DEM modelling of cone penetration tests in a double-porosity crushable granular material

A three-dimensional discrete element model is used to investigate the effect of grain crushing on the tip resistance measured by cone penetration tests (CPT) in calibration chambers. To do that a discrete analogue of pumice sand, a very crushable microporous granular material, is created. The particles of the discrete model are endowed with size-dependent internal porosity and crushing resistance. A simplified Hertz–Mindlin elasto-frictional model is used for contact interaction. The model has 6 material parameters that are calibrated using one oedometer test and analogies with similar geomaterials. The calibration is validated reproducing other element tests. To fill a calibration chamber capable of containing a realistic sized CPT the discrete analogue is up-scaled by a factor of 25. CPT is then performed at two different densities and three different confinement pressures. Cone tip resistance in the crushable material is practically insensitive to initial density, as had been observed in previous physical experiments. The same CPT series is repeated but now particle crushing is disabled. The ratios of cone tip resistance between the two types of simulation are in good agreement with previous experimental comparisons of hard and crushable soils. Microscale exploration of the models indicates that crushing disrupts the buttressing effect of chamber walls on the cone.     

地面有效辐射气候学模型评估和参数优化

基于中国19个辐射站1993-2012年的地面辐射平衡资料和气象资料,分析评估了布朗特法、彭曼法、别尔良德法、FAO24法、FAO56-PM法、邓根云法和童宏良法7种参数化方案计算中国地面有效辐射的适用性;并以均方根误差最小为目标函数,利用步长加速法和多元回归法迭代求解最优参数,建立适合于中国的最优参数化逐日有效辐射估算方法。结果表明:参与评估的7种方案都不同程度低估了中国的有效辐射;从全中国总体误差水平看,童宏良法的平均绝对百分比误差和均方根误差小于其他6种方案,分别为27.0%和24.5 W/m2,估算效果较好;其次是彭曼法和邓根云法;FAO56-PM法精度较低,不适用于中国的有效辐射估算。针对单站来说,邓根云法在东部平原地区的精度最高,童宏良法由于考虑了海拔高度的订正,适用于西部高原地区。相关分析表明水汽压是影响有效辐射估算误差的最关键因素,因此根据水汽压的地理分布规律,分东部区和西部区建立分区方案。基于观测资料建立的全中国方案和分区方案的均方根误差分别为20.8和21.4 W/m2,精度均高于已有参与评估的7种方案;而且在绝大多数站点,分区方案的误差小于全中国方案,所以划分东部区和西部区进行有效辐射模型参数化很有必要。同时发现,分区方案在西部区明显优于邓根云法,在东部区明显优于童宏良法,因此推荐其作为中国有效辐射的计算方法。      

Diagenesis of the Triassic Yanchang Formation Tight Sandstone Reservoir in the Xifeng–Ansai Area of Ordos Basin and its Porosity Evolution

This work aims to reveal the evolution of the porosity in the Triassic Yanchang Formation tight sandstone reservoir of the Xifeng–Ansai area of Ordos Basin. Based on destructive diagenesis(compaction and cementation) and constructive diagenesis(dissolution) of sandstone reservoirs, this study analyzed the diagenesis characteristics of the tight sandstone reservoirs in this area, and discussed the relationship between sandstone diagenesis and porosity evolution in combination with present porosity profile characteristics of sandstone reservoir. The effect simulation principle was employed for the mathematical derivation and simulation of the evolution of porosity in the Yanchang Formation tight sandstone reservoirs. The result shows that compaction always occurs in tight sandstone reservoirs in the Yanchang Formation, and cementation occurs when the burial depth increases to a certain value and remains ever since. Dissolution occurs only at a certain stage of the evolution with window features. In the corresponding present porosity profile, diagenesis is characterized by segmentation. From the shallow to the deep, compaction, compaction, cementation and dissolution, compaction and cementation occur successively. Therefore, the evolution of sandstone porosity can be divided into normal compaction section, acidification and incremental porosity section, and normal compaction section after dissolution. The results show that the evolution of sandstone porosity can be decomposed into porosity reduction model and porosity increase model. The superposition of the two models at the same depth in the three stages or in the same geological time can constitute the evolution simulation of the total porosity in sandstone reservoirs. By simulating the evolution of sandstone reservoir porosity of the eighth member in Xifeng area and the sixth member in Ansai area, it shows that they are similar in the evolution process and trend. The difference is caused by the regional uplift or subsidence and burial depth.     

Characterization of cloud microphysical properties in different cloud types over East Asia based on CloudSat/CALIPSO satellite products

利用CloudSat/CALIPSO卫星资料,本文揭示了东亚三个代表性区域的云微物理属性,为评估和改进模式云微物理过程提供重要的观测基础.研究的云微物理量包括云水/冰质量,数浓度和有效半径.研究表明:暖云中云水质量和数浓度随高度增加而减小,有效半径处于8-14μm范围.对于冰云,云冰质量和有效半径随高度增加而减小,而数浓度在垂直方向上变化不大.此外,云微物理属性在不同云型之间存在显著差异:积云的云水质量和数浓度最大,而卷云的云水质量和数浓度最小.从三个区域的对比结果来看,相比于华东和西北太平洋地区,青藏高原地区暖云的云水质量和数浓度较小,而冰云的则较大.     

库车坳陷东部异常流体压力特征及其对构造变形的控制

为探究库车坳陷东部异常流体压力特征及其对构造变形的影响,在研究区25口井的钻井、完井及测井资料基础上,利用“等效深度法”计算出泥岩段流体压力,并结合实测流体压力对其进行校正,从而刻画出该地区依奇克里克构造带、秋里塔格构造带以及阳霞凹陷超压发育特征,在此基础上拟合流体压力随深度的变化规律,估算出在依奇克里克构造带以及秋里塔格构造带基底滑脱层有效摩擦系数为0.138∽0.238;通过解释过井的地震剖面,运用构造楔相关理论计算出基底滑脱层强度F = 0.103 4∽0.172 9,将其与利用基底滑脱层流体压力比计算出来的有效摩擦系数进行比较,发现两者之间存在比较好的吻合性,以此证明估算基底滑脱层有效摩擦系数的可信度;计算出若研究区不发育流体超压,则基底滑脱层有效摩擦系数应为0.342∽0.485,说明研究区广泛发育的流体超压有效降低了原基底滑脱层有效摩擦系数的59.1%∽69.8%,意味着在研究区沿基底滑脱层发生剪切作用所需要的构造应力大幅度减小。     

Determination of groundwater solute transport parameters in finite element modelling using tracer injection and withdrawal testing data

The groundwater tracer injection and withdrawal tests are often carried out for the determination of aquifer solute transport parameters. However, the parameter analyses encounter a great difficulty due to the radial flow nature and the variability of the temporal boundary conditions. An adaptive methodology for the determination of groundwater solute transport parameters using tracer injection and withdrawal test data had been developed and illustrated through an actual case. The methodology includes the treatment of the tracer boundary condition at the tracer injection well, the normalization of tracer concentration, the groundwater solute transport finite element modelling and the method of least squares to optimize the parameters. An application of this methodology was carried out in a field test in the South of Hanoi city. The tested aquifer is Pleistocene aquifer, which is a main aquifer and has been providing domestic water supply to the city since the French time. Effective porosity of 0.31, longitudinal dispersivity of 2.2 m, and hydrodynamic dispersion coefficients from D = 220 m²/d right outside the pumping well screen to D =15.8 m²/d right outside the tracer injection well screen have been obtained for the aquifer at the test site. The minimal sum of squares of the differences between the observed and model normalized tracer concentration is 0.00119, which is corresponding to the average absolute difference between observed and model normalized concentrations of 0.035 5 (while 1 is the worst and 0 is the best fit).     

Numerical modelling of lumpy clay landfill

Two trial motorway embankments built on a landfill consisting of clayey lumps were monitored over the period of 3 and 5 years, respectively. The subsoil of the embankment was instrumented by hydrostatic levelling profiles, pore pressure transducers and depth reference points installed in boreholes. An advanced constitutive model for clays (hypoplastic model for clays with meta‐stable structure) was used for numerical modelling of both case histories. Basic hypoplastic model for clays was calibrated using isotropic compression tests and triaxial compression tests on reconstituted clay. Three additional model parameters describing the effects of lumpy structure were calibrated using oedometer tests on specimens prepared from scaled‐down lumpy material (material with smaller size of clay lumps). The performance of the model was evaluated by comparison with the results of the centrifuge model of self‐weight consolidated landfill. Finally, the hypoplastic model was used for simulation of both trial embankments and the results were compared with in situ measurements. The degradation of the lumpy structure of the upper layer of the in situ landfill due to weathering was back analysed using monitoring data. Copyright © 2010 John Wiley & Sons, Ltd.     

Numerical modelling of multiphase immiscible flow in double‐porosity featured groundwater systems

A numerical model describing the flow of multiphase, immiscible fluids in a deformable, double‐porosity featured soil has been developed. The model is focused on the modelling of the secondary porosity features in soil, which is more relevant to groundwater contamination problems. The non‐linear saturation and relative permeabilities were expressed as functions of the capillary pressures. The governing partial differential equations in terms of soil displacement and fluid pressures were solved numerically. Galerkin's weighted‐residual finite element method was employed to obtain the spatial discretization whereas temporal discretization was achieved using a fully implicit scheme. The model was verified against established, peer‐reviewed works, and the assumption that the immiscible fluids (non‐aqueous phase liquids) will flow preferentially through the secondary porosity features in soil was validated. Copyright © 2011 John Wiley & Sons, Ltd.     

Constitutive modeling of unsaturated aggregated soils

A coupled water retention–mechanical constitutive model for unsaturated aggregated soils is presented here. Based on the multi‐scale experimental results, the model incorporates the inter‐particle bonding, fabric and partial saturation effects in a single framework. It is formulated within the framework of hardening elasto‐plasticity and is based on the critical state concept. Prior to model validation, we evaluate the model parameters and propose determination procedures for the main new parameters. Finally, the model is examined for its capability in simulating the experimental results of aggregated and bonded soils. Results of these simulations show that the model addresses the most features arising from the combined effects of soil structure and partial saturation. Copyright © 2010 John Wiley & Sons, Ltd.     

Soil as a capacitor: Considering soil water content improves temporal models of productivity

Above-ground net primary production (ANPP) in arid and semiarid ecosystems is mainly explained by precipitation (ppt). However, when this relationship is evaluated taking into consideration data from different years in the same site (i.e. temporal models of productivity) the relation is weak, and sometimes it does not exist. In spite of this, the inclusion of previous year's ppt and/or ANPP frequently improves temporal models. In this study we analyze if considering NDVI and mean annual soil water content or transpiration (instead of different combinations of current-year ppt and previous year's ppt or ANPP) improves temporal models of productivity in the Southern Monte (Argentina). Current-year ppt only explained 39.7% of variation in ANPP, while mean soil water content explained 85.3%. The remaining models, which include current-year ppt together with previous-year's ppt or previous-year's ANPP, improve the first model; but the explanatory power of the model based only on mean soil water content is never reached. Our results also show that water losses exceed annual ppt in dry years, whereas the opposite occurs during years with above-average ppt. This carryover effect of soil water indicates that soil acts as a capacitor, accumulating water during wettest years and releasing it during following years.