Permafrost

and seismic response of infrastructures in cold regions. However, there is little literature
documenting systematic studies of the effects of environmental variables on the dynamic
properties of civil structures. This paper presents the detailed results of more than one year’s
monitoring and analysis of the effects of environmental variables on the dynamic properties of a
selected bridge system.
First the seismic instrumentation of the selected bridge is described in details. Using these
instruments, the ambient noises, traffic induced vibrations, and earthquake ground motions has
been recorded and processed for a time period spanning from November 1, 2004 to December
27, 2005. Based upon the collected field data, the dynamic properties of the bridge, including
modal frequencies, mode shapes and damping ratios are identified by using System
Identification tools. The fundamental frequency of the bridge is found to change by as much as
15% due to environmental impacts within one year, implying about 30% change in the stiffness
of the bridge foundation system. A three-dimensional finite element model of a typical bridge
pier is built and the analysis results show that the seasonal frozen soil can contribute as much as
10% change to the fundamental frequency.
In the mean time, the environmental variables recorded from a nearby meteorological
station are gathered to provide temperature and frozen soil depth for modeling purpose. The
seasonal frozen soil depth was evaluated by Stefan Equation, which is calibrated by using data
obtained by a Ground Penetrating Radar (GPR). In the end, a multiple-input ARX model is built
with the temperature and frozen soil depth as the input and the fundamental frequencies as the
output for structural health monitoring. The model is then used to predict the dynamic
properties changes for two scenario cases.
In conclusion, the environmental variables including air temperature and seasonal frozen soil
can have significant impact on the dynamic properties and hence the seismic behavior of a
bridge structure. The findings suggest that seasonal frozen soil can significantly change the
stiffness of the bridge foundation system and soil-foundation-structure interaction. Further
investigation is needed to better understand soil-foundation-structure interaction considering the
effects of seasonal frozen soil and provide input to design code provision.
Key Words: Seasonal Frozen Ground, Soil-Foundation-Structure Interaction, GPR, ARX
Study on the Influence of Artificial Frozen Soil Layer to the
Temperature Field and Displacement Field of the Frozen Wall
Zhi-qiang Ji, Xue-yan Xu, Lin-lin Yu
(School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China)
Abstract: Frozen wall has been widely used in civil engineering; foundation pit supported by
plane frozen wall is attracting increasing attention of the researchers. In cold seasonal frozen
soil area, the thickness of seasonal soil is large and the strength of the seasonal soil is high. It is
necessary to consider the interaction between the seasonal frozen soil and the artificial frozen
wall. This paper presents a model which based on 2D heat conduction, and calculates the
temperature distribution in the frozen wall. The frozen soil layer provides an initial and
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