Variation of infiltration rate through karstic surfaces due to land use changes: A case study in Murgia (SE-Italy)

Groundwaters of the Murgia carbonate aquifer represent the main groundwater resource of the Apulia region (SE Italy). In the highlands (Alta Murgia) karst crops out in different forms and textures which have been preserved up to the 1970s: little evolved agriculture and sheep rearing produced only a marginal modification of the epikarst while a high degree of division into parcels by drystone walls helped in preserving soils from erosion. In the last years the original scenery of the Alta Murgia changed due to widespread transformations of surface karstic textures for agricultural purposes, with undeniable negative consequences on the hydrogeological balance, concerning both the infiltration and the runoff terms. Stone shattering led to flattening and deep alteration of a large part of the original karstic landscape and to demolition of drystone walls.In a study area of about 139 km² located in the Alta Murgia, the comparison of aerial photos related to the period 1950–2001 indicated that stone shattering had occurred for about 42% of the area.The hydrological behaviour of the first soil layer of experimental parcels representing both shattered stone and natural karstic surface textures was analysed by using the numerical model Hydrus-2D with the aim of estimating the variation on infiltration rate due to stone shattering. Intensive field and laboratory measurements concerned soil texture, soil water content, pressure head, saturated hydraulic conductivity, pan evaporation and meteorological parameters.     

Effect of Inter-Column Spacing on Soil Stresses due to Vibro-Installed Stone Columns: Interesting Findings

This paper reveals the interesting relation between the inter-column spacing and the corresponding alteration of soil state of stresses due to the vibro-installation technique. This relation is inferred from analyses for load settlement records of various field load tests, performed for stone columns arrangements with different inter-column spacing values. In order to have adequate confidence in the findings, a well-documented case history, involving three columns patterns along with their relevant field and laboratory test results, is utilized for this study. Moreover, a well-tested finite element model, capable of simulating both elasto-plastic and time dependent soil deformations as well as pore water pressure building and dissipation, is employed in the analysis. Instead of determining the soil response to the test load, based on known initial soil stresses and material properties, the analysis is inversely posed to determine the soil initial stresses, based on the recorded settlements and the post-installation material properties. The alteration in the soil state of stress is represented by the increase in the post-installation horizontal to vertical stress ratio, K*, as a function of the inter-column spacing. It is found that this alteration experiences a systematic decrease in its magnitude as the inter-column spacing increases.     

Anatomy of shelf deltas at the edge of a prograding Eocene shelf margin, Spitsbergen

Abstract Although shelf‐edge deltas are well‐imaged seismic features of Holocene and Pleistocene shelf margins, documented outcrop analogues of these important sand‐prone reservoirs are rare. The facies and stratigraphic architecture of an outcropping shelf‐edge delta system in the Eocene Battfjellet Formation, Spitsbergen, is presented here, as well as the implications of this delta system for the generation of sand‐prone, shelf‐margin clinoforms. The shelf‐edge deltas of the Battfjellet Formation on Litledalsfjellet and Høgsnyta produced a 3–5 × 15 km, shelf edge‐attached, slope apron (70 m of sandstones proximally, tapering to zero on the lower slope). The slope apron consists of distributary channel and mouth‐bar deposits in its shelf‐edge reaches, passing downslope to slope channels/chutes that fed turbiditic lobes and spillover sheets. In the transgressive phase of the slope apron, estuaries developed at the shelf edge, and these also produced minor lobes on the slope. The short‐headed mountainous rivers that drained the adjacent orogenic belt and fed the narrow shelf, and the shelf‐edge position of the discharging deltas, made an appropriate setting for the generation of hyperpycnal turbidity currents on the slope of the shelf margin. The abundance of organic matter and of coal fragments in the slope turbidites is consistent with this notion. Evidence that many of the slope turbidites were generated by sustained turbidity currents that waxed then waned includes the presence of scour surfaces and thick intervals of plane‐parallel laminae within turbidite beds in the slope channels, and thick spillover lobes with repetitive alternations of massive and flat‐laminated intervals. The examined shelf‐edge to slope system, now preserved mainly below the shelf break and dominated by sediment gravity‐flow deposits, has a threefold stratigraphic architecture: a lower, progradational part, in which the clinoforms have a slight downward‐directed trajectory; a thin aggradational zone; and an upper part in which clinoforms backstep up onto the shelf edge. A greatly increased density of erosional channels and chutes marks the regressive‐to‐transgressive turnaround within the slope apron, and this zone becomes an angular unconformity up near the shelf edge. This unconformity, with both subaerial and subaqueous components, is interpreted as a sequence boundary and developed by vigorous sand delivery and bypass across the shelf edge during the time interval of falling relative sea level. The studied shelf‐margin clinoforms accreted mostly during falling stage (sea level below the shelf edge), but the outer shelf later became estuarine as sea level became re‐established above the shelf edge.     

Mitigation of liquefaction and associated ground deformations by stone columns

Soil liquefaction and associated ground failures have been a major source of damage during the past earthquakes. The risk of liquefaction and associated ground deformation can be reduced by various ground-improvement methods including the stone column (gravel drain) technique. This paper presents the current state of the stone column technologies as a liquefaction countermeasure. A comprehensive review is provided aiming to: (a) identify key considerations for the general use of stone columns as a liquefaction countermeasure, (b) provide insights for design and construction, (c) compile the latest research developments, and (d) identify sources of useful information. Case histories of field applications and observed field performance are cited to portray different stone column applications and observed effectiveness. The paper identifies areas where more research is needed and includes recommendations for future research and development.     

田黄萝卜纹的矿物组成与成因分析

萝卜纹是田黄的重要鉴定特征。本文通过岩石薄片、X射线衍射分析和电子探针分析等手段,确定萝卜纹的组成矿物为伊利石;萝卜纹的成因为田黄的原岩受到构造应力作用后产生了显微裂隙,次生的伊利石填充了显微裂隙;显微裂隙中的伊利石与岩石中的主要矿物迪开石光学性质差别较大而呈丝缕状(萝卜纹)。     

云南石林岩溶发育的古环境研究

以地质地貌景观调查、填图为基础,应用区域地层、古地磁资料、植物和孢粉化石、岩石与古土壤的化学成分(含稀土元素)、古土壤粘粒硅铝比值、钙华、溶蚀率等资料,研究了石林岩溶各主要演化阶段的古环境特点。石林地区能保留有早二叠世晚期至第四纪的石林岩溶是源于该区特殊古地理环境演变所控制的不同古环境下的岩溶过程差异。按照岩溶与环境的关系,可将石林岩溶演化的漫长过程分别划分出有利于石林岩溶发育与有利于石林岩溶保存的不同时期。石林地区的石林岩溶经历了古热带湿热海岸边缘、古热带行星风系干旱环境、半干旱山地湖泊环境与热带低海拔湿热气候到高原亚热带干湿季风气候演变。石林地区是研究漫长地质时期的不同环境下石林岩溶发育与保存的较好地点之一。      

承德避暑山庄砂岩文物的基本性质和风化机理

世界文化遗产地承德避暑山庄内有大量的砂岩文物。在长期风化作用下,很多砂岩文物发生了严重的风化病害,亟须保护。通过现场调查,发现避暑山庄砂岩文物的风化病害主要为开裂、剥落、粉化、生物寄生等。通过室内测试,得出了该砂岩的矿物学、岩石学性质和物理、力学性质。在此基础上,分析了该砂岩的风化机理,认为钙质胶结物的溶解、干湿交替和盐分结晶膨胀是造成该砂岩粉化、剥落风化的主要原因。相关研究为该砂岩文物的修复保护提供科学支撑。     

考虑加载过程及桩体固结变形的碎石桩复合地基固结解析解

为了完善碎石桩复合地基固结理论,通过假设从桩体排出的水量等于流入桩体的水量与桩体体积变化之和以及地基扰动区土体水平渗透系数呈线性变化,并考虑上部荷载逐渐施加,推导了考虑桩体体积变化的碎石桩复合地基超静孔压及固结度解析解。当加载时间趋于零时,本文解可退化为瞬时加载情况下的解;当加载时间及桩径同时趋于零时,本文解可进一步退化为Terzaghi一维固结解,这证明了本文解的正确性。通过与已有解的比较,对地基固结性状进行了分析。结果表明,加载过程对地基固结度影响显著,加载历时越长,固结越慢;在各种条件下,不考虑桩体固结变形时地基固结始终比考虑桩体变形时快,并且其影响随着加载历时变小、桩径比变小、桩土模量比变小、桩土渗透系数变小而逐渐增大,这说明在实际工程固结计算中不考虑桩体固结变形是偏于不安全的。     

Non-periglacial stone stripes? An example from North Wales

A set of active stone stripes below a small debris cone in North Wales is described. In form they do not appear to resemble stone stripes described elsewhere. They are of particular note because their form is not controlled by conventional periglacial processes, but by stones moving downslope when sheep disturb the debris cone above. This downslope movement of stones has resulted in a complex pattern of stripes and horizontal terraces, the exact form of which appears to be controlled by probability. These observations add to the debate over the mode of formation of active stone stripes in Britain and the role of non-periglacial processes.     

散体材料桩复合地基极限承载力计算

以土力学及弹塑性理论为基础，分析了散体材料桩的塑性应力分布。推导出了单桩极限承载力和单桩复合地基的极限承载力计算公式。得出了提高桩体材料的内摩擦角和桩周土对桩的径向围限力是提高散体材料桩复合地基承载力的有效途径的结论。给出了工程实例，验证了文中计算公式的实用性。