Descriptions
The gauge operates on the principle that a tensioned wire, when plucked, vibrates at its resonant frequency. The square of this frequency is proportional to the strain in the wire. Around the wire is a magnetic coil which when pulsed by a vibrating readout or data logger interface plucks the wire and measures the resultant resonant frequency of vibration.
A change in distance between the anchors caused by the crack opening or closing causes the inner free-sliding rod to move within the outer body which changes the tension on the spring and the vibrating wire thus altering the resonant frequency of the wire.
VWCM-4000 crack meters are installed by grouting, bolting, bonding or fixing expandable anchors to the structure to be monitored. The anchors incorporate ball joints where they are fixed to the gauge to accommodate any differential cross-axis movement and prevent the inner rod from binding within the outer casing.
Case Studies
Baish Dam
The Baish Dam is a gravity dam on Wadi Baish about 35km northeast of Baish in the Jizan Region of south-western Saudi Arabia.
The dam has many purposes including flood control, irrigation and groundwater recharge. The total reservoir capacity of the dam is 192 million m3.
The dam was constructed between 2003 and 2009 and at 106m high on completion, it was the tallest dam in Saudi Arabia. It is owned and operated by the Ministry of Water and Electricity.
Baish dam is one of six dams currently undergoing the change from a manual to a fully-automated monitoring system.
The original instrumentation equipment was installed during construction and was entirely manually-read. The Ministry made the decision to upgrade the instrumentation to a modern automatic system including full data logging of all instruments together with alarm trigger levels and data access via the Internet.
Baish Dam Case Study
Tishreen Dam
Completed in 1991 and situated within the Tigris-Euphrates basin, the 630MW hydro-electric Tishreen Dam has a storage capacity of 1.9 km3 and generates 1.6 billion kWh of electricity every year.
The dam is constructed with a chalk impervious core and seepage beneath it controlled by a Bentonite/cement cut-off wall. The complex comprises the main dam, a powerhouse constructed as a gravity dam and a small fuse plug.
The original instrumentation equipment was installed during construction and was entirely manually read.
Due to a serious dam failure in Syria the General Organisation for Euphrates Dam (GOED) decided to upgrade the instrumentation to a modern automatic system including full data logging of all instruments together with alarm trigger levels.
After consultation with the GOED Engineers, Geosense designed a new system installing new instruments side by side with the existing instrumentation and upgrading several areas to provide a fully integrated and automatic dam safety monitoring system.
All the new instruments were connected into a data logging system and provided real time visualisation within the dam control room.
Tishreen Dam Case Study
