Geohazards and large, geographically distributed systems
A general classification for scale in geotechnical engineering is used to explore the modelling of large, geographically distributed systems and their response to geohazards. Both component and network performance are reviewed. With respect to components, prototype-scale experiments of underground pipeline response to abrupt ground deformation are described, including control of soil properties, soil–pipeline interaction, and performance of high-density polyethylene pipelines. Direct shear (DS) apparatus size is shown to have a significant effect on DS strength, and the most reliable DS device is identified from comparative tests with different equipment. Mohr–Coulomb strength parameters for partially saturated sand are developed from DS test data and applied in finite element simulations of soil–pipeline interaction that show excellent agreement with prototype-scale experimental results. Apparent cohesion measured during shear failure of partially saturated sand is caused by suction-induced dilatancy. With respect to networks, the modelling of liquefaction effects on the San Francisco water supply is described, and a case history of its successful application during the Loma Prieta earthquake is presented. The systematic analysis of pipeline repair records after the Northridge earthquake is used to identify zones of potential ground failure, and correlate pipeline damage rates with strong ground motion. Hydraulic network analyses are described for the seismic performance of the Los Angeles water supply, with practical applications for emergency response. The effects of Hurricane Katrina are reviewed with respect to the New Orleans hurricane protection system, Gulf of Mexico oil and gas production, and interaction between electric power and liquid fuel delivery systems. The sustainability of the Mississippi delta is discussed with regard to flood control, maintenance of wetlands and barrier islands, and catastrophic change in the course of the Mississippi River.