Microfabric of fractured Boom Clay at depth: a case study of brittle–ductile transitional clay behaviour

Recent Underground Research Facility (URF) gallery excavation works in the Boom Clay at 224 m below the surface revealed intense fracturing of this weak claystone. Large fault planes (meter-scale) and joints were observed during tunnelling and found to belong to the excavation-disturbed zone (EDZ). Samples taken from the new gallery have been investigated using scanning electron microscope (SEM) imagery and microstructural analysis. This revealed a brittle–ductile transitional behaviour of the mudstone sediment regarding deformation, implying dilatant shear and hybrid fractures in high strain zones and ductile, compacted plastic shear bands in the lower strain zones, following an elasto-plastic constitutive model. Microfabric analysis contributed in this way to a better understanding of clay behaviour and effective fracturing. This information is primordial for understanding the rheology of the clay and assessing the influence of fracturing on permeability, critical issues in radioactive waste management.     

Effect of excavation induced fractures on radionuclide migration through the Boom Clay (Belgium)

In Belgium, the Boom Clay is being evaluated as a potential host formation for the disposal of high-level nuclear waste. In order to investigate this option, an underground research facility composed of two access shafts and 200 m of galleries was excavated. Excavation induced fractures were observed in a zone of approximately 1 m around the galleries. In this study, the potential effect of these fractures on radionuclide migration in the Boom Clay is investigated. Therefore, a hydrogeological model of the clay is built with a radionuclide source in the middle of the clay layer surrounded by different fracture configurations. Two types of fracture configurations are inserted in the model. The first type of fracture properties is drawn stochastically from the probability distributions of the properties of the fractures observed around previously excavated galleries. These fracture patterns are considered to be realistic although in this study it is conservatively assumed that no self-sealing occurs. The model is run for a large number of stochastically drawn fracture configurations and the results are compared to a model without fractures. These calculations show that the radionuclide fluxes through the clay are not significantly influenced by these fractures. For the second type of fracture configurations, the fracture properties are varied over a much larger range. Hypothetical fractures with much higher values of fracture extent, aperture, dip and frequency than observed are modeled. With these hypothetical fracture configurations, the critical values of the fracture parameters are determined that must be exceeded to have a significant effect on the radionuclide fluxes through the clay. These calculations show that the extent of the fractured zone has the largest effect on radionuclide migration. The other fracture parameters (aperture, spacing and dip) have a limited effect on the radionuclide fluxes. To obtain a total radionuclide flux through the lower clay boundary that is respectively 10%, 50% and 100% larger than without a fractured zone, the extent of the hypothetical fractured zone should be respectively 27.97 m, 43.86 m and 46.92 m. Such fractures are not expected to be generated by mechanical excavation in the Boom Clay. The obtained critical extent values of the hypothetical fractures are a factor 30 to 40 higher than the measured values of the extent of the excavation disturbed zone. These calculations thus indicate that it is very unlikely that the extent of the fractured zone around the galleries will be large enough to have a significant effect on the radionuclide fluxes through the Boom Clay. This conclusion is further supported by the conservative assumption that no self-sealing occurs. These calculations can function as a preliminary robustness test in ongoing safety analysis studies.     

Structural and hydrogeological characterisation of the excavation-disturbed zone in the Opalinus Clay (Mont Terri Project, Switzerland)

The fracture network in the excavation-disturbed zone (EDZ) of an argillaceous formation, the Opalinus Clay in the Mont Terri Rock Laboratory in Switzerland, is characterised by applying structural and hydrogeological techniques. Unloading fractures are studied by mapping side walls of newly excavated niches and by analysing resin-injected overcores taken from the EDZ. The result is a structural data set of fracture orientations, frequencies, and extent of the EDZ. Pneumatic and hydrogeological tests are carried out in short boreholes crossing the EDZ to derive hydraulic parameters such as permeability and transmissivity distributions of the fracture network. Hydraulic transmissivities are orders of magnitude higher when compared to those of undisturbed rock, and are in the order between 1E−8 and 1E−7 m²/s. Regular repetition of these hydrotests resulted in decreasing transmissivities in the range of two orders of magnitude over a time period of about 2 years. These observations indicate a hydraulic self-sealing of the initially highly transmissive fracture network with ongoing saturation of the EDZ. The dynamic evolution of EDZ fractures can be derived by interpreting pore water pressure measurements during gallery excavation.Finally, all structural and hydrogeological information is synthesised in a conceptual model of the EDZ in the Mont Terri Rock Laboratory.     

Determination of gas diffusion coefficients in saturated porous media: He and CH4 diffusion in Boom Clay

Boom Clay is presently studied as the reference host formation for the disposal of high-level and long-lived radioactive waste in Belgium. In a geological repository, the production of gas is unavoidable. Gas is produced by different mechanisms: anaerobic corrosion of metals in waste and packaging, radiolysis of water and organic materials in the packages and microbial degradation of various organic wastes. Corrosion and radiolysis yield mainly hydrogen while microbial degradation leads to methane and carbon dioxide. The generated gas will dissolve in the ground water. As transport in Boom Clay is dominated by diffusion, the dissolved gas is transported away from the repository by diffusion as dissolved species. If the rate of gas generation is larger than the diffusive flux into Boom Clay, the pore water within the disposal gallery will become oversaturated and a free gas phase might form. If the gas pressure keeps increasing, free gas ingress into Boom Clay will occur, most likely through creation of new pathways. In order to make a good evaluation of the balance between gas generation and gas dissipation through engineered barriers and host formation, good estimates for the gas diffusion coefficients of the gases are needed. The currently available gas diffusion parameters for hydrogen in Boom Clay suffer from a large uncertainty, and by application of conservative values for both the source term and the gas migration term the formation of a free gas phase can presently not be excluded for some waste types.In this study a versatile method was developed to determine more precisely the gas diffusion coefficient for dissolved gases in Boom Clay. For the development of the technique, He and CH₄ were used.The proposed method is based on a through diffusion methodology and allows for two dissolved gases to diffuse through a clay sample at the same time. From the evolution of the diffusant concentration in both compartments, the apparent diffusion coefficients of dissolved He and CH₄ were obtained: 12.2 × 10^− 10 and 2.42 × 10^− 10 m²/s, with uncertainties of 10%, respectively.     

A critical review of laboratory and in-situ hydraulic conductivity measurements for the Boom Clay in Belgium

The Boom Clay has been investigated for more than 30 years as a candidate host formation for the disposal of high-level and long-lived radioactive waste in Belgium. The very low hydraulic conductivity (on the order of 10^− 12 m/s) in combination with limited hydraulic gradients over the host formation (0.02–0.04) results in water flow in the Boom Formation being negligible and diffusion the dominant transport mechanism. The assessment of the long-term barrier function of the host clay formation in the framework of radioactive waste disposal requires rigorous quantitative characterization of key formation properties such as the hydraulic conductivity (K).Hydraulic conductivities of Boom Clay measured through various testing techniques in the laboratory, i.e. tracer percolation experiments, constant head permeameter experiments and isostatic experiments, exhibit similar K values in the order of 10^− 12 m/s. Based on a large set of test samples, the impact of sample scale, hydraulic gradient range adopted in the tests, stress controlled methods and pre-existing fissures in the sample on the K value is shown to be quite limited. In situ measurements obtained from both several-centimetre long piezometer filters and percolation into a 7-metre long gallery and 21-metre long shaft at the HADES underground research facility yield K values that are very similar to values measured in the laboratory on samples of a few centimetres. This indicates that the K measurements for the Boom Clay obtained through various techniques are very consistent. K values measured on a centimetre-scale are also representative at the metre-scale, which is often the size of grid cells used in numerical simulations for long-term safety assessments.Spatial analysis of K values across the Boom Clay at the Mol site reveals a typical profile with a very homogenous 61-m thick central part, i.e. the so-called Putte and Terhagen Members, which is also the least permeable part of the Boom Clay. The geometric mean of the vertical (K_v) and horizontal (K_h) hydraulic conductivities for the Putte and Terhagen Members at the Mol site are 1.7 × 10^− 12 and 4.4 × 10^− 12 m/s, respectively, with a vertical anisotropy K_h/K_v of about 2.5. Higher K values, but still low (10^− 12 to 10^− 10 m/s), are observed in the more silty zones above and below the Putte and Terhagen Members, i.e. the Belsele–Waas Member and the Boeretang Member, as well as in the double band of the lower Putte Member.A regional analysis of vertical K variability of the Boom Clay in the northeast of Belgium based on test results from five boreholes shows an increase in hydraulic conductivity from the east towards the west. Statistical analyses indicate that the effect of the samples' stratigraphic position on hydraulic conductivity is strongly related to different grain-size characteristics. However, a general K–grain-size model does not explain the geographical differences in K values satisfactorily. Geographical differences can be best explained by different K–grain-size relationships at the different boreholes. The regional variation in K could be attributed in part to porosity, which in turn is related to the burial depth of the clay.     

盾构施工对临近地层影响的近场动力学分析

针对传统的有限元方法在面对不连续情况时会出现奇异性这一问题,本文采用基于非局部作用思想建模的近场动力学方法研究了地铁盾构开挖问题,并完善体积修正公式,建立能够考虑隧道开挖过程中衬砌、注浆层作用的近场动力学模型。结果表明:近场动力学解与有限元解在临近地层位移的影响上呈现出相同变化趋势;盾构隧道开挖引起隧道上方土体沉降,下方土体隆起,左右两侧土体向隧道中心方向移动。近场动力学结果与现场实测结果的对比分析表明近场动力学方法在盾构施工模拟中具有较高的精度,在隧道工程施工的数值模拟研究领域具有应用前景。     

隧道爆破掘进超欠挖原因分析及控制措施

爆破掘进产生的超欠挖问题一直是影响隧道工程建设质量、安全及成本的重要因素,针对当前隧道爆破掘进后轮廓面不平整、超欠挖问题突出、喷射混凝土超耗严重的现状,系统地分析了隧道爆破掘进超欠挖的危害,从环境、技术、管理、奖惩、观念等方面分析了造成超欠挖的原因,并探究了相应的超欠挖控制措施。建议优先采用光面爆破技术,通过合理选择爆破参数,严格按工艺流程施工,加强现场管理,可将隧道超挖控制在10 cm以内。     

Mechanical properties and applications for floor tiles of a composite from clay and maleated polyethylene

New composites were prepared from dried waste mud containing clay (Clay) and maleated polyethylene (MPE) by melt mixing. Scanning electron microscopy showed strong adhesion of MPE to Clay in the MPE–Clay composite, and this was probably due to the increased compatibility between MPE and Clay. With an increase in the Clay concentration to 60 wt %, the tensile strength of the MPE–Clay composite increased. Furthermore, the smaller elongation of the MPE–Clay composite indicated effective transfer of the high tensile strength of Clay to the MPE matrix through the strong adhesion between Clay and MPE. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1176–1182, 2005     

Stabilization of sludge from earth pressure balance for use in earth embankments

The increasing use of earth pressure balance in tunnel excavations has created a challenge for constructors, namely, the handling of excavation sludge. This is an important environmental problem, and it must be solved in an efficient, economical and innovative way. This study presents a new technique for in-situ treatment of the waste by mixing it with lime. To predict the material behavior before the process, the chemical composition, morphology and texture of three samples of sludge from excavation works in a tunnel were analyzed. A quick and economical testing procedure was developed, based on the measurement of the electrical conductivity in typical mixtures. The control parameters of the in-situ treatment process were optimized to obtain enhanced soil as a final product.     

Spatial variability of transport parameters in the Boom Clay

Several transport parameters (as hydraulic conductivity K, apparent diffusion coefficient D_p and diffusion accessible porosity η of HTO and iodide) have been intensively measured in the laboratory on high-quality cores taken at the Mol-1 borehole of the Mol site, in Belgium. The borehole was cored in 1997 from about 145 to 325 m depth, including the whole thickness of the Boom Formation, a Tertiary clay situated between 186 and 288 m depth (ground level), and part of the surrounding layers.The hydraulic conductivity measurements confirm the low permeability of the Boom Clay. An upper 90-m-thick clay layer within this formation can be considered as homogeneous with respect to the hydraulic conductivity. The vertical hydraulic conductivity K_v (i.e. K perpendicular to the bedding) is in the order of magnitude of 10⁻¹² m s⁻¹ and the average is 2.3×10⁻¹² m s⁻¹. This layer comprises from top to bottom the “Transition Zone”, the Putte Member, the Terhagen Member and the top of the Belsele-Waas Member of the Boom Formation. The 12 m at the base of the Formation, which corresponds to the lower part of the Belsele-Waas Member is characterised by larger K_v values (ranging between 10⁻¹¹ and 9×10⁻¹¹ m s⁻¹).The same thick clay layer can also be considered as homogeneous, regarding the values of the apparent diffusion coefficient and the diffusion accessible porosity η of tritiated water (HTO) and iodide. The average value of the diffusion accessible porosity is 0.37±0.03 for HTO and 0.16±0.02 for iodide. The apparent diffusion coefficient varies from 1.1×10⁻¹⁰ to 5.5×10⁻¹⁰ m² s⁻¹ for HTO and from 9.1×10⁻¹¹ to 5.2×10⁻¹⁰ m² s⁻¹ for iodide.     

Preparation and characterization of Polyethylene/Clay/Silver nanocomposites using functionalized polyethylenes as an adhesion promoter

The performance of Polyethylene (PE)/Clay/Silver nanocomposites is dependent to a great extent on the properties of filler–matrix interface. To improve the interfacial properties in PE/Clay/Silver composites, different types of compatibilizers or adhesion promoters were introduced. The compatibilization provided by maleic anhydride (MA), itaconic acid (IA) and 2-[2-(dimethylamine)-ethoxy] ethanol (DMAE) functionalized PEs for forming PE-based nanocomposites was studied and compared. IA was grafted into PE by melt mixing to obtain PEgIA (compatibilizer 1), thereafter, PEgIA and PEgMA (compatibilizer 2) were reacted with DMAE also by melt mixing to obtain PEgI-DMAE (compatibilizer 3) and PEgM-DMAE (compatibilizer 4). These compatibilizers were reacted using ultrasound with a solution of AgNO₃ 0.04 M and ethylene glycol. Ammonium hydroxide was added in a ratio of 2:1 M with respect to silver nitrate. These silver coated compatibilizers were mixed with PE and with a quaternary ammonium modified montmorillonite clay (Nanomer I28E), thus forming the different hybrid PE/Clay/Silver nanocomposites. FTIR confirmed the formation of these compatibilizers. All the DMAE compatibilized nanocomposites had better filler (clay and silver) dispersion and exfoliation. XRD, oxygen and water transmission rate as well as antimicrobial properties attained showed that the PEgI-DMAE produced the better dispersed PE, clay and silver nanocomposites. The obtained nanocomposites showed enhanced barrier properties and outstanding antimicrobial properties against bacteria, E. coli. PEgI-DMAE offers an outstanding capability for preparing nanocomposites with highly exfoliated and dispersed filler into the PE matrix that offers a new option for obtaining hybrid nanocomposites with enhanced properties to be used in packaging applications.     

《天工开物》中粳米土与糯米土考证

《天工开物》中记载,景德镇烧器所用之土出自婺源高梁山和祁门开化山,两地之土分别被称作粳米土和糯米土。目前学术界对粳米土与糯米土的原料所指还存在争议。本文从文献史料和工艺学实验两个方面对这一问题进行考证,认为古代工匠是依据高温下成瓷性能的差异,将高岭土称作粳米土,瓷石称作糯米土。     

Hybrid clay‐carbon nanotube/PET composites: Preparation,processing, and analysis of physical properties

The aim of this work was the preparation of novel composites of poly(ethylene terephthalate) (PET) and nano‐hybrid systems based on clay used as catalyst for the growth of multi walled carbon nanotubes (Clay‐CNTs), through catalytic chemical vapor deposition (CCVD). The carbon content into the hybrid filler was 58.1 wt %. Composites with 1.0, 1.5, 2.0, 3.0 wt % of Clay–CNTs were obtained by melt compounding and processed using a microinjection molding press. Unfilled PET was processed in the same composites conditions. Structural characterization and physical properties (thermal, degradation, mechanical, and electrical) were analyzed and correlated to the hybrid filler loading, and carbon nanotubes amount. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40441.     

Preparation of nanocomposites by melt compounding polylactic acid/polyamide 12/organoclay at different screw rotating speeds using a twin screw extruder

This study analyzes the effect of different screw rotating speeds on the clay dispersion and mechanical properties of nanocomposites prepared by melt compounding polylactic acid (PLA) with an organoclay in a co‐rotating twin screw extruder. Polyamide 12 (PA12) was used as an additive. Two different screw rotating speeds, 65 rpm and 150 rpm, were used in this study. According to the tensile strength data, the Young's modulus of the PLA/clay nanocomposites showed improvement at a screw rotating speed of 150 rpm. The Young's modulus improved with the addition of the organoclay to PLA matrix, but decreased when PA12 was added to the PLA matrix. The tensile strengths and elongations become small by adding organoclay to PLA matrix. The tensile strengths of the PLA/organoclay nanocomposites increased for the higher screw rotating speed (150 rpm). The d‐spacing of PLA/PA12/Clay nanocomposites was independent of the addition of PA12. The size of the clay aggregates in the PLA/PA12/Clay nanocomposites is smaller than that of PLA/Clay. Furthermore, the thermal stability of the PLA/Clay nanocomposite increases with addition of PA12, while on the whole, it had little influence on the tensile properties. POLYM. COMPOS., 29:1–8, 2008. © 2007 Society of Plastics Engineers     

Characterization and use of clays from the Rio Bonito Formation/Paraná Basin for ceramic industry application

Raw materials with different technological properties found in the same geological region can constitute a ceramic formulation upon proper mixing. This study aims to demonstrate the best way to develop a mixture using a mixture design method, emphasizing the geology of three clays in the Rio Bonito Formation/Paraná Basin. The mineralogical and chemical characteristics of these clays were investigated by X-ray diffraction and X-ray fluorescence, respectively, along with elementary (CNH), differential thermal and thermogravimetric analysis, and dilatometry. Ten formulations and their technological properties, including apparent density, shrinkage, water absorption, and mechanical resistance, were investigated. The results showed the potential of the studied mineral deposit clays for application in the ceramic industry in different materials. Clay 1 showed refractory characteristics, and Clay 3 was more plastic. The mixtures with higher contents of Clay 1 showed ideal for monoporosa tile recipes. The mixtures with higher contents of Clay 3 were ideal for porcelain tile pastes.     

天甲橡胶提高陶土在NR中的补强性能研究

用ＭＧ４９和ＭＧ３０改性陶土,通过ＳＥＭ以及界面作用强度表征值、补强程度和力学性能等的测定,研究了改性方法、天甲橡胶的改性程度和用量以及陶土用量对陶土填充ＮＲ硫化胶补强性能的影响。结果表明：天甲橡胶湿法改性陶土较有效地增强了陶土与ＮＲ基质间的界面作用强度,改善了陶土填充ＮＲ硫化胶的力学性能,提高了陶土的补强效果。ＭＧ４９改性陶土的补强效果优于ＭＧ３０。接枝程度高的天甲橡胶（ＭＧ４９）,其最适用量较低（７５％）;接枝程度低的天甲橡胶（ＭＧ３０）,其最适用量较高（１０％）     

New clay‐supported Ziegler–Natta catalyst for preparation of PE/Clay nanocomposites via in situ polymerization

Polyethylene/clay (PE/Clay) nanocomposites were prepared by the in situ polymerization of ethylene using the new Clay/butyl octyl magnesium (BOM)/Chloroform/EtOH/TiCl₄/tri ethyl aluminum (TEA) catalyst system in heptane where BOM and TEA were the support for the clay modification and cocatalyst, respectively. The influence of the modified clay using BOM on the catalyst and polymerization was investigated. Also, the effect of temperature, pressure, hydrogen, and the molar ratios of TEA/Ti on the catalyst yield and ethylene consumption (polymerization rate) were studied. It was found that the above clay‐supported catalyst was an efficient Ziegler–Natta type catalyst due to its suitable yield for the polymerization of ethylene toward the production of the PE/Clay nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of organo clay content on proton conductivity and methanol transport through crosslinked PVA hybrid membrane for direct methanol fuel cell

In the present study, crosslinked poly(vinyl alcohol) (PVA) membranes were prepared using poly(styrene sulfonic acid-co-maleic acid) (PSSA_MA) (PVA:PSSA_MA = 1:7). The PSSA_MA was used both as a crosslinking agent and as a donor of the hydrophilic group (–SO₃H and/or –COOH). The hybrid membranes were prepared by modified clay such as Clay Na⁺, Clay 30B, and Clay 15A. The thermal, water uptake, proton and methanol transport properties of the hybrid membrane were found to be sensitive to the clay type and content. The hybrid membrane with Clay 30B shows higher proton conductivity than other hybrid membranes due to hydroxyethyl group. The membrane with Clay 15A showed the lowest methanol permeability due to lower specific gravity than other clay. Compared to the membrane without modified, the PVA/PSSA_MA/Clay 15A containing 4 wt% of Clay 15A showed both high proton conductivity (0.023 S/cm) and low methanol permeability (2.19 × 10^?7 cm²/s).     

聚合物／粘土纳米复合材料最新进展

介绍聚合物/粘土纳米复合材料独特的结构和其良好的力学性能及优良的耐热、气密性等性能。及用尼龙、聚丙烯等不同聚合物与粘土制备的纳米复合材料的最新进展情况。     

Morphology,biodegradability, mechanical,and thermal properties of nanocomposite films based on PLA and plasticized PLA

In this study, melt intercalation method is applied to prepare poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG)‐plasticized PLA nanocomposite films including 0, 3, and 5% organoclay (Cloisite 30B) using a laboratory scale compounder, which is connected to a microcast film device. To evaluate the nanomorphology and the dispersion state of the clays, X‐ray diffraction (XRD) and transmission electron microscopy (TEM) are conducted. Tensile tests are performed to characterize the mechanical behavior of the films. Biodegradation rate is determined by degradation tests in composting medium. Differential scanning calorimeter (DSC) is applied to observe the thermal behavior of the films. XRD and TEM show that the exfoliation predominantly occurrs in plasticized PLA nanocomposites, whereas unexfoliated agglomerates together with exfoliated clays are observed in the nonplasticized PLA. Tensile tests indicate that the addition of 3% clay to the neat‐PLA does not affect the strength; however, it enhances the modulus of the nanocomposites in comparison to neat‐PLA. Incorporation of 3% clay to the plasticized PLA improves the modulus with respect to PLA/PEG; on the other hand, the strain at break value is lowered ～ 40%. The increase in the rate of biodegradation in composting medium is found as in the order of PLA > PLA/PEG > 3% Clay/PLA/PEG > 5% Clay/PLA/PEG > 3% Clay/PLA. DSC analysis shows that the addition of 3% clay to the neat PLA results in an increase in T_g. The addition of 20% PEG as a plasticizer to the neat‐PLA decreases T_g about 30°C, however incorporation of clays increases T_g by 4°C for the plasticized PLA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009