What is the Ideal Test Piece Diameter for Laboratory Penetration Soil Resistance (SPR) Testing?

Abstract

The objective of this work was to determine the adequate diameter of soil samples as a function of the cone base area for soil penetration resistance (SPR) tests in the laboratory. The experiment was conducted at the Faculty of Agronomy and Animal Science (FAAS) – UFMT. The experimental design was completely randomized in a 3 x 3 x 2 factorial scheme, with 3 basal areas of the cone (11.05 mm2, 33.70 mm2, 52.17 mm2), 3 diameters of the specimen (50 mm, 100 mm, 150 mm) and presence and absence of volumetric rings during the penetrometer tests, with a total of 11 replicates, which were divided between two data acquisition speeds. The specimens were prepared in a protected environment (greenhouse) undergoing a curing process, with 54 cycles of drying and moistening (6 months). The soil density was obtained in the field, to reproduce the same density in the laboratory. In this way, the volume of the dry mass of soil was calculated for each ring starch. All the rings were made with 12 cm of height and 10 cm were occupied by the soil. Tubes (PVC) intended for the production of unconfined test specimens were opened longitudinally to enable their removal at the time of testing without damaging the structure. The SPR tests were performed in the Laboratory of Agricultural Machines and Motors (LAMAM). The data obtained were analyzed by variance. The specimen of 50mm diameter was insufficient to be representative of the field. The presence of the ring influenced the SPR, causing an increase of the same. The cone of a smaller size (11.05 mm²) was shown to be more suitable for SPR in the laboratory. The SPR test proved to be more efficient without the volumetric ring.