Application case analysis of self-drilling anchor
by Anchor S. Web DesignerAs an advanced construction technology, self-drilling hollow anchor bars are widely used in foundation support projects, effectively solving the construction problems of unstable rock masses such as strongly weathered rocks. In the Huangshan Pedestrian Mall foundation support project, the use of R38 self-drilling anchor bolts not only overcomes the difficulty of drilling holes in the round gravel layer but also give full play to its advantages of improves construction efficiency and reduces comprehensive construction costs.
1. Background and challenges
The total planned land area is about 36372
m2, the building height is 13m. The rock and soil layers from top to bottom in
the proposed site are mixed fill, silt, fine sand, round gravel, strongly
weathered siltstone, strongly weathered phyllite, moderately weathered
siltstone, moderately weathered phyllite and a lot of construction waste. In
actual construction, it is difficult to drill holes in the round gravel layer,
so a casing is required. However, drilling with casing is inefficient and
costly, and it can cause infrasound damage to the surrounding area. Finally,
the construction plan was changed, Sinorock R38 self-drilling anchor bolts were
used, and drilling and grouting simultaneously can solve the problem of hole
formation.
2. Construction plan
Due to the complex geological conditions, the
hollow rods need to penetrate the tangent supporting pile and drill into gravel
and a strong weathered layer. And it is difficult to drill and form holes in
the round gravel layer. In order to solve this problem, the constructor uses
the HYZ133-100A drilling rig, SER38/18 hollow anchor bar, ESF R38/90 drill bit
for rotary percussion drilling, and drill hole depth is 18 meters. The grout is
pumped through the hollow hole, with a water-cement ratio of 0.5-0.55. The grouting
pressure is 0.3-0.5MPa, and the compressive strength of the grouting body is
20MPa. Simultaneously drilling and grouting can directly improve the
surrounding soil quality, and improve the anchoring force.
The self-drilling anchor rod is used for construction,
which is convenient and efficient and can greatly improve construction
efficiency. When the construction work face is convenient, a team drills up to
500 meters in 12h.
3. Test
After grouting, install breast beam, plate,
wedge, and hex nut in sequence. The design pull-out value is 15kN/m, the number
of tests is not less than 3% of the total number, and not less than 5, and the
design pulling-out force is 270kN. After testing, the anchoring force of the
anchor bar meets design requirements.
4. Project Summary
The project was originally designed for
construction with casings. Self-drilling anchor rods were adopted because it
was difficult to make holes in the ground and could not be drilled effectively,
thus the construction cost was high. The use of self-drilling anchor bolts
effectively solves the difficult problem of anchoring in loose rock and soil.
The simultaneously drilling and grouting technology makes grouting more full,
improves construction efficiency, and guarantees construction quality.
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Created on Jun 23rd 2021 01:48. Viewed 144 times.