Borehole Geophysics

Borehole geophysics takes advantage of using regular geophysical techniques at depth down a borehole. The techniques operate in the same manner as they would on the surface, with the advantage of providing high resolution data at depth. Borehole seismic surveys are used to obtain in situ properties of soil and rock strata and are often used as part of a comprehensive geotechnical investigation .
 

Applications

  • Dynamic rock moduli
  • Foundation design for dynamic (vibratory) loads
  • Rock velocity and quality assessment
  • Geologic layering
  • Pile / foundation geometry and depth

Borehole Geophysics Techniques

  • Downhole Seismic Testing (DST)
  • An external seismic energy source, such as a hammer striking a plate, is applied adjacent to the borehole on the ground surface. Clamping geophones in borehole measure the one-way travel time of the initial arrival of the generated seismic energy, and the distribution of compression and the shear wave velocity as a function of depth in the vicinity of the borehole. Our tests conform to ASTM standards.
     
  • Crosshole Seismics
  • The crosshole test measures the one-way travel times of seismic waves emanating from an external source placed in a source borehole to geophones placed in a receiver hole or holes. The results provide velocity information and dynamic properties with depth, which are useful for civil and environmental engineering purposes (velocity anomalies may represent voids of faults between the boreholes). Requires 2 or more boreholes.
  • Parallel Seismic Testing (PST)
  • Many UK cities have been built over numerous times. The ground is often full of old foundations. Therefore the re-use of old piles is becoming increasingly necessary. As part of the investigation of old piles (or sheet piles) to test load bearing capacity, parallel borehole geophysics can be used successfully to characterise the geometry of the piled foundation. A borehole is also required. RSK can provide the driling services for this.
     
  • Borehole Ground Penetrating Radar - use of a single integrated borehole antenna down a borehole to locate buried foundations or map fracture zones.
     
  • Borehole Magnetics - use of downhole magnetometry to detect ferrous material such as reinforced piles, sheet piling, or UXO during the drilling of boreholes
     
In this example downhole GPR and magnetic techniques were used to investigate the depth of the pile to a high degree of accuracy.