A região costeira do Estado do Rio Grande do Norte (RN), no nordeste do Brasil é constituída por materiais sedimentares que formam tabuleiros costeiros, dunas, falésias e praias arenosas. A exuberância paisagística dessa área representa um atrativo para a ocupação humana e desenvolvimento de atividades turísticas. Esse processo de urbanização potencializa a ocorrência de movimentos de massa nas falésias, resultante doaumento da carga no topo das falésias, remoção da vegetação e aumento da erosão superficial. Estudos anteriores desenvolvidos nas falésias da região indicam que a linha de costa se encontra em processo de recuo, o que põe em risco a infraestrutura instalada e seus usuários. O presente artigo visa compreender os mecanismos de movimentos de massas que ocorrem nas falésias e resultam no seu recuo. O trabalho sistematiza as informações existentes, adiciona observações de campo e propõe um modelo conceitual contemplando os mecanismos de ruptura e processos erosivos identificados, ao longo da porção sul do litoral Oriental do Estado do Rio Grande do Norte. Os principais mecanismos identificados estão diretamente relacionados à erosão superficial em episódios de chuvas intensas, umedecimento do material e a erosão basal, caracterizada pela remoção de material do pé das falésias, devido a ação das ondas.

Deep mining operations require special measures in order to keep safe and economic aspects. After mine ore is extracted, voids are created and need to be filled with high-strength, low-cost materials. Cemented Paste Backfill (CPB) has recently become one of the main alternatives in filling stopes. Although numerous papers have mentioned the magnitudes of the strength of this material, its behavior under high confining pressures is still not well understood. Therefore, the purpose of this study is to increase the knowledge regarding the CPB behavior. Triaxial compression tests were performed using a Hoek Cell and Load Frame System under high confining pressures. Samples with two different binder contents were used in order to obtain the CPB strength improvement. Besides the self-weight consolidation curing method, samples were subjected to a different curing method that simulated a zero gravity condition (rotating wheel) in the first curing day to compare their mixture properties. The results suggested that both curing method and binder content have influenced the geomechanical properties of Cemented Paste Backfill. By increasing the curing time, the CPB shear strength has increased slightly, whereas specimens with higher binder content presented a significant increase in shear strength values.

Landslides are part of the natural processes of Earth’s surface dynamic, which could be accelerated or triggered by anthropic interference. Inadequate occupation of areas highly susceptible to landslide processes is the principal cause of accidents on Brazilian urban slopes, especially those occupied by settlements and slums. In Natal, Rio Grande do Norte state, Brazil, the existence of areas with steep and densely occupied slopes makes the municipality susceptible to landslides. In this context, the present study aimed to map the risk of landslides in an urban area located in the city of Natal. Using the quali-quantitative model proposed by Faria (2011), adapted for the conditions of the study area, which applies a multicriteria analytical hierarchy process (AHP) to a Geographic Information System (GIS), 11 risk indicators were submitted to pairwise comparisons by 10 risk management specialists in order to determine the relative importance (weighting) for each of these factors as a function of their contribution to the risk. The weightings obtained were combined to produce the final risk map of the study area, using a map algebra framework. The results show the existence of a critical risk for the resident population, primarily related to the possibility of a landslide, with potentially negative economic, environmental, and mainly social impacts.

Foundation engineering has continually sought to understand the behavior of piles subjected to loads and their influence on the overall structural behavior. Recently, more load tests are being performed in construction due to the recommendations of the NBR6122/2010 Brazilian code. The available literature offers few reports on pile behavior in a faulty foundation. Therefore, the present study assessed the behavior of a single pile with and without a defect: 5 m long, small-diameter (f = 0.25 m) bored piles were embedded in diabase soil (porous, lateritic and unsaturated) at Experimental Site II (Unicamp). The piles behavior were compared by laboratory tests, numerical analysis using the finite element software LCPC Cesar v.4.07 and experimental results from slow maintained load (SML) tests. Strain gauge instruments were installed at the top and tip of each pile. As predicted by the numerical analyses, when subjected to the first stage of the pile load test, the defective region of the pile failed structurally; however, the pile was still able to resist or "absorb" loading. Factors related to the loading ratio of the foundation, the total and differential displacements and the rotation of the top block were examined. The results obtained in the two analyses (numerical and in situ) were satisfactory and showed significant agreement, providing greater understanding of the complex behavior of this foundation system.

The methodologies used to calculate piled raft foundations are normally more complex than conventional foundations due to the large number of variables involved in the problem. In the conventional block, the interaction variables considered are only between the pile and the soil. In the piled raft, all the interaction effects must be considered, as follows: plate-soil, plate-piles and piles-soil, simultaneously. The Finite Element Method (FEM) has proven to be a useful tool in analyzing these types of problems. This study aims at assessing the behavior of piled rafts using the Cesar-LCPC numerical tool, version 4.0, which is based on the finite element method. Literature cases of rafts supported by 9, 15 and 16 piles were analyzed. The results obtained were compared with analysis methods presented in the bibliography. The following parameters were assessed: relative spacing (S/D), relative length (L/D), relative stiffness between piles and the soil (KPS), and settlement of piles and the raft. The spacing between piles has a significant influence on load distribution between piles and the raft. Very small spacing provides stiffness to the foundation, which then functions as a conventional pile foundation, in which only the piles absorb the load from the superstructure. The larger the L/D ratio, the lower the settlement and for a given modulus of elasticity of the pile, the increase in relative stiffness (KPS) causes an increase in settlement. In all analyses, the data obtained corroborated the results presented by other methods published in the literature.

The behavior of sands subjected to diverse loading conditions has been the object of many studies in recent decades. Constitutive models that are able to simulate the behavior of sands have been developed based on critical state theory. Researchers have shown that the defining parameters of the critical state line (CSL) can be obtained by performing drained and undrained tests on samples with different initial densities. This work aims to verify the drained and undrained behavior of aeolian sand from Natal, Brazil, based on critical state soil mechanics. Drained and undrained tests were performed on samples with initial void ratios equal to 0.7 and 0.8, which correspond to loose and medium-dense relative densities, respectively. Samples with both void ratios were subjected to confining stresses equal to 50, 100, 200 and 300 kPa. The results show that the critical state line can be defined from the drained and undrained tests performed on samples with loose and medium-dense initial relative densities. The parameters from the critical state theory were obtained using projections on the planes p'-q and lnp' -v. The critical state friction angle is equal to 31.5°, and it is compatible with clean and uniformly graded sands with angular to subangular features and composed mostly of quartz. The obtained M, G and l values are equal to 1.26, 1.863 and 0.03, respectively. The obtained parameters will be used in analyses and numerical simulations of the geotechnical structures built on aeolian dune deposits from the city of Natal, Brazil.

Artigo apresentado no III Congresso de Iniciação Científica do CEFETRN (2005) RESUMOUm dos principais problemas da zona costeira é o avanço da linha de costa. Para analisar a estabilidade dos taludes que compõem essas linhas de costa no município de Tibau do Sul, RN, foi realizado este trabalho. Ele consiste em realizar simulações a respeito da estabilidade dos taludes através do cálculo do Fator de Segurança (valor adimensional que exprime a estabilidade do talude na sua situação mais crítica), utilizando métodos de equilíbrio limite pelo software SLOPE/W da GEO-SLOPE Versão Estudante. Foram realizadas simulações variando-se o grau de saturação do solo das falésias, a fim de se conhecer a influência da saturação na instabilização dos taludes, assim como obter o limite de saturação que as falésias suportam sem que haja ruptura. Também se obteve a provável superfície de ruptura em caso de instabilização. Pelos resultados pôde-se constatar que a saturação total do solo pode reduzir em até quatro vezes o valor do Fator de Segurança, acarretando deslizamentos de grande intensidade nas falésias em que não está presente a camada cimentada com óxido de ferro. PALAVRAS-CHAVE:Estabilidade de Taludes, Falésias, Tibau do Sul-RN, Coesão, Ângulo de Atrito, Superfície de Ruptura, Fator de Segurança, SLOPE/W. THE STABILITY ANALISIS OF CLIFFS IN TIBAL DO SUL USING THE LIMITED BALANCE METHOD ABSTRACTOne of the main problems of the coastal zone is the advance of the shoreline. To analyze the stability of the slopes that compose these shorelines in the city of Tibau do Sul, RN, was carried through this work. It consists of to carry through simulation regarding stability of slopes through calculation of Factor of Security (undimension value that it states the stability of the slope in its more critical situation), using limited balance methods for software SLOPE/W of the Geo-slope Version Student. Simulations had been carried through varying the degree of saturation of the ground of the slopes, in order to know the influence of the saturation in the instability of slopes, as well as getting the saturation limit that the slopes support without that it has rupture. Also the probable surface of rupture in instability case was gotten. For the results it could be evidenced that the total saturation of

No abstract