Experimental And Mechanism Study On Sand Flow Method For Immersed Tube Tunnel Foundation

Along with the rapid development of social and economic, rivers, Strait on both sides of theBay urban development and transportation have become increasingly outstanding, theconstruction of underwater tunnel has become a trend at home and abroad across the river (sea)transport carrier. Immersed tube tunnel its superiority and the main types of underwater tunnelconstruction. Sand flow method is advanced immersed tube tunnel foundation treatmentmethod, widely used.Series of sand flow experimental investigation of the previousengineering practice and get some results, but there are even more vague gaps: the lack ofpipe section elevation, different construction boundary, the bottom surface roughness of thepipe section on the sand flow method research.In addition, so far no foundation trench flow field distribution and the expansion process ofthe sand tray, sand tray cannot be extended size, full density, water pressure and otherparameters give a reasonable explanation, thereby constraining the sand flow method design,construction take value.Problems sand flow method for the foundations of the immersed tube tunnel reinforcementtechnology, this article on the basis of previous studies by large sand flow method scale test ofdetailed experimental data; explore the elevation of the pipe section, the constructionsequence of the sand tray resistance of silt measures, the bottom surface roughness of the pipesection and other factors affect the extension of the sand tray; analysis of the characteristicparameters and construction parameters of the sand tray association; the sand traymorphology obtained by the combination of model test, the use of numerical calculation andtheoretical analysis and interpretation the sand tray formation mechanism of expansionFinally, the corresponding recommendations were given for engineering practice. In thispaper, the findings and conclusions as follow:（1）Foundation reinforcement of the immersed tube tunnel by the sand flow method scale testof principle. The construction of large-scale the sand flow method full-scale test model systemto simulate the construction of a sand tray within the pipe section; test model, test equipment,test materials, test conditions can be enough feet to simulate the actual project and guide theselection of engineering practice. Developed a sand tray detectors and for the real-time detection of the test sand tray; improved situ sand replacement method and used for sand traydensity test（2）The pipe section uplift the overall process in line with the exponential rising displacementmode, can be divided into three phases, with a fast-slow-fast. The sand flow method toenable the pipe section elevation instantaneous beat modest and basic to maintain the level ofuplift. The elevation of the pipe section has no effect on the balance of sand tray extension,but significantly reduced the growth rate of the sand disk radius, affecting fullness.Engineering practice weights and effective measures to be taken to ensure that the pipesection elevation occurred in the sand tray is extended to the design radius; design elevationto allow the case to the appropriate use of uplift I stage can reduce the flow seam, thethickness of the chute, and increase the density of the sand tray.（3）At the boundary of the sand tray still full of foundation trench. Plugging the boundary thesand disk of the uneven pace of expansion, but no significant effect on the direction of thesand tray extension and sand tray overall expansion trend. Short pipe section at the edge ofthe boundary blocking can improve the sand tray "projecting", is conducive to increasing thesand tray full of degrees. The border closure the pressure sand system water pressure and themodel plate bottom water peak pressure has no effect, but significant effect on the blockingside water pressure fluctuation characteristics; reduce to some extent the upper density of thesand tray, and making layers of sand tray the increased density in the plane distribution ofdiscrete; sand rent density is not particularly affected on the closure side. Engineeringappropriate boundary closure can "force" the sand disk formed approximate rectangular Sand,improve the sand tray fullness, save construction time, too many boundaries adverse sandtray.（4）Different pipe section bottom surface roughness of sand tray size and fullness. Theroughness of the underside of the pipe section so that the sand tray extension faster, betterbalanced. The project should take adequate measures to ensure the flatness and smoothness ofthe underside of the pipe section; the sand tray size up to850cm, the design may beappropriate to increase the radius of the sand tray.（5）The sand flow method process has gone through two main phases of the sand tray "form"and "expansion" phase. The formed phase leads to a clear separation of the sand particles, "extended" phase formation sand tray oblique layered texture, but sorting weakened. Sandflow method in the base slot gap formed sand tray, alluvial pit flow seam, launder, obliquelayered texture structure.（6）Flow seam, the spatial and temporal distribution of the chute decided to lose the amountof sand of the sand tray, extended balance one of the factors affecting the sand tray. Sand eachdisk with the sand disk radius increases to the rate of expansion and the gradual emergence ofdifferences (uneven expansion), sand disc radius expansion trends over time showed aquadratic relationship.（7）Sand pump outlet water pressure from the construction conditions and the influence oftime, only sand pump characteristics; the pipe section throughout the bottom water pressureincrease with the expansion of the sand tray fluctuations. The pipe section at the end of thecentral area of water pressure trend of increase in the fluctuations in the linear peak before theend of the test, the pipe section at the end of the maximum water pressure.