Characteristics and Engineering Properties of Peaty Soil Underlying Cranberry Bogs

Peat is an organic complex soil, well known for its high compressibility and low stability. Peat forms naturally by the incomplete decomposition of plant and animal constituents under anaerobic conditions at low temperatures. A relocation of state highway No. 44 in Carver, Massachusetts requires the construction of sheet pile walls, fills and embankments through cranberry bogs and ponds containing deep peat deposits. The engineering properties of Carver peat in Southern Massachusetts (south of Boston) were investigated via laboratory testing including standard index tests, scanning electron micrographs, fiber content, engineering classification, permeability, consolidated undrained triaxial tests, and oedometer tests. The tests were carried out on vertically (V) and horizontally (H) oriented undisturbed samples. Unlike inorganic clays, the secondary compression of peat is of great significance as it dominates its deformation and takes place over a long period of time. The presented testing program examines the deformation properties of the peat. The biodegradation of peat seems to increase the coefficient of secondary compression C_α and the coefficient of tertiary compression C_k. The drained friction angle (from triaxial tests) of Carver peat yielded values of (12°) and (10°) for vertically and horizontally oriented samples, respectively. The drained cohesion intercept (from triaxial tests) was 11.45 (kPa) and 12.42 (kPa) for vertically and horizontally oriented samples, respectively. The obtained engineering properties were found to be overall within the range reported for other peat types.