Stability of swelling clay embankments

Abstract

A common occurrence in cuts or fills of swelling soils is their reduction in strength with time. At the time of compaction, the clay generally has a high matrix suction. Correspondingly, it has a high strength and will stand at relatively steep side slopes. With time, the soil generally tends towards saturation and the matrix suction reduces towards zero. There is a reduction in total strength and if the gravitational forces are too large, the slope fails.During the past several years, numerous cut and fill slopes have been observed in the Regina area of Saskatchewan. Many of these slopes have remained stable for 4–6 years and then failed. There has been a 20 year history of observations on the Belle Plaine overpass west of Regina. Field and laboratory investigations have been conducted.With a knowledge of the geometry of the slope and failure plane, the simplified Bishop method of stability analysis was used to perform a 'back-analysis' to assess the shear strength parameters. The shear strength parameters from the laboratory program are compared with those calculated from the stability analyses. The analyses indicate that the peak shear strength parameters from triaxial tests on the softened Regina clay (i.e., c' = 5 kPa and [Formula: see text]), with the appropriate pore water pressures, give a factor of safety of 1 for the failed surface. The effect of spring thawing appears to be to produce the condition of most serious pore water pressures.

Effect of soil suction on slope stability at Notch Hill

“…This may have resulted in sufficient moisture concentrations near the slope surface after the ground had thawed to allow the suction to approach zero. The mechanism appears to be similar to that observed by Widger and Fredlund (1979) on a highway overpass built of expansive soils. The reason for the instability being concentrated some distance below the crest but above the toe is also open to speculation.…”

Hydro-mechanical coupling effect on surficial layer stability of unsaturated expansive soil slopes

“…The basic mechanical parameters (including unit weight, effective cohesion and internal friction angle) for saturated condition recommended by Widger and Fredlund [60] through performing a back analysis on a failed embankment constructed of Regina clay at Belle Plaine, Saskatchewan are used in this study. The shear strength parameters are not required for intact soil layer, because the focus of the present study is related to the stability of surface layer.…”

“…This city is situated on glacial Lake Regina consisting of over-consolidated expansive clays [60]. Most of the rain-induced failures in this region occur 4-6 years after their construction and exhibit typical shallow and regressive characteristics initiating from the toe of the slope.…”

Stability Analysis of an Expansive Clay Slope: A Case Study of Infiltration-Induced Shallow Failure of an Embankment in Regina, Canada

“…Infiltration (rain or snow)-induced shallow slope failures in expansive soils is one of the major problems that continues to challenge both the researchers and the practitioners in Canada. For example, numerous shallow failures of cut and fill slopes were continuously reported in the city of Regina which is situated on glacial deposit basin consisting of over-consolidated expansive clays (Widger andFredlund 1978, Chowdhury 2013).…”