TEMPORAL MEASUREMENT AND PREDICTION OF PORE PRESSURE RESPONSE TO CLIMATIC EVENTS IN CLAY DEPOSITS

The St-Lawrence Valley (Quebec, Canada) is characterized by thick and extensive post-glacial marine clay deposits that are susceptible to landslides. One important factor responsible for landslide development is the pore water pressure increase due to water infiltration in the soil when snow melt in the spring, or during extreme climate events, such as heavy precipitations, which reduces the effective strength in the soil. In the context of climate change, these extreme events are likely to occur more often. This study aims at understanding and predicting pore pressure response to climatic events in clay deposits which will lead to a better knowledge of the mechanisms that trigger landslides and could help to reduce their impact.

The study site is located in Ste-Anne-de-la-Pérade (Quebec, Canada), on a flat terrain, selected in order to simplify data acquisition and interpretation. The stratigraphy was determined by cone penetration tests, drilling and continuous sample collection. The bedrock, located at a depth of 36,7m, is formed of black shale and limestone. Above, a till deposit is present, overlained by a layer of silty clay. Then, sand and silt are found, followed by a second layer of clay. Finally, sand and silt continue to the surface and include the water table at a depth of about 2m.

The study relies on high resolution spatial and temporal meteorological, geotechnical and hydrogeological observations. The site therefore hosts a weather station, 22 vibrating wire piezometers, 9 hydraulic piezometers and a set of 10 tensiometers, 8 thermistors and 15 water content sensors in the unsaturated zone. One year of data has been collected so far on most sensors and allowed to observe water infiltration and pore pressure variations in the soil.

Field investigations, slug tests and a long-term pumping test, are underway in order to measure the hydraulic and elastic properties of the soils. Preliminary results from the slug tests suggest that the sand layers are quite permeable but the till is not. Laboratory tests on samples from the site provide the water retention curve characteristics along with the relative permeability of the unsaturated soil.

The poster will present the context of the study and a detailed description of the study site. Instrument installation will also be detailed and preliminary data will be presented.