裂隙性膨胀土饱和-非饱和渗流分析

降雨入渗条件下的裂隙性膨胀土边坡稳定性与其渗流场分布密切相关,对渗流分析中的积水深度进行了数值模拟,结果显示,不同的积水深度对渗流场的影响很小,因此,在进行裂隙性膨胀土渗流分析时,积水深度为0的假定是可以接受的。基于膨胀土开裂裂隙的规模及渗透性的不同,提出了考虑裂隙系统的膨胀土边坡渗流分析方法,计算结果表明,土体开裂显著改变了膨胀土内部的渗流场分布。该方法可以更好地模拟坡渗流场随时间的变化规律,以及更合理地解释了降雨入渗引起的膨胀土边坡浅层滑动机制。     

桶形基础平台负压沉贯数据分析处理系统

介绍了桶形基础平台负压沉贯数据分析处理系统的组成及数据分析处理方法.该数据分析处理系统是为保证海上桶形基础平台现场施工能顺利沉贯到位而研制,可对海上平台现场施工过程进行实时监测,对沉贯数据进行快速分析、处理,并根据桶形基础平台状态对负压沉贯过程进行智能控制.     

筒型基础负压沉贯流固耦合渗流分析模型

分析筒型基础沉贯作用的土层,利用 流动理论各项同性硬化原理,研究海积软土颗粒本构关系,结合离散元方法计算土体体应变,并将其引入海积软土的物性参数动态计算模型。根据筒型基础沉贯特征,结合体应变以及物性参数动态模型,由有效应力原理和瞬时质量守恒原理分别确定应力和渗流方程,并给出上述模型的定解条件。建立了新的流固耦合渗流的数学模型,求解筒型基础沉贯渗流场分布。     

考虑基质吸力变化时非饱和土的一维本构模型

当地下水位上升或地面遇水浸润时,土的饱和度将因毛细作用而变化,以此使土体产生变形。其中由于含水量增加而使土的重度增大,从而引起压缩变形;同时含水量的增加而使基质吸力下降,从而引起土的回弹变形,因此最终变形取决于上述两种变形趋势的综合效应。根据广义Hook定律、Fredlund的双应力状态变量及Brooks和Corey关于基质吸力与饱和度之间的经验关系,建立了K0状态下非饱和土的一维本构模型。将这一模型与分层总和法相结合,可以计算基质吸力变化时土的竖向变形。通过研究发现,非饱和土的地面变形不仅取决于土的性质与土层的厚度,而且依赖于土中吸力变化前后的分布及应力状态等因素。所建议的一维本构模型可以用于非饱和土地基上基础的沉降估算。     

运城黄土吸力特性的试验研究

应用张力计、热传导探头等吸力量测手段,对山西省运城地区黄土的吸力特性进行试验研究,测出了该黄土在脱湿过程的土-水特征曲线,该法较压力板法简单,还用FredlundandXing(1994)方程对实测数据进行了拟合。     

非饱和膨胀土SWCC研究

研究土体吸力与含水量关系,对于非饱和土的变形和强度问题,有重要的应用价值。利用非饱和土三轴仪对膨胀土进行试验研究,比较系统地分析了矿物成分、孔隙结构、土体应力状态、应力历史等因素对土-水特征曲线的影响。尤其土的矿物成分和孔隙结构是主要的影响因素。综合考虑各种因素的影响,通过室内和野外吸力量测,对土-水特征曲线进行拟合、比较,建立了幂函数模型。由土-水特征曲线可知,室内干湿循环土-水特征曲线具有明显的差异性,野外土-水特征曲线的差异性不明显,并与室内浸湿曲线相似。将野外曲线和浸湿曲线结合起来,推算非饱和状态下土的渗透性、抗剪强度等指标,可以较好地解决岩土力学问题。     

防波堤椭圆形桶式基础结构的贯入受力特性实验研究

某工程拟在深水软土地基上修筑防波堤,为了尽量减少地基处理充分利用天然地基,创新性设计出一种轻型薄壁的预制防波堤结构,其挡浪部分为直立薄壁圆筒,基础部分则为倒扣的薄壁椭圆形桶,并且椭圆形下桶为外壁和内隔板分成9个格室,防波堤结构浮运至指定位置后,拟采用负压工法施工安装就位。这种新型防波堤结构为国内外首次提出,其下沉施工设计尚无规范可循,为此开展了土工离心模型试验,在模型加速过程中模拟了椭圆形下桶基础在淤泥层中的自重下沉,之后利用新研发了一种大行程作动加载装置给椭圆形下桶施加下推力,让其继续向下贯入直至穿越整个淤泥层,以模拟负压工法的贯入下沉。试验测量了下桶贯入下沉过程中的推力与贯入位移,还尝试测量了桶壁和内隔板断面的压应变,由此分析了下桶基础的下沉总阻力、桶壁摩擦力以及截面压应变随贯入位移的变化。结果发现,这些曲线均出现了转折点,根据转折点对应的下沉总阻力确定了椭圆形下桶基础贯入过程所遭遇的临界下沉总阻力值,据此估算了负压工法中所需施加的压力差。     

水平荷载情况下深海吸力锚稳定性研究

深海吸力锚基础的极限承载能力是海洋工程结构设计中的一个关键问题,达到极限平衡状态时,吸力锚的极限承载能力与其失稳模式密切相关。本文基于Cou lom b摩擦对原理,给出了一种精确模拟吸力锚承载能力的有限元模型。在该数值模型基础上,利用通用有限元分析软件ABAQU S,研究了系泊点位置、长径比对吸力锚承载能力的影响,并给出了深海吸力锚失稳模式。研究结果表明,系泊点位置极大地影响着吸力锚的极限承载力和稳定性,系泊点位置的变化,会导致吸力锚出现前倾转动、平移滑动和后仰转动等的失稳模式。     

Seasonal soil water dynamics in the jarrah forest,Western Australia. II: Results from a site with fine-textured soil profiles

Seasonal soil water dynamics were measured at a fine-textured, upslope site within the jarrah forest of southwest Western Australia and compared to the results from a coarse-textured hillslope transect. Gravity drainage dominated during winter and early spring. This reversed in early summer and an upward potential gradient was observed to 7 m depth. A shallow ephemeral saturation zone was observed above a clay pan at 1.5 m depth. This saturation zone persisted through late winter and early spring, contrasting with the short-lived saturation in the duricrust on the hillslope transect. The annual maximum to minimum unsaturated soil water storage was about 530 mm, 50 mm greater than the hillslope transect and higher than most values reported elsewhere in Australia. Significant soil water content changes following winter rain were generally restricted to 6 m but at one site occurred to 9 m. These depths were significantly less than the coarser-textured hillslope transect. Soil water drying rates averaged 5 mm day^?1 during extended dry periods compared to 3.5 mm day^?1 on the hillslope transect. The drying rate occurred uniformly through the profile until late summer when a significant decrease in the upper 3 m was observed.     

Seasonal soil water dynamics in the jarrah forest,Western Australia. I: Results from a hillslope transect with coarse-textured soil profiles

Seasonal soil water dynamics were measured on a hillslope transect in the jarrah forest of southwest Western Australia over the period 1984-86 using mercury manometer tensiometers, gypsum blocks, and a neutron moisture meter. The soil water potential gradients indicated downward vertical drainage flux through winter and spring. There was generally a change to an upwards flux in early summer which was sustained through to autumn. A shallow ephemeral saturation zone was identified in and above a duricrust layer, lasting up to three days after heavy, late winter rainfall. The annual maximum to minimum unsaturated soil water storage on the hillslope was approximately 400 mm to 6 m depth and 480 mm to 15 m depth. This did not change significantly in years of substantially different winter rainfall. The magnitude of seasonal soil water storage was similar to other forested areas with deep soil profiles. The depth of observable infiltration was dependent on annual rainfall. This was consistent with the observation that groundwater levels responded to rainfall over the whole hillslope in wet years but only responded on the lower slopes in dry years. The average summer drying rate of the soil profile to 6 m depth of 3.5 mm day^?1 was within the range of values reported for forests elsewhere. In late summer, following an extended drought period, the drying rate decreased downslope but increased midslope.