Frozen Soil Area Research Articles

Thermal Condition of Snow and its Response to Meteorological Factors at Field Scale

To study the variation pattern of snow cover in seasonal frozen soil areas and the effect of related meteorological factors on the snow cover temperature, four land cover patterns (bare land, normal snow, compacted snow, and thickened snow) were created using a field test of a freezing and thawing period. The thermal state of the snow cover and its upper and lower boundary conditions were determined and combined with ground meteorological observation data, and the effect of the thermal state on the upper and lower boundaries of the snow cover was analyzed via statistical analysis and gray correlation analysis. The main meteorological factors affecting the snow cover temperature were selected, and the relationships between the stratification temperature and main meteorological factors were determined. The results show that the differences in snow melting time for different land cover patterns are small and that the snow density and snow depth have only slight effects on the melting rate. The variability of the heat fluxes of the snow layers was above the moderate degree, and the variability of snow from the surface layer to the bottom layer had an increasing-decreasing tendency. The heat exchange at the snow-frozen soil interface during the stable period was weak, and solar radiation could effectively influence the heat flux of 10 to 20 cm of snow. In the freezing period, snow cover treatment compared with bare land can significantly improved the soil temperature and increased the heat preservation effect in the following order: thickened snow > compacted snow > normal snow. When snowfall is certain, compacted snow treatment can increase the net radiation transmission within the snow layer, improve the temperature of the snow layer, and increase the heat preservation effect of the soil. The increase in snow density can increase the internal temperature variation of the snow and significantly change the snow thermal conditions. The regression relationship between the surface of the snow cover and the main meteorological factors was notable, while the model reliability for the middle and bottom layers was poor.

Influence of freeze-thaw cycles on mechanical properties of a silty sand

Freeze-thaw cycling is a very common phenomenon in seasonally frozen soil areas and it will affect the mechanical properties of soils which should be taken into account for geotechnical engineering. To study the variation of mechanical properties of seasonally frozen soils, fine-grained silty sand was compacted in the lab and was then exposed to a maximum of 12 closed-system freeze-thaw cycles. The stress-strain curve, failure strength, elastic modulus, cohesion and angle of internal friction were measured for samples before and after the freeze-thaw cycles. The mechanical properties were considerably affected by the number of freeze-thaw cycles, whereas the influence of cooling temperature was not obvious. The highest decrease rate of elastic modulus was about 26%–45% and for failure strength it reached at 32%–45% compared to the unfrozen soil which did not experience the freeze-thaw cycles. The cohesion decreased after the first few freeze-thaw cycles and then kept nearly stable after about 9–12cycles while the internal friction angle decreased at first and then increased during the freeze-thaw cycles, reaching the minimum values at about the 7cycles. The method of significance was used to analyze the influence of different factors. Results showed that the number of freeze-thaw cycles had significant influence on the mechanical properties and the cooling temperature had less influence. The normalized stress-strain relationship considering the influence of freeze-thaw cycling as well as confining pressure was established and can predict the stress-strain relation well compared with the experimental data.

Research on Frost Heaving of Subgrade Filling in Seasonal Frozen Soil Area

Research on frost heaving of high speed railway subgrade filling in seasonal frozen soil area is developed indoor. Through freezing and thawing strength and frost heaving amount test, the research analyzes factors affecting frost heaving of subgrade filling, points out that water content, fine stuff admixing amount and plasticity of fine-grained soil have relatively large influence on frost heaving, while freezing temperature and freezing and thawing cycle index have relatively small influence. Water content is main factor to have effect on frost heaving of subgrade filling. When the water content reaches to some certain value, even coarse-grained soil can produce considerable frost heaving amount. Therefore, taking effective waterproof and drainage measures is of great importance in subgrade frost heaving prevention and treatment.

Tests and Research on Characteristics of Shear Strength of Cement Improved Soil under Freeze-Thaw Cycle

Roadbed filling undergo at least one freeze-thaw cycle every year in seasonal frozen soil areas, which will lead subgrade to boiling, settlement, strength weakening etc. and has a strong impact on traffic safety and smooth, need to be solved urgently . In recent years, cement improved soil is applied to dissolve frost damage because it can be obtained locally, and has high performance and low price. However, how to evaluate strength of cement soil under repeated freeze-thaw cycles is the key to its further application in those regions. In the paper, the cement improved silty clay is selected as the object which is most common in Heilongjiang roadbed, many groups of freeze-thaw tests and direct shear tests are conducted at different conditions. From these tests, some conclusions about shear strength index and are obtained: 1. the first freeze-thaw cycle has important effect on cohesion of cement soil, during freeze-thaw cycle, the lower temperature is, the faster is decreasing. 2. decreases with freeze-thaw cycles increase, and there is a peak value existing after the seventh cycle, then reduce rapidly. 3. the internal friction angle appears decreasing – increasing–reducing– increasing trend during cycles but the range of change is little. 4. reduces smaller and increases more when temperature is lower.

Experimental Research on Shear Strength of Subgrade Soil and Plasticity Index under Different Freeze-Thaw Cycles

Three different plasticity index subgrade soils are selected from seasonal frozen soil area. Triaxial compression test under different confining pressures are executed on the samples exposed to 0 to 7 times closed-system freeze-thaw cycles. The conclusion gotten is that to the same kind of soil under the same freeze-thaw cycles, the shear strength increases with confining pressure; Shear strength with the same confining pressure decreases with the number of freeze-thaw cycles; With the same confining pressure and the same freeze-thaw cycles, shear strength increases with the plasticity index. Exponential function is adopted for multiple nonlinear fitting on the test results. The relationship between shear strength and confining pressure, plasticity index, freeze-thaw cycles is obtained and shows a good correlation.

Simulation of freezing and thawing soils in Inner Mongolia Hetao Irrigation District, China

Inner Mongolia Hetao Irrigation District, in north of China, is typical of seasonal frozen soil areas in the region. Irrigation in autumn is required to leach soil salt and to provide a reserve of soil water for the next year's crop. However, improper autumn irrigation results in the secondary salinization of soil. The objective of this study is to simulate soil water and heat dynamics during winter period with the one-dimensional Simultaneous Heat and Water (SHAW) model to assess its capability for simulating overwinter water storage. SHAW model soil parameters were calibrated by data of 1995–1996 and 2002–2004 and validated by data of 1996–2001 and 2005–2006 using field measured soil water contents and temperatures during freezing and thawing periods. Using calibrated and validated soil parameters, the paper simulates the process of soil freezing–thawing, and the dynamic variation of moisture–heat transfer, including soil water content, temperature, frost depth, soil evaporation, and water flux in the seasonal freezing–thawing period. These are useful to determine proper autumn irrigation management, and can be used in future research to address overwinter solute migration to reduce soil secondary salinization.

Thermal Interaction between Permafrost and the Qinghai-Tibet Railway

Measures were taken to protect the thermal regime of the roadbed embankment after construction and to lower permafrost temperatures in the rich-ice and warm permafrost regions along the Qinghai-Xizang Railway. However, these measures were taken only for some sections of the railway, leaving many sections unprotected. This article addresses those areas where no measures were taken and presents analysis of the variation of soil temperatures under the embankment in seasonal frozen soil areas, degrading permafrost areas, and warm and cold permafrost areas. The results show that soil temperatures, maximum seasonal freezing depth, and the permafrost table under the embankment differ according to the different frozen soil areas after embankment construction. In seasonal frozen soil areas and degraded permafrost areas, the seasonal frost layer remained frozen the next year under the shaded shoulder of the embankment. In degrading permafrost areas, a thaw layer between the permafrost table and the bottom of the se...

Soil moisture initialization for climate prediction: Characterization of model and observation errors

While it has been shown that soil moisture data assimilation techniques can be used to constrain land surface model predictions with remotely sensed soil moisture observations to provide optimal climate model surface and root zone soil moisture initialization, a good understanding and quantification of both model and observation error are required. In this paper we therefore evaluate the catchment‐based land surface model (CLSM) and scanning multichannel microwave radiometer (SMMR) soil moisture estimation errors using long‐term in situ soil moisture measurements available for Eurasia. Generally, the CLSM surface and root zone soil moisture was found to be biased less than 0.08 vol/vol dry in dry climate and frozen soil areas and biased over 0.08 vol/vol (as high as 0.16 vol/vol) wet in wet climate areas. Moreover, the CLSM suffered from an underestimation in surface zone seasonal soil moisture variation. While the SMMR soil moisture estimates were also biased, less than 0.05 vol/vol dry in dry climate and over 0.10 vol/vol (as high as 0.2 vol/vol) wet in wet climate, they generally had accurate seasonal variations. This error characterization study is crucial for practical Eurasian data assimilation, as unbiased observations and model predictions, and reliable knowledge of relative observed and model predicted soil moisture errors are key data assimilation assumptions. This study therefore provides the error information required for data assimilation and emphasizes the need for careful bias representation when assimilating SMMR data into the CLSM. The potential deficiencies in this error assessment are acknowledged and discussed, including the disparate time‐space representation of the various soil moisture sources.

Simulation method for calculating stress and deformation of highway embankment on frozen soil area

As the seasons go on, the variation of water content and temperature distribution of highway embankment is not regular in permafrost zone. It results in heterogeneous changes of the property of embankment soil. This leads to heterogeneous deformation of the embankment. If the deformation goes beyond the allowable value, the highway would be threatened by collapse. All of these phenomena should be taken into account with emphasis in the design of highway passing through the permafrost area. But at present no favorable measure has been derived. This paper bases on the elasto-plasticity theory and creep theory, by simulation of the variation of water content and temperature distribution and soil property, establishes a two-dimensional model to calculate the stress and deformation of highway embankment in permafrost area. In this model the creep deformation, the self-deformation in volume and the instantaneous deformation are considered. Especially the creep and instantaneous deformation behaviors under the changing process of soil property with time are studied.

Simulations of LGM climate of East Asia by regional climate model

Climate conditions in the Last Glacial Maximum (LGM) were remarkably different from the present ones. Adopting a regional climate model (RCM) which has included a detailed land surface scheme, LGM climate of East Asia has been simulated. The effects of vegetation changes on LGM climate have been diagnosed by adding forces of LGM paleovegetation reconstructed from the geological records. The results of the simulations by RCM indicate that large decreases in whole year temperature of East Asia continent caused strongly enhanced winter monsoon and weakened summer monsoon. The strengthening and westward-stretching of the Subtropical High of West-Pacific are the key reasons of decreases of LGM summer precipitation in eastern China. Precipitation and effective precipitation were increased in the Tibetan Plateau and Middle-Asia, while the humid condition in the Tibetan Plateau was mainly caused by increase of precipitation. Accumulated snow of LGM was also increased in the Tibetan Plateau, which was helpful to developing glacier and permafrost. This experiment has simulated that the frozen soil areas extend southward to 30° N. In LGM climate simulation, climate effects caused by external forces were amplified by added paleovegetation, therefore, decreases of temperature, changes of precipitation and snowfall, and other climatic parameters were further strengthened, making the simulation results more approach to geological evidences.

Soil freeze/thaw cycles over snow‐free land detected by passive microwave remote sensing

The timing, duration, and areal extent of the near‐surface soil freeze/thaw status were investigated using passive microwave satellite remote sensing data for the 1997/98 winter over the contiguous United States. A frozen soil algorithm was validated using soil temperature data at 0 cm and 5 cm depths from more than 20 sites over the study area. Results indicated that a negative spectral gradient and a cut‐off 37‐GHz vertical polarized brightness temperature of 258.2K can be used to determine near‐surface soil freeze/thaw status with confidence. The microwave freeze/thaw boundary generally agreed with −5.0°C isotherm of air temperature although frozen soils occurred sporadically between 0°C and −5.0°C isotherms. The maximum frozen soil area over snow‐free land surface was about 3.75 × 106 km² or about 37% of the total study area during the 1997/98 winter. The near‐surface soils often froze before snow covered the land surface, but soil freeze/thaw status under snow cover cannot be detected using this microwave technique. The onset of soil freeze mainly occurred in October and November, while the last days of soil freeze occurred in March and April, resulting in the duration of soil freezing varying from five to seven months over the majority of the study areas. The number of days of surface soil freezing varied from several days to longer than five months.

EXPERIMENTAL STUDY OF INFILTRATION INTO A BEAN STUBBLE FIELD DURING SEASONAL FREEZE-THAW PERIOD

Infiltration characteristics of frozen soils are of prime interest for a variety of concerns, including water conservation, runoff, flooding, and erosion. Although frozen soil infiltration is typically not associated with irrigation practices, winter and spring irrigation in northern and north-western China is conducted mostly during the freeze-thaw period when water is available. The shortage of water resources is an important factor affecting and restricting development of crop and livestock in northern and northwestern parts of China. Therefore, improving irrigation efficiency and determining irrigation parameters have become key problems for agricultural management. This paper examines the infiltration characteristics during different freeze-thaw stages through the winter based on water infiltration in a green bean standing stubble field. The variation in 90-minute cumulative infiltration capacity and final infiltration rate were examined for the transient freeze-thaw stage, the steady freezing stage, and the thawing stage. Results showed that during the transient freezing stage, the effect of the frozen layer on infiltration characteristics was limited only at the beginning of infiltration. During the steady freezing stage, cumulative infiltration and final infiltration rates decreased as soil frost depth increased. During the thawing stage, cumulative infiltration and final infiltration rates increased with the increase in thaw depth. The exchanges of water and heat between surface soil and atmosphere and the phase change of soil water were the main reasons for the variation in infiltration characteristics. Results from this study have practical significance for directing the winter and spring irrigation in seasonally frozen soil areas and also have hydrologic implications for predicting runoff and flooding associated with rainfall and snowmelt on frozen soil.