Axial load tests and numerical modeling of single-helix piles in cohesive and cohesionless soils

Acta Geotechnica - Small-diameter helical piles have been increasingly used in Western Canada, but there is a lack of research. The present research investigates the axial behavior of three types...     

Field loading tests of screw micropiles under axial cyclic and monotonic loads

Unlike conventional grouted micropiles, screw micropiles have been recently introduced to the foundation industry. Full-scale field tests of screw micropiles were carried out at a cohesive soil site. The screw micropiles have a diameter varying from 76 to 114 mm and a length varying from 1.6 to 3 m, and spiral threads welded on the lower half of the steel tubular shaft. Site investigation from cone penetration tests (CPT) and laboratory testing implies that the soil was medium to stiff, low plasticity clay. Six axial monotonic and three axial cyclic load tests were performed on three micropiles. One micropile was instrumented with strain gauges to investigate the shaft load distribution during loading. The axial cyclic loading was intended to simulate cyclic inertia load during vertical ground motions. Results showed that the micropiles behave as frictional piles during monotonic tests; the unit shaft resistance and adhesion coefficient were calculated and compared with results in the literature. The end installation torque was estimated using CPT shaft resistance and was shown to agree reasonably with the measured torque. Under axial cyclic loading, the micropiles underwent small cumulative displacements and the magnitude of the displacement decreased with increasing pile length and diameter. Cyclic loading redistributed the load transfer along different segments of the micropile. Negative skin resistance was observed along the smooth pile shaft when the pile underwent decreasing axial loading.

     

Investigation of Adsorption–Desorption,Induced Strains and Permeability Evolution During N2–ECBM Recovery

Natural Resources Research - In this study, the adsorption–desorption/induced strains/permeability characteristics of seven columnar coal samples with Ro.ran ranging from 0.42 to 3.23% were...     

Spatial Association Between Orogenic Gold Mineralization and Structures Revealed by 3D Prospectivity Modeling: A Case Study of the Xiadian Gold Deposit,Jiaodong Peninsula,China

Natural Resources Research - The Xiadian orogenic deposit with?~?100 t of gold resources, located in the Jiaodong Peninsula, Eastern China, shows an economically attractive gold...     

粤港澳大湾区气溶胶对白天城市热岛强度的影响

以粤港澳大湾区为例,利用卫星遥感资料结合大气化学模式模拟,分析2003―2018年城市热岛强度、气溶胶光学厚度的变化规律,定性和定量研究气溶胶对白天城市热岛强度的影响。结果表明：2003―2018年粤港澳大湾区城市热岛强度呈波动上升趋势,夏季热岛强度最大,冬季热岛强度最小;气溶胶光学厚度呈波动下降趋势,春季气溶胶光学厚度最大,冬季气溶胶光学厚度最小。在年际和季节尺度,城市热岛强度与城区、郊区气溶胶光学厚度之差均呈弱的正相关。基于WRF-Chem的模拟实验表明,气溶胶的存在导致城区、郊区地表向下总辐射减少、地表温度降低,且城区地表向下总辐射减少多于郊区、降温幅度大于郊区,进而导致了热岛强度减弱。气溶胶对城市热岛强度的贡献率为?2.187%,冬季贡献率绝对值略高于夏季。     

Multi‐scale approach to mining significant spatial co‐location patterns

Spatial co‐location pattern mining aims to discover a collection of Boolean spatial features, which are frequently located in close geographic proximity to each other. Existing methods for identifying spatial co‐location patterns usually require users to specify two thresholds, i.e. the prevalence threshold for measuring the prevalence of candidate co‐location patterns and distance threshold to search the spatial co‐location patterns. However, these two thresholds are difficult to determine in practice, and improper thresholds may lead to the misidentification of useful patterns and the incorrect reporting of meaningless patterns. The multi‐scale approach proposed in this study overcomes this limitation. Initially, the prevalence of candidate co‐location patterns is measured statistically by using a significance test, and a non‐parametric model is developed to construct the null distribution of features with the consideration of spatial auto‐correlation. Next, the spatial co‐location patterns are explored at multi‐scales instead of single scale (or distance threshold) discovery. The validity of the co‐location patterns is evaluated based on the concept of lifetime. Experiments on both synthetic and ecological datasets show that spatial co‐location patterns are discovered correctly and completely by using the proposed method; on the other hand, the subjectivity in discovery of spatial co‐location patterns is reduced significantly.     

基于景观基因“地域机制”的客家文化保护与传承开发——以湖南省炎陵县为例

根据客家文化景观基因理论及其"地域机制",以客家扩展聚居区炎陵县为例,结合历史文献查阅和实地调研,发掘分析该县客家文化的景观基因。研究结果表明:(1)迁徙由来、地域背景分别是客家文化景观的共同基因、本土基因;(2)由共同基因以"反客为主"的作用方式与本土基因形成了地方客家景观本质特性的主体基因;(3)保护与传承意识形态是决定其主体基因能否在世代遵循并坚守着"原汁原味"文化传统和文化精神传承过程中的人为基因。基于这些独特基因构成内在相关联的地域机制而所表达的特征,提出了应加强客家文化景观基因的数字化保护管理、传承开发政策等对策。     

Generating urban road intersection models from low-frequency GPS trajectory data

Detailed real-time road data are an important prerequisite for navigation and intelligent transportation systems. As accident-prone areas, road intersections play a critical role in route guidance and traffic management. Ubiquitous trajectory data have led to a recent surge in road map reconstruction. However, it is still challenging to automatically generate detailed structural models for road intersections, especially from low-frequency trajectory data. We propose a novel three-step approach to extract the structural and semantic information of road intersections from low-frequency trajectories. The spatial coverage of road intersections is first detected based on hotspot analysis and triangulation-based point clustering. Next, an improved hierarchical trajectory clustering algorithm is designed to adaptively extract the turning modes and traffic rules of road intersections. Finally, structural models are generated via K-segment fitting and common subsequence merging. Experimental results demonstrate that the proposed method can efficiently handle low-frequency, unstable trajectory data and accurately extract the structural and semantic features of road intersections. Therefore, the proposed method provides a promising solution for enriching and updating routable road data.     

Changes in record-breaking temperature events in China and projections for the future

Theoretical and Applied Climatology - As global warming intensifies, more record-breaking (RB) temperature events are reported in many places around the world where temperatures are higher than...     

基于全视野数字图像的能见度估算方法

基于全视野数字图像的能见度估算方法是将全视野图像大气透射率与大气能见度通过曲线拟合方法建立联系,得到估算模型进行能见度估算。首先通过历史全视野图像和对应时刻的大气能见度建立样本数据集,再利用暗原色先验理论获取全视野图像大气透射率,通过多项式拟合方法建立离散样本数据集中大气透射率与对应时刻大气能见度的关系,即全视野图像能见度估算模型,最终将所需估算时刻的数字图像输入估算模型进行能见度估算,得到大气能见度数值。结果表明:建立的基于全视野数字图像能见度估算模型在环境光照均匀时大气能见度估算值与能见度实测值有较好的一致性,可作为前向散射仪的补充观测方法,弥补其采样存在的局限性。