Geology and Geotechnical Properties of Laterite Gravel.

Laterization processes were studied and samples of laterite gravel collected at 40 sites in Thailand, Australia, Brazil, Ghana, Portuguese Angola, and Georgia USA to determine classification, field associations, genesis, and engineering properties important in road and airfield construction. Lateritic soils are self-hardening and may contain either laterite rock or nodular, laterite gravel. Tropical soils which are not self-hardening and which lack appreciable laterite rock or laterite gravel are called here tropical red soils. The soils studied in this report classify as sands and gravels in the Unified Soil Classification System. Generally they are poorly sorted, strongly fine-skewed, leptokurtic, and, on the average, contain approximately 12 percent fines. These soils have originated by the hydrolytic destruction of primary silicate minerals in warm, tropical to subtropical weathering environments which exhibit distinct wet and dry seasons, and are generally free draining. Laterite gravel is of primary importance in construction. Laterite rock requires crushing, and self-hardening laterite may be difficult to identify and thus may be confused with tropical red soils. Foreign engineers have found that two official U.S. specifications are too restrictive. They have developed base and subbase specifications suitable for road and airfield construction using laterite gravel.