Shear strength characteristics of sand-mixed with granular rubber   总被引：1，自引：0，他引：1  

Mahmoud Ghazavi 《Geotechnical and Geological Engineering》2004,22(3):401-416

Waste materials such as waste tires, rubbers, and plastic materials are normally produced in every society, entering the environment and causing serious problems. These problems may be somehow reduced by finding applications for them in engineering, for example, as lightweight materials for backfill in geotechnical projects. To this aim, this paper demonstrates how shear strength characteristics of sand mixed with various percentages of waste garden hose grains are altered. A relatively, uniform sand has been mixed with waste hose grains in loose and slightly compacted states. Waste hose grains were prepared with special popular machinery in a local area. Various sand-rubber mixtures having 0%, 10%, 15%, 20%, 50%, 70%, and 100% waste hose particles by weight were chosen. The rubber grains were distributed in the sand such that uniform mixtures are obtained. In order to compare the shear strength of different sand-rubber samples, two compaction states were considered. The results show that the influencing parameters on shear strength characteristics of sand-rubber mixtures are normal stress, mixture unit weight, and rubber content. With the selected waste hose particles, compaction states, and rubber contents, the initial friction angle φ₁ does not change significantly. However, an apparent cohesion appears in the mixtures. From environmental point of view and due to lightweight material for the sand-waste hose particles, it may be useful to use such materials in corresponding geotechnical projects. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Unprecedented last-glacial mass accumulation rates determined by luminescence dating of loess from western Nebraska     

Helen M. Roberts  Daniel R. Muhs  Ann G. Wintle  Geoff A. T. Duller  E. Arthur Bettis  III 《Quaternary Research》2003,59(3):411-419

A high-resolution chronology for Peoria (last glacial period) Loess from three sites in Nebraska, midcontinental North America, is determined by applying optically stimulated luminescence (OSL) dating to 35–50 μm quartz. At Bignell Hill, Nebraska, an OSL age of 25,000 yr near the contact of Peoria Loess with the underlying Gilman Canyon Formation shows that dust accumulation occurred early during the last glacial maximum (LGM), whereas at Devil’s Den and Eustis, Nebraska, basal OSL ages are significantly younger (18,000 and 21,000 yr, respectively). At all three localities, dust accumulation ended at some time after 14,000 yr ago. Mass accumulation rates (MARs) for western Nebraska, calculated using the OSL ages, are extremely high from 18,000 to 14,000 yr—much higher than those calculated for any other pre-Holocene location worldwide. These unprecedented MARs coincide with the timing of a mismatch between paleoenvironmental evidence from central North America, and the paleoclimate simulations from atmospheric global circulation models (AGCMs). We infer that the high atmospheric dust loading implied by these MARs may have played an important role, through radiative forcing, in maintaining a colder-than-present climate over central North America for several thousand years after summer insolation exceeded present-day values.  相似文献   

Some observations on the chemical weathering of the Dartmoor granite     

Andrew G. Williams  Les Ternan  Martin Kent 《地球表面变化过程与地形》1986,11(5):557-574

The majority of geomorphological papers about Dartmoor have been essentially speculative, particularly when discussing weathering processes and the evolution of the Dartmoor landscape. In contrast, this article presents a synthesis of several experimental investigations aimed at studying the chemical weathering of Dartmoor granite through the systematic analysis of soil and water samples. This involved the computation of a geochemical budget to determine the amount of erosion in the catchment, as well as more detailed mineralogical investigations within a soil profile. The annual output of solutes due to weathering was 116 kg ha^?1 a^?1 of which the majority was silica (93 kg ha^?1 a^?1). From an examination of the soil mineralogy, it was calculated that these solutes were derived from the dissolution of approximately 200 kg ha^?1 a^?1 plagioclase, 90 kg ha^?1 a^?1 biotite, and 40 kg ha^?1 a^?1 orthoclase. As well as the weathering of granite, there was also the production of kaolinite (150 kg ha^?1 a^?1) and gibbsite (0.02 kg ha^?1 a^?1). Analysis of the soil water chemistry confirmed that kaolinite was the stable mineral phase in the regolith, although in areas where interflow was the dominant mode of water movement, the solute composition was in equilibrium with both kaolinite and gibbsite. Examination of the clay mineralogy confirmed these results. The microtexture of quartz grains was examined by the scanning electron microscope as another means of investigating the hydrochemical environment in the soil. Silica was found precipitated on all the grains examined but the maximum amount occurred in the Bs horizon. This evidence showed that, firstly, the dissolution of aluminosilicate minerals is greater than that calculated by the chemical budget and, secondly, that models of granite weathering must take localized weathering in the soil profile into account. The final part of the paper highlights the limitations of calculating denudation rates for an entire catchment and stresses the need to consider weathering as a highly localized phenomenon, particularly where there are high volumes of interflow at hill crest sites. Observations on granite decomposition in the future should be quantitative in approach and be related to the local site conditions.  相似文献   

化探找金中几个问题的讨论     

刘庆成 《华东地质学院学报》1987,(3)

本文讨论了化探找金中指示元素选择、取样层位、富集粒度等问题,并提出了解决这些问题的办法,这些问题都直接影响找矿效果。  相似文献   

单轴受拉时冻土结构变化及其机理初析     

沈忠言  王家澄 《冰川冻土》1996,18(3):262-268

土体地单轴拉应力作用下，轴向经历变形，结构发生本质性的变化，径向同时出现收缩。这种应变特性改变了矿物颗粒间的微应力场，它是土体在径向上发生颗粒错位，定向排列，微裂隙等发育等结构变化的源动力。  相似文献   

Agribusiness and farmers in Mexico: the importance of contractual relations   总被引：1，自引：0，他引：1  

FLAVIA ECHÁNOVE  CRISTINA STEFFEN† 《The Geographical journal》2005,171(2):166-176

In recent decades contract farming as a mechanism that integrates and subordinates agricultural production to export oriented agribusiness has expanded in Third World countries. In Mexico contract farming dominates the production of horticultural crops for processing and export. It is also used for barley and to grow some varieties of wheat for Cargill . The contract farming labour agreement represents an institution that links local and global processes where agribusiness is the key actor that integrates local farmers to national and world markets. The purpose of this paper is to analyse the implications of contract farming for productive relations by examining its impact upon farmers and firms. The study found that despite the disadvantages of contract farming for growers, and the disproportional risks born by producers, they enter into contract farming labour agreements because they lack alternatives for financing, technical assistance and access to markets. The experience of contract farming in Mexico and several Third World countries shows that its growth is related to the implementation of neo-liberal policies that are accompanied by the withdrawal of state support and regulation of agricultural production. In this context, contract farming represents a livelihood strategy for many Mexican growers.  相似文献   

海南岛乐东盆地白垩系研究新进展     

符国祥  符策锐  汪迎平 《地层学杂志》2001,25(1):63-68

对海南岛乐东盆地白垩系进行了深入研究 ,将原报万组上部一套冲积相划分出来 ,新建长茅组 ;厘订后的报万组限定在长茅组之下 ,为一套河湖相沉积 ,二者为整合接触 ,含孢粉化石 ,时代为早白垩世最晚期到晚白垩世。  相似文献   

鲁西北西向断裂的断层泥及其地震地质意义   总被引：2，自引：1，他引：2       下载免费PDF全文

王华林  晁洪太 《地震地质》1992,14(3):265-274,T001

对鲁西北西向断裂的断层泥进行了较系统的研究。通过对断层泥的宏观特征、断层泥中石英碎砾的表面结构特征和断层泥的成熟度的研究,确定了断裂活动的地质时代、运动方式、破裂形式和活动度,并对断层泥的地震地质意义进行了讨论  相似文献   

Exploring the potential of luminescence methods for dating Alpine rock glaciers     

《Quaternary Geochronology》2013

Rock glaciers contain valuable information about the spatial and temporal distribution of permafrost. The wide distribution of these landforms in high mountains promotes them as useful archives for the deciphering of the environmental conditions during their formation and evolution. However, age constraints are needed to unravel the palaeoclimatic context of rock glaciers, but numerical dating is difficult. Here, we present a case study assessing the potential of luminescence techniques (OSL, IRSL) to date the inner sand-rich layer of active rock glaciers. We focus on the signal properties and the resetting of the signal prior to deposition by investigating single grains. While most quartz shows low signal intensities and problematic luminescence characteristics, K-feldspar exhibits much brighter and well-performing signals. Most signals from plagioclases do not show suitable properties. Luminescence signals far below saturation indicate distinct but differential bleaching. The finite mixture model was used to determine the prominent populations in the equivalent dose distributions. The luminescence ages represent travel times of grains since incorporation into the rock glacier and hence, minimum ages of rock glacier formation. Luminescence ages between 3 ka and 8 ka for three rock glaciers from the Upper Engadine and Albula region (Swiss Alps) agree well with independent age estimates from relative and semi-quantitative approaches. Therefore, luminescence seems to have the potential of revealing age constraints about processes related to the formation of rock glaciers, but further investigations are required for solving some of the problems remaining and reducing the dating uncertainties.  相似文献   

Mechanisms for avulsion on alluvial fans: Insights from high-frequency topographic data     

Anya Leenman  Brett Eaton 《地球表面变化过程与地形》2021,46(6):1111-1127

Avulsion is a key process in building alluvial fans, but it is also a formidable natural hazard. Based on laboratory experiments monitored with novel high-frequency photogrammetry, we present a new model for avulsion on widely graded gravel fans. Previous experimental studies of alluvial fans have suggested that avulsion occurs in a periodic autogenic cycle, that is thought to be mediated by the gradient of the fan and fan-channel. However, those studies measured gradients at low spatial or temporal resolutions, which capture temporally or spatially averaged topographic evolution. Here, we present high-resolution (1 mm), high-frequency (1-minute) topographic data and orthophotos from an alluvial fan experiment. Avulsions in the experiment were rapid and, in contrast to some previous experimental studies, avulsion occurrence was aperiodic. Moreover, we found little evidence of the back-filling observed at coarser temporal and spatial resolutions. Our observations suggest that avulsion is disproportionately affected by sediment accumulation in the channel, particularly around larger, less mobile grains. Such in-channel deposition can cause channel shifting that interrupts the autogenic avulsion cycle, so that avulsions are aperiodic and their timing is more difficult to predict.  相似文献