Quantitative assessment of the residual risk in a rockfall protected area

Quantitative Risk Assessment (QRA) has become an indispensable tool for the management of landslide hazard and for planning risk mitigation measures. In this paper we present the evaluation of the rockfall risk at the Solà d’Andorra slope (Andorra Principality) before and after the implementation of risk mitigation works, in particular, the construction of protective fences. To calculate the risk level we have (i) identified the potential rockfall release areas, (ii) obtained the volume distribution of the falling rocks, (iii) determined the frequency of the rockfall events, and (iv) performed trajectographic analysis with a 3D numerical model (Eurobloc) that has provided both the expected travel distances and the kinetic energy of the blocks. The risk level at the developed area located at the foot of the rock cliff has been calculated taking into account the nature of the exposed elements and their vulnerability. In the Forat Negre basin, the most dangerous basin of the Solà d’Andorra, the construction of two lines of rockfall protection fences has reduced the annual probability of loss of life for the most exposed person inside the buildings, from 3.8×10⁻⁴ to 9.1×10⁻⁷ and the societal risk from 1.5×10⁻² of annual probability of loss of life to 1.2×10⁻⁵.     

A model, study on seasonal spatial-temporal variability of the Lagrangian Residual Circulations in the Bohai Sea

1 IntroductionThe BohaiSea is a sem i-closed shallow sea w ith a m ean depth ofaround 20 m ,com posed oftheLiaodong Bay,the BohaiBay,the Laizhou Bay and the BohaiBasin,and connected to the N orthY ellow Sea through a latitudinal strait. The tidal dynam ic…     

Vertical structure of residual slope circulation driven by JEBAR and tides: an idealised model

The residual circulation over the continental slope, and in particular, its vertical structure, is analysed by means of an idealised hydrodynamic model. The model is based on the depth-dependent shallow-water equations under uniform along-isobath conditions and is forced by a prescribed meridional density gradient and tidal velocities. By means of expansion in the small Rossby number solutions are analysed for conditions representative for the continental slopes off the Hebrides and in the Bay of Biscay. The steady solution at zeroth order consists of a linear density-driven flow. At order a tidally rectified flow is found and a stationary flow due to self-interaction of the zeroth-order density-driven flow. At order ² the leading-order effect of the interaction between the zeroth-order density-driven flow and the tides is found: the ‘interaction current’. The solutions up to and including order ² constitute an along-isobath steady slope current which is comparable to field data. The slope current and the accompanying cross-shelf circulation depend strongly on the shelf and flow characteristics. For the Hebridean case the density forcing predominates, but for the Biscay case the tidal effects are of the same order of magnitude as the density effects. Under those conditions the interaction current is significant which implies that linear superposition of density and tidal effects differs from the non-linear combination of both. It is also shown that the depth-average of the interaction current differs essentially from the solution obtained from a depth-averaged model.     

胶州湾三维潮流及潮致余环流的数值模拟

运用一个三维正压湍流封闭数值的模式，成功模拟了胶州湾M2分潮的潮汐与潮流分布，模拟结果表明，胶州湾的潮流以往复流为特征，最大流速出现在胶州湾口，量值为95cm/s，潮臻余流的水平结构是：团团转”的多涡结构，其中5个余流涡旋的位置得到观测资料的证实，在模拟结果的基础上，比较了欧拉余流和拉氏余流的差异，并分析潮致拉氏余流涡的垂向结构特征，垂向湍粘性系数的水平分布与水吩布形态相似，呈现出底，表层小，中层大的垂直分布结构。     

Small waterplane area ship models: Re-analysis of test results based on scale effect and form drag

The first systematic model series of hulls with small waterplane area (both single hulls and twin-hulls) was designed and tested in Krylov Shipbuilding Research Institute in the middle of the 1980's. The series was intended to cover a broad range of Froude numbers, hull aspect ratios, design drafts, and spacing between hulls. In the present paper, these test results are re-analyzed by accounting for the scale effect in the form drag, obtained from the comparison with test data of larger out-of-series models. Illustrative results are also given for the influence of the cross-section hull shape, strut configuration, and shifted hulls on the residual resistance and for dynamic trim and draft. Some data are compared with those of the later series tests of twin-hull models with small waterplane area carried out in HSVA, Germany. Factors influencing the residual resistance of ships of this type are discussed.     

Monitored and simulated variations in matric suction during rainfall in a residual soil slope

This research combines field, laboratory and numerical investigations to estimate the development of a wetting front within a 1.2 m residual soil mantle on a steep forested slope during rainfall events. The field-monitored variations in matric suction due to rain-water infiltration during various events revealed that the maximum infiltration rate was much higher when the wetting front resided in the upper 20 cm of soil compared to the case when the wetting front advanced to depths > 20 cm. Laboratory investigations on soil hydraulic properties (i.e., soil water characteristic curve, and hydraulic conductivity) were useful to establish the parameters of a multilayer finite-element model for one-dimensional vertical infiltration. These parameters were subsequently calibrated by matching the predicted and field measured transient pore water pressure responses during actual rainstorms with irregular rainfall patterns. The calibrated simulation model was used to assess the migration of the wetting front under uniform rainfall with different intensities. Based on the numerical results, a hyperbolic equation was developed to predict the duration of uniform rainfall required for the propagation of wetting front to a certain depth for a given rainfall intensity. The proposed equation was subsequently tested against field-monitored advancements of the wetting front during real rainstorms with variable rainfall intensity.     

Spatio-temporal variation of vegetation coverage and its response to climate change in North China plain in the last 33 years

Global climate change has led to significant vegetation changes in the past half century. North China Plain, the most important grain production base of china, is undergoing a process of prominent warming and drying. The vegetation coverage, which is used to monitor vegetation change, can respond to climate change (temperature and precipitation). In this study, GIMMS (Global Inventory Modelling and Mapping Studies)-NDVI (Normalized Difference Vegetation Index) data, MODIS (Moderate-resolution Imaging Spectroradiometer) – NDVI data and climate data, during 1981–2013, were used to investigate the spatial distribution and changes of vegetation. The relationship between climate and vegetation on different spatial (agriculture, forest and grassland) and temporal (yearly, decadal and monthly) scales were also analyzed in North China Plain. (1) It was found that temperature exhibiting a slight increase trend (0.20 °C/10a, P < 0.01). This may be due to the disappearance of 0 °C isotherm, the rise of spring temperature. At the same time, precipitation showed a significant reduction trend (−1.75 mm/10a, P > 0.05). The climate mutation period was during 1991–1994. (2) Vegetation coverage slight increase was observed in the 55% of total study area, with a change rate of 0.00039/10a. Human activities may not only accelerate the changes of the vegetation coverage, but also c effect to the rate of these changes. (3) Overall, the correlation between the vegetation coverage and climatic factor is higher in monthly scale than yearly scale. The correlation analysis between vegetation coverage and climate changes showed that annual vegetation coverage was better correlatend with precipitation in grassland biome; but it showed a better correlated with temperature i the agriculture biome and forest biome. In addition, the vegetation coverage had sensitive time-effect respond to precipitation. (4) The vegetation coverage showed the same increasing trend before and after the climatic variations, but the rate of increase slowed down. From the vegetation coverage point of view, the grassland ecological zone had an obvious response to the climatic variations, but the agricultural ecological zones showed a significant response from the vegetation coverage change rate point of view. The effect of human activity in degradation region was higher than that in improvement area. But after the climate abruptly changing, the effect of human activity in improvement area was higher than that in degradation region, and the influence of human activity will continue in the future.     

A mechanism for strain relaxation of barre granite: Opening of microfractures

Summary Strain relaxation in the Barre Granite and surrounding metasediments in Vermont, was measured by overcoring strain gauge rosettes bonded to outcrop surfaces. The average maximum expansion upon relieving 15.2 cm diameter cores trends N55°W, while the average maximum expansion of 7.6 cm diameter cores coaxial with 15.2 cm cores trends N70°W. The maximum strain relief of the internal overcores is normal to the microfracture fabric. Therefore, the mechanism of strain relaxation is attributed to the opening of microfractures either parallel to the rift direction of the Barre Granite or parallel to the foliation of the metasediment. The lack of parallelism between the normal to the rift plane and the maximum expansion of the initial overcore suggests an extenrally applied strain superimeposed on the strain caused by opening of microfractures.Lamont-Doherty Geological Observatory Contribution No. 2455.     

A numerical hydro-geotechnical model for marine gravity structures

A new finite-volume solver named “geotechFoam” is developed within OpenFOAM®¹ for modelling soil-structure-interaction for marine gravity structures. The fully-coupled and fully-dynamic Biot’s governing equations are solved in a segregated approach. Two simplifications of the governing equations are introduced and tested. The spatial domain is composed of several zones with different material properties and/or constitutive models. A multi-yield surface plasticity model is implemented to simulate soil response under cyclic loads. Moreover, soil-structure interaction is modelled via a frictional contact model and boundary conditions accounting for skeleton-pore fluid coupling. Five benchmark cases and two sets of physical model tests are applied for the validation.     

The Tianjin geothermal field （northeastern China）： Geochemistry and implications for possible plugging phenomena

The low-enthalpy geothermal system of Tianjin is located in and around the City of Tianjin （China）, in the NE part of the North China plain, a tectonic depression affected by subsidence since the Neogene. The regional aquifer system is from the top to the bottom, as follows： （1） the ＂Quaternary aquifer＂, in continental sediments; （2） the ＂Tertiary aquifer＂, in the continental depositional series; （3） the ＂Lower Palaezoic-Sinian aquifer＂, in Ordovician-Sinian calcareous rocks. Shallow （300-600 m） and deep （up to 2600 m） producing wells discharge water at up to 50 and 90 C, respectively. Exhausted fluid re-injection started in the 90＇s. Subsequently, a reduction in the injection process was observed, suggesting that sealing or plugging occurred in the reservoir（s）. The present work, based on chemical and isotopic data on fluids and minerals from productive and re-injection wells, describes the causes of the permeability reduction at the bottom hole of the re-injection wells. Geochemical data processing using speciation codes indicates that （1） sealing caused by precipitation of both calcite or amorphous silica is very unlike; （2） the saturation indices for several Fe and Zn sulfides and hydroxides are very positive, although fluids have neutral pH and low temperature （Fe- and Zn-rich minerals are present mainly as transported solids）; （3） pipes, casings, heat exchangers and steel flames are made of low-quality Fe and show evident oxidation effects; casings and producing liners in the wells are likely in the same conditions; （4） thermal fluids sampled in summer, when most wells are shut down, are characterized by more negative redox potential and lower pH than those collected in winter, probably because in summer there is less casing-hot water interaction and, consequently, Fe-oxidation in the casing is reduced. Accordingly, the plugging problem does not seem to be a natural process related to the chemical characteristics of the produced fluid. It is, on the contrary, possibly induced by the oxidation of casings, pumps, pipes, etc.