Aim of monitoring is to receive data to design parameters of bolting system such as bolts capacity, length, pattern and if necessary supplementary cable bolts.
Basic instrument is strain gauge bolt and extensometer.
For routine visual control telltales are used.

Tell-tale are used for routine, permanent measurement of strata movement throughout bolted roadways. Instrument is easy to install.
There can be single, dual and multi height telltales. Available is also telltale with water diverting system. Where when and how to install instruments is determined by authorized expert.

One high tell-tale to measure high or low displacement

1 – Wire ø1,5÷ ø 2 -L
2 – Spring ø20
3 – Sleeve
4 – Color indicator ( yellow)
5 – Low displacement indicator (white)


One height tell-tale
To low and high displacement measurement
  Water diverting dual high tell-tale


Strain gauge bolt

Strain gauge bolt is used to measure the distribution of bolt loads for design purposes. Computer software gives graph of working forces, their magnitude and range. Data obtained by software determine:

- axial load and strains;
- high strain zones;
- bending loads.

On customer requirement strain gauge bolts can differ in length, quantity and location of tensometers.

Sonic probe


Flexible sonic probe extensometer allows detailed measurement of ground movement in time (roof, ribs, floor).
Consists of anchors installed in up to 7.5m long borehole, flexible probe and readout unit. Up to 20 points can be measured in one borehole. Extensometer is used to measure displacement and horizons of displacement of strata, height of failure of roof softening and shows trends of strata deformation.

Anchors for sonic probe