Hello, everyone.
This is Enta.
I received a question on Twitter regarding my recent post.
Since I think this is something that design consultants and government officials might not understand, I’d like to explain it.
If double-tube drilling cannot be used and self-drilling rock bolts must be used instead, how should the design be approached?
(1) It is generally intended for use in areas where the borehole wall is not stable.
(2) Uncertainty arising from the loss of circumferential friction between the grout and the surrounding rock when the borehole wall collapses— Kurokuro (@vEVaav0lwtpgbpx) March 24, 2023
When you can't drill a double-pipe hole, and the hole wall won't hold on its own even with self-drilling bolts!
In this case, drilling is generally done by hand, but
Even in a place like thisWe have no choice but to use self-tapping bolts!
I think it's safe to say that there are basically no other methods (for now).
Since we’ll be using self-drilling rock bolts for this project, there’s something I absolutely want you to do.
Self-drilling rock bolts must alwaysPlated finish; uses a swivelI'd like you to drill a hole there.
The reason is that we want to avoid clogging the tip of the self-tapping bolt to ensure a reliable injection!
Doing so increases the likelihood of a successful injection.
I'm sure you understand the benefits of using plated bolts. (They solve the problem of material corrosion.)
It's hard to understand why a swivel is used in this type of hand-dug hole, isn't it?
I think you'd generally use a leg drill like this when drilling holes for self-drilling rock bolts.
When you lower the lever on this leg drill, it performs a rotating and striking motion.
The lever is in the middle, in the neutral position.
Pull the lever up to supply air.
You can't send air to the tip while performing a spinning strike.
That means the hole at the tip tends to get clogged.
Suspended core drills bore holes using rotation, percussion, and air at the drill bit tip, right?
That's why drilling is pretty fast, and it produces a good amount of drilling slime (the slime that comes out during drilling).
Chestnut FlourThat refers to the white powder in the YouTube video.
The shape and appearance of drill cuttings vary depending on the bedrock, soil, and clay being drilled.
This state, in which the chestnut flour is easily released, is one in which the interior of the pore walls remains intact and self-supporting due to a continuous stream of air from the tip.
The drilling slurry is forced out from the tip toward the outlet (hole opening).
Since air is being expelled at the same time as the rotary impact, you can see that this reduces clogging at the tip and allows for more efficient drilling, right?
Drilling with a hand-operated leg drill is
Lower Lever: Rotation and Striking
↓
Pull the lever: Release the air to dispense the flour.
↓
Lower Lever: Rotation and Striking
↓
Pull the lever: Release the air to dispense the flour.
We'll keep moving forward, little by little.
For people who are inexperienced at drilling, the hole at the tip is almost always clogged, andCannot inject!
In short, it's a construction defect.
That is precisely why it is necessary to perform the drilling properly to ensure the injection is successful.
You can see that it’s absolutely essential for the grout to be injected through those air holes, so they must not be clogged.
Now, suppose the borehole wall collapses after drilling.
If the tip isn't clogged, the grout will flow out of the tip and rise up around the bolt head.
At that time,
Wiggle the bolt up, down, left, and right to let it blend with the grout! (This is really important.)
This alone should be enough to create a self-drilling rock bolt that provides a secure hold.
It's okay to jig while jigging
(The photo above shows packing being inserted to prevent backflow through the hole.)
There are tons of job sites where the only way to install the system is by self-drilling.
This machine can be used even on job sites where the leg drill has a reach of about 1.0 m and, considering the width of a person, there is only about 1.5 m of space available.
(If it's 1.0 m or less, there are other options.)
Even without using a support, you can be sure the installation will be successful if you follow the method described above, but,
I’d really like to have an experienced crew handle this if possible, lol.
Or, if there's someone who can provide solid guidance, I think things will work out.
Since it’s necessary to come up with ways to ensure reliable construction even in difficult-to-reach areas,
Let's proceed with the construction based on our knowledge and experience.
Furthermore, on the design consulting side, the self-drilling rock bolts are plated, and
I think you should just specify that a swivel is to be used. (That way, the contractors can ensure the work is done properly.)
See you later.
Manual Drilling and Grout Injection for Self-Drilling Rock Bolts
Inspection of the Finished Product for Self-Drilling Rock Bolts
