Lecture 8 Deformation behavior for unsaturated soils.ppt

CSL for unsaturated soils * * * * * * 称为压缩系数，KPa-1 a1-2常用作比较土的压缩性大小 土的类别 a1-2 (MPa-1) 高压缩性土 ≥0.5 中压缩性土 0.1-0.5 低压缩性土 0.1 e-logp曲线及压缩指数 三轴等向压缩和回弹 ?? = 0, ?u = 0 变形： 塑性变形 ?vp 弹性变形 ?ve 正常固结线 超固结土 欠固结土：不稳定态 正常固结线 If under?monofonic stress path Soil deformation is independent with the stress path Cui and Delage 1996 Consolidation for unsaturated soils(Alonso et al. 1990) 不排水三维等向压缩试验（初始试样不饱和） 浸水阶段 等向压缩阶段 What’s the swelling pressure for soil in confining state? swelling pressure Swelling pressure Pf The reduction of suction can be considered equally as the decrease of normal stress P0 is the equivalent normal stress of current suction P0 Example 1 * Shear behavior (for sand; same ???) t s dx H dz gxz gxz = dx/H ez = - dz/H = ev g Dense (D) ? Loose (L) e g D L g ev D L Dilatancy Contractancy * Critical state Critical states (ultimate states) For granular materials A constant volume during subsequent shearing ?p / ??q = ?q/ ??q = ??v / ??q = 0 Regardless of initial states Related to the normal stress * Critical state line I g D2 L2 D1 L1 s’ e s1 s2 g ?c * Critical state line II Parallel to NCL Critical OCR At critical state, qf - p’f - ef relation is unique * Soil states: Wet/dry states Sands Clays * Soil states: Dilatancy Soil at a dry state before shear Volume increase in straining (dilatancy) * Soil states: Peak state Dilantancy angle ? = ??v / ?h ? ??v / ?? Related to the initial OCR ? ? ? ? ? / g ev / ? ? ? Shearing Behavior of saturated soils g ev D L Dilatancy Consolidation g Dense (D) ? Loose (L) Stress train curves at ó3 = 50 kPa and various controlled suctions (Cui and Delage 1996) * Stress train curves at ó3 =40kPa and various controlled suctions (Cui and Delage 1996) * Determination of the yield points in triaxial tests at ó3 = 200 kPa (Cui and Delage 1996) * * 膨胀土边坡滑塌 膨胀土坡面防护 膨胀土属于粘性土，具有一般粘性土所共有的物理力学性质外，最重要的特性是强亲水性、多裂隙性、强膨胀性、强收缩性等。 当含水量增加，表现出体积增大的能力，即具有强烈的膨胀性；若收到约束，产生的内力为膨胀力。 相反则产生收缩。具有胀缩特性，而且胀缩变形可随环境温度和湿度的变化往复发生。 膨胀土的性质及膨胀原理 粒度组成中，通常黏粒含量大于30%。