Soil mechanics

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. This allows research to be undertaken alongside populating BGS datasets with parameters key to the understanding of soil behaviour. The primary focus of research is performing novel tests to obtain data that underpin the national datasets of the BGS on the geotechnical properties of UK soils. Staff experience includes soil and rock mechanics, engineering geology, biological sciences, petroleum engineering, hydrogeology, and numerical modelling.

Data from these studies are used in the development of robust models that describe the geotechnical properties of soils and feed into the national databases on geotechnical properties of soils.

The testing facilities at BGS underwent a comprehensive refurbishment and upgrade in early 2011. This state-of-the-art facility allows testing of soils in a number of ways, including:

  • GDS Stress-Path Triaxial: PC Computer-controlled and logged strength and deformability testing, local strain (Hall effect) and mid-plane pore pressure measurement, CU, CD, CIU, SHANSEP, permeability, saturation, consolidation, cyclic loading, creep testing on undisturbed, compacted, or remoulded specimens (50, 70 and 100 mm).
  • WF Standard Triaxial: PC computer-logged strength and deformability testing UU, CU, CD, CIU. Compressed-air pressure system with low-friction cell; testing on undisturbed, compacted, or remoulded specimens (35, 50, 70 and 100 mm).
  • Consolidation: 1-dimensional.PC computer-logged oedometer testing (50mm-100 mm) with digital logging; collapse tests, double oedometer tests; undisturbed, compacted, remoulded specimens. Stresses to 2.5 MPa (75mm). Rowe-cells for consolidation with pore-pressure control (75 and 250 mm) to BS1377 (1990).
  • Shear Box: PC computer-logged shear strength testing, on undisturbed, shear plane, or remoulded specimens and cut-plane tests (60 and 100 mm).
  • Ring Shear: PC computer-logged testing (Bromhead), residual shear strength, on remoulded specimens (200 g).
  • Shrinkage Limit (SHRINKiT): PC controlled and logged (non-standard) test for shrinkage Limit and volumetric shrinkage strain, developed at BGS, on undisturbed, compacted or remoulded specimens (100 mm).
  • 1D Swelling Pressure and 1D Swelling Strain to BS1377 (1990) on undisturbed or remoulded specimens (50 and 100 mm)
  • 3D Swelling Strain to ISRM (1981) on undisturbed or remoulded specimens (50 and 100mm).
  • Index Testing to BS 1377 (1990): Particle size (Sedigraph/sieving), Atterberg Limits, Shrinkage Limit (SHRINKiT), Linear Shrinkage, Specific Gravity, Water content.
  • Erodibility: Pin-hole test for dispersibility and& erosion to ASTM (D4647).
  • Permeability: Constant Head, Falling Head to BS1377 (1990) on undisturbed or remoulded specimens.
  • Pore water extraction by squeezing: High pressure pore fluid extraction of pore 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.
  • Soil suction: Measurement of pF suction curve, pore volume, field capacity of undisturbed or remoulded clay specimens (50 mm).

Parameters

Apparatus and experimental systems are customised to meet specific requirements of a project. Experiments are performed under simulated stresses, pore pressure and chemical conditions (including anaerobic conditions) using triaxial, shear box, ring-shear and pore-water extraction apparatus. All of our facilities are carefully temperature controlled so as to maintain constant temperature conditions (normally 20°C). With careful attention to experimental design, choice of instrumentation, calibration and regulation of testing conditions, BGS is able to quantify key parameters including:

  • saturation and consolidation parameters
  • intrinsic permeability, dispersibility
  • shear strength (total and effective)
  • shrinkage index and volumetric shrinkage strain; linear shrinkage
  • 1D and 3D swelling strain; 1D swelling pressure
  • particle size distribution
  • compressibility (total and effective)
  • Atterberg limits (liquid limit, plastic limit, shrinkage limit)
  • pore fluid geochemistry
  • soil suction behaviour

Soil samples are often subject to complex stress paths simulating realistic engineering or environmental conditions. As such, experimental methodologies are tailored to the needs of the specific stakeholder and where appropriate are performed over prolonged periods to yield information on the temporal evolution of parameters and the stability of geological systems.

Applications

Our research outputs are used widely within the BGS and feed into many of the models produced by the BGS. Our customers are British, European and international agencies, regulatory bodies, private-sector companies and consultancies working in:

  • engineering geology
  • hallow geohazards
  • foundation engineering
  • embankment/dam engineering
  • radioactive waste disposal
  • aquifer protection
  • pollutant movement in clays
  • water movement in faults in clay and mudstone
  • soil/water and clay/water interaction studies

Examples of experimental studies include:

  • frozen soil consolidation (proxy for methane hydrates)
  • measurement of shear plane strength in landslides

Recent publications (2000 - 2011):

Hobbs, P R N, Northmore, K J , Jones, L D , and Entwisle, D C. 2000. Shrinkage behaviour of some tropical clays. Unsaturated Soils for Asia pp 675—680. Rahardjo, Toll and Leong (eds.) (Balkaema, Rotterdam, Netherlands.)

Hobbs, P R N and Jones, L D. 2000. Clay shrinkage research at the British Geological Survey. Slips, Shrinks, and Swells — Clay Minerals and Geotechnics. Joint Meeting of the Clay Minerals Group of the Mineralogical Society and Engineering Group of the Geological Society. (Keyworth, Nottingham, UK. December 2000.)

Brew, D S, Balson, P S, Pearson, S, Hobbs, P, Williams, R, Robinson, D, Moses, C, and Walkden, M. 2004. The implications of cohesive shore platform erosion for coastal management. Littoral 2004, 20—22 September. (Aberdeen, Scotland, UK.)

Lovell M A, Camps, A, Howard, K, Williams, F, Jackson, P, Long, D, Rochelle, C, Gunn, D, Rees, J, Bateman, K, Noy, D, Hobbs, P and Nelder, M. 2005. Gas Hydrates, Formation Evaluation in Tight Gas Reservoirs. London Petrophysical Society, 21 June 2005. (Geol. Soc. London, UK.)

Hobbs, P R N amd Jones, L D. 2006. Shrink rethink. Ground Engineering magazine, publ: Emap Construct, January 2006, pp 24-25.

Brew, D S, Balson, P S, Hobbs, P, Charman, R, Moses, C, and Williams, R. 2006. Erosion of cohesive shore platforms: case studies from two UK coastal sites. EOS Trans. AGU, 87(52), Fall Meeting. Suppl. Abstract, 11—15 Dec 2006. (San Francisco, USA.)

Hart, A B, Ruse, M E, Hobbs, P R N, Efthymiou and M, Khadjicharalambous, K. 2010. Landslide activity in Paphos District, Cyprus. IAEG 2010.

Northmore, K J, Entwisle, D C Reeves H J , Hobbs, P R N and Culshaw, MG. 2011. The relevance of lithostratigraphy in the assessment and investigation of engineering ground conditions in UK mudstones. Proceedings of the XV European Conference on Soil Mechanics and Geotechnical Engineering (ECSMGE 2011), 12—15 September 2011. (Athens, Greece.)

Contact

Please contact David Entwisle for more information