noun
test pit; pilot tunnel
Technical term in mining, civil engineering, and geology for a small excavation or borehole made to investigate ground conditions.
トンネル工事の前に、地質を調べるため試掘坑を掘った。
Before tunnel construction, they dug a test pit to investigate the geology.
試掘坑の調査結果から、この場所は軟弱地盤だと分かった。
From the test pit survey results, it was found that this location has soft ground.
Compound of 試 (test) + 掘 (dig) + 坑 (pit/tunnel). A straightforward technical term formed from Sino-Japanese morphemes.