A Study On Construction Technology Of Large Diameter Slurry Balance Shield Tunneling In Upper-soft Lower-hard Ground

With the rapid construction of railway, large diameter slurry balance shields are used in constructing more and more tunnels. In the course of tunneling process, shields will inevitably encounter all sorts of different geological conditions. Especially in the pan-pearl river delta region, shields will often encounter upper-soft lower-hard ground.They have gradually been a hot yet difficult area of research in tunnel engineering. Various disasters will happen, such as shield off axis, spewing, excavation surface instability, mud cake, cutter serious wear, hard and soft interface tool cleft, leading to serious land subsidence,and so on. This not only increases the difficulty of construction, but also delays the construction period which increasing the costs of project management. Taking the current situation into account, A study on construction technology in tunneling upper-soft lower-hard ground becomes more urgent and important for large diameter slurry balance shields.Combining with a case study of SHIZIYANG tunnel, the results of this dissertation are systematically summed up, the construction technology of FEM numerical simulation, cutter configuration, driving parameter selection, gesture control technology in tunneling upper-soft lower-hard ground. the shield construction technology is greatly enriched to give similar formation construction strong reference and guiding significance. There are wide and good prospects for popularizing this technology. It is concluded as follows:1. After analysis and comparison of FEM numerical simulation, it is concluded as follows:Shield excavation construction makes the upper soil subsidence displacement field. The lower layers disturbance displacement field is smaller. Near the tunnel floor layers appear smaller. At the same time, shield construction parameters have an effect on the maximum displacement and minimum buoyancy.2. In construction process of tunneling upper-soft lower-hard ground, the cutter head of large diameter slurry balance shields adopts the panel. Its aperture ratio is about30%. Cutting tools configuration is4-6the hob in outer ring, new rotating scraper in the median ring, the hob and scraper mix of tools in the inner ring, along with the excavation surface hard rock ratio and strength to adjust the proportion of the hob.If upper-soft lower-hard ground is longer, it should be considered a hob and a spatula on the outer ring the same track line layout, and the scraper should be slightly higher than that of hob. 3. In construction process of tunneling upper-soft lower-hard ground, driving parameters settings of large diameter slurry balance shields is,normally, which the torque coefficient is generally not less than10, which torque should not be greater than the maximum torque of80%.It should not be over-emphasized driving speed. In fully pay attention to the cutter structure strength and shield design under the premise of maximum capacity, reducing rotating speed of cutter is1.1～1.2rpm, increasing the cutter torque is5000～11000kNm, reducing the driving speed is10～12mm/min, increasing thrust is4000～5000t.4. In construction process of tunneling upper-soft lower-hard ground, the segment of attitude should adapt to the shield attitude, focus on the attitude control is the relative position relationship between the two. In the course of tunneling process, shields attitude mutation use the method of correcting the partition pressure difference. In the case of segments implosion and deviation from the axis too large, the stress release and change the amount of jack in order to correct an error. During the course of deviation, deviation correction radius must be larger than the offset radius should be slow, long distance deviation.