The usability of bottom ash as an engineering material when amended with different matrices

This study aims at investigating the utilization of bottom ash obtained from four different power stations as a construction fill and landfill bottom liner. For the matrix material, commercial powdered bentonite, construction lime and natural clay were used. Compaction tests (Standard Proctor and vibratory hammer) were carried out on the different ratios of bottom ash and matrix material. The optimum water content ranged from 40 to 45% yielding a dry density mostly ca 1 Mg m⁻³. Uniaxial compressive strength of mixtures ranges from 0.1 to 0.5 kgf cm⁻² which showed a 3–20-fold increase when tested on 28-day cured specimens. Triaxial compression tests yield varying rates of shear strength which also showed as high as an 11-fold increase for cured specimens. The hydraulic conductivity of those mixtures was mostly ca 10⁻⁴ cm s⁻¹, which is not considered to be low enough for landfill lining. Leaching tests using deionized water were also performed to investigate the possible effect of leachate produced from the mixtures on the environment. In conclusion a light density and environmentally friendly mixture is determined and proposed as construction filler.     

Seismic activity along the central america volcanic arc: is it related to subduction of the Cocos plate?

We determine seismic strain rate of tectonic earthquakes along the Central America Volcanic Arc. We then compare this result to those obtained from earthquakes related to the convergence of the Cocos and Caribbean plates and to earthquakes in the back-arc region of northern Central America.

The seismic strain-rate tensor for shallow-focus earthquakes along the Central America volcanic arc since 1700, has a compressive eigenvector with a magnitude of 0.7 × 10⁻⁸ year⁻¹, and oriented in a 357° azimuth. The extensive eigenvector is oriented in a 86° azimuth, with a magnitude of 0.82 × 10⁻⁸ year⁻¹. When only Centroid Moment-tensor solutions (CMT) are considered, the respective eigenvectors are 1.2 × 10⁻⁸ year⁻¹ and 1.0 × 10⁻⁸ year⁻¹.

The compressive eigenvector from the seismic strain-rate tensor for earthquakes along the Cocos-Caribbean convergent margin is 2.0 × 10⁻⁸ year⁻¹, plunging at 25°, and oriented in a 29° azimuth. Its magnitude and direction are similar to those of the compressive eigenvector for earthquakes along the volcanic arc. The extensive eigenvector along the convergent margin, on the other hand, has a large vertical component. The compressive and extensive eigevenvectors are 4.9 × 10⁻⁸ year⁻¹ and 4.6 × 10⁻⁸ year⁻¹, using only CMTs as the database.

Earthquakes along the grabens of northern Central America yield a seismic strain-rate tensor whose extensive eigenvector has a magnitude of 2.4 × 10⁻⁸ year⁻¹, oriented in a 109° azimuth. Magnitude and direction are similar to those of the extensive eigenvector for earthquakes along the volcanic arc. The compressive eigenvector along the grabens is practically vertical.

Similarities in magnitudes and directions for compressive and extensive eigenvectors suggest to us that the strain field along the Central America volcanic arc is the result of compression along the convergent Cocos-Caribbean margin, and extension in the back-arc region, along the grabens of northern Central America. This field is resolved as strike-slip faulting along the arc.     

Equilibria in the system Au–Ag–S–fluid: computed and experimental data

We present results of computations on the interaction of solid-phase electrum–argentite–pyrite (weight ratios 210⁻⁵/ 210⁻³/1 and 210⁻⁵/410⁻²/1) association with Cl-containing aqueous moderately acid solutions (0.5m NaCl, pH = 3.08) at 300 °C and 500 bars. These data are a physicochemical basis for predicting the geochemical behavior of Au and Ag during the hydrothermal-metasomatic transformation of Au-Ag-pyrite. We also propose a technique of study of this process based on the phase equilibria of the subsystem Au–Ag–S with the aqueous solution at different liquid/solid (l/s) ratios, with the use of new graphic diagrams. The relationship of the composition of the solid-phase association with l/s ratio in real boundary conditions (Au = 17 ppm, mAu/mAg = 10^–3.57–10^–2.28) is shown. The maximum l/s values for complete leaching of gold and silver (l/smax = 200–800) are estimated. It has been established that argentite is the first to dissolve when mAu/mAg(s) > mAu/mAg(sol), and electrum, when mAu/mAg(s) < mAu/mAg(sol).

The experimental results showed that at 300 °C, the conversion of electrum (N_Au = 300‰) nonequilibrated with pyrite into an Au-richer form (N_Au = 730‰) and argentite follows an intricate kinetic scheme. Using the Pilling-Bedwords kinetic equation for processing data yielded the process rate constant K = 2.8(±0.5)10⁻⁵ g²cm⁻⁴day⁻¹. With this equation, the time of the complete conversion of 200 μm thick flat gold grains is 604 days. These data evidence a significant role of kinetic factors in hydrothermal-metasomatic processes involving native gold, which requires combination of thermodynamic and kinetic approaches on the construction of geologo-genetic models for hydrothermal sulfide formation.     

Interactions of uranium with bacteria and kaolinite clay

We assessed the accumulation of uranium (VI) by a bacterium, Bacillus subtilis, suspended in a slurry of kaolinite clay, to elucidate the role of microbes on the mobility of U(VI). Various mixtures of bacteria and the koalinite were exposed to solutions of 8 × 10^− 6 M- and 4 × 10^− 4 M-U(VI) in 0.01 M NaCl at pH 4.7. After 48 h, the mixtures were separated from the solutions by centrifugation, and treated with a 1 M CH₃COOK for 24 h to determine the associations of U within the mixture. The mixture exposed to 4 × 10^− 4 M U was analyzed by transmission electron microscope (TEM) equipped with EDS. The accumulation of U by the mixture increased with an increase in the amount of B. subtilis cells present at both U concentrations. Treatment of kaolinite with CH₃COOK, removed approximately 80% of the associated uranium. However, in the presence of B. subtilis the amount of U removed was much less. TEM–EDS analysis confirmed that most of the U removed from solution was associated with B. subtilis. XANES analysis of the oxidation state of uranium associated with B. subtilis, kaolinite, and with the mixture containing both revealed that it was present as U(VI). These results suggest that the bacteria have a higher affinity for U than the kaolinite clay mineral under the experimental conditions tested, and that they can immobilize significant amount of uranium.     

Strain rate effect on the compressive strength of frozen sand

Cylindrical specimens of fine Ottawa sand (A.S.T.M. designation C-109), compacted at the optimum moisture content and saturated before unidirectional freezing, have been tested in uniaxial compression at a cold room temperature of —5.5°C and strain rates between 10⁻⁷ and 10⁻² s⁻¹. The results agree with an extrapolation of data obtained by Sayles and Epanchin [1], but are much higher than those obtained by both Goughnour and Andersland [2] and Perkins and Ruedrich [3] at strain rates below 10⁻⁵ s⁻¹. There is evidence that this may be due to variation in total moisture (ice) content, the conditions under which the specimens were frozen (closed system or an open system) and to the end effects at the platen—specimen interface.     

Formation of vivianite in holocene clay sediments

Concretions of vivianite attaining 0.5 g occur in the upper 4 m of the bottom sediments of the Åsrum lake, Vestfold, S. Norway. The vivianite-bearing zone is of lacustrine origin. Vivianite is absent in the underlying lagunal and marine sediments. Electro-chemical and chemical data are given for the interstitial water and the clay.

Solubility product of vivianite is determined. The equilibrium constant is K = 10⁻⁴⁰ for the reaction 3 Fe⁺⁺ + 2 HPO₄⁻ + 2 OH⁻ = vivianite. The concretions grew by diffusion from a slightly supersaturated interstitial water phase. The degree of supersaturation is calculated. The stability relations of vivianite and hydroxyl apatite are discussed.     

Determining mineral weathering rates based on solid and solute weathering gradients and velocities: application to biotite weathering in saprolites

Chemical weathering gradients are defined by the changes in the measured elemental concentrations in solids and pore waters with depth in soils and regoliths. An increase in the mineral weathering rate increases the change in these concentrations with depth while increases in the weathering velocity decrease the change. The solid-state weathering velocity is the rate at which the weathering front propagates through the regolith and the solute weathering velocity is equivalent to the rate of pore water infiltration. These relationships provide a unifying approach to calculating both solid and solute weathering rates from the respective ratios of the weathering velocities and gradients. Contemporary weathering rates based on solute residence times can be directly compared to long-term past weathering based on changes in regolith composition. Both rates incorporate identical parameters describing mineral abundance, stoichiometry, and surface area.

Weathering gradients were used to calculate biotite weathering rates in saprolitic regoliths in the Piedmont of Northern Georgia, USA and in Luquillo Mountains of Puerto Rico. Solid-state weathering gradients for Mg and K at Panola produced reaction rates of 3 to 6×10⁻¹⁷ mol m⁻² s⁻¹ for biotite. Faster weathering rates of 1.8 to 3.6×10⁻¹⁶ mol m⁻² s⁻¹ are calculated based on Mg and K pore water gradients in the Rio Icacos regolith. The relative rates are in agreement with a warmer and wetter tropical climate in Puerto Rico. Both natural rates are three to six orders of magnitude slower than reported experimental rates of biotite weathering.     

Water-enhanced dynamic recrystallization and solution transfer in experimentally deformed carnallite

Cylindrical samples of polycrystalline carnallite (KMgCl₃, 6H₂O) were deformed in a triaxial apparatus at 60°C, at confining pressures between 0.1 and 31 MPa and at strain rates between 10⁻⁴ and 10⁻⁸ s⁻¹. In a number of cases, small amounts of saturated carnallite brine were added. Samples without added brine deform by intracrystalline slip, mechanical twinning, cracking, and by frictional sliding on crack surfaces. Stress-strain curves of these samples are strongly dependent on confining pressure. Addition of brine has a dramatic effect on both microstructural development and mechanical properties. Grain-boundary migration is strongly enhanced. At lower strain rates, additional intracrystalline effects start to appear, together with the onset of solution transfer. Rapid compaction in samples deformed with added brine causes high fluid pressures to develop. At higher strain rates addition of brine results in a decrease of the flow stress by a factor of two. This weakening will increase even further at strain rates below about 10⁻⁹ s⁻¹, when solution transfer becomes rate controlling. It is argued that deformation of carnallite in nature is adequately described by the flow law found for samples deformed with added brine.     

Assessment of crushed shales for use as compacted landfill liners

The possibility of using crushed shales as landfill liners is investigated in this study. Two types of shales were studied by performing the following laboratory tests: hydraulic conductivity, compaction, swelling, consolidation, X-ray diffraction (XRD), scanning electron microscope (SEM) and chemical analysis. For both compacted shales, the hydraulic conductivity was in order of 10^− 7 cm/s or less which satisfies the specifications for landfill liners. The results of XRD and SEM support the low values of the hydraulic conductivity. Because of the dominant presence of low-activity kaolinite, there was no significant change in the hydraulic conductivity when the compacted shales are exposed to calcium chloride solution. The compressibility of the compacted clay was low and no serious post-construction settlement is expected. The shear strength of the compacted shales was within the usual expected range for earthen liners and, therefore, should pose no challenges with respect to shear strength. The crushed shales also satisfy the other criteria related to Atterberg limits and grain size.     

A review and analysis of silicate mineral dissolution experiments in natural silicate melts

We present a database and a graphical analysis of published experimental results for dissolution rates of olivine, quartz plagioclase, clinopyroxene, orthopyroxene, spinel, and garnet in basaltic and andesitic melts covering a range of experimental temperatures (1100–1500°C) and pressures (10⁵ Pa-3.0 GPa). The published datasets of Donaldson (1985, 1990) and Brearly and Scarfe (1986) are the most complete. Experimental dissolution rates from all datasets are recalculated and normalized to a constant oxygen basis to allow for direct comparison of dissolution rates between different minerals. Dissolution rates (ν) range from 5·10⁻¹⁰ oxygen equivalent moles (o.e.m.) cm⁻² s⁻¹ for olivine in a basaltic melt to 1.3·10⁻⁵ o.e.m. cm⁻² s⁻¹ for garnet in a basaltic melt. Values of ln ν are Arthenian for the experiments examined and activation energies range from 118 to 1800 kJ/o.e.m. for quartz and clinopyroxene, respectively.

The relationship between calculated A/RT for the dissolution reactions, where A is the thermodynamic potential affinity, and values of ν is linear for olivine, plagioclase, and quartz. We interpret this as strong evidence in support of using calculated A as a predictor of ν for, at least, superliquidus melt conditions.     

Studying the migration behaviour of selenate in Boom Clay by electromigration

For the disposal of high-level waste (HLW) in a deep geological formation as Boom Clay, safety assessment studies have shown that long lived ⁷⁹Se is one of the more critical fission products. Therefore, the knowledge of its migration properties (diffusion, retention) through the geological barrier (Boom Clay) is of paramount importance. The migration behaviour of selenium strongly depends on its speciation. Under reducing conditions, selenide would be the dominant species and selenium migration would mainly be controlled by the low solubility of Se(−II)-bearing minerals. However Se species are often found in redox disequilibrium and more oxidized species might also coexist. Therefore, the study of selenate migration requires attention, as it might be the most mobile selenium species in the host rock. Electromigration experiments performed with a ⁷⁵Se-labeled selenate in Boom Clay indicate a high mobility for this species. The apparent diffusion coefficient (D_app) of selenate in Boom Clay is estimated from electromigration experiments performed under different electric fields. Using two independent approaches, the value of D_app for selenate is shown to fall in the range from 1.7×10⁻¹¹ to 6.2×10⁻¹¹ m² s⁻¹. Moreover, no reduction of selenate in Boom Clay was observed.     

Landfill site selection using integrated fuzzy logic and analytic network process (F-ANP)

Locating a suitable place to dispose the municipal solid wastes hygienically (sanitary landfill) is one of the fundamental subjects relating the environmental stability of cities and, in general, the human settlements. This final stage of solid waste management requires observance of a series of principles and criteria mainly including environmental, social, economical, and general acceptance criteria. The set of these criteria along with their sub-criteria causes some complexities in decision making for landfill site selection. Considering effective parameters and criteria, we developed an integrated fuzzy logic and analytic network process (i.e. F-ANP) to locate a suitable location for landfilling municipal solid wastes generated in Kahak Town, Qom, Iran. Our findings revealed that integration of fuzzy logic and ANP can give better idea compared with other models like AHP, fuzzy logic, and ANP (individually). Therefore, this model can be applied in site selection for landfill of other similar places.     

Gum rosin (colophony): A suitable material for thermomechanical modelling of the lithosphere

We investigate the use of a ductile material with temperature-sensitive viscosity for thermomechanical modelling of the lithosphere. First, we consider the scaling of mechanical and thermal properties. For a normal field of gravity, the balance of stresses and body forces sets the stress scale, in proportion to the linear dimensions and the densities. The equation of thermal conduction sets the time scale. The activation enthalpy for creep sets the temperature scale; but the thermal expansivity provides an additional constraint on this temperature scale.

Gum rosin appears to be a suitable material for lithospheric modelling. We have measured its flow properties, at various temperatures, in a specially designed rotary viscometer with unusually low machine friction. The rosin is almost Newtonian. Strain rate depends upon stress to the power n, where 1.0 <n < 1.14. The viscosity varies over 5 orders of magnitude, from about 10² Pa s at 80°C, to about 10⁷ Pa s at 40°C. The activation enthalphy is thus about 250 kJ/mol. Measured with a needle probe, the thermal conductivity is 0.113 ± 0.001 W m⁻¹K⁻¹; the thermal diffusivity, (6±3) ×10⁻⁷ m² s⁻¹. Calculated from X-ray profiles, the thermal expansivity is about 3 × 10⁻⁴ K⁻¹. These thermal and mechanical properties make gum rosin suitable for thermomechanical models, where linear dimensions scale down by a factor of 10⁶; time, by 10¹¹; viscosity, by 10¹⁷; and temperature change, by 10¹.     

A statistical model of the earth's crust: Method and results

A model of the earth's crust has been adopted for interpretation of seismic reflection profiles in Kazakhstan. Within it, the smooth variation of seismic velocities with depth becomes complicated by small random fluctuations of various scales. These velocity fluctuations are manifested in oscillations of amplitudes and arrival times of the recorded signals.

The inhomogeneity of the medium is characterized by its coefficient of intrinsic attenuation. Investigation of this coefficient shows that for the crust, its mean value (at a frequency of 7 Hz) is equal to 10⁻³ km ⁻¹ and that over the depth interval of 10–25 km its value is very small, almost zero. It is therefore most surprising that this same depth interval (10–25 km) contains nothing unusual within the cross-section of its determined component wave velocity.     

GPS-measured land subsidence in Ojiya City, Niigata Prefecture, Japan

Land subsidence caused by compression of clay layers in Ojiya City, Japan was measured by global positioning system (GPS) between 1 April 1996 and 31 December 1998.

Three baselines were selected in and around the city, and height difference on a WGS-84 ellipsoid was measured by GPS on each baseline. The ground at the GPS station in the city subsides and rebounds 7 cm every winter and spring, respectively. Measurement accuracy was 9.5 mm standard deviation. Ground water level was observed at a well near the GPS station. Regression analysis between total strain, calculated as ratio of the height difference displacement to the total thickness of the clay layers, and the layers' effective stress change with ground water level change gave good correlation. The slope of regression line 7.0×10⁻¹¹ m²/N was obtained as an average apparent coefficient of volume compressibility of the layers.     

In situ determination of long-term basaltic glass dissolution in the unsaturated zone

Maximum in situ weathering rates of basaltic glass measured at the El Malpais National Monument in New Mexico are on the order of 2–5×10⁻¹⁹ mol/cm² s. Rates were calculated from backscattered electron (BSE) imaging of weathered porosity and are equivalent to 1.7–5% of the surface per 1000 years. Weathering is independent of glass composition but appears to increase with flow elevation at El Malpais. Measured rates represent weathering over 3000 years and are substantially lower than glass dissolution rates measured in the laboratory over much shorter time spans. Basaltic glass is a close chemical analogue to glass hosts proposed for encapsulation of high-level nuclear wastes. Radionuclide release rates predicted from the basis of in situ field rates are substantially less than those predicted from short-term laboratory experiments.     

Engineering characterization of hydraulic properties in a pilot rock cavern for underground LNG storage

Feasibility of storing LNG in a lined rock cavern was evaluated using a pilot cryogenic rock cavern constructed in Daejeon, Korea. The pilot program included hydrogeological and engineering characterization of the rock mass around the cavern, design and construction of a drainage system, and pilot operation of the cryogenic cavern. An appropriate drainage system is most important to protect the containment system of LNG from thermal shocks due to ice lenses and hydrostatic pressure of groundwater. As a part of the pilot program, this study focused on the evaluation of hydraulic and engineering properties of the rock mass around the cavern. For this purpose, engineering logging of the rock cores, single and cross-hole hydraulic tests, and recharge/drainage tests were performed using seven drilled holes with different trends and plunges. Three main joint sets were found from the logging of the rock cores, acoustic borehole televiewer, and window mapping. The orientations of the three major joint sets were 60/209, 40/171, and 29/331, which can provide the main groundwater flow paths. Mean RQD values ranged from 56 to 88, which were classified as fair and good, although varying with depth along single boreholes. Hydraulic conductivity from the single and cross-hole hydraulic tests estimated in the order of 10⁻⁶ or 10⁻⁷ m/s and corresponding transmissivity ranged between 10⁻⁵ and 10⁻⁶ m²/s. Permeable intervals identified from the hydraulic tests were mostly located above the cavern roof. Below the roof, the permeable zone was difficult to observe. According to the hydraulic communication tests performed for some designated intervals, hydraulic connection between boreholes was highly varied with depth or location, which indicated a very different distribution of water conducting joint sets along the boreholes. When water was injected at R1 with constant or varying flow rates, monotonous and stable seepage was observed at observation boreholes. From this, some stable drainage was expected even in relatively heavy rainfalls. When designing the drainage system of the cavern, the drainage holes should be orientated to maximize frequency of encountering the major joint sets and the permeable intervals identified from this study.     

Upper Mississippi embayment shallow seismic velocities measured in situ

Vertical seismic compressional- and shear-wave (P-and S-wave) profiles were collected from three shallow boreholes in sediment of the upper Mississippi embayment. The site of the 60-m hole at Shelby Forest, Tennessee, is on bluffs forming the eastern edge of the Mississippi alluvial plain. The bluffs are composed of Pleistocene loess, Pliocene-Pleistocene alluvial clay and sand deposits, and Tertiary deltaic-marine sediment. The 36-m hole at Marked Tree, Arkansas, and the 27-m hole at Risco, Missouri, are in Holocene Mississippi river floodplain sand, silt, and gravel deposits. At each site, impulsive P- and S-waves were generated by man-made sources at the surface while a three-component geophone was locked downhole at 0.91-m intervals.

Consistent with their very similar geology, the two floodplain locations have nearly identical S-wave velocity (V_S) profiles. The lowest V_S values are about 130 m s⁻¹, and the highest values are about 300 m s⁻¹ at these sites. The shear-wave velocity profile at Shelby Forest is very similar within the Pleistocene loess (12 m thick); in deeper, older material, V_S exceeds 400 m s⁻¹.

At Marked Tree, and at Risco, the compressional-wave velocity (V_P) values above the water table are as low as about 230 m s⁻¹, and rise to about 1.9 km s⁻¹ below the water table. At Shelby Forest, V_P values in the unsaturated loess are as low as 302 m s⁻¹. V_P values below the water table are about 1.8 km s⁻¹. For the two floodplain sites, the V_P/V_S ratio increases rapidly across the water table depth. For the Shelby Forest site, the largest increase in the V_P/V_S ratio occurs at 20-m depth, the boundary between the Pliocene-Pleistocene clay and sand deposits and the Eocene shallow-marine clay and silt deposits.

Until recently, seismic velocity data for the embayment basin came from eartquake studies, crustal-scale seismic refraction and reflection profiles, sonic logs, and from analysis of dispersed earthquake surface waves. Since 1991, seismic data for shallow sediment obtained from reflection, refraction, crosshole and downhole techniques have been obtained for sites at the northern end of the embayment basin. The present borehole data, however, are measured from sites representative of large areas in the Mississippi embayment. Therefore, they fill a gap in information needed for modeling the response of the embayment to destructive seismic shaking.     

Heavy metal migration at a landfill site, Sarnia, Ontario, Canada—2: metal partitioning and geotechnical implications

Heavy metal profiles below a 15-year old sanitary landfill overlying a 30 m thick natural clay deposit are presented. Results indicate that unlike soluble species such as Cl⁻ and Na⁺ which have migrated distances up to 130 cm, Cu, Zn and Pb have migrated only up to 10 cm. The extent of Fe migration is estimated to be 20 cm. Highly reducing conditions at the interface (E_h= −130mV), coupled with the alkaline nature of the clay pore waters, have resulted in the precipitation of migrated heavy metals as carbonates. At the clay/waste interface, 88, 84 and 80% of the excess Fe, Zn and Pb, respectively, are present as secondary carbonates. This is confirmed by selective chemical dissolution analyses which also show that Fe, Zn, Pb and, to a greater extent, Cu are present in solid organic forms at the interface. Batch equilibrium studies clearly show that Cu and Pb removal from leachate is significantly increased by the presence of carbonates in the soil. For example, 75% more Pb is removed by the carbonate-rich bulk soil than the carbonate-free soil. The batch studies also show that when thepH> 5.2, removal of metal increases significantly due to precipitation as carbonates. From the results it is concluded that the presence of metal sludges in landfills lined naturally or artifically by a carbonate-rich clayey barrier reduces the rate of migration of numerous toxic transition metals and may also decrease the barrier porosity by precipitation. The decreases in porosity will be beneficial to the performance of the barrier due to reductions in both advection and diffusion.     

垃圾填埋场地特征及其工程地质问题分析

以徐州某垃圾填埋场工程为例,以勘察工作成果为基础,对区域稳定性、地震效应等方面进行了探讨。重点研究和评价了水文地质条件,分析了垃圾填埋场建设所涉及的主要工程地质问题。研究结果表明:本场地的变形特性、边坡稳定性等满足填埋场使用要求,不会出现承压水突涌现象,填埋场的修建不会对地下水产生不良影响,场地作为垃圾填埋场的建筑场地是适宜的。