Experimental Study On The Effect Of Water Level Change On The Development Of Frozen Wall

As a special construction method,artificial ground freezing method is a flexible,reliable and green technical scheme to solve the three difficult problems of "water,soft and unpredictable deformation" faced by underground engineering construction.However,with the rapid development of society,affected by the extraction of groundwater in the construction of dense urban buildings and large-scale lifeline projects,the regional or local groundwater level is in continuous change,and the shape of water level funnel is constantly evolving,which will lead to differences in the buried depth of groundwater level in different regions,and the existence of water directly affects the construction process of artificial freezing method.Therefore,in the design and construction of artificial freezing,the effects of different groundwater levels on freezing temperature field,development and thickness of freezing wall and frost heave should be considered.Through the three tube freezing model test,taking the typical muddy soil and sand in the construction of artificial freezing method as the research object,this paper systematically studies the formation and development law of frozen wall in the process of soil freezing,the relationship between frost heaving and water replenishment of muddy soil under the open system,and the reasons for the difference of temperature field between the two kinds of soil by using two research methods of numerical simulation and physical model test.The main research results are as follows:(1)The rise of water level delays the expansion of the freezing front of muddy soil and prolongs the intersection time of freezing wall.The intersection time of muddy soil40 wl is 42% longer than that of 0wl,while the effect of water level on the development of sand freezing wall is the opposite.The main reason is that the change of temperature field of mucky soil under different water levels is mainly related to the degree of soil water migration.During freezing,the water migration in unfrozen area and the replenishment of water source under open system affect the water content of soil.Because of its large porosity and high permeability coefficient,the gas phase in unsaturated pores will dissipate part of the cooling capacity in the process of heat transfer and delay the cooling rate of soil,On the contrary,the freezing effect of saturated sand is better than that of unsaturated sand.(2)When the water level reaches 20 wl and does not pass through the freezing pipe,the soil temperature field is no longer symmetrical about the L axis.The location of groundwater level changes the spatial distribution of cooling capacity in freezing area.(3)In the open system,the rise of water level increases the amount of make-up water in the freezing process of muddy soil.Compared with 20 wl,the amount of make-up water in 40 wl increases by 68%.Under the action of water migration,the water content in the freezing area increases,which leads to the expansion of soil after the water phase turns into ice and increases the amount of frost heaving.(4)Through the numerical simulation study with COMSOL,the formation process of sand freezing wall under different water storage models is simulated,which provides a certain theoretical basis for studying the influence of different groundwater levels on the development of freezing wall and the difficulty of freezing wall intersection.There are 37 figures,6 tables and 103 references in this paper.