Experimental Study On Circular Frozen Soil Wall For Pit Excavation In Seasonally Frozen Area

Artificial Ground Freezing has not yet been widespreadly applied in pit engineer-ing up to now, and one of the most important reasons is that Artificial Ground Freezingneeds plenty of energy, which hinders the promotion and generalization of this"green"engineering construction technology. There is a great deal of seasonally frozen region inChina, and it must save greatly vast energy to carry out Artificial Ground Freezing undernaturallow temperature conditioninseasonallyfrozen layer. Hence, the circlefrozen walllarge-scale model test was performed with seasonally frozen layer, in order to reveal arti-ficialcharacteristicsandlawof initialtemperaturefield, calorifics, mechanicsandenergy-saving of freezing wall along length, which is theoretically and practically valuable andsignificant to promote the development of pit supporting technology in seasonally frozenregion.Based on systemic sum-up and profound analysis of the relative national and inter-national research, the circle frozen wall was mainly studied by large-scale model test withthe menus temperature condition of seasonally frozen layer, as well as through numericalcalculation, frost-heave model and so on, the fulfilled research work as follows:1. 8 items of tests were conducted on 37 Xuzhou silty clay samples, and the charac-teristics of physics, calorifics and mechanics were obtained, which provided experimentalparameters for model test and numerical calculation.2. According to similarity criterion, a large-scale model test equipment was de-signed, developed and rebuilt to satisfy the requirement of experiment projects. Thematched freezing, loading and monitoring systems were also developed to insure the ra-tionality of test results.3. Large-scalemodelcircleartificialfrozenwalltestswerecarriedouton10kindsofexperimental conditions with or without seasonally frozen layer to investigate the changelawoftemperatureandfrost-heaveforceoffrozenwallwithseasonallyfrozenlayer. Afterexcavation, the air balloon was compressed to simulate horizontal ground stress and studythe variation of displacement. The influence law of seasonally frozen layer on the energyexpenditure of artificial frozen wall was got by monitoring the flow-rate consumption offreezing salt water. 4. Intermsofthecollectedtestdata, theformationtimeofcircleartificialfrozenwallwas obtained with seasonally frozen layer, as well as the important and obvious restrictionon horizontal displacement, increment of freezing velocity and the relative experienceformula.5. The energy-wasting characteristics of 2-dimension plane numerical model offrozen wall was founded and calculated by FEM software, which provided the feasibleproof for large-scale model test.6. Based on the background of engineering construction by artificial ground freez-ing, the necessity of foundation of macro frost-heave model was proposed, of which thenumerical calculation method was developed, and the model was validated by frost-heavetest and experimental data from international researchers.Through all above research work, the main study production was achieved as fol-lows:1. Therulesweregainedfromtheaffectionofseasonallyfrozenlayerontemperaturefield, frost-heave force, deformation from load, energy-wasting of artificial frozen wall ,and so on. It can be concluded that the lower the temperature of seasonally frozen layerwas, the faster the temperature field went down to the menus value, and the stronger theresisting force of frozen wall against load, but, at the same time, the bigger frost-heaveforce was.2. The results from model tests and numerical calculation demonstrate that the ex-istence of seasonally frozen layer will obviously reduce the formation time of artificialfreezing wall and the energy waste.3. From the change rules along depth of all kinds of monitoring data of frozen wallmodel tests, it can be seen that the influence range of seasonally frozen layer on the frozenwall.4. The relationship between change rate of porosity and segregate potential in freez-ing frontier on the foundation of segregate potential theory was founded, also the FEMcalculation formula of frost-heave.5. Numericalsolutionofmacrofrost-heavemodelwasperformedthroughABAQUSby using Fortran and python language, and the numerical calculation model was founded.By comparison, the results of numerical calculation was almost correspondent with thoseof numerical calculation.