Citation

Arman A, Thornton SI. Highw. Res. Rec. 1973; 426: 14-22.

Copyright

(Copyright © 1973, National Research Council (U.S.A.), Highway Research Board)

DOI

unavailable

PMID

unavailable

Abstract

In Southwest Louisiana, experience with widespread surface deposits (as thick as 5 ft) for use in earth structures has shown that some soils can withstand the design load, but others exhibit characteristics of a collapsible soil in the presence of load and moisture. All of these soils are classified as silt; the collapsible soils cannot be distinguished from normal silts by using routine tests. The known and conjectured areas containing collapsible silts fall within a 30- mile band through the coastal prairie terrace, the mississippi river terraces, and the loessial hills. The dominant clay mineral in the collapsible silts is montmorillonite; kaolinite and illite are also present. These silts attract and suspend moisture in their pores by electrochemical forces. They become virtually impermeable when a polar liquid, such as water or ethylene glycol, is added. If a collapsible silt is mixed in a solution of sodium hexamaetaphosphate (calgon) and allowed to settle, the liquid turns black. This color change is attributed to lignin. Along with a determination of the presence and location of collapsible soils in Louisiana, criteria for distinguishing these soils from normal silts are established. When two of the following four conditions are met, these soils may be considered collapsible: In situ unit weight of the undisturbed silt is less than 80 lb cube ft; maximum dry density is less than 104 lb cube ft; after the solids of the suspected soil have settled out in a 3 percent solution of sodium hexametaphosphate (used in routine hydrometer analyses), the supernatant liquid is black; and a total strain of at least 15 percent occurs at the end of the 16-tsf loading in a collapse test. /author/

Language: en

Keywords

ROADS AND STREETS; SOILS - Classification