SECONDARY COMPRESSION OF PEAT WITH OR WITHOUT SURCHARGING

Secondary compression is important in pl:at deposits because they exis t at high void ratios and exhibit high values of compression index C-c , display the: highest values of C-a/C-c among geotechnical materials, and primary consolidation is completed in weeks or months in typical field situations. Secondary compression of Middleton peat was investig ated by oedometer tests on undisturbed specimens. The observed seconda ry compression behavior of this fibrous peat, with or without surcharg ing, is in accordance with the C-a/C-c concept of compressibility. Nea r the preconsolidation pressure, the secondary compression index, C-a, increases significantly with time. In the compression range C-a decre ases only slightly with time, and for most practical purposes a consta nt C-a with time can be used to compute secondary settlement. Postsurc harge secondary compression index, C-a', always increases with time. T his is predicted by the C-a/C-c concept of compressibility. A secant p ostsurcharge secondary compression index, C-a'', is therefore introduc ed for a simple computation of secondary settlement.