An experimental investigation into the permeability and filter properties of pervious concrete for deep draining trenches

The reduction of pore water pressures is one of the most effective measures that can be taken to stabilise landslides or to improve the stability conditions of marginally stable water-bearing slopes. To this end, draining trenches have been used long since. When deep trenches are needed, the usual conventional construction techniques fail and recourse must be made to secant piles or to adjacent vertical panels built by means of the methods well established for diaphragm walls. However, unbonded materials cannot be used, since the excavation of a panel adjacent to previously built ones will instabilise these latter. The problem can be solved using pervious concrete rather unbonded material. It must meet the following requirements: relatively high hydraulic conductivity, filtering capacity in order to prevent the internal erosion of the soil in which the trench drain is installed, sufficient residual hydraulic conductivity after possible clogging, sufficient shear strength after a short curing time to avoid the instabilisation of adjacent previously built panels or piles. Results of a laboratory experimental research on the mix-design, the filter capacity, residual permeability and strength of pervious concrete are reported in the paper, proving that proper mix-design can be devised meeting the above requirements; in particular, it is demonstrated that the shear strength of the concrete after a short curing time permits to excavate intermediate panels deep tens of meters without jeopardising the stability of previously built ones.