Properties of compaction of rockfills of el cajon dam

The 1st International Symposium on Rockfill Dams

PROPERTIES OF COMPACTION REACHED IN THE ROCKFILLS OF THE EL CAJÓN DAM
Abimael Cruz Alavez1, David Yáñez Santillán2, Juan Enrique Filloy3, Hildebrando Gallardo Quiroz4 1, Comisión Federal de electricidad (CFE) and proffesor of Geotecnia at the University SEPI-ESIA-IPN, México, D. F., México, E-mail:abimael.cruz@cfe,gov,mx 2, Manager ofEngineering Department of Constructora El Cajón, S.A. (CECSA-ICA), DF, México, E-mail: david.yanez@icacc.com.mx 3, Geotechnical Engineer - Intertechne, Curitiba, Brasil, E-mail: ef@intertechne.com.br 4, Comisión Federal de Electricidad (CFE)- Residencia de construcción PH El Cajón, Tepic, Nay. México,Email: hildebrando.gallardo@gmail.com ABSTRACT: This paper includes the properties of compaction reached inthe rockfills of the El Cajón Dam, as much of the test embankment constructed previous to the bid, that was used as base for the design and specifications of construction of the curtain, and the one constructed by the contractor to determine the properties reached with its equipment, previous to be used in the construction. The properties reached in the body of the curtain are also described. Thecompaction properties are expressed in dry densities and void ratio, and the mechanical properties in static and dynamic modules of deformation, and in Poisson ratio. The results show that the properties considered in the design and the specifications of construction were conservative, with respect to the properties reached in the construction, which guarantees good behavior of the dam during itsoperation. Key words: Compaction of rockfills.

1

Background

The studies of materials carried out previous to the bid for the construction of the curtain of El Cajõn Dam, included geological aspects of the rock bank El Vertedor, laboratory and field tests to determine the properties of the rockfill materials. The geological studies included surface studies, drillings, geophysicalprospection and determination of available volumes of the rockfill; the particular studies of the rockfill consisted of the excavation in the bank, test blastings, construction of a test embankment with different layer thicknesses and roller passes, field and laboratory tests to estimate granulometric properties, densification, module of deformation and the shearing strength on compacted materials (Reportof CFE 2002ª). The test embankment was carried out in two stages. During the first stage a plain vibratory Roller with 7.5 tons of static weight was used, together with rocks extracted from the first 18 mts depth. In the second stage, a 10.6 ton roller was used, together with material from major depth and better quality. In both cases the rock used was ignimbrite identified in the project asTicU3, which was extracted directly from the excavations, without processing. It was built in layers of 0.90 m, 0,60 m and 0,40 m thickness when loose and compacted with 4, 6 and 8 passes, adding water as specified (200lt/m3). The dry density and number of passes were determined excavating 61 giant volumetric pits in the first phase and 43 in the second. Confined plate tests were also carried out toobtain the module of deformation and permeability tests Matsuo-Akai type, as well as seismic refraction tests to determine the dynamic modules. The tests showed: 1) In general, the dry densities of the competed rockfill increase with the roller weight and the number of passes, and decrease with the growth of the layers thickness. 2) The results are somehow erratic in the case of the layers withhigher thickness.

The 1st International Symposium on Rockfill Dams

3) Although the rock of the first stage was of lower quality, since it was extracted from minor bank depth, and in the second stage the quality was higher corresponding to a major exploitation depth, no remarkable discrepancies were observed between the results for both stages. Considering the results of the test embankment...