The progress of a landslide over time can damage pipelines and put them out of service. Three symmetrically disposed vibrating wires, chosen as the most at risk according to a preliminary engineering evaluation, were installed in several sections at a distance of 50/100 m. These sensors were very helpful, but could not fully cover the length of the pipeline and could only provide local measurements.
Aim of monitoring:
Three types of sensors were used: SMARTape, SMARTcord and Temperature Sensing Cable. The SMARTape sensor consists of a sensing optical fibre integrated into the 200 micrometers thick fibre-reinforced composite tape. Three parallel lines constituted of five segments of this sensor were installed over the whole length of the concerned area. The lengths of segments ranged from 71 m to 132 m and the position of the sensors, with respect to the pipeline axis, were at 0°, 120° and –120° approximately. The strain resolution of the SMARTape is 20 micro-strains, with a spatial resolution of 1.5 m and an acquisition range of 0.25m, which provides monitoring of average strains, average curvatures, and the deformed shape of the pipeline. The SMARTcord sensor consists of a sensing optical fibre integrated into the fibre of a reinforced plastic cord with a diameter of 6 millimetres. Below the pipeline, a single 500 meter long sensor was installed in the soil to monitor the strain changes. The resolution of the SMARTcord is the same as for SMARTape. These measurements have been correlated with the SMARTape measurements in order to evaluate the strain transfer from the soil to the pipeline. The Temperature Sensing Cable was installed onto the upper line (0°) of the pipeline in order to compensate the strain measurements for temperature. The temperature resolution of the sensor is 1°C with the same resolution and acquisition of the SMARTape. All the sensors are connected to a Central Measurement Point by means of extension optical cables and connection boxes. They are read from this point by using a single DiTeSt® reading unit. Since the landslide process is slow, the
measurements sessions are performed once a month. In case of an earthquake, a series of measurements are performed immediately after the event. All the measurements obtained with the DiTeSt® system will be correlated with the
measurements obtained with vibrating wires.
At present stage, all the sensors are successfully installed and the first measurement session was performed. A gas leakage simulation was performed with success using the temperature sensing cable.
|INSTALLATION PERIOD||TYPE OF SENSORS||NUMBER OF SENSORS|
|2003||DiTeSt / DiTemp , SOFO||23|