Permafrost

earing capacity of the foundation soil is, in the general case, the most reliable method for
determining soil strength.
It is of fundamental importance that the obtained с and ϕ values require no statistical
averaging, because they characterize the studied soil mass as a whole.
Key words: Strength parameters, permafrost, functional characteristics, foundation soil stability
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Influence of freeze-thaw on the strength of overconsolidated soils
Jilin Qi 1 , Pieter A. Vermeer 2
(1. State Key Laboratory of Frozen Soil Engineering, Cold and Arid Regions Environmental and Engineering
Research Institute, 260 Donggang West Road, Lanzhou, 730000, China; 2. Institute of Geotechnical
Engineering, Stuttgart University, Pfaffenwaldring 35, D-70569 Stuttgart, Germany)
Abstract : It has become a common understanding that freeze-thaw cycling is a kind of
weathering process which considerably changes the engineering properties of soils. Therefore,
the influence of freeze-thaw must be taken into account when selecting soil parameters for
stability and deformation analysis of slopes, embankments and cuts in cold regions, where
newly exposed soil layers are to be submitted to freeze-thaw cycling. In this paper, freeze-thaw
induced changes in strength of two overconsolidated soils are studied. The soil samples are
subjected to one freeze-thaw cycle. Then mechanical testing and SEM micro-fabric scanning
are carried out on both unfrozen and thawed samples. It has been found that the strength
parameters of the soils, the cohesion and friction angle change in an opposite way. Novel
explanations on the mechanism of the change are given both using SEM quantitative analysis
and according to the deforming process during freeze-thaw.
Key Words: freeze-thaw, overconsolidation, strength, micro-fabric
Study on the Formation and Mechanisms of High Subgrade Diseases of
the Qinghai-Tibet Highway
Jian-bing Chen 1,2 , Shuang-jie Wang 1 , Jin-zhao Zhang 1 , Wei Ma 2
(1. The First Highway Survey and Design Institute of China; Xi'an; 2.State Key Laboratory of Frozen Soil
Engineering, CAREERI, CAS, Lanzhou Gansu 730000, China)
Abstract: Since paving the black colored road surface in 1973, the subgrade diseases ,the
majority of these is thaw settlement, in permafrost region are always chronic and stubborn
disease, and have a long resistance to treatment. Before the mid-1990s, many researchers in
frozen soil engineering field had researched into the characteristic and causes of subgrade thaw
settlement in the permafrost region of Qinghai-Tibet highway. Their study showed that
subgrade diseases was mainly caused by the formation and development of thaw bulb under
embankment, and brought forward that higher embankment could protect the permafrost