| Lianyungang marine soft clay is deposited by muck and mucky soil. It has the following characteristics:high moisture content,high void ratio,high compressibility,low permeability,low strength,low bearing capacity and obvious rheological characteristic. It is necessary to predict post construction settlement of expressway embankment on this soft soil accurately in order to guarantee the safety running of expressway in its service time.Surcharge preloading is one of the most frequently used soil improvement methods in expressway construction in Jiangsu province. Experiences in present preject practices are generally appled to solve problems occuring in preloading design. So it is necessary to investigate preloading effect. Based on the work completed by predecessors,a lot of work on laboratory tests and numerical analysis is made and the research achievements are as follow:1) In order to study the engineering properties of Lianyungang marine soft clay,a large number of triaxial rheological tests are completed. Accordingly the creep properties of the Lianyungang marine soft clay are put forward. And the empirical constitutive relationship of Lianyungang marine soft clay has been presented based on the test result. Furthermore,the coefficient of viscosity and critical creep yield stress of Lianyungang marine soft clay on different stress level are analyzed.2) Based on the analysis and summarization of the rheological laboratory tests results and some settlement phenomena of an expressway embankment in Lianyungang region,the generalized Bingham model is selected to describe the rheology behavior of Lianyungang marine clay. To combine the two-yield-surface elastic-plastic model with the generalized Bingham model,in terms of viscoplastic theory,a 2-D FEM calculation program is perfected. With the use of the FEM program,some sectional settlement in construction stage and post construction stage of an expressway in Lianyungang region are analyzed. The result of calculation settlement is coincided with the data measured in the field.3) Using the program mentioned above,taking some sections of an expressway in Lianyungang region as example,preloading effect of different preloading time and surcharge height are analyzed. Based on the test and FEM analytic result,research on maximum filling height of preloading for Lianyungang marine soft clay has been presented. |
