The difficulties associated with the calculation of a factor of safety aiming at assessing stability conditions of slopes in clay are well known. More than thirty years of experience in the Province of Quebec have shown an important variability in the geotechnical ...

Terrestrial photogrammetry was used to monitor movements of previously driven piles during the installation of 116 concrete piles in sensitive marine clay. The technique and equipment used are described and the sources of error discussed.

The results reported are of an investigation of a group of thirteen 30cm diameter precast concrete piles diven through 18m of sensitive marine clay followed by 3m of silt and sand and 4m of very dense silt to end bearing in glacial till.