Calculation Of Regional Freezing Index Frequency And Anti Freezing Design Of Engineering In Cold Regions

The freezing index is an important indicator for studying engineering frost heave resistance design,climate change,and frozen soil degradation.The frost heave damage of engineering in cold regions of China is severe,and the scientific determination of the freezing index is a prerequisite for ensuring the safe construction of engineering.In response to the lack of meteorological data in uninhabited areas in cold regions of China and the large discrepancies in the values of freezing index in current regulations,this article uses meteorological data from 502 stations across the country from 1960 to 2020.Firstly,it analyzes the spatiotemporal distribution characteristics of temperature and freezing index in China and the relationship between them.The main influencing factors of freezing index are also analyzed,and a regional frequency calculation method for scaling freezing index is proposed.Taking the Ningxia region as an example,the correctness and rationality of this method were verified,providing a new method for accurately calculating and interpolating the frequency value of freezing index in areas without data.Secondly,based on the characteristics of physical geography and the statistical characteristics of freezing index,the freezing index of cold regions in China is divided by fast clustering method;And using the regional frequency calculation method in this article,the spatial distribution characteristics of the freezing index for different partition design frequencies were analyzed.Finally,taking the main canal in Ningxia irrigation area as an example,the frost heave deformation laws of the canal under different design frequencies were given,providing a reference basis for the freezing index value of frost heave resistance design for different levels of engineering in cold regions.The main research conclusions are as follows:（1）The annual trend of temperature change in China is bounded by 1978,with a slight downward trend from 1960 to 1978 and a clear upward trend from 1979 to 2019.The linear tendency rate of East China,North China and Northwest China is 0.4°C·（10a）^-1,which is higher than the average level of China by 0.3°C·（10a）^-1,and the temperature rises rapidly.The interdecadal changes in national temperature from the 1960s to the 2010s showed significant interdecadal changes in temperature across the country and regions,with a general upward trend.In the 1990s,temperature showed a jumping increase,consistent with the era of significant global warming.The average temperature over the years gradually increases from northwest to southeast,and is significantly influenced by the dual effects of latitude and altitude,with latitude playing a dominant role.The temperature analysis results indicate that the high latitude cold regions in China are significantly affected by global warming.（2）China’s freezing index showed a slight downward trend from 1960 to 1978,and a clear downward trend from 1979 to 2019.Among them,the northwest,northeast,north China,and southwest regions show an obvious downward trend,with a linear tendency of-31.9～-50°C·d·（10a）^-1 greater than the average level of China of-21.7°C·d·（10a）^-1.From the perspective of interdecadal changes,the freezing index has gradually decreased since the1960s,and the temperature has increased rapidly in the past 30 years.Its average value is44°C·d less than the average value in the past 60 years.The lower the temperature,the more significant the negative correlation between freezing index and temperature.Latitude and altitude are important factors that affect the freezing index.In the high latitude areas of Northeast and North China,the correlation between freezing index and latitude is extremely high;For areas with significant differences in altitude between the southwest and northwest,the freezing index is influenced by a combination of latitude and altitude.（3）A method for calculating the frequency of the scaled freezing index region was proposed,which achieved the decomposition of the deterministic and stochastic components of the freezing index sequence in the station freezing index time series.At the same time,the influence of altitude and latitude deterministic factors was considered,while preserving the randomness rules of interannual time.Taking the frozen index sequence from 1960 to 2019 in Ningxia region as an example,the reliability and accuracy of the method proposed in this paper were verified by comparing the results of the frequency calculation of the scaled frozen index region with the frequency calculation of the non consistent sequence based on trend analysis at a single station.This indicates that the method proposed in this paper has the advantages of improving data representativeness and reducing the randomness of a single station.Compared with the results of spatial inverse distance interpolation,the method proposed in this paper has higher spatial interpolation accuracy.（4）Selecting typical cold regions in China（Heilongjiang,Inner Mongolia,Jilin,Qinghai,Xinjiang,Liaoning,Gansu,Shanxi,Tibet,Ningxia,Hebei,Beijing,Shaanxi,Sichuan,Tianjin,Shandong,Henan）as research objects,using the dispersion coefficient Cv and skewness coefficient Cs as clustering factors,the fast clustering method is used to divide China’s cold regions into 20 frozen index categories.Combining geographical characteristics and climate zoning,the cold regions in China were simplified into 15 freezing index zones using visual methods,and rationality tests such as zone consistency and uniformity were conducted.Based on the frequency calculation method of scaling freezing index,a study was conducted on the probability distribution of each freezing index partition.The Goodness of fit evaluation shows that the optimal distribution of 80%stations is the generalized extreme value（GEV）distribution.（5）Taking the main canal of Ningxia irrigation area as an example,the Stephen’s frozen depth calculation formula was used to clarify the corresponding relationship between the recommended values of freezing index in different specifications and the recurrence period of freezing index,that is,the average and maximum values of freezing index for many years are similar to the freezing index for once every ten years and once every hundred years,respectively.Based on the empirical curve of silt frost heave rate suggested by the specifications,the frost heave distribution law of lined channels under different frequency freezing indices was compared and analyzed,and a design method for frost heave resistance was provided.