压实黄土平面应变方向的主应力特性

对不同含水率压实黄土进行等小主动主应力σ_x的平面应变三轴试验,研究了含水率w及小主动主应力σ_x对加载过程中平面应变方向主应力σ_y特性的影响,根据试验结果提出了描述平面应变方向与其它方向主应力双线性关系的表达式,验证了基于典型强度准则的中主应力公式描述压实黄土σ_y变化的适用性。研究结果表明:在等向固结及初始加载阶段,平面应变方向主应力不是中主应力σ_2,而是小主应力σ_3;平面应变方向主应力比σ_y/σ_x随着主动主应力比R的增大先平缓后快速增大,转折点前后主应力之间分别呈线性和非线性关系;转折点处的主动主应力比Rz大于平面应变方向主应力由小主应力转变为中主应力临界点处的主动主应力比Rc,w及σ_x对Rz的影响较大,对Rc的影响很小。R较小时,w及σ_x对加载过程中σ_y/σ_x几乎没有影响。主应力参数K(=2σ_y/(σ_x+σ_z))与主动主应力比R之间呈双直线;前段为水平直线,K近似为常数Kc;后段为倾斜向上的直线;Kc及直线斜率m与w及σ_x的大小无关。提出的双线性函数能较好地预测压实黄土加载过程中σ_y的变化特性,而仅在土样破坏时,基于Lade-Duncan及SMP准则的中主应力公式的预测值与试验值比较接近。

Characteristics of principal stress of compacted loess in plane strain direction

The plane strain triaxial tests in which the minor active principal stress (also called σ_x) keeps invariable are performed on the compacted loess with different water contents. The influences of σ_x and water content (also called w) on characteristics of the principal stress in plane strain direction (also called σ_y) during loading are studied. Based on the test results, the expressions describing the bilinear relationships between the principal stress in the plane strain direction and that in other directions are proposed. It is verified whether or not σ_y can be predicted by the expressions for the intermediate principal stress based on different strength criteria for compacted loess. The test results show that σ_y is not the intermediate principal stress (also called σ₂) but the minor principal stress (also called σ₃) during the isotropic consolidation and the initial loading stage. The ratio of the principal stress in the plane strain direction to the minor active principal stress (also called σ_y/σ_x) fast increases after the gentle development stage with the increase of the ratio of the major active principal stress to the minor one (also called R), and the relationships between the principal stresses are respectively linear and nonlinear before and after the turning point. The ratio of the major active principal stress to the minor one at the turning point (also called R_z) is larger than that at the critical point where σ_y transforms σ₂ to σ₃ (also called R_c). w and σ_x have obvious influences on R_z but little ones on R_c. The effects of w and σ_x on σ_y/σ_x are little as R is small. The relationships between the principal stress parameter (=2σ_y/(σ_x+σ_z), also called K) and R can be describedas two-stage lines. The one is horizontal and K is constant K_c in the first stage. The other one is inclined upward in the second stage. The slope m and K_c are irrelevant to w and σ_x. The change of σ_y during the loading can be better predicted by the proposed bilinear function. The predicted results are approximately equal to the test ones only at the failure of soil samples, using the expressions for the intermediate