Collaborative Research: Surface Flux for Cracked and Intact Clays for Ponded and Sloped Conditions

在基础设施的寿命（饱和或干燥性能）的极端湿润状态的非饱和土壤的假设有显着的影响，设计，施工，功能，安全和结构寿命。 对地下饱和度的评估需要了解和量化实际的地表通量，这是土壤表面条件的复杂函数，特别是包括土壤吸力、开裂程度和边坡几何形状。 在岩土工程应用中，有两个主要的相关研究问题尚未得到充分解决：（1）体积变化敏感性粘土表面开裂对非饱和流动特性函数的影响，以及（2）排水条件（良好倾斜表面与排水不良）对开裂和完整粘土表面通量的影响。 由于土壤储存条件的变化，土壤的季节性开裂导致径流和渗透的估计不佳（Arnold等人，2005年）。 从土壤性质和数值模拟的角度来看，土壤吸力剖面的预测需要在当前能力方面进行实质性的改进。 几种条件下提出的数值解的挑战：（一）强非线性土壤性质，（二）突然变化的水分条件在表面边界和湿润锋，以及（iii）存在的地表径流条件（Scanlon等。例如，2002年）。 非饱和裂缝土壤的行为是完全不同的，从完整的土壤，进一步复杂化的粘土表面通量条件的评估。 这项研究解决了关键的剩余问题很少，或只是表面上，在岩土工程文献中讨论，并面向改造的表面通量建模能力的开裂和完整的粘土。 岩土工程研究小组将与应用数学的一名合作研究员合作，通过开发以下内容来满足这些需求：（1）开裂粘土的非饱和土壤特性的数据和模型，包括裂缝和基质的体积变化;（2）良好倾斜（倾斜）和水平坡度裂缝和完整径流的数据和模型（3）改进的表面通量（包括径流）的求解方法，以及（4）与模型和数据一致性的与排水和破裂相关的现场损害的评估。 这项研究的一个关键因素是合作伙伴（亚利桑那州立大学？先进的非饱和土试验设备和SDSU？s独特的倾斜表）。非饱和土引起了一系列的问题。 据估计，仅膨胀粘土对基础设施的损害就高达150亿/年（Nuhfer等人，1993; Wray and Meyer 2004）。 克罗恩和Slossom（1980年）估计，美国20%的表层土壤会发生收缩-膨胀（和开裂）。 对污染物向深层移动的关注提高了人们对了解非饱和流以及气候、人类地表活动和非饱和土壤次表层条件和过程之间复杂相互作用的兴趣。 研究人员已经证明了非饱和土的行为在碎石引起的边坡破坏中的作用（Toll，1999; Yin，1998）。 地表通量和地表径流对边坡的性能至关重要，而裂缝对通量或边坡稳定性本身的影响知之甚少。 1982年，在加州，有超过18，000次滑坡在几乎没有任何警告的情况下冲下斜坡，破坏了房屋，造成14名居民死亡（Ellen和Wieczorek，1988年）。 美国每年的滑坡修复费用超过20亿美元，几乎所有的滑坡都是由地震引起的，每年造成25-50人死亡（Spike和Gori，2003年）。 这项研究将通过加强我们对地表通量和非饱和流的理解和建模，对所有这些问题的解决方案产生影响。学生将接受培训，并将参与传播，包括会议和出版物。 调查结果将在亚利桑那州立大学和SDSU的CE教室，并整合到亚利桑那州立大学？的数学课程，学生将进行数值模拟，并与现有的代码和数据进行比较。 正在进行的亚利桑那州立大学招聘计划，重点是教师和代表性不足的学生将被用来把这项研究的各个方面到初中和高中课堂。 一套讲座将在研究过程中开发，并在圣地亚哥高中有82%的女性和非白人男性学生的身体。 学生们还将参观实验室。与工程预科教师合作，Co-Is将开发一种吸引学生进行工程和研究的方法。

Assumptions of extremes of wetted state of unsaturated soils during infrastructure lifetime (saturated or dry properties) have significant implications for design, construction, functionality, safety, and structural longevity. Assessment of the degree of saturation that occurs in the subsurface requires understanding and quantifying actual surface flux, a complex function of soil surface conditions, including in particular soil suction, degree of cracking, and slope geometry. There are two major related research issues yet to be adequately addressed in geotechnical applications: (1) the effect of surface cracking in volume-change-sensitive clays on unsaturated flow property functions, and (2) the effect of drainage conditions (well-sloped surface versus poorly drained) on surface flux of cracked and intact clays. Seasonal cracking of soil results in poor estimates of runoff and infiltration due to the changing soil storage conditions (Arnold et al, 2005). Prediction of soil suction profiles requires substantial improvements in current capabilities, both from a soil property and numerical modeling perspective. Several conditions present numerical solution challenges: (i) strong nonlinearities in soil properties, (ii) abrupt changes of moisture conditions at the surface boundary and wetting front, and (iii) the presence of surface runoff conditions (Scanlon et. al., 2002). The behavior of unsaturated cracked soil is quite different from that of intact soil, further complicating evaluation of surface flux conditions for clays. This study addresses key remaining questions rarely, or only superficially, discussed in the geotechnical literature, and is geared toward transformation of surface flux modeling capabilities for cracked and intact clays. The geotechnical research team will work with a co-investigator in Applied Math towards addressing these needs through development of: (1) data and models for unsaturated soil properties of cracked clays including volume change of both the cracks and matrix; (2) data and models for run-off for well-inclined (sloped) and level-grade cracked and intact (3) improved solution methods for surface flux, including run-off, and (4) evaluation of field damage related to drainage and cracking for consistency with modeling and data. A key element of this research is the collaboration and sharing of physical resources among partners (ASU?s advanced unsaturated soils testing equipment and SDSU?s unique tilt table). A wide range of problems arise from unsaturated soils. Damage to infrastructure from expansive clays alone is estimated to be as much as 15 billion/yr (Nuhfer et al., 1993; Wray and Meyer 2004). Krohn and Slossom (1980) estimated that 20% of surface soils of the U.S. are subject to shrink-swell (and cracking). Concerns over movement of contaminants to great depth have heightened interest in understanding unsaturated flow and the complex interactions between climate, human surface activities and unsaturated soil subsurface conditions and processes. Researchers have demonstrated the role of unsaturated soil behavior in rainfall-induced slope failure (Toll, 1999; Yin, 1998). Surface flux and surface runoff are critical to the performance of slopes, and little is known about the influence of cracks on the flux or on slope stability itself. In California in 1982, over 18,000 slides swept down slopes with little warning, damaging homes and killing 14 residents (Ellen and Wieczorek, 1988). U.S. costs for landslide repairs exceed $2 billion/yr and landslides, nearly all rainfall-induced, result in 25-50 deaths/yr (Spike and Gori, 2003). This research will have impact on solutions to all of these problems through enhancing our understanding and modeling of surface flux and unsaturated flow. Students will be trained and will be engaged in dissemination, including conferences and publications. Findings will be presented in CE classrooms at ASU and SDSU, and integrated into ASU?s Math program where students will perform numerical simulations and compare with existing codes and data. On-going ASU recruiting programs focused on teachers and underrepresented students will be used to bring aspects of this study into junior and high school classrooms. A set of lectures will be developed on the research process and presented at a San Diego high school having an 82% female and non-white male student body. Students will also tour labs. Working with pre-engineering teachers, Co-Is will develop a means of attracting students to engineering and research.