Fluidization Behavior of Sands Based on Ring Shear Tests-Effects of Grain Size and Fine‐Particle Content-

Abstract

土砂の流動化のメカニズムを調べるために、硅砂及び硅砂とレスの混合サンプルを用いてリングせん断試験を実施した。その結果、非排水状態において、せん断ゾーンが形成しうることと粒子破砕はせん断ゾーンにおいて発生することが分かった。粗な試料には構造破壊(Collapse〉によって流動化するが、より密度の大きな場合でもせん断の進行とと・もに流動化が発生し得る。ピーク強度と流動化後の強度の差とピーク強度の比(BrittlenessIndex)は初期応力状態の影響が強い。また、ピークせん断強度と流動限界勾配を規定する流動化後の定常状態強度は、粒径が小さい場合ほど細粒部分の比率が高いほど小さくなる.

Using a newly developed ring shear apparatus, several sets of undrained ring shear tests were conducted on sands of different grain size and fine‐particle content to study the effects of samples on the fluidization behavior within the shear zone.By inserting slices of Toyoura sand with different color into the shear box, the deformation of sands within the shear box was observed after 3‐cm of undrained shearing, and it was made clear that localized shearing was formed in both the tests on loose sand and dense sand. Grain size analysis on the samples from the shear zone after the undrained shear tests revealed that grain crushing was initiated in the shear zone.By performing tests on sands of the same density at different stress states, the collapse behavior of loose sands in ring shear tests were examined, and the collapse line was found passing through the origin, and dependent on sample's initial density and grain size. The brittleness index increased with increasing initial normal stress and shear stress.Based on the tests results, the effects of grain size and fine‐particle content on the undrained shear behavior were examined. And the results showed that, given their relative densities being the same, when the grain size became finer or fine‐particle content became greater, both the undrained peak shear strengths and steady state shear strengths became smaller, meanwhile, the dissipation of generated high pore pressure from the shear zone became slower after the shear box was turned into drained condition.