Radial Consolidation of Soft Soils in Vietnam's Red River Delta: Effect of Drain Diameter on Undisturbed and Remolded Samples

Abstract Given the increasing demand for soft soil improvement in Red River Delta of Vietnam in the past decade, this study is dedicated to characterizing radial consolidation behaviour of clayey soils in the delta, while varying drain size in the radial consolidation test. Undisturbed soil samples were collected from 3 different sites and subjected to a series of radial and vertical consolidation tests. The central drain diameter in radial consolidation test is varied from 12 to 28 mm, corresponding to the drain spacing ratio n changing from 5.17 to 2.21, to investigate the influence of drainage length on the interpreted outcomes. The alteration of consolidation parameters induced by soil remolding is also studied by comparing the test results of undisturbed and remolded soils. The test results indicate that smaller drain diameter (i.e., larger drainage length) results in larger coefficient of radial consolidation ( c r ), for example, c r increases by a factor of 2 when the drain size varies from 28 mm ( n = 2.21) to 20 mm ( n = 3.1). However, when n > 3.1, the influence of drainage length on the value of c r decreases apparently, despite the applied pressure rising from 25 to 800 kPa. New correlations describing the relationship between the value of c r and n are proposed. On the other hand, soil remolding can cause permeability and coefficient of consolidation to decrease by a factor of 2 to 10. The soil parameters determined from this study are used to implement finite element analysis, resulting in acceptable accuracy of settlement prediction, thus considerable values to practical design of soft soil improvement by PVDs in Red River Delta.