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The cliff-section between Happisburgh and Weybourne, on the north Norfolk coast, provides one of the most representative exposures of glacial sediments in the British Isles and this sequence is now generally accepted as being the product of the Lowestoft Stage. The Cromer Till, as defined in the Geological Survey Memoir, forms the lowermost part of the glacial sequence and is composed of two tills separated by a layer of laminated silts and clays; these units may be termed as follows:Upper Cromer Till'] Laminated Beds ~-Cromer Till Lower Cromer Till J The Lower Cromer Till is a dense, stiff, fissured grey or dark grey sandy boulder clay which lies on the Cromer Forest Bed, the Leda Myalis Beds and the associated deposits. The Laminated Beds rest on the hummocky, locally faulted, surface of the till. At Happisburgh two divisions of laminated sediments have been recognized, the upper unit being finer-grained and having a more evenly-bedded structure. The Upper Cromer Till is a dense, fissured grey-blue sandy boulder clay containing a significant proportion of chalk pebbles.The sequence within the Cromer Till represents the three phases of an ice advance followed by retreat associated with the development of a glacial lake followed by a re-advance. The coarse-grained lower unit of the Laminated Beds at Happisburgh is not present at Cromer and this may reflect the early history of the glacial lake while ice was still present in the vicinity of Cromer. The upper unit of the Happisburgh sequence is coarser than that at Cromer and this condition is reflected by variations in liquid limit measured on scrape samples. A wide range of sedimentary structures, which have been formed by traction and fall-out processes associated with turbulent suspension, occur within the Laminated Beds. The associations of structures present are the product of specific bed forms and can be related to flow r~gimes. Many beds are the result of rapid deposition from turbidity currents.All the sediments studied have been heavily over-consolidated and are fissured to a greater or lesser degree. Disturbed, block and scrape samples were collected in the field and soil mechanics classification, strength and consolidation tests carried out. Particular attention has been given to different methods of assessment of the effects of pre-consolidation load and the variation in properties of the Laminated Beds with orientation. The influence of the pre-consolidation load has been examined by a field study of fissuring in the Laminated Beds based upon the dissection of excavated blocks, undrained and drained shearbox testing of samples taken from the Lower Cromer Till and consolidation testing of Q.

Synopsis The investigation of foundation conditions is an essential preliminary to the design of any dam. However, the results of such exploratory works are rarely published. In consequence, comparatively few systematic methods of describing and interpreting rock for engineering purposes have been developed and this has contributed to the problem of predicting foundation conditions. Various techniques of recording information from borehole cores, excavations and natural outcrops are reviewed. This introduction is associated with a discussion of the type of geological information which is required for engineering purposes. The geological conditions at three dams—Roseires (Sudan), Kariba (Rhodesia), and Latiyan (Iran)— are described with particular relation to the manner in which the exploratory work was carried out. At the Roseires and Latiyan dams, rock grade classifications were developed in order to provide an engineering assessment of rock quality in situ. La recherche sur les conditions des fondations est un préliminaire essentiel à la conception de tout barrage. Pourtant, les résultats de tels travaux exploratoires sont rarement publiés. Par conséquent, comparativement peu de méthodes systématiques de description et d'interprétation de la roche à des fins de construction, ont été élaborées, et cela a contribué au problème de prédiction des conditions des fondations. Diverse techniques d'enregistrement des renseignements sur les noyaux de forage, les excavations et les affleurements naturels sont passées en revue. Cette introduction est associée avec une discussion du type de renseignement géologique qu'il faut obtenir à desfins de construction. Les conditions géologiques à trois barrages—Roseires (Soudan), Kariba (Rhodésie) et Latiyan (Iran)—sont décrites avec leur rapport particulier sur la manière avec laquelle les travaux exploratoires ont été exécutés. Aux barrages de Roseires et de Latiyan les classements de roche par qualité ont été développés de manière à fournir une évaluation technique de la qualité de la roche in situ.