【正文】
prediction methods on field measurement observation , which have indicated promising results and bee an accepted method to estimate final settlements and rates of settlements. Stage construction is a typical procedure for embankments on the soft ground. With a certain period of consolidation at every stage construction ,the safety factor of the embankment can be generally raised and the post construction settlement may be reduced. The settlement time curve during stage construction may be more plicated than it is with instantaneous loading. The period for primary consolidation at a definite final load with stage construction may be increased significantly , in spite of the fact that the post construction settlement can be reduced. In order to speed up the rate of settlement and minimize the post construction secondary settlement of soft clays , surcharge is often used in practice ,which can be taken as a type of stage construction with temporary loading and unloading stages . Problems related to the settlement analysis of stage construction for embankments on soft clays are of the following types: (1) Prediction of the deformation behavior of stage construction from the results of borings and tests . (2) Prediction of the final settlement at permanent load from the behavior of the first stage construction. (3) Prediction of the post construction settlement at the permanent load and corresponding time of surcharge removed from the behavior of the surcharge. The first of these problems is heavily dependent on the theory , which is necessary in design. The other two predictions require empirical rather than theoretical methods because they are based on observational data. In any case , the fact that the second and third predictions are derived from field observations makes them more reliable than the theoretical predictions . Leroueil et al revealed the effective stress path and analyzed the relationship between vertical settlement and lateral displacement during stage construction. Stamatopoulos and Kotzias developed a method to determine the final settlement at permanent load from the behavior of surcharge, but it is based on the elastic theory and difficult to calculate the rate of the settlement . The hyperbolic method is based on the total load settlement relationship to predict the final settlement , which is not sensitive to the nature of the initial loading condition. This paper presented a method for the prediction of the final settlement at permanent load from the behavior of the first stage construction based on the Asaoka method. 2. Stage observational method Asaoka proposed an‘observational procedure’to estimate the final settlement and in2situ coefficient of consolidation from the field observational data. This method is being increasing popular because of its simplicity and effectivity. The method is based on the fact that one dimensional consolidation settlements S0 , S1 , S2 , … , Sj at times 0 , ? t , 2? t , … , j? t can be expressed as a first order approximation by which represents a straight line in a Sj vs Sj1 plot , where 0? is the intercept and 1? is the slope of the line. When the ultimate settlement has been reached : Sj= Sj1=Sf , therefore ,the ultimate settlement Sf can be given by and ln 1? = 26H tCV? (both top and bottom drainage) ln 1? = 22H tCV? (top drainage) The constant 1? has been suggested by Magnan and Deroy to be related to the coefficient of consolidation Cv as follows: for horizontal radial drainage only for vertical drainage only where De , H are the drainage path length respectively. Asaoka method also stated that the straight line in Sj Sj1 space would moved up in the case of multistaged loading , moreover , the shifted lines bee almost parallel to the initial when the settlement is relatively small pa