Search

Abstract: Choice between cut-slope and shallow tunnel alternatives is a common decision-making problem in the construction of highways or railways in mountainous regions. This paper outlines a risk-based decision making framework. Five indicators, including construction cost, duration, casualties, time overruns and economic loss, are adopted to evaluate the two alternatives, cut-slope and shallow tunnel. Landslide and tunnel collapse risks are analyzed quantitatively for these two alternatives. Based on reliability analysis, the probabilities of landslide and tunnel collapse are estimated. The extent of likely impacted area is delimited based on the failure potential. Then, according to the exposed elements within the impacted area, the consequences are estimated using Monte-Carlo simulation and event tree approach. A computer code was developed for quantitative risk assessment and multi-objective optimization, and an example is presented to illustrate the entire process. [Copyright &y& Elsevier]

The US Gulf of Mexico coastal region has repeatedly been subjected to major flood events. Local geotechnical site characteristics and geomorphology can change due to sediment transport processes during such events. However, field measurements during extreme conditions are challenging. This paper discusses initial attempts at a combined geotechnical and geophysical site investigation of the uppermost layers of riverbeds following severe flooding events at three different rivers in Texas: the Guadalupe, Brazos, and Colorado Rivers in terms of sediment strength derived from a portable free fall penetrometer, backscatter intensity recorded by a chirp sonar, and soil sample characterization. Results show low strength sediments (<40 kPa) along the investigated sections of the Guadalupe and Brazos riverbanks. Although sediments in the center of the Brazos River were characterized with higher strength (>50 kPa) and larger grain sizes (d 50 ∼ 0.3 mm), sediment strength of the Guadalupe and Colorado Rivers displayed more variations around bridge piers. The spatial variations likely resulted from sediment remobilization processes and local scour under severe hydrodynamic conditions. Both, geotechnical and geophysical results, reflected the observed variations in the riverbed sediments; nonetheless, a quantitative correlation among the rivers was impeded by challenges primarily related to limitations of spatial accuracy and the significant riverbed heterogeneity, as well as shallow water limitations of the chirp sonar. • Combined geotechnical and geophysical site characterization at three Texas river sections • Measurements from small vessels and in areas of unknown riverbed conditions • Sediment dynamics were reflected in geotechnical and geophysical data • Qualitative relationship between portable free fall penetrometer and chirp sonar • Three river sections differed significantly in local sediment properties [ABSTRACT FROM AUTHOR]