Engineering characteristics and environmental impacts of the expansive Ankara Clay,and swelling maps for SW and central parts of the Ankara (Turkey) metropolitan area

Volume-changing clay soils constitute the most costly natural hazard to buildings on shallow foundations. With the existing expansive clays in Ankara, low-rise buildings at the southwest part of the city have shown damage resulting in considerable maintenance costs. This paper reports the findings of an experimental investigation emphasizing the swelling behavior of Ankara Clay and correlations between the swelling parameters and other soil properties, and present a synthesis of observed damage details. The poor performance of the affected light-weight structures is assessed in the light of environmental conditions. In addition, swelling maps for SW and central parts of the Ankara metropolitan area, based on measured and predicted swelling parameters, are constructed for the purposes of land-use planning and general assessment of environmental problems. The experimental results suggest that the clay has high-to-very high activity, depth of active zone generally ranges between 1–2 m, the use of remolded and desiccated specimens seems to be a better approach in swelling tests, and the empirical equations based on two or more index or physical properties are good predictors for the estimation of the swelling potential of the clay. High swelling pressures exerted by the soil, flat topography and poor drainage, climatic conditions and poor construction methods are the main reasons of the structural damage observed at the study site.     

Environmental geological and geotechnical investigations related to the potential use of Ankara clay as a compacted landfill liner material, Turkey

Clay-bearing Upper Pliocene red clastics and Quaternary alluvial deposits occupy the Ankara basin. The clayey levels of the Upper Pliocene deposits, referred to as Ankara clay, is considered as a source for compacted clay liners due to their low coefficients of permeability and widespread distributions throughout Ankara. This study investigates the geological, geotechnical and mineralogical properties of the founding clayey soils at two sites of the Ankara region. The geotechnical index properties along with the hydraulic conductivities of the clayey soil samples collected from these sites were determined. A mathematical relation between the clay mineralogical content and hydraulic conductivity was established. The results of this investigation show that, from a geotechnical point of view, Ankara clay may be regarded as a highly suitable material for a compacted clay landfill liner given that its mineralogical compatibility with leachate is confirmed.     

用孔压静力触探和室内固结试验求取土的固结系数的对比研究

土的固结系数是软土地基计算与处理设计中的关键参数，本文根据先进的孔隙水压力静力触探技术现场测试求出的固结系数和室内固结试验所求固结系数，进行了大量统计对比研究，发现两者之间存在很好的线性相关关系，并论述了两种方法求取固结系数的原理及步骤，以及孔压静力触探求固结系数的许多优点。     

人工冻土围压SHPB试验与冲击压缩特性分析

利用分离式Hopkinson压杆（SHPB）,以铝质套筒作为围压装置,分别研究温度为-8、-12、-16 ℃在不同应变率下的人工冻结黏土围压状态变形特征和轴向动态应力-应变关系。研究结果表明：在围压状态下,冻土呈黏塑性破坏特征;当人工冻结黏土温度为-16 ℃、平均应变率分别为410、457、525、650、827 s-1时,其最大应力分别为10.76、12.18、14.27、20.24、23.34 MPa,最大应变分别为0.081 7、0.097 2、0.105 0、0.131 0和0.166 0,表现出较强应变率效应;-12 ℃和-16 ℃时在应变率为457 s-1下的最大应力分别为8.28 MPa和12.18 MPa;当应变率相同时,温度越低,最大应力越大,冻结黏土表现出较强的温度相关性。人工冻土的动力学特性为冻土开挖方法的研究提供依据。     

粘土对地下水中U（VI）的吸附作用及其污染控制研究

进行了U（VI）在粘土上吸附的批实验，其中，粘土样采自我国南方某大型铀尾矿库库底。实验结果表明U（VI）在粘土上的吸附与浸泡液的pH值呈强烈的非线性关系，在pH值近中性时，U（VI）在粘土上的吸附达到了一个最大值，而在偏酸性或偏碱性条件下，U（VI）在粘土上的吸附迅速减少；运用表面络合理论建立了U（VI）在粘土上吸附的表面络合模型（DLM），该模型很好地拟合了实验数据。模型检验表明，它可以精确预测U（VI）在不同热力学条件下的吸附行为；此外，模拟结果表明，U（VI）的粘土上吸附在酸性条件下受固液比（M／V）影响明显，而在碱性条件下主要受浸泡液中HCO3^-和CO3^2-的控制。     

抛石挤淤深度的计算方法和模型试验

在含水率大、抗剪强度低的淤泥中采用抛石挤淤的办法加固地基或建造围埝,处理效果好且经济效益显著,因此得到了广泛地应用。抛石在软弱地基中下沉,直至其重力与地基承载力平衡为止。挤淤所形成截面的形状及抛石下沉深度的计算是此项研究的重点,基于抛石截面为倒梯形和矩形两种形状的假定,考虑淤泥表面隆起对承载力的影响,利用土体极限平衡理论,推导出抛石挤淤深度与抛石高度的关系。通过抛石挤淤的模型试验和现场挤淤的数据,分析比较两种假定下挤淤公式的准确性和适用性,试验结果与公式吻合性很好,该研究结果可为相关工程的设计和施工提供参考。     

现场室内两用大型直剪仪研制(I)：结构设计

直剪仪是测定岩土体抗剪强度参数应用最为普遍的一种试验仪器。从直剪仪的结构和大型直剪仪的研制两个方面对直剪仪的研究现状做了介绍，在此基础上，对新近研制的现场室内两用大型直剪仪的结构组成、工作机理及其特点进行了详细分析。该大型直剪仪与常规直剪仪相比，具有较大的优越性，其测试结果更加准确。适用范围广，测试精度高，可应用于现场和室内试验。     

现场室内两用大型直剪仪研制(I):结构设计

直剪仪是测定岩土体抗剪强度参数应用最为普遍的一种试验仪器。从直剪仪的结构和大型直剪仪的研制两个方面对直剪仪的研究现状做了介绍,在此基础上,对新近研制的现场室内两用大型直剪仪的结构组成、工作机理及其特点进行了详细分析。该大型直剪仪与常规直剪仪相比,具有较大的优越性,其测试结果更加准确。适用范围广,测试精度高,可应用于现场和室内试验。     

大型现场室内两用直剪仪研制(II):试验测试

利用新近研制的大型现场室内两用直剪仪,对两种不同性质的砂样进行了剪切试验。在对干砂的直接剪切试验特性进行综述的基础上,从多方面对该大型直剪仪得出的干砂剪切试验数据进行了分析验证,结果表明该大型直剪仪得出的试验数据一致性好、可靠性较高,说明该大型直剪仪的基本剪切性能稳定,可进一步应用于相关岩土材料的试验研究。     

软粘土的各向异性和小应变条件下的本构模型(ASM)

以能量方程为基础推导出各向异性和小应变条件下弹塑性的本构方程,并将屈服面与修正桥模型和试验测得的屈服面进行了对比,表明新的屈服面比修正剑桥模型更接近试验结果,采用从初始应力到状态边界面的距离为参数的系数来修正硬化准则以模拟土体小应谱条件下的应力－应变特征。将新的本构模型编入有限元程序,对小应变试验进行了计算分析,计算结果表明,新的模型比修正剑桥模型能更好地反映土体的主要力学特性。     

Modification of the liquefaction potential index and liquefaction susceptibility mapping for a liquefaction-prone area (Inegol,Turkey)

Although some liquefaction assessment methods were proposed to evaluate the liquefaction potential of sandy soils, the conventional method based on the standard penetration test (SPT) has been commonly used in most countries and in Turkey. However, it alone is not a sufficient tool for the evaluation of liquefaction potential. The liquefaction potential index was proposed to quantify the severity of liquefaction. Nevertheless, the liquefaction potential index and the severity categories do not answer the question: "Which areas will not liquify?" Besides, the categories do not include a "moderate" category; on the other hand, the "high" and "low" categories are included. This situation is also contrary to the nature of classification schemes. In this study, the liquefaction potential index and the liquefaction potential categories were modified by considering the existing form of the categories based on the liquefaction potential index. While the category of low was omitted, the categories of moderate and "non-liquefied" were adopted. A factor of safety of 1.2 was assumed as the lowest value for the liquefaction potential category of non-liquefied. In addition, the town of Inegol in the Marmara region became the case study for checking the performance of the liquefaction potential categories suggested in this study.     

Comparison between Neuman (1975) and Jacob (1946) application for analysing pumping test data of unconfined aquifer

Pumping test of a water table aquifer is carried out to estimate the aquifer parameters, the obtained data were analysed through the solution of both Neuman (1975) and Jacob (1946) methods through AQTESOLV and Spreadsheet programs, the results of each methods are compared to evaluate the applicability and accuracy of the solution theoretically and practically. In the paper an example is presented, which is conducted for a constant rate pumping test from Ohio, in Fairborn (near Dayton), and it supplied by S.E. Norris (U.S. Geological Survey, Columbus, Ohio). The main objective of this study is to introduce both program and the way of the applications, and compare the results and the hand on of both programs in the field.     

Landslide susceptibility mapping for a landslide-prone area (Findikli,NE of Turkey) by likelihood-frequency ratio and weighted linear combination models

Landslides are very common natural problems in the Black Sea Region of Turkey due to the steep topography, improper use of land cover and adverse climatic conditions for landslides. In the western part of region, many studies have been carried out especially in the last decade for landslide susceptibility mapping using different evaluation methods such as deterministic approach, landslide distribution, qualitative, statistical and distribution-free analyses. The purpose of this study is to produce landslide susceptibility maps of a landslide-prone area (Findikli district, Rize) located at the eastern part of the Black Sea Region of Turkey by likelihood frequency ratio (LRM) model and weighted linear combination (WLC) model and to compare the results obtained. For this purpose, landslide inventory map of the area were prepared for the years of 1983 and 1995 by detailed field surveys and aerial-photography studies. Slope angle, slope aspect, lithology, distance from drainage lines, distance from roads and the land-cover of the study area are considered as the landslide-conditioning parameters. The differences between the susceptibility maps derived by the LRM and the WLC models are relatively minor when broad-based classifications are taken into account. However, the WLC map showed more details but the other map produced by LRM model produced weak results. The reason for this result is considered to be the fact that the majority of pixels in the LRM map have high values than the WLC-derived susceptibility map. In order to validate the two susceptibility maps, both of them were compared with the landslide inventory map. Although the landslides do not exist in the very high susceptibility class of the both maps, 79% of the landslides fall into the high and very high susceptibility zones of the WLC map while this is 49% for the LRM map. This shows that the WLC model exhibited higher performance than the LRM model.     

A mantle- and a lower crust-derived bimodal suite in the Yusufeli (Artvin) area, NE Turkey: trace element and REE evidence for subduction-related rift origin of Early Jurassic Demirkent intrusive complex

The Yusufeli area, in the Eastern Black Sea Region of Turkey, contains a crystalline complex that intruded into the Carboniferous metamorphic basement and is composed of two intrusive bodies: a gabbro-diorite and a tonalite-trondhjemite. The mafic body (45–57 wt% SiO₂) displays a broad lithological spectrum ranging from plagioclase-cumulate to quartz diorite. Primitive varieties of the body have Mg-number, MgO and Cr contents that are close to those expected for partial melts from mantle peridotite. Data are consistent with the magma generation in an underlying mantle wedge that was depleted in Zr, Nb and Ti, and enriched in large ion lithophile elements (K, Rb, Ba, Th). However, high Al₂O₃, CaO and generally low Ni (<65 ppm) contents are not in agreement with the unfractionated mantle-derived primitive magmas and require some Al₂O₃- and CaO-poor mafic phases, in particular, olivine and orthopyroxene. Absence of orthopyroxene in crystallization sequence, uralitization, and a common appearance of clinopyroxene surrounded by hornblende imply an anhydrous phase fractionated from highly hydrous (5–6%) parent. Geochemical modelling suggests derivation by 15–20% melting of a depleted-lherzolitic mantle. The tonalite-trondhjemite body (58–76 wt% SiO₂) ranges in composition from quartz diorite to granodiorite with a low-K calc-alkaline trend. Although LILE- and LREE- enriched characteristics of the primitive samples imply a metasomatic sub-arc mantle for their source region, low MgO, Ni and Cr concentrations rule out direct derivation from the mantle wedge. Also, lack of negative Eu anomalies suggests an unfractionated magma and precludes a differentiation from the diorites of mafic body, which show negative Eu anomalies. Their Na enrichments relative to Ca and K are similar to those of Archean tonalites, trondhjemites and granodiorites and Cenozoic adakites. However, they exhibit important geochemical differences from them, including low-Al (<15 wt%) contents, unfractionated HREE patterns and evolution towards the higher Y concentrations and lower Sr/Y ratios within the body. All these features are obtained in experimentally produced melts from mafic rocks at low pressures (≤5 kbar) and also widespread in the rocks of arc where old (Upper Cretaceous or older) oceanic crust is being subducted. Major and REE modelling supports formation of the quartz dioritic parent to the felsic intrusive rocks by 70% partial melting of a primitive gabbroic sample (G694). Therefore, once taking into account the extensional conditions prevailing in the Pontian arc crust in Early Jurassic time, former basic products (gabbros) seem to be the most appropriate source for the tonalite-trondhjemite body. Magmatic emplacement of stratigraphically similar lithologies in the Pulur Massif, just southwest of the Yusufeli, was dated to be 184 Ma by the ⁴⁰Ar/³⁹Ar method on amphibole, and is compatible with the initiation of Early Jurassic rifting in the region.