This Lecture emphasizes and illustrates the importance of predictions to the practice of civil engineering. Predictions are examined and classified, and comparisons are made between predicted performance and measured performance for eight constructed facilities. Although there are many techniques for predicting internal stresses, deformations and stability for a geotechnical facility, the application of these techniques haslimitations. The major limitations are the difficulty of determining fully and accurately the field situation and the mechanisms which will occur, and the selection of soil parameters to use with prediction methods. The greatest need appears to be for devices and techniques to determine, in situ and continuously with depth, fundamental subsoil properties, such as stress, strength and stress-strain modulus. Cette communication insiste sur l'importance des prévisions dans la pratique du Génie Civil, et donne des exemples de cette importance. On examine et on classifie divers types de prévision. On compare les comportements prévus aux comportements observés lors de la construction de huit installations. Bien qu'il y ait de nombreuses techniques de prévision des contraintes, des déformations et de la stabilité d'une installation géotechnique, il y a des limites à l'utilisation de ces techniques. Les principales limitations sont: difficulté de déterminer complètement et exactement les conditions en place et les mécanismes des phénomènes qui surviendront, et de sélectiormer les paramètres du sol nécessaires à la mise en œuvre de ces méthodes de prévision. La plus grande nécessite à l'heure actuelle semble être dans la conception de méthodes et de techniques de détermination des propriétés fondamentales du sous-sol, par exemple: contrainte, résistance, module contrainte-déformation, en place, et leurs variations continues avec la profondeur.

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This paper aims to demystify the use of risk assessment as a decision management tool and present a methodology that places quantitative risk assessment within reach of every geotechnical engineer, even for routine engineering assignments. In particular, we propose using quantification of expert judgment ͑i.e., subjective probabilities͒ as a practical alternative for determining probability of slope failure. The writers present a semiempirical relationship between factor of safety and annual probability of failure that permits estimation of slope failure probabilities with relatively modest effort. The case study for a tailings dam shows that risk assessment based on quantification of expert judgment provides a framework to arrive at rational management and engineering decisions related to dam safety and other geotechnical problems. Using the semiempirical relationship presented here, practicing engineers can use this helpful tool by applying their current skills.

The permeability of a soil is one of its most fundamental and important properties. It enters into nearly all seepage, settlement, and stability problems confronting the soil engineer. The amount of leakage through and under dams, the rate at which a building settles, and the ate at which the strength of a deposit increases after it has been subjected to a consolidating pressure are typical of the many problems in which the permeability of a soil can be a critical factor. The importance of evaluating the permeability of a pervious soil has been long recognized and test techniques for measuring it have been well developed and are widely used. The permeability of fine-grained soils, however, has not received extensive study. Soils with permeabilities of less than 1 /t per sec are often considered “impervious” and are not subjected to permeability testing. Soil permeabilities less than 1 y. per sec are becoming increasingly important to soil technologists from both practical and theoretical considerations. More use is being made of “impervious” soil to line canals and reservoirs and to construct cores for earth dams. Research workers are studying the permeability of finegrained soils to learn more of the nature of particle surfaces and the thickness of adsorbed water (7). A look at some of the factors influencing the permeability of fine-grained soils, therefore, is timely.

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