Clay squeezing

BGS's high pressure pore fluid extraction by squeezing facility is unique in the UK and one of a limited number of such facilities worldwide. It is designed to extract water from low permeability clays and mudstones for geochemical and isotope analysis, but has also been used successfully on peat, glacial till, marl, sandstone, chalk, diatomite and man-made backfill barrier materials.

Typically, the extracted porewaters extracted from drillcore at different depths are analysed in the BGS analytical geochemistry and isotopes laboratories for ions, stable and, sometimes, radioactive isotopes. The hydrochemical profiles produced from the data are used to model their movement through the clay or mudstone. Also, a number of water samples may be analysed from a single test squeeze, so-called sequential testing, which may show changes in the water chemistry that relate to clay/water interaction. The main constraints on water extraction are the stiffness and degree of saturation of the sample.

Anaerobic chamber
Squeezing equipment

The facility contains five sets of standard pore fluid extraction systems, designed by BGS scientists, each capable of providing a maximum stress of about 110 MPa. A new squeezing cell, nearing completion, will produce stresses up to 300 MPa. The test cells accommodate a sample 75 mm diameter and 100 mm long and the tests may be carried out under temperature controlled conditions. Tests take between a few hours to several weeks depending on sample characteristics and extraction requirements.

Oxygen sensitive samples may be prepared and tested in a bespoke anaerobic chamber that provides an atmosphere of about 2 ppm oxygen and contains a standard squeezing cell.

Over three hundred fifty samples have been tested for:

  • host rock and engineered backfill barrier for the radioactive waste industry in the UK and worldwide
  • aquifer protection
  • pollutant movement in clays
  • water movements in faults in clay and mudstone
  • soil/water and clay/water interaction studies


Please contact David Entwisle for further information