Relevant Aspects Of The Geotechnical Design For ‘La Yesca’ Hydroelectric Project And Of Its Behavior During The Construction Stage

RD 2011
CFRD 16

RELEVANT ASPECTS OF THE GEOTECHNICAL DESIGN FOR ‘LA YESCA’ HYDROELECTRIC PROJECT AND OF ITS BEHAVIOR DURING THE CONSTRUCTION STAGE: THE MEXICAN EXPERIENCE IN CONCRETE FACE ROCKFILL DAMS
Juan de Dios Alemán-Velásquez1, Humberto Marengo-Mogollón1, Rigoberto Rivera-Constantino2, Armando Pantoja-Sánchez 1 and Amós Francisco Díaz-Barriga1 1, Comisión Federal de Electricidad,juan.aleman@cfe.gob.mx, humberto.marengo@cfe.gob.mx 2, Facultad de Ingeniería, Universidad Nacional Autónoma de México

ABSTRACT This paper presents the geotechnical design of “La Yesca” concrete face rockfill dam (CFRD), currently under construction that takes into account the index and mechanical properties obtained from laboratory test results and from rockfill test embankments using the materialswith which the dam is being built. Description is made of the procedure applied to achieve the compaction determined from the rockfill embankments and the behavior of the dam is analyzed based on the results of the instrumentation installed. Finally, its behavior is compared with other dams of the same type built in Mexico, namely, Aguamilpa and El Cajón. The behavior of the dams referred to isanalyzed in terms of settlements for the following conditions: end of construction, first filling, and long-term performance using for this purpose the information resulting from the instrumentation installed at the embankment and with special emphasis paid to the physical and mechanical characteristics of the geotechnical zoning of each of the embankment dams as well as to the compaction procedureused in the field, being these factors directly related to the recorded behavior Key words: CFRD, Dam, Behavior, Settlements, Rockfill properties

1. BACKGROUND 1.1 Overview This paper describes some of the most relevant aspects related to the geotechnical design of “La Yesca” Hydroelectric Project currently under construction (progress achieved to date, may 2011, amounts to 82% in theplacement of materials in the embankment) and an account of its behavior during the construction stage is also presented. Brief mention is made too for comparison purposes of the behavior of two other large concrete face rockfill dam completed in our country, i.e. Aguamilpa and El Cajón, both located downstream from the hydrological system of the Santiago River in the state of Nayarit, Mexico. 1.2 Factorsaffecting the deformability of the CFRDs Because the materials used in the different zones of a CFRD have in general very good quality, the slope stability of the dam is no longer a relevant problem but the deformations that can be experienced by the concrete slab during the construction stage, first filling and accidental loads (earthquakes) are of serious concern; therefore, the compressibilityproperties of the different zones, particularly of material 3B that acts as a support to the concrete face, should be carefully analyzed because the
The Second International Symposium on Rockfill Dams

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objective is to achieve an embankment with low compressibility that ensures a suitable behavior of this element.. The major factors affecting the characteristics of compressibility of theCFRDs are related to the physical and mechanical properties of the constitutive materials of the various zones of the embankment, namely: grain size distribution, grain shape, size and mineralogy of the particles (hardness), relative density (represented by the void ratio or the dry unit weight), tightness or interlocking, the state of confining stresses, the degree of saturation and the rate ofapplication of the load. In addition, it is a known fact that the geometry of the valley also affects importantly the deformations likely to be experienced by the dam because of the arching phenomenon. Mention should be made that the compaction process used during construction is fundamental in the values of the module of compressibility that are obtained in order to achieve a suitable behavior...