There are two types of Sub surface Investigation:
1)Geotechnical
2)Geophysical (IRC 123:2017)
-a) Engineering Geophysics ( for bridge & road) and (b) Applied Geophysics (for oil exploration & mineral exploration)
Geotechnical Sub surface Exploration :
1) Number of Boreholes :
Separate Exploration shall be done for retaining wall.
If width of bridge is more than 15m , number of borehole shall increase.
Box type Bridges : Multi cell Box Bridge
2) Extent of Boreholes :
where , foundation level is not available/decided, it may be taken 3m below lowest bed level.
To reduce the number of borehole, Geophysical investigation can be done before geotechnical investigation to know the number & location of borehole required.
