Vibrating Wire Concrete Stress Cell
The cell consists of a rectangular ﬂat jack formed from two plates of steel welded together around the periphery. The narrow gap between the plates is ﬁlled with hydraulic oil. A Vibrating Wire Pressure Transducer is connected to the cell by a short length of steel tubing, forming a closed hydraulic system.
- Uses proven Vibrating Wire technology
- Measures stress on and within linings of underground excavations
- Monitors the stress distribution within rock
- Compensation tube oﬀsets the eﬀects of concrete hydration shrinkage, restoring cell contact pressure
- Internal thermistor monitors temperature variations
- Stainless steel cell construction
- Over 30 years of expertise in the design and manufacture of Vibrating Wire instrument technology
- Accurate, repeatable readings over long cable lengths
- Long working life, longterm stability and reliability
- Suitable for remote reading and data logging
- Over-voltage surge arrestor protects against electrical damage
- Connecting cable is strong, armoured and ﬂexible
Both cell and transducer are embedded in the medium to be monitored. As the concrete or shotcrete cures, the cell expands due to the rise in temperature.
Upon cooling, a slight gap forms between the cell and the concrete. The compensating tube allows adjustment of initial cell volume to offset concrete shrinkage. This forces extra oil into the cell, thereby expanding it to establish firm contact with the cooled concrete.
An armoured, screened cable connects the transducer to a terminal unit, a portable readout unit or data logger.
The Concrete Vibrating Wire Stress cell measures radial and tangential stresses in shotcrete, concrete and rock, usually in tunnel linings. Cells can also monitor stress changes in the rock walls of underground works. In this case, slots are ﬁrst machined by diamond wheel sawing, or line drilling, and the cell is embedded in cement mortar within the slot.
Typical monitoring applications include:
- Tunnel linings
- Mass concrete