Influence of stress-level due to self-weight on the hydraulic conductivity of permeable concrete for geotechnical applications

Abstract

Permeable concrete is effectively used in many fields of civil and environmental engineering, including some geotechnical applications such as drainage piles, deep drainage trenches, and as a permeable backfill material for retaining walls. The principal requirements that a pervious concrete must have for geotechnical applications are those that simultaneously guarantee enough hydraulic conductivity and good filter properties against internal erosion of the soil in which the drains are realised. These requirements can be effectively achieved through special mix-designs in which a non-negligible amount of sand is added to the aggregates, unlike the permeable concretes used for example in the road construction sector where the aggregates are essentially made only of gravel and the concrete is a “no-fines” concrete. The permeability of the pervious concrete depends on many factors among which the stress level due to the self weight of the column of fresh concrete when the depth of the same column is non negligible, as it is in the geotechnical applications. Results of an experimental study on this aspect are reported in the paper. These results show that the hydraulic conductivity reduced with the vertical stress level due to the self weight of the fresh permeable concrete. This reduction is very significant in the range of vertical stress σv of 1–100 kPa (that correspond to the self-weight of a column of “classical” fresh pervious concrete h* ranging from about 0.1 to 6 m). Subsequently this reduction is less marked up to the maximum stress level reached in the tests (σv=700kPa, h* about 40 m). The minimum hydraulic conductivity (hydraulic conductivity for σv=700kPa) is, however, still sufficient and adequate for draining medium to fine-grained base soils (soil near piles or trench drains) such as clays, silty-clays, sandy-silts, silty-sands, and fine sands.