Study on the evaluation method of in-situ deformation-strength characteristics of granular material with breakable particles

通过实验和分析研究，得出了以下结果：1.对以易碎颗粒为主的颗粒材料的应力变形行为进行合理评价。火山粗粒土在低围压下具有与致密砂相似的应变硬化-软化特征。在高围压剪切作用下，发现了与粘土相似的塑性行为。无论剪切条件或应力系统的不同，均可发现细粒DELTAFc增量与破坏p'f时有效平均主应力之间存在独特的关系。这表明，DELTAFc值是表征剪切作用下颗粒破碎的合适参数。在相同剪切条件下的试验结果表明，原状试样的强度值高于原状试样的强度值。这是由于胶结作用，可以防止颗粒破碎。火山土在平面应变条件下的强度高于轴对称应力条件下的强度，这在正常颗粒材料中可以看出。这种趋势在火山土中比在托尤拉沙中更为显著。颗粒破碎对粗粒火山土力学性能的影响在平面应变条件下比在轴对称应力条件下更为显著。因此，粗粒火山土的应变硬化特性与颗粒破碎和剪切条件（二维或三维变形和应力路径差异）密切相关。在轴对称试验中没有发现固有的各向异性效应，从而允许三维变形。然而，这种影响明显存在于平面应力状态下的破坏状态。

The following results were obtained from experimental and analytical researches aimed study the rational procedures which can evaluate the stress-deformation behavior of granular material mainly constituted by breakable particles.1. Shear behavior of volcanic coarse grained soils has a strain hardening-softening characteristics similar to that of dense sand at lower confining pressure. And plastic behavior similar to clay has been found on the shearing with higher confining pressure.2. A unique relationship between the increment of finer fraction DELTAFc and effective mean principal stress at failure p'f can be found regardless of the difference in the shear condition or in the stress system. This facts show that the value DELTAFc is an appropriate parameter which can express particle breakage induced by shearing.3. From the experimental results under the same shear condition, it has been shown that strength values for undisturbed samples are higher than ones of disturbed samples. This is attributed to the cementation effect which may prevent particle breakage.4. Strength of volcanic soil was higher under the plane strain condition than under the axisymmetric stress condition, as can been seen in the normal granular materials. This tendency was more remarkable in volcanic soils than Toyoura sand.5. Effect of particle breakage on the mechanical properties of coarse volcanic soil is more significant under plane strain condition than under axisymmetric stress condition. Consequently, strain hardening properties of coarse volcanic soil is closely related to particle breakage and shear condition(two or three-dimensional deformations and difference in stress path).6. Inherent anisotropy effect was not found on the axial-symmetry tests which allows three-dimensional deformation. However, such effect was obviously kept to the failure states on the plane stress condition.