In-situ Measurements of Cutter Forces on Boring Machine at Äspö Hard Rock Laboratory Part II. Characteristics of Cutter Forces and Examination of Cracks Generated

Summary By means of spectral analysis, the measured normal forces, tangential forces, and side forces acting on two button cutters on the boring machine in ?sp? Hard Rock Laboratory were analysed and the basic characteristics of the cutter forces were determined. After the measurements of the cutter forces, some rock core samples were taken from the bottom and the wall of the test borehole. These samples were cut, polished, and examined by means of a Scanning Electron Microscope (SEM). The lengths of the major cracks in the rock samples were measured, and a relation between the length of the median cracks and the relevant cutter forces was investigated. Received October 5, 2001; accepted June 25, 2002; Published online November 19, 2002     

探地雷达在隧道衬砌混凝土质量检测中的应用

简要介绍了应用探地雷达对隧道衬砌混凝土质量进行检测的方法、原理及其实际应用效果。测试结果表明,探地雷达能及时、快速地发现衬砌混凝土的质量问题,为工程质检和评价提供依据,是一种能很好地对衬砌混凝土的质量进行检测的无损检测方法。     

湘桂地区中新生代走滑断裂系统对铀成矿的控制作用

湘桂地区是我国的重要铀成矿区之一。该区自中生代末期以来进入了全新的陆内走滑作用阶段,并经历了两次重大的构造转换,即晚三叠纪末至侏罗纪末的会聚走滑和白垩纪至第三纪早期的离散走滑。三条NNE向的主走滑断裂(PDZ)和一系列NE向的同向右侧列走滑断层(P)以及NW向的反向走滑断层(R')组成了复杂的走滑断裂网络系统,并直接控制了湘桂地区铀矿床(田)在时间和空间上的分布。     

Carbon–oxygen isotope and trace element constraints on how fluids percolate faulted limestones from the San Andreas Fault system: partitioning of fluid sources and pathways

Understanding the way fluids flow in fault zones is of prime importance to develop correct models of earthquake mechanics, especially in the case of the abnormally weak San Andreas Fault (SAF) system. Because fluid flow can leave detectable signatures in rocks, geochemistry is essential to bring light on this topic. The present detailed study combines, for the first time, C–O isotope analyses with a comprehensive trace element data set to examine the geometry of fluid flow within a significant fault system hosted by a carbonate sequence, from a single locality across the Little Pine Fault–SAF system. Such a fault zone contains veins, deformation zones, and their host rocks. Stable isotope geochemistry is used to establish a relative scale of integrated fluid–rock ratios. Carbonate δ¹⁸O varies between 28‰ and 15‰ and δ¹³C between 5‰ and −7‰. From highest to lowest delta values, thus from least to most infiltrated, are the host rocks, the vein fillings, and the deformation zone fillings, respectively. Infiltration increases toward fault core. The fluids are H₂O–CO₂ mixtures. Two fluid sources, one internal and the other external, are found. The external fluid is inferred to come essentially from metamorphism of the Franciscan formation underneath. The internal (local) fluid is provided by a 30% volume reduction of the host limestones resulting from pressure solution and pore size reduction. Most trace elements, including the lanthanides, show enrichment at the 100-m scale in host carbonate rocks as fluid–rock ratios increase toward the fault core. In contrast, the same trace element concentrations are low, relative to host rocks, in veins and deformation zone carbonate fillings, and this difference in concentration increases as fluid–rock ratio increases toward the fault core. We suggest that the fluid trace elements are scavenged by complexation with organic matter in the host rocks. Elemental complexation is especially illustrated by large fractionation of Y–Ho and Nb–Ta geochemical pairs. Complexation associated with external fluid flow has a significant effect on trace element enrichment (up to 700% relative enrichment) while concentration by pressure solution associated with volume decrease of host rocks has a more limited effect (up to 40% relative enrichment). Our observations from the millimeter to the kilometer scale call for the partitioning of fluid sources and pathways, and for a mixed focused–pervasive fluid flow mechanism. The fluid mainly flows within veins and deformation zones and, simultaneously, within at least 10 cm from these channels, part of the fluid flows pervasively in the host rock, which controls the fluid composition. Scavenging of the fluid rare earth elements (REE) by host rocks is responsible for the formation of REE-depleted vein and deformation zone carbonate fillings. Fluid flow is not only restricted to veins or deformation zones as commonly believed. An important part of fluid flow takes place in host rocks near fault zones. Hence, the nature of the lithologies hosting fault zones must be considered in order to take into account the role of fluids in the seismic cycle.     

Urban agriculture in Cameroon: an anti-politics machine in the making?

Urban agriculture in Africa is a growth area for development institutions and researchers. It is often portrayed as a coping strategy through which the urban poor have adapted to structural adjustment. It is enframed in an apolitical, ahistorical way because development institutions seek to create spaces into which development projects can be inserted in the future. This paper uses a case study from the town of Buea in south-west Cameroon to illustrate the differences between the international image of urban agriculture and its practice in one particular place. The increase in agricultural production in Buea in the 1990s initially appears to conform to the standard picture of urban farming as a recent, pragmatic and unplanned response to falling household incomes. However, such a portrayal neglects the history of urban farming, the pleasure that agriculture brings to farmers and the political consequences of expanding agricultural production. One of the concrete outcomes of increased urban agriculture in Buea in the 1990s has been to act as a `safety valve' against social unrest. It has acted as an `anti-politics machine'; a mechanism through which a sensitive political operation (reducing the salaries of civil servants) is achieved through apparently disconnected apolitical acts (enabling urban households to expand agricultural production). The Cameroonian government has opportunistically encouraged urban agriculture during a period of rapid economic change as one strategy for reproducing existing social relations.     

人地系统动力学研究的现状与展望

文章系统地综述了当前国内外对表层地球系统研究的现状、发展趋势，提出从人地系统动力学入手，深入开展可持续发展理论与方法研究的基本内容，以期表述人类活动对地球系统的影响——地球系统演变之“人类驱动力”的机制     

The Delivery Tunnel North, Lesotho Highlands Water Project

Summary The Delivery Tunnel North starts in Lesotho and continues into South Africa. It is divided into two sections by the Caledon and Little Caledon rivers. It runs through the mudrocks and sandstones of the Tarkastad Subgroup, and the Elliot and Molteno Formations. The tunnel was excavated by a double-shield tunnel boring machine, except for the sections beneath the two rivers, which were constructed by drill and blast methods. The tunnel boring machine was selected to bore through the anticipated changing ground conditions and also was capable of installing the segmental lining of the tunnel. Boreability tests showed that the sandstones and siltstones had good boreability, but that it was very low in the dolerite dykes. At depth, the weaker mudstones presented the worst tunnelling conditions, giving rise to squeezing ground and to shear failure with accompanying overbreak. Initially a small amount of cracking occurred in the tunnel lining but this was reduced significantly as experience was gained. Cracking was observed predominantly in the weaker rock types, and this was probably associated with overbreak.     

地下坑道开挖前方结构面超前探测

本文在分析总结现有地球物理勘探方法的基础上, 提出了一种适合地下工程开挖前方结构面探测的新的方法--TVSP法, 同时对该方法进行了必要的分析。     

楔形双滑面稳定性动态分析及其在削坡治理中的应用──以神府-东胜和准格尔煤田露天采场斜坡为例

本文提出了可以连续地计算任何坡高不同坡角的双滑面楔形四面滑体的稳定系数，以便求得某一稳定性系数的最优化坡角。本方法经神府－东胜及准格尔煤田采场斜坡验算，得知两煤田采场斜坡还有较大的安全储备。     

我国地球动力学的研究进展与展望

综述我国地球动力学的研究进展1994年以前的情况在臧绍先总结的基础上作一些补充外，着重讨论1994年以后的进展分别从地质构造运动的力学分析、岩石层动力学、地慢流动、地核动力学、地球介质力学性质、反演的数学方法和非线性科学等部分进行介绍．最后提出有待发展的研究方向．