A new theoretical method to evaluate the internal stability of granular soils

Abstract

The geotextile filter design is particularly complex when granular base soils are internally unstable. In these conditions, the design criteria available in literature are not always reliable. This paper deals with a new theoretical method developed to evaluate the internal stability of granular soils. To simulate, theoretically, the filtration process inside these soils, a set of spherical particles and different soil relative densities have been considered. The soil has been represented by means of a sequence of parallel layers, containing constrictions and particles, placed upon each other at a distance, in the direction of hydraulic flow, which is a function of the soil relative density. The movement of the fine particles through the different soil layers has been simulated by means of a mechanism that compares each particle contained in the i layer with the constrictions contained in the next i + 1 layer. The results of the numerical simulations were used to evaluate the internal stability of the analyzed granular soil and the corresponding critical diameter of suffusion, Dc. Finally, the reliability of the proposed theoretical method was evaluated by means of the results of experimental long-term filtration tests performed using a rigid-wall permeameter on different unstable granular soils.

Analysis of the internal stability of granular soils using different methods

“…In particular, the theoretical analysis of the internal stability was performed using the Simulfiltr method developed recently by the authors (Moraci et al, 2012a) while the experimental evaluation of the internal stability was carried out by means of long term filtration tests. In particular, the theoretical analysis of the internal stability was performed using the Simulfiltr method developed recently by the authors (Moraci et al, 2012a) while the experimental evaluation of the internal stability was carried out by means of long term filtration tests.…”

“…Example of evaluation of F according to the different internal stability criteria.THEORETICAL ANALYSIS OF INTERNAL STABILITYIn order to verify the internal stability of the different granular soils by theoretical methods, the soils have been analysed by means of the Simulfiltr method recently developed by the authors(Moraci et al, 2012a and2012b).In Simulfiltr, the filtration process is simulated considering the granular soil as a set of spherical particles with different packing (corresponding to different relative densities). A sequence of parallel layers, containing constrictions and particles, represents the soil placed one upon the other one at a distance, in the direction of the hydraulic flow, function of the soil relative density.…”

“…Example of evaluation of F according to the different internal stability criteria.THEORETICAL ANALYSIS OF INTERNAL STABILITYIn order to verify the internal stability of the different granular soils by theoretical methods, the soils have been analysed by means of the Simulfiltr method recently developed by the authors(Moraci et al, 2012a and2012b).In Simulfiltr, the filtration process is simulated considering the granular soil as a set of spherical particles with different packing (corresponding to different relative densities). The results of the numerical simulations, described in detail in recent papers(Moraci et al, 2012a and b, Dallo andWang, 2012), allow the evaluation of the internal stability of the analysed granular soil. The D r a f t movement of the fine particles through the different soil layers is simulated by means of a mechanism that compares each particle contained in the i-layer with the constrictions contained in the next i+1 layer.…”

“…A sequence of parallel layers, containing constrictions and particles, represents the soil placed one upon the other one at a distance, in the direction of the hydraulic flow, function of the soil relative density. Moreover, Simulfiltr provides the corresponding critical diameter of suffusion, D c, which is relevant because it provides information about the characteristics and the behaviour of the granular soil and about the design of the geotextile filter(Moraci et al, 2012b).The results obtained by the Simulfitr method, for the sixteen granular soils, in terms of critical diameter of suffusion D c and mass ratio M f/s are summarized in The results of the numerical simulations, described in detail in recent papers(Moraci et al, 2012a and b, Dallo andWang, 2012), allow the evaluation of the internal stability of the analysed granular soil.…”

Reply to the discussion by Ni et al. on “Analysis of the internal stability of granular soils using different methods”

“…For these soils, for which it is very complex to perform proper experimental tests, the authors suggest using geometricprobabilistic methods, such as the Simulfiltr method proposed by Moraci et al (2012bMoraci et al ( , 2012c. These methods are capable of simulating (i) the real soil grain-size distribution considering soil relative density (or porosity) and (ii) the fine particle movement inside the pores of the solid skeleton constituted by the coarse particles (regardless of interaction with the filter).…”