open timbering

open timbering

[′ō·pən ′tim·bə·riŋ]
(mining engineering)
A method of supporting the ground in a mine shaft or tunnel; supports are several feet apart, with the ground between them secured by struts.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

open sheeting, open sheathing, open timbering

open sheeting
Horizontal or vertical planks or boards placed at intervals along the face of an excavation; used where the soil is sufficiently firm to make close sheeting unnecessary and where groundwater is not a problem.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.