Shear Resistance of Sands under Undrained Condition and Potential for Rapid Flow Phenomena by Means of Ring Shear Tests

Abstract

長距離せんだんが可能なリングせん断試験および三軸圧縮試験において発揮される砂の非排水せん断挙動の解明を目的に, 細粒系さおよび風化火成岩資料を対象に実験を実施した。また, 排水時の摩擦係数と見かけの摩擦係数の比を「高速流動ポテンシャル」と定義した。リングせん断試験だけでなく三軸圧縮試験においても, せん断が進み試料中にせん断面が形成されると, 粒子に破砕が進行し間隙水圧が上昇するため, 高い高速流動現象ポテンシャルを示すことが示された。

Shear resistance of two kinds of sands (fine silica and weathered granitic sands) mobilized within shear zone subjected to large shear displacement is examined. The undrained shear strengths at steady state of the specimens formed over the wide range of initial void ratios by ring shear tests are directly compared with those from the undrained triaxial compression tests. The steady state strengths in ring shear tests were smaller than those in triaxial compression tests due to grain crushing. While, small steady state strengths were observed by triaxial compression tests on dense fine silica sand in which there were clearshear surfaces and shear deformation must be concentrated on these surfaces to generate excess pore pressure. To express extent of apparent reduction of internal friction, the new parameter (Pf) was proposed as ratio of drained internal friction angle to apparent friction angle. Potential for rapid flow phenomena of employed two kinds of sands are clearly evaluated by Pf over the wide range of void ratio.