| In the cold area,there is a layer of freezing-thawing layer on the surface of the foundation,which is frozen in winter and thawed in summer.During the freezing-thawing process,the soil properties change,which directly affects the stability of road structure.Especially in soft soil area,because of its low strength,high compressibility and poor permeability,if improperly treated,it will also produce various highway diseases such as foundation instability,slope instability,excessive settlement and so on.There is a large area of soft soil in Hulun Buir area of northeastern Inner Mongolia.At the same time,the frost period of soil layer lasts for more than seven months,and there is no freezing state in five months from June to October every year.The stability of roadbed is affected by both seasonal and geological conditions.Therefore,it is of great practical significance to study the compression characteristics of soft soil and the settlement law of roadbed in cold region for highway engineering construction and operation.The main research contents and achievements of this paper are as follows:(1)Based on the highway engineering of Labdarin-Hadatu section of National Highway 332,the typical soft soil along the highway is selected as the research object,and the basic physical and mechanical properties of soil samples are determined.The comparison with the engineering properties of soft soil in other areas proves that the soft soil foundation in cold regions can learn from the mature treatment methods of highway soft soil foundation in other areas to a certain extent.(2)Typical highway sections are selected for subgrade temperature and settlement monitoring,and the variation law of subgrade temperature field and settlement is analyzed.The results show that the maximum frozen depth of the test section is about 3.25m;the annual variation curve of soil temperature in each depth is approximately cosine type,and there is a time delay with temperature change;the settlement curve with time is affected by temperature to a certain extent;compared with the dynamic compaction replacement of rubble.The method(0.5m)and replacement method(0.5m)are better for soft soil foundation treatment.(3)According to the basic physical properties of soft soil and the results of temperature monitoring in situ,by improving the existing uniaxial consolidation apparatus,three unconventional compression test methods,i.e.constant temperature variable load,constant load variable temperature and variable temperature variable load,are designed.Three influencing factors,namely water content,temperature and consolidation pressure,are selected to carry out a multilevel whole group of tests.The results show that the amount of compression produced by the soil under negative temperature condition is the same as that produced by the soil under negative temperature condition.The temperature can be regarded as a generalized load.When the soft soil is in the temperature range of-1.5?0 degrees,the increase of temperature will lead to a sharp increase of compression;the total relative compression coefficient and temperature change exponentially;the effect of temperature will make the soil produce certain additional compression and yield under the action of high consolidation pressure.The additional compression of raw material is large.(4)According to the results of constant temperature and variable load compression test,the influence degree of three factors on the compression coefficient of soft soil is evaluated by one-way ANOVA,and the multiple linear regression analysis model under different combinations of three factors is evaluated.The better prediction model of the compression coefficient of soft soil is obtained,and the test value of compression test and the calculation value of prediction model are compared and analyzed to verify the prediction.The accuracy of the model.According to the actual situation of the project,the calculation parameters of the soft soil compression coefficient prediction model are set up.The calculation values of the compression coefficient are calculated by the layered summation method and the consolidation degree method,and compared with the field measured values.The applicability of the compression coefficient prediction model in the settlement calculation of soft soil foundation in cold regions is proved. |
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