Adopting the BOT （build-operate-transfer） delivery method has brought opportunities and challenges in construction time and quality for urban infrastructure. Many studies investigate the upstream issues of BOT proje...Adopting the BOT （build-operate-transfer） delivery method has brought opportunities and challenges in construction time and quality for urban infrastructure. Many studies investigate the upstream issues of BOT projects such as concessionaire selection criteria and risk factors. But the project execution becomes complicated such as the escalated quality supervision organization and procedure at the construction stage. This extra supervision may have constituted hidden redundancies as waste to economic sustainability. This paper investigated construction quality supervision of BOT projects to pinpoint adequate degree of supervision and detect redundant organization and procedures. The study adopted ten subway construction projects as cases in which five were from the traditional design-bid-build （DBB） and five from the BOT methods. Thirty six project participants including owners, contractors, designers, and concessionaire managers of the ten projects were interviewed to tell their views on these issues. The quality supervision measures of the DBB projects were used as the baseline and compared with those of the BOT projects. The research results show that the construction quality seems no difference for the DBB and BOT projects. Construction quality comes out of supervision but excessive supervision organization and procedures do not necessarily improve quality. This finding indicates that adequate degree of supervision is enough to achieve required quality to save immense paperwork for large construction projects.展开更多
Based on the equations of motion and the assumption that ocean turbulence is of isotropy or quasi-isotropy, we derived the closure equations of the second-order moments and the variation equations for characteristic q...Based on the equations of motion and the assumption that ocean turbulence is of isotropy or quasi-isotropy, we derived the closure equations of the second-order moments and the variation equations for characteristic quantities, which describe the mechanisms of advection transport and shear instability by the sum of wave-like and eddy-like motions and circulation. Given that ocean turbulence generated by wave breaking is dominant at the ocean surface, we presented the boundary conditions of the turbulence kinetic energy and its dissipation rate, which are determined by energy loss from wave breaking and entrainment depth respectively. According to the equilibrium solution of the variation equations and available data of the dissipation rate, we obtained an analytical estimation of the characteristic quantities of surface-wave-generated turbulence in the upper ocean and its related mixing coefficient. The derived kinetic dissipation rate was validated by field measurements qualitatively and quantitatively, and the mixing coefficient had fairly good consistency with previous results based on the Prandtl mixing length theory.展开更多
文摘Adopting the BOT （build-operate-transfer） delivery method has brought opportunities and challenges in construction time and quality for urban infrastructure. Many studies investigate the upstream issues of BOT projects such as concessionaire selection criteria and risk factors. But the project execution becomes complicated such as the escalated quality supervision organization and procedure at the construction stage. This extra supervision may have constituted hidden redundancies as waste to economic sustainability. This paper investigated construction quality supervision of BOT projects to pinpoint adequate degree of supervision and detect redundant organization and procedures. The study adopted ten subway construction projects as cases in which five were from the traditional design-bid-build （DBB） and five from the BOT methods. Thirty six project participants including owners, contractors, designers, and concessionaire managers of the ten projects were interviewed to tell their views on these issues. The quality supervision measures of the DBB projects were used as the baseline and compared with those of the BOT projects. The research results show that the construction quality seems no difference for the DBB and BOT projects. Construction quality comes out of supervision but excessive supervision organization and procedures do not necessarily improve quality. This finding indicates that adequate degree of supervision is enough to achieve required quality to save immense paperwork for large construction projects.
基金supported by National Natural Science Foundation of China(Grant Nos. 40776020, 41106032 and 40531005)National Basic Research Program of China (Grant Nos. G1999043800, 2006CB403600,2010CB950300 and 2010CB950404)
文摘Based on the equations of motion and the assumption that ocean turbulence is of isotropy or quasi-isotropy, we derived the closure equations of the second-order moments and the variation equations for characteristic quantities, which describe the mechanisms of advection transport and shear instability by the sum of wave-like and eddy-like motions and circulation. Given that ocean turbulence generated by wave breaking is dominant at the ocean surface, we presented the boundary conditions of the turbulence kinetic energy and its dissipation rate, which are determined by energy loss from wave breaking and entrainment depth respectively. According to the equilibrium solution of the variation equations and available data of the dissipation rate, we obtained an analytical estimation of the characteristic quantities of surface-wave-generated turbulence in the upper ocean and its related mixing coefficient. The derived kinetic dissipation rate was validated by field measurements qualitatively and quantitatively, and the mixing coefficient had fairly good consistency with previous results based on the Prandtl mixing length theory.
