Il calcestruzzo poroso per il miglioramento delle condizioni di stabilità dei pendii sede di falda idrica

Abstract

Reduction of pore water pressures is a useful strate-gy to improve the stability conditions of slopes. Deep draining trenches can be used for this scope. For the realisation of deep trenches, the usual con-ventional construction techniques are not adequate and the use of adjacent vertical panels, built by means of the methods well established for dia-phragm walls, is necessary. However, unbonded ma-terials (i.e. gravels) cannot be used, since the excava-tion of a panel adjacent to already built ones will cause instability. For this scope a bonded material such as the pervious concrete can be used. It must have high permeability, filtering capacity in order to prevent the internal erosion of the soil in which the trench drain is installed, sufficient shear strength af-ter a short curing time so to avoid the instability of adjacent previously built panels or piles. Results of an extensive laboratory experimental research on the mix-design, the filter capacity and residual hydraulic conductivity prove that proper mix-design can be devised meeting the above requirements. Experi-mental results show, in particular, that the shear strength of the concrete after a short curing time permits to excavate intermediate panels tens of me-ters deep without jeopardising the stability of previ-ously built ones. Moreover the hydraulic conductivi-ty of pervious concrete subjected to vertical stress level corresponding to the weight of a column of concrete of about 40 metres deep drops to a third of its value at low stress level. Nevertheless, it is still acceptable for draining trenches installed in many soils including fine-grained ones (fine sands, silts, clays).