압축성(壓縮性) 모래의 3차원(次元) 변형거동(變形擧動)

Three Dimensional Deformation Behaviour of Compressible Sand

압축성(壓縮性) 모래를 사용하여 주응력(主應力)을 각기 독립적으로 조절할 수 있는 입방체삼축시험(立方體三軸試驗)을 하였다. 그 결과 초기(初期) 변형계수(變形係數)는 b값의 증가와 더불어 증가하고 중간주응력(中間主應力)이 b값이 적을 때는 주변형율간(主變形率間)의 거동(擧動)에 영향을 미치지 못하고 배수(排水) 경우는 b=0.3, 비배수(非排水)경우는 b=0.6 값에서부터 b값이 커질수록 최대주변형율(最大主變形率)(${\varepsilon}_1$) 값이 더 적은 값에서 파괴(破壞)된다. 파괴시(破壞時) 소성변율(塑性變形率) 중분벡터의 방향은 배수조건(排水條件)에 무관하고 직교조건은 3축면(三軸面)에서는 만족되지 않으나 팔면체면(八面體面)에서는 만족되는 재료(材料)임을 알았다.

A series of cubical triaxial tests with independent control of the three principal stresses were performed on a compressible sand. All specimens which were formed by depositing the fine sand loosely, were used. It was found that slope of the stress-strain curve increased with increased b value, and the major principal strain at failure first remains approximetely constant for b values smaller than about 0.3 for drained condition and 0.6 for undrained condition respectively, and thereafter decreases with increasing value of b. The test results showed that the direction of the strain increments at failure form acute angles with the failure surfaces for both the drained and undrained condition. The results are thus not in agreement with the normality criterion from classic plasticity theory. However, it was found that the projections of the plastic strain increment vectors on the octahedral plane are perpendicular to the faiure surface in that plane.