Rheological properties of clayey soils originating from flow-like landslides

Flow-like landslides in clayey soils represent serious threats for populations and infrastructures and have been the subject of numerous studies in the past decade. However, despite the rising need for landslide mitigation with growing urbanization, the transient mechanisms involved in the solid-fluid transition are still poorly understood. One way of characterizing the solid-fluid transition is to carry out rheometrical tests on clayey soil samples to assess the evolution of viscosity with the shear stress. In this study, we carried out geotechnical and rheometrical tests on clayey samples collected from six flow-like landslides in order to assess if these clayey soils exhibit similar characteristics when they fluidize (solid-fluid transition). The results show that (1) all tested soils except one exhibit a yield-stress fluid behavior that can be associated with a bifurcation in viscosity (described by the critical shear rate \( \dot{\gamma_c} \)) and in shear modulus G; (2) the larger the amplitude of the viscosity bifurcation, the larger the associated drop in G; and (3) the water content (w) deviation from the Atterberg liquid limit (LL) seem a key parameter controlling a common mechanical behavior of these soils at the solid-fluid transition. We propose exponential laws describing the evolution of the critical shear stress τ_c, the critical shear rate \( \dot{\gamma_c} \), and the shear modulus G as a function of the deviation w-LL.     

Bulk Mixing and Decoupling of the Nocturnal Stable Boundary Layer Characterized Using a Ubiquitous Natural Tracer

Vertical mixing of the nocturnal stable boundary layer (SBL) over a complex land surface is investigated for a range of stabilities, using a decoupling index ( $0 < D_{rb} < 1$ ) based on the 2–50 m bulk gradient of the ubiquitous natural trace gas radon-222. The relationship between $D_{rb}$ and the bulk Richardson number ( $R_{ib}$ ) exhibits three broad regions: (1) a well-mixed region ( $D_{rb} \approx 0.05$ ) in weakly stable conditions ( $R_{ib} < 0.03$ ); (2) a steeply increasing region ( $0.05 < D_{rb} < 0.9$ ) for “transitional” stabilities ( $0.03 < R_{ib} < 1$ ); and (3) a decoupled region ( $D_{rb} \approx 0.9$ –1.0) in very stable conditions ( $R_{ib} > 1$ ). $D_{rb}$ exhibits a large variability within individual $R_{ib}$ bins, however, due to a range of competing processes influencing bulk mixing under different conditions. To explore these processes in $R_{ib}$ – $D_{rb}$ space, we perform a bivariate analysis of the bulk thermodynamic gradients, various indicators of external influences, and key turbulence quantities at 10 and 50 m. Strong and consistent patterns are found, and five distinct regions in $R_{ib}$ – $D_{rb}$ space are identified and associated with archetypal stable boundary-layer regimes. Results demonstrate that the introduction of a scalar decoupling index yields valuable information about turbulent mixing in the SBL that cannot be gained directly from a single bulk thermodynamic stability parameter. A significant part of the high variability observed in turbulence statistics during very stable conditions is attributable to changes in the degree of decoupling of the SBL from the residual layer above. When examined in $R_{ib}$ – $D_{rb}$ space, it is seen that very different turbulence regimes can occur for the same value of $R_{ib}$ , depending on the particular combination of values for the bulk temperature gradient and wind shear, together with external factors. Extremely low turbulent variances and fluxes are found at 50 m height when $R_{ib} > 1$ and $D_{rb} \approx 1$ (fully decoupled). These “quiescent” cases tend to occur when geostrophic forcing is very weak and subsidence is present, but are not associated with the largest bulk temperature gradients. Humidity and net radiation data indicate the presence of low cloud, patchy fog or dew, any of which may aid decoupling in these cases by preventing temperature gradients from increasing sufficiently to favour gravity wave activity. The largest temperature gradients in our dataset are actually associated with smaller values of the decoupling index ( $D_{rb} < 0.7$ ), indicating the presence of mixing. Strong evidence is seen from enhanced turbulence levels, fluxes and submeso activity at 50 m, as well as high temperature variances and heat flux intermittencies at 10 m, suggesting this region of the $R_{ib}$ – $D_{rb}$ distribution can be identified as a top-down mixing regime. This may indicate an important role for gravity waves and other wave-like phenomena in providing the energy required for sporadic mixing at this complex terrain site.     

3D ground model development for an active landslide in Lias mudrocks using geophysical,remote sensing and geotechnical methods

A ground model of an active and complex landslide system in instability prone Lias mudrocks of North Yorkshire, UK is developed through an integrated approach, utilising geophysical, geotechnical and remote sensing investigative methods. Surface geomorphology is mapped and interpreted using immersive 3D visualisation software to interpret airborne light detection and ranging data and aerial photographs. Subsurface structure is determined by core logging and 3D electrical resistivity tomography (ERT), which is deployed at two scales of resolution to provide a means of volumetrically characterising the subsurface expression of both site scale (tens of metres) geological structure, and finer (metre to sub-metre) scale earth-flow related structures. Petrophysical analysis of the borehole core samples is used to develop relationships between the electrical and physical formation properties, to aid calibration and interpretation of 3D ERT images. Results of the landslide investigation reveal that an integrated approach centred on volumetric geophysical imaging successfully achieves a detailed understanding of structure and lithology of a complex landslide system, which cannot be achieved through the use of remotely sensed data or discrete intrusive sampling alone.     

北山柳园地区中志留世埃达克质花岗岩类及其地质意义

北山柳园地区发育的埃达克质片麻状花岗闪长岩为钙碱性岩浆系列,具有较高SiO₂ (>56%),Al₂O₃ (>15%)和较低的MgO (<3%)含量,Na₂O>K₂O; 并且具有高的Sr含量(>400×10^-6)和Sr/Y比值; 样品轻重稀土强烈分异(La/Yb)_N ＝18~86,强烈亏损重稀土Yb与Y,具有不明显的Eu异常(δEu＝0.90~0.95); 富集LREE和大离子亲石元素(LILE),而亏损HREE、高场强元素(HFSE: Nb、Ta),与世界上典型的俯冲洋壳熔融形成的埃达克岩相似。然而样品具有相对高的(⁸⁷Sr/⁸⁶Sr)_I (0.70635~0.70636)和相对低的ε_Nd(t) (-0.8~-0.9),以及锆石具有相对较低的ε_Hf (t) (-0.8~+2.7)同位素特征,比典型的俯冲洋壳熔融形成埃达克岩具有更多的放射成因,推测可能是源区加入了地壳物质/沉积物/或特殊的洋壳(OIB/E-MORB)熔融,以及侵位过程中地壳物质的混染所造成的。埃达克质片麻状黑云母花岗岩锆石LA-ICPMS年龄为424±4Ma,代表了花岗岩埃达克花岗岩的结晶年龄。花牛山岛弧带在中晚志留世时期具有较高的地热梯度,发育了大面积高ε_Nd(t)钙碱性花岗岩和区域围岩发生了高温变质作用。因此,柳园埃达克岩是由于热的洋壳向花牛山岛弧地体俯冲过程中熔融形成的,俯冲洋壳熔融是本地区早古生代大规模地壳增生的重要方式之一。     

Introduction: Geographic Contributions to Agrobiodiversity Conservation

Abstract

Since the period of bank deregulation in the 1980s, deferred deposit loan operations, better known as payday lenders, have become commonplace in the landscapes of many American cities. At the same time, traditional banking facilities have become less common, especially in the inner city. Growing disparities in the type of and accessibility to credit in the inner city has generated calls for greater regulation to curb practices by payday lenders that critics claim disproportionately affect poor and minority consumers. Payday lenders argue that they serve communities neglected by traditional banks. This article analyzes the site-location strategies of banks and payday lenders in metropolitan Louisiana, and in Cook County, Illinois, and finds that disenfranchised neighborhoods are simultaneously targeted by payday lenders and neglected by traditional banks. The implications these findings have for public policy and for ongoing discourses on the urban condition, race, and class are briefly discussed.

     

Pleistocene geochronologies for fluvial sedimentary sequences: an archaeologist's perspective

Current models of Pleistocene fluvial system development and dynamics are assessed from the perspective of European Lower and Middle Palaeolithic stone tool assemblages recovered from fluvial secondary contexts. Fluvial activity is reviewed both in terms of Milankovitch‐scale processes across the glacial/interglacial cycles of the Middle and Late Pleistocene, and in response to sub‐Milankovitch scale, high‐frequency, low‐magnitude climatic oscillations. The chronological magnitude of individual phases of fluvial activity is explored in terms of radiocarbon‐dated sequences from the Late Glacial and early Holocene periods. It is apparent that fluvial activity is associated with periods of climatic transition, both high and low magnitude, although system response is far more universal in the case of the high magnitude glacial/interglacial transitions. Current geochronological tools do not permit the development of high‐resolution sequences for Middle Pleistocene sediments, while localised erosion and variable system responses do not facilitate direct comparison with the ice core records. However, Late Glacial and early Holocene sequences indicate that individual fluvial activity phases are relatively brief in duration (e.g. 10² and 10³ yr). From an archaeological perspective, secondary context assemblages can only be interpreted in terms of a floating geochronology, although the data also permit a reinvestigation of the problems of artefact reworking. Copyright © 2005 John Wiley & Sons, Ltd.     

Internal wave signal processing: a model-based approach

A model-based approach is proposed to solve the oceanic internal wave signal processing problem that is based on state-space representations of the normal-mode vertical velocity and plane wave horizontal velocity propagation models. It is shown that these representations can be utilized to spatially propagate the modal (depth) vertical velocity functions given the basic parameters (wave numbers, Brunt-Vaisala frequency profile, etc.) developed from the solution of the associated boundary value problem as well as the horizontal velocity components. These models are then generalized to the stochastic case where an approximate Gauss-Markov theory applies. The resulting Gauss-Markov representation, in principle, allows the inclusion of stochastic phenomena such as noise and modeling errors in a consistent manner. Based on this framework, investigations are made of model-based solutions to the signal enhancement problem for internal waves. In particular, a processor is designed that allows in situ recursive estimation of the required velocity functions. Finally, it is shown that the associated residual or so-called innovation sequence that ensues from the recursive nature of this formulation can be employed to monitor the model's fit to the data