Numerical Assessment of Factors Affecting Waveform Based on Low Strain Testing of Piles
In this paper dynamic testing of piles using the low strain method is performed by means of numerical analyses based on solid finite element model. To this end, velocity-time curves are presented investigating the influence of various parameters such as mesh density, impulse width, receiving point, and soil modulus on the waveform characteristics. Then, find regularity of waveform affected by different parameters to provide reference of the real project detection.
Estudo numérico da avaliação de integridade de estacas de concreto com o ensaio pile integrity test (PIT)
OBJETIVO: Investigar a aplicacao do ensaio dinâmico de baixa deformacao, conhecido como PIT, na avaliacao da integridade de estacas de concreto, bem como sua modelagem numerica. METODOS: Foram modeladas e simuladas numericamente 5 estacas de concreto, representando respectivamente 2 estacas integras e 3 com variacoes ao longo do fuste . Na modelagem numerica foi adotado o perfil do solo adotado identificado numa sondagem a percussao realizada por Belincanta e Costa Branco (2003 ) no municipio de Campo Mourao, Parana. As estacas integras foram simuladas, primeiro considerando que a estaca estava envolta por duas camadas distintas de solo; e posteriormente, por apenas uma camada de solo. As variacoes adotadas nas demais estacas foram respectivamente, um aumento brusco na secao da estaca, uma diminuicao brusca na secao da estaca, e por ultimo, a simulacao de uma trinca. RESULTADOS: As simulacoes do ensaio PIT geraram reflectogramas de velocidade em funcao do tempo, apresentando reflexoes, ou “picos” nas posicoes onde haviam variacoes de impedância ao longo fuste. CONCLUSOES: O ensaio PIT apresenta grande potencialidade referente a deteccao de variacoes ou danos ao longo do fuste da estaca, levando assim a um maior controle de qualidade do estaqueamento de uma construcao. Os resultados obtidos foram coerentes quando comparados com a literatura, apresentado apenas uma limitacao quando a uma modelagem mais realista do solo que envolve a estaca.
A quantitative measure of nitrifying bacterial growth.
Nitrifying bacteria convert ammonia (NH3) to nitrate (NO3-) in a nitrification reaction. Methods to quantitatively separate the growth rate of these important bacterial populations from that of the dominant heterotrophic bacteria are important to our understanding of the nitrification process. The changing concentration of ammonia is often used as an indirect measure of nitrification but ammonification processes generate ammonia and confound this approach while heterotrophs remove nitrate via denitrification. Molecular probe methods can tell us what proportion of the microbial community is nitrifying bacteria but not their growth rate. The technique proposed here was able to quantify the growth rate of the nitrifying bacterial populations amidst complex ecological processes. The method incubates [methyl-3H] thymidine with water samples in the presence and absence of an inhibitor of nitrification-thiourea. The radioactively labeled DNA in the growing bacteria was extracted. The rate of incorporation of the label into the dividing bacterial DNA was used to determine bacterial growth rate. Total bacterial community growth rates in full-scale and pilot-scale fixed-film nitrifying reactors and an activated sludge reactor were 2.1 x 10(8), 4.1 x 10(8) and 0.4 x 10(8)cell ml(-1)d(-1), respectively; the growth rate of autotrophic-nitrifying bacteria was 0.7 x 10(8), 2.6 x 10(8) and 0.01 x 10(8)cell ml(-1)d(-1), respectively. Autotrophic-nitrifying bacteria contributed 30% and 60% of the total bacterial community growth rate in the nitrifying reactors whereas only 2% was observed in the activated sludge reactor that was not designed to nitrify. The rates of ammonia loss from the nitrifying reactors corresponded to the rate of growth of the nitrifying bacteria. This method has the potential to more often identify factors that enhance or limit nitrifying processes in both engineered and natural aquatic environments.