Analysis of water retention in soil horizons of two open trenches on a slope of Serra do Mar, Brazil, susceptible to landslides

Abstract

This research presents and analyzes the results of Soil Water Characteristic Curves (SWCC) for the soil horizons (A, B and C) of two different trenches (TR3 and TR7) opened along a slope located in the Serra da Mar mountain range, Brazil. Microaggregations were observed in soil horizons of both trenches, which changed the textural classification of the soils. TR7 showed more macropores than TR3, especially on horizon C. Unimodal SWCC were obtained for soils of the horizon A for both trenches. Instead, bimodal SWCC were obtained for soils of the deeper horizons (B and C). All soil horizons showed the phenomenon of hysteresis, and it’s more expressive in the macroporosity part. In TR7 the water retention capacity is lower in B and C, facilitating the drainage, however, horizons B and C of TR3 presented greater water retention capacity for the same matric suction value. Depending on the intensity and duration of rainfall, the horizons B and C of both trenches may suffer a decrease of shear strength, without necessarily saturating. The A horizon of TR3 can undergo an erosive process for heavy and short rains.