The Friant-Kern canal : a forgotten example of lime-treated structure in hydraulic conditions
Résumé
The Friant-Kern irrigation canal is located along the foothills of the Sierra Nevada, south-east of Fresno, California. It has a length of approximately 240 km, and was designed for a maximum waterflow of 150 m³/s. It was built in the late 1940’s using highly expansive clay; the earth-lined sections have 2:1 slopes, a bottom of 17.7 m width, and a top width of 45 m. Since the construction period, the earthen banks have suffered periodic damage from cracks, slips and slides. Concrete–lined sections also show failures due to the swelling of expansive soils. In the 1970’s, the Bureau of Reclamation decided to repair approximately 13.5 km of failed sections using lime treatment of clays taken from the banks of the canal. The methodology and devices used for the quicklime treatment are explained in the paper. The treated clay was replaced and compacted by a sheepfoot roller, to achieve a typical thickness between 60 cm (top and bottom of the canal) to 1.2 m (slopes). The observed performance after 12 years [Gutschick, 1985] and 35 years of service (visit in 2010, and testimonial of maintenance department) is very relevant. No new slips or slides have been observed since the rehabilitation works in the 70’s. Despite the fact that the lime-treated soil has been in constant direct contact with the waterflow, without protective cover, only minor erosion was observed along the waterline. The small holes in the surface of the banks were caused at the construction stage by the loss of “clay balls”, i.e. small lumps of clay that were not completely mixed due to the poor efficiency of the mixing devices used at this time. In addition to the achievement of the initial objective, which was the mechanical stabilization of the banks of the canal, the Bureau of Reclamation reported other advantages of the lime-treatment procedures: the cost savings during the repair works, and the very limited maintenance operations in the lime-treated sections in comparison with others (e.g. concrete-lined sections).
Origine : Fichiers produits par l'(les) auteur(s)
Loading...