生石灰激发GGBS固化高含水率香港海相沉积物的物理力学性质研究

海相沉积物处置已成为一项全球范围的挑战。在传统固化/稳定化方法中,环境污染严重的波兰特水泥(PC)是一种被广泛使用的固化剂。在此背景下,一种环境友好型的固化剂(生石灰与粒化高炉矿渣(简称GGBS)的混合料)取代PC来用在土壤改良领域。使用生石灰激发GGBS固化处理高含水率海相沉积物,并与PC固化海相沉积物进行比较。通过物理、化学试验及无侧限抗压强度试验分析了生石灰-GGBS固化海相沉积物的物理、化学和强度特性。结果表明:与PC固化海相沉积物相比,生石灰-GGBS固化沉积物具有体积收缩大、含水率低和密度略高的物理特性。随着生石灰比例的降低和养护时间的延长,生石灰-GGBS固化沉积物的pH值逐渐降低。生石灰-GGBS固化沉积物的无侧限抗压强度呈先增大(生石灰:固化剂为0.05～0.15)后减小(生石灰:固化剂为0.15～0.3)再增大(生石灰:固化剂为0.3～0.4)的趋势;当生石灰与固化剂的比值为0.15及0.4时,强度达到最大值;当生石灰与固化剂的比值为0.15时,生石灰-GGBS固化沉积物达到的峰值强度是相同条件下PC固化沉积物强度的1.4倍。该研究结果证实了GGBS与少量生石灰组合...     

Simulation of cement-improved clay structures with a bonded elasto-plastic model: A practical approach

Engineering practice has usually dealt with the treated soil bodies using simplistic constitutive models (e.g. elastic perfectly-plastic Mohr–Coulomb). In this paper, a more refined bonded elasto-plastic model is here applied, with emphasis on the ease of calibration. Empirical studies have identified the ratio of cement content to the cured mixture void ratio as a controlling variable for mechanical response. This observation is elaborated upon to show that measuring porosity and unconfined compressive strength is enough to initialize the state variables of a bonded elasto-plastic model. Data from cement-improved Bangkok clay is employed to illustrate and validate the calibration procedure proposed. The structure-scale consequences of the constitutive model choice for the soil–cement are explored through the parametric analysis of an idealized excavation problem. A treated soil–cement slab is characterized by increasing cement contents in the clay–cement mixture. Two sets of parametric analysis are run characterizing the clay–cement either with a linear elastic-perfectly plastic model or with the bonded elasto-plastic model. The same values of unconfined compressions strength (UCS) are specified for the two models to make comparisons meaningful. Results from both series of analysis are compared highlighting the differences in predicted behaviour of the retaining wall and the excavation stability.     

活性MgO碱性激发粒化高炉矿渣固化黏土的抗硫酸盐侵蚀试验研究

通过系列室内试验,研究了硫酸盐长期浸泡环境下GGBS-MgO固化黏土的物理和力学性质及微观特征变化规律,并与水泥固化黏土进行对比,揭示了GGBS-MgO固化黏土抵抗硫酸盐侵蚀的机制。与水泥固化黏土相比,硫酸盐浸泡条件下GGBS-MgO固化黏土表面完整度较好;质量变化率在浸泡120 d时仅为水泥固化黏土的0.25倍;固化黏土体pH略小于同期水泥固化黏土;浸泡初期GGBS-MgO固化黏土强度增长达20%,同周期时无侧限抗压强度较水泥固化黏土高15%～80%。X射线衍射试验（XRD）表明,硫酸盐侵蚀下GGBS-MgO固化黏土中水化硅酸钙（C-S-H凝胶）的峰值高于水泥固化黏土,而钙矾石（AFt）的XRD图谱峰值明显低于水泥固化黏土。电镜扫描试验结果表明,两种固化黏土中钙矾石形态明显不同：钙矾石在水泥固化黏土中以团聚型晶体存在,可具较强膨胀性,而在GGBS-MgO固化黏土中则以细短形态分布于颗粒间,可有效填充试样孔隙,使其具备良好的抗硫酸盐侵蚀能力。     

结构性海积软土的弹塑性研究

通过对天津市欠固结海积软土进行的大量试验,研究了土的结构性和弹塑性变形本构关系两个方面的问题。首次引入结构强度系数,建立了微结构定量参数与力学参数之间的关系,并提出一种综合考虑结构性影响的应力应变关系模型,为海积软土的结构性模型研究及实际应用提供了一条新的途径。     

Geotechnical Behavior of Recycled Copper Slag-Cement-Treated Singapore Marine Clay

Copper slag is a by-product obtained from production of copper metal. As copper slag contains silica and alumina, it may exhibit pozzolanic property, and hence it may be re-use in ground improvement applications as a partial replacement of cement. Present study evaluates systematically the possible pozzolanic property of copper slag as well as studies the effect of copper slag on engineering properties of cement-treated clay. X-rays diffraction method was employed to assess the possible pozzolanic property of copper slag. Effect of copper slag on engineering properties (i.e. compressive strength and compressibility) of cement-treated clay was studied with samples prepared with constant water content and workability. The test results showed that with sufficient curing time and at constant workability, the compressive strength of cement-treated clay was found to be increased with increasing amount of copper slag at high cement content but the compressive strength remained the same with increasing amount of copper slag at low cement content. Compressibility of cement-treated clay was found to be unchanged with increasing amount of copper slag. It was concluded that copper slag can be used as partial replacement of cement in treating soft marine clay.     

Relevance of SEM to Long-Term Mechanical Properties of Cemented Paste Backfill

This paper is an attempt to relate the microstructure to long-term mechanical properties of the cemented paste backfill produced from a hard rock mine tailing from North Queensland in Australia bound with flyash-based geopolymer (geopolymer), flyash-blended cement (FBC), and general purpose cement (GPC). A relatively high slump (260 mm) paste backfill mix with 74 wt% solids has been used to prepare cylindrical paste backfill samples with a diameter of 50 mm and a height of 100 mm. The uniaxial compressive strength tests were conducted on all samples after curing for 112 days to obtain their strength, failure strain and Young’s modulus. Fractured samples were examined under scanning electron microscope to understand the failure mechanisms at the microstructural scale. The results show that binders significantly affected the mechanical properties of paste backfills (ANOVA, p < 0.05). The paste backfill bound with geopolymer gave the lowest strength and Young’s modulus, while the paste backfills bounded with FBC and GPC showed comparable higher strength and modulus values. This was attributed to the relatively well-packed paste backfills with less cracks and smaller pore sizes in these paste backfills bound with FBC and GPC binders. In particular, needle-shaped particles, which were originally identified in GPC, highly influenced the mechanical property of paste backfills. These results indicate that fly ash can be used to partially replace the cement as a binder for paste backfills to achieve economic and environmental benefits.     

Undrained Triaxial Behavior of Cement Treated Marine Clay

Clays treated with lower cement contents often exhibit behaviour similar to stiff clays with planar failure surface under triaxial compression. In the present work the behaviour of a marine clay treated with 5 % cement, subjected to undrained triaxial compression tests is studied. The pre-consolidation pressure of the cemented clay due to the cementation bonding is observed to be very high. It is attempted to model the behaviour of cement treated clay using a bounding surface plasticity formulation as the plastic behaviour of the cemented clays within the yield surface has to be considered. The effect of cementation is included in the model as the pre-consolidation pressure obtained from consolidation tests. The tensile strength due to cementation bonds is included in the equation of the bounding surface. Simulations of the undrained triaxial compression tests on cemented clays are carried out and the results are validated with the experimental results.     

Diagenesis in the Middle Jurassic Khatatba Formation sandstones in the Shoushan Basin,northern Western Desert,Egypt

The Middle Jurassic Khatatba Formation acts as a hydrocarbon reservoir in the subsurface in the Western Desert, Egypt. This study, which is based on core samples from two exploration boreholes, describes the lithological and diagenetic characteristics of the Khatatba Formation sandstones. The sandstones are fine‐ to coarse‐grained, moderately to well‐sorted quartz arenites, deposited in fluvial channels and in a shallow‐marine setting. Diagenetic components include mechanical and chemical compaction, cementation (calcite, clay minerals, quartz overgrowths, and a minor amount of pyrite), and dissolution of calcite cements and feldspar grains. The widespread occurrence of an early calcite cement suggests that the Khatatba sandstones lost a significant amount of primary porosity at an early stage of its diagenetic history. In addition to calcite, several different cements including kaolinite and syntaxial quartz overgrowth occur as pore‐filling and pore‐lining cements. Kaolinite (largely vermicular) fills pore spaces and causes reduction in the permeability of the reservoir. Based on framework grain–cement relationships, precipitation of the early calcite cement was either accompanied by or followed the development of part of the pore‐lining and pore‐filling cements. Secondary porosity development occurred due to partial to complete dissolution of early calcite cements and feldspar. Late kaolinite clay cement occurs due to dissolved feldspar and has an impact on the reservoir quality of the Khatatba sandstones. Open hydraulic fractures also generated significant secondary porosity in sandstone reservoirs, where both fractures and dissolution took place in multiple phases during late diagenetic stages. The diagenesis and sedimentary facies help control the reservoir quality of the Khatatba sandstones. Fluvial channel sandstones have the highest porosities and permeabilities, in part because of calcite cementation, which inhibited authigenic clays or was later dissolved, creating intergranular secondary porosity. Fluvial crevasse‐splay and marine sandstones have the lowest reservoir quality because of an abundance of depositional kaolinite matrix and pervasive, shallow‐burial calcite and quartz overgrowth cements, respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

Nanochemomechanical assessment of shale: a coupled WDS-indentation analysis

Establishing the links between the composition, microstructure and mechanics of shale continues to be a formidable challenge for the geomechanics community. In this study, a robust methodology is implemented to access the in situ chemomechanics of this sedimentary rock at micrometer length scales. Massive grids of coupled wave dispersive spectroscopy (WDS) and instrumented indentation experiments were performed over representative material surfaces to accommodate the highly heterogeneous composition and microstructure of shale. The extensive datasets of compositional and mechanical properties were analyzed using multi-variate clustering statistics to determine the attributes of active phases present in shale at microscales. Our chemomechanical analysis confirmed that the porous clay (PC) mechanical phase inferred by statistical indentation corresponds to the clay mineral phase defined strictly on chemical grounds. The characteristic stiffness and hardness behaviors of the PC are realized spatially in regions removed from silt inclusions of quartz and feldspar. At the microscale shared by indentation and WDS experiments, a consistent chemomechanical signature for shale emerges in which the heterogeneities of the PC are captured by the standard deviations of indentation properties and concentrations of chemical elements. However, these local behaviors are of second order compared to the global trend observed for mean mechanical properties and the clay packing density, which synthesizes the relative volumes of clay and nanoporosity in the material. The coupled statistical indentation and WDS technique represents a viable approach to characterize the chemomechanics of shale and other natural porous composites at a consistent scale below the macroscopic level.     

Influence of grain size gradation of sand impurities on strength behaviour of cement-treated clay

In nature, soils are often composed of varying amounts of clay, silt and sand. Variation of the percentage of these compositions can affect the final strength of the soils when stabilised with cement. In this study, focus was placed on clayey soils with different gradation of sand impurities up to 40% in mass. An extensive study of such clayey soils treated with cement was investigated. For the results, it is noted that water:cement ratio was a major influence of strength development of cement-treated clayey soils. In contrast, the soil:cement ratio was found to have minor effects on the strength development. The presence of sand impurities has a significant reduction on the strength development of the cement-treated clayey soil mixture due to more free water available for hydration. The use of free-water:cement ratio is adopted which was shown to be capable of adjusting for such change in amount of free water and water holding capacity of the clay which is determined with Atterberg’s liquid limit tests. The effects of gradation (fine, coarse and well-graded) of the sand impurities were found to affect strength development minimally, owing to similarities in their liquid limits when mixed with clay. Ordinary Portland cement (OPC)-treated clayey soils produced a more rapid gain in strength but lower final strength at 28 days of curing as compared with Portland blast furnace cement (PBFC). This is found to be persistent for different gradation of sand impurities. A linear correlation can be established based on the log of the unconfined compressive strengths developed at different curing age, with slopes of these linear trends found to be similar for PBFC and OPC-treated clayey soil specimens. Finally, a strength prediction model comprising of these findings is developed. The parameters adopted in this model coincide with values proposed by past studies, thereby validating the robustness of the model. The practical benefits from this study offer a quality control scheme to forecast long-term performance of cement-treated clayey soils as well as optimise cement dosage in cement stabilisation to produce a more cost-effective and less environmental-invasive usage of the technology in geotechnical applications.

     

Shrinkage Properties of Soft Clay Treated with Cement and Geofibers

In this study, effects of two types of geofibers, namely polypropylene and recycled carpet, on three dimensional shrinkage properties of cement treated kaolinite and bentonite clays are investigated. Cement treated clay specimens were prepared with cement contents of 5, 10, and 15 % by weight of dry soil for kaolinite samples, and 30, 40 and 50 % for bentonite samples. To investigate and understand the influence of different fiber types and contents, three different percentages of fiber content (i.e. 0.1, 0.2 and 0.5 % polypropylene fibers; and 0.5, 0.75 and 1 % carpet fibers) were adopted. The results of shrinkage tests on 126 cylindrical samples of cement treated clay with various cement and fiber contents were analysed to understand the relationships between these parameters and the shrinkage percentage of treated soil. Results of this study indicate that combination of cement and fiber is effective in reducing the volume change of clayey soils undergoing drying process. In the applied ranges of cement and fiber contents, the influence of cement addition on the shrinkage reduction is more significant than the addition of fibers for the treated kaolinite. However, addition of fibers in curtailing the shrinkage of bentonite clay is more significant than the cement addition.     

不同水泥土混合桩周围土体的扰动与强度恢复

针对由深层搅拌法或高压旋喷法施工的水泥土混合桩周围土体的扰动与强度恢复的问题,采用两种常用的施工法：高压旋喷混合法（简称旋喷法）和水泥浆搅拌混合法（简称湿法）,在日本有明黏土中施工以观测周围土体力学特性的变化。测试结果表明,水泥土混合桩周围土体的扰动程度与其施工方法有关;两种不同施工方法施工后周围土体的当日强度与原状土的强度之比分别是0.42（旋喷法）和0.68（湿法）,施工30 d后,旋喷法有44 %,湿法有40 %的初始强度得到恢复。结果亦表明周围土体模量恢复要慢于强度恢复的速度。     

Evaluation of Engineering and Cement–Stabilization Parameters of Clayey–Sand Mixtures under Soaked Conditions

Clay soils, especially clay soils of high or very high swelling potential often present difficulties in construction operations. However, the engineering properties of these clay soils can be enhanced by the addition of cement, thereby producing an improved construction material. Higher strength loss of cement stabilized clay soils after soaking in water is attributed to water absorbing capacity of the clay fraction (e.g. montmorillonite). Kaolinite and illitic soils are largely inert and resist to water penetration. These clays generally develop satisfactory strengths resulting to low strength reduction [Croft, 1967]. The swelling clays such as bentonite soaked in water, due to environmental conditions, result to volume increase causing macro and micro-fracturing in engineering structures. These fractures accelerate water penetration and consequently cause greater strength loss [Sällfors and Öberg-Högsta, 2002]. The water intrusion during soaking creates swelling and disrupts the cement bonds. The development of internal and external force systems in soil mass, due to soaking conditions, establish the initiation of slaking. Internal force system of a stabilized clayey soil consists of the resultant stresses established by the bonding potential of a cementing agent and the swelling potential of a clay fraction. In an effort to study this influence of soaking conditions and final absorbed water content on the stabilization parameters (cement, compaction, curing time), both unconfined compressive strength and slaking (durability) tests were carried out on two different cement stabilized clayey mixtures consisted of active bentonite, kaolin and sand.     

Modelling thermo-elastic–viscoplastic behaviour of marine clay

Marine clay supporting high-temperature offshore structure susceptible to random movements (such as a buckling high-temperature pipeline) experiences variable shearing rates at an elevated temperature that is higher than the marine environment (typically 4 °C). This practically implies that the undrained shear strength (s_u) of the marine clay being routinely characterized in situ by penetrometers at a constant rate under an isothermal condition (4 °C) should be carefully corrected, by taking into account the temperature and rate dependency. To date, the combined effects of rate and temperature on the undrained shear behaviour of marine clay are merely investigated experimentally and theoretically. This study presents the development of an anisotropic thermo-elastic–viscoplastic model and a series of temperature- and rate-controlled triaxial tests for validation purpose. Compared to the modified Cam-Clay model, the proposed model only introduces three new parameters to characterize the temperature dependency, rate dependency and the inherent anisotropy of K₀-consolidated marine clay. The predictive capability of the model has been validated by the triaxial test results. Based on the new model, an explicit equation is formulated for quantifying the temperature- and rate-dependent s_u of marine clay. Calculation charts are also developed to quantify s_u of marine clay with different plasticity indexes under various strain rates and temperatures.

     

Utilization of Silica Fume to Maximize the Filler and Pozzolanic Effects of Stabilized Soil with Cement

Silica fume is identified as a pozzolan and supplementary cementitious material that can utilize to improve the mechanical properties of stabilized soil with cement. Silica fume wherein mixes with cemented soil in a proper dosage, it is susceptible to induce pozzolanic effect in cemented soil due to its fineness and high content of SiO₂ and Al₂O₃. The pozzolanic effect is vital to ensure ongoing strength of stabilized soil with cement. Up to now, stabilization of clay with cement and silica fume is not completely explored. This paper investigates: (i) the capability of utilizing the silica fume as a supplementary material for cement to maximize the filler and pozzolanic effects of compacted and stabilized soil (ii) the mechanical properties of compacted and stabilized clay with various proportions of cement and silica fume. For this purpose, a total of 120 untreated and stabilized soil admixtures were prepared by replacing ordinary Portland cement with silica fume. The influence of partial replacement of cement with silica fume on the bearing capacity, shear and compressive strength of compacted and stabilized soil was investigated. To achieve such aims, the stabilized soil specimens were examined in laboratory under direct shear, unconfined compression and California bearing ratio tests. Based on the findings of this paper the 28-day UCS of the stabilized soil with 2% partial substitution of cement with silica fume is almost 3.5-fold greater than that of the untreated. It was found that the optimum mix design for the stabilized soil is 6% cement and 2% silica fume. In conclusion, a notable discovery is that the partial substitution of cement with 2% silica fume in the optimum mix design significantly refined the pore spaces as a result of pozzolanic activity and filler effect of silica fume.     

Use of clay as a pozzolona in high strength Portland cement and its thermal activation

In this investigation local clay from Cherat mines, Nowshera District, NWFP, Pakistan, has been tested as a pozzolanic material in high strength Portland cement. Thermal treatments were performed as a means of activation of the clay. It was found that thermal treatment of the clay can increase its pozzolanic activity. Different blended mortars, containing different amounts of clay, activated at different temperatures were studied for compressive strength, consistency, and setting times. It was concluded that the mechanical properties of the blended cements were mainly governed by the percentage of incorporation of the calcined clay. Blended cement composition has been formulated, with optimal results of 20% calcined clay at a temperature of 600℃.     

重塑石灰土的强度恢复方法与机制初探

石灰稳定土工程翻修改造后会产生大量的石灰土弃渣,为避免污染环境和节约工程投资,需重新利用破碎的石灰土进行填筑。但石灰土破碎后强度急剧降低,需要添加胶凝材料提升其力学性能。以重塑石灰土为研究对象,通过添加5%石灰或水泥进行再改良,对比分析两种再改良土的强度和压缩性等力学指标,结果表明,石灰再改良土的力学特性优于水泥再改良土。借助粒度分析、电镜扫描、X衍射和热重分析试验手段揭示了石灰再改良土性能优越的内在机制,发现石灰再改良土中的石灰和石灰土团粒能形成很好的胶结;但水泥未能和石灰土团粒形成有效胶结,自身形成了边-面和边-边接触的片状多孔架构。重塑石灰土残存的氢氧化钙是引起水泥再改良土性能劣于石灰再改良土的主要诱因。     

Geotechnical evaluation of Turkish clay deposits: a case study in Northern Turkey

Clay deposits in Oltu-Narman basins (Erzurum, northern Turkey) have been studied to determine their engineering properties and to evaluate their uses for geotechnical applications. These deposits are concentrated in two different stratigraphic horizons namely the Late Oligocene and the Early Miocene sequences. Clay-rich fine-grained sedimentary units are deposited in shallow marine and lagoonar mixed environments. Their clay minerals originated by the alteration of Eocene calc-alkaline island-arc volcanics, preferably from pyroclastics (trachite and andesite flow), which form the basement for the Oltu depression. Smectite group clay minerals are found abundant in clay deposits. The experimental results show that the clay soils have high plasticity behaviors and low hydraulic conductivity properties. The optimum water content, the free swell, and the swelling pressure of clay samples decreased and the maximum dry unit weight of clay samples increased under high temperature. Consequently, it is concluded that the expanding of clay soils is an important soil problem that cannot be avoided in the significant parts of Oltu city and its villages. However, the soils of clay-rich layers in the outcrops-section of clay deposits can be successfully used to build compacted clay liners for landfill systems and to construct vertical and horizontal barriers for protection of ground water and for preventing soil pollution in geotechnical applications.     

Unfrozen water as a function of clay microstructure

A previous study of microstructural changes in freezing clay suggested that a “dispersed” freshwater clay should have a higher percentage of unfrozen water than a (leached) marine clay with similar mineralogical and granulometrical compositions. This report describes an investigation where two such clays were actually compared concerning their contents of unfrozen water. The results confirmed the hypothesis. Thus, the influence of clay microstructure on the amount of unfrozen water was clearly shown. The degree of particle aggregation and the density of the particle aggregates are the main microstructural parameters.     

Shear behavior of sensitive marine clay–steel interfaces

Many soil–structure interaction problems require the knowledge of the shear resistance and behavior between the soil and construction materials. Although sensitive marine clay deposits are widely found in Canada (Leda clay) and many regions in the world (e.g., Scandinavia), and steel is a common construction material for many civil engineering structures, our understanding of the interface shear behavior between sensitive marine clay and steel is still limited. This paper presents the results of an experimental study on the interface shear behavior between Leda clay and steel. In this research, direct shear tests (DSTs) are conducted to investigate the interface shear strength parameters and behavior between Leda clay and steel, and the effect of several factors (e.g., steel surface roughness, properties of the Leda clay) on the interface shear behavior and parameters. All tests have been carried out with a standard DST apparatus at normal loads which range from 250 to 450 kPa. The results show that the Leda clay interface shear behavior can be significantly affected by the steel surface roughness, the Leda clay’s OCR, dry density, and salt content. The results presented in this paper will contribute to a more cost-effective design of geotechnical structures in Leda clay.