Dams: Canales Dam clay core

Case study: SOFO System

Monitoring of clay core using mutipoint extensometer

Project Description

Summary: Deformation monitoring and crack detection of Canales dyke clay core in depth between 60 and 110 m approximately using SOFO sensors enchained in multipoint extensometers.

Clients: IIC

Place: Granada (Spain)

Period: 2006 - N/A

Installation: IIC

Structure's short description: The Canales Dam is built on the Genil River, in Granada, Spain. Itwas constructed during period 1975?1989, and exploitation started in 1989. The dam is 156m tall and the crown is 340m long. The dam accumulation is used to produce electrical power, but it is also an important tourist attraction, notably for people who like fishing. The Canales Dam controls the river flow duringthe year, ensuring that there is always sufficient water to keep the river ?alive? even during the driest months of July and August. A view of the Canales Dam is given in Figure 1.

Aim of monitoring: The aim of the monitoring has been crack detection and deformation of the stiff-clay core of the dam. The zone where the cracks can occur was estimated to be between 60 and 110 m deep in the clay core. This whole length was equipped with a 50 m long multipoint extensometer with 10 measurement zones (10 enchained 5 m long deformation sensors). Preparation of the extensometer for the installation is shown in Figure 2. The sensors were installed in a 110 m deep and 30 degrees inclined borehole using a purpose developed installation procedure and special setup. A mass with wheels was attached to the low-stiffness cord and slipped into the borehole. While the mass was pulling the cord into the borehole, the extensometer was attached to the cord, so the cord was used as a guide for the extensometer. The installation procedure is shown schematically in Figure 3. After the placement of the extensometer in the desired position, the boreholewas alternatively filled with grout on the anchor pieces and sand over the active zone, in order not to perturb the strain field in the clay core and to guarantee good deformation transfer from the clay core to each deformation sensor making a part of the extensometer.

Number of sensor: 10

Main Results: The results of the monitoring are not disclosed.

Figure 2: A 50 m long multipoint extensometer ready for the installation in the borehole

Figure 3: Schema of the installation procedure

Bibliography:

Fibre Optic Methods for Structural Health Monitoring , Branko Glisic and Daniele Inaudi, Johh Wiley & Sons, Ltd, 2007