Notice of RetractionRisk analysis of shield tunnel segment failure based on Fuzzy Fault Tree method
Through analyzing and summarizing the types of shield tunnel segment failure and the relevant causes of the accident, Fuzzy Fault Tree Analysis (FTA) was employed to study the failure risk of segment and the Fuzzy Fault Tree system model of segment and segment-related systems were established. The potential failure modes of risk accidents and their influencing factors were discussed through qualitative and quantitative analysis. With its application on practical project, some effective control measures were proposed. This research could be valuable reference for the design, construction and control of shield tunnel segments.
Risk analysis of cutter head failure of composite EPB shield
All kinds of accident examples and their potential reasons are analyzed and summarized for cutter head failure of composite earth pressure balance(EPB) shield.In order to research the mechanism of the failure mode on cutter disc,cutters and other different cutting components in composite EPB shield machine,fault tree analysis(FTA) is applied to establishing an analytical model on cutter head failure.Firstly,potential failure modes and effect factors of different failures are all analyzed and calculated by set theory in qualitative and quantitative methods.Then,relevant control measures are proposed to reduce the cutter head failure of composite EPB shield.The results will be useful for cutter head design and construction by composite EPB shield in China.
Ozonation of polycyclic aromatic hydrocarbons in oil/water-emulsions: mass transfer and reaction kinetics.
The ozonation of highly condensed polycyclic aromatic hydrocarbons (PAH) was studied in oil/water-emulsions, which are comparable to poorly water-soluble PAH in industrial wastewaters and at contaminated sites. As there was a lack of knowledge about the ozonation in oil/water-emulsions, first the ozone mass transfer was studied and optimized from the gas to the water phase and from the water to the oil phase. The ratio of mass transfer and oxidation reaction was determined by the Hatta-number and revealed a slow, quasi homogeneous reaction of ozone with PAH inside the oil droplets. Because the ozone gas concentration had no influence under the optimized conditions, the selective PAH-ozonation could be described microkinetically by a direct ozone reaction of pseudo-first order regarding PAH-concentrations. The determined PAH mean reaction rate constants of 1.02 min(-1) in oil/water-emulsions are in the upper range as found for PAH dissolved in water. These results give a new insight into the ozonation in the three-phase systems and into the treatment of highly condensed, hardly biodegradable PAH.