Abstract
Some of principal problems related to the required discharge capacity of the prefabricated vertical drain remain ambiguous in practice on the product quality check. Of these hydraulic gradient required when testing, and reducing pro perties of discharge capacity due to confining pressure are especially important. They were proved in the conference held in Kochi in 2000 that the required discharge capacities presented by some concerning countries were different from each other on the similar condition and the hydraulic gradients required in the quality test wasn't associated with by some countries. Therefore, actually demanding concept is to indicate how to predict the required discharge capacity regards with appropriate improvement of soft ground, not showing unified controlling value itself. In this paper, two items, the discharge capacity defined by the hydraulic gradient of one and reducing tendency of discharge capacity due to confining pressure, are made the targets as primary problems and the group of equations is presented to evaluate the discharge capacity characteristics. And comparing with the results of FDM calculation and laboratory test results, the signification of hydraulic gradient of one is described to become the useful criteria and the result of analyzing shrinkage of passage area for water can derive the role of membrane enveloping test specimen affecting amount of discharge capacity.
