The Effects of Negative Pressure and Drain Spacing in the Horizontal Method for an Early Settlement of Dredged and Filled Grounds

In this paper, the laboratory test results with middle-sized soil box test in modeling the in-situ installing of horizontal drains are discussed for the estimation of the optimum negative pressure. The test was carried out in the different vacuum pressure conditions together with the measurement for the settlement and volume change of drained water by the installed drains during the consolidation process. After the test, the water content was measured to both directions of lateral distance from the drain and depth of the soil, to find out the distribution of ground improvement and strength enhancement. From the analysis on the distribution of water content, the gradual application of vacuum pressure to higher level by pre-determined stages starting from low vacuum pressure is found to be effective and desirable. In the comparison of the degrees of consolidation with elapsed time, the calculated value by the prediction method based on the Barron's conventional theory showed a good agreement with the measured value. With this, it is positively considered that the applicability of the prediction method based on Barron’s theory to the practical design of horizontal drains can be justified such as in the calculation of drain spacing and consolidation period.