AES-Marconi offers a number of techniques to determine the geological characteristics on site. Usually combinations of intrusive and non-intrusive methods are used.

Trial pits

Physical determination of site conditions to a depth of <4m.

Boreholes

Light cable percussion boreholes to determine site conditions to approx. 20m depth.

Seismic Refraction Survey:   

2-D acoustic imaging technique. Travel time calculations of sound wave “echoes” from source to receiver arrays. This provides a measurement of velocity which is a function of the density and elasticity of the medium through which it is travelling. This information can be correlated with available borehole data i.e. Soil, rock or boulder clay. The thickness, rippability and depth to the underlying strata can be calculated.

Resistivity Survey:   

2-D Electrical imaging technique. Electrical is current passed through the ground via electrodes. Variations identify concrete obstructions, isolated services crossing the site and changes in rock type or soil composition. Can also detect the likelihood of underground corrosion of the metal structure.

E.M. Inductive conductivity:

This parameter is the reciprocal of the earth’s resistivity. This is a rapid reconnaissance technique recording measurements to a depth of 5-6m with the EM31 or deeper using EM34. To map geological variations the data must be tied to surface geology or boreholes.

Ground Penetrating Radar:   

Is a fairly mobile technique in which high frequency (50-500Mhz) radar pulses are transmitted into the ground and corresponding reflections from the underlying strata are recorded.

Magnetic Survey:   

This type of survey utilises measurements of variations in the earth’s magnetic field caused by anomalous underlying magnetic material e.g. ferrous metals (old drums/pipe works), old mine shafts and workings. This method is particularly useful in areas underlain by igneous rock types.

Gravity Survey:   

Measurement of variations in the earth’s gravitational field. These variations are correlated with variations in thickness and density of sub-surface soils and rocks. A topographic survey is required in conjunction with the gravity survey making it costly. However, information can be gathered on overburden thickness, lateral variation in rock density, location of cavities and dissolution features. This makes gravity surveying ideal for testing heavy equipment bases or floors for weaknesses.