Dear reader, scope of geotechnical investigation is defined by registered professional involved in foundation design. They also define types of boring/sounding and numbers too, sampling equipment, drilling equipment, test program in laboratory and equipment for in-situ testing, if required.
In case of deep foundation, geotechnical investigation is more important, as cost involvement in drilling and construction of foundation is much higher than shallow foundation and right method of drilling and selection of foundation type are mostly dependent on proper investigation.
Unless adequate data are available depending on which foundation design & installation can be performed, IBC recommended to investigate including following:
a. Recommendation for types of deep foundation and also installed capacities.
b. Recommendation for spacing of foundation element (spacing means distance measured center to center).
c. Driving criteria
d. Procedures of installation
e. Procedures of inspection and reporting of field performance.
f. These are essential to verify installed capacity of foundation element.
g. Requirements of load testing.
h. Suitability of foundation materials considering ambient environment (durability perspective).
i. Designation of the bearing strata
j. Recommendation for defining group capacity of deep foundation elements generally reduction is experienced in group action.
Code also provided for requirements for doubtful characteristics in rock structure. When subsoil profile at project site shows variations in characteristics, to avoid confusion additional boring should made up to a depth equal or greater than 10 ft below foundation level. This provides assurance of soundness of foundation bed & bearing capacity as well.