03-12-2012, 06:22 PM
BRIDGE SITE INVESTIGATION
BRIDGE Site Investigation.doc (Size: 246.5 KB / Downloads: 56)
Introduction
Site Investigation is the gathering of information about the proposed location of the highway. The reason for this can be twofold. Firstly to assist in the location of the highway and secondly to ascertain ground conditions. Site investigation in the United Kingdom is concerned solely with the ground conditions. Avoidance of towns, villages, historic buildings, areas of outstanding natural beauty, rail and river crossings and land severance all must be considered. Only in extreme cases such as marshlands or landslip areas will ground conditions grossly affect the cost of construction.
Desk Study
The desk study is work taken up prior to commencing the work on site and the Ground Investigation. It should always be the first stage of the Site Investigation and is used to plan the Ground Investigation. The work involves researching the site to gain as much information as possible, both geological and historical.
• A good starting point is to use OS maps. These allow the site to pinpointed and an accurate grid reference to be obtained. This permits much more accurate references on the geological maps used later. In addition to present maps, historical maps are used. These are stored in the British museum and allow much information to be obtained such as former uses of the site; concealed mine workings; infilled ponds; old clay, gravel and sand pits; disused quarries; changes in topography and drainage; changes in stream and river courses; coastal erosion; changes in potential landslide areas.
• Geological Maps and memoirs are probably the most important source of information as these give an excellent indication of the sort of ground conditions likely to be encountered.
Ground Investigation
Ground investigation is taken to be that other than the information available from the walk over survey as discussed previously.
There are two principal methods of investigating the ground conditions, trial pits and boreholes. In addition, the reader should be aware of geophysical techniques such as seismic surveys, which are not discussed here.