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  • Why should I spend money on a Ground Investigation for my proposed development?

    The risk of unknown ground conditions is a major cause of cost over runs on construction projects.  A poor knowledge of ground conditions can not only lead to delays in completion but it can result in significant revisions to the proposed design.  A comprehensive ground investigation should provide sufficient information to inform the Contractor and provide the most cost effective price for construction.

  • What elements should I include in my Ground Investigation package?

    The exact content of the Ground Investigation package will depend on a host of items such as the size of the development, the number of structures, the types of structures, the footprint of the infrastructure (roads, underground utilities etc), the type of landforms present (flat field, "brownfield" site, slopes, cliffs, etc.), habitat (agricultural lands, marsh, peat, rock, etc.).

    As a rule of thumb it is important to determine ground information (soil and rock types, layer thicknesses, level of water table and strength data) for the site of each structure which requires a foundation.  The ideal separation between the points for which we have information will depend on the variability of ground conditions, the vulnerability of the intervening infrastructure and ancillary structures and any specific design differences.

     Normally exploratory holes are used to gather this information, either by using boreholes or by assessment of excavations (trial pitting).  The depth of such intrusive works will depend on size and significance of the foundations structures required and the loads to be imposed on them.

    Where the development site is significant in size geophysical methods can be employed to extrapolate the information gained by the intrusive geotechnical investigations. Alternatively, where the land is sensitive and the project would benefit from minimal intrusion geophysical techniques can be used on their own to collect the relevant information.  The choice of geophysical technique will depend on the type of ground information required.

    Supplementary forms of ground investigation such as in-situ testing, gas and water monitoring etc are very site specific and their will depend on preliminary results from the ground investigation campaign.

  • What can Geophysical Techniques be used for?

    Geophysics can assist in understanding the sub-surface in the following ways:-

    Mapping of the thickness of soils overlying rock and determining their relevant strength.

    Identifying of buried underground utilities and culverts.

    Locating and mapping of anomalies (e.g. buried mineshafts, cavities, archaeological features, metal objects).

    Non-destructive assessment of infrastructure, such as roads to determine as-built construction detail.

  • What Geophysical Techniques are available and which one should I use?

    The following list indicates the most common geophysical survey methods and their relevance to geotechnical engineering:-

    • Seismic Refraction Survey (Mapping of soil thickness, rock depth, soil competence and rock integrity)
    • Seismic Reflection Survey (Mapping of soil and rock layer interfaces)
    • MASW Seismic Survey (Mapping of soil thickness, rock depth, determination of modulii of Elasticity of soils and rock)
    • 1D Electrical Resistivity (Determination of subsurface variation in ground resistance with depth - used in grounding studies for structures)
    • 2D Electrical Resistivity Imaging (Mapping of soil thickness, rock depth, water table, faults, fractures and cavities)
    • Electromagnetic Survey (2D mapping of soil conductivity - used to determine location of shallow cavities (<6m), buried culverts, brick-lined mineshafts, buried foundations, graves, archaeological features and other buried artifacts)
    • Ground Penetrating Radar (Mapping of underground utilities, assessment of concrete structures, as-built determination of road construction detail and location of sub-surface anomalies)
  • What type of Land Contamination do you normally find on sites?

    The type of contamination present of sites varies greatly.  It can generally be split into three different classes, as follows:-

    1. Naturally occurring contamination such as methane gas or radon gas, that require the installation of barriers or other geotechnical solution to manage.
    2. Contamination from previous or existing industrial usage.  This can be anything from heavy metal contamination (e.g. Lead, copper, zinc etc.) to organic compounds produced in industrial processes.
    3. Contamination arising out of an incident or spill.  The majority of these are hydrocarbon related and originate from heating oils, diesel or petrol fuels entering the soils.