COMPARISON OF THE HYPERBOLIC AND ASAOKA OBSERVATIONAL METHOD OF MONITORING CONSOLIDATION WITH VERTICAL DRAINS
1996 年 36 巻 3 号 p. 31-42
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1996 年 36 巻 3 号 p. 31-42
The use of vertical drains and surcharge to accelerate the consolidation of clayey soils is well established in soil improvement technology. For this method of soil treatment, it is important to monitor the progress of consolidation where the average degree of consolidation is usually defined as the ratio of current settlement to the ultimate settlement due to primary consolidation. An accurate estimate of the ultimate primary settlement is, therefore, required in order to determine the state of consolidation, and the appropriate time for surcharge removal when the desired degree of consolidation has been achieved. Recently, Tan (1995) proposed a new hyperbolic method to identify the 60% and the 90% consolidation stages from field settlement data due to one dimensional consolidation. Knowing the settlement at these points, it is possible to determine the ultimate primary settlement. Once sufficient data has been recorded to identify the linear portion of the hyperbolic plot between the 60% to 90% consolidation stages, the method can be employed. This method has been validated by application to various well documented case histories in the published literature. In Japan, however, Asaoka's method for estimating ultimate primary settlement from field observation has been widely used and is well accepted by the geotechnical engineering community. This research paper presents a comparison of two different observational methods for monitoring the progress of consolidation to determine their similarity and differences, and their accuracy of predictions compared to actual observations. First, the theoretical basis of the two methods are examined. It was found that settlement data beyond the 60% consolidation stage are needed in both methods to make accurate predictions of ultimate primary settlement. Next, both methods are applied to oedometer laboratory consolidation data for kaolin specimens in order to determine how prediction of ultimate primary settlement and coefficient of consolidation would compare in carefully controlled laboratory experiments. Finally, both methods are applied to several well documented case histories of vertical drain projects, and the predictions of ultimate primary settlement and in situ coefficient of consolidation are compared. It was found that both methods gave good agreement with predictions, making them complementary tools for use in monitoring consolidation in field applications.
