Application case analysis of self-drilling anchor
by Anna S. Optimization SpecialistAs 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 gives full play to the advantages of it,
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 22nd 2021 23:33. Viewed 149 times.