Tset Research On Soil Improvement Technology For EPBS In Beijing Sandy Pebble Stratum

Now the urban rail transit construction in Beijing is facing unprecedented upsurge.In the tunnel construction, we often encounter the adaptability of earth pressure balancing shield construction in sandy pebble, which bring new technical difficult and challenges.One of the key technology in EPBS construction is soil improvement techniques, which is added soil-ameliorators in the soil and makes the soil to achieve the ideal of "plastic flow state", so as to meet the construction requirements.This article rely on EPBS construction practice of Beijing metro line 9,10 ,according to Beijing typical sandy pebble stratum, through theoretical analysis and large numbers of laboratory and in-situ tests, Research new foam agents and slurry system. Then apply these in practical engineerings and achieve following results.(1) Propose the preliminary of soil improvement agent performance evaluation system and evaluation method and design of mixing test of friction coefficient test, adhesion resistance test, slump laboratory test.(2) Foam modifier was researched conducted a number of laboratory and in-situ test about the interaction between sandy-pebble and foam modifier. Evaluation of the new type foam modifier stating by foam and two technical indexes of half-time, foaming multiple lies between 5～20, half period is more than 5 min. By laboratory and in-situ tests, confirmed the research foam modifier have good effect.(3) Developed a new type of mud improver conducted a number of laboratory and in-situ test about the interaction of sandy pebble and mud improver. The new mud improver full consideration the economic and environmental factors, contemporarily added guar gum clay grain and other materials. Through a series of tests find reasonable slurry preparation scheme and achieve optimal performance.(4) Summarized the interaction between improver,sandy pebble and shield, solved some technical problems in Beijing subway construction.According to the layer particle size distribution and material test to determine a reasonable injection proportion..Sandy pebble stratum shield construction need adding compound materials to improve the stratum. Foam and mineral material is good materials which enhance the waste plastic flowability and impermeability.Reduction of tool wear and saving driving cost achieved very good soil improvement effects.