Experimental And Numerical Study On Artificial Rapid Freezing And Hardening Of Saturated Soft Clay Layer

Compared with the traditional brine freezing method,the liquid nitrogen freezing method has the advantages of rapidity,environmental protection,and simple process.Using the liquid nitrogen freezing method to freeze the surface of the soft clay stratum and form a hard crust permafrost layer can be used for dredging fill soil solidification equipment and materials in sea areas.The dredging reclamation area and the water-rich soft soil area are quickly opened to traffic to provide traffic passages.Due to the fact that there are few studies on the formation of hard crust permafrost on the surface of liquid nitrogen freezing strata,this thesis carried out the liquid nitrogen rapid freezing saturated soft clay test based on this,and at the same time carried out the freezing test of conventional cold liquid,which highlighted the liquid nitrogen freezing method.the rapidity.After obtaining the internal temperature field and bearing capacity of the frozen soil under different pipe layout methods under the liquid nitrogen freezing test,a multi-level full-combination numerical calculation was carried out,and the effects of the number of frozen pipes and the buried depth of the frozen soil on the bearing capacity of the frozen soil were obtained.Ability to influence law.The joint bearing of the frozen soil foundation and the underlying weak layer is simulated,and the deformation characteristics of the frozen soil foundation and the underlying weak layer are obtained.The main work carried out and the main results obtained in this thesis are as follows:(1)The relevant physical parameters of the test soil were measured according to the specifications of the soil test.The curves of initial freezing temperature and unfrozen water content of the test soil with temperature were determined by NMR test.Among them,the initial freezing temperature is used as the basis for judging whether the soil is frozen,and the unfrozen water content curve is used as the connection item of the hydrothermal equation in the numerical simulation.(2)The liquid nitrogen freezing test system and the conventional freezing test system were built according to the similarity theory,and the freezing tests of three pipe layout methods were carried out respectively,and the general temperature field and settlement law were obtained.In the early stage of freezing,the cooling rate of liquid nitrogen freezing can reach 71.4 times that of conventional freezing methods;the rate of crossing circles between liquid nitrogen freezing tubes is more than 7 times that of conventional freezing;The average rate of expansion to each measuring point below the freezing tube was about 11 times that of the conventional freezing test.The order of carrying capacity under different pipe layout methods is three-pipe buried depth8cm>double pipe buried depth 8cm>double pipe buried depth 4cm.(3)Using the COMSOL numerical calculation software to expand the number of levels of physical experiment factors,the number of frozen tubes and the burial depth of frozen tubes 4×4 full combination of freezing and loading simulations were carried out.Increasing the number of frozen pipes and the buried depth can improve the bearing capacity of the permafrost foundation and reduce surface settlement.The order of the influence of various factors on the bearing capacity of the frozen soil foundation is freezing time > buried depth of frozen pipes > number of frozen pipes,and the increase of freezing time will weaken until the influence of the number of frozen pipes and buried depth is covered.(4)Calculate the settlement of frozen soil under the same amount of nitrogen,and evaluate the freezing efficiency of each pipe layout method.In this simulation,the freezing efficiency is the highest under the burial depth of 8cm and seven-pipe freezing pipe arrangement.Similarly,with the increase of freezing time,the influence of the number of frozen tubes and buried depth will be weakened until the coverage is reached.The joint bearing simulation of the frozen soil foundation and the underlying weak layer shows that the weak layer mainly undergoes compression deformation,and the frozen soil foundation shows overall settlement with the compression of the underlying weak layer.