Melhoramento de solos moles: equipamento triaxial modificado para ensaios de expansão de membrana interna em laboratório

Abstract

The technique of soft soil improvement called Geoenrijecimento (CPR Grouting) has been used in many places where thick layers of compressible soil are found. The technique consists in the pumping of higher viscosity grout under high pressures, combined with drains previously installed. The improvement induces the soil to lose water and volume, which results in an increase in strength and stiffness of the whole (soft soil and grout bulbs). In order to better understand the behavior of the technique, a modified triaxial equipment which allows cavity expansions to be performed through an injection needle positioned inside the specimen is presented. A latex membrane that is expanded with varying volumes, which simulates the formation of the compression bulbs that occur in the field, is placed at the tip of this needle. The tests performed in this research were called Internal Membrane Expansion tests, and aimed to simulate the behavior of the technique under laboratory conditions. The results allowed investigating and quantifying some parameters used in the calculation methodology of Geoenrijecimento, such as the consolidation potencial (λc), and evaluating the generation of the poropressions, the expansion pressures and the deformation after improvement. It was observed that λc is extremely dependent on the ratio of substitution (Rs) and also on the characteristics of the soil tested. The tests satisfactorily reproduced the behavior of the technique thus becoming a new device for geotechnical engineers, mainly for those who are concerned with the improvement of soft soils.