Ultra-high rockfill dam with combination of the reinforced concrete face and clay-cement diaphragm

The article deals with design validation of a new type of an embankment dam structural design, i.e. rockfill dam with combination of two types of non-soil seepage-control elements – a reinforced concrete face (in the dam upper part) and a clay-cement diaphragm made of bored piles (in the dam lower part). The dam of the considered design has a number of advantages over classical structural design of concrete faced rockfill dam (CFRD). First of all, conjugation of the seepage-control element with rock foundation does not require arrangement of a pit. Secondly, repairs of the dam lower part may be carried out by arrangement of a grout curtain. But the most important advantage of this design is more favorable conditions of the reinforced concrete operation, i.e. the face is subject to not tensile, but compressive longitudinal force. This decreases the risk of cracking in the face. Design validation of this structural design was conducted on the example of a 235 m high dam. Numerical modeling of the dam stress-strain state (SSS) was performed with consideration of construction and loading sequence, as well as with consideration non-linearity of rockfill deformation. Impact of four main factors on the dam SSS was studied: rockfill deformation, clay-cement deformation, diaphragm height and reinforced concrete thickness. Several alternatives of the dam design parameters were considered. Design of the numerical experiment was conducted by the method of factor analysis. This permitted revealing the impact of the considered factors on the dam SSS, as well as solving the problem on optimization of the dam structural solution. It was revealed that for providing the necessary level of the dam design safety the rockfill deformation modulus should be at least 250 MPa, and the diaphragm should be made of plastic clay-cement concrete. More favorable turned to be the case when the diaphragm height is 20 m but not 35 m.