Study On The Frost Heaving Characteristics Of The Artificial Freezing Marine Soft Soil

China's coastal areas are widely distributed with deep marine sedimentary soft soil layer.Artificial ground freezing method(AGFM)as a ground reinforcement method can can effectively solve the problems of poor engineering properties,such as low strength,creep and thixotropy.However,when AGFM is used in marine soft soil,there are two aspects of the problem urgently to be solved.On the one hand,there are few studies on the thermophysical parameters of marine soft soil,and the corresponding basic data are not available.On the other hand,the frost heaving characteristics of marine soft soil under artificial freezing condition are still blank.In order to successfully apply AGFM in marine soft soil layer,in this paper,a series of studies on the frost heaving characteristics of marine soft soil under artificial freezing were carried out by means of the combination of laboratory test,theoretical analysis and numerical simulation.First of all,the physical and mechanical parameters of marine soft soil under artificial freezing condition were studied by laboratory experiments.Due to the intrusion of seawater,marine soft soil has a certain amount of soluble salt.Based on indoor salinity determination in two typical marine soft soil layers of Ningbo area,the physical parameters such as initial freezing temperature,thermal conductivity,specific heat capacity of frozen soil,elastic modulus of frozen soil and uniaxial compressive strength of frozen soil were studied.The effects of different factors on the thermophysical parameters of marine soft soil were obtained.Then,The frost heaving characteristics of marine soft soil under artificial freezing condition were studied by indoor frost heaving test.On the basis of a set of simple indoor frost heaving test device designed by the author,the orthogonal experiment and the single factor experiment of frozen-heave factor were carried out.The frost heaving test is carried out under the condition of one dimension freezing from bottom to top.The influence of four factors on frozen-heave factor,such as salt content,water content,cold end temperature and external load were obtained.So was The primary and secondary relation of four factors on frozen-heave factor.At the same time,the law of temperature field and the distribution of water redistribution in the test process were obtained through the measurement of the temperature and the moisture content in different parts of the soil sample after the freezing test.Moreover,in this paper,considering the phenomenon of two phase transition in the process of cooling and freezing of marine soft soil,the moisture and salt field,temperature field and stress field equation was modified.The frost heave prediction model of four dimensional coupling of water,salt,heat and force was established.Finally,on the basis of reasonable simplification of frost heave prediction model,the frost heave prediction model had been calculated by the PDE module in the two development of the finite element numerical simulation software COMSOL.Thus,the prediction of frost heave prediction model had been realized.The results of numerical simulation were compared with the measured results of the frost heaving test in the room,and the two proves the correctness of the study on the frost heaving characteristics of marine soft soil under artificial freezing.