Self Drilling Hollow Anchor Bolt Application in Yuxi-Mohan Railway Tunnel
by Anna S. Optimization SpecialistSelf-drilling anchor bolt is a kind of anchor that
integrates drilling, grouting and anchoring functions together. It can
construct in complex formations with high construction efficiency and good
anchoring quality. Self-drilling anchor support can give full play to
the self-stabilization ability to surround rock, and it is widely used in
tunnel surrounding rock support.
Manmushu Tunnel in Yuxi-Mohan The railway is located in Mengla County, Xishuangbanna Prefecture, Yunnan Province,
with a total length of 11.6 kilometers and a maximum buried depth of 660m. It
is a high-risk control project for the China-Laos Railway. The surrounding rock
is grade IV-V and is mainly mudstone intercalated with carbonaceous mudstone,
and the groundwater is mainly bedrock fissure water, which is poorly developed
and has a small amount of water. The 30m-buried shallow weathered layer of the
DK431+534-564 section of the tunnel entrance is relatively thick, and the
double-line V-level reinforced type II composite lining is adopted.
In order to solve the
problems of difficult drilling and low construction efficiency of ordinary
bolts in special surrounding rock conditions with more weathered rocks, ZYS113
drilling rigs and R51 hollow anchor bars are used for construction, and the
single-hole drilling depth is 21m. During drilling, there are 17 holes in each
ring at the top of the tunnel end face. The hole spacing is 400mm, which is inclined
upwardly at an angle of 1-2°. The drilling diameter is 76mm, and each hole is
equipped with 3 6m long hollow anchor bars and 1 3m long R51 hollow anchor rods.
The overlapping distance between each pipe roof ring is 3 meters. After
drilling, the hollow anchor bar can be used as a grouting channel for grouting
from inside to outside. The grout is returned from the hole bottom. The grouting
pressure is 0.4MPa, the water-cement ratio of grout is 0.45, and the pressure
maintenance time when the overflows are not less than 10 minutes, which can
realize rapid and full penetration of the grout along the rock mass fissures. Pressure
grouting can ensure that the grout spreading radius is large, and the surrounding
rock will be consolidated into a whole to achieve the purpose of permanently
anchoring the surrounding rock.
Self
drilling anchor bolt has
obvious efficiency increase due to its advanced technology. The average drilling
time for 21m hole is 40 minutes, and the drilling time for each ring of 17
holes are about 11 hours, and the minimum time is 9 hours. Its economic
advantages are obvious.
Self
drilling anchor bolt
can simplify the drilling, grouting, and anchoring procedures. The full length
of the bolt is fully anchored, and it can provide a certain supporting
resistance immediately after excavation, effectively suppressing the loosening
and deformation of the surrounding rock, and avoid or slow down the occurrence
of disease accidents during construction and use of the project. The use of self
drilling anchor bolt and drill bits can ensure the grouting layer is at least
20mm, which fully guarantees the durability of the bolts, and is especially
suitable for supporting and strengthening complex formations and broken
surrounding rocks.
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Created on Jul 18th 2021 20:57. Viewed 227 times.