Desenvolvimento de equipamento laboratorial para estudo da resposta do solo de aterro de encontros de pontes integrais sujeitos a movimentos laterais cíclicos

Abstract

This work aims at presenting and discussing the development and validation of a laboratory equipment designed to model the response of a soil subjected to cyclic lateral displacements. The equipment included, a steel testing box capable of containing a maximum volume of soil with dimensions of 300 x 300 x 350 mm. The box is instrumented with pressure and displacement transducers, connected to a low-cost data acquisition system developed with open-source hardware and software. One of the walls of the testing box is able to apply cyclic rotational or translational displacements in the soil mass, in order to simulate the behavior of the backfill soil of an integral bridge abutment subjected to temperature fluctuations. The soils selected for the tests were a pure sand and a gravel. Lateral pressure variations in the soil were obtained using miniature pressure sensors installed on the face of the movable wall in contact with the soil. Settlements on the soil surface and deformation fields within the soil mass were obtained with the digital image correlation (DIC) technique. The images were recorded from a transparent side wall of the testing box and were processed using the Ncorr algorithm. The tests with the laboratory models were divided into two stages: preliminary tests, for the validation of the equipment and the developed data acquisition system, and definitive tests, for the general evaluation of the soil behavior under cycling. The results of the preliminary tests revealed the excellent performance of the equipment for tests with pure sand backfill, subjected to rotational movements around the base. The low-cost data acquisition system produced reading errors of magnitudes similar to those of commercial data acquisition systems. The results of the definitive tests revealed a significant increase of the maximum lateral earth pressures since the first cycles and the occurrence of large surficial settlements adjacent to the movable wall as well as surface heave at greater distances from the movable wall. Volumetric and shear strains in the soil increased with the increase of the lateral displacement amplitude. The results indicated that cumulative plastic strains in the soil reduced gradually with the cycles, which suggests that the soil remained within plastic shakedown.