Permafrost

oundary condition which have a lower temperature. The results show that the freezing speed of
the frozen wall under the circumstances of seasonal frozen soil is higher than that of a frozen
wall which not in this circumstances. The author studies the influence of the space between
frozen pipes on the thickness and average temperature of the frozen wall, also studies the
influence on the time to complete the freezing. The optimum spacing interval is about 1 meter
to 1.5 meter. The seasonal frozen soil and the frozen wall adhesively bond each other, forming a
spatially integral structure, improving the integrity of the frozen wall. The frozen soil layer
constrains the horizontal movement of the frozen wall; the curves of deformation of deep
foundation pit with the existence and the non-existence of frozen soil layer are obtained,
horizontal displacements of the frozen wall are compared. The results show that there is
variation in horizontal displacement from excavation stage to stage for the excavation. Under
the circumstances of seasonal frozen soil layer, the horizontal displacement of frozen wall is
limited by 48% maximum on the top of the frozen wall, and meanly cut down by nearly 30%.
In cold region the frozen wall is economical and steady for pit excavations; the application
potential of frozen wall is huge in cold seasonal frozen soil area.
Key words: seasonal frozen soil layer; frozen wall; temperature; deformation
78
Experimental research on thermal conductivity of undisturbed frozen
samples from permafrost regions on Qinghai-Tibetan plateau
Zhi Wen, Yu Sheng, Wei Ma, You-sheng Deng, Ji-lin Qi, Ji-chun Wu
(State Key Laboratory of Frozen Soil Engineering, CAREERI, CAS, Lanzhou, Gansu 730000, China)
Tel.: +86-0931-4967-299. E-mail address: wenzhi@ns.lzb.ac.cn.
Abstract: Thermal conductivity is an important parameter for engineering design to estimate
thermal regime of permafrost regions. Using a thermophysical instrument, the thermal
conductivity of undisturbed frozen samples from Beiluhe in Qinghai-Tibetan plateau was tested.
Experimental data showed that there was significant difference in thermal conductivity between
undisturbed frozen samples from the permafrost regions and their remoulded frozen samples.
We found that volumetric ice content controlled the thermal conductivity of shallow permafrost
layers. As for shallow permafrost layers with the same soil texture, structure and consolidation
condition, results indicated that their thermal conductivity had negative correlativity with
volumetric air content and positive correlativity with natural density, respectively. On the other
hand, volumetric air content was a dominant factor for the thermal conductivity of ground ice
and deep permafrost layers. At the same time, ground ice in Qinghai-Tibetan plateau had
equivalent thermal conductivity with pure ice, and volumetric air content affected the
magnitude of its thermal conductivity. The study will be helpful for thermal calculation on
permafrost regions of Qinghai-Tibetan plateau.
Key words: Permafrost; Beiluhe; Qinghai-Tibetan plateau; Thermal conductivity