Compressibility and monotonic shearing behaviour of Toronto peat

Abstract

The shearing behaviour of organic soils, such as peat, under monotonic loading can be very different than those of inorganic soils due to the presence of fibers. A series of one-dimensional consolidation, direct simple shear, and bender element tests are conducted to investigate the compressibility and the monotonic shear strength of a peat deposit from the Port Lands area of Toronto, Ontario, Canada. Laboratory specimens are trimmed from block samples collected from a depth of about 4.0 to 4.5 m. The samples' organic content ranges from about 42% to 60%, with a fiber content of 20% to 30%. Because of their moderate organic and water (180%–237%) contents, the peat samples are found to be less compressible with a slower consolidation rate than several other surficial peat deposits reported in the literature. All samples exhibit a ductile shearing behaviour with undrained strength ratios ranging from 0.32 to 0.57 and a residual effective friction angle of about 30°. The monotonic tests are further examined within the framework of critical state soil mechanics. Bender element measurements are used to develop empirical relationships between several engineering parameters of Toronto peat with shear wave velocity.