遗址土劣化进程中微观结构变化的类比研究

长期的风化会使遗址土体劣化,进而威胁到遗址本体的安全,但在自然条件下这一演化过程尚不明确。遗址土体微观结构的变化是该过程的重要体现,研究选取风化条件近似而暴露时间不同的黄土质边坡作为类比对象,采用扫描电镜法（SEM）和压汞法（MIP）分别对表部以及内部土样的微观孔隙结构进行观察和量测。试验结果表明,表部土体微观结构的变化程度大于内部土体,并呈现一定的规律性;与内部土体相比,表部土体的土颗粒排列为致密的叠片状;其孔径分布为双峰模式,团聚体内孔隙占比较大;随着风化时间的增长,表部土体的孔隙总体积和表面分形维数逐渐减小,导致孔壁粗糙程度降低,减小了颗粒间的摩擦,在宏观上容易诱发土体表层的剥离损耗或其他病害。     

Effect of concrete waste particles on infiltration characteristics of soil

Demolition of old buildings to create space for new development resulted in the near surface soil (topsoil) to be mixed with particles derived mostly from concrete wastes. This condition could affect the infiltration capacity and surface runoff, therefore, storm-water management of the area. This paper presents results of study on the effect of concrete waste particles on the hydraulic properties and infiltration capacity of the topsoil. Laboratory tests were performed to compare the hydraulic properties of the topsoil and the mixture of topsoil and concrete particles. Laboratory infiltration column test was performed on the mixture to evaluate its infiltration capacity. Results from the laboratory tests indicated that the presence of particles from concrete waste decreased the water-holding capacity and permeability, thereby the infiltration capacity of the ground surface. The results were supported by numerical analysis performed using the same material and boundary conditions as the column test. Parametric study was performed on both the topsoil and the mixture to extend the results of infiltration test to different materials under different ranges of rainfall intensity. The parametric study showed that the presence of concrete particles increased the run-off and the effect increased as the rainfall intensity increased. Therefore, the increase in runoff coefficient should be considered for the storm-water management when the near surface soil is mixed with concrete waste.     

Enhancing the interface friction between glass fiber-reinforced polymer sheets and sandy soils through sand coating

ABSTRACT

Soil-pile interface friction is an important geotechnical engineering factor to be considered in achieving a safe and cost-effective design. Conventional materials such as concrete, steel, and wood exhibit serious long-term soil substructure problems, particularly with regard to durability, deterioration, and corrosion. Fiber-reinforced polymer (FRP) composites are potential alternatives for addressing these long-term problems. This paper describes the results of an experimental study of the interface friction between sandy soil and glass FRP (GFRP) sheets coated with different ratios of sand per unit of surface area. A direct shear test was used to study 18 different groups of GFRP specimens. The test parameters were the amount of silica sand coating and normal stresses in the direct shear tests. The GFRP specimens were sheared against three types of soil: sand, silty sand, and sandy lean-clay, of which the first two were used in both dense and loose states. The experimental results showed that coating the GFRP sheets with silica sand was effective in enhancing the interface friction with sandy soils under different normal stresses. A pile implication analysis was also performed to compare the effect of sand coated GFRPs on the load capacity of friction piles with different length to diameter ratios.     

桩土接触面单元参数分析

桩的抗拔特性与接触面的特性密切相关，正确选定接触面的力学参数对于分析桩的抗拔机理有重要意义。根据桩土接触面点面接触模型和库仑摩擦变形原理，在10组土－结构（钢、混凝土）剪切摩擦试验分析的基础上，对桩土接触面摩擦参数的取值问题进行了研究，得到了一些结论，对于桩土接触面力学参数正确取值有一定的参考价值。     

Characterization of indoor and outdoor atmospheric pollutants impacting architectural monuments: the case of San Jerónimo Monastery (Granada, Spain)

Indoor and outdoor concentrations of atmospheric gaseous pollutants as well as composition, size, and morphology of particulate matter have been investigated at the monastery of San Jerónimo in Granada (Southern Spain). Complementary micro- and nano-analytical techniques were applied; elemental and mineralogical composition and morphological characteristics of particulate matter were investigated combining electron probe microanalysis at the single particle level, and bulk aerosol samples were analyzed using energy-dispersive X-ray fluorescence, X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray analyzer and transmission electron microscopy (TEM). Microclimatic conditions at the monastery were monitored, and gas concentrations were assessed by means of diffusion tubes subsequently analyzed with ion chromatography. Results revealed high abundances of soil dust particles (aluminosilicates, calcite, dolomite, quartz), salt aerosols (chlorides, sulfates and ammonium-rich salts), and NO₂ and SO₂ both outdoors and indoors. Amorphous black carbon particles had surprisingly high abundances for Granada, a non-industrialized city. The composition of indoor particles corresponds to severe weathering affecting the construction materials and artworks inside the church; moreover their composition promotes a feedback process that intensifies the deterioration. Chemical reactions between chloride-rich salts and pigments from paintings were confirmed by TEM analyses. Indoors, blackening of surface decorative materials is fostered by particle re-suspension due to cleaning habits in the monastery (i.e. dusting). This is the first air quality study performed in a monument in the city of Granada with the aim of developing a strategy for preventive conservation.     

混凝土大坝冻融破坏问题的数值计算分析

根据大坝上游水库水温和气温观测资料,建立了大坝上游水库水温和当地气温的回归模型。采用有限元数值计算方法,分析了混凝土大坝的温度场,研究了混凝土大坝由于气温变化引起的应力场交替变化。研究表明,由于气温随季节的交替变化,大坝下游面浅层的最大主应力远大于混凝土的抗拉强度,进而导致混凝土大坝下游面的冻融老化甚至破坏。计算结果表明,有限元数值模拟结果与现场勘查结果基本一致。     

Construction Technology of Floor Slab for Deep and Large Top–Down Excavation in Soft Clay

The construction quality and elevation of floor slab obtained using the top–down construction method in soft clay may be affected by soil uplift due to excavation unloading and recompression settlement due to the weight of concrete. Based on the Shanghai EXPO axis and underground complex project (Shanghai EXPO axis excavation), soil uplift is studied by conducting centrifugal model test and numerical simulation. The soil uplift process for soft clay in Shanghai EXPO Axis excavation is mainly concentrated during the 14 days after excavation, attaining approximate 84 % of the final values. The configuration of soil uplift is serrated. The maximum soil uplifts for excavation depths of ?1.08, ?9.10, ?12.80, and ?17.30 m (WSEY) are 85, 127, 143, and 153 mm respectively. On-site monitoring reveals that the floor slabs and beams are settling during concrete casting. The settlement values are related to concrete weight, bearing capacity of soils under the excavation surface, and stiffness of scaffold. Based on these findings, exposure time duration between soil excavation and concrete casting and reasonable pre-camber values of scaffold are proposed. The results of this paper demonstrate that the application of these values is effective in controlling construction quality and elevation of floor slab and beam.     

昌乐玄武岩内刚玉巨晶（蓝宝石）中发现富碳酸盐和硫酸盐熔融包裹体及其意义

山东昌乐新生代玄武岩内的刚玉巨晶(蓝宝石)中含有多种类型熔融包裹体,其成分对了解华北深部地幔交代过程中的流/熔体性质和刚玉母岩浆特点具有重要意义.详细的岩相学和激光拉曼分析鉴定出一类富碳酸盐和硫酸盐成分的原生熔融包裹体以及一类含硫酸盐和氯化物等成分的次生熔融包裹体,二者同时还含有CO2和H2O.碳酸盐和硫酸盐成分在世界范围玄武岩内刚玉巨晶中是首次发现,结合已有的包裹体稀有气体同位素和测温资料,反映两种成分可能来源于交代地幔的碳酸岩熔体,预示着华北深部地幔不仅经历了硅酸盐成分的交代还经历了富碳酸盐和硫酸盐成分(碳酸岩)的交代,同时也显示刚玉母岩浆成分复杂,至少有富这两类成分物质的参与,刚玉很可能是硅酸盐岩浆/岩石和幔源碳酸岩岩浆相互作用的产物,后被玄武岩喷发携带至地表.     

Sulfates on Mars: A systematic Raman spectroscopic study of hydration states of magnesium sulfates

The martian orbital and landed surface missions, OMEGA on Mar Express and the two Mars Explorations Rovers, respectively, have yielded evidence pointing to the presence of magnesium sulfates on the martian surface. In situ identification of the hydration states of magnesium sulfates, as well as the hydration states of other Ca- and Fe- sulfates, will be crucial in future landed missions on Mars in order to advance our knowledge of the hydrologic history of Mars as well as the potential for hosting life on Mars. Raman spectroscopy is a technique well-suited for landed missions on the martian surface. In this paper, we report a systematic study of the Raman spectra of the hydrates of magnesium sulfate. Characteristic and distinct Raman spectral patterns were observed for each of the 11 distinct hydrates of magnesium sulfates, crystalline and non-crystalline. The unique Raman spectral features along with the general tendency of the shift of the position of the sulfate ν₁ band towards higher wavenumbers with a decrease in the degree of hydration allow in situ identification of these hydrated magnesium sulfates from the raw Raman spectra of mixtures. Using these Raman spectral features, we have started the study of the stability field of hydrated magnesium sulfates and the pathways of their transformations at various temperature and relative humidity conditions. In particular we report on the Raman spectrum of an amorphous hydrate of magnesium sulfate (MgSO₄·2H₂O) that may have specific relevance for the martian surface.     

基于地表冲击荷载作用下的城市地下空间结构动力响应分析

由于地震效应、重载车辆的震动效应或由于不同爆炸物引起的强烈冲击效应,都会给城市地下空间结构带来较大的影响。通过土体的混凝土改进剑桥动力本构模型和混凝土塑性损伤本构模型,建立地表爆炸冲压荷载简化计算模型,对城市地下空间结构在TNT当量100 kg的炸药爆炸冲压荷载作用下进行了动力分析,研究了结构埋深、土体刚度对结构动力响应的影响,分析了远场爆炸地震波作用下地下空间结构的动力响应。计算结果表明,地下空间结构中部顶板产生了轻微的拉伸损伤;当埋深小于5 m时,结构动应力响应较大;结构覆盖土刚度越小,土对爆炸能量的吸收作用越显著;由于爆炸产生的地震波频率高,其对结构动应力的影响较小。研究结果对地下结构的抗爆设计具有一定的参考意义     

某基坑复合土钉墙土钉内力超限分析

土钉与预应力锚杆的联合支护在基坑工程中运用广泛,近年来的研究也取得很大进展,但对其受力情况及作用机理仍未完全认识,在实际工程中也有一些失败的教训。本文以内蒙古地区某产品煤槽仓工程为例,针对监测中土钉内力超预警值的情况,从共同作用机理及施工过程控制等方面对数据进行了分析。分析结果表明,未及时喷射混凝土面板致使土体由于缺乏表面约束产生塑性变形是造成土钉内力超限的主要原因,而在土体表面没有混凝土面板约束的情形下开挖过深并施加大的施工扰动更使得被监测的土钉内力值进一步加大。由此可见混凝土面板对于提高被开挖土体稳定性的作用十分明显,此外分析结果还表明了土体和支护结构之间存在时间及空间效应,在施工中应避免超挖和减少施工扰动。     

Optimization approach to retrieve soil surface parameters from single-acquisition single-configuration SAR data

This study suggests a novel approach to the retrieval of soil surface parameters using a single-acquisition single-configuration synthetic-aperture radar (SAR) system. Soil surface parameters such as soil moisture and surface roughness are key elements for many environmental studies, including Earth surface water cycles, energy exchange, agriculture, and geology. Remote sensing techniques, especially SAR data, are commonly used to retrieve such soil surface parameters over large areas. Several backscattering models have been proposed for soil surface parameters retrieval from SAR data. However, commonly, these backscattering models require multi configuration SAR data, including multi-polarization, multi-frequency, and multi-incidence angle. Here we propose a methodology that employs single-acquisition single-configuration SAR data for the retrieval of soil surface parameters. The originality is to use single-acquisition single-configuration SAR data to retrieve the soil surface parameters using an optimization approach by the genetic algorithm (GA); we have used the modified Dubois model (MDM) in HH polarization as the backscattering model. Three HH polarization and C band data sets from Quebec (Radarsat-1), Ontario (SIR-C), and Oklahoma (AIRSAR) were analyzed. The retrieved values of soil moisture and soil surface roughness were then compared to ground truth measurements with corresponding parameters. We employed diverse criteria, including the mean absolute error (MAE), the root mean square error (RMSE), the coefficient of performance (CP), and the correlation coefficient to investigate the performance of the proposed methodology. This analysis suggests the capability of the GA for the retrieval of soil surface parameters. Based on our findings, this method presents a viable alternative approach to the retrieval of soil surface parameters when only single-acquisition single-configuration SAR data is available.     

国外常用的检查井修复方法介绍

在市政管道建设中,检查井主要作用是方便地下管线清淤、疏通以及修复等维护工作。检查井不仅承担路面车辆活荷载,还承担外部周围土体的土压力以及地下静水压力,井壁内部环境也十分复杂,长期受到废液和废气的腐蚀,十分容易出现破坏。针对这一情况,有必要对检查井及时地进行修复,防止其进一步恶化。保证检查井的密封性以及结构完整性。检查井的修复方法包括预制检查井更换,原位浇筑混凝土内衬,原位固化衬里,砂浆喷涂,黄麻纤维加聚氨酯树脂预聚物以及速凝水泥修复技术,各方法的设计施工特点以及适用范围有所不同。     

Behavior of mercury in the supergene zone of geothermal deposits,southern Kamchatka

Mercury distribution was determined in all types of solid materials from the supergene zone of geothermal deposits in southern Kamchatka: rocks, hydrothermally altered rocks (metasomatic rocks), soils, soil—pyroclastic cover, bottom sediments of perennial and intermittent streams, hydrothermal clays, artificial siliceous precipitates, and iron sulfides formed owing to thermal water discharge from a well. The mercury content varies from background values for the Kurile-Kamchatka region in fresh rocks to high and extremely high values in hydrothermal clays and monomineralic pyrite samples. The sources, migration conditions, and concentration mechanisms of mercury were evaluated. Mercury is supplied to the surface of geothermal deposits and thermal fields by a deep hydrothermal flow and is concentrated on thermodynamic barriers in hydrothermal clays, siliceous sinters (silica gel), and soils showing high salinity owing to the deposition in them of silica, sulfates, and other compounds from a vapor-water mixture. Newly formed clay minerals, iron sulfides (pyrite), silica gel, and biological materials (peat) can probably efficiently sorb mercury under geothermal conditions at atmospheric pressure and temperatures from 20°C to 120°C.     

某高层建筑基坑塌方分析及极限分析有限元法模拟

某高层建筑基坑在施工过程中由于没有严格按照设计施工、基坑边坡土层没有完全封闭、边坡顶部和底部裸露,致使雨水从坡顶排水沟下部渗到边坡面层内,经雨水浸泡后的土体抗剪强度降低,大量土块失稳落下,喷射混凝土面层内形成了大片空洞,锚索的预应力损失,最终导致整个面层坠下,造成塌方事故。采用二分法改进的极限分析有限元法对该基坑边坡进行模拟,得到了基坑边坡的安全系数和滑动面,用二分法对土体强度参数进行折减,提高了极限分析有限元法的求解效率。     

Utilization of fly ash for stabilization/solidification of heavy metal contaminated soils

Pozzolanic-based stabilization/solidification (S/S) is an effective, yet economic remediation technology to immobilize heavy metals in contaminated soils and sludges. In the present study, fly ash waste materials were used along with quicklime (CaO) to immobilize lead, trivalent and hexavalent chromium present in artificially contaminated clayey sand soils. The degree of heavy metal immobilization was evaluated using the Toxicity Characteristic Leaching Procedure (TCLP) as well as controlled extraction experiments. These leaching test results along with X-ray diffraction (XRD), scanning electron microscope and energy dispersive X-ray (SEM–EDX) analyses were also implemented to elucidate the mechanisms responsible for immobilization of the heavy metals under study. Finally, the reusability of the stabilized waste forms in construction applications was also investigated by performing unconfined compressive strength and swell tests. The experimental results suggest that the controlling mechanism for both lead and hexavalent chromium immobilization is surface adsorption, whereas for trivalent chromium it is hydroxide precipitation. Addition of quicklime and fly ash to the contaminated soils effectively reduced heavy metal leachability well below the nonhazardous regulatory limits. Overall, fly ash addition increases the immobilization pH region for all heavy metals tested, and significantly improves the stress-strain properties of the treated solids, thus allowing their reuse as readily available construction materials. The only potential problem associated with this quicklime–fly ash treatment is the excessive formation of the pozzolanic product ettringite in the presence of sulfates. Ettringite, when brought in contact with water, may cause significant swelling and subsequent deterioration of the stabilized matrix. Addition of minimum amounts of barium hydroxide was shown to effectively eliminate ettringite formation. Overall, due to the presence of very high levels of heavy metal contamination along with sulfates in the solid matrices under study, the results presented herein can be applied to the management of incinerator and coal fly ash, boiler slag and flue gas desulfurization wastes.     

Characterization of PM2.5 by X-ray diffraction and scanning electron microscopy–energy dispersive spectrometer: its relation with different pollution sources

Atmospheric PM_2.5 samples were collected by using Mini-Vol TAS air sampler. Samples were characterized directly on the collecting substrate using X-ray diffraction and scanning electron microscopy–energy dispersive spectrometer. From the analysis, it was found that Si dominate over other elements which follows the trend as Si > S > Zn > Cu > Na > Al > K > Ca > P > Fe > Mg > Ti. Based on the measurements of a population of 840 particles, particle morphology was determined by quantitative image analyzer and value of roundness (R) varies from 0.23 to 1.0 (mean 0.75) which suggests that particles vary in shape from nearly irregular to perfectly spherical shape. The mineral particulate matter identified in the atmosphere of Pune was made up of: silicates (52 %), oxides (22 %), sulfates (8 %), phosphates (7 %), carbonates (3 %) and others. A factorial analysis was carried out to determine the main elements related to the emission sources such as soil and building material erosion (~44.6 %); oil combustion (20.6 %) and fuel and biomass burning (18.3 %). Besides these factors, soot particles are abundantly present in all studied samples. Mineral particles such as sulfates aggregated to soot could have produced localized climatic effect in Pune. The emphasis of the present study is to give insight and detailed analysis of morphological and chemical composition of atmospheric particles at discrete level.     

Failure Mechanism of Soil Nail—Prestressed Anchor Composite Retaining Structure

Enhancing the strength of retaining structure with soil nails and prestressed anchors is a new technique that can be used in the excavation of deep foundation pit. Finite element analysis (FEA) based on ABAQUS is presented in this paper to investigate the failure mechanism of such retaining structure. The model used in the FEA is firstly validated by comparing the modelled results with field measurements for a specific case. The model is then extended to investigate the influence of the prestressed anchor on the (1) horizontal deformation of foundation pit and (2) the distribution of axial forces along the soil nails. It is found that the magnitude of anchor force is the key factor governing the performance of the entire retaining system. However, the influence of the prestressed anchor is sensitive to the rigidity of the concrete surface layer of the retaining structure. Based on the results of the modelling, the failure mechanism of soil nail—prestressed anchor composite retaining structure is discussed.     

水平荷载下纵截面异形桩承载特性试验

针对纵截面异形桩（扩底桩和楔形桩）、等混凝土用量常规等直径桩的水平向承载特性进行对比模型试验研究,测得不同水平荷载等级下扩底桩和楔形桩的内力、变形、极限承载力和桩侧土压力分布等变化规律特性;初步探讨3种桩型的水平极限承载特性和桩侧土压力分布规律。考虑纵向截面异形效应,基于水平土抗力与水平位移（p-y）曲线法建立纵截面异形桩水平向承载特性理论计算方法,进一步分析弯矩分布规律,并开展影响因素分析。研究结果表明,在当前试验条件下,等混凝土用量楔形桩的水平向承载力比等直径桩的高,砂性土和黏性土中楔形桩水平向极限承载力约分别为等直径桩的1.25倍和1.33倍。相关研究成果可为今后类似土层下水平受荷纵截面异形桩的设计与计算提供参考依据。