Asphalt membranes for dams of local materials

Abstract

The expansion of hydraulic engineering construction in regions with severe climatic conditions has necessitated the development of new design solutions for the watertight membranes of dams of local materials, since, when erecting cutoff wails and cores from clay earths, concrete cutoff wails, and reinforced-concrete membranes, a large amount of imported material is necessary, and working in frost and unfavorable weather is very difficult. The construction of rockflll dams, with a high level of mechanization of the work, remits in greater settlements of the body of the dam and substantial deformations of the watertight membrane, particulariy if made from a rigid material. Following the well-known failure of the reEnforced-concrete cutoff wail at the San Gabriel dam in the USA, the walls were made in several layers, with rows of slabs up to six [1], and more recently, in order to avoid tension on the surface wail or inclined membrane, a proposal was advanced for adopting a profile in the form of a circular or hyperbolic curve, or again a hyperbola, with a depth of curvature equal to the theoretical depth of curvature of the reinforced-concrete coating under the action of the head of water and settlement of the body of the dam [2].The membrane is the most economical structure for the watertight member of a dam, requiring a minimum of material, and exposed to the least deformation during settlement of the body of the dam, but it must satisfy severe requirements as regards reliability, on account of the thinness and flexibility of the whole structure. Collapse of one of the earliest rockfill dams, the Lower Authie in California, cleariy demonstrates the inadequacy of rigid membranes. The membrane was made from two layers of concrete, each 30 cm thick, with a sheet of steel 6.5-8.5 mm thick in between, coated with bitumen and canvas. In 1916, after 19 years service, during the flood period, the membrane burst and the 45.6-m high dam was breached, some parts of the membrane being carried 15 km downstream [1].In order to reduce the rigidity of the membrane, horizontal joints were cut, so that a large part of the head was absorbed by the resistance of the downstream shell of the dam embankment [3]. However, an attempt to give even more mobility to the membrane resulted in proposals for constructing vertical joints also, compensating the nonuniformity of deformations of the individual sections and temperature stresses [4], and even making a reinfo-c ?d concrete membrane of individual free-standing rigid blocks, held only by the resistance of the downstream shell of the dam [5]. This type of complex system of breaks greatly complicates the construction of the membrane and requires reliable sealing of numerous joints. Hence, abroad, there is an increased tendency to achieve flexibility of the watertight structures on earth and rockfill dams by using asphalt concrete and plastics. It is not surprising that American engineers have observed [6] that replacing the reinforced concrete cutoff wall of the Montgomery rockfill dam, s...

Possible application of floated asphalt concretes for the diaphragms of dams of local materials

“…Floated asphalts, as compared with compacted, actually have a higher density, greater imperviousness and water resistanc% increased deformation and resistance to fissuring, including self-heating of cracks. This is confirmed by not only laboratory experiments, but also the operation of the screen of the Et-Grib dam [1], where floated asphatt was used for serf-healing of the cracks in asphatt concrete.…”