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Interception by vegetation is one of the main variables controlling hydrological and geo-environmental problems such as erosion, landslides and floods. Interception, along with precipitation and evapotranspiration, is required for the modeling of infiltration, percolation and runoff. Unfortunately, the measurement of interception in the field is time consuming, burdensome and subject to testing parameters with relatively high variability. In this context, experiments using rainfall simulators (RSs) have the potential to provide an alternative approach that addresses most of the limitations of field experiments. This paper presents a new approach to evaluate interception that combines a RS and the monitoring of the wetting front using pore-water pressure instrumentation at specific locations of the specimen. Two specimens are required, one with and another without vegetation. The proposed approach was applied to Paspalum notatum (bahiagrass) and a tropical soil. The results indicated an average interception of 5.1 mm of the simulated rainfall for a slope at 15 degrees, rainfall intensity of 86 mm h−1, and duration of 60 min. Furthermore, the vegetation decreased the surface runoff that contributes to erosion. The proposed method will enable studies on the interception mechanisms and the various involved variables, with benefits to the modeling of soil-vegetation-atmosphere interaction.

Investigar as propriedades mecânicas do solo é imprescindível para que se tenha um bom resultado no cálculo de projeto nas obras de engenharia. É necessário compreender as diferentes condições de campo em que o solo se encontra e como estas influenciam em seu comportamento, uma vez que o solo é um material heterogêneo e, muitas vezes, não saturado. Neste contexto, insere-se a sondagem PANDA 2, muito conhecida pela sua praticidade, leveza e rapidez na execução de sondagens rasas do subsolo. Assim, este estudo visa, por meio da sondagem PANDA 2, analisar a influência das distintas condições de campo, nos períodos seco e chuvoso, nos parâmetros de resistência à penetração do solo de um campo experimental da Escola de Engenharia Civil e Ambiental (EECA) da Universidade Federal de Goiás (UFG). Foram executadas seis sondagens, sendo três no período seco e três no período chuvoso, ao longo de cinco metros de profundidade. Os resultados indicaram que os primeiros 0,75 m apresentam os maiores valores de resistência à penetração (qd). Verificou-se que o PANDA 2 apresentou considerável sensibilidade na aquisição dos dados em função da condição de campo, e que o acréscimo de coesão devido à variação da sucção matricial do solo tem grande influência no parâmetro qd ao longo da zona ativa do solo. PALAVRAS-CHAVE: Ensaio in situ. Resistência à penetração qd. Sucção do solo. Sondagem ABSTRACT: Investigate mechanical properties of the soil is essential for the good design of engineering constructions. It is necessary to understand how different field conditions influence the soil behavior due to its heterogeneity and unsaturated state. In this context, useful to investigate shallow depths, the PANDA 2 soil survey is known for being practical, quick and easy to perform. This study aims to analyze the influence of distinct fields conditions, rainy and dry seasons, in the penetration strength of the soil located in the experimental field of the School of Civil and Environmental Engineering (EECA) of the Federal University of Goiás (UFG). Six soils surveys were performed, three in the dry season and three in the rainy season, along of five meters of depth. The results indicate the first 0.75 m show the highest values of penetration strength (qd). It was found that PANDA 2 showed considerable sensitivity in data acquisition according to the field condition , and the increase in the cohesion due to the variation in matric suction has significant influence in the parameters qd along the active zone of the soil.

Os solos tropicais possuem características bastante peculiares, sendo uma delas relacionada ao enriquecimento do solo com óxidos de ferro e alumínio capazes de formar aglutinações das suas partículas conhecidas como agregações. Em função destas agregações, o solo tropical pode apresentar curva característica solo-água (CCSA) bimodal. A CCSA de um solo contém as informações mais importante de solos não saturados das quais é possível extrair parâmetros hidromecânicos tais como condutividade hidráulica, resistência ao cisalhamento e parâmetros de deformabilidade. Porém, medir CCSA é trabalhoso, envolve custo, tempo e complexidade de procedimento. Diversas equações para prever CCSA são encontradas na literatura. No entanto, a maioria dessas equações foram propostas para solos granulares ou solos finos com estrutura unimodal. Neste artigo, verificou-se a aplicabilidade do método de previsão proposto por Satyanaga et al. ( 2013) em solos tropicais com CCSA bimodais. Os resultados obtidos revelam que os parâmetros das equações para curva de distribuição de tamanho de grãos (GSD) são capazes de descrever bem as propriedades físicas do solo tropical bimodal, porém eles não são capazes de produzir previsões razoáveis, resultando em sucções subestimadas.

The particle-size distribution (PSD) is the key information required by several models for prediction of the soil-water characteristic curve (SWCC). The performance of these models has been extensively investigated in the literature; however, limited studies have been undertaken with respect to the uncertainty associated with the SWCC predictions resulting from the variability in the PSD. This study aims to investigate the influence of the variability of the PSD in the prediction of SWCCs using five different models applied to three different glass beads (GBs). The PSD curves were determined by sieve analysis, laser diffraction, and image analysis. The various testing procedures were statistically evaluated to understand the influence of variability of the PSD in terms of the coefficient of uniformity (CU) and de size of particles corresponding to 10% in the PSD (D10). For each prediction model, a combination of PSD curves and their coefficient of variation were used to estimate the SWCCs. Both the CU and D10 proved to have a strong relationship with the predicted SWCCs. The CU appears to influence more the residual suction prediction while the D10 seems to have a major role for the transition and residual stages.

The development of theoretical and semi-empirical models to study capillary mechanisms and predict the soil-water characteristic curve (SWCC) generally requires the idealization of pore space and pore water, considering simplifying hypotheses. The study of ideal materials comprised of particles with controlled shape and size allows the evaluation of such simplifying hypotheses and the subsequent generalization to actual soils. In this paper, four theoretical and semi-empirical models for the prediction of the SWCC are applied to the prediction of artificial materials comprised of spherical particles. Nineteen grain-size distribution curves, with varying coefficients of uniformity are considered. The dataset is comprised of materials previously published and additional tests carried out by the authors, under highly controlled conditions. The analyses allowed the evaluation of the effect of grain-size distribution curve and shape of the particles. The limitations and advantages of each prediction model was investigated, and a detailed comparison is presented, guiding future implementations of improved models.

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