement and structural form of anchor cable frame beam

Anchor cable length 19.5 ~ 29.5 mm, spacing 3m, anchor cable length 10m, anchor hole diameter10mm, inclination angle 15. The anchor cable body is composed of three φ 15.2 steel strands, and the single-hole anchoring force is 260KN. The anchor beam is cast-in-situ with C30 reinforced concrete, and the cross section is 0.5m*0.6m.

Third, the anchor beam construction process

Construction process of anchor cable frame beam: measurement and positioning → drilling → hole cleaning → anchor cable production → anchor cable installation → grouting → frame beam construction → anchor cable tensioning → supplementary tensioning locking → anchor head sealing.

Fourth, the construction process

(1) survey and setting out of anchor hole: excavation and reinforcement during slope construction, that is, excavation level 1 and protection level 1, and it is not allowed to dig to the end at one time. Accurately measure the anchor hole position on the slope with total station, and the hole position error shall not exceed 50ram. In case of uneven slope brushing or special difficult sites, it is necessary to relax the positioning accuracy or adjust the positioning of anchor holes with the consent of the design supervision unit and on the premise of ensuring slope stability and structural safety.

(2) Scaffolding: ￠5 Omm steel pipe scaffold is used to build the working platform, and the scaffold must meet the corresponding bearing capacity and stability conditions.

(3) Rig installation and drilling: Install the fixed rig accurately according to the hole position measured on the slope, and adjust the position strictly and carefully. The hole position error shall not exceed 0.2m, the inclination and direction of drilling shall meet the design requirements, and the inclination deviation shall not exceed 2. Dry drilling is required for drilling, and it is forbidden to use rhinestones to ensure that the anchor cable construction will not worsen the engineering geological conditions of the slope rock mass and ensure the bonding performance of the hole wall. The drilling speed should be strictly controlled according to the performance of the drilling rig and the anchoring stratum, so as to prevent drilling deformation and shrinkage, resulting in anchoring difficulties or other accidents. During drilling, the site construction records of formation change, drilling state (WOB, ROP), groundwater and some special situations should be made. If bad drilling phenomena such as hole collapse and hole shrinkage are found, drilling should be stopped immediately, and solid wall grouting should be carried out in time (grouting pressure is 0.1~ 0.2 MPa a). After the initial setting of cement mortar, re-sweep the drill. Borehole diameter and depth shall not be less than the design value. In order to ensure the diameter of the anchor hole, the actual diameter of the drill bit is required to be not less than the design aperture. In order to ensure the depth of anchor hole, the actual drilling depth is required to be more than 0.2 meters above the design depth.

(4) hole cleaning: after drilling reaches the design depth, it is not allowed to stop drilling immediately, and it is required to stabilize drilling 1 ~ 2 min to prevent the bottom of the hole from sticking out and failing to reach the design aperture. There must be no sediment and water attached to the borehole wall, and it must be cleaned up. After the completion of drilling, high-pressure air (wind pressure 0.2 ~ 0.4 MPa·a) should be used to remove all the rock powder and water in the hole, so as not to reduce the bond strength between cement mortar and rock and soil on the hole wall. In addition to the hard and complete rock mass anchorage, high-pressure water flushing shall not be adopted. If there is confined water flowing out of the anchor hole, the anchor rod and grouting can only be installed after the water pressure and water volume become smaller, and drainage holes are set at appropriate positions around if necessary. If the design requires to deal with the accumulated water in the anchor hole, grouting and secondary drilling are generally adopted.

(5) Inspection of anchor holes: After the drilling of anchor holes is completed, the next working procedure can only be carried out after the on-site supervision has passed the inspection. In general, under the supervision of the site, check the hole diameter and hole depth with the designed hole diameter, drill bit and standard drill pipe. During hole inspection, it is required that the drill bit advances smoothly without impact and jitter, the inspection length of drilling tools meets the design anchor hole depth, and the drilling tools exit smoothly. There is no obvious splash of dust and water when blowing with high-pressure wind. At the same time, it is required to review the position, inclination and orientation of the anchor hole. After all sub-projects of anchor hole construction are qualified, the drilling and manufacturing inspection of anchor hole can be regarded as qualified.

(6) Fabrication and installation of anchor cable body: firstly, straighten and truncate the steel strand, the length of which is the actual length of drilling hole+the thickness of external anchor pier+the length of jack+the thickness of tool anchor and working anchor+the tension operation allowance, and the truncation error should also be considered, that is, cut out 50 ~100 mm.. Cutting machine should be used to intercept steel strand, and gas welding and arc welding are strictly prohibited.

Lay the cut steel strand flat, check the quality one by one, and register, mark and mark the anchor cable number (corresponding to the hole number) for the qualified ones. According to the design, measure the length of the inner anchorage section and the anchor cable, and mark them separately. Within the scope of the internal anchor section, wear a centering isolation bracket every 1m, and tie an iron wire between the two brackets. The steel strand in the tensioning section should be put into a plastic pipe and injected with butter (rust-proof, free from forming). After installing the guide cap at the end of the anchor cable, put it away smoothly for use.

Hoist the assembled anchor cable into the hole (when the distance is far, the anchor cable disc can be 1.5 ~ 2.0m diameter disc, and then transport it). After checking that the number of anchor cables is consistent with the number of holes, first clean the holes with high-pressure air, then slowly insert the anchor cables into the bottom of the holes, and install the grouting pipe together with the anchor cables. The distance between the nozzle and the bottom of the hole should be 30 ~ 50 cm. Please note during installation:

(1) Keep the anchor cable straight, send the force evenly, and don't sway from side to side;

(2) Before anchoring cables, check the binding quality of each anchor cable to ensure that there are no undesirable phenomena such as looseness and corrosion, and check the hole number to avoid wrong anchoring cables. Steel strand adopts high strength, low relaxation and unbonded prestressed steel strand (= 15.24mm).