Permafrost

54
Laboratory Study on the Dynamic Strength Characteristic
on Frozen Silty Clay
Shujuan ZHANG, Yuanming LAI, Xiaoxiao CHANG
(State Key Laboratory of Frozen Soil Engineering, Cold and Arid Regions Environmental and Engineering
Research Institute, Chinese Academy of Sciences, Lanzhou, Gansu, 730000, China)
Abstract: Using triaxial cycle tests with constant stress amplitude under confining pressures
between 0.3MPa and 16.0MPa at a temperature of -4℃ and at a frequency 2Hz, dynamic
strength characteristics of frozen silty clay were studied. The results showed that the dynamic
strength depended not only on the confining pressure and the number of vibration, but also on
maximum loading stress at constant minimum loading stress. Additionally, pressure melting of
pore ice and growth of micro-cracks also influence dynamic stress response. The critical
number of vibrations and the critical confining pressure were put forward. Finally, the dynamic
and static strength tests were conducted to assess the design of foundation base in permafrost
regions.
Key words: Frozen silty clay, dynamic strength characteristic, vibrating number, confining
pressure
Practical Modeling for Frost Heave Estimation of Chilled Gas Pipeline
Buried in Frost Susceptible Soil
Shunji Kanie 1 , Satoshi Akagawa 2 and Takashi Mikami 3
(1.Associate Professor, Graduate School of Engineering, Hokkaido Univ., Kita 13, Nishi 8, Kitaku,
Sapporo,Japan, 0608628, Tel:+81-11-706-6175, e-mail: kanie@eng.hokudai.ac.jp (Corresponding Author);
2. Professor, Graduate School of Engineering, Hokkaido Univ., Kita 13, Nishi 8, Kitaku,
Sapporo,Japan,0608628,Tel:+81-11-706-7246,Fax:+81-11-706-7246,e-mail:akagawa@eng.hokudai.ac.jp;
3. Professor, Graduate School of Engineering, Hokkaido Univ., Kita 13, Nishi 8, Kitaku, Sapporo,
Japan,0608628, Tel:+81-11-706-6174, e-mail: tmikami@eng.hokudai.ac.jp)
Abstract: It has been known that chilled gas pipeline buried through a boundary between
permafrost and non-permafrost is likely to suffer bending deflection due to frost heave since the
pipeline is held tightly in permafrost whereas the other end in non permafrost is surrounded by
growing frost bulb and is subjected to frost heaving. As a result, large deflection of pipeline is
expected to occur near the boundary and it may cause fatal damage to the pipeline.
For the frost heave estimation of structure buried in frost susceptible soil, various methods
have been proposed so far. However, most of those require many parameters to explain this
complicated phenomenon as a numerical model since the frost heave depends on freezing rate,
permeability of the soil, amount of water migration and etc. The authors, then, propose to adopt
Takashi’s equation for the frost heave estimation. Introducing only three parameters obtained
through indoor experiment, Takashi’s equation relates the frost heave ratio with the constraint
pressure at the freezing front and its freezing rate. This equation has been confirmed to give
satisfactory estimation for one-dimensional frost heave so that the procedure of the indoor