Hello, everyone.

This is Enta.

Since I received a question regarding the application of Site Conditions I, II, and III in rebar installation work, I thought I’d write about it.

 

Site Conditions I

This is drilling using a well-known suspended drilling rig.

This drilling method always requires a crane.

If a crane is required, that means construction cannot proceed unless the construction yard in front of the site is large enough to accommodate a crane.

When I go to job sites, I often find overhead power lines, which makes it impossible to carry out the work.

Please make sure to verify this thoroughly during the design and cost estimation phases.

In addition, since the drilling method is single-pipe drilling (single-hole drilling), the undisturbed ground must remain stable after drilling.

The hole will be drilled to a diameter of φ65.

Drill the hole using the bit shown above.

Attach this to the tip of the rod, and use the drifter (the hammer part) to apply impact and rotation to drill the hole.

The main body of the machine is called a "drifter."

This part generates impact and rotation.

Connect the shank rod to a rod up to 5.5 meters long using a sleeve (coupling), and then attach it to the bit at the tip.

Hoses run from the control panel to various parts of the system, so there is a distance of about 30 meters between the drilling site and the control panel.

 

Drilling proceeds through a combination of impact and rotation.

Once you've drilled to the specified depth, pull the drill out to complete the drilling.

Reinforcing bars are inserted immediately after drilling, and if the undisturbed soil is stable at that point, the bars slide right in.

However, in the case of mountains where it is difficult to stand on their own, no rebar is installed.

It is possible to insert it to some extent, but since the injection hose must be held in place while inserting it, it is quite difficult to insert into areas where the borehole wall has collapsed, and this can easily lead to construction defects.

Be sure to position the injection hose at the tip, and it is absolutely essential to inject from the bottom.

Since the grout hose used in this case is a standard type with an outer diameter of 21 mm, when inserting a D19 rebar into a φ65 borehole, the clearance on one side will be approximately 11 mm.

To put it bluntly, if it collapses by as much as 10 mm, it will be quite difficult to get in.

(Injection hose = 21 mm; D19 rebar maximum outer diameter 22 mm; 21 + 22 = 43 mm; 65 - 43 = 22 mm; 11 mm on each side)

It's best to make the drill hole as large as possible, but,

If the borehole wall collapses, then this “Site Condition I” does not hold.

Strictly speaking,Using rope scaffolding,Construction Methods for Sites Where Cranes Can Be Set Up on Hills with Self-Supporting and Stable Slope WallsThat's how it works.

The specific conditions for cost estimation are

Types of Scaffolding	Slope Vertical Height	Drilling Length	Drill Hole Diameter
Rope Scaffolding (Main Rope)	30 meters or less	1 m ≤ L ≤ 5 m	42 mm ≤ φ ≤ 65 mm

The table above is included in the civil engineering construction unit prices, but it does not specify whether the borehole walls are self-supporting.

However, since construction is impossible if the borehole walls are not self-supporting, consultation with the local government is necessary.

Ideally, it would be great if we could do test drilling or something during the design phase... but when placing a provisional order, these conditions tend to be the norm (because it's cheaper).

It's a hassle to make the change, but if you do a test installation using single-pipe drilling, it will be easier to switch to double-pipe drilling later.

 

Even a slight increase in the drill hole diameter makes insertion easier and reduces the number of installation defects.

For this reason, we use bits with a slightly larger diameter at Enta.

Besides that, this bit has so many benefits that I highly recommend it.

Found a great product! (Bit for singles)

The downside is that the dosage goes up a little bit, lol.

 

See you later.

Next Time: Site Conditions II