Properties of the London Clay at the Ashford Common Shaft: in-Situ and Undrained Strength Tests*

Summary During the construction of the Ashford Common shaft by the Metropolitan Water Board undisturbed block specimens were obtained from six levels at depths varying from 30 to 140 ft in the London Clay. At the same levels a series of plate loading and penetrometer tests were carried out in the shaft. In a special boring alongside the shaft a series of Dutch cone penetrometer tests were made and some special samples taken. The Metropolitan Water Board also made available the results on conventional borehole samples from eight borings in the neighbourhood of the shaft. In this Paper the results of an extensive series of quick undrained compression tests on the block specimens are presented and the undrained shear strength–depth relationships obtained from the several types of laboratory and in-situ tests compared. These vary considerably and the differences are discussed in terms of the fissured nature of the clay and the effects of excavation. The penetrometer tests cannot bc evaluated satisfactorily. A...