12/21/22, 1:19 PM Geostrata - February/March 2022 - Have You Heard of Stacked Drifts? https://www.readgeo.com/geostrata/february_march_2022/MobilePagedArticle.action?articleId=1762335#articleId1762335 1/11 T he use of "stacked drifts" in the sequential excavation method of tunnelling has been employed for over four decades and has allowed for the construction of tunnels and underground caverns approaching nearly 30-m width under clear cover thickness of 5 m or less, more typically in soft ground geology. The method essentially involves constructing a series of smaller-diameter tunnels, configured side- byside, arched, and/or vertically "stacked." Typically, each small tunnel is backfilled with i Privacy Notice - This site uses cookies and other technology to improve your experience. By continuing to use this site, you are agreeing to our Privacy Policy.