Anchorage Peat Study

Abstract

The peat assessed in this study is Sphagnum moss that formed during the Holocene in wetland bogs around Anchorage, Alaska. Undisturbed peat in these bogs has a water content that ranges from 400 to 1,000% and averages 620%. An assessment of this peat’s compressibility was made by measuring the water content, specific gravity, and degree of saturation of 10 sample sets obtained from five bogs. At four bogs, this peat had been compressed by either fill or aeolian silt for 50 days to 7,500 years. At the fifth bog, this peat was compressed under its own weight after being drained with ditches. Statistics were performed to calculate the average and standard deviation of water contents for each sample-set. Based on these average water contents, two characteristic stages of peat compression under a 15 to 70 kPa overburden pressure are identified: noncompact compression (Ca=1.2), followed by compact compression (Ca=0.15). The transition from noncompact to compact compression occurs in 20 years or less, and around an average void ratio of 3.5. For undisturbed peat, the average settlement ratio (ΔH/Ho) is 0.6. The peat’s compression can be interrupted by frost action.