In the field, the ground settlement behavior is monitored through the instrumentation. Based on the measurement results, future settlement is predicted and evaluated. Soft soil improvement using both preloading and vertical drain is generally adopted with a staged filling at the construction site. To determine an optimal filling height and filling loading period the settlement should be predicted. Therefore, Hyperbolic method, Asaoka method, and other methods are being used in the field for this purpose. However, these methods are only able to predict settlement after a certain filling stage (usually the final filling stage). In addition, the reliability of these methods are significantly varied depending on the geologic profile, instrument condition, and etc in the field. Therefore the engineers should be very cautions and have a correct judgement when using these methods for the prediction of settlement.
This study suggests new three methods which are improved the weak points of the existed methods. The suggested methods are Kang′s method, 2nd-Hyperbolic method, and 1-D Theory Simulation method, respectively. The Kang's method, the 2nd-Hyperbolic method, and the 1-D Theory Simulation method are based on the horizontal drainage theory, the existed Hyperbolic method, and Terzaghi's theory, respectively. Especially, the Kang's method can be able to incorporate the field's soil properties. The Kang's method can indirectly predict soil parameters and verify the ground characteristics through the back analysis of the predicted settlement. Also, this method can be used for estimation of drain's characteristics related to the consolidation effect.
To verify the applicability of the Kang's method, the 2nd-Hyperbolic method, and the 1-D Theory Simulation method, two sites near the Nackdong-river are selected. The ground of these sites were improved by a vertical drain. The settlements are predicted by both the existed and the new methods and then are compared to the measured data.
The settlement predicted by the Kang's method shows little compared to those of the other methods. However, the comparison results indicate the Kang's method has enough reliability to use for the settlement prediction. The 2nd-Hyperbolic method predicts little higher settlement compared to that of the Hyperbolic method, but it shows much better reliability compared to the Hoshino method. It also shows that the 1D-Theory Simulation method overestimates settlement with very irregular trend on the vertical drain improved ground.
Using the Kang's method, the settlement data measured during the initial filling are analyzed to obtain the soil parameters which need to predict the settlement curve. Then using the obtained soil parameters the time - settlement curve is predicted for the next filling stage and compared to the measured one. The predicted settlement is well matched with the measured one. Based on the study results, the Kang's method is able to predict settlement during the staged filling with only the initial settlement data and might be used usefully for construction management of the staged filling project.