Study On The Property And The Influence To Surrounding Environment Of Artificial Freezing Soil's Thaw-settlement

The paper based on the case of shield tunneling horizontal freezing reinforcing engineering of Nanjing Subway Branch No.2 Yixianqiao Station. A comprehensive analysis approach, consisting of laboratory experiment, field measurement, theoretical analysis and numerical simulation calculation, was employed to study the property of artificially frozen soil thaw settlement, the physical and mechanical property of freezing thaw soil. In addition, the influence to surrounding environment and the prevention measurements of the freeze-thaw effect were also proposed.The primary studies are as followed.1.The thaw settlement property laboratory experiment was carried out to test some typical soil of Nanjing with the self-made thaw settlement testing devices. The cod junction temperature, water content, dry density, load and melting temperature were tested for the influence to thawing settlement coefficient. Prediction model of artificial frozen soil thawing settlement coefficient was built up with BP artificial neural network.2.Another laboratory experiment was taken on the widely distributed silt clay in Nanjing. The difference of physical and mechanical properties between intact soil and thawed soil was studied systematically. Furthermore, the effects of initial water content, initial dry density, opening condition, cold junction temperature, melting temperature to the physical and mechanical property of thawed soil were also detected.3. Referring to the features of artificial freezing method, a finite element modeling method, which is able to respond to the environment-influencing factors including frozen soil thawing settlement, changes of thawed soil constitutive relation, consolidation of thawed soil, soil body opening uninstall, was proposed.4.A finite element analysis was made to the actual case of hield tunneling horizontal freezing reinforcing engineering of Nanjing Subway Branch No.2 Yixianqiao Station by using the 3-D finite element modeling method mentioned above.5.The 3-D finite element modeling was employed to systematically analyze the relationship between different parameters and melting temperature field, ground displacement field,ground settlement speed.6.In the application of numerical simulation, the influence of the thawing methods,position of grouting, quantitiy of grouting, the times of grouting and grouting mode to ground settlement were analyzed, pointing out the method of thaw settlement grouting after divisional forced thaw is the effective measures to prevent artificial frozen soil from thawing settlement.