If the anchor cable is used in the foundation pit construction, in order to verify whether the anchoring force of the anchor cable meets the requirements of the design documents and guide the construction, the construction unit should carry out the basic test of the anchoring performance, and there is a problem in this test..
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The upper part of the surface of the cutting section is covered with a thin layer of Quaternary residual soil, and the lower part is weathered sandstone
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The maximum height of the slope is 45.3M, which is divided into five levels, and each level is set with a 4m wide platform
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Prestressed anchorage technology is adopted for slope support
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Three rows of unbonded prestressed anchor cable grid beams are set for each grade of the lower four grade slope, and the anchor cable spacing of grid beam is 4m
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The basic test of anchorage performance is carried out by the construction unit
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The tensioning is divided into two stages: pre tensioning and over tensioning, and the “double control method” is adopted
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After the anchor cable is locked, the remaining exposed anchor cable is cut by electric arc, and 5 ~ 10cm leakage anchor cable is left
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The construction supervisor found the problems in time and corrected them
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It turns out that after the anchor cable is locked, mechanical cutting should be used instead of arc cutting
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There are many hidden dangers in the improper use of anchor cable, so we must not ignore the safety precautions in the construction（ 1) The pre tightening force of anchor cable installation shall not be less than 90kN
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The row spacing between anchor cables must meet the design requirements, and the error shall not exceed ± 100mm； Allowable deviation of anchor cable installation angle ± five °， The exposed part of the anchor cable shall not exceed 300 mm, and the anchoring force of the anchor cable shall not be less than 200 kn（ 2) When installing the anchor cable, a special stirring driver is installed at the lower end of the anchor cable, and two people cooperate with each other to hold the anchorage agent with the anchor cable and slowly send it into the drilling hole (pay attention not to repeatedly pull the anchor cable), so as to ensure that all the anchorage agents are sent to the bottom of the hole（ 3) Insert the hexagonal head at the tail of the special mixing driver into the anchor bolt machine
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One person holds the head of the anchor bolt machine, and the other operates the anchor bolt machine
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The mixing time is controlled at 40 ~ 50s（ 4) In the process of mixing resin cartridge with anchor cable, it is not allowed to stop and repeatedly stir（ 5) After the mixing is stopped, keep the thrust of the anchor bolt machine for about 3 minutes, then retract the anchor bolt machine and move it away to drill the next anchor cable hole（ 6) After 30min, first remove the special mixing driver, install the joist, tray and lock, and hold it close to the channel steel
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In addition to the above operation common sense, the following principles must be kept in mind when drilling anchor cable, dry drilling must be used to ensure the bonding performance of hole wall（ 1) Dry drilling is required for drilling, and water drilling is prohibited, so as to ensure that the anchor cable construction will not worsen the engineering geological conditions of slope rock mass and ensure the bonding performance of hole wall（ 2) The cohesive force of soil is mainly affected by shear angle and cohesive force coefficient
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Wet operation will affect the cohesive force coefficient of soil and the bearing capacity of anchor cable（ 3) Generally speaking, the drilling machine is pneumatic percussion drilling machine
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In order to prevent hole collapse, eccentric drilling followed by wall protection casing should be used
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During drilling, ash, slag and air leakage should be observed, and the position of sliding surface, staggered surface and other weak surfaces should be recorded to judge whether the hole section enters into stable rock (soil) layer, In order to ensure that the depth of the hole section into the stable rock and soil is not less than the length of the anchorage section required by the design
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Considering the thickness of ballast, the hole bottom should be over drilled by 30 ~ 50cm
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After the hole is formed, high pressure air is used to clean the hole wall to ensure the adhesion between the mortar and the hole wall
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Finally, we will give some popular science to the friends who don’t know much about Foundation Pit Construction: Although there is a word difference between anchor rod and anchor cable, they are two completely different methods
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Anchor rod and anchor cable are different in quantity, not in quality, but in tension medium
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The tension part of the anchor cable is made of steel strand, and the anchor rod is mainly made of high-strength finish rolled rebar
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Generally, the anchor cable is used in large tonnage anchoring engineering
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The tension bar of anchor cable is made of steel strand, and the anchor rod is made of steel bar or steel pipe
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Generally, the stress of anchor cable is large, and the stress should be added
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The stress form is divided into anchorage section and free section, which can be used as permanent anchorage engineering..
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