| Heilongjiang Province is located in the northeast of the border of the motherland.It is a large irrigation Province Based on agricultural production.It is located in a typical deep season frozen soil area.Affected by the geographical location and climate conditions,Heilongjiang Province has a long and dry winter.Frost heaving disasters and freeze-thaw erosion occur frequently,causing serious damage to the local water transmission and distribution channels and various hydraulic structures,which not only seriously restricts the economic development of Heilongjiang Province,It also threatens the safe operation of large buildings.In order to better analyze the law of soil freezing and reveal the mechanism of frost heaving deformation,single factor frost heaving tests were carried out in the laboratory with low liquid limit clay as the research object under open system.The temperature field,temperature gradient,frost heaving rate and water supplement amount of each sample during freezing were analyzed,and the thermal physical parameters under various working conditions were measured by "transient method".According to the similarity criterion of field prototype and indoor model,the size of physical slope model is reasonably determined,and the temperature control mode is designed according to the multi-year daily average temperature change process in Mohe City,Heilongjiang Province.Several freeze-thaw cycle tests are completed in the laboratory to determine the change law of physical and mechanical properties of slope soil during the freeze-thaw cycle,so as to supplement the theoretical study of freeze-thaw cycle effect on beach failure process.The main achievements are as follows(1)In the laboratory,the basic physical parameters of soil are measured according to the test specifications,and the test scheme is determined according to the actual physical parameters and basic physical indexes in the field.The boundary conditions are reasonably designed to explore the influence of the cold end temperature,moisture content and dry density on the frost heaving characteristics of soil under the open system.The temperature of the sample is controlled by the geotechnical frost heaving test box,and the temperature and position are used The temperature and displacement of soil layer in the freezing process are monitored by the displacement sensor in real time.The test results show that: in the test of determining the initial freezing temperature of samples,the temperature change curve of samples can be divided into four stages: supercooling stage,temperature sudden increase stage,pore water crystallization stage and stable freezing stage.Because the initial parameters of samples are different under different working conditions,the initial freezing temperature is not the same.The development process of temperature field can be divided into rapid cooling stage,stable cooling stage and constant temperature freezing stage.The top of the sample is most affected by the cooling capacity of the roof,and the bottom is least affected by it.The peak temperature gradient increases with the decrease of the cold end temperature,and the temperature gradient first increases and then decreases with the increase of the test duration Low and gradually stable trend.The lower the cold end temperature is,the faster the freezing front moves and the greater the freezing depth is,and the final frost heaving rate increases with the decrease of cold end temperature.In the test range,the frost heave rate of the sample is positively correlated with the moisture content and dry density.During the freezing process,affected by the temperature of the cold end and the driving force of moisture,the original water in the sample redistributes,and the moisture extracted from the bottom plate accumulates behind the freezing front,and the moisture content in the frozen edge area is the largest.(2)Remolded soil samples were prepared to explore the influence of temperature,moisture content and dry density on soil thermal physical parameters.According to the principle of "transient method",the thermal conductivity,volumetric heat capacity and thermal diffusivity of each sample under different working conditions were measured by portable thermal characteristic analyzer.The experimental results show that the thermal conductivity,volumetric heat capacity and thermal diffusivity of the sample almost do not change with the temperature when the temperature is 5 ～ 20 ℃.When the temperature is-5 ～ 5 ℃,the thermal conductivity and thermal diffusivity of the sample increase sharply,while the volumetric heat capacity decreases.When the temperature is-20 ～ 5 ℃,the thermal conductivity and thermal diffusivity of the sample increase sharply The results show that the thermal properties of soil are affected by unfrozen water content and frost heave cracks,and fluctuate at 0 ℃.Affected by the change of water state,the thermal conductivity and thermal diffusivity of frozen soil are significantly higher than that of thawed soil,and the volumetric heat capacity is opposite.The thermal conductivity,volumetric heat capacity and thermal diffusivity are positively correlated with moisture content and dry density.(3)According to the similarity criteria between the actual field prototype and the model in the laboratory,and combined with the specifications of the low temperature environment simulation laboratory,the indoor slope model size is reasonably designed,the ten-year daily average temperature of Mohe city in Heilongjiang Province is collected and sorted out,and the temperature control process is simplified.Combined with the similarity criteria and the laboratory correction coefficient,the temperature control mode in the laboratory is designed,so as to control the complete freezing process The change process of melting cycle temperature.According to the actual soil parameters in the field,a physical slope model is built in the laboratory flume,and several freeze-thaw cycle tests are carried out on the slope model according to the designed temperature control mode.The following conclusions can be obtained: the soil temperature of the slope presents a sinusoidal change,and the closer it is to the cold source of the roof,the more obvious the soil temperature change,and the larger the fluctuation range of the soil temperature,0～ 18 The results show that the temperature change is obvious within cm depth,and the influence of roof temperature on deep soil is small.It can be seen from the change process of freezing depth that the experimental design can simulate the field "one-way freezing,two-way melting" process.The freezing depth development process of slope model can be divided into six stages: unfrozen stage,rapid freezing stage,stable freezing stage,slow freezing stage,forward melting stage and reverse melting stage.The forward and reverse melting stages are carried out one after another,not at the same time In the slow freezing stage,the maximum freezing depth appears,and the freezing depth increases with the increase of freeze-thaw cycles.(4)In the process of freeze-thaw cycle,the soil will experience frost heaving and thawing settlement.The height of the sample can not return to the initial state,but there is a certain amount of residual deformation.The residual deformation will gradually increase with the increase of freeze-thaw times,but the increase amplitude will gradually decrease.During the test,the dry density of the surface soil decreases with the increase of freeze-thaw cycles,and the porosity increases gradually.When the freeze-thaw cycles reach seven times,the residual deformation tends to be stable.The results show that the shear strength,cohesion and internal friction angle decrease with the increase of freeze-thaw cycles.Finally,combined with the experimental results and laws,the mechanism of beach erosion process is analyzed theoretically.The freeze-thaw cycle can increase the particle spacing,increase the porosity and enhance the dispersion.The freeze-thaw cycle can intensify the beach erosion process.At the same time,according to the relative exposure theory and the physical characteristics of viscous fine sediment,it is pointed out that the beach erosion process is mainly affected by the freeze-thaw erosion and water erosion. |
PDF Full Text Request