Estudo do comportamento tensão-deformação e estabilidade de taludes de solo melhorado para aplicação em aterros rodoviários

Abstract

This research aimed at evaluating the stress-strain behavior of the Guabirotuba Formation soil, improved with three materials: Rice husk ash (RHA) (5-10-15%), Portland cement (PC) (2-5%) and polypropylene fiber (PPF) (0.5%). Twelve blends were analyzed (B1 to B12), and geotechnical characterization tests were carried out for pure soil and 12 blends (Atterberg limits, specific gravity, X-ray fluorescence and X-Ray Diffraction), Proctor compaction test, unconfined compressive strength (qu) and splitting tensile strength (qt) tests in three curing times (7-28-90 days). These results were statistically analyzed by following the errors analysis to define the best blends, which were subsequently subjected to triaxial tests in the non-drained condition. Finally, with the parameters obtained in the triaxial tests, road embankment stability analyzes varying the height (3-5-10-15-20 m) and inclination angle (45-63.43º) were performed. These analyzes were made with Slide2 software and the simplified Bishop method, where safety factor (FS) was obtained for saturated and saturated with N’water = H conditions. The characterization results showed variation in the Atterberg limits. This led to a reduction of 91.2± 0.5% in the plasticity index (PI) in B12 in relation to the pure soil PI. Compaction tests showed that the maximum dry unit weight (γdmax) decreased and the optimum moisture content increased as the contents of additive and PPF increased, being higher in B12 where γdmax had a decreased of 1.46 kN/m3 and the optimum moisture content increased 10.7 p.p in relation to the pure soil. Statistical analysis of the qu and qt tests showed that the best resistances in relation to pure soil were for blends B3, B6, B9, B12 obtaining increments in qu of (114 ± 3)%, (474 ± 8)%, (192 ± 4)% and (493 ± 8)% respectively. On the other hand, the increments in qt were (188 ± 9)%, (842 ± 28)%, (320 ± 14)% and (998 ± 27)% respectively. The triaxial tests showed that the effective cohesion increased from 4.8 kPa to 179 kPa and 182 kPa, and the effective friction angle increased of 32.7º to 41.2º and 44.6° in the pure soil for B6 and B12, respectively. In slope stability analysis, the soil exhibited an instability state from 5 m in high and 63.43º of inclination, obtaining the most critical condition as FS<1, which changed to FS of 3.1 on B12 blend. The variation of the inclination angle generated a greater decrease in the FS than the saturation condition with N’water = H. This variation was in the range of 0.1 to 5.3 units in the FS, changing from 45° to 63.43° in degree slope. In the condition from saturation for saturation with N’water = H the variation was between 0.1 and 2.2 units in the FS. Finally, it is concluded that RHA is a potential substitute for PC in the geotechnical improvement of soils. Besides, these materials (combined with PPF) contribute to the ductility of the compound. In the stability analyzes it was concluded that it is important to consider the geometry and the saturation conditions of the embankment, with which it becomes possible to define the blends that will be the best alternative when studying slopes embankments composed by improvement soils of the Guabirotuba Formation.