| In recent years,the development of super high-rise buildings and urban underground space has developed rapidly.The design and construction technology of foundation pit engineering has been continuously innovated,and many new foundation pit support methods have appeared.Especially in order to solve some silt-based layers and projects that cannot be used for precipitation by dewatering wells,the artificial freezing method can be used for construction.The artificial freezing method has little impact on the underground structure of surrounding buildings,and does not cause pollution and damage to groundwater and underground pipelines.The frozen soil retaining wall formed after the soil is frozen not only has a certain strength to withstand the earth pressure,but also has the function of stopping water.It is a practical,green,and pollution-free construction technology.Because the artificial freezing method is rarely used in foundation pit engineering,and the complexity of the soil itself,there are many wall parameters that affect the frozen soil retaining wall of the foundation pit,so the application of artificial freezing technology in foundation pit engineering needs further research.This article has carried out research on the parameters of the frozen soil retaining wall of the foundation pit.The specific research content and conclusions are as follows:(1)Introduced the supporting principle,the scope of application,the design theory of the embedded depth and width of the retaining wall,and the method of checking the stability of the retaining wall.(2)The influence parameters and regular analysis of the strength of the frozen soil retaining wall of the foundation pit are studied.The silty clay of the Changchun area of the same dry density is used,and the soil with the moisture content of 14%,18%,22%,26% and 30% is used.Frozen at constant temperature to-10℃,-15℃,-20℃,-25℃ and-30℃,the soil samples were subjected to uniaxial compression and triaxial shear tests,and the frozen soil temperature was-10℃～-15°C,as the moisture content increases,the uniaxial compressive strength gradually increases.At-20℃,the inflection point of frozen soil compressive strength decreases.In the range of-20℃～-30℃,as the temperature continues to drop,the compressive strength of frozen soil gradually increases;when the temperature is between-10°C and-15°C,the shear strength of frozen soil gradually decreases with the decrease in temperature,and the shear strength is the lowest at-15°C.When the temperature is-15℃～-30℃,the shear strength of frozen soil gradually increases with the decrease of temperature;the moisture content is between 14% and 18%,and the compressive strength of frozen soil increases with the increase of moisture content.However,when the moisture content further increases,the compressive strength gradually decreases.In the interval of 14% to 30%,the shear strength gradually decreases as the moisture content increases.(3)The initial freezing temperature test of silty clay in Changchun area has been carried out,and it is concluded that the initial freezing temperature of silty clay in Changchun area is lower than-0.25℃ at water content of 14%,18%,22%,26% and30%,the interval range is-1.3℃～-0.25℃.(4)Using the existing equipment in the frozen soil laboratory,the equipment assembly for the frozen soil retaining wall test of the foundation pit was carried out.The test equipment for the frozen soil retaining wall of the foundation pit consists of four parts,an environmental test chamber,a refrigeration system,a circulation pipeline and a temperature measurement system,and the whole process of the test is introduced in detail.Collect the freezing process by changing the water content parameters(18%,22%,26%,and 30%)of the frozen soil retaining wall of the foundation pit and the freezing liquid temperature parameters(-15℃,-20℃,-25℃ and-30℃),the temperature and time change data,analyzed the influence of the freezing liquid temperature and the initial moisture content of the soil on the freezing process of the frozen soil retaining wall of the foundation pit,and found that the freezing liquid temperature directly affects the freezing speed,and the lower the freezing liquid temperature,the faster the soil freezes,and the larger the initial moisture content of the soil,the lower the temperature at which the soil freezes and stabilizes,and the freezing radius increases at the same negative temperature.(5)The basic concept of temperature field and thermal parameters(thermal conductivity,specific heat,latent heat of phase change,convective heat transfer coefficient)were introduced,and numerical simulation of wall parameters was carried out using finite element software ABAQUS,and the freezing range of single-row pipes was found the ellipse expands outward,and the simulation results are analyzed.Finally,the simulation results of the temperature field are compared with the indoor retaining wall test data.The results are shown to be consistent,which proves the feasibility of the finite element numerical simulation and the correctness of the test law of forming the frozen soil retaining wall of the foundation pit is verified.The results of the research and analysis on the parameters of the frozen soil retaining wall of foundation pits in this paper can provide guidance for the design and construction of artificial freezing foundation pit engineering and provide important reference materials for deep foundation pit freezing technology. |
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