Mechanical Behavior of Microbially Induced Calcite Precipitation Cemented Sand

Geotechnical and Geological Engineering - New sustainable ground improvement techniques have been recently required for applications in onshore and offshore geotechnical structures. The...     

微生物矿化作用改善不同孔隙砂岩抗冻融特性试验研究

砂岩是地质遗迹和石质文物最为常见的岩石类型,冻融循环导致的风化劣化是引起其发生地质灾害的主要原因。降渗加固是解决该问题的根本途径。文章引入国际上新型的岩土体加固技术—微生物诱导碳酸钙沉淀（MICP）,以中粒砂岩和微粒砂岩为例,通过开展MICP处理和冻融循环试验,研究其改善不同孔隙砂岩抗冻融特性的可行性,分析其改善机理。研究结果表明：（1）MICP作用能显著提高两类砂岩的抗冻融特性,主要改善机理是MICP过程生成的碳酸钙不仅填充了岩石孔隙,减小了孔隙水的体积和冻融损伤作用力,同时也加强了岩石颗粒之间的胶结强度,但孔隙因素对该过程有一定影响;（2）3轮次MICP处理后的岩样在冻融循环40次后未见明显表观破坏,而未经处理的岩样当冻融循环达到40轮次时在棱角处出现局部表观破坏且中粒砂岩破坏程度略大于微粒砂岩;（3）40轮次冻融循环作用后,中粒砂岩和微粒砂岩岩样孔隙率增加率从17.0%和14.8%降低到了4.4%和6.3%,质量损失率从0.22%和0.14%下降到了0.04%和0.02%,吸水率从6.8%和4.4%减小到了0.75%和1.5%,波速降低率从18.5%和12.4%降低到了7.3%和3.8%;（4）由于中粒砂岩孔隙大于微粒砂岩,其碳酸钙沉淀效率更高,有效处理深度更深,表层孔隙间距更大,从而在进行相同轮次MICP处理时,其孔隙率降低率、吸水率降低率、质量增长率、波速增长率均较大。     

一株岩生真菌对方解石的风化作用

选用一株从碳酸盐岩表面分离的真菌,研究了实验条件下该真菌对方解石的风化作用.通过检测风化培养基与对照培养基的pH值、Ca2+浓度、挥发性代谢产物以及分析真菌一矿物相互作用过程中的矿物表面微观形态变化,研究该真菌对方解石的风化过程和作用机理.结果表明:在实验条件下该真菌对方解石具有较强的风化作用,风化培养基上清液中的Ca2+浓度分别是死菌对照的3.98倍和纯水对照的13.73倍;该真菌生长过程中会分泌有机酸和醇类等代谢产物,真菌和矿粉之间会形成菌体-矿物聚集体或复合体,促进方解石的风化.分析认为该真菌对方解石的风化作用包括机械破坏,代谢产物溶蚀、络合作用以及多种因素之间的协同作用.     

Dissolution and Deformation Characteristics of Limestones Containing Different Calcite and Dolomite Content Induced by CO2-Water-Rock Interaction

To investigate the impacts of mineral composition on physical and mechanical properties of carbonate rocks, limestone specimens containing different contents in calcite and dolomite are selected to perform CO2-water-rock reaction experiments. The X-ray Diffraction (XRD) and Nuclear Magnetic Resonance (NMR) are carried out to examine the change characteristics of mineral dissolution and pore structure after reaction. The core flooding experiments with Fiber Bragg gratings are implemented to examine the stress sensitivity of carbonate rocks. The results show that the limestones containing pure calcite are more susceptible to acid dissolution compared to limestone containing impure dolomite. The calcite content in pure limestone decreases as the reaction undergoes. The dissolution of dolomite leads to the formation of calcite in impure limestone. Calcite dissolution leads to the formation of macropore and flow channels in pure limestone, while the effects of impure dolomite in impure limestone results in mesopore formation. When confining pressure is lower than 12 MPa, pure limestones demonstrate higher strain sensitivity coefficients compared to impure limestone containing dolomite after reaction. When confining pressure exceeds 12 MPa, the strain sensitivity coefficients of both pure and impure limestones become almost equal.     

角质型金珊瑚与黑珊瑚的宝石学特征研究

采用常规宝石鉴定方法、偏光显微镜、X射线荧光光谱仪、光栅光谱仪及红外光谱仪对未处理和覆膜处理的角质型金珊瑚、黑珊瑚样品的宝石学特征进行了测试研究。结果表明,该珊瑚样品的实测折射率为1．4851．505,密度为1．3361．349g／cm^3;其横截面呈同心环状结构,纵切面呈粗细不均的纤维结构,证明其横纵空间生长的机理;样品的主要化学成分为纯有机质,主要化学元素为I,次要的Cl,Br,S和Ba,少量Si,Ca,Mg,Na以及微量元素Zn,Ti,Mn,Cu,V等,未出现Fe;耐酸蚀实验表明,样品在HCl和HNO3中不溶,在H2SO4中可缓慢溶解;样品的红外光谱具有3组弱-中-强特征吸收峰,表明其存在一系列氨基酸等有机成分。     

Micronized Calcite Potential,Production and Principle Characteristics of Nigde (Turkey)

Marble that exploited for micronized calcite production in Nigde area (South Central Turkey) occur in the Upper Cretaceous Gümü ler, A gedi i, and Kaleboynu Formations of the Nigde Massif. Although there are a few marble producing quarries in the area, it is long been known that the marbles of this area are generally highly fractured and don’t yield large blocks or suitable slabs meeting the industrial demands. Thus, most of the production is currently carried out mainly as building stone, crushed stone and micronized calcite. Due mainly to high demand, micronized calcite has been becoming very significant export product to the state’s economy. Because the Nigde marbles are coarse grained with high CaCO3 content, high purity and whiteness, they are considered to be the highest quality micronized calcite quarries in the country. Consequently, the area drew many national and international investors resulting in significant increase in the number and extent of micronized calcite plants in the area. In early 1980’s, the city of Nigde had only one or two plants, it is now well over 5 including foreign investors and joint ventures. Annual production is also considerably increased from 20,000-30,000 tones to almost half a million tones and it is still in increasing trend.     

安徽蓬莱仙洞不同滴水点差异PCP作用及其古气候记录研究意义

正石笋由于分布广泛、定年准确,并且具有丰富的气候和环境代用指标(如氧碳稳定同位素~([1,2])、微层厚度~([3])、微量元素~([4~6])等),因而受到古气候学家广泛关注。其中,微量元素和稳定碳同位素常被用来间接地反映局地干湿变化。当降水减少时,洞穴滴水在洞顶储存时间较长,使岩溶水在补给石笋之前已经发生了方解石沉积作用。由于Mg,Sr和Ba在方解石和溶液中的分配系数远小于1~([7,8]),从而使Ca优先于Mg,Sr和Ba沉积出来,使得溶液(渗流水及其所形成的滴水)和现代次生碳酸盐沉积物中的Mg,Sr和Ba富集,进而导致Mg/Ca,Sr/Ca和Ba/Ca比值增大~([4,5,9]),这种现象被称为方解石前期沉积作用(Prior Calcite Precipitation,简称PCP)。此外,当降水减少,洞穴滴水滴率变慢(即PCP作用增强)时,CO_2脱气时间增长也会导致石笋碳同位素偏     

尾矿砂的堆存特征及其抗剪强度特性

以国内多座尾矿库的勘察试验资料为基础 ,从坝体尾矿砂堆存的物理特征出发 ,对尾矿砂沿尾矿库纵、横方向的颗粒变化规律 ,尾矿砂的粒径、含水量、孔隙比以及相对密度与尾矿砂的内摩擦角的关系进行探讨。结果表明 :孔隙比和相对密度对尾矿砂内摩擦角影响较大 ,且表现为线性相关 ;尾矿砂的内摩擦角和堆存深度的相关性不强 ;增大尾矿砂的相对密度或减小其孔隙比对提高坝体抗剪强度非常有利 ;在尾矿砂中铺设土工织物可显著地提高其粘聚力数值     

Effect of Biochar Produced from Mesquite on the Compaction Characteristics and Shear Strength of a Clayey Sand

Biochar is a carbon-rich and low microbial degrading material obtained after pyrolysis of biomass in the absence or limited content of oxygen. The impact of biochar on hydraulic properties of soil is extensively studied in agricultural and geotechnical or geoenvironmental engineering for potential application in bioengineered structures. While a little study is conducted to assess its effect on soil mechanical properties, especially shear strength. However, the effect of biochar on the combined shear strength and compaction characteristics of soil is not studied. The shear strength of biochar amended soil is thought to be related to the compaction characteristics. In addition, the effect of biochar on the shear strength of the soil is soil and biochar specific. In this study, an attempt was made to investigate and better understand the effect of biochar on the shear strength and compaction characteristics of a clayey sand for potential application in bioengineered structures. Standard proctor, direct shear and unconfined compression tests were conducted on bare soil and soil amended with 5, 10 and 15% (w/w) biochar. The experimental results revealed that the amendment of biochar from 5 to 15% (w/w) decreased the dry density and increased the shear strength parameters such as cohesion (c) and angle of internal friction (ϕ) of the soil. While it decreased the undrained shear strength (c_u) at higher compaction density (> 0.95MDD) and increased at lower compaction density (< 0.9MDD). Thus, in undrained condition, the initial compaction density has a strong influence on the shear strength of biochar amended soil. In addition, the increased c and ϕ and decreased dry density in biochar amended soil is observed to increase the stability of slopes (hypothetical). The increase of c and ϕ is believed to be due to the roughness and active chemicals (functional groups) present on the surface of the biochar. The decreased c_u at higher density is believed to be due to the lubricating effect by the higher water content.

     

Evaluation of Strength Characteristics of Tropical Black Clay Treated with Locust Bean Waste Ash

An expansive tropical black clay (also known as black cotton soil because the cotton plant thrives well on it) was treated with up to 15 % locust bean waste ash (LBWA) to assess its soil improvement potential. Samples were subjected to index, compaction using three energy levels (British Standard light, BSL, West African Standard, WAS or ‘Intermediate’ and British Standard heavy, BSH), shear strength (unconfined compressive strength, UCS), California bearing ratio, CBR and durability tests. Results obtained show that the natural soil is not suitable for road construction. The maximum dry density (MDD) and optimum moisture content (OMC) decreased and increased, respectively. Regardless of the compactive effort and curing period, strength and durability properties increased with higher LBWA content with the BSL effort recording the best improvement. However, based on durability results, the optimal 12.5 % LBWA treatment of black cotton soil did not satisfy criteria for its use in road construction as a stand alone additive. Also, significant improvement in soil properties was obtained using the BSL compactive effort, which is easily achieved in the field. The benefits of the application include reduction in the cost of soil improvement and the adverse environmental impact of locust bean waste.     

Geochemical Characteristics of Calcite and Its Significance in Sanqisan Uranium Deposit

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贵州紫云方解石矿床地球化学特征及成因研究

贵州紫云方解石矿床是在贵州西南部新发现的非金属矿床,方解石矿体呈脉状、透镜状和似层状产出。对紫云火山关、达则等方解石矿床开展同位素地球化学及微量元素、稀土元素研究,结果表明碳、氧同位素显示成矿物质来源于海相碳酸盐岩,成矿流体以富含HCO3-为主,大气水参与成矿,与岩浆作用关系不大。其中达则矿段相对于围岩,成矿物质具有较高的Sr、Zn和Ni含量,稀土元素配分曲线明显区别于围岩,δEu显示正异常等特征,暗示可能有深部流体参与成矿。火山关、打劳等其他矿段,矿体和围岩具有相似的稀土配分模式和∑REE变化规律,表明成矿物质来源于碳酸盐岩围岩。通过区域成矿作用比较,认为成矿时代可能属于印支—燕山期。     

Calcite and aragonite precipitation from seawater solutions of various salinities: Precipitation rates and overgrowth compositions

The reaction rate and composition of calcite and aragonite overgrowths precipitated from seawater solutions of various salinities (i.e. S=5, 15, 25, 35, 44) were determined at 25°C and 10^−2.5-atm. CO₂ partial pressure using a constant disequilibrium seeded technique. The rate data were fitted to an empirical rate law of the form:

logR=n(ω_{c(or a)}-1)+logk

where n is the empirical reaction order; and k is the rate constant. Calcite precipitation rates in seawater solutions do not vary appreciably as a result of salinity variations over the range investigated, while those for aragonite show an increase in going from the higher (i.e. S=35, 44) to the lower (i.e. S=5, 15, 25) salinity range. This study also confirms previously published findings that above a given saturation state (i.e. Ω_c>/2.6) aragonite precipitates more rapidly than calcite at 25°C.

The incorporation of Sr²⁺ in aragonite and Mg²⁺ in calcite overgrowths are independent of the precipitation rate. The partition coefficient of Sr²⁺ in aragonite is approximately equal to unity and is unaffected by salinity variations between 5 and 44. However, the Mg²⁺ partition coefficient in calcite, increases with decreasing salinity of the parent seawater solutions, possibly as a result of variations in the sulfate content of the solutions and solids.

The experimental results were discussed in the context of a number of geological environments.     

原位激发微生物成矿加固钙质砂的剪切与压缩特性研究

钙质砂广泛分布于热带海岸地区,其抗剪强度较低,在较高应力条件下极易破碎。因此,对以钙质砂为主要原料的地基材料进行加固,是海洋岩土工程领域的研究热点。基于尿素水解过程的碳酸钙成矿技术（MICP）是近年来地基材料加固领域的一项新技术。目前广泛使用的生物强化法实现MICP存在成本昂贵及环境适应性差等问题,制约了其大规模工程应用。研究采用原位生物激发MICP法对钙质砂进行加固,并对加固后试样开展直剪和一维压缩试验。结果表明：原位生物激发MICP方法可以在钙质砂中形成有效胶结,胶结水平最大可达6.26%。采用高浓度胶结溶液或增加注射次数可提高胶结水平。同时,加固后钙质砂的最大应力比、最大剪胀角以及残余内摩擦角均随胶结水平增加而显著增大,但竖向应力水平增大会抑制这些力学指标的增大。随胶结水平升高,试样压缩性显著减小;压缩后的原位激发MICP加固钙质砂中,细颗粒与粗颗粒的比例均随胶结水平的增加而增大。     

Compressibility and Strength Behaviour of Sand–tyre Chip Mixtures

Scrap tyres can be shredded into chips and can easily be mixed with granular soils. To assess the behaviour of the admixtures, compressibility and triaxial compression tests were carried out by varying chip size and chip content. The results demonstrated that sand–tyre chip mixtures up to 20% could be a potential material for highway construction and embankment construction up to around 10 m height.     

Qualitative and Quantitative Characteristics of Modeled and Natural Oscillatory Zoning Patterns in Calcite

Four types of oscillatory zoning patterns (OZP) produced by a dynamic model are described qualitatively and quantitatively and displayed as simulated cathodoluminescence images. The behavior of the dynamic model was investigated in terms of the parameter θ, which is the ratio of diffusivities of Ca²⁺ and H₂CO₃, and in terms of the parameter γ, which is the product of θ and the ratio of concentrations of Ca²⁺ and H₂CO₃ far away from the crystal surface. Qualitatively, the dynamics of the model has been characterized by a stable focus, an unstable focus changing to a stable node or to a stable limit cycle, and by periodical behavior with constant amplitude. Quantitative characteristics, including amplitude of oscillations and duration of oscillations, change between the patterns. It is shown that the process of forming oscillatory zoning in calcite with conditions corresponding to periodical behavior with constant amplitude is very slow in comparison to other OZPs. The oscillatory zoning pattern in a natural calcite crystal is described qualitatively in terms of four general OZPs produced by the dynamic model.     

疏水材料处理吉林西部乾安地区盐渍土的力学强度试验

为了给吉林西部乾安地区盐渍土边坡水渠工程施工提供理论依据及施工参考,利用新型泥土超疏水乳液（CN）对该区盐渍土进行了处理,研究了不同处理条件下CN对盐渍土土体力学强度的影响,将经过不同处理的素土与CN土无侧限抗压强度进行对比,结果表明：1）在不同含水率条件下,CN土的无侧限抗压强度均有较大提升,且在14.86%含水率时取得最大提升率98.90%;随着含水率的增加,素土与CN土应力-应变曲线均存在由硬化型向软化型的转变,其阈值在最优含水率附近。2）随着压实度的增加,CN土无侧限抗压强度逐渐增强,在90%压实度条件下取得最大提升率130.77%;且CN处理后,原本呈塑性硬化型的素土转变成脆性软化型。3）盐分的增加对于CN土无侧限抗压强度起到了抑制作用,在0.3%含盐量条件下取得最大无侧限抗压强度1.33 MPa;过量的盐分结晶会破坏CN形成的纳米结构疏水膜,使得在高含盐量条件下,CN土的抗压强度低于素土。4）扫描电镜实验对CN土微观机理探讨,CN处理后使得土颗粒团聚呈大颗粒,颗粒表面光滑,孔隙发育减少。结构单元体和孔隙单元体的分析证明了处理后土体连结更为紧密,从而提升抗压强度。     

The Direct Shear Strength and Dilatancy of Sand–gravel Mixtures

A total of 87 direct shear tests in a large direct shear-box apparatus have been used to investigate the strength and dilatancy of sand–gravel mixtures. This paper focuses on the differences in behaviour between a silica sand (yellow Leighton Buzzard sand) and sand–gravel mixtures obtained by adding fractions of two kinds of gravel to the sand. The purpose is to find a relation between the grain-size characteristics of the materials and the shearing resistance. Experimental results are analysed in terms of the frictional and dilatant contributions to the strength of mixtures as a function of their relative density, and are compared with dilatancy theories and empirical equations. The addition of gravel to the mixtures, even at low fractions (less than 0.1 by volume), causes an increase in peak friction angle (Φ ′_peak) which results both from higher dilatancy at failure (ψ_max) and higher constant volume friction angle (Φ ′_cv). Use of the minimum voids ratio (e_min) of the materials allows the data for the two families of mixtures to be normalized and interpreted in terms of Φ ′_cv and the ratio (Φ ′_peak − Φ ′_cv)/ψ_max. The relationships between relative density (D_r), ψ_max and Φ ′_peak − Φ ′_cv are only partly explained on a physical basis, so we develop empirical equations to predict the peak shear resistance of sand–gravel mixtures (up to gravel contents of 0.5) on the basis of easily measurable quantities. Such equations constitute a practical tool to overcome the problems arising from the impracticality of testing coarse material in the standard shear-box apparatus.     

河床底部沙火山特征、演化及其研究意义

沉积后尚未固结的砂体在外部动力的干扰下容易发生液化,形成沙火山、液化砂岩脉等沉积构造,地震是触发液化的最常见动力.在河床现代沉积中发现大量的沙火山构造,其产生过程虽受人为活动影响,形成条件却在盆地特殊构造部位可以满足,分析其特征、演化及动力可以为震积岩及其他成因软沉积变形研究提供参考.研究结果显示,不同规模及对应特征的...     

Erosional and depositional characteristics of regional overwash deposits caused by multiple hurricanes

Regional-scale washover deposits along the Florida Gulf and Atlantic coasts induced by multiple hurricanes in 2004 and 2005 were studied through coring, trenching, ground-penetrating radar imaging, aerial photography, and prestorm and poststorm beach-profile surveys. Erosional and depositional characteristics in different barrier-island sub-environments, including dune field, interior wetland and back-barrier bay were examined. Over the eroded dune fields, the washover deposits are characterized by an extensive horizontal basal erosional surface truncating the old dune deposits and horizontal to slightly landward-dipping stratification. Over the marshes in the barrier-island interior, the washover deposits are characterized by steep tabular bedding, with no erosion at the bottom. Overwash into the back-barrier bay produced the thickest deposits characterized by steep, prograding sigmoidal bedding. No significant erosional feature was observed at the bottom. Washover deposits within the dense interior mangrove swamp demonstrate both normal and reversed graded bedding. The washover deposits caused by hurricanes Frances (2004) and Jeanne (2004) along the southern Florida Atlantic coast barrier islands are substantially different from those along the northern Florida barrier islands caused by Ivan (2004) and Dennis (2005) in terms of regional extension, erosional features and sedimentary structures. These differences are controlled by different overall barrier-island morphology, vegetation type and density, and sediment properties. The homogeneity of sediment along the northern Florida coast makes distinguishing between washover deposits from Ivan and Dennis difficult. In contrast, along the Atlantic coast barrier islands, the two overwash events, as demonstrated by two phases of graded bedding of the bimodal sediments, are easily distinguishable.