Reviews in Engineering Geology
This is the second in a series of volumes prepared by the Geological Society of America Division on Engineering Geology designed to summarize the states of knowledge on various aspects of the application of geology to engineering problems. Through an unfortunate series of delays, publication of the book was delayed several years beyond the completion of the contained papers. The geologic principles are still sound, however, and are certain to be useful to the practicing engineering geologist. Nine papers review the following subjects: foundations for heavy structures; geology and pedology in highway soil engineering; clay as a canal sealant; Portland cement and concrete; pozzolan; geocryology and engineering; land subsidence due to withdrawal of fluids; land subsidence due to the application of water; and geologic settings of subsidence.
Conveyance losses in irrigation canals commonly range from 20 to 40 per cent: however, the high costs of construction of conventional canal linings, such as those of concrete, asphalt, and plastic, often prevent large-scale efforts to control seepage. Thus, the idea of lowering costs by utilizing flowing canal water for placement of sealing clays in the leaky zones of canals is an attractive one. This paper traces the development of water-borne clay sealants for canals, from natural silting to the recently developed methods of sediment-sealing with bentonite.
In general, the water-borne clays are best for sealing coarsely rocky to gravelly canal bed materials. Less favorable results are obtained when clays are used for sealing fine-grained silty to sandy canal materials. Lack of penetration and short life are the main problems with clays used for sealing fine-grained soils.
The cost of clay-sealing ranges from less than $.01/square yard of canal area to an extreme value of about $2.00/square yard. Concrete linings, which are usually considered the best answer to most seepage loss problems, seldom cost less than $2.00 per square yard.