Drilling Investigations

Geotechnical investigations are performed to obtain information on the physical properties of soil and rock around a site in order to design earthworks and foundations for proposed structures or for repair of distress to structures caused by subsurface conditions.

Fairbrother Geotechnical Engineering offer the following drilling investigation methods:

1. Trial Pits – This method uses hand or machine excavated trenches to determine groundwater levels. This method takes a disturbed sample.

2. DPSH Testing (Dynamic Probe Super Heavy) – This method consists of driving a sacrificial solid cone through the layers of soil. This test produces a N-value which is used to calculate the bearing pressures of soils. This method does not produce any soil samples.

3. Cone Penetration Test with Piezocones (CPTu) – This method is generally used in soft and silty environments below the water table and is commonly used when doing marine geotechnical investigations. The electric cone simultaneously records measurements for cone resistance and sleeve friction at a continuous rate of penetration. The measurements can also be taken for pore water pressure through a porous filter located in the probe (Dissipation Tests).

4. Diamond Core Drilling –  This method makes use of either a diamond impregnated or harmit bit on the end of a double or triple tube corebarrel in order to extract core samples. Core samples are retrieved by extracting the corebarrel from the hole, carefully removing the sample and packaging it in coreboxes for logging by the geologist. Fairbrother Geotechnical Engineering can offer a range of sizes, namely B-size, N-size, H-size and P-size.

The following in-situ tests can be performed within the borehole:

  • SPT Sampling – is carried out in accordance with the international reference test procedure laid down in the proceedings of the First International Symposium on Penetration Testing (ISOPT-1) 1988. The SPT tests are typically carried out in order to determine the N-value which is used for the determination of bearing capacities of soils. The advantage of a SPT sampler (Raymond Spoon) is that it is able to collect a disturbed sample. This sampler can be used in soils ranging from sand to very stiff clays.
  • Shelby Tube Sampling – is carried out in accordance with the American Society for Testing and Materials (ASTM) test method D1587. Shelby Sampling is best used in cohesive soils and clays and consists of pressing a stainless steel tube into the soils to produce an ”undisturbed” sample. This sample is most often used for tri-axial testing.
  • In-situ Shear Vane Sampling –  is carried out in accordance with the American Society for Testing and Materials (ASTM) test method D2573. Fairbrother Geotechnical Engineering makes use of the Geonor H-10 shear vane tester. Testing can be carried out up to a depth of 30m. A hand-held shear vane tester is also available as part of the service offered.
  • Water Pressure Testing – is carried in accordance with BS5930. The purpose of the testing is to determine the permeability of the rock.

Other in-situ testing offered includes:

  • Piston tube sampling
  • Core orientation
  • Plate load tests
  • Ground water monitoring
  • Environmental investigation with hollow stem augers

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