Time-dependent stress change during failure of rocks

The energy balance of a solid subject to fracture has been explored using heat and mass transfer equations with regard to the volumetric and superficial components. In the suggested model, brittle fracture of a cracked solid considered as a heterogeneous two-phase medium is described by an equation analogous to the Griffith’s criterion for propagation of a single crack. The derived equation is used, together with estimates of relative change in specific interface area, to study the respective change of free strain energy and pressure in rocks associated with failure.     

An implementation of rock engineering system for ranking the instability potential of natural slopes in Greek territory. An application in Karditsa County

This paper presents an application of rock engineering system (RES) in an attempt to reveal and assess the inherent instability potential of 388 sites where equivalent landslides have been manifested and recorded in the region of Karditsa County, Greece. The main objective has been defining the principal causative and triggering factors responsible for the manifestation of landslide phenomena, quantify their interactions, obtain their weighted coefficients, and calculate the instability index, which refers to the inherent potential instability of each natural slope of the examined region. From the statistical interpretation of the data reported in a well-documented database and concerning the examined failure sites, a clear correlation between the instability index and the area affected by a single landslide event has been revealed. Almost the entire failure sites, 98% of the examined slope sites, exhibit an instability index value over 55, a value which is thought to be a critical threshold for landslide manifestation concerning natural slopes in Karditsa County. It is argued that the presented RES methodology, engaging the selected set of parameters, could be considered as an effective expert's tool for ranking, in an objectively optimal and simple way, the instability potential of natural slopes in Karditsa County, and thus providing a tool for sound zoning landslide hazard.     

祁连山南部地区三叠纪弧后前陆盆地——基于沉积填充与大地构造的证据

本文通过对祁连山南部地区三叠纪沉积充填特征的研究,建立了盆地形成过程中沉积充填与区域构造演化的关联。依据沉积充填特征、构造接触关系及区域地质背景,认为祁连山南部地区三叠纪盆地具有弧后前陆盆地的构造属性;综合分析年代学、沉积物性和盆地内部填充单元的差异划分出与柴达木岛弧带和祁连山南部弧后前陆盆地相关的区域大地构造单元。认为早三叠世-中三叠世中期,南部遭受俯冲作用持续向北挤压推覆导致盆地挠曲沉降;中三叠世中期-晚三叠世中期发生弧(东昆仑-柴北缘)-陆(巴颜喀拉地块)碰撞,祁连山南部盆地挠曲沉降增大,其间形成区域性断裂和不整合等盆地记录的地质事件;晚三叠世晚期祁连山南部盆地发生过补偿陆相填充,弧后前陆盆地消亡。     

重视和加强岩矿物性的测量研究

本文从物探科学技术的进步,勘查任务的发展变化、物探方法应用范畴的扩大和物性勘探等几个方面,论述了岩石和矿物物理性质测量、研究的重要性,指出：物性工作不可能毕其功于一役,并提出了五点建议：１．深入研究各类矿藏及其围岩（直至地面）物性的空间变化规律,为选择、研究合适的物探方法,提高物探效果,进一步探讨“直接”找矿问题,提供依据;２．这项工作可专门进行,但最好尽可能利用为其他目的而设计的钻井进行;３．物     

Experimental investigation of the elastic modulus of a fractal system—A model of fractured rocks

The elastic properties of a physical model representing a damaged rock matrix were studied using a square lattice deformed under tensile stress. The elastic modulusM of such a system varies in agreement with percolation theory as|x–x _c | ^f , wherex is the damage parameter andx _c the threshold value of the damage parameter,f3.6. Atxx _c the scale dependence ofM can be expressed asML ^–f/v , whereL is the size of the sample andv the correlation exponent in percolation theory.The experimental results are of interest in assessing elastic properties in earthquake focal zones and fault zones in general.     

Engineering geological studies and tunnel support design at Sulakyurt dam site, Turkey

This paper presents the results of engineering geological investigations and tunnel support design studies, carried out at the Sulakyurt dam site, northeast of Ankara, Turkey. The Sulakyurt dam will be used for flow control and water storage for irrigation projects. Studies were carried out both in the field and the laboratory. Field studies include engineering geological mapping, intensive discontinuity surveying, core drilling and sampling for laboratory testing. The diversion tunnel will be driven in rock mass, consisting of granite and diorite. Empirical, analytical and numerical methods were combined for safe tunnel design. Rock mass rating (RMR), Rock mass quality (Q) and Geological strength index (GSI) systems were used for empirical rock mass quality determination, site characterization and support design. The convergence–confinement method was used as analytical method and software called Phase², a 2D finite element program, was utilized as numerical method. According to the results acquired from the empirical, analytical and numerical methods, tunnel stability problems were expected in both granite and diorite rock masses. The support system, suggested by empirical methods, was applied and the performance of suggested support system was evaluated by means of numerical modelling. It was concluded that the suggested support systems were adequate, since after applying the suggested support system to granite and diorite, tunnel deformation and the yielded elements around the tunnel decreased significantly. Thus, it is suggested that for more reliable support design empirical, numerical and analytical methods should be combined.     

A Practical Procedure for the Measurement of Fragmentation by Blasting by Image Analysis

Summary. The operation of a digital image analysis system in a limestone quarry is described. The calibration of the system, required in order to obtain moderately reliable fragmentation values, is done from muckpile sieving data by tuning the image analysis software settings so that the fragmentation curve obtained matches as close as possible the sieving. The sieving data have also been used to extend the fragment size distribution curves measured to sizes below the system’s optical resolution and to process the results in terms of fragmented rock, discounting the material coming from a loose overburden (natural fines) that is cast together with the fragmented rock. Automatic and manual operation modes of the image analysis are compared. The total fragmentation of a blast is obtained from the analysis of twenty photographs; a criterion for the elimination of outlier photographs has been adopted using a robust statistic. The limitations of the measurement system due to sampling, image processing and fines corrections are discussed and the errors estimated whenever possible. An analysis of consistency of the results based on the known amount of natural fines is made. Blasts with large differences in the amount of fines require a differentiated treatment, as the fine sizes tend to be the more underestimated in the image analysis as they become more abundant; this has been accomplished by means of a variable fines adjustment factor. Despite of the unavoidable errors and the large dispersion always associated with large-scale rock blasting data, the system is sensitive to relative changes in fragmentation.     

On the origin of rock fragment mulches on Vertisols: A case study from the Ethiopian highlands

Many Vertisols in Tigray, Ethiopia, typically carry a discontinuous rock fragment (RF, size 0.5–> 40 · 10^− 2 m) cover with 10 to 100 RFs m^− 2. Such RF mulches are of agricultural and environmental significance because they influence the water balance in the underlying soils and the crop yield. Natural RF concentrations are mostly considered as eolian or hydraulic lag deposits, or as the result of lateral transport over the soil surface from a rock outcrop, upslope. In cultivated areas RF mulches can develop by tillage.This paper presents the case of a natural RF mulch whose lithology indicates that the RFs are up-squeezed by the local Vertisol. The study site is located in the pass of Enda Maryam, Tigray, Northern Ethiopia (39°8′ E and 13°36′ N). A circular area of 10 m diameter, about 200 m away from the water divide in the valley has been cleared annually between 01/1999 and 05/2003. During this period, 625 RFs, 17 being > 7.5 · 10^− 2 m in size, totalling a mass of nearly 62 kg, have been collected. After correction for measurement procedures, the rate of RF up-warping by the Vertisol at Enda Maryam is assessed at 5 RFs m^− 2 in 3 years. At this rate of appearance, the formation of current RF concentrations on top of active valley Vertisols is only a matter of 10^1–2 years, provided the availability of RFs below the soil surface.Although important underground displacements were measured in the Vertisol between 01/1999 and 05/2002, the supposed link between up-squeezing of RFs and plastic deformations of ‘chimney’, ‘diapir’ or ‘intrusion’-like type in the Vertisol could not be evidenced. Instead, RFs are clearly concentrated on the soil surface as well as in depth, along the existing vertical desiccation cracks, often > 1 m deep which display polygonal configurations at the soil surface. Further, bundles of slickensides containing some RFs, have been mapped at the base of the Vertisol. The slickenside configuration suggests that the RF-bearing substrate is being scraped off.While the underground displacement of RFs along active slickensides seems normal, the process of RFs ascending in ‘upright’ position in the edge of desiccation cracks needs explanation. The closure of a desiccation crack is a peristaltic-like movement, following ascent or descent of the capillary fringe. It is hypothesized that this movement gradually pushes the RF to the surface or to another place or level in the soil profile where the crack closes in last instance.The apparent young age of the valley Vertisol mulches in Ethiopia might indicate the very recent formation of yearly recurrent desiccation cracks of Vertisols in the area. Available information confirms that most valleys in the study area used to be perennially marshy. Under these conditions no movements of RFs in the soil profile are expected to occur. Gullying, leading to pronounced seasonal desiccation of the Vertisols, started in several cases not more than 50 years ago.     

Surface temperature differences between minerals in crystalline rocks: Implications for granular disaggregation of granites through thermal fatigue

Thermal expansion differences between minerals within rocks under insolation have previously been assumed to drive breakdown by means of granular disaggregation. However, there have been no definitive demonstrations of the efficacy of this weathering mechanism. Different surface temperatures between minerals should magnify thermal expansion differences, and thus subject adjacent minerals to repeated stresses that might cause breakdown through fatigue failure. This work confirms the existence of surface temperature differences between minerals in granitic rocks under simulated short-term temperature fluctuations so as to discriminate their potential for initiating granular disaggregation. The influence of colour, as a surrogate for albedo, and crystal size, as a function of thermal mass are specifically identified because of their ease of quantification. Four rock types with a range of these properties were examined, and subjected to repeated short-term temperature cycles by radiative heating and cooling under laboratory conditions. Results show that while albedo is the main control for overall and individual maximum temperatures, crystal size is the main factor controlling higher temperature differences between minerals. Thus, stones with large differences of mineral sizes can undergo magnified stresses due to thermal expansion differences.     

Processes and rates of rock fragment displacement on cliffs and scree slopes in an amba landscape, Ethiopia

Distinct rock fragment displacements occur on the ambas, or structurally determined stepped mountains of the Northern Ethiopian Highlands. This paper describes the rock fragment detachment from cliffs by rockfall, quantifies its annual rate, and identifies factors controlling rock fragment movement on the scree slopes. It further presents a conceptual model explaining rock fragment cover at the soil surface in these landscapes. In the May Zegzeg catchment (Dogu'a Tembien district, Tigray), rockfall from cliffs and rock fragment movement on debris slopes by runoff and livestock trampling were monitored over a 4-year period (1998–2001). Rockfall and rock fragment transport mainly induced by livestock trampling appear to be important geomorphic processes. Along a 1500-m long section of the Amba Aradam sandstone cliff, at least 80 t of rocks are detached yearly and fall over a mean vertical distance of 24 m resulting in a mean annual cliff retreat rate of 0.37 mm y^− 1. Yearly unit rock fragment transport rates on scree slopes ranged between 23.1 and 37.9 kg m^− 1 y^− 1. This process is virtually stopped when exclosures are established. Corresponding mean rock fragment transport coefficients K are 32–69 kg m^− 1 y^− 1 on rangeland but only 3.9 kg m^− 1 y^− 1 in densely vegetated exclosures. A conceptual model indicates that besides rockfall from cliffs and argillipedoturbation, all factors and processes of rock fragment redistribution in the study area are of anthropogenic origin.