On October 16, the Japan Atomic Energy Agency (JAEA) announced
that it has demonstrated a method for predicting how quickly
groundwater flowing into a tunnel declines naturally,
500 meters underground at the Horonobe Underground Research Center in Hokkaido.
The result comes from research conducted with Taisei Corporation,
and the method was used to decide whether measures against water inflow were needed.
The Challenge: Stopping Groundwater Takes Time and Money
Groundwater that flows into a tunnel is called water inflow.
Grouting, a typical countermeasure,
is a method that injects cement or other materials into the rock
to seal the paths through which water flows.
According to the announcement, it takes several months and costs a great deal.
Deep underground, high injection pressure is required,
which also increases safety risks.
On the other hand, water inflow sometimes declines naturally.
If the rate of decline could be predicted in advance,
it might be possible to determine whether countermeasures are needed.
What Changes: Estimating from Inflow Observations and Skipping Permeability Tests
The new method observes changes in the amount of water flowing
from a borehole drilled at the planned excavation site,
and estimates how the groundwater flow paths are connected
and how quickly water inflow will decline naturally.
Previously, the connectivity of flow paths was estimated
through permeability tests,
but these take time and money,
making it impractical to apply them to every tunnel.
Because the new method estimates connectivity from changes in inflow,
these permeability tests can be skipped.
At 500 meters underground, JAEA predicted that water inflow after excavation
would fall to about one-tenth of its initial level after one day
and to about one-hundredth after ten days.
Based on this, measures against water inflow were omitted,
and the excavation was completed without a large inflow of water.
In contrast, at 350 meters underground,
JAEA predicted that inflow would fall only to about one-tenth
of its initial level even after 100 days,
so the tunnel layout was changed to avoid the inflow point.
Rather than a technology for skipping countermeasures across the board,
it is a method for deciding construction approaches site by site.
Future Applications: Geological Disposal and Underground Storage
In the demonstration, inflow from the borehole was observed for more than ten days.
JAEA says that because the trend in the natural rate of decline
was nearly constant, predictions can be made with data from just a few days.
It envisions using the method to decide whether countermeasures are needed
almost in parallel with excavation.
In addition to ordinary tunnel construction,
the method is expected to be applied to projects
that use deep underground space,
such as geological disposal of high-level radioactive waste
and underground oil storage.
LC Signal’s Perspective: Determining Whether Measures Are Needed Before Adding Them
At 500 meters, countermeasures were omitted;
at 350 meters, the excavation route was changed.
It is a concrete example of the same research facility
reaching different construction decisions depending on the prediction.
If the method can reduce not only water-stopping work
but also the effort spent on investigation,
it seems likely to make it easier to direct time and money
toward the measures that are actually needed.
Key Sources
-
Japan Atomic Energy Agency official announcement (Japanese), October 16, 2026:
深度500ｍトンネルでの湧水量変化をリアルタイム予測
―地下深部の掘削工事 効率性と安全性の向上に貢献―
(Real-time prediction of changes in water inflow in a tunnel at a depth of 500 m:
Contributing to more efficient and safer excavation deep underground)
This article was prepared with AI assistance using publicly available information
as of October 17, 2026.
Announcement dates follow the dates shown on the official pages.
Predicted inflow values are distinguished from actual construction results,
and the observation period actually used is distinguished
from future application prospects.
“LC Signal’s Perspective” reflects this publication’s interpretation
of the available information.