Assessment of dynamic site response of the peat deposits at an industrial site (Turkey) and comparison with some seismic design codes

Peat is an organic soil type with properties of high compressibility and high water content. Peat deposits are often unsuitable for supporting structures of any kind due to their susceptibility to cause a number of geo-engineering problems, such as settlement, slope instability and soil amplification. There are peatlands in Turkey, although these are not so extensive as in other countries, such as Canada, where peatlands are very common. One of the peat deposits in Turkey is located close to the city of Kayseri (Central Anatolia), and industrial structures have been built on these deposits. This paper focuses on one part of a comprehensive research project conducted by the authors on various geo-engineering aspects of the peat deposits in this industrial site, with the main aims to investigate and assess some of the dynamic properties of the peat deposits in this area, to determine and assess their seismic site response and to compare them with the design spectra recommended in the current seismic codes of Turkey and Europe. In the study shear wave velocities of the peat deposits were determined with seismic measurements, and some dynamic properties of the peat were obtained from the resonant column and torsional shear tests. Then site response analyses were carried out and the results were compared with the design spectra recommended for loose-soft soils by the Turkish Seismic Design Codes and European Construction Design Codes. The comparisons suggest that the response spectra of the investigated peat deposits are greater than those recommended in the Turkish Seismic Codes and that at periods of > 0.3–0.5 s the peat will cause an increase in amplification. Although the response spectra of the peat tested show a better agreement with those recommended in the European codes, they show differences at periods of > 1 s.

     

Link between DOC in near surface peat and stream water in an upland catchment

Hydrologic transport of dissolved organic carbon (DOC) from peat soils may differ to organo-mineral soils in how they responded to changes in flow, because of differences in soil profile and hydrology. In well-drained organo-mineral soils, low flow is through the lower mineral layer where DOC is absorbed and high flow is through the upper organic layer where DOC is produced. DOC concentrations in streams draining organo-mineral soils typically increase with flow. In saturated peat soils, both high and low flows are through an organic layer where DOC is produced. Therefore, DOC in stream water draining peat may not increase in response to changes in flow as there is no switch in flow path between a mineral and organic layer. To verify this, we conducted a high-resolution monitoring study of soil and stream water at an upland peat catchment in northern England. Our data showed a strong positive correlation between DOC concentrations at -1 and -5 cm depth and stream water, and weaker correlations between concentrations at -20 to -50 cm depth and stream water. Although near surface organic material appears to be the key source of stream water DOC in both peat and organo-mineral soils, we observed a negative correlation between stream flow and DOC concentrations instead of a positive correlation as DOC released from organic layers during low and high flow was diluted by rainfall. The differences in DOC transport processes between peat and organo-mineral soils have different implications for our understanding of long-term changes in DOC exports. While increased rainfall may cause an increase in DOC flux from peat due to an increase in water volume, it may cause a decrease in concentrations. This response is contrary to expected changes in DOC exports from organo-mineral soils, where increase rainfall is likely to result in an increase in flux and concentration.     

Strip loading test theory and equipment development

One of the important issues for geotechnical engineers is the characterization of soil properties such as cohesion and internal friction angle by means of soil testing. A new experimental method of soil characterization based on the surface displacement of strip loaded soils is proposed. The theory to relate the soil deformation/displacement to soil strength properties is presented and compared with a series of conventional soil characterization techniques with direct shear tests. The proposed/developed strip loading tests provide reasonably accurate results compared with traditional direct shear tests. The new strip loading physical simulation and testing devices are helpful for understanding soil strength concepts and also provide an effective bridge connecting with engineering mechanics and foundation engineering courses instructions wherein derivation of bearing capacity theory equations is based on the same Mohr-Coulomb soil strength parameters. The advantages, limitations, and use of the strip loading modeling/testing technique in engineering education and further more in depth researches are discussed in the concluding remarks part.     

The chronology of anthropogenic,atmospheric Pb deposition recorded by peat cores in three minerogenic peat deposits from Switzerland

Peat cores were collected from three minerogenic peatlands in Switzerland: La Tourbière des Genevez (TGE), in Canton Jura; Gola di Lago (GDL), in Canton Ticino; and Mauntschas (MAU), in Canton Grisons. Chemical analyses of the pore waters and the peats document the increasingly minerogenic character with depth. In particular, the Sr concentration profile in the peats reflects the growing importance of mineral sediment dissolution with increasing distance below the peat surface. Despite this circumstance, Pb concentrations are greatest in the surface layers, and decrease with depth. Thus, dissolution of the basal sediments at these sites appears to be an unimportant source of Pb, compared with atmospheric deposition. Twenty-one new radiocarbon age dates for the three cores provide a chronology of Pb enrichment, and these are consistent with the record of atmospheric Pb deposition recorded by the ombrotrophic peat bog 'Etang de la Gruère' (EGR). Sediment samples from TGE and EGR were reacted at pH 5 with ammonium acetate to dissolve the carbonate fraction, filtered, and the residues analyzed using XRF. These analyses show that much of the Ca, Mg, Sr and Mn is lost when the carbonate fraction is dissolved, but this process does not measurably affect Pb. This finding suggests that carbonate dissolution dominates the weathering of the sediments underlying these peat deposits, but this fraction does not contain significant concentrations of Pb. Minerogenic peat deposits such as those described here, therefore, can serve as reliable archives of atmospheric Pb deposition, provided that mineral dissolution in the underlying sediments does not contribute measurably to the Pb inventory of the peat profile.     

Effects of fine aggregate content on the mechanical properties of the compacted decomposed granitic soils

Decomposed granitic soil is widely used as the subgrade material in Korea. The mechanical behavior of the soil can differ depending on the fine aggregate content of the soil. Due to particle crushing during loading and compaction, the soil may behave as either cohesive or cohesionless. In order to evaluate the effects of fine aggregate content on the mechanical properties of the compacted decomposed granite soils, the direct shear test, the triaxial shear test as well as some fundamental property tests were made by using samples with the five different fine aggregate contents of 10, 20, 30, 40, and 50% by weight. Results of the triaxial tests showed that as the percentage of the fine aggregates decreased, the cohesion decreased as well as the internal friction angle increased. In the direct shear test, the soils containing lower amount of fine aggregates exhibited that the shear strength was considerably reduced after it reached the peak value. Comparably, soils with the high fine aggregates showed that the shear strength was quite constant after the peak strength. The critical state friction parameter showed that the parameter decreased with an increase of the fine aggregate content. Results of the triaxial and direct shear tests indicated also that the fine aggregate content of 30% could be one indicator for soil materials behaving either as sand or as clay materials. Thus fine aggregate content, less than 30% by weight, could be more obtainable for the subgrade materials when leading also to the increased stability of the roads. With the lower fine aggregate content the soils then also show similar and better characteristics of sands not clays. Further studies are recommended on understanding of the mechanical behavior of the decomposed granitic soils.     

Influence of sample preparation and mode of testing on the shear strength characteristics of laterite soils from Southwestern Nigeria

The Shear Strengths of four laterite soils from Southwestern Nigeria are investigated through:

1. consolidated undrained triaxial compression tests with pore water measurements on Standard Proctor compacted soils and
2. direct shear tests on remoulded soils.

The Shear Strength parameter obtained in both cases are high with those of the first method being generally higher than those of the second method. However, in view of the relative ease of execution, the second method is preferred especially with regards to local/minor and farm constructions.     

昆明泥炭、泥炭质土的力学特性研究

昆明盆地由于阳光充足,水温适宜,又有湖泊、河流、洼地等地貌条件,有利于水生、湿生植物的生长蔓延,向沼泽化辟落发展,所以泥炭、泥炭质土的分布,是有其地区特点的。现建设现代新昆明,有许多建筑必须建设在这样的地基土上,因此,有关昆明泥炭、泥炭质土工程特性及工程应用的研究     

新疆昭苏县草甸土的工程性质试验研究

由于目前对草甸土的工程性质了解甚少,一方面引起了草甸土与草炭土、泥炭等的混淆,另一方面导致了在设计过程中不知如何选择相应的处治措施。鉴于此,以新疆伊犁昭苏县草甸土层为研究对象,参照一般土体的室内土工试验方法,测试了草甸土的比重、重度、烧失量、渗透系数、抗剪强度、无侧限抗压强度等物理力学指标,并将试验结果与国内外草炭土、泥炭、泥炭质土的工程特性进行了对比分析。结果表明:按照有机质含量分类,新疆昭苏县草甸土属于泥炭质土;其含水率处于泥炭质土的低限附近,而重度则高于一般泥炭和泥炭质土的重度,具有较好的渗透性、很高的压缩性;草甸土中的草根可以显著提高土体的黏聚力,但对内摩擦角的影响不明显;无侧限抗压强度试验过程中草甸土未发生类似于一般黏土的剪切破坏,而是产生了很大的压缩变形和鼓胀变形;草甸土在受荷载后主固结沉降完成很快,其主固结系数随着固结压力的增大线性减小;当固结压力超过100 k Pa时,草甸土的主固结比较小,说明此时草甸土的次固结变形量不容忽视,地基沉降计算中应予以考虑。     

Changes in chemical composition and engineering properties of gypseous soils through leaching: an example from Mashhad,Iran

Gypseous soils are considered problematic when used as the foundation in civil engineering structures such as roads, buildings and dams, due to their solubility. These soils are resistant and have good engineering properties in their dry state. However, when saturated by rainwater or a rising groundwater table, the soluble minerals are washed out, resulting in the subsidence of the structures built on them. In the recent decades, buildings constructed in the Southern Mashhad Metropolitan Area, Iran, have been widely faced with this problem. Since the changes in chemical composition and engineering properties of these soils are based on the amount of dissolved gypsum, the focus of this study is to characterize the soluble soils of this area and their changes throughout the leaching process. Thirty-eight samples were taken from different locations in the area. Chemical tests were conducted on the samples and the gypsum and sulfate concentration maps were produced based on these results, combined with the previously available data from 511 boreholes drilled in the area. Seven soil samples with different gypsum concentrations were selected for further analysis in four major groups of tests, including hydraulic tests (permeability and solubility), chemical tests (chemical analysis of soils samples and total dissolved solids, calcium hardness and chlorine of the leachate samples), physical tests (grain size analysis, Atterberg limits and specific gravity) and mechanical tests (consolidation and direct shear). Changes in the mentioned parameters were investigated through a 5-day leaching process. The results indicate that extensive dissolution of gypsum and removal of gypsum bonding between soil particles change soil chemical composition and decrease the soil compressibility and strength parameters. Therefore, the structures built in this area are in high risk of subsidence and foundation failure; proper measures should be taken to improve the soil quality before construction.     

Geotechnical characterization of collapsible salty sands subjected to monotonic and cyclic loadings – A case study for areas with high seismicity

Collapsible soils are typically found in arid regions and often have an aeolian or alluvial origin. In their natural states, they may have a low moisture content and cemented structure that can contribute to high strength and stiffness; however, wetting or saturation can reduce the strength and stiffness due to loss of the cementation. This paper presents a geotechnical characterization of collapsible salty sands in the highly seismic southern coast of Peru, which makes the characterization of their dynamic properties and expected response to earthquake-induced demands (e.g., liquefaction) of primary importance. The geotechnical characterization was performed on intact and remolded samples utilizing various field and laboratory tests, including oedometer, direct shear, static triaxial, cyclic simple shear, torsional resonant column, plate loading, and MASW tests. The results revealed insights on the geotechnical properties and mechanical response of collapsible soils and the effects of salt cementation. The results indicated: 1) a decreasing brittle and collapsible behaviors with decreasing cementation while maintaining consistent post-collapse residual strength; 2) oedometer and in situ plate loading tests showed a sudden increase in deformations once cementation is broken; 3) higher dilation potential of collapsible soils as compared to natural sands; 4) decrease in the maximum shear modulus due to the loss of cementation; 5) increase in the stress dependence of the maximum shear modulus with loss of cementation; and 6) a higher resistance to liquefaction for the collapsible soils, even after washing, as compared to natural sands, which may be ascribed to the more pronounced dilation potential.     

土的卸载体缩与可恢复剪胀

卸载体缩是很多土在剪切试验中表现出的一种变形特性。它与土的物理性质、试验的应力路径、试验的边界条件等因素有关 ,也和土的各向异性有关。卸载体缩源于土的可恢复剪胀变形 ,在剪胀过程中土颗粒一般是从低势能状态向高势能状态变化 ,处于不稳定状态 ,当剪应力消除时 ,有很大部分的剪胀变形将会恢复。     

滨海吹填造陆地区岩土工程勘察问题分析与评价

围海造陆是当今沿海国家及城市开发土地资源的重要措施之一。以天津滨海某工程勘察为例,根据建设项目的构筑物特点、地基基础方案及场地土工程性质,采用了钻探取样、标准贯入试验、剪切波测试、十字板剪切测试、浅层平板载荷试验、室内试验等多种勘察手段获得了准确详实的地质资料,并对勘察过程中涉及到的冲填土、液化土、软土震限、负摩阻力、大面积群桩施工影响等关键技术问题进行了分析与评价,为该工程的设计及施工提供了可靠的岩土参数及建议。     

黑麦草根系加固粘土的剪切强度性能研究

植被在增强边坡稳定性方面有着积极的作用,其作为一种兼顾生态保护和边坡治理的护坡方式,在工程实践中得到了广泛的应用.为了研究植物根系加筋土的抗剪特性,以室内培育的黑麦草根系为加筋土的筋材,制备了不同含根量和含水率的重塑试样,通过直剪试验分析其抗剪强度特性的变化规律.研究结果表明:黑麦草根系加筋增强了土体的抗剪强度,表现为...     

深部土层失水变形时土与井壁相互作用试验与理论研究

介绍了用高压直剪仪和三轴伺服仪测定大埋深土与井壁相互作用试验方法 ,得到了土与井壁相互作用剪应力 -位移曲线、单位刚度系数和强度等参数。结合试验结果 ,分析了深部土层失水变形时 ,土与井壁接触带相互作用深部为塑性浅部为弹性的变形特点。建立了土与井壁相互作用理想弹塑性分析模型 ,得到了计算井壁附加竖直位移、应变和附加应力的解析公式 ,并讨论了其随深度和深部土层压缩量等因素变化的规律。最后给出计算实例 ,说明了理论研究的实用性     

Investigation on shear modulus and damping ratio of Algiers marls under cyclic and dynamic loading conditions

A sound knowledge of the dynamic properties of soils is needed to solve several geotechnical engineering problems associated with earthquakes. Here we describe a laboratory investigation performed to measure the dynamic properties of the Plaisancian deposit of marls in the Algiers region using cyclic triaxial tests, cyclic double specimen direct simple shear tests, cyclic torsional shear tests and dynamic resonant column tests. The key parameters governing the nonlinear soil behavior under cyclic/dynamic loading and their relative importance in terms of affecting the dynamic properties of soils, wich are communaly represented by the normalized equivalent shear modulus reduction and damping ratio curves, are illustrated and discussed. We also address the differences in the deduced parameters obtained with different tests, procedures and interpretation criteria. The comparison between test results and empirical or semi-empirical relations for normalized equivalent shear modulus and damping ratio curves highlights a number of limitations and shortcomings of predictive models currently widely used.

     

典型红粘土与膨胀土的对比试验研究

通过室内试验对广西贵港红粘土、湖北荆门弱膨胀土与中膨胀土的物理力学性质指标、原状样脱湿过程中的强度变化、击实样泡水前后强度变化以及脱湿吸湿性能等方面进行了对比试验研究。结果表明：3种土原状样脱湿过程中的强度指标在土体裂隙性与基质吸力双重因素的作用下表现出完全不同的变化规律；由于红粘土与膨胀土膨胀性能上的差异，不同含水量的击实样泡水后的干密度峰值与加州承载比(CBR)峰值所对应的原击实样含水量比最优含水量有不同程度的增大；土体因矿物成分的差异而表现出明显不同的脱湿、吸湿速率。广西贵港红粘土与荆门膨胀土虽然在一些物理力学指标上具有相似之处，但其力学特性与水敏性特征具有明显的差异，在实际工程中应给予充分重视。     

Coal Bottom Ash as a Geomaterial: Influence of Particle Morphology on the Behavior of Granular Materials

Previous studies of mechanical properties of solid residue byproducts such as coal bottom ash have been restricted to small and intermediate shear strains of approximately 0.1-20%, due to the limitations of the standard equipment used (e.g. triaxial and direct shear tests) and to confining pressures up to around 1.5 MPa. The objective of the present research was to study the behavior of coal bottom ash sampled in southern Brazil, ranging from very small to very large shear strains, as well as to high isotropic pressures, to determine its complete behavior. Comparisons are made with results from a granular soil with a similar grading and also with those of uniform sand with similar average particle size. High pressure isotropic compression and bender element tests, as well as standard triaxial tests and ring shear tests were carried out on compacted specimens of coal bottom ash, a sandy residual soil with a similar grain size distribution, as well as on a uniform sand. In order to explain the effect of the particle morphology of the coal bottom ash on its mechanical behavior, an investigation was also undertaken based on thin section and scanning electron micrographs, which revealed intra-particle voids in the coal ash. The results indicate that the general behavior of the bottom ash compares favorably with conventional granular materials, providing a promising solution to the disposal problem, and also an economic alternative to the use of conventional soils as construction materials.     

防渗土样的分散性与渗透变形试验研究

 通过碎块、双比重计、针孔、孔隙水可溶盐及交换性钠百分比等5种方法的土样分散性试验和渗透变形试验，对拟建的青海班多土石坝防渗心墙土样进行分散性鉴定及渗透稳定性试验研究。研究结果表明，虽然土样具有强分散性，但在合适的反滤料保护下，分散性土样仍具有较高的抗渗性能，裂缝土体也不会发生流失；在做好反滤层设计的前提下，用分散性土样作为防渗心墙的填筑土样是可行的。     

防渗土样的分散性与渗透变形试验研究

通过碎块、双比重计、针孔、孔隙水可溶盐及交换性钠百分比等5种方法的土样分散性试验和渗透变形试验,对拟建的青海班多土石坝防渗心墙土样进行分散性鉴定及渗透稳定性试验研究。研究结果表明,虽然土样具有强分散性,但在合适的反滤料保护下,分散性土样仍具有较高的抗渗性能,裂缝土体也不会发生流失;在做好反滤层设计的前提下,用分散性土样作为防渗心墙的填筑土样是可行的。     

Definitions and engineering classifications of tropical lowland peats

Peat classification methods for engineering purposes and the main factors and aspects of these classification systems are discussed. Among the factors that enter into the classification of tropical lowland peats are the organic content and degree or level of humification (on the von Post scale). The organic content as a percentage of the total content determines whether an organic soil is classified as a slightly organic soil (3–20 % organic content), an organic soil (20–75 % organic content), or a peat (more than 75 % organic content). The ASTM standard method of classifying peat is outlined in the Standard Classification of Peat Samples by Laboratory Testing (ASTM D 4427), which includes the use of the ASTM D 5715 (fiber content by field testing for degree of humification) field test method. The von Post humification test (von Post classification system) involves squeezing the peat and the material that is extruded between the fingers, examining the material, and classifying the soil as belonging to one of ten (H1–H10) humification or decomposition categories. Peats are then further subdivided into fibric or fibrous peats (humification range of H1–H3), hemic or moderately decomposed peats (H4–H6), or sapric or amorphous peats (H7–H10). The classification of organic soil or peat for engineering purposes mainly involves using the ignition test (ASTM D 2974) to determine the organic content or determining the percentage of organic content lost on ignition.