Characterization of Complex Soil Stratigraphies by VisCPT and Adaptive Remeshing

最先进的岩土工程和地质环境现场表征现在普遍采用直接推动技术。锥体穿透测试（CPT）及其变体，压电锥体（uCPT）和地震锥体（SCPT），在提供最全面的现场地层评估和确定工程（机械和地质水文）土壤特性方面领先于直接推入技术。然而，如果土壤沉积物很复杂，CPT往往不能提供准确的地层信息，所得的性质也不可靠。这些复杂性可能包括不寻常的场地应力历史（地貌）和薄层地层。目前的研究工作利用了两种最新开发的技术来创建程序，以全面评估现场地层学，并确定即使是薄土层（如砂缝和粘土透镜）的土壤特性。第一个工具是有限元建模中的“自适应网格划分”。较硬的外来物体（如钢锥贯入计）对土壤的大量渗透会在较软的材料中产生较大的位移和应变。因此，有限元网格变得非常压缩和扭曲，导致数值不稳定。然而，通过自适应重新划分土壤，可以模拟出米数量级的穿透。因此，本研究将利用该工具来研究土壤对CPT的响应。将模拟穿过不同土壤之间的界面以及穿过薄地层的渗透，以了解在这种条件下典型的CPT特征。将探讨正常固结和超固结应力状态。将自适应网格划分结果外推到现场条件，特别是确定薄层的工程性质，将需要了解这些层的实际厚度和原位位置。为此，将使用最近开发的“视锥穿透仪”（vis锥穿透仪）。以前的研究已经导致了这种传统CPT增强的发展，它允许土壤柱的连续图像记录。即使是薄至0.5厘米的层也很容易被检测到，从而提供了传统CPT所缺少的信息。一旦确定了土层厚度，就可以通过自适应网格的有限元研究结果来预测土壤的性质。该研究的更广泛影响包括广泛的跨学科研究，向行业的直接技术转移以及重新设计本科实验室经验，以包括vispt技术。对场地特征的改进将导致更安全、更经济的土木工程建设。有了更精确的地下信息，建筑行业将能够降低目前为防止意外情况而需要的高安全系数。

State-of-the-art geotechnical and geoenvironmental site characterization now ubiquitously employs direct-push technologies. The cone penetration test (CPT) and its variants, the piezo-cone (uCPT) and seismic-cone (SCPT), lead the direct-push technologies in providing both the most comprehensive assessment of site stratigraphy and determination of the engineering (mechanical and geohydrologic) soil properties. However, if the soil deposits are complex, the CPT often fails in providing accurate stratigraphic information and yields unreliable properties. These complexities may include unusual site stress history (geomorphology) and thin layering of strata. The present research effort utilizes two recently developed technologies to create procedures for comprehensively assessing site stratigraphy and for determining the soil properties of even thin soil layers such as sand seams and clay lenses. The first tool is "adaptive remeshing" in finite element modeling. Large penetration of soil by stiffer foreign objects such as a steel cone penetrometer creates large displacements and strains in the softer material. Therefore, a finite element mesh becomes very compressed and distorted leading to numerical instability. However, by adaptively remeshing the soil, penetrations on the order of meters can be simulated. The present research will therefore utilize this tool to study the response of soils to the CPT. Penetration across interfaces between dissimilar soils as well as through thin strata will be simulated to gain an understanding of the typical CPT signature in such conditions. Both normally consolidated and overconsolidated stress states will be explored.Extrapolation of the adaptive remeshing results to field conditions and specifically the determination of engineering properties of thin strata will require knowledge of the actual thicknesses and locations of these layers in-situ. For this, a recently developed "vision cone penetrometer" (VisCPT) will be utilized. Previous research has resulted in development of this augmentation to the conventional CPT, which allows for continuous image recording of the soil column. Even layers as thin as 0.5 cm are easily detected by the VisCPT thereby providing the missing information from the conventional CPT. Once a layer thickness is established, the soil properties can be predicted by the results of the finite element studies with adaptive remeshing.The broader impacts of the study include extensive interdisciplinary research, immediate technology transfer to industry and redesign of undergraduate laboratory experience to include VisCPT technology. Improvements to site characterization will lead to safer and more cost effective civil engineering construction. With more precise subsurface information, the construction industry would be able to reduce the typically high factors of safety that are presently needed to protect against unexpected conditions.