In situ stress measurements

Overcoring Doorstopper

The Doorstopper tests measure the Bidimensional Stress Tensor  in a point of a rock or concrete.

The Doorstopper tests is suitable for punctual shallow depth stress measurements (0-10 m).

The ability to use a “local approach” for the measurement of the elastic modulus, makes this test particulary reliable and accurate.

It is possible to study the trend of the stress along the thickness of a tunnel lining or reatining wall , executing stress tests at several depth in the same borehole.

Our Doorstopper cells are equpped with 4 strain gages rosette and temperature sensor, to check the statististical quality of the measurement and to perform the compensation of thremal variations effects.

Typical operating fields are:

  • underground structures, niches, adit walls, tunnels, room-pillar mining
  • concrete lining of tunnels
  • concrete beams, pillars, floor slabs
  • concrete dams from adits and external surfaces

The know how, the equipment and the experimental/interpretation procedures we currently use concern a large field of applications:

  • test depth up to 10 m (for best results we suggest a max depth of 5 m)
  • drillings in any direction (downwards depth is limited to about 1.5 m because of the need to extrac water and perfectly dry the bottom of the hole for gluing the measuring cell)
  • borehole diameter 76 mm
  • sample diameter 61 mm
  • temperature compensating measuring head and readout unit
  • ithe use of a 4 strain gauges rosette, positioned at 45° the one from the other, allows a statistical analysis of the test results.  

Drilling with electric coring machine is at our charge: the perforation is a part of the test that we provide.

The service includes the radial compression test and the eventual thermal variation test on the sample instrumented with the Doorstopper cell.

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