Secondary compression of peat with or without surcharging

Secondary compression is important in peat deposits because they exist at high void ratios and exhibit high values of compression index C_c, display the highest values of Cα/C_c among geotechnical materials, and primary consolidation is completed in weeks or months in typical field situations. Secondary compression of Middleton peat was investigated by oedometer tests on undisturbed specimens. The observed secondary compression behavior of this fibrous peat, with or without surcharging, is in accordance with the Cα/C_c concept of compressibility. Near the preconsolidation pressure, the secondary compression index, C_α, increases significantly with time. In the compression range C_α decreases only slightly with time, and for most practical purposes a constant C_α with time can be used to compute secondary settlement. Postsurcharge secondary compression index, C′_α, always increases with time. This is predicted by the C_α/C_c concept of compressibility. A secant post-surcharge secondary compression index, C″_α, is therefore introduced for a simple computation of secondary settlement.