Performance Testing And Research Of Foaming Agent Used In EPB Shield

EPB(Earth Pressure Balance)shield construction technique,which been widely used currently has great advantages in the tunnel construction comparing to other shield construction technique,including low impact on ground,high construction efficiency and meet social demand.However,jam,break and spewing issues always happened during EPB shield construction as the soil nature.To solve these issues,foaming agent been investigated and results shows the foaming agent can not only optimize the soil state but also have negligibly small impact to our environment.In this paper,three kinds of foaming agents are selected for commercial EPB shield investigation.The foaming properties and the properties of foamed improved soil are studied in a progressive manner,which provides references for engineering development.Main investigation results as follows:(1)Based on mixing experiment results,the foaming ability of BASK and KDK is better than SYSAM no matter in adequate or inadequate foaming conditions.BASF shows good foaming ability under partial foaming condition,the foam height reach high level within 1 min and achieve full foam within 1.5 min.For KDK,it can achieve full foam within 2 min,slightly worse than BASF.From half-life side,SYSAM foam half-life more than 9 min while higher half-life will bring more geotechnical difficulties to the foam modified rock & soil treatment.The half-life gap between BASF and KDK is small,but the BASF foam dehydration speed is low and the bubble can maintain the initial frame with sufficient dehydration.In the study of the influence of temperature on foaming quantity and half-life,found the temperature have big impact on foaming quantity while few impact on half-life.The foaming rate test shows that the foam obtained by BASF is more homogeneous and more concentrated with a particle size range,while the concentration range of KDK foam is larger,so the KDK foam size distribution is more uniform.The total number of bubbles collected from BASF and KDK increased with the increase of gas-liquid ratio.BASF can produce more effective foam at a higher gas-liquid ratio.The attenuation experiment showed that KDK foam have fastest foam number decrease rate and big diameter bubble number increase rate within foam machine shutdown 1 min.The larger gas-liquid ratio lead to smaller foam particles number.Also,with the increase of time,the number of small particle bubbles decreases and the number of large diameter bubbles increases.(2)In the compression test,when the BASF foam was used to improve the soil,the compression volume at the same pressure increased obviously with the increase of injection rate.After the injection rate was over 60%,the compression volume did not change significantly with the injection rate.The amount of compression for KDK foam improved soil was also improved,but after injection rate was over 40%,the injection rate did not change significantly,and the BASF foam had greater injection rate.The BASF foam has better regulation effect when the injection rate is large.In shear test,the torque of soil improved by BASF decreases with the increase of injection rate under the same pressure,while that of soil improved by KDK decreases with the increase of injection rate,but the difference between the injection rate of 60% and 80% is not obvious,and the reduction of torque is smaller than that of soil improved by BASF.The slump test shows that different moisture content has great influence on foam injection effect,and foam can only regulate soil better when the soil has certain moisture content.In the direct shear test,it is known that the BASF foam injection rate decreases significantly in the 20%~40% interval.After that,the cohesion decreases with the increase of injection rate,but the improvement is slightly.The injection rate selected as 20%~40% can achieve the best effectiveness and cost-effective.For the improvement of friction angle,the effect of different injection rate ranges increases approximately.(3)The formulation of BASF foaming agent was analyzed and the related literature was investigated.Finally,the foaming agent,foam stabilizer,tackifier and auxiliaries were determined as foam composition.Six kinds of surfactants were selected and two kinds of surfactants,sodium dodecyl sulfate(SDS)and dodecyl dimethyl betaine(BS-12),were optimized through a large number of experiments.It was found that when the ratio of SDS: BS-12 was 4:1,the foaming effect of the system was the best.Then,sodium carboxymethyl cellulose(CMC)was selected as tackifier,and the foaming and foaming stability were better when the concentration was 1.5g/L.Finally,ammonium chloride is selected as an additive to determine a self-made foaming agent formula for EPB shield construction.