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Peat deposits are widely encountered in many parts of the world and present various challenges for the geotechnical engineering community because of their low bearing capacity and very high compressibility and creep potential. This paper describes extensive index and oedometer testing to investigate the compressibility behaviour/properties of deep, strongly to completely humified peat and highly organic fine-grained soil layers at the northeast shore of Dian-Chi Lake in Kunming, southwest China; a region that recently is experiencing significant infrastructure construction. Compared to surficial peat deposits, the peaty soil layers investigated, with organic contents ranging 23.5–80.0%, have been subjected to a 6.7-m depth of inorganic soil overburden, such that they have substantially lower water content and void ratio and higher preconsolidation stress. Nevertheless, with deduced C α / C c = 0.04–0.07, C r / C c = 0.14–0.18 and C k / e 0 = 0.23, the Dian-Chi peaty soils exhibit similarities with surficial fibrous peats from other countries/regions. Unlike fibrous peats, however, the Dian-Chi peaty soils have extremely low permeability, with deduced k v values of the order of 1 × 10−9 to 1 × 10−10 m/s, consistent with their hunification level. Existing linear C c – w 0 correlations were found inadequate for the Dian-Chi peaty soils, such that a new C c – w 0 correlation is proposed from curve-fitting of the gathered experimental data to better capture their non-linear relationship. • Compressibility and permeability of peaty soils in Dian-Chi Lake area, China, investigated through oedometer testing. • Indices and their correlations for Dian-Chi peaty soils compared with those for other locations around the world. • New compression index – water content correlation for Dian-Chi peaty soils to represent their nonlinear relationship. [ABSTRACT FROM AUTHOR]

Rapid sliding in a rock avalanche may occur from strain- and strain-rate- weakening of the rupture-surface strength. However, existing research on rock-avalanche dynamics pays little attention to rupture-surface weakening. In this paper, we used high-speed-friction tests on limestone and shale of the Qixia Formation to determine strain- and strain-rate- weakening of the rupture surface of the Jiweishan rock avalanche. The strain- and strain-rate- weakening model inferred that the friction coefficient of the rupture surface decreased rapidly to a residual value of <0.1 within a short interval after rock-avalanche failure, which was collectively determined by shear rate and shear displacement. We used this rate-weakening in a numerical model to investigate the dynamics of the rock avalanche, and compared it with another model that used a constant value of friction. Our model results suggested that rupture-surface weakening could cause the disintegration of the sliding body and influence the post-failure motion of the Jiweishan rock avalanche. With strain- and strain-rate- weakening, a larger sliding-out velocity (~ 13–27 m/s) of the rock mass was modelled due to reduction of frictional energy consumption causing by rupture-surface weakening. Hence a strain and strain-rate- weakened rock mass could both fly farther in the air and strike the ground at a lower angle maintaining more kinetic energy. The transport distance of such a sliding rock mass would have been ~50–500 m longer than in a model without weakening. Our study suggested that strain- and strain-rate- weakening behavior of a rupture surface would significantly increase the rock-avalanche transport distance. Use of such a model might provide more accurate prediction of the disaster reach of rock avalanches. • Rupture-surface strength decreases rapidly after rock-avalanche initiation. • Rupture-surface strength is quantitatively studied by numerical modeling. • Rupture-surface strength weakening promotes the disintegration of a rock avalanche. [ABSTRACT FROM AUTHOR]