Physical properties of southeastern Washington loess related to cut slope design: Beard, L D; Higgins, J D; Fragaszy, R J; Kilian, A P; Peters, A J Trans Res RecN1089, 1986, P29–38

Abstract

Loess is an aeolian soil consisting primarily of silt. The silt particles along with a lesser percentage of sand are coated by a clay binder, giving loess its unique structure. Because of the lack of development in the loessial soils of southeastern Washington, little is known about their engineerng characterisics. However, recent highway construction requiring large cut slopes has prompted interest. The results of a literature review of engineering characteristics of loess and an evaluation of the physical properties of southeastern Washington loess related to design of cut slopes are presented. A map shows the general distribution of clayey, silty, and sandy loess. Results to date indicate that the basic physical properties of southeastern Washington loess are quite similar to those from deposits in the central United States. Water content tends to increase from west to east because of increasing clay content and precipitation to the east. Washigton loess has a slightly lower plasticity than midwestern deposits, possibly because of greater illite and lower montmorillinite content. Based on experience in the midwestern United States and observations of existing cut slopes in southeastern Washington, design recommendations are presented. Near-vertical cuts are recommended in silty loess with low water content, and flatter cuts (approximately 2.5:1 H:V) are recommended in clayey loess and silty loess with high water content. Adequate surface drainage is a key factor of slope design. erest.