The Characteristic of Consolidation by Suction Drain Method and Influence of Hardening Zone

Abstract

The purpose of this study is to assess the degree of improvement per duration of improvement for suction drain method which does not require surcharge load and sealing sheet and to evaluate the impact of hardening zone in order to improve soft ground for its purposes. The laboratory column test was performed varying the duration to apply suction pressure. The fixed factors of this test were the suction pressure applied (0.8kg/cm 2), the length of drain (50cm), and thickness of sealing layer (50cm) and the duration of application for suction pressure was varied to 5 different periods such as 4, 8, 12, 16 and 20 days. The result in settlement indicated that the degree of improvement increased when the duration of application for suction pressure increased and it converged gradually after 16 days. When the distribution of strength occurred by the distance from drain was normalized by the suction pressure applied, ratio of increased strength increased upon the increasing duration of application of suction pressure. It showed however, that the ratio of increased strength decreased when the distance from drain was apart from 2/5 of the total improvement area. With an assumption that the ratio of coefficient of permeability was an influential factor of hardening zone, the ratio of coefficient of permeability were adjusted and analyzed among theories of radical consolidation (Hansbo). The result indicated the closest measured value occurred when the ratio of coefficient of permeability was set to 4. INTRODUCTION Although the vacuum preloading method was suggested as an alternative to the existing consolidation acceleration method, many problems have been identified. High prices of sealing sheets which provided to maintain suction, frequent breakdowns during installation and the reduced efficiency of vacuum pump due to the long operation hours are some of the problems identified.