Oso Tunnel

New Mexico, United States

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Last updated

July 1, 2026

Quick Summary

The Oso Tunnel in New Mexico, United States, experienced a significant challenge during its construction in 1967. While initially progressing well through hard shale, the tunneling machine encountered a buried valley filled with water-bearing sand and gravel approximately 1,000 feet from the portal. This unexpected geological condition buried the machine, causing a six-month delay. After repairs, the machine resumed work and set new world records for its advance rate, averaging 240 feet per day. This incident highlights the critical importance of thorough geologic investigation in tunneling projects to anticipate and mitigate risks associated with varied ground conditions.1

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tunnels and underground excavations
Geologic investigation
The five-mile Oso Tunnel in New Mexico offers one example. There, in 1967, a mole had begun to progress well in hard shale, until 1,000 feet from the portal it hit a buried valley filled with water-bearing sand and gravel, which buried the mole. After six months’…
Read More
The five-mile Oso Tunnel in New Mexico offers one example. There, in 1967, a mole had begun to progress well in hard shale, until 1,000 feet from the portal it hit a buried valley filled with water-bearing sand and gravel, which buried the mole. After six months’…
Read More