Pressure, Resistance, and Stability of Earth - American Society of Civil Engineers: Transactions, Paper No. 1174, - Volume LXX, December 1910 by J. C. Meem
page 55 of 92 (59%)
page 55 of 92 (59%)
|
Another reason for calling this paper dangerous for beginners is that it is improbable that experienced engineers or contractors will omit the bracing at the bottom, although, since the paper was printed, a glaring instance has occurred where comparatively little bracing was put in the bottom of a 40-ft. cut, the result being a bad cave-in from the bottom, although all the top braces remained in place. Most engineers will agree that nearly every crib which has failed slipped out from the bottom, and did not turn over. The objection to the angle of repose is that it is not possible to ascertain it for any material deposited by Nature. It could probably be ascertained for a sand bank deposited by Man, but not for an excavation to be made in the ground, for it is known that nearly all earth, etc., has been deposited under great pressure, and is likely to be cemented together by clay, loam, roots, trees, boulders, etc., and differs in character every few feet. A deep vertical cut can often be made, even in New York quicksand, from which the water has been drawn, and, if not subjected to jars, water, etc., this material will stand for considerable time and then come down like an avalanche, killing any one in its way. In such cases very little bracing would prevent the slide from starting, provided rain, etc., did not loosen the material. The author, of course, treats dry and wet materials differently, but there are very few places where dry material is not likely to become wet before the excavation is completed. In caisson work, if the caisson can be kept absolutely plumb, it can be |
|