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The No-Filter Factor of Safety against Piping through Sands
Progressive internal erosion by piping still presents a major failure threat to dams built with and/or over cohesionless soils. Many engineers do not understand the mechanics of piping and design using an empirical method more than 60 years old. We now know enough to improve this situation. A review of 115 horizontal piping tests indicates the predominant importance of a sand's coefficient of uniformity in determining the hydraulic gradient needed to develop piping, with layer depth, pipe length, density, anisotropy, layering and inclination also having important effects. This paper adds to our physical knowledge about piping, connects piping with liquefaction and presents a new test-based design method for determining the factor of safety and reliability vs. piping at any point in a trial piping path in cohesionless soils. When using filters for safety vs. piping, the new method provides redundancy. It uses the simplifying concept that very low effective stresses and the vertical seepage gradients at the advancing end of the pipe determine its advance, and that the pre-pipe gradients at any point in the pipepath have an important effect on the degree of safety at that point. Section 6 presents a design method for the safety factor vs. piping, with an example. Sections 2 through 5 give the theoretical and practical details leading to the new method. Section 7 discusses some of the possible criticisms of the method.
The No-Filter Factor of Safety against Piping through Sands
Progressive internal erosion by piping still presents a major failure threat to dams built with and/or over cohesionless soils. Many engineers do not understand the mechanics of piping and design using an empirical method more than 60 years old. We now know enough to improve this situation. A review of 115 horizontal piping tests indicates the predominant importance of a sand's coefficient of uniformity in determining the hydraulic gradient needed to develop piping, with layer depth, pipe length, density, anisotropy, layering and inclination also having important effects. This paper adds to our physical knowledge about piping, connects piping with liquefaction and presents a new test-based design method for determining the factor of safety and reliability vs. piping at any point in a trial piping path in cohesionless soils. When using filters for safety vs. piping, the new method provides redundancy. It uses the simplifying concept that very low effective stresses and the vertical seepage gradients at the advancing end of the pipe determine its advance, and that the pre-pipe gradients at any point in the pipepath have an important effect on the degree of safety at that point. Section 6 presents a design method for the safety factor vs. piping, with an example. Sections 2 through 5 give the theoretical and practical details leading to the new method. Section 7 discusses some of the possible criticisms of the method.
The No-Filter Factor of Safety against Piping through Sands
Schmertmann, John H. (author)
Geo-Congress '98 ; 1998 ; Boston, MA
Judgment and Innovation ; 65-132
2015-12-20
Conference paper
Electronic Resource
English
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