Geotechnical soils properties

Shrinkit, automated shrinkage limit
GDS Stress path Triaxial equipment

The Geotechnical Soil Laboratories are a comprehensive testing facility that includes both standard (e.g. BS1377) and specialised test equipment and forms part of the BGS laboratory research facilities. In-house designed equipment simplifies and improves standard commercially available apparatus.

Soil testing facilities include:

  • GDS stress-path triaxial PC: computer-controlled, temperature controlled testing (50mm—100 mm), local strain, mid-plain pore pressure measurement, CU, CD, CIU, SHANSEP, permeability, saturation, consolidation, cyclic loading, creep testing on undisturbed, compacted, or remoulded specimens
  • triaxial: standard PC computer-logged testing (35—100 mm) UU, CU, CD, CIU; compressed-air system with low-friction cell
  • consolidation: 1-dimensional, PC computer-logged oedometer testing (50mm—100 mm) with digital strain gauges, collapse tests, double oedometer tests, undisturbed, compacted, remoulded specimens. Stresses to 2.5 MPa (75 mm)
  • high-pressure consolidation: 1-dimensional, PC computer-logged Denison oedometer (50—100 mm) with load cell and digital strain gauge. Stress to 34M Pa (75 mm)
  • shear box: PC computer-logged testing (60 — 100 mm), on undisturbed, shear plane, or remoulded specimens. Cut-plane and multi-reversal tests.
  • ring shear: PC computer-logged testing (Bromhead), residual strength, on remoulded specimens (200g )
  • shrinkage limit (SHRiNKIT): 1D swelling pressure to BS1377 (1990) and 3D swelling strain to ISRM (1981)
  • index testing to BS 1377 (1990): Atterberg limits, shrinkage limit, linear shrinkage, particle size, specific gravity, water content

Specialist in-house developed equipment - shrinkage limit test

3D swell pressure equipment

The shrinkage limit test is very rarely carried out in the UK partly because the British Standard test methods use mercury, but the shrinkage limit is an important parameter when investigating the volume change of clay and mudstone. The shrinkage limit apparatus, developed at BGS, does not use mercury.

Specimen dimensions are measured with a laser rangefinder for the calculation of volume change. Weight is measured simultaneously from which water content is calculated. Shrinkage limit is calculated from the plot of water content versus volume. A prototype was first developed in 1994 and an automated shrinkage limit test and an automated version, SHRINKiT, is nearing completion.

3D swell strain

The 3D swell strain apparatus was developed at BGS by adapting a design taken from the International Society for Rock Mechanics (ISRM). The apparatus measures the orthogonal strains of a cube specimen of clay or mudstone immersed in water and subject to swelling. From the data the overall volumetric strain is calculated and, if required, the strain anisotropy. The BGS design is simple in concept and, whilst fulfilling the criteria of ISRM specification, does not require leak-proof seals for the strain gauges armatures illustrated in the ISRM method.

BGS 1D swelling pressure apparatus

1d swell pressure equipment

BGS's automated 1D swelling pressure apparatus was developed by combining a small triaxial load frame with an oedometer consolidation cell. The swelling of the flooded specimen soil is sensed by a transducer and an electronic feedback system initiates a vertical force sufficient to counteract the swelling strain is applied via the load frame motor. The load is logged and the result are summarised in a plot of swelling pressure versus time. The test fulfils the specifications of the British Standards swelling pressure test. Clay-rich formations are capable of exerting considerable stresses on foundations and services when exposed to an increase in water content from the desiccated state. The 1D swelling pressure test enables the susceptibility of these formations to be determined.

Contact

Please contact David Entwisle for further information