A note on the consolidation settlement of a rigid circular foundation on a poroelastic halfspace

This paper uses Biot's poroelasticity approach to examine the consolidation behaviour of a rigid foundation with a frictionless base in contact with a poroelastic halfspace. The mathematical development of the mixed boundary value problem involves a set of dual integral equations in the Laplace transform domain which cannot be conveniently solved by employing conventional procedures. In this paper, a numerical solution is developed using a scheme where the contact normal stress is approximated by a discretized equivalent. The influence of limiting drainage boundary conditions at the entire surface of the halfspace on the degree of consolidation of the rigid circular foundation is investigated. The results obtained in this study are compared with the corresponding results given in the literature. Copyright © 2016 John Wiley & Sons, Ltd.     

Stress‐dependent hardening and failure surfaces of dry sand

During several triaxial compression experiments on plastic hardening, softening, and failure properties of dense sand specimens, it was found on various stress paths that the size of the failure surface was not constant. Instead, it changed depending on the current state of hydrostatic pressure. This finding is in contrast to the standard opinion consisting of the fact that the failure surface remains constant, once it has been reached during an experiment or in situ. In general, the behaviour of cohesionless granular‐material‐like sand is somehow characterised in between fluid and solid, where the solid behaviour results from the angle of internal friction and the confining pressure. Although the friction angle is an intrinsic material property, the confining pressure varies with the boundary conditions, thus defining different solid properties like plastic hardening, softening, and also failure. Based on our findings, it was the goal of the present contribution to introduce an improved setting for the plastic strain hardening and softening behaviour including the newly found yield properties at the limit state. For the identification of the material parameters, a complete triaxial experimental analysis of the tested sand is given. The overall elasto‐plasticity concept is validated by numerical computations of several laboratory foundation‐ and slope‐failure experiments. The performance of the proposed approach is compared with the standard concept of a constant failure surface, where the corresponding yield surfaces are understood as contours of equivalent plastic work or plastic strain. Copyright © 2012 John Wiley & Sons, Ltd.     

Accounting for sparsely observed rainfall space—time variability in a rainfall—runoff model of a semiarid Tunisian basin/Prise en compte d'observations peu denses de la variabilité spatiotemporelle de la pluie dans une modélisation pluie—débit d'un bassin semi-aride Tunisien

Abstract

The management of water excesses and deficits is a major task in semiarid Mediterranean regions, where the variability of rainfall inputs is high at different time and space scales. Thus intense hydrometeorological events, which generate both potential resource and hazards, are of major interest. A simple method is proposed, with the example of the Skhira basin (192 km²) in central Tunisia, to account for the event space–time variability of rainfall in a rainfall–runoff model, in order to check its influence on the shape, magnitude and timing of resulting hydrographs. The transfer function used is a geomorphology-based unit hydrograph with an explicit territorial significance. Simulations made for highly variable events show the relevance of this method, seen as the first step of a downward approach, and its robustness with respect to the quality and the density of rainfall data.     

Re‐establishment of soil water repellency after destruction by intense burning in a Mediterranean heathland (SW Spain)

Soil water repellency has been conventionally considered as a fire‐induced effect, but an increasing number of studies have suggested that natural background repellency occurs in many soil types, and many of them have suggested that water repellency can be re‐established over time after being destroyed. An experimental fire was conducted to study changes of the soil surface during the first 18 months following intense burning. The main objectives of this paper are as follows: (1) to investigate in situ water repellency changes at three soil depths (0, 2 and 4 cm) immediately after burning; (2) to evaluate the medium‐term evolution of water repellency under field conditions; and (3) to outline the main hydrological consequences of these changes. Also, different water repellency tests (water drop penetration time, ethanol percentage test (EPT) and contact angle (CA) between water drops and the soil surface) were carried out for comparison purposes. Field experiments showed that soil water repellency was partly destroyed after intense burning. Changes were relatively strong at the soil surface, but diminished progressively with depth. Levels of water repellency were practically re‐established 18 months after burning. This suggests that water repellency in the studied area is not necessarily a consequence of fire, but can instead be a natural attribute. Finally, although limited in time, destruction of soil water repellency has important consequences for runoff flow generation and soil loss rates, and, indirectly, for water quality. Copyright © 2009 John Wiley & Sons, Ltd.     

Slump debris flows in the Akovolwo Mountains area of Benue State,Nigeria

In September 1979, rain-induced complex landslides occurred in two separate localities along the slopes of the Akovolwo Mountains near Jato-Aka in the Kwande Local Government area of Benue State, Nigeria.The two movements developed on bedrock slopes covered by a veneer of colluvium and (or) residuum no more than 1.5 to 2m deep. Each started as a slump and graduated into a debris flow. The slump, extending downhill a short distance away from the head scarp, had been reconstituted into a debris flow as the initial movement (sliding movement) of the soil mass caused remoulding of the saturated moving mass into viscous debris-laden mud. The resulting mass moved partly along a pre-existing mountain stream channel and partly along a fresh channel it cleared in the savanna forest. At the break of slope, the mass of boulders was dumped and a trail of smaller fragments littered the channels towards the Katsina-Ala River.     

Estimating the crush zone size under a cutting tool in coal

Summary As part of an effort to understand the mechanics of fine fragment formation in coal, which is important in studies of respirable dust due to mining, fracture toughness measurements and the strain energy density (SED) theory were applied to calculate the crush zone size under a cutting tool in coal. This zone is the major source of fine fragments in the 1 to 10 µm size range. The model used in these calculations is a boundary element program containing a failure criterion based on the SED theory. The boundary element program calculates linear elastic stresses at numerous points in the coal material ahead of a cutting bit. These stresses are then input to a subroutine called critical flaw length and orientation (CFLO) which uses the SED theory to determine the CFLO for a small crack at the boundary element stress computation point. The extent of crushing is based on earlier postulates about the role of inherent flaws in a fragmentation process. To form 1 to 10 µm fragments requires firstly a local stress strong enough to activate flaws with a characteristic length less than 1 to 10 µm and secondly, a flaw density sufficient to provide an average spacing between flaws also on the order of 1 to 10 µm. The locus of active 10 µm flaws represents the maximum possible extent of fine fragmentation in the 10 µm or less size range assuming that a sufficient inherent flaw density exists. The approach offers a first order approximation to the extent of crushing under a tool tip. The size and shape of the crush zone volume is affected by the attack angle and geometry of the tool.     

岩浆包裹体化学成分研究

岩浆包裹体化学成分研究难度较大,为了获得可信的数据,应当注意:1.非演化型岩浆包裹体的化学成分可以代表其初始成分。演化型岩浆包裹体应先均一、淬火后再行测定。2.均一演化型岩浆包裹体应严格遵守加热规则,否则过热作用会使包裹体壁部分熔化,造成淬火后所测包裹体成分与其真正的初始成分并不相当。3.实测资料证明,“边界层效应”对于岩浆包裹体化学成分影响微不足道。4.岩浆包裹体的化学成分只能代表其主矿物结晶时周围岩浆的成分,即仅相当于岩浆液相线上的一个点。5。把显微冷热台测温、激光喇曼探针和电子探针分析技术结合使用,对查明单个包裹体中挥发组分的性状和浓度具有很大的潜力和前途。     

西藏丁青地区与玻镁安山岩类有关的蛇绿岩的矿物学特征

西藏丁青蛇绿岩的东杂岩体是一种与玻镁安山岩(Boninite)有关的特殊的蛇绿岩类型。其 堆晶斜方辉石岩、辉长岩和辉绿岩的岩石化学、微量元素以及稀土元素的地球化学特征均与西太平洋诸岛(伊豆—马利亚纳、巴布亚新几内亚、新喀里多尼亚等)的玻镁安山岩相似。此外,超镁铁质构造岩中的橄榄石和顽火辉石富镁,指示残余地幔具强烈亏损的性质。尖晶石的Cr含量中等至较高,与深海橄榄岩及大洋中脊玄武岩中的尖晶石不同。堆晶岩和辉长岩中的古铜辉石富镁,斜长石富钙,也明显不同于典型大洋中脊环境的特征,表明丁青东蛇绿岩形成的环境不像大洋中脊或弧后盆地,而可能是在洋内俯冲带之上的岛弧底部。     

山区年、月平均温度推算方法的研究

本文提出了山区年、月平均温度空间分布的推算方法,并提供了相应的小地形温度订正值。该方法在福建省沙溪流域山区实际应用的结果表明,能有效地揭示山区年、月平均温度空间分布的宏观与微观变化,效果满意,精度较高。