geomorphic evolution and genesis of laterites around the east coast of madras tamil nadu india abstract laterites and lateritic soils red soils of the east coast especially around madras tamil nadu have been formed in different geomorphic conditions and on various geological deposits they occur as caprocks over recent alluvium upper gondwana sandstones and shales and precambrian basement rocks the laterite profiles studied around madras are generally 2 to 5 m thick and exposed 5 to 45 km inland from the present day shoreline detailed analysis micromorphological and chemical and the bore hole litho log data reveal that lateritisation was not continuous but occurred in phases lateritisation could have taken place in humid to sub humid conditions with a rich source of iron in the parent rock and sediment and efficient internal drainage geoarchaeological investigations and quaternary stratigraphical studies date the lateritic crust surface to the early late neogene neotectonics have played a vital role in shaping the present landscape

stability assessment of stope sequence scenarios in a diminishing ore pillar abstract numerical modelling is a vital tool in the mining industry and is widely used for planning purposes as well as for examining phenomena on a mine wide scale in this paper a comprehensive rock mechanics study is conducted for the planned mining sequence within an orebody that leads to the formation of a diminishing ore pillar at the vale garson mine in sudbury ontario a mine wide numerical model is first constructed in flac 3d with input parameters derived from laboratory tests and borehole log data and is then calibrated based on in situ stress measurements the planned mining sequence scenario comprising mining fronts advancing from the eastern and western sides of the orebody is examined based on a combined numerical volumetric analysis a qualitative assessment of ore at risk is first made based on two instability indicators the brittle shear ratio bsr and major principal stress 1 in addition two other sequence scenarios are examined in which mining is accelerated in the east a quantitative comparison of the results is then made for the three options using the same instability indicators based on the optimum sequence scenario an assessment is conducted of effects emanating from variations in constitutive models and the presence of a shear zone in the final phase the bsr and the presence of tensile conditions are used as instability indicators to study the volume of ore at risk in stopes adjacent to an opening during a mining stage it is shown that the proposed methodology while simple can nevertheless be a powerful tool for the planning and validation of stope extraction sequence scenarios and can be used in conjunction with multiple stability indicators

effects of pre existing discontinuities on the residual strength of rock mass insight from a discrete element method simulation abstract when rock failure is unavoidable the designer of engineering structures must know and account for the residual strength of the rock mass this is particularly relevant in underground coal mine openings pre existing discontinuities play an important role in the mechanical behavior of rock masses and thus it is important to understand the effects of such pre existing discontinuities on the residual strength for this purpose the present study demonstrates a numerical analysis using a discrete element method simulation the numerical results indicate that fracture intensity has no significant influence on the residual strength of jointed rock masses independent of confining conditions as confining pressures increase both peak and residual strengths increase with residual strength increasing at a faster rate the finding was further demonstrated by analyzing documented laboratory compressive test data from a variety of rocks along with field data from coal pillars a comprehensive interpretation of the finding was conducted using a cohesion weakening friction strengthening cwfs model the effect of rock bolts on rock mass strength was also evaluated by using a discrete element method model which suggested that rock bolts can significantly increases residual strength but have limited effect on increasing the peak strength of rock masses

a new method for sampling and analyzing volcanic sublimates application to merapi volcano java abstract a new method for the sampling of sublimates from high temperature volcanic gases has been used at merapi volcano java in 1978 the sublimates were collected on the inner walls of silica tubes introduced into fumarolic vents volcanic gases were allowed to move freely through the tubes and as they cooled a fraction of the volatile components condensed on the inner walls of the tubes along the temperature gradient the sublimates were then analyzed by a combination of light microscopy scanning electron microscopy electron microprobe and x ray diffraction six successive zones of different compositions and mineralogical associations have been identified along the covered range of temperatures 900 to around 400 c from the high to the low temperatures these zones are composed of 1 cristobalite magnetite hercynite 2 molybdenite 3 acmite 4 halite sylvite 5 sphalerite pyrite and 6 galena equilibrium calculations show that these crystalline phases are stable for ps 2 pc 1 and po 2 values typical of magma buffered gases that have not been contaminated by atmospheric oxygen the deposits observed in the tubes may be useful in aiding the understanding of the mechanisms acting during the cooling of the gaseous phase on its way to the surface and before its emission into the atmosphere

field gas chromatograph analyses of gases from a glowing dome at merapi volcano java indonesia 1977 1978 1979 abstract a new field gas chromatograph fgc and conventional evacuated bottle eb techniques have been used to study high temperature 600 c volcanic gases from merapi volcano indonesia during 1977 1978 and 1979 the fgc design allows analysis of h2o co2 so2 h2s h2 cos ch4 co n2 ar and o2 in a manner that prevents loss of sulfur and water by condensation inhibits corrosion from reactions of gases with lead in tubes and minimizes atmospheric contamination the fgc analyses are highly superior to the eb data especially with respect to prevention of sulfur loss from reaction of so2 and h2s in addition to providing much improved h2s data the fgc system minimizes oxidation of h2 and co from contaminating atmospheric o2 because of the elimination of a lengthy time interval between collection and analysis thermodynamic calculations indicated small errors for h2 and ch4 in the 1978 analyses provided by the proto type fgc device a later model fgc provided excellent analyses that were shown by thermodynamic calculations to be nearly equilibrium mixtures requiring only minor corrections the merapi gases are h2o rich 88 95 containing small amounts of co2 3 5 to 7 5 so2 0 3 to 1 2 and h2s 0 3 to 1 2 they resemble excess volatiles rubey 1955 except for too high a sulfur content thermodynamic calculations based on the analyses indicate that the gases were once at temperatures of at least 915 c with o2 fugacities near quartz magnetite fayalite and that they have not been significantly diluted by disequilibrium admixture of meteoric water below these temperatures this conclusion takes on special importance because stable isotope studies allard 1980 1982 of merapi gases have shown that the water is meteoric and that much of the carbon and sulfur could be from sedimentary sources the merapi gases therefore may be magmatic even though they are not juvenile but recycled crustal volatiles

numerical simulation of cumulative damage and seismic energy release during brittle rock failure part i fundamentals abstract this paper presents a numerical approach for the simulation of damage initiation and propagation causing seismic energy release during unstable failure of brittle rock with a newly developed numerical code rfpa2d rock failure process analysis the progressive failure process leading to the development of a shear or fault zone and the eventual collapse of a heterogeneous rock sample is modeled since the constitutive law for each element in the model is elastic brittle seismic energy is radiated whenever an element fails it is assumed that the radiated energy is equal to the energy stored in the element before failure is triggered due to the heterogeneity of rock properties seismic quiescence may occasionally occur within the nucleation zone the cumulative seismic damage calculated based on the seismic event rate from the simulation can be used as a damage parameter to describe the damage evolution it was found that significant decreases followed by sudden increases in radiated seismic energy may be an indicator of potentially unstable nucleation

evidence for an acidic ocean on mars from phosphorus geochemistry of martian soils and rocks recent analyses of elemental concentrations and mineralogy of iron bearing compounds of martian soils and rocks by the mars exploration rovers at meridiani planum and gusev crater demonstrate that phosphorus concentration is correlated with sulfur and chlorine the positive correlation of these three elements with each other in soils at both sites argues for a globally homogeneous soil component sulfur and possibly chlorine in martian soils and meridiani planum outcrop rocks is likely derived from volcanic exhalations but phosphorus must be derived from the weathering of igneous rocks here we show that the similar concentration of phosphorus in soils at the two mars exploration rover sites coupled with positive correlations to chlorine and sulfur is best explained as resulting from mixing and homogenization of phosphate sulfate and chloride in a large acidic aqueous reservoir such as an acidic ocean acidic thin film or acid fog weathering cannot readily produce the similar p s and p cl ratios of soils measured on mars and more important cannot explain the high phosphorus content of ancient ca 3 4 ga sulfate rich rocks in outcrop at meridiani the existence of a global acidic hydrosphere or ocean at some time in early martian history can also explain the lack of extensive carbonate deposits on the martian surface

robust geochemical indices for redox and weathering on a granitic laterite landscape in central uganda abstract most geochemical studies of laterite formation have been based on detailed examinations of a small number of hopefully representative profiles due to spatial variability in bedrock composition and geomorphic processes that sort materials by size density and other properties experimental designs developed for the geochemical analysis of single soil profiles are of limited use in landscape investigations in this study of a laterite landscape on a granitic rock in uganda we used element concentrations from neutron activation analysis naa to develop a suite of robust geochemical indices for landscape scale analysis of weathering and oxidation reduction redox processes in laterite formation to capture k feldspar weathering the k hf ratio served as a good proxy for feldspar zircon mineral ratios while k na ratios indexed feldspar concentration to quartz using principal components analysis we derived an index of rare earth elements ree leaching relative to th and an index of heavy to light ree hree lree fractionation we used the fe sc ratio to ascertain the absolute redox vs relative weathering fe accumulation in laterite formation with absolute fe accumulation also associated with lower fe as ratios mn ce ba nodules and concretions were identified by characteristically high ce values with individual ce values as high as 5000 g g 1 the relatively large amounts of k feldspar k avg is 4000 g g 1 and low degree of hree lree fractionation suggest that this landscape is weathered less than generally assumed the fe and mn derived indices highlight the important role of oxidation reduction processes in iron accumulation overall our findings suggest that the current ferricrete mantled hilltops were formerly located on a lower poorly drained part of the landscape

arsenic in volcanic gases total arsenic contents were determined in volcanic gases by analysis of fumarolic condensates collected in the period 1984 1992 from different volcanoes around the world arsenic concentrations range from 0 006 to 30 g g the highest values 1 2 30 g g were found at vulcano aeolian islands southern italy the analytical data show that volcanic gases have a large variability of arsenic contents possibly related to both the different physicochemical features of magma source and rock properties within the volcanic system

magmatic gases in well fluids aid the mapping of the flow pattern in a geothermal system abstract gas composition and silica concentrations of well fluids are used in conjunction with pressure temperature and enthalpy data to obtain a model of the drilled part of the krafla geothermal field northeast iceland a magma chamber is located at 3 8 km depth under the field magmatic gases emanate from the chamber and travel via a channel reaching the surface at the hveragil eruptive fissure the composition of the gases is apparently modified on the way in that sulphur which presumably is in the form of sulphur dioxide to begin with is removed on the way and what remains is in the form of hydrogen sulphide at the end it is suggested that the major removal mechanism is the deposition of pyrite and pyrrhotite during the passage of the gases through the hydrothermal system the hydrothermal system is divided into a lower part whose temperature exceeds 300 c and whose fluids are to a varying extent affected by the magmatic gases and an upper part whose temperature is ca 200 c this upper part is a run off from the lower part but the magmatic effects have mostly disappeared there

characterization of strain burst rock fragments under a scanning electron microscope an illustrative study abstract fractures around excavations in hard fine grained brittle rock sometimes display unique patterns from which an interpretation of the manner of failure fracture propagation can be made igneous rock fragments from a strain burst event at a site in western australia have been studied under a scanning electron microscope sem in order to characterize their surficial features sem image analysis indicates that anisotropy a contrast in geomechanical properties geometry and contact patterns present at the micro scale as they do at the large mine drive scale it is proposed that these micro scale features can lead to anisotropic material behaviour and stress concentrations that manifest as strain burst events

microseismic monitoring and stability analysis of the left bank slope in jinping first stage hydropower station in southwestern china risks associated with the left bank slope of jinping first hydropower station in southwestern china are growing as a result of excavation of the dam foundation ditch and various tunnels as well as grouting to soft strata to improve our understanding of the slope instability and resolve the complex subsurface conditions of the highly fractured rock mass a microseismic monitoring system was installed in june 2009 which is the first time such a technique has been introduced into stability analysis of a high steep rock slope in china the microseismic monitoring system consists of a data acquisition unit a data processing unit and a three dimensional array of uniaxial accelerometers in order to analyze the correlation between seismicity and potential slip surface of the slope a numerical model was implemented to analyze the failure processes and stability of the slope the monitoring results illustrate that microseismic events mainly occur as a strip along the spandrel groove of the dam which coincides with the potential slip surface obtained from numerical analysis especially at the bottom of the slope therefore the comprehensive method incorporating microseismic monitoring and numerical analysis has been proven to be very promising in instability prediction of rock slope subject to identification and delineation of potential slip surface and failure regions

rockburst mechanism and prediction based on microseismic monitoring abstract in this study the rockburst definition is comprehensively described and several main rockburst theories the strength theory the energy theory the bursting liability theory the rigidity theory and the instability theory are analyzed the two body interaction theory based on the newton s law can explain the rockburst mechanism most reasonably the rockburst development process is a static process and the rockburst occurrence process is within the scope of dynamics in addition some precursors exist before rockburst occurrence reflected by the consistency between acoustic emissions and damage variables in rock mass which can be summarised as three seismogenic models according to the tempo spatial distribution by utilizing the 3s stress buildup stress shadow and stress transfer principle in seismology three rockburst criteria are proposed in this paper namely the stress tempo spatial evolution the magnitude energy and concentration degree of microseismic events sudden change of apparent volume finally by comparing the results obtained by microseismic monitoring and landsonar positioning it is shown that the root cause of rockburst occurrence is rock heterogeneity and the existence of joints and fractures the fracture intersection points are the locations for rockburst initiation it is proven that the two body interaction principle can perfectly explain the rockburst mechanism

a zoning model for coal mining induced strata movement based on microseismic monitoring a microseismic monitoring technique is adopted to investigate the distribution regularity of microseismic events released by the coal mining induced roof rock mass along the vertical and horizontal directions in combination with mine geological data on the basis of the quantity and energy distributions of the microseismic events recorded using the microseismic monitoring technique a zoning method is first established for the roof strata movement in the vertical and horizontal directions the vertically zoning method is then applied to analyze the microseismic monitoring results obtained in the dongjiahe coal mine which divides rock mass into six zones along the vertical direction i e the caved zone the block zone the vertical fracture through going zone the vertical fracture zone the separation zone and the continuous zone the horizontally zoning model divides the roof strata movement into three zones i e the calm zone the generation zone impacted by working face and the historical generation zone after that based on the horizontally zoning model a method is developed to determine the displacement angle using the microseismic monitoring data which has been verified in the dongjiahe coal mine

genesis of acid sulfate alteration and au cu ag mineralization at summitville colorado the summitville au cu ag deposit occurs within a porphyritic quartz latite primarily in a zone of vuggy silica alteration characterized by leaching of all major elements except silica and iron vuggy silica is best developed between an elevation of 3 700 and 3 500 m where it occurs in irregular pipes and lenticular pods up to 70 m wide and is enclosed by up to 30 m of intense quartz alunite alteration the vuggy silica zones diminish in size with decreasing elevation and rarely exceed a width of 2 m below an elevation of 3 400 m these deep vuggy silica zones are enclosed by quartz kaolinite alteration with little or no alunite sulfide mineralization occurs primarily within the vuggy silica the sulfide assemblage changes with decreasing elevation from covellite luzonite or native gold to chalcopyrite tennantite sulfides occur lining voids or in microveinlets and are accompanied by minor kaolinitc but not by alunite gold also occurs in a near surface barite goethite jarosite assemblage that crosscuts the vuggy silica consideration of alunite kaolinitc and pyrite stability relations and of aluminum speciation at 250 degrees c indicates that a ph of 2 or below and a log f sub o 2 of 31 or 1 at 250 degrees c were necessary to produce vuggy silica alteration the chalcopyrite tennantite mineralization occurring at depth in the vuggy silica zone is indicative of less oxidizing and less acidic conditions the covellite luzonite or gold assemblage requires conditions intermediate between those necessary for vuggy silica alteration and for deep sulfide mineralization barite gold mineralization is interpreted as a near surface assemblage produced under highly acidic oxidizing conditions these textural and geochemical relationships indicate that sulfide and gold mineralization postdate the formation of vuggy silica alteration in the deposit and are not directly related to the highly acidic solutions necessary for this early acid leaching event the change from extreme acid leaching to copper sulfide and precious metal deposition may represent a transition from a magmatic vapor dominated to a liquid dominated system leading to more reducing and less acidic conditions during sulfide deposition

in situ monitoring of rockburst nucleation and evolution in the deeply buried tunnels of jinping ii hydropower station abstract rockbursts occurred frequently during the excavation of several parallel tunnels in the jinping ii hydropower station under a maximum overburden of 2525 m over an average length of 17 5 km in order to investigate the nucleation and evolution mechanism of rockbursts a comprehensive monitoring campaign consisting of a digital borehole camera cross hole acoustic apparatus and sliding micrometer was undertaken for in situ measurements in two specially excavated test tunnels b and f this paper presents the comprehensive monitoring methods applied and results of numerical analysis applied to a typical rockburst that fortuitously occurred during the testing period precursory characteristics preceding rockbursts are a abundant crack initiation propagation and coalescence b deformation of surrounding rock mass involving an accelerated deformation stage quiescence stage and reaccelerated deformation stage and c decrease of the characteristic elastic wave velocity of the rock mass the nucleation and evolution of rockbursts discussed consist of four stages a stress adjustment b energy accumulation c crack initiation propagation and coalescence and d fractured rock collapse and ejection the results provide a direct case history to assist the prediction and support of rockburst disasters and contribute to field excavation of deeply buried tunnels

development of a comparative index for the assessment of the severity of violent brittle failures around underground excavations abstract in order to assess the severity of a violent brittle failure strain burst around the vicinity of complex underground excavations an index parameter has been developed the index incorporates measures of the induced stress path and accumulated plastic strain and is calculated after brittle failure conditions are identified by the established damage initiation threshold and spalling limit dit sl the comparative index developed provides guidance to minimize strain burst hazard for geotechnical design application of the index to a conceptual model shows that strain burst hazard can be related to geological boundaries and their exposure in excavation faces the potential violence of these strain burst failures can be quantified by changes in principal stress and plastic strain within a numerical model

volatilization transport and sublimation of metallic and non metallic elements in high temperature gases at merapi volcano indonesia abstract condensates silica tube sublimates and incrustations were sampled from 500 800 c fumaroles and lava samples were collected at merapi volcano indonesia in jan feb 1984 with respect to the magma merapi gases are enriched by factors greater than 105 in se re bi and cd 104 105 in au br in pb and w 103 104 in mo cl cs s sn and ag 102 103 in as zn f and rb and 1 102 in cu k na sb ni ga v fe mn and li the fumaroles are transporting more than 106 grams day g d of s cl and f 104 106 g d of al br zn fe k and mg 103 104 g d of pb as mo mn v w and sr and less than 103 g d of ni cu cr ga sb bi cd li co and u with decreasing temperature 800 500 c there were five sublimate zones found in silica tubes 1 cristobalite and magnetite first deposition of si fe and al 2 k ca sulfate acmite halite sylvite and pyrite maximum deposition of cl na k si s fe mo br al rb cs mn w p ca re ag au and co 3 aphthitalite k na sulfate sphalerite galena and cs k sulfate maximum deposition of zn bi cd se and in higher deposition of pb and sn 4 pb k chloride and na k fe sulfate maximum deposition of pb sn and cu and 5 zn cu and k pb sulfates maximum deposition of pb sn ti as and sb the incrustations surrounding the fumaroles are also chemically zoned bi cd pb w mo zn cu k na v fe and mn are concentrated most in or very close to the vent as expected with cooling atmospheric contamination and dispersion the highly volatile elements br cl as and sb are transported primarily away from high temperature vents ba si p al ca and cr are derived from wall rock reactions incomplete degassing of shallow magma at 915 c is the origin of most of the elements in the merapi volcanic gas although it is partly contaminated by particles or wall rock reactions the metals are transported predominantly as chloride species as the gas cools in the fumarolic environment it becomes saturated with sublimate phases that fractionate from the gas in the order of their equilibrium saturation temperatures devolatilization of a cooling batholith could transport enough acids and metals to a hydrothermal system to play a significant role in forming an ore deposit however sublimation from a high temperature high velocity carrier gas is not efficient enough to form a large ore deposit re se cd and bi could be used as supporting evidence for magmatic fluid transport in an ore deposit

crystallization of apatite in natural magmas under high pressure hydrous conditions with particular reference to orogenic rock series two separate series of hydrous experiments involving 1 imposing apatite saturation on a series of igneous rock compositions from basanite to rhyolite and 2 crystallizing similar natural rock compositions progressively until apatite appears demonstrate a close dependence between apatite saturation and silica content of the magma and determine p2o5 levels at a given silica value and temperature at which that composition may be expected to crystallize apatite the effect of pressure on apatite solubility is not great and is most significant for silicic compositions

coupled disaster causing mechanisms of strata pressure behavior and abnormal gas emissions in underground coal extraction the generalization and application of fully mechanized caving with super great mining height sgmh face a series of new issues of which strata pressure behavior and abnormal gas emissions are the most prominent disasters and display a close relationship the tashan coalmine was chosen as the experiment base because of its sgmh and the overlying hard and thick main roof htmr this coalmine had experienced many damaging hydraulic support and abnormal gas emission accidents induced by strata pressure behavior the key strata theory and the fracture failure process analysis model established by 3dec were used to analyze the structural characteristics and fracture failure process of the htmr the geostress reduction and permeability enhancement redistribution of the adjacent coal measure strata were studied by the geostress and permeability distribution model established by flac 3d the htmr controlled the failure extent and the movement evolution of the entire overburden stratum the htmr acted as a large double sided embedded rock beam during primary fracturing and a cantilever articulated rock beam during periodic fracturing and it generated a huge hanging space above the gob the fully mechanized caving with sgmh caused large scale disturbances and permeability enhancements in the adjacent rock and coal strata then the substantial amounts of gas stored in the remaining coal surrounding rock strata and adjacent coal seam rushed out and aggregated in the caved and fissured zones of the gob forming a huge gas warehouse the strata pressure behavior and abnormal gas emission disasters primarily occurred after the primary and periodic fracturing of the htmr these disasters are predominantly caused by the escaping of the abundant gas that existed in the gob during mine pressure behavior processes when the ultimate broken span was reached as the htmr rotated and collapsed the substantial amounts of gas that accumulated in the gob escaped into the working face which easily caused abnormal gas emissions hydraulic presplitting and gas drainage technologies are proposed to solve these disasters

fault creep growth model and its relationship with occurrence of earthquakes summary a fault model is used to analyse creep growth process of microcracks in damage zone near the tips of fault by means of the rheology fracture mechanics when microcracks in the zone link each other and their deformation quickly intensifies it means that an earthquake is taking place to a certain degree the relationships among some key parameters that are correlated to the growth of microcracks are analysed theoretically these parameters include failure time of fault number of microcracks in unit area stresses field yield strength and rheological properties of medium the results indicate that the model proposed here is reasonable to describe the pregnant process of an earthquake in the meantime this research shows that with the results of in situ surveys and lab experiments it is possible to estimate the time span for a fault expanding

scaling of ground motion parameters state of stress and focal depth the ground motion parametersrv and ra where r is hypocentral distance v is peak velocity is density and a is peak acceleration are found observationally to be strong functions of stress state and linearly related to focal depth z if the stress state and focal depth are properly taken into account then the ground motion parameters depend on the seismic moment m0 as expected from basic scaling principles that is rv m01 3 and ra is independent of earthquake size regression lines fitted to observations covering broad ranges in seismic moment and focal depth indicate that for extensional and compressional tectonic regimes corresponding to normal and thrust or reverse faulting earthquakes respectively peak acceleration is given by ra 1 08 mpa 3 06 mpa km z normal and ra 5 65 mpa 8 76 mpa km z thrust and for peak velocity rv m01 3 10 4 m2 s n m 1 3 3 00 0 69 km 1 z normal and rv m01 3 10 4 m2 s n m 1 3 4 63 1 82 km 1 z thrust for strike slip earthquakes the data currently are insufficient to define regression fits but such lines would definitely lie between those for the normal and thrust stress regimes these equations are appropriate for ground motion at small hypocentral distance as recorded in a whole space it follows that for comparable hypocentral depth peak acceleration in a compressional tectonic regime for example much of the eastern united states is a factor of about 3 greater than in an extensional regime such as nevada and for peak velocity a similar comparison yields a factor of 2 difference the similarity in behavior of the peak acceleration parameter to crustal strength estimated from byerlee s law of friction with respect to depth and stress state indicates that crustal strength is probably the factor governing the seismic source processes that give rise to the high frequency peak ground motion analysis of the peak acceleration data in the context of crustal strength suggests bounds on this ground motion parameter as recorded at a typical surface site that depend on stress state specifically a normal 0 5 g and a thrust 1 9 g thus the state of stress as well as the focal depth clearly is an important factor to be taken into account in the prediction of seismic ground motion

partition of arsenic and phosphorus between volcanic gases and rock part i analytical data and magmatic conditions of mt usu japan abstract in order to understand the behavior of arsenic and phosphorus in volcanic environments ejecta and volcanic gases collected at mt usu were analyzed and the differentiation of the two elements was investigated results of analyses show that phosphorus is depleted in the gas phase while it is abundant in the rock on the other hand arsenic is found to have a high volatility comparable to that of a major component of active volcanic gases like chloride the apparent partition coefficient as p gas as p rock is calculated to be in the range from 104 to 105 in order to examine the existing state of p and as in magmatic gases the fugacity ratios among chemical species of p and those of as are calculated it is suggested that p exists overwhelmingly as po2 while as exists as as4 under the usu magmatic conditions temp 1200 k fh2o 400 atm fo2 400 atm etc on the assumption that fpo2 is controlled by the equilibrium with the mineral assemblage ca3 po4 2 sio2 casio3 in orthopyroxene the calculated p content is 106 times less than that measured in the condensates several possible causes of this discrepancy are discussed the discrepancy may be due to 1 the admission of phosphorus from wall rock through interaction of ascending volcanic gases with wall rock if apatite is present in the magma and 2 the formation of po2 exclusively from po43 ion in the magma with the absence of apatite though thermodynamic estimation of fpo2 is not possible an absolute value of fas4 cannot yet be obtained because of the lack of thermodynamic data of arsenic bearing minerals the difference in the behavior of arsenic and phosphorus in volcanic environments seems to be closely related with the redox properties of the two elements

influence of tunneling methods on the strainburst characteristics during the excavation of deep rock masses abstract it is widely known that blasting and tbm are the general methods for the deep rock mass excavation and can respectively induce transient release of in situ stress tris and quasi static unloading of in situ stress qsuis on the excavation boundary as one of the most important triggers the unloading of in situ stress caused by excavation frequently induces strainbursts however little attention has been focused on the influence of the tunneling methods on the strainburst characteristics in this paper the cracking of surrounding rock masses and associated energy dissipation under the different tunneling methods was analyzed the influence of different tunneling methods on the evolution characteristics of strainburst was also discussed results show that compared with the tbm excavation the blasting excavation aggravates the cracking of surrounding rock masses and enlarges the energy dissipation during the cracking process during the unloading process of in situ stress the total energy and the releasable strain energy for the case of blasting excavation are much higher than that for the tbm excavation this makes that the intensity and frequency of immediate strainbursts induced by blasting excavation are much greater than that caused by tbm excavation while after the unloading of in situ stress as the surrounding rock masses dissipate larger energy during its cracking process the releasable strain energy for the case of blasting excavation is lower than that for the tbm excavation this brings down the risk of time delayed strainbursts for the blasting excavation in addition a case study at diversion tunnels in jinping ii hydropower project was presented as a verification

numerical and experimental study on progressive failure of marble this study presents a framework for numerical simulations based upon micromechanical parameters in modeling progressive failures of heterogeneous rock specimens under compression in our numerical simulations a weibull distribution of the strength and elastic properties of the finite elements is assumed and the associated weibull parameters are estimated in terms of microstructural properties such as crack size distribution and grain size through microscopic observations of microcracks the main uncertainty in this procedure lies on the fact that various ways can be used to formulate a microcrack size distribution in relating to the weibull parameters as one possible choice the present study uses the number of counted cracks per unit scanned volume per grain size to formulate the crack distributions finally as a tool the rock failure process analysis code rfpa2d is adopted for simulating the progressive failure and microseismicity of heterogeneous rocks by using an elastic damage finite element approach to verify our framework compression tests on marble specimens are conducted and the measured acoustic emissions ae are compared with those predicted by the numerical simulations the mode of failure compressive strength and ae pattern of our simulations basically agree with experimental observations

numerical simulation of the dynamic impact breakage testing of rock laboratory drop weight tests and numerical modelling have been used to study the effect of impact energy on the degree of fragmentation of cylindrical granite specimens the drop weight tests indicated that the degree of fragmentation of the granite formed a non linear relation with impact energy in the modelling of the drop weight test the shear localisation developed in the granite was assumed to represents discrete fracture planes image analysis of the model outputs was undertaken to determine particle size distributions corresponding grading curves from the numerical modelling were then validated against the laboratory derived curves indicating the potential of numerical modelling to simulate the fragmentation process of brittle rocks

a field and reactive transport model study of arsenic in a basaltic rock aquifer abstract the use of geothermal energy as a source for electricity and district heating has increased over recent decades dissolved as can be an important constituent of the geothermal fluids brought to the earth s surface here the field application of laboratory measured adsorption coefficients of aqueous as species on basaltic glass surfaces is discussed the mobility of as species in the basaltic aquifer in the nesjavellir geothermal system iceland was modelled by the one dimensional 1d reactive transport model phreeqc ver 2 constrained by a long time series of field measurements with the chemical composition of geothermal effluent fluids ph eh and occasionally fe and as dissolved species measurements di tri and tetrathioarsenic species as oh s 2 2 ass 3 h 2 ass 3 3 and as sh 4 were the dominant form of dissolved as in geothermal waters exiting the power plant 2 556 m total as but converted to some extent to arsenite h 3 aso 3 and arsenate haso 4 2 oxyanions coinciding with rapid oxidation of s 2 to s 2 o 3 2 and finally to so 4 2 during surface runoff before feeding into a basaltic lava field with a total as concentration of 0 882 m following dilution with other surface waters a continuous 25 a data set monitoring groundwater chemistry along a cross section of warm springs on the lake thingvallavatn shoreline allowed calibration of the 1d model furthermore a series of ground water wells located in the basaltic lava field provided access along the line of flow of the geothermal effluent waters towards the lake the conservative ion cl moved through the basaltic lava field 4100 m in less than10 a but as was retarded considerably due to surface reactions and has entered a groundwater well 850 m down the flow path as arsenate in accordance to the prediction of the 1d model the 1d model predicted a complete breakthrough of arsenate in the year 2100 in a reduced system arsenite should be retained for about 1 ka

arsenic in surface and up to 90 c ground waters in a basalt area n iceland processes controlling its mobility the concentrations of as in surface and up to 90 c ground waters in a tholeiite flood basalt area in n iceland lie in the range 0 5 g kg as the as content of ground waters increases on the whole with rising temperature arsenic is highly mobile in the basalt water environment of the study area an insignificant fraction of the as dissolved from the rock is taken up into secondary minerals arsenic is less mobile than b but considerably more mobile than na which has the highest mobility among the major aqueous components a significant fraction of the as in the basalt occurs in an easily soluble form the as hosted in the primary minerals is expected to be concentrated in the titano magnetite this mineral is stable in contact with both surface and ground waters and does not therefore supply as to the water explaining the difference in mobility between as and b aqueous as concentrations are a reflection of water rock ratios i e how much rock a given quantity of water has dissolved this ratio increases with increasing temperature and increasing residence time of the water in contact with the rock the distribution of as species has been calculated on the assumption of equilibrium at the redox potential retrieved from measurement of aqueous fe ii and fe iii concentrations these calculations indicate that pentavalent as is stable in surface waters and in ground waters with an in situ ph of 10 and would occur mostly as h 2 aso 4 and haso 2 4 in higher ph ground waters the concentrations of the arsenite species h 2 aso 3 is significant at equilibrium up to 65 of the total dissolved as

crater lake and post eruption hydrothermal activity el chichon volcano mexico abstract explosive eruptions of volcan el chichon in chiapas mexico on march 28 and april 3 4 1982 removed 0 2 km3 of rock to form a 1 km wide 300 m deep summit crater by late april 1982 a lake had begun to form on the crater floor and by november 1982 it attained a maximum surface area of 1 4 105 m2 and a volume of 5 106 m3 accumulation of 4 5 m of rainfall between july and october 1982 largely formed the lake in january 1983 temperatures of fumaroles on the crater floor and lower crater walls ranged from 98 to 115 c by october 1983 the maximum temperature of fumarole emissions was 99 c in january 1983 fumarole gas emissions were greater than 99 vol h2o with traces of co2 so2 and h2s the water of the lake was a hot t 52 58 c acidic ph 0 5 dilute solution 34 046 mg l 1 dissolved solids cl s 20 5 sediment from the lake contains the same silicate minerals as the rocks of the 1982 pyroclastic deposits together with less than 1 of elemental sulfur the composition and temperature of the lake water is attributed to 1 solution of fumarole emissions 2 reaction of lake water with hot rocks beneath the lake level 3 sediments washed into the lake from the crater walls 4 hydrothermal fluids leaching sediments and formational waters in sedimentary rocks of the basement 5 evaporation and 6 precipitation

evaluation of gas data from high temperature fumaroles at mount st helens 1980 1982 abstract the mount st helens fumarole gases show linear composition trends during periods of noneruptive degassing between september 1980 and october 1981 the trends are characterized by increasing h2o and decreasing co2 and sulfur maximum fumarole temperatures also show a linear decrease during this period high temperature fumarole gases collected from the crater and dome between september 1980 and july 1982 are all h2o rich 90 with 1 10 co2 and small amounts of h2s so2 h2 co hc and hf trace amounts of cos and s2 are present and occasional observations of minor ch4 appear to result from contamination or low temperature reactions in sample vessels the o2 fugacities of the gases remain near ni nio during cooling the low sulfur content of the gases obviates the need for extensive gas rock oxygen exchange to maintain fo2 s near ni nio a detailed thermodynamic analysis of 50 gas samples collected between september 1980 and december 1981 led to improved compositions for 22 samples the gases were initially in a state of equilibrium but disequilibrium modifications from atmospheric oxidation of h2 and to a lesser extent co occurred within the upper portions of the fumarole vents the last temperatures of equilibrium for the fumarole gases range from 800 c to 650 c and are nearly always higher than the collection temperatures no evidence was found of disequilibrium admixture of surface waters if such modifications of the fumarole gases occurred the water must have been added at depth and have reequilibrated with the other gas species at magmatic or near magmatic temperatures the highest quality analytical data are obtained by field gas chromatograph measurements and from caustic soda bottle samples samples collected in evacuated bottles or by pumping through double stopcock tubes tend to be severely deficient in sulfur due to post collection reactions between h2s and so2 it is also necessary to infer the water content of the latter samples

aeolian accumulation an alternative origin of laterite on the deccan plateau india abstract laterite is ubiquitous in india and has been extensively studied however it is still controversial with respect to its origin definition classification and implications in paleoclimate tectonic history and topography evolution of those the origin of laterite either in situ weathering of protoliths or weathering of allochthonous input is the most critical to address the ca 25 m thick laterite duricrust capping the deccan plateau is conventionally hypothesized to derive from in situ weathering of the topmost basalt however this thick laterite lacks upward progressive weathering which is characteristic of lateritic profile instead it displays 1 homogeneity in weathering intensity through the duricrust 2 a clear unconformable contact of laterite with red clay which together suggests that this thick laterite is genetically unrelated to in situ weathering of the topmost basalt lines of evidence in mineralogy granularity and geochemistry proved the disconnection between this laterite and basalt and in contrast indicated its correlation to aeolian accumulation in this study the laterite together with the red clay was proposed to derive from aeolian dust accumulation and weathering since 65 ma within context of indian plate drifting across the equator from southern to northern hemisphere

information entropy of earthquake populations in northeastern italy and western slovenia abstract the spatio temporal evolution of eight seismicity populations preceding and following moderate earthquake sequences occurred in ne italy and w slovenia are investigated by means of the normalized shannon entropy and the fractal dimension three phases are recognized in the temporal seismic series the period preceding the mainshock is characterized by oscillations of the shannon entropy around a nearly constant level and by fluctuations of the fractal dimension the phase of mainshock and aftershock sequences is characterized by a significant decrease of the shannon entropy a simultaneous marked decrease of the fractal dimension is observed in five cases after the sequence the entropy recovers the nearly constant trend before the mainshock and the fractal dimension is characterized by fluctuations we interpreted the fluctuations of the normalized shannon entropy and the fractal dimension caused by the coupling between the stress field and the mechanical heterogeneities of the crust that results in spatial and temporal fluctuations of the strain energy

estimating in situ rock stress from spalling veins a case study stress induced failures have typically been considered as engineering disasters in deep underground excavations this paper highlights the importance of stress driven rock failures as a means to estimate the in situ rock stress at the depth the method which is based on the observation and documentation of a failure mode referred to here as spalling in deep tunnels or caverns is put forward and presented to estimate the macro scale rock stress using the proposed method the orientation of the principal stresses in situ can be deduced by the spalling intensity and associated stress induced spalling veins in the rock mass surrounding the opening and the magnitude of the principal stresses can be estimated by the assumed crack initiation stress required to generate spalling in the given rock by careful documentation of spalling failure characteristic in the field a real case study at baihetan powerhouse site has been carried out and indicates that the proposed method is an available way to enriching recognition of in situ rock stress and a helpful supplement to traditional methods of stress measurements after strictly numerical verification analysis of the regional tectonic setting as well as measurements of in situ stress supports the results by the suggested approach

microseismic monitoring and stability evaluation for the large scale underground caverns at the houziyan hydropower station in southwest china abstract the stability of underground caverns and the excavatability of rock masses are important for geotechnical engineering practices during the design and construction stages the risks associated with underground caverns at the houziyan hydropower station in southwest china are growing due to excavation induced unloading to assess the instability of underground caverns and resolve the complex subsurface conditions of the highly fractured rock mass a high resolution microseismic monitoring system was established in deep underground caverns this system was used to determine the relationship between the measured microseismic activities and the excavation damage zones of the surrounding rock mass the excavation damage zones and potential risk regions in the underground caverns were identified by analyzing the tempo spatial distribution of microseismic activities in addition the correlation between microseismic activities and pre existing geological structures was determined and traditional monitoring results were analyzed to validate the correlation between seismicity and the excavation damaged zones of the underground caverns a numerical model was employed to further evaluate the deformation and stability of the surrounding rock mass the monitoring results demonstrate that microseismic events mainly occurred in high stress concentration regions corresponding with the results obtained from the numerical analysis therefore this comprehensive method which incorporates microseismic monitoring numerical analysis traditional monitoring and field observations is promising for predicting the deformation and instability of surrounding rock masses in the underground caverns subjected to excavation

simulating electropulse fracture of granitic rock abstract electropulse treatments employ a series of high voltage discharges to break rock into small fragments as these methods are particularly suited to fracturing hard brittle rocks electropulse treatments can serve to enhance or substitute for more traditional mechanical approaches to drilling and processing of these materials nevertheless while these treatments have the potential to improve hard rock operations the coupled electro mechanical processes responsible for damaging the rock are poorly described the lack of accurate models for these processes increases the difficulty of designing controlling and optimizing tools that employ electropulse treatments and limits their range of application this paper describes a new modeling method for studying electropulse treatments in geotechnical operations the multiphysics model simulates the passage of the pulse electrical breakdown in the rock and the mechanical response at the grain scale it also accounts for the contributions from different minerals and porosities allowing the effect of material composition to be considered in so doing it provides a means to investigate the different physical and operational factors influencing electropulse treatments

correlative and comparative characterization of main ion concentrations in laterite groundwater in semi arid northern burkina faso about 24 samples from hand dug wells and boreholes were used to characterize concentrations of the main inorganic ions in a laterite environment under semi arid climatic conditions in tikare northern burkina faso it was found that the most represented groundwater anion in groundwater was hco3 with average levels of 49 1 mg l in the dry season and 33 5 mg l in the rainy season the most represented cation was ca2 with mean concentrations of 13 7 and 9 5 mg l respectively the main processes which influence the concentrations of these ions are evaporation dry season local enrichment of recharge water in some elements ion exchange and fixation by clay minerals in case of k the best correlations were found between ca2 and mg2 r 0 95 cl and na r 0 95 hco3 and mg2 r 0 89 hco3 and ca2 r 0 89 and between hco3 and na r 0 80 in general the quality of the groundwater from the different wells sampled for this study was good enough to serve as drinking water however there were situations where the quality of water was polluted because of anthropogenic contaminants mainly no3 k cl from septic tanks and manure pits located in the vicinity of some sampled wells in addition application of fertilizers also represents a potential anthropogenic contamination source with regard to so4 2 ca2 k na and mg2 considering the high concentrations of so4 2 mg2 na and ca2 found in one borehole the deeper fractured aquifers were also likely to be enriched in these elements in contrast the shallow aquifers are likely to be contaminated with cl no3 and k cl and k seem to be locally present in recharge water as shown by their relative higher mean concentrations in the rainy season samples

brittle ductile transition and associated seismicity experimental and numerical studies and relationship with the b value the acoustic emission ae and the mechanical behavior of granite samples during triaxial compression tests have been analyzed the size of ae events displays power law distributions conforming to the gutenberg richter law observed for earthquakes which is characterized by the b value as the confining pressure increases the macroscopic behavior becomes more ductile for all different stages of the rock mechanical behavior linear nonlinear prepeak nonlinear postpeak shearing there is a systematic decrease of the b value with increasing confining pressure a numerical model based on progressive elastic damage and the finite element method allows simulations of the main experimental observations on ae and of a wide range of macroscopic behaviors from brittleness to ductility the model reproduces a decrease in the b value that appears to be related to the type of macroscopic behavior brittle ductile rather than to the confining pressure both experimental and numerical results suggest a relationship between the b value and the brittle ductile transition moreover these results are consistent with recent earthquake observations and give new insight into the behavior of the earth s crust

volcanic emission of se te and as from kilauea volcano hawaii abstract the se te and as content of the eruptive gas and of sulfur sublimates from the current jan 1983 through mar 1985 east rift eruption of kilauea volcano hawaii have been determined these data in combination with previous data suggest that most of the se and te in eruptive plumes occur in the particulate fraction while most of the as is in the gas phase eruptive emissions to the atmosphere have been estimated at 10 metric tons each of se and as and 2 tons of te over the first 14 months of the eruption material balance calculations suggest 0 28 ppm se and 0 017 ppm te for the initial kilauean magma content of these elements only one third of the original se and te is lost from the magma by degassing

airborne aerosol measurements in the quiescent plume of mount st helens september 1980 atmospheric particulate matter and condensed volatile species were collected in the quiescent plume of mount st helens volcano in sept 1980 using air filter systems mounted aboard a nasa turbo prop p 3 aircraft concentrations of 27 elements were determined by instrumental neutron activation analysis and ion chromotagraphy the volatile elements cl br f zn w in s cd se sb hg as and au were enriched relative to bulk ash emitted during the earlier eruptions by factors of 50 to 20 000 particulate s concentrations were approx 3 mu g m sup 3 and accounted for 6 of the total plume sulfur gas phase hg concentrations were 2 5 to 16 ng m sup 3 fluxes of elements were estimated by normalizing elemental concentrations to the concurrently measured total sulfur flux emission rates vary from 3500 kg day for particulate cl to 3 kg day for au with substantial quantities of the enriched elements zn as hg sb se and cd also being released estimated global fluxes of these elements from volcanoes to the atmosphere are in reasonable agreement with other literature estimates

discrimination between different water bodies from a multilayered aquifer kaluvelly watershed india trace element signature in the multilayered aquifer of kaluvelly india comprising various sedimentary layers overlying a charnockitic basement concentrations of trace elements were measured in aquifer formations and in groundwaters to identify geochemical tracers for water bodies the two main sandstones cuddalore and vanur originate from the charnockites and the cuddalore sandstone has experienced lateritization in the studied area two charnockite end members were identified a dioritic and a granitic one mineralogical composition and whole rock ti concentrations confirmed the charnockite which displayed the granitic composition as the parent rock of the two sandstones titanium distribution indicates that the cuddalore sandstone originates from a more intense weathering of the parent material than the vanur sandstone despite extensive differences in trace element contents recorded in aquifer formations only a few trace elements were suitable to distinguish the water bodies among soluble elements li in the vanur aquifer and ba in the charnockite and carbonaceous aquifers can be used as tracers as the input of these elements in solution is mainly regulated by the available stock for a given mineralogical origin there is a direct link between the aquifer formation composition and water signature with the exception of as concentrations of redox sensitive elements were not preserved during pumping because of oxidation preventing their use as tracers low mobility elements such as la ce th zr nb hf or ta were too insoluble to be detected in waters and or to record the aquifer formation signature their input in solution was not regulated by the available stock but by the dissolution rate of rock forming minerals only ti can be used to distinguish between two out of the three aquifers charnockite and vanur the specific behavior of ti recorded in these waters may be linked to rutile inclusions within plagioclases and to the influence of climate on ti solubility

a new method to estimate location and slip of simulated rock failure events abstract at the laboratory scale identifying and locating acoustic emissions aes is a common method for short term prediction of failure in geomaterials above average ae typically precedes the failure process and is easily measured at larger scales increase in micro seismic activity sometimes precedes large earthquakes e g tohoku l aquilla oceanic transforms and can be used to assess seismic risk the goal of this work is to develop a methodology and numerical algorithms for extracting a measurable quantity analogous to ae arising from the solution of equations governing rock deformation since there is no physical property to quantify ae derivable from the governing equations an appropriate rock mechanical analog needs to be found in this work we identify a general behavior of the ae generation process preceding rock failure this behavior includes arbitrary localization of low magnitude events during pre failure stage followed by increase in number and amplitude and finally localization around the incipient failure plane during macroscopic failure we propose deviatoric strain rate as the numerical analog that mimics this behavior and develop two different algorithms designed to detect rapid increases in deviatoric strain using moving averages the numerical model solves a fully poro elasto plastic continuum model and is coupled to a two phase flow model we test our model by comparing simulation results with experimental data of drained compression and of fluid injection experiments we find for both cases that occurrence and amplitude of our ae analog mimic the observed general behavior of the ae generation process our technique can be extended to modeling at the field scale possibly providing a mechanistic basis for seismic hazard assessment from seismicity that occasionally precedes large earthquakes