Calcrete, gypcrete and soil classification in Algeria

Abstract

Calcrete deposits are widespread in the subhumid and semi-arid zones of Mediterranean Algeria and the Sahara. They present a diversity of ages, degrees of development and weathering. Their complex history is the result of two contradictory processes: a diagenetic trend leading to hardpan formation, and a weathering trend with dissolution of calcite and its precipitation in dusty grain-size and partial leach-out from the soil profile. Calcrete is an excellent road-paving material if used within the climatic conditions corresponding to the stability of calcite in the soil profiles. A tentative classification of calcrete gravels is proposed on the basis of the Los Angeles abrasion test results. Gypsum sands recovered from massive deposits may also be used as a paving material wherever annual precipitation is not over 100 mm. The geotechnical characteristics of calcrete and gypsum soils make it difficult and even impossible for usual identification tests, such as the Atterberg limits, to supply reliable classification figures or estimates of important engineering properties of these soils. Other parameters must therefore be chosen in order to characterize calcrete and gypsum soils. This article considers the introduction of new soil classes into the Unified Soil Classification System (USCS). This revision is intended to strengthen the universal character of the USCS.