Combining spatial models for shallow landslides and debris-flows prediction

Mass movements in Brazil are common phenomena, especially during strong rainfall events that occur frequently in the summer season. These phenomena cause losses of lives and serious damage to roads, bridges, and properties. Moreover, the illegal occupation by slums on the slopes around the cities intensifies the effect of the mass movement. This study aimed to develop a methodology that combines models of shallow landslides and debris-flows in order to create a map with landslides initiation and debris-flows volume and runout distance. The study area comprised of two catchments in Rio de Janeiro city: Quitite and Papagaio that drained side by side the west flank of the Maciço da Tijuca, with an area of 5 km2. The method included the following steps: (a) location of the susceptible areas to landslides using SHALSTAB model; (b) determination of rheological parameters of debris-flow from the back-analysis technique; and (c) combination of SHALSTAB and FLO-2D models to delineate the areas more susceptible to mass movements. These scenarios were compared with the landslide and debris-flow event of February 1996. Many FLO-2D simulations were exhaustively made to estimate the rheological parameters from the back-analysis technique. Those rheological coefficients of single simulation were back-calculated by adjusting with area and depth of the debris-flow obtained from field data. The initial material volume in the FLO-2D simulations was estimated from SHALSTAB model. The combination of these two mathematical models, SHALSTAB and FLO-2D, was able to predict both landslides and debris-flow events. Such procedures can reduce the casualties and property damage, delineating hazard areas, to estimate hazard intensities for input into risk studies providing information for public policy and planning

The influence of saturation degree on soil elasticity modulus: application on prediction the reach of rockfalls

O processo de queda de blocos rochosos é um dos mais destrutivos movimentos de massa em encostas. Considerando a baixa previsibilidade da sua deflagração, tem sido dada atenção à determinação das trajetórias dos blocos como método para redução de riscos. O coeficiente de restituição (ε) é o principal parâmetro físico envolvido na análise do alcance dos blocos, pois representa as perdas de energia após os choques do bloco de rocha com diferentes materiais geológicos em sua trajetória. Trata-se de um parâmetro ainda pouco conhecido na literatura geológica e geotécnica, sobretudo quando se considera a interação dos blocos de rocha com solos em diferentes umidades. Este artigo teve a finalidade de avaliar o efeito da umidade do solo sobre o módulo de elasticidade (E), parâmetro elástico que afeta a rigidez no contato entre rocha e solo no momento do choque e, por conseguinte, o próprio ε. Para fins de comparação, um solo derivado de rocha ácida e outro de rocha básica foram coletados na região serrana do Estado do Rio de Janeiro. Procedeu-se à caracterização da mineralogia das rochas de origem e dos solos derivados, bem como dos índices físicos dos solos. Após a determinação da curva característica, os solos foram moldados em diferentes teores de umidade e submetidos a ensaios de compressão triaxial do tipo não adensado e não drenado. Os resultados mostraram variação de mais de uma ordem de grandeza do (E) em função da umidade do solo, indicando que esta tem considerável influência na rigidez do contato entre o solo e a rocha, tornando os alcances dependentes da variação sazonal de umidade nas encostas.Rock falls are one of the most destructive mass movements in hillslopes. Considering the low predictability of its triggering, attention has been paid in determining the paths of the blocks as a method to reduce risks. The coefficient of restitution (ε) is the primary physical parameter involved in the analysis of the reach of the blocks. It represents the loss of energy after each shock of a rock block with different geological materials in its trajectory and it is still little known in geological and geotechnical literature, especially when considering the interaction of rock blocks with soil at different humidities. This article aimed to evaluate the effect of soil moisture on the elasticity modulus, an elastic  parameter that affects the stiffness at the contact between rock and soil at the time of shock and, therefore, the actual coefficient of restitution. For comparison purposes, soils derived from acid rock and from basic rocks were sampled in the mountainous region of the State state of Rio de Janeiro. The procedure was to characterize the mineralogy of source rocks and its derived soils, as well as the physical indices of the soils. After determining the characteristic curve, the soils were molded at different moisture contents and subjected to unconsolidated and undrained triaxial compression tests. The results showed variation of elasticity modulus in more than an order of magnitude depending on the soil moisture, indicating that moisture has considerable influence on the stiffness of the contact  between soil and rock during shocks, making the length of trajectories dependent of the seasonal variation of moisture in hillslopes

Infiltration of atrazine in an Oxisol under no-tillage and conventional tillage

O objetivo deste trabalho foi comparar a lixiviação e o potencial de contaminação de lençóis de água com atrazina, em solos sob manejo de plantio direto (PD) e convencional (PC). Foram realizados experimentos em campo e em colunas com Latossolo Vermelho-Escuro distroférrico, submetido ao manejo PD e PC, em Dourados, MS, Brasil. Os valores de condutividade hidráulica e potencial mátrico, determinados com o permeâmetro de Guelph no PD, demonstram fluxo contínuo de água no solo. A maior condutividade na superfície, associada ao potencial mátrico negativo, demonstrou descontinuidade hidrológica, na comparação das camadas subjacentes, verificada no PC em relação ao PD. No entanto, o PD apresentou deslocamento vertical de atrazina menor que o PC. Os resultados mostraram que as perdas de atrazina por lixiviação ocorreram mais intensamente com as primeiras chuvas, logo após a aplicação do produto. O PD apresentou maior concentração de atrazina em comparação ao PC, tendo reduzido as perdas por lixiviação. Os dados indicam que a tecnologia de plantio direto pode reduzir o impacto ambiental provocado pelos pesticidas.The aim of this work was to compare leaching and potential groundwater contamination in soil under no-tillage and conventional tillage. This experiment was carried out in field conditions and soil columns, using an Oxisol under no-tillage (NT) and conventional tillage (CT) systems in Dourados, MS, Brazil. The determination of the hydraulic conductivity and matrix flux potential, with the use of a Guelph permeameter in the NT, showed a continue flow of water into the soil. Greater conductivity found in the surface soil, associated with the negative matrix flux potential, showed the discontinued hydraulic conductivity, when comparing subsurface layers, in the CT in relation to NT. However, NT resulted in less vertical displacement of atrazine than CT. The largest atrazine losses by leaching occurred more intensely after the first rainfall that followed the product application. Greater atrazine concentrations were retained in NT soil than in CT soil. This resulted in low levels of leaching from the NT soil, which indicates that no-tillage technology can reduce the environmental impact of pesticides

Analysis of bookshelf mechanisms using the mechanics of Cosserat generalized continua.

Bookshelf type mechanisms are commonly used to explain antithetic accommodation of deformations caused by direct shear. Stress analysis of such mechanisms have been proposed, mainly through the use of classic Mohr circle graphical constructions. The present work introduces an alternative framework for analysis, the mechanics of generalized Cosserat continua, although maintaining the same tools (Mohr circle construction). In this type of mechanics, kinematics of the material points incorporates independent rotational degrees of freedom besides the classic translational ones. In the equilibrium equations, quantities involving moments are generated and the stress tensor is in the general case non-symmetric. Such characteristics of generalized Cosserat continua make it suitable for the analysis of Bookshelf mechanisms, as these are, in essence, rotational antithetic mechanisms induced by shear stresses having different magnitudes in perpendicular planes. The paper applies the mechanics of generalized continua to the analysis of a specific bookshelf mechanism, related to crustal extension. In the Appendices, a review of the generalized Cosserat continua and details of the graphical Mohr circle representation of stresses for such media are presented

Mechanical characterization of rock splitting planes in granitic rocks.

Submitted by Pedro Henrique da Silva Assunção ([email protected]) on 2015-04-16T14:13:29Z No. of bitstreams: 1 ARTIGO_MechanicalCharacterizationRock.pdf: 300766 bytes, checksum: 3b2cb1c07cf0a895ff7e299c18f17eda (MD5)Approved for entry into archive by Oliveira Flávia ([email protected]) on 2015-04-16T20:05:13Z (GMT) No. of bitstreams: 1 ARTIGO_MechanicalCharacterizationRock.pdf: 300766 bytes, checksum: 3b2cb1c07cf0a895ff7e299c18f17eda (MD5)Made available in DSpace on 2015-04-16T20:05:13Z (GMT). No. of bitstreams: 1 ARTIGO_MechanicalCharacterizationRock.pdf: 300766 bytes, checksum: 3b2cb1c07cf0a895ff7e299c18f17eda (MD5) Previous issue date: 200

Application of the discrete element method for modeling of rock crack propagation and coalescence in the step-path failure mechanism.

The present study evaluates the discrete element method (DEM) as a tool for understanding the step-path failure mechanism in fractured rock masses. Initially, the study simulates crack propagation and coalescence in biaxial and triaxial laboratory tests. The results of this analysis showthat the DEMaccurately represents these processes in comparison to other studies in the technical literature. The crack propagation and coalescence processes are important in the step-path failure mechanism for slopes. Simple examples of this mechanism were modeled, and their results were compared with those of the analytical model proposed by Jennings (1970). Among the possibilities suggested by Jennings,modelingwith DEMdid not provide a good approximation for the case of coplanar cracks, forwhich failures in the intact rock bridges should only be caused by shear forces. Inmodelingwith DEM, tensile failures occur within the sliding block, generating forces that are not considered in the Jennings model. The non-coplanar crack condition provided a better approximation, since the Jennings model formulation for this case includes the tensile failure of the rock. The main advantage of the DEM over other computational tools is its micromechanical representation of discontinuous media, which permits a better understanding of the step-path failure mechanism. However, good calibration of the macroscopic parameters of the rock and its discontinuities is necessary to obtain good results

Infiltração de atrazina em latossolo submetido aos sistemas de plantio direto e convencional Infiltration of atrazine in an Oxisol under no-tillage and conventional tillage

O objetivo deste trabalho foi comparar a lixiviação e o potencial de contaminação de lençóis de água com atrazina, em solos sob manejo de plantio direto (PD) e convencional (PC). Foram realizados experimentos em campo e em colunas com Latossolo Vermelho-Escuro distroférrico, submetido ao manejo PD e PC, em Dourados, MS, Brasil. Os valores de condutividade hidráulica e potencial mátrico, determinados com o permeâmetro de Guelph no PD, demonstram fluxo contínuo de água no solo. A maior condutividade na superfície, associada ao potencial mátrico negativo, demonstrou descontinuidade hidrológica, na comparação das camadas subjacentes, verificada no PC em relação ao PD. No entanto, o PD apresentou deslocamento vertical de atrazina menor que o PC. Os resultados mostraram que as perdas de atrazina por lixiviação ocorreram mais intensamente com as primeiras chuvas, logo após a aplicação do produto. O PD apresentou maior concentração de atrazina em comparação ao PC, tendo reduzido as perdas por lixiviação. Os dados indicam que a tecnologia de plantio direto pode reduzir o impacto ambiental provocado pelos pesticidas.The aim of this work was to compare leaching and potential groundwater contamination in soil under no-tillage and conventional tillage. This experiment was carried out in field conditions and soil columns, using an Oxisol under no-tillage (NT) and conventional tillage (CT) systems in Dourados, MS, Brazil. The determination of the hydraulic conductivity and matrix flux potential, with the use of a Guelph permeameter in the NT, showed a continue flow of water into the soil. Greater conductivity found in the surface soil, associated with the negative matrix flux potential, showed the discontinued hydraulic conductivity, when comparing subsurface layers, in the CT in relation to NT. However, NT resulted in less vertical displacement of atrazine than CT. The largest atrazine losses by leaching occurred more intensely after the first rainfall that followed the product application. Greater atrazine concentrations were retained in NT soil than in CT soil. This resulted in low levels of leaching from the NT soil, which indicates that no-tillage technology can reduce the environmental impact of pesticides