Abstract
Abstract Quaternary tectonic and volcanic activity, and glaciation, have created conditions in the Andes which have complicated the engineering of many dams. A notorious feature often encountered is the “paleocauce”, a former river bed blocked during Quaternary times and now filled with thick sediments, subsequent erosion having formed a new, displaced river bed. In many cases more severe problems have been caused by the presence of a paleocauce, particularly when this was only detected at an advanced stage of studies, than have arisen from the damming of the new river course, The paper describes a particular problem which arose during design of the San Jacinto project in southern Bolivia, and was due to the dispersive character of the Pleistocene deposits filling the paleocauce of the river Tolomosa. To fully evaluate the phenomenon of dispersivity, the Standard “pinhole test” has to be per formed, in conjunct ion with two other tests, on a large selection of samples. The results of these tests on samples from San Jacinto suggested that Classification diagrams for dispersive soils may have to be modified from case to case to reflect specific properties of the soil of the respective sedimentary facies.
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