Genesis And Hardening Of Laterite In Soils

The papers in this volume cover micromorphological studies of a wide variety of topics, at various scales from ultramicro- to mesoscopic. Topics included are: soil management; soil structure; surface crusts; hardpans and cemented layers; soil biota; soil genesis; hydromorphic soils; paleosols; archeology; and general pedology. The range of papers reflects the growing use of soil micromorphology in understanding soil problems in land-use and the increasing use of quantitative techniques, together with more traditional applications in pedology. The book is well illustrated with micrographs and contains both author and keyword indices.

In comparison with engineering, geology is a relatively new domain of know ledge. Man has been building almost from the moment he came down out of the trees or emerged from the caves. All of his structures were founded in or upon rock or soil. Before the end of what we call ancient history, he had learned a great deal about materials, mechanics, and structures. This empirical information had become an organized field of practical knowledge by the time of Leonardo da Vinci. Although both foundations and ma terials of construction were largely earthy, codified knowledge of neither one nor the other existed at that time. During the last two centuries, geology has emerged and has recently begun to take on a more quantitative aspect. A generation ago, it joined hands with civil engineering to create soil mechanics. Engineers began to apply the science of geology to foundations and materials with astoundingly successful results, and geologists began to acquire an understanding of engineering methods, applying what they could to their problems. Geologi cal engineering was born of this union. People of an older time employed stone and brick in construction, although cut brick and sawed stone were used more sparingly because of a scarcity in both suitable raw materials and techniques. They were used in Cambodia, for example. A material able to meet requirements was found nearby, known as itica culla. In India it was called vettu culla, but F. A.

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.

In the tropics, residual soils probably form the largest group with which the engineer has to deal. Being formed in situ, these soils have particular characteristics that distinguish them from material deposited from transported soils.