Experimental Study on Seepage Failure of Uniform and Gap-Graded Soils

• Main Authors: Jyun-Yen Wang, 汪俊彥
• Other Authors: Kuo-Hsin Yang
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/9s722t

碩士 === 國立臺灣科技大學 === 營建工程系 === 100 === Soil piping is a hydraulic and geotechnical phenomenon that soil hydraulic fails due to seepage. Soil piping can happen in geotechnical engineering and ecosystem. An upward seepage testing system is developed to study the seepage failure of soil. The testing system consists of a transparent acrylic permeameter, a constant head device and a data acquisition system. Using this test apparatus, a series of experiments on uniform sand and gap-graded sand are carried out to observe the process of seepage failure of specimen and to determine the critical hydraulic gradient. This study found the seepage failure mode is depended on the internal stability of soil which mainly depends on the grain size distribution and can be assessed using stable criteria. Test result shows seepage failure of uniform sand (internally sable soil) typically experiences an expansion of specimen thickness and the liquefaction of specimen, which is associated with the condition of effective stress equals zero. Seepage failure of gap-graded sand (internally unstable soil) is related to the internal erosion of fines which shows the finer particles in specimen will be vigorously eroded out with upward seepage flow, but the coarser particles remain comparatively stable. Further, the critical hydraulic gradients icr of soil obtained from test are compared with the predicted icr using theoretical equation proposed by Terzaghi. It is found the values of icr of uniform sand range from 0.89 to 1.21 which are close to the predicted icr. The values of icr of gap-graded sand range from 0.27 to 0.43 are far lower than the predicted icr. A database of icr of soil is compiled from this study and relevant literatures, and is used to compare different icr prediction methods and identify a best prediction method. Comparison result shows there is no a best methods can accurate predict the icr for all types of soils, but Terzaghi’s equation can predict the icr well of soil which satisfies the stable criterion proposed by Kenny and Lau (1985). Finally, this study is expected to provide the contribution in geotechnical engineering for a better understanding of seepage failure of soil and their critical hydraulic gradient.