Study On Frost Heaving Property Of Silty Soil And The Effect Of Freeze-thaw Cycle On The Permeability

Silty soil is a kind of plain soil with low natural water content and small soil particles.And the size of soil's particles is between the silt and sand.There are not only frost heave diseases but also the diseases from the changes of its permeability causing by freeze-thaw cycles when it's used in cold regions engineering.Therefor we used the filler,which was selected along the national road G214 in Maduo County,Qinghai Province,to do frost heave test and the infiltration experiment after the freeze-thaw cycle.On this basis,the frost heave characteristics and the permeability change characteristics after the freeze-thaw cycle were studied.The main contents include:1.Firstly,there were some basic physical tests including particle analysis test,compaction test,permeation experiment,freezing point test.Then the filler was defined as silty soil and its biggest dry density,optimum water content,permeability coefficient and freezing point were analysed,which was prepared for the later researches.2.Heat transfer mechanism in air cooling is different from liquid cooling from the mechanism.Designing and manufacturing a new type of air-cooled and unidirectional freezing equipment of soil is necessary.Then there is a feasibility for the device.It provided a new method to research the frost heave disease of the soil in cold area engineering.After that the device is described in detail.The device was made up of several parts include sample cylinder,temperature control device,displacement monitoring device,temperature monitoring device,makeup water device,cryogenic thermostat,negative temperature gas channel.It was aimed at fully simulate the frost heaving situation of the soil which is at the surface of subgrade,side slope,dam and so on.3.Orthogonal tests were designed with water content,temperature,and degree of compaction as variables.The soil was frozen in close system.The frost heave characteristics and its sensitivity characteristics were analysised.Then the amount of frost heave,temperature field and water field were shown.After that the optimal combination of the variables was got to let the amount of frost heave became biggest,which was worst to the cold regions engineering.Studies have also shown that the amount of frost heave first increase then decrease with the decrease of the freezing temperature,and it is positively related to water content and the degree of compaction within limits.And water content has the greatest contribution to the amount of frost heave.4.The penneability of soil used in subgrade filling will change when subjected to freeze-thaw cycle.Orthogonal tests were also designed with water content,temperature,and degree of compaction as variables to measure the changes of its permeability.The permeability change characteristics were analysised.The equipment introduced before was reformed to do those tests.Studies shown that the permeability coefficient of the soil increased after subjected to freeze-thaw cycle.Also the increase of the frozen soil's permeability was different from the one of unfrozen soil.And the former was larger than the latter.Orthogonal analysis shown that water content had the greatest contribution to the increase of the permeability.It's the same to the experimental results of frost heaving.