1、Settlement prediction of embankment s with stage LIU Song-yu（ Institute of Geotechnical Engineering, Southeast University,Nanjing 210096,China） JING Fei（ Institute of Geotechnical Engineering, Southeast University,Nanjing 210096,China） Abstract: The magnitude and rate of the settlement are the key e
2、lements subjected to design analysis of embankments on soft ground. The observational Institute of Geotechnical Engineering,Southeast University,Nanjing210096,China methods based onfield measurement have indicated the promising results and become effective methods to predict the final settlement, wh
3、ile the uncertainties of parameters and theories limit significantly the accuracy of settlement estimation. This paper presents an observational method to predict the settlement performance of embankments with stage construction on soft ground based on Asaoka method. The case studies show the accord
4、ance of the predicting results with the field measured data. It is also given from the case study that the value of Eu / Cu ratio ranges from 50 to 100 for Jiangsu Marine clay and its actual coefficient of consolidation is almost one order of magnitude larger than the laboratory data. Key words: set
5、tlement, embankment, observational method, stage construction 1. Introduction Settlement and stability are two primary considerations systematically related to the design of an embankment on soft ground. The tools available for the stability evaluation seem to be satisfactory. The key element of lon
6、g term behavior of the embankment routinely subjected to design analysis is the settlement. In other words , the settlement analysis is the most appropriate approach to the embankment analysis . The settlements of embankments on soft clays result from the consolidation and the lateral flow under the
7、 embankments. Many researches have been made on performance of embankments on soft ground. Although many experiences have shown the practical value of the theory for estimating settlements and settlements rates , they also illustrated some of the problems in volved in making accurate prediction of t
8、he settlement .Duncan (1993) and Olson (1998) analyzed the uncertainties causing the shortcomings in the current state of the art for settlement prediction respectively. These uncertainties sometimes make it difficulty or impossible to estimate the magnitude and rate of settlement for embankments .
9、Although the numerical analysis may be possible to improve the accuracy , the soil models may involve many parameters that can not be determined economically. However , the evolution of numerical methods with computer may result in simpler models and complete codes that are increasingly becoming ava
10、ilable. It is desirable therefore to develop observational methods based upon which the settlement can be estimated once sufficient data has been recorded. Many researchers developed the settlement prediction methods on field measurement observation , which have indicated promising results and becom
11、e 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 cons
12、truction settlement may be reduced. The settlement - time curve during stage construction may be more complicated 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 th
13、e 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 . Pro
14、blems 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
15、 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 pred
16、ictions 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 s
17、tress 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 difficul
18、t 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
19、permanent load from the behavior of the first stage construction based on the Asaoka method. 2. Stage observational method Asaoka proposed anobservational procedureto estimate the final settlement and in2situ coefficient of consolidation from the field observational data. This method is becoming inc
20、reasing 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 Sj-1 plot , where 0 is the intercept and 1 is the slope of the line. When the ultimate settlement has been reached : Sj=
