Book Description

Present Corps of Engineer (CE) filter criterion (EM 1110-2-1901, Appendix D) dates from the early 1950's, and some uncertainty exists as to the applicability and adequacy of this criterion under various conditions. Laboratory filter tests were conducted on uniform and poorly-graded cohesionless base materials protected by various filters, and internal stability tests were conducted on various graded filter materials. Based upon the limited tests conducted, the following changes to CE filter criterion are proposed. For a uniform (poorly-graded cohesionless base material, the second stability ratio should not be used, and there is no need for requiring parallelism of filter and base gradations should be retained. For a poorly-graded cohesionless base material, the second stability ratio should not be used, but the requirement for parallelism of filter and base, gradations should be retained. Poorly-graded gravelly sand and sandy gravel are internally unstable and should not be used as filters when the coefficient of uniformity> or = 20.