Sensitive Clay Deposits Research Articles

Geological and geomorphological controls of landslides in Ottawa Valley, Ontario

Seventeen maps at a scale of 1:50 000 showing the distribution of sensitive clay deposits and associated landslides in Ottawa Valley have been compiled. The following map-units have been used: rock, till, and gravel older than the clay; sensitive clay associated with the Champlain Sea; sand and gravel overlying clay; and organic deposits overlying clay. Also shown on the maps are landslides that could be identified on aerial photographs and a line representing the maximum limit of marine transgression.From data collected from several test borings, the sensitive clay has been divided into four distinct stratigraphic units. Visual identification criteria have been developed and average index properties are given. These results show that ‘Leda’ clay is not a clay with unique properties, but displays considerable variability. The four stratigraphic units have been related to the history of transgression and regression of the Champlain Sea. Many of the large landslides occurred early in the history of the area during a period when a considerably larger Ottawa River cut several broad channels through the sediment.By combining the surficial geology and the stratigraphic profiles obtained by drilling it has been possible to classify sensitive clay slopes into two geologic settings. One setting consists of clay at the surface and the other has a thin layer of fine sand overlying the sensitive clay. The majority of the large retrogressive slides have occurred in slopes of the latter setting. A comparison study is being carried out on the two settings and some preliminary results are presented here.

Risk analysis of slopes and its application to slopes in Canadian sensitive clays

The problem of defining better measures of the safety of slopes has been approached from a probabilistic point of view. Using a mechanistic description of stability (the method of slices), a first order probability analysis was implemented in order to allow for a rational evaluation of the different sources of uncertainty involved. A preliminary sensitivity analysis shows that the uncertainties in the cohesion parameter, the pore-pressure and the method of analysis are the relevant ones in governing the resulting uncertainty in the slope safety. The method developed serves, however, to predict the probability of failure of a given slope once the different types of uncertainty can be quantified. The analysis of an actual case of slope failure in sensitive clay deposits leads to a number of graphs showing the variation of risk with (a) level of uncertainty in the involved parameters, and (b) the degree of correlation of soil properties. A relationship between mean safety factor and probability of failure is then developed for the conditions likely to prevail in Champlain Sea deposits. This relationship compares well with previous published results based only on empirical observations. Le problème de la détermination de meilleures mesures pour la sécurité des pentes a été approché au point de vue probabilité. En utilisant une description mécanique de stabilité (la méthode des tranches), une première règle d'analyse de probabilité fut exécutée afin de permettre une évaluation rationnelle des différentes sources d'erreurs en cause. Une analyse préliminaire de sensibilité montre que les erreurs relatives au paramètre de cohésion, à la pression interstitielle et à la méthode d'analyse, sont les plus importantes en ce qui concerne les erreurs finales dans la securité des pentes. La méthode développée sert néanmoins, à prédire la probabilité de rupture d'une pente donnée, une fois que les différents types d'erreurs peuvent être quantifiés. L'analyse d'un cas réel d'une rupture de pente dans des dépôts d'argile sensible au remaniement, conduit à un nombre de graphiques montrant la variation du risque avec: (a) les erreurs dans les paramètres en jeu, et (b) le degré de corrélation des propriétés du sol. Une relation entre un facteur de sécurité moyen et une probabilité de rupture est alors établie pour les conditions probablement dominantes dans les dépôts de mer de Champlain. Cette relation correspond bien aux résultats publiés antérieurement et basés seulement sur des observations empiriques.

The Analysis of Two Slope Failures in Cemented Champlain Clays

Detailed investigations have been made on the sites of two landslides which occurred in the sensitive Champlain clay deposits of the Saint-Laurent Lowlands. Laboratory tests made on specimens cut from block samples have led to a better understanding and evaluation of the brittle behavior of these cemented clays. The results have shown that very little strain is required for the strength to decrease from a well defined peak value to a residual value; this brittle behavior is evident only when tests are made at sufficiently low stress level such that the cementation bonds are preserved during consolidation.The analyses of the slides have shown that the use of the peak strength parameters led to a gross overestimate of the factors of safety; the residual strength parameters, however, give a fairly accurate assessment of the stability, the calculated factors of safety being close to unity. That behavior may be explained by the fact that the cemented clay is extremely brittle and, like any other strain softening material, is subjected to the mechanism of progressive failure. This study leads to a very efficient practical approach to the analysis of the stability of natural slopes.

Foundations in the crust of sensitive clay deposits : Mitchell, RJ Sangrey, DA Webb, GS In Performance of earth and earth support structures, Vol. 2. Proc. Speciality Conference, Purdue Univ. 1972. 10F, 2T, 29R. ASCE, New York, 1972, P1051–1072

Foundations in the crust of sensitive clay deposits : Mitchell, RJ Sangrey, DA Webb, GS In Performance of earth and earth support structures, Vol. 2. Proc. Speciality Conference, Purdue Univ. 1972. 10F, 2T, 29R. ASCE, New York, 1972, P1051–1072