In situ stress measurements

Simple Flat Jack

The simple Flat Jack test gives an accurate measurement of the surficial uniaxial stress of rock  or concrete materials; that is, it gives a measure of the normal stress component acting in th direction perpendicular to the jack.

In an isotropic material, it gives also an estimate of the Young modulus.

Typical application scopes are: underground tunnels, excavation faces of quarries, ornamental stone underground quarries, concrete dam bodies, masonry walls of historical buildings, reinforced concrete retaining walls.

Depending on the size and expected stress regime of the structure, flat jacks of different shape and size can be used.

The equipment and experimental / interpretative procedures that we use are suitable to investigate a wide range of situations:

  • the cuts are made by means of a diamond saw; they are 4 mm thick, with depth varying from 120 to 260 mm;
  • the flat jack pressure can reach  20 MPa.

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