Experimental Study On Shield Foam Performance Evaluation And Microscopic Mechanism

With the rapid development of urban rail transit construction,the earth pressure balance shield has been widely applied as an advanced construction method.However,when this method is used in the construction of sand and gravel soil,the improvement agent must be added to make the excavation soil "plastic flow",and the foam is the most economical and efficient soil amendment.At present,the foam used in engineering practice is mostly dependent on foreign imports,and the unified evaluation standard of foam is not formed.And most of the research on foam is limited in macro aspects.Therefore,it is very necessary to study the foam performance and analyze and evaluate the micro morphology.In this paper,three kinds of reagent which are commonly used in the market,and five kinds of foam reagents in the laboratory are studied.The theoretical study and laboratory test are combined to systematically evaluate the foaming and stability of the foam,and the analysis is made from the micro angle of the foam morphology and particle size inch.The main work is summarized as follows:(1)By reading a large number of relevant literature,the basic theoretical knowledge of foam is understood and the microstructure,structural composition and growth process of the foam are described in combination with microcosmic experiments.According to the foaming process,the foaming capacity and stability of foam were measured by the bubble volume,half life time and foam comprehensive index,and the foam properties were evaluated qualitatively and quantitatively,and the influencing factors were analyzed.(2)The Warning-Blender agitation method was used to foam the test reagents.The large concentration range of foreign1,foreign2 and civil3 was pretested,and the reasonable concentration gradient was determined.The foaming property and stability of foaming agent solution at different concentrations were comprehensively evaluated,and the recommended value of suitable concentration was proposed.3% concentration of foreign1 and C reagent were used to test the temperature,and the change of foam performance with temperature was studied.The results were analyzed and the mechanism was explained.It was pointed out that the temperature had a significant effect on the half life time.(3)The Baiter particle image analysis system BT-1600 was used to carry out microscopic tests to observe the morphology and structure of the foam under optical microscope.3% different concentrations of eight reagents were used to obtain the foam size distribution at the initial time,which belonged to the micro foam system.Taking foreign1 reagent as an example,the influence of different concentration on the size distribution of foam was studied,and the mechanism of influence was explained.The dynamic change of diameter of the overall foam system was studied,and the mechanism of foam decay was analyzed from the aspect of bubble size.