Methodology for Pavement Design Reliability and Back Analysis Using Markov Chain Monte Carlo Simulation

Given the increasing cost of designing and building new highway pavements, reliability analysis has become vital to ensure that a given pavement performs as expected in the field. Recognizing the importance of failure analysis to safety, reliability, performance, and economy, back analysis has been employed in various engineering applications to evaluate the inherent uncertainties of the design and analysis. The probabilistic back analysis method formulated on Bayes' theorem and solved using the Markov chain Monte Carlo simulation method with a Metropolis-Hastings algorithm has proved to be highly efficient to address this issue. It is also quite flexible and is applicable to any type of prior information. In this paper, this method has been used to back-analyze the parameters that influence the pavement life and to consider the uncertainty of the mechanistic-empirical pavement design model. The load-induced pavement structural responses (e.g., stresses, strains, and deflections) used to predict the pavement life are estimated using the response surface methodology model developed based on the results of linear elastic analysis. The failure criteria adopted for the analysis were based on the factor of safety (FOS), and the study was carried out for different sample sizes and jumping distributions to estimate the most robust posterior statistics. From the posterior statistics of the case considered, it was observed that after approximately 150 million standard axle load repetitions, the mean values of the pavement properties decrease as expected, with a significant decrease in the values of the elastic moduli of the expected layers. An analysis of the posterior statistics indicated that the parameters that contribute significantly to the pavement failure were the moduli of the base and surface layer, which is consistent with the findings from other studies. After the back analysis, the base modulus parameters show a significant decrease of 15.8% and the surface layer modulus a decrease of 3.12% in the mean value. The usefulness of the back analysis methodology is further highlighted by estimating the design parameters for specified values of the factor of safety. The analysis revealed that for the pavement section considered, a reliability of 89% and 94% can be achieved by adopting FOS values of 1.5 and 2, respectively. The methodology proposed can therefore be effectively used to identify the parameters that are critical to pavement failure in the design of pavements for specified levels of reliability. DOI: 10.1061/(ASCE)TE.1943-5436.0000455. (C) 2013 American Society of Civil Engineers.

Numerical back-analysis of energy pile test at Lambeth College, London

Energy Piles present an efficient solution for long-term carbon emission reduction and sustainable construction. However, they have received only partial acceptance by the industry, because of concerns regarding the impact of cyclic thermal changes on the serviceability of energy pile foundations. This paper investigates the applicability of the hybrid load transfer approach to load-settlement analysis of single piles behavior during thermal energy exchange processes. Back-analysis results in terms of the thermal and mechanical response of energy piles show good agreement with field test results from Lambeth College in London. © ASCE 2011.

Analysis of stability of earthen dams in kachchh region, Gujarat, India

The Kachchh region of Gujarat, India bore the brunt of a disastrous earthquake of magnitude M-w=7.6 that occurred on January 26, 2001. The major cause of failure of various structures including earthen dams was noted to be the presence of liquefiable alluvium in the foundation soil. Results of back-analysis of failures of Chang, Tappar, Kaswati and Rudramata earth dams using pseudo-static limit equilibrium approach presented in this paper confirm that the presence of liquefiable layer contributed to lesser factors of safety leading to a base type of failure that was also observed in the field. Following the earthquake, earth dams have been rehabilitated by the concerned authority and it is imperative that the reconstructed sections of earth dams be reanalyzed. It is also increasingly realized that risk assessment of dams in view of the large-scale investment made and probabilistic analysis is necessary. In this study, it is demonstrated that the probabilistic approach when used in conjunction with deterministic approach helps in providing a rational solution for quantification of safety of the dam and in the estimation of risk associated with the dam construction. (C) 2007 Elsevier B.V. All rights reserved.

Analysis and visualization of energy use for university campus

The reduction of greenhouse gas emissions is one of the big global challenges for the next decades due to its severe impact on the atmosphere that leads to a change in the climate and other environmental factors. One of the main sources of greenhouse gas is energy consumption, therefore a number of initiatives and calls for awareness and sustainability in energy use are issued among different types of institutional and organizations. The European Council adopted in 2007 energy and climate change objectives for 20% improvement until 2020. All European countries are required to use energy with more efficiency. Several steps could be conducted for energy reduction: understanding the buildings behavior through time, revealing the factors that influence the consumption, applying the right measurement for reduction and sustainability, visualizing the hidden connection between our daily habits impacts on the natural world and promoting to more sustainable life. Researchers have suggested that feedback visualization can effectively encourage conservation with energy reduction rate of 18%. Furthermore, researchers have contributed to the identification process of a set of factors which are very likely to influence consumption. Such as occupancy level, occupants behavior, environmental conditions, building thermal envelope, climate zones, etc. Nowadays, the amount of energy consumption at the university campuses are huge and it needs great effort to meet the reduction requested by European Council as well as the cost reduction. Thus, the present study was performed on the university buildings as a use case to: a. Investigate the most dynamic influence factors on energy consumption in campus; b. Implement prediction model for electricity consumption using different techniques, such as the traditional regression way and the alternative machine learning techniques; and c. Assist energy management by providing a real time energy feedback and visualization in campus for more awareness and better decision making. This methodology is implemented to the use case of University Jaume I (UJI), located in Castellon, Spain.

Back analyses for slope failures in rock

Some of the geotechnical parameters used in the analysis may not be accurately measured directly from laboratory tests due to effects of sample disturbance and errors of tests. The back analysis or the observational method are thus often applied to determine the representative and/or dominant strength parameters based on field observations in practice. Based on the Hoek-Brown failure criterion, it was known that the disturbance factor (D) should be determined with caution. The difficulty of measuring rock mass disturbance accurately has been shown. Three rock slope failures will be investigated in this paper using back-analysis technique. In addition, various rock mass strength parameters are taken into consideration.

An outbreak of Potato spindle tuber viroid in tomato is linked to imported seed

In 2011, an outbreak of the quarantine-regulated pathogen Potato spindle tuber viroid (PSTVd) occurred in a commercial glasshouse-grown tomato crop in Queensland, Australia. Phylogenetic studies showed that the genotype of this isolate grouped in a cluster of PSTVd genotypes from tomato and Physalis peruviana, and exhibited an interesting mutation (U257→A) that has previously been linked to lethal symptom expression in tomato. Transmission studies showed that the viroid could be mechanically transmitted from crushed fruit sap, but not from undamaged fruits. A low rate of asymptomatic infection was determined for plants in the affected glasshouse, demonstrating the efficacy of using symptoms to detect PSTVd infections in tomato. No PSTVd infections were detected in solanaceous weeds located outside of the infected glasshouse, excluding them from playing a role in the viroid epidemiology. Monitoring and subsequent testing of new tomato crops grown in the facility demonstrated successful eradication of the pathogen. A trace-back analysis linked the outbreak of PSTVd to an infected imported tomato seed-lot, indicating that PSTVd is transmitted internationally through contaminated seed

Fazendo o caminho de volta: análise do exercício profissional dos assistentes sociais em emergência de grande porte do Rio de Janeiro

O trabalho que ora apresentamos tem como objetivo analisar o exercício profissional dos Assistentes Sociais em uma emergência de grande porte da cidade do Rio de Janeiro. A importância desta análise se inscreve na centralidade alcançada pela saúde na constituição da cidadania brasileira, após a Carta Constitucional de 1988. Este documento assegurou a saúde como direito de todos e dever do Estado, contudo a conjuntura política e econômica iniciada nos anos 90 e aprofundada nos anos 2000, capitaneada pela Contrarreforma do Estado, imporá limites à materialização da política de saúde preconizada pelo Sistema Único de Saúde, impossibilitando que esta seja implementada de acordo com a nova concepção. O que percebemos nos anos 2000 é uma política de saúde focalizada no atendimento emergencial, que abandonou a dimensão da prevenção e da promoção da saúde e que se distancia, progressivamente, do principio da universalidade. Neste contexto de adversidade e limitação do acesso e do atendimento se insere o Assistente Social. Nosso objetivo é delinear o exercício profissional, por nós analisado, a fim de identificar as possibilidades de materialização do projeto ético-político profissional em condições tão adversas e contrárias àquelas que nortearam a interlocução entre o Serviço Social e a saúde nos anos 80. Para tanto este trabalho busca oferecer elementos que nos permitam compreender não somente a dinâmica interna do Hospital por nós analisado, como também a política de saúde em sua totalidade, além de identificar as potencialidades da rede do entorno. Nessa perspectiva, buscamos compreender a dinâmica dos Conselhos de Saúde e a configuração adquirida por estes em tempos de restrição de direitos, sucateamento e desmonte da saúde pública. Nossos estudos indicam que possibilidades de atuação profissional congruentes com o Projeto Ético-Político Profissional estão colocadas na realidade, imiscuídas nas dificuldades impostas pela conjuntura e somente podem ser apreendidas sob a perspectiva de um trabalho coletivo em saúde.

Análise das deformações dos aterros que compõem a obra do Arco Metropolitano do Rio de Janeiro.

O presente trabalho tem como objetivo a análise numérica do comportamento dos aterros instrumentados que compõem a obra do Arco Metropolitano do Rio de Janeiro. Os resultados da instrumentação de campo serão retroanalisados, juntamente com dados disponíveis na literatura, buscando-se a definição de parâmetros confiáveis, representativos do comportamento da argila compressível da região em estudo. O Arco Metropolitano do Rio de Janeiro é uma rodovia projetada que servirá como ligação entre as principais rodovias que cortam o município do Rio de Janeiro. Devido a presença de grandes espessuras de solo compressível em alguns trechos da região, cortados pelo traçado da rodovia, instrumentos de monitoramento, como placas de recalque e inclinômetros, foram utilizados para avaliar os deslocamentos verticais e horizontais dos aterros durante o processo construtivo. Para este trabalho foram selecionados trechos de aterros representativos, devido à magnitude dos recalques, qualidade do resultado da instrumentação e diferentes métodos construtivos. A partir da análise dos parâmetros de projeto e dos parâmetros encontrados na literatura, procede-se à simulação numérica do processo construtivo dos aterros selecionados com o programa PLAXIS, de elementos finitos, através de modelagem bidimensional. Os resultados numéricos são confrontados com a instrumentação de campo (placas de recalque e inclinômetros) e com os resultados de previsões teóricas (teoria de adensamento unidimensional). Os resultados comprovaram que a modelagem numérica mostrou-se uma ferramenta adequada para a previsão dos recalques totais, tempos de adensamento e ganho de resistência ao longo do tempo. A retroanálise do comportamento de aterros sobre solos moles permite a reavaliação das premissas de projeto, uma vez que as limitações das teorias de análise e a dificuldade na seleção de parâmetros, muitas vezes acarretam em estimativas de recalque incoerentes com as observações de campo.

Um estudo de caso envolvendo a retroanálise de tensões residuais de cravação.

As tensões residuais de cravação ocorrem quando a estaca e o solo não são totalmente descomprimidos após dissipação completa da energia transferida à estaca durante sua instalação. Este assunto tem merecido a atenção de vários pesquisadores, uma vez que a presença das tensões residuais na estaca causa uma alteração no seu comportamento quando carregada. A presente dissertação reuniu estudos anteriores que estabeleceram os principais fatores que influenciam as tensões residuais de cravação. Procurou-se executar uma série de simulações objetivando melhor entender o desenvolvimento das tensões residuais com a porcentagem de resistência de ponta, em continuidade aos estudos de Costa (1994). Costa (1994) observou que a porcentagem de carga na ponta é um fator relevante na avaliação das tensões residuais de cravação. Uma análise paramétrica efetuada confirmou estudos anteriores, verificando que a razão entre a carga residual na ponta em relação à capacidade de carga global cresce, a medida que a porcentagem de carga na ponta aumenta, chegando a um valor máximo para, em seguida, diminuir. Este comportamento é similar ao da curva de compactação do solo, quando, ao aumentar a umidade, o peso específico seco aumenta, até um valor máximo, correspondente à umidade ótima, para em seguida reduzir. Verificouse, ainda, semelhantemente ao aumento da energia de compactação, que vai transladando a curva para cima e para à esquerda do gráfico umidade x peso específico seco, que o aumento do comprimento da estaca apresenta um comportamento similar. O aumento do comprimento leva a curva para cima e para a esquerda. Finalmente, selecionou-se um caso de obra com condições propícias para o desenvolvimento de altas tensões residuais de cravação. Trata-se de um caso de estacas metálicas longas, embutidas em solo residual jovem, de elevada resistência, bem documentado com extensa instrumentação, por ocasião da instalação. A retroanálise de cinco estacas do banco de dados mostrou que as cargas residuais previstas, num programa de simulação de cravação, se aproximaram muito dos valores experimentais. Foi observado também que a profundidade do ponto neutro previsto e medido apresentou uma excelente concordância. O resultado mais relevante desta pesquisa foi quando os valores de porcentagem de ponta foram introduzidos no eixo das abscissas e os valores da razão entre a carga residual na ponta e a capacidade de carga global, no eixo das ordenadas, e se observou o aspecto da curva semelhante à de compactação. A dissertação ilustra ser possível e simples a previsão das tensões residuais de cravação através de uma análise pela equação da onda.

基于精细结构描述及数值试验的断续节理岩体力学参数智能选取

Evaluating the mechanical properties of rock masses is the base of rock engineering design and construction. It has great influence on the safety and cost of rock project. The recognition is inevitable consequence of new engineering activities in rock, including high-rise building, super bridge, complex underground installations, hydraulic project and etc. During the constructions, lots of engineering accidents happened, which bring great damage to people. According to the investigation, many failures are due to choosing improper mechanical properties. ‘Can’t give the proper properties’ becomes one of big problems for theoretic analysis and numerical simulation. Selecting the properties reasonably and effectively is very significant for the planning, design and construction of rock engineering works. A multiple method based on site investigation, theoretic analysis, model test, numerical test and back analysis by artificial neural network is conducted to determine and optimize the mechanical properties for engineering design. The following outcomes are obtained: (1) Mapping of the rock mass structure Detailed geological investigation is the soul of the fine structure description. Based on statistical window，geological sketch and digital photography，a new method for rock mass fine structure in-situ mapping is developed. It has already been taken into practice and received good comments in Baihetan Hydropower Station. (2) Theoretic analysis of rock mass containing intermittent joints The shear strength mechanisms of joint and rock bridge are analyzed respectively. And the multiple modes of failure on different stress condition are summarized and supplied. Then, through introducing deformation compatibility equation in normal direction, the direct shear strength formulation and compression shear strength formulation for coplanar intermittent joints, as well as compression shear strength formulation for ladderlike intermittent joints are deducted respectively. In order to apply the deducted formulation conveniently in the real projects, a relationship between these formulations and Mohr-Coulomb hypothesis is built up. (3) Model test of rock mass containing intermittent joints Model tests are adopted to study the mechanical mechanism of joints to rock masses. The failure modes of rock mass containing intermittent joints are summarized from the model test. Six typical failure modes are found in the test, and brittle failures are the main failure mode. The evolvement processes of shear stress, shear displacement, normal stress and normal displacement are monitored by using rigid servo test machine. And the deformation and failure character during the loading process is analyzed. According to the model test, the failure modes quite depend on the joint distribution, connectivity and stress states. According to the contrastive analysis of complete stress strain curve, different failure developing stages are found in the intact rock, across jointed rock mass and intermittent jointed rock mass. There are four typical stages in the stress strain curve of intact rock, namely shear contraction stage, linear elastic stage, failure stage and residual strength stage. There are three typical stages in the across jointed rock mass, namely linear elastic stage, transition zone and sliding failure stage. Correspondingly, five typical stages are found in the intermittent jointed rock mass, namely linear elastic stage, sliding of joint, steady growth of post-crack, joint coalescence failure, and residual strength. According to strength analysis, the failure envelopes of intact rock and across jointed rock mass are the upper bound and lower bound separately. The strength of intermittent jointed rock mass can be evaluated by reducing the bandwidth of the failure envelope with geo-mechanics analysis. (4) Numerical test of rock mass Two sets of methods, i.e. the distinct element method (DEC) based on in-situ geology mapping and the realistic failure process analysis (RFPA) based on high-definition digital imaging, are developed and introduced. The operation process and analysis results are demonstrated detailedly from the research on parameters of rock mass based on numerical test in the Jinping First Stage Hydropower Station and Baihetan Hydropower Station. By comparison，the advantages and disadvantages are discussed. Then the applicable fields are figured out respectively. (5) Intelligent evaluation based on artificial neural network (ANN) The characters of both ANN and parameter evaluation of rock mass are discussed and summarized. According to the investigations, ANN has a bright application future in the field of parameter evaluation of rock mass. Intelligent evaluation of mechanical parameters in the Jinping First Stage Hydropower Station is taken as an example to demonstrate the analysis process. The problems in five aspects, i. e. sample selection, network design, initial value selection, learning rate and expected error, are discussed detailedly.