Hello, everyone.
This is Enta.
The other day, I went to check out the site where we had previously installed drainage boreholes.
As for the scope of the work, this was a private-sector project where part of the structure had already collapsed, and the client requested that we prevent any further collapse.
There are no stone walls or anything like that; it's just a bare mountainside.
There is a bamboo grove at the top.
"Every time it rains, the bamboo sways, and it's scary," she said.
And apparently, there’s quite a bit of murky water.
Although large machinery couldn't be brought onto the site, as for the construction method, for the time being...Reinforcement Bar Insertion and Drainage BoringWe addressed the issue using this combination.
Railway companies such as JR frequently use dewatering drilling methods, and I believe this method is best suited for dealing with small-scale collapses like these.
Why Is Drainage Boring Effective Against Minor Landslides?
Here's a brief explanation for the general public.
One of the main causes of landslides isRise in pore water pressureThat's it.
When water accumulates in the soil, the soil becomes more slippery.That's common knowledge among us in the industry.
When rainwater seeps into the ground, water pressure builds up in the spaces between soil particles.
When this pressure increases, the soil particles can no longer hold their ground, so the water lifts the soil and it slips right out from under them.
It’s easier to understand if you imagine a sandbox: sand that’s saturated with water crumbles more easily than sand that’s completely dry, right?
It's the same principle as that.
That's whyIf you drain the water, the soil will return to a state where it can hold its shape.。
That is the essence of dewatering drilling.
In soil mechanics, shear strength is expressed as τ = c’ + (σ − u) tan φ’.
"Guidelines for Road Earthworks: Cut Works and Slope Stabilization"
Draining the water will restore the effective stress, causing the slope to stabilize.
It goes without saying that it’s incredibly effective—the mechanism behind it is crystal clear.
Drainage boring is also a standard method for slope disaster prevention measures in the railway sector and is clearly outlined in the manuals of various companies.
This construction method is included in the Ministry of Land, Infrastructure, Transport and Tourism’s “Guidelines for Landslide Prevention Technologies” and has a very extensive track record of use in public works projects.
My Design Focus: Primarily Reinforcement Insertion Methods, with Drainage Boring Methods as a Secondary Focus
As for my recent design trends, first of all,Reinforcing Bar Installer, and as a supplementDrainage Boring Worker...is the norm.
The reason is that it makes it easier for rebar installers to explain things to the government office, lol.
To be honest, because I’m still inexperienced, I can’t quantify the dewatering borehole work and give a clear explanation like, “Based on this theory, this is why we need this many boreholes!”
That's the bottom line.
The rebar insertion method is a conventional technique that government agencies find easy to understand, andYou can quickly create and submit design calculation sheets...is one of its strengths.
Even for private construction projects, if asked to explain, it’s easier to convince people by saying, “This is the standard construction method used in public works projects.”
If anything, the design is a breeze, lol (even though I know I shouldn't be thinking this...)
While addressing surface collapse by using rebar insertion to increase the strength of the natural ground,
If you drain the water using a dewatering drilling method to prevent the soil pressure from increasing any further,Even betterThat's the idea.
How much water actually came out?
This video was filmed on site. (Filmed by the client)
It's a little hard to see, but quite a bit of water is coming out now.
The entire slope isVegetation MatWe took measures to prevent erosion.
Vegetation mats are a fundamental part of erosion control, but at sites with high water levels, simply protecting the surface isn’t a permanent solution—so draining the water from the interior is really the key.
If this much water is coming out, does that mean the drainage drilling crew was the real star of the show?
Given that water is flowing constantly like this, it feels like...Primary job: drainage well driller; secondary job: rebar inserterThat's the impression I get.
I'm sure you're all well aware that dewatering drilling is extremely effective.
However, it's beyond my ability to prove and explain this using numbers.
There is a disconnect between the "invisibility" of the design and the "obvious effects" observed on-site.
I feel like this is the frustrating part of being a dewatering driller. (Though it’s really just my inexperience and laziness...)
As far as I know, I'm the only one who can explain this clearly.Ota GeoI only know Mr. Ota and a few others!
Drainage Boring Work for Minor Landslides in Private Areas
Measures to Prevent Minor Collapses in Private BuildingsDrilling for drainage is generally done by hand.
For public projects, the borehole diameter is generally between φ50 mm and φ100 mm, and a strainer pipe (SGP pipe, stainless steel pipe, or PVC pipe) is inserted.
Although there is also a method of draining water from driven piles, I believe that drilling is the most reliable approach if we aim to construct the project as closely as possible to the design specifications.
Even if the space behind the installation site is narrow, we can still install it up to a minimum of 50 centimeters.
Although there are aspects of the dewatering drilling method that are difficult to explain,It's exceptionally effective as a measure against heavy rainThat's it.
On slopes like the one at this job site, where water is constantly seeping out, I don’t think there’s any option but to install this.
I still have a lot to learn myself, but for now, I believe that dewatering drilling is an essential construction method.
See you later.
