Engineering Characteristics of Peat Deposits in Manitoba
Earl Marvin de Guzman, Cory-Jay Pyziak, and Marolo Alfaro
Department of Civil Engineering, University of Manitoba
Muskeg or peat deposits (organic soil deposits) overlying high plastic clays cover large areas in
Northern Manitoba. Peat deposit in test area has a thickness of 3 to 3.5m. Standard laboratory
tests, such as the moisture content, organic content, and Von Post classification were conducted
on samples collected at site. The upper 1.5 m thick layer of peat is classified as fibrous while the
lower layer is amorphous with strong to complete decomposition. Organic matter content is
around 93% to 95% within the peat layers and 57% at the interface of peat and the underlying
clay layer. Hydraulic conductivity tests were carried out at different vertical pressures to
determine the permeability of the soil layers.
Conventional incremental oedometer tests were conducted to determine the consolidation
properties of peat. For comparison, constant-rate-of strain (CRS) tests were also performed. The
compressibility index obtained from oedometer tests was found to be generally higher than the
values obtained from the CRS tests, indicating most likely the occurrence of secondary
compression during the 24-hour incremental loading. Triaxial tests were conducted to determine
the shear strength of peat. The effective friction angles were found to be equal to 29° and 31° for
fibrous and amorphous peat, respectively. They were obtained based on the method that
considers the additional shear strength provided by the rearrangement of peat particles and the
tension action of fibers.
This paper presents the results of the characterization of peat deposits in Northern Manitoba. The
results of the laboratory tests will be used in numerical modelling to assess the performance of
newly constructed highway embankment on peat. A companion paper titled “Performance
Evaluation of Highway Embankment on Peat Deposits Constructed under Winter Conditions”
that focuses on the results of full-scale and fully-instrumented field test sections of newly
constructed highway embankment is also submitted.