North Sea Foundation investigation techniques

Abstract

Abstract Foundation investigations for large platforms in the harsh North Sea environment are costly, consequently, investigations are undertaken in progressive stages so that structural concepts can be developed with due regard to soil conditions. The shallow geological environment surrounding a platform site is explored by high resolution geophysical techniques, and interpretation of the seismic profiling data can be improved when results from one or two soil borings are available for correlating strati‐graphic boundaries. Geotechnical properties of soils and rocks to penetrations of 150 m are determined from laboratory testing of recovered samples and from in situ testing. Deep penetration push sampling and cone penetrometer testing have been conducted with the recently developed Stingray system. Sampling technique has no marked effect upon the shear strength of heavily overconsolidated North Sea clays but wireline percussion sampling reduced soil stiffness by 25 to 50 percent. Continuous in situ cone ...