Investigation of expansive soils in Obhor Sabkha,Jeddah-Saudi Arabia

Expansion or swelling of soil is a worldwide geotechnical problem that occurs in arid and semiarid regions where sabkha soils may occur as well. Expansive soil is dominated by the presence of active clay minerals. The expansive and sabkha soils are characterized by a large seasonal variation in soil moisture content leading to a large change in the volume and the consistency of the soil and, thus, causing serious damages to buildings and infrastructure. Although sabkha soil covers large and strategically important areas along the Red Sea and Arabian Gulf coasts in Saudi Arabia, no one paid proper attention to the type of clay minerals in those soils or to their expansion potential, which is a crucial step prior to any construction. The geotechnical properties, active clay mineral types, and the degree expansion potential of soils were investigated in Obhor area at the north of Jeddah City. Twenty disturbed soil samples were collected at depths of 80 and 120 cm. Three different types of soils are identified: clayey soil with high plasticity, clayey soil with low plasticity, and poorly graded silty to clayey sand soil. Furthermore, active clay minerals were identified with a significant proportion of montmorillonite (14.24 %), illite (24.65 %), kaolinite (28.78 %), and chlorite (32.34 %). The results indicated that a considerable part of the study area has high expansion potential, but most parts of Obhor area have low to none potential of soil expansiveness.     

Cultural implications of architectural mortar selection at Mesa Verde National Park,Colorado

Architectural mortar from two ancestral Pueblo sites (Spruce Tree House and Nordenskiöld's Ruin 12) located in Mesa Verde National Park was investigated using visual, mineralogical, and geochemical techniques. Results indicate ancestral Pueblo people had a preference for mortars composed of sand and clay contents that produce a USDA textural class of sandy clay loam to clay loam. A temporal trajectory of soil selection is observed at Spruce Tree House, with mesa‐top soils being preferred during the early period of occupation, but with soils below cliff dwellings preferred during later periods. Mortar geochemical composition is found to differ between cliff dwellings, and sometimes between households within a cliff dwelling, due to local soil differences and/or potential amendment additions. Results from Spruce Tree House indicate that contemporaneous households shared access to mortar sources. The prevalence and possible origins of gypsum found in mortar are discussed. Finally, this research examines the possibility that land tenure rights may have extended beyond those lands used exclusively for agricultural purposes. © 2011 Wiley Periodicals, Inc.     

Insight into the effects of clay mineralogy on the cyclic behavior of silt–clay mixtures

Results of a systematic testing program showed that the cyclic behavior of silt–clay mixtures is greatly influenced by the dominant clay minerals in the mixture. In particular, it was demonstrated that given the same amount of clay/clay mineral and/or same value of plasticity index, the montmorillonitic soils have the highest cyclic strength, followed by the illitic soils, and then by the kaolinitic soils. Moreover, the rate of increase in cyclic strength with increasing % clay mineral and PI is again the highest in the montmorillonitic soil, lowest in the kaolinitic soil and intermediate in the illitic soil. Therefore, without considering clay mineralogy, the % clay fraction, % clay mineral and plasticity index are unreliable indicators of the liquefaction susceptibility of fine-grained soils. The differing adhesive bond strength each clay mineral develops with the silt particles is deemed to largely explain the observed differences in the response of the three different soil mixtures to cyclic loading.     

Accumulation of trace elements in paddy topsoil of the Wudang County, Southwest China: parent materials and anthropogenic controls

The properties of soils derived from carbonate rock, red residua, and sand-shale in Guizhou province, China are essentially different. However, the effects of parent material and anthropogenic activities on the concentration of trace elements when the soils are converted into paddy soils are unknown. A total of 319 paddy topsoil samples (0–20 cm) were collected in a typical region to determine their relative contribution to the concentrations of trace elements in the soil. The results indicated that the contents of trace elements were far beyond the uncultivated soil background and the input of organic fertilizers was presumably responsible for accumulation of trace elements. In addition, principal component analysis showed that the first component included Cd, Cr, and As, which strongly associated with anthropogenic activities. Pb and Hg formed the second component, which related to both parent materials and anthropogenic input. Furthermore, the Cr and Hg contents in paddy soil derived from carbonate rock have higher values than other types of soils partly because of the high background values as well as slightly alkaline condition. In the paddy soil derived from red residua, high physical clay content accounted for enrichment of Pb.     

Spatial distribution and source of heavy metals in reclaimed lands of Homebush Bay: The venue of the 2000 Olympic Games,Sydney, New South Wales

A large part of the Sydney 2000 Olympic Site at Homebush Bay was reclaimed over several decades using an estimated 9 Mt of domestic, commercial and industrial waste. Past activities, such as reclamation of wetlands, land clearing, shoreline remodelling and industrial practices, have caused an adverse environmental impact on the Homebush Bay site. Core samples (n = 4513) collected from the reclaimed lands of Homebush Bay show that, prior to remediation, soil contaminated by heavy metals (Cr, Cu, Pb, Zn) may have posed a threat to groundwater in the area. Mean Pb concentrations from the three land types at the Olympic site range from 65 to 374 μg/g in reclaimed areas, 78–167 μg/g in landfill areas and 44–52 μg/g in non‐infilled areas, respectively. Heavy‐metal concentrations in soils from non‐infilled areas indicate that these parts of the site were uncontaminated. The distribution of heavy metals in soil samples revealed a close association between elevated concentrations and the presence of fill materials at the site. Metal concentrations were frequently above Australian and New Zealand Guidelines for Fresh and Marine Water Quality. The Olympic Coordination Authority's remediation strategy to clean up the Homebush Bay site included consolidating contaminated waste into landscaped hills, which were capped with impermeable clay and thermal destruction of scheduled waste on site. The primary aims of the current study were to provide a scientific foundation for the remediation/rehabilitation of natural systems, and to make a contribution to the Olympic Coordination Authority's Development Plan and Environmental Management System for the site.     

广西北部湾地区土壤锗分布特征、影响因素及其生态环境评价

Ge在工业和医疗领域具有良好应用前景,有机锗化合物是一种毒性较低、具有较强抗癌活性的物质,富Ge土壤具有广阔的开发利用价值,但目前我国对土壤Ge的研究程度较低。基于广西壮族自治区多目标区域地球化学调查成果,对北部湾地区表层土壤及深层土壤Ge的空间分布特征进行了研究,阐明了不同成土母质地区表层土壤及深层土壤Ge含量情况,总结了影响土壤Ge含量的因素。结果表明,广西北部湾地区表层土壤Ge含量平均值是1.43 mg/kg,深层土壤Ge含量平均值是1.64 mg/kg。土壤Ge含量主要受控于成土母质,碳酸盐岩分布区土壤Ge含量最高,其次为花岗岩分布区、第四系沉积物分布区以及砂-页岩分布区。表层土壤与深层土壤Ge含量的比值显示表层土壤Ge含量受人为活动影响小。不同成土母质形成的土壤Ge含量的影响因素存在差异,花岗岩分布区表层土壤与深层土壤Ge含量主要受土壤黏土矿物、三水铝石以及石英的影响,碳酸盐岩、砂-页岩及第四系沉积物分布区表层土壤Ge含量主要受土壤黏土矿物、三水铝石、次生含铁矿物、无定形铁氧化物/氢氧化物、石英及有机质的影响,深层土壤Ge含量主要受土壤黏土矿物、三水铝石、次生含铁矿物、无定形铁氧化物/氢氧化物及石英的影响。研究区53.32%的表层土壤Ge含量达到较丰富水平,30.21%的表层土壤Ge含量达到丰富水平,对富Ge农作物的生长非常有利,具有开发利用价值。本文的研究成果旨在为土壤Ge的生态地球化学特征提供基础资料,为富Ge土地资源评价和富Ge农产品开发利用提供依据。     

Red and yellow soils and laterite formation in the Northeast Plateau, Thailand

Data of a study on red and yellow soils in the Northeast Plateau, Thailand, indicate that the soils are highly leached and well developed under oxidizing condition. They have been developed on slope wash materials and local alluvium underlain by cemented gravels and laterite. Appreciable amounts of Fe-oxides can be found in these soils, mainly in the form of goethite and hematite and in both silt and clay fractions. Other important constituents of these soils are quartz and kaolinite. The soil fabric contains argillan and ferri-argillan on skeleton grains and pore walls, indicating prolonged leaching and oxidizing state of the solum. Laterites found are both massive and pisolithic gravels. Since spot accumulation and separation of argillan and Fe-oxides were not observed in the soils it seems that the soils and laterite have been controlled by different sets of genetic processes.     

Assessing the control exerted by soil mineralogy in the fixation of potentially harmful elements in the urban soils of Lisbon,Portugal

The main purposes of this study are the textural, chemical and mineralogical characterization of the urban soils of Lisbon and the identification of probable relations between the several soil properties. The results are used to infer which soil properties control the superficial dispersion of potential harmful elements to human health. Soil sampling was carried out in 51 selected sites all through the city, under the criterion that such sites should be spaces usually frequented by children. The concentrations of 42 elements in the >2 mm soil size fraction were determined at a commercial laboratory in Canada (ActLabs, LTD), by ICP-MS/ICP-OES after an acid digestion with aqua regia. The soil mineralogy was determined by X-ray diffraction in the <2 and <62 μm size fractions. The results indicate that the urban soils have mainly a sandy texture and a main mineralogical assemblage of quartz, K-feldspar, plagioclase and calcite. In terms of clay minerals, smectite, illite and kaolinite are the main clays in the soil. Smectite and illite show a dichotomy in their distribution, with the smectites prevailing in the soils of the volcanic complex of Lisbon, which are classified as being residual, and illite prevailing in the remaining soils, which are considered mainly as man-made soils. Smectite seems to exert an important role in the fixation of Ni and Cr. The results of the geochemical study show that Ni and Cr have concentrations above the soil guideline value established to the UK and pose a probable risk to human health.     

Soil development on recent end moraines of the Klutlan Glacier,Yukon Territory,Canada

Data on soils with six Neoglacial moraines of the Klutlan Glacier have been compared with those from moraines at the warm, moist coastal site of Glacier Bay, 160 km south. Percentage organic matter increases rapidly for the first 100 to 150 yr of soil development and then continues to rise gradually for the next 100 yr. Soil pH falls from 8.0 in recent till to approximately 6.0 in 200-yr-old soils. Nitrogen levels in the mineral soil increase from near zero in recent tills to 0.7% in soils 175–200 yr old; organic horizons of soils associated with spruce forests in later successional stages contain approximately 1% nitrogen. Concentrations of certain inorganic phosphate ions in the different-aged soils increase continually throughout the succession. Data for nine chemical variables were subjected to a principal components analysis; the major pattern in the data reflects the differences between soils of low organic content and high pH present in early successional stages, and nutrient-rich soils with high organic content and low pH present after succession has progressed toward the spruce forest. These trends in soil development with time are strikingly similar to those reported from Glacier Bay, except that the changes in soil properties appear to be delayed by 50–100 yr at the Klutlan terminus. Although numerous signs of nitrogen deficiency have been identified in plants growing on new soils at Glacier Bay, none was observed visually in living plants or in nutrients measured in samples of foliage from three plant taxa (Epilobium latifolium, Salix spp., and Populus balsamifera) taken from the Klutlan moraines. Concentrations of nitrogen and other nutrients (Ca, Mg, K, total P) in the foliage samples show no clear trends with increasing soil development. Low temperatures, a short growing season, and very low mean annual precipitation probably limit plant growth and account for the delayed soil development on the Klutlan moraines.     

Metals and grain size distributions in soil of the middle Rio Grande basin, Texas USA

 This paper deals with the problem of increased heavy metal constituents in agricultural soils due to the expanded use of fertilizers and elevated atmospheric deposition. It discusses the extent of contamination in soil and establishes an environmental monitoring program in the chosen area of concern in the southern coastal region of Texas. Grain size, pH, and metals (Cu, Cd, Zn, Pb, Ni, Ba, As, Cr, Mn, and Fe) were determined in soils of the middle Rio Grande basin. The soils were mainly of sand texture and alkaline in character. Fine sand constituted the major proportion of the soil, and clay and silt ranged from 8–30% of the soil. Correlations of metal concentrations to grain size and iron contents were performed. Metals, except Cd and Pb, gave positive to negative relationships with decreases in grain size. Silt gave no relationship with metal content while clay and silt had a positive relationship. All these metals had a positive correlation with iron in the soil. The results indicate metals are associated with coarse sand, clay, and iron hydroxides surfaces of the soil. The comparison of metal content in soil of the middle Rio Grande basin with metals from other areas of the world suggests that it is relatively uncontaminated. Received: 14 December 1998 · Accepted: 19 Jaunuary 1999     

Upper Ordovician graptolites from the Wagonga Beds near Batemans Bay,New South Wales

Two graptolite faunas are described from outcrops of the Wagonga Beds near Batemans Bay on the south coast of N.S.W. They are of late Eastonian and early Bolindian age. The faunas have been found in two geographically separate localities and, in spite of structural complexities, it is now suggested that the greater part of the Wagonga Beds was deposited in the Late Ordovician. The chert and volcanicrich Wagonga Beds were accumulated prior to, or as contemporaneous lateral facies equivalents of, the thick undifferentiated Upper Ordovician ‘slates and grey‐wackes unit’ that crops out in the same general region.     

SH固土剂对滨海盐渍土的固化作用评价

为评价SH固土剂的固化作用及对盐渍土的固化效果,分别完成了固化前后蒙脱石、高岭石、石英砂、盐渍土的X射线衍射与红外光谱测试、4种固化土的实体显微镜和偏光显微镜观察、固化前后盐渍土的扫描电镜微观观察,以及固化盐渍土的力学性能测试与冻融实验。实验结果表明:4种固化土的X射线衍射谱图和红外光谱图与固化前的吻合;各固化土的矿物成分没有发生改变,SH固土剂的官能团与黏土矿物均未发生化学键的结合,没有生成新相物质;SH固土剂干燥后形成弹性立体丝网,将土颗粒黏结在一起,提高了固化土的强度;固土剂填塞部分孔隙,减小了土的孔隙度;SH固土剂包裹土颗粒,增强了土的憎水性。固化盐渍土的力学性能测试和冻融实验结果证实,掺加SH固土剂提高了土的强度与抗变形性能、水稳性、抗渗性和抗冻融性能。SH固土剂与黏土矿物及盐渍土未发生化学反应,固化土力学性能的提高为固土剂的物理作用所致。     

Characteristics and formation of rain forest soils derived from late Quaternary basaltic rocks in Leyte,Philippines

This study was conducted to evaluate the physical, chemical, and mineralogical characteristics of rain forest soils derived from late Quaternary basaltic rocks in Leyte, Philippines. Four sites along a catena were selected at an elevation of 75–112 m above sea level with an average annual rainfall of 3,000 mm and an average temperature of 28°C. Results indicate that the soils are deep, clayey, and reddish in color, which is indicative of the advanced stage of soil development. They also posses excellent physical condition (friable and highly porous) although they are plastic and sticky when wet as is usual for clayey soils. In terms of chemical characteristics, the soils are acidic with low CEC values and generally low in organic matter and nutrient contents. The clay mineralogy of the soils is dominated by halloysite and kaolinite with minor amounts of goethite and hematite, and they also have generally high dithionite-extractable Fe contents confirming the advanced stage of their development. The soils in the more stable slope positions (PL-1, PL-2, and PL-4) have generally similar characteristics and appeared more developed than the one in the less stable position (PL-3). The most important pedogenic processes that formed the soils appear to be weathering, loss of bases and acidification, desilification, ferrugination, clay formation and translocation, and structure formation. The nature of the parent rock and climatic conditions prevailing in the area as well as slope position appear to have dominant effects on the development of the soils.     

The ‚loess’︁ section at Borden,Kent, SE England

A 5.3m profile originally described as loess with a buried interglacial soil is reinterpreted from petrographic evidence and thermoluminescence dating as a Holocene colluvial accretionary soil. Mineralogical analyses of coarse silt (16–63 μm) fractions suggest that most of the silty colluvium was derived from weathered Thanet Beds upslope, though some loess was incorporated during the final depositional phase. Thin sections show that clay illuviation occurred penecontem-poraneously with deposition of colluvium. Thermoluminescence properties suggest partial optical bleaching of the grains during rapid deposition, which is consistent with a Holocene colluvial origin.     

非饱和红粘土和膨胀土抗剪强度的比较研究

红粘土是对环境湿热变化敏感的塑性粘土,具有一般膨胀土吸水膨胀失水收缩的特性。与普通粘性土相比,红粘土与膨胀土的强度特性更为复杂。它既是土体抵抗剪切破坏能力的表征,也是计算路堑、渠道、路堤、土坝等斜坡稳定性以及支挡构筑物土压力的重要参数。通过试验研究讨论了红粘土与膨胀土的强度特性以及与一般粘性土的差别及其各种影响因素,并探讨了非饱和红粘土与膨胀土的抗剪强度指标与含水量之间的相关关系。试验结果表明,红粘土与一般膨胀土的吸水膨胀规律完全相同。其试验结果可为红粘土与膨胀土地区工程设计与建设提供参考依据。     

Deforestation effects on soil properties,runoff and erosion in northern Iran

Improper cultivation practices are seriously degrading native forest ecosystems in northern Iran. Hence, the objectives of this study are to compare selected soil properties, runoff amount, erosion and also introducing equations to predict the runoff and soil erosion in three types of land use (forest, garden and cultivated). A simple portable rainfall simulator has been set in 90 random points to create experimental rainfall. Result showed that changes in natural forest led to a significant clay, organic carbon of soil, total N and antecedent soil moisture decrease and sand, pH and bulk density increasing. The rainfall runoff experiments indicate that runoff content of the natural forest soils was 35 % and respectively 38.45 % higher than the garden and cultivated land soils .This result could be related to the higher antecedent soil moisture in natural forest compared with the other land uses. According to the obtained results, garden soil erosion and cultivated land was 1.351 and respectively 1.587 times higher than the forest. The correlation matrix revealed that runoff content was positively correlated with antecedent soil moisture, bulk density and silt, and negatively with soil organic carbon, total N and sand. Also, soil organic carbon, total N, clay and sand showed negative correlation with soil erosion, while there is a positive correlation between erosion and silt, bulk density, pH and antecedent soil moisture. The results of multiple linear regression showed that runoff in forest, garden and cultivated land can be predicted with correlation coefficient of 0.637, 0.547 and 0.624, respectively. The correlation coefficients of 0.798, 0.628 and 0.560 in equations indicate their moderate potential in simulating soil erosion.     

Mid-Paleocene event at Gabal Nezzazat,Sinai, Egypt: planktonic foraminiferal biostratigraphy,mineralogy and geochemistry

The Qreiya Beds that record the ‘mid-Paleocene event’ at Gabal Nezzazat occur within the Igorina albeari (P3b) Zone and constitute part of a 14-m thick shale succession that ranges in age from Early to Late Paleocene. They are composed of four alternating dark grey and brown shale beds, which are thinly laminated, phosphatic, organic-rich and extremely sulphidic. They are characterized by distinct enrichment and high peak anomalies in chalcophiles (Zn, Co, Ni, Cu and Pb) and organic association elements (V and Cr), especially within the brown organic-rich beds. It is concluded that these elements are incorporated into the phosphatic debris, sulphides and organic matter. In contrast, the grey beds are enriched in clay minerals and quartz. Clay mineral assemblages indicate alternating periods of warm/humid climate (high kaolinite) and dry climate (low kaolinite) during the formation of the grey and brown beds, respectively. The sediments of the Qreiya Beds yield lithological, biotic, geochemical and mineralogical data indicative of suboxic/anoxic marine environments as a result of high productivity and/or upwelling. The top metre of the succession below the Qreiya Beds is characterized by a progressive change from faunas dominated by praemurcurids to faunas dominated by Morozovilids, and by a progressive upward decrease in δ¹³C_carb and δ¹⁸O_carb values. The foraminiferal faunal change may reflect shallowing and warming preceding deposition of the Qreiya Beds. The change in isotopic values is inferred to be the result of surface weathering, fluvial input and diagenesis with no evidence of any primary change that could support presence of a hyperthermal event.     

基于生物酶的固土技术在香港的应用研究

传统加固土体的方法主要是通过在土中加入一定量的高性能掺合剂使之成为一种强度较高的复合土体,但这种方法需要较长的养护时间,且不经济。利用一种新型实用的生物酶固化技术,针对香港地区3种常见的海洋黏土、完全风化花岗岩和完全风化凝灰岩,开展了土体加固试验研究。试验结果表明,生物酶对海洋土的加固效果最好,强度增加最高可达20%,而生物酶对完全风化花岗岩的加固效果则不太理想,抗剪强度指标只有少许改变。此外,海洋土和完全风化凝灰岩的压缩性因为生物酶的作用反而有所增强。最后,从微观上分析了生物酶固土作用的本质,指出固土效果主要缘自于生物酶分子与土中的黏土矿物分子发生相互作用产生的胶结作用。     

蒋家沟砾石土的特性及其对斜坡失稳的意义

云南蒋家沟是世界上著名的由降雨导致泥石流、浅层滑坡频发的沟谷之一。组成蒋家沟斜坡表层的砾石土具有孔隙度高、级配宽、不均匀系数大等特点,级配曲线为上凹型或双峰型,为内在不稳定性土。X射线衍射分析表明,粒径小于1 mm 的细粒部分主要由绿泥石和伊利石等黏土矿物及次生石英组成,黏土矿物会影响砾石土的物理力学性质。在环境电镜扫描中观测了砾石土的微观结构,发现一种特殊的“桥式”胶结结构,并在遇水条件下发生断裂,不仅降低了微弱黏聚力,而且土颗粒容易分离成粒径为数十微米的散微粒。这与砾石土中黏性部分具有高分散性有关。此外这些散微粒在自滤过程中会能发生运移,并在孔喉等处积聚而堵塞孔隙,会降低砾石土的渗透性以及有利于斜坡中暂态上层滞水的积聚。     

吸附离子对粉质粘土及改良土特性的影响

利用疏浚土有机质含量高、吸附能力强和低渗透性等特点,探讨将其作为填埋场黏土衬垫改性材料的可能性。针对粘土垫层所关心渗透性及强度两个基本问题,比较了粉质黏土、改良土（粉质黏土添加疏浚土）吸附离子前后的变化。吸附K+、Cu2+后粉质黏土、改良土的渗透系数随着土中离子含量的增加而增大,但对改良土渗透系数的影响要小于粉质黏土;吸附离子后,粉质黏土摩擦角增幅不大,黏聚力有较大增长,而改良土的黏聚力增长较少,摩擦角增长较快。总体而言,添加一定量的疏浚土能改善吸附离子对黏土垫层的影响。采用SEM电镜试验拍摄了离子吸附前后土体微观结构的变化,并从扩散双电层理论出发,解释了吸附离子对粉质黏土及改良土的影响。