quantification of rock mass damage in underground excavations from microseismic event monitoring abstract rock mass damage assessment is required for many applications in rock engineering practice including support design contamination transport control stope design amongst others while various methods such as displacement measurement seismic refraction and direct observation using borehole camera have been used relatively few efforts have been made to use microseismic monitoring to quantify the rock mass damage from laboratory tests it is well known that microseismic events are indicators of fracturing or rock damage as the rock mass is brought to failure at high stress by capturing the microseismic events underground excavation induced rock mass degradation or damage can be located but can the amount of damage in terms of changes to strength or deformation properties be measured in the present study a method of characterizing rock mass damage near excavations based on microseismic event monitoring is developed and a damage driven numerical model is presented that takes the microseismic data as input to determine the damage state described by fracture density the approach is built on the discovery that a realistic crack size corresponding to a seismic event can be established by applying a tensile cracking model instead of the traditional shear model commonly used in earthquake analysis the rock mass is softened by the introduction of cracks and this is simulated by a micro mechanics based constitutive model the material property input for the model are young s modulus poisson s ratio of the intact rock and information obtained from the monitoring of microseismic events such as the location and the source size of each event calculated from source parameters using data from the atomic energy of canada limited mine by experiment this model has been verified by investigating the linkage between microseismicity rock mass damage and ground deformation it is found that when damage related softening based on microseismic data is considered predicted rock mass displacements are in good agreement with extensometer measurements

late wenlock sequence and bentonite stratigraphy in the malvern suckley and abberley hills england abstract the late wenlock series homerian stage of the central midland platform occupies an area stretching from ledbury to the malvern suckley and abberley hills based upon the establishment of a sequence stratigraphic framework for the much wenlock limestone formation and the immediately under and over lying coalbrookdale and lower elton formations comparisons can now be made with key sections across the northern midland platform and beyond these correlations have been strengthened by the determination of apatite rare earth element ree geochemical signatures obtained from four volcanic ash layers bentonites at whitman s hill quarry herefordshire which allow for comparisons with published coeval sections at wren s nest hill west midlands and wenlock edge shropshire as well as with bentonites described from the island of gotland sweden across the study area fifteen parasequences associated with two pronounced regressive episodes separated by a marked transgression can be identified the lithological responses to these relative sea level changes are the same as those reported from the west midlands including the threefold division of the much wenlock limestone formation into lower quarried limestone nodular beds and upper quarried limestone members apatite ree geochemical signatures from whitman s hill quarry identify three bentonites which probably originated from a granodiorite magmatic source while a fourth bentonite has a distinctively mafic composition more akin to that of a gabbro or syenite this distinctively mafic bentonite is preserved on a marked flooding surface within the nodular beds member and appears compositionally and stratigraphically equivalent to a bentonite at wren s nest hill west midlands furthermore in both sections this bentonite is of notable thickness 120 200 mm allowing for its identification in other sections across the region comparisons with gotland identify three closely spaced bentonites of a similar mafic composition to the bentonite described from the midland platform while similarities in stratigraphic position and composition do not at present allow for the identification of a single ash fall event covering both the midland platform and gotland they are indicative of a shared source region which may offer the possibility for future bentonite correlation between these regions

microseismic and precursor analysis of high stress hazards in tunnels a case comparison of rockburst and fall of ground abstract in rock engineering microseismic monitoring technology has been extensively applied for the interpretation and forecast of rockburst hazards however highly stressed hard rocks could suffer dynamic geological hazards rockburst and gravity driven geological hazards fall of ground both of which have distinct developmental processes and precursory features that await comprehensive exploration hence in this study we adopted microseismic monitoring and an advanced method based on the source parameters of seismic energy seismic moment and apparent stress the ems method the source parameter space was constructed to ascertain microseismic events as stress adjusting deformation driven or energy releasing type the evolution of the event type and the microseismic path precisely revealed the characteristics of the hazard development in a case study of a deeply buried tunnel we analyzed the process by which high stress hazards occur using the proposed method and distinguished between the respective microseismic characteristics of the rockburst and fall of ground in the development and occurrence stages finally we proposed the key precursory of rockburst and fall of ground in high stress rock masses while deformation driven events increase notably in rockburst stress adjusting events are dominant in fall of ground overall this study could facilitate precise interpretation and warning about different high stress hazards and provide effective measures to curb the development of hazards

a systematic engineering geological evaluation of diabase dikes exposed at the underground caverns of dagangshan hydropower station southwest china dagangshan hydropower station is located in the middle of dadu river southwest china many diabase dikes were exposed in the adamellite granite body during excavation of the underground caverns the dikes are highly directional have crushed interiors exhibit strong alteration and have poor contact relationships with surrounding rocks all of which is inconsistent with the characteristics of typical diabase this paper describes systematic research that focused on the dikes spatial distribution macroscopic characteristics physical and mechanical properties and common instability modes factors influencing their stability and their corresponding control measurements are discussed in the context of the site and its conditions results show that most of the dikes located in the underground caverns are the branches of the main dike 9 which produced from a strong basic magma extrusion overflow event happened in between the permian and triassic due to multiple strong tectonic activities the chlorite alignment of these dikes generally tended to be significant and leaded the physical and mechanical properties to be poor then excavation and repetitive blasts resulted in strong disturbances to the original dikes and even caused rock unloading collapse rock block fall and groundwater runoff system water inflow change according to the common instability modes and reasons of diabase dikes some specific control measures including solidified rubbles reinforcement methods pre grouting and small ducts are implemented in order to keep the surrounding of diabase safety and the results show that the control methods perform a proper effect on these engineering problems

trace element mobility during early diagenesis of volcanic ash applications to stratigraphic correlation abstract we have analyzed the relative mobility of trace elements in five rhyolitic and two basaltic tephra layers preserved in both altered and unaltered states as a means of developing a rapid whole rock method for correlating altered tephra layers the tephra layers were altered to zeolites or clay minerals in either saline alkaline pore fluids characteristic of small ephemeral lakes or slightly more dilute pore fluids associated with perennial lakes and brackish coastal groundwaters comparison of whole rock trace elements analyses from the unaltered and altered portions of each tephra layer indicates that immobile elements such as ti zr hf and ta retain their initial concentrations relatively more reactive alkaline and alkaline earth elements such as rb sr and cs are generally mobile the lanthanide elements display variable mobility the light rare earth elements lree generally retain their initial concentrations whereas the heavy rare earth elements hree are generally depleted in alkaline solutions but immobile in more dilute pore fluids we suggest that differences between lree and hree mobility result from the combined effects of lree partitioning into stable accessory minerals and hree transport as solution complexes although our data set was not designed for quantitative analysis of these proposed mechanisms where both the diagenetic environment and the accessory mineral compositions are well constrained the trace element signatures of the unaltered and altered tephra layers can be used to correlate an altered tephra layer to its unaltered equivalent and to distinguish between different altered tephra layers four of the seven altered tephra layers canbe distinguished on the basis of ratios of immobile elements e g zr ti vs hf ti the remaining three all w type rhyolitic ashes can be largely differentiated using cluster analysis on a combination of immobile elements and elements with similar mobilities

a tensile model for the interpretation of microseismic events near underground openings for small scale microseismic events the source sizes provided by shear models are unrealistically large when compared to visual observations of rock fractures near underground openings a detailed analysis of the energy components in data from a mine by experiment and from some mines showed that there is a depletion of s wave energy for events close to the excavations indicating that tensile cracking is the dominant mechanism in these microseismic events

dynamic analysis of rock mass deformation in large underground caverns considering microseismic data abstract the underground powerhouse of a hydropower project is one of the most significant structures that will be permanently in use large scale excavation induced rock mass damage may pose a threat to the stability of the underground powerhouse in the present study a microseismic ms monitoring system was established to capture microcracks induced by excavation of the underground powerhouse caverns at the houziyan hydropower station based on tempo spatial characteristics of the ms events the relation between ms activities and field construction was analyzed and the main damage regions were revealed a damage driven model considering the effect of ms source sizes is adopted for dynamic analysis of rock mass deformation of the underground caverns the rock mass damage is simulated by a micro mechanics based constitutive model described by the fracture density determined by the ms source radius a numerical model of a typical profile of the underground powerhouse was established the ms data monitored in each bench excavation period of the underground powerhouse caverns was imported to the numerical model for dynamic analysis of deformation the results showed that the effect of rock damage played a significant role in the rock mass deformation of the underground powerhouse during each bench excavation the displacements of rock mass considering ms data obtained from the numerical analysis can provide better predictions for real conditions on site

distribution and tectonic setting of ordovician k bentonites in the united kingdom twenty five ordovician k bentonite samples ranging in age from llanvirn to ashgill and representing both sides of the lapetus suture were analysed by inaa and xrf and compared on magmatic and tectonic discrimination diagrams the proportional distribution of nb y ti zr hf ta th and ree indicates that source volcanics were erupted in a setting that changed from subduction related in the llanvirn llandeilo to marginal basin extensional volcanism in the caradoc ashgill welsh k bentonites appear to be derived from volcanoes within the welsh basin but k bentonites from the southern uplands to not have characteristics consistent with a fore arc setting further suggesting a source related to ensialic marginal basin extensional volcanism

fdm predictive methodology for subsidence due to flat and inclined coal seam mining abstract a subsidence estimation methodology to predict subsidence troughs due to flat and inclined coal seam exploitation is described the foundations of the procedure are the correct definition of the rock mass behaviour model its adequate characterization and its implementation in the code flac fast lagrangian analysis of continua was written by p a cundall and is marketed by itasca cons group inc of minneapolis mn usa which is based on the finite difference method or fdm numerical modelling technique the method is first validated for flat coal seam longwall mining with caving in british basins because of the large number of data from this area which includes subsidence measurements and characterization parameters the method is then applied to gently inclined seams and the results are seen to fit empirical observations finally for steeply inclined and sub vertical seams the proposed methodology allows observation of two different movement trends in the overlying strata the former is perpendicular to the strata direction in the same way as the one observed in flat seam subsidence and the latter which becomes the most important one in seams dipping by more than 75 is parallel to the strata these two different trends produce subsidence troughs presenting two relative subsidence maxima and extending along large surface areas thus it would be unlikely to predict and assess these troughs this may be a possible reason why so little coherent data about this kind of subsidence exists these numerical observations of steeply inclined coal seams need to be validated empirically

correlation of the ordovician deicke and millbrig k bentonites between the mississippi valley and the southern appalachians 1 two widespread rocklandian age middle ordovician k bentonite beds the deicke and millbrig can be correlated from southern minnesota and northwestern iowa through eastern missouri across kentucky and central tennessee to the valley and ridge of the southern appalachian mountains they are equivalent to beds previously called t 3 or pencil cave and t 4 or mud cave metabentonites and thus constitute ordovician chronostratigraphic marker horizons throughout much of the eastern mid continent previous correlations of these beds in the mississippi valley by chemical fingerprinting is extended toward the southern appalachian basin by tracing in surface exposures and on wireline logs both beds thicken toward the southeast indicating a volcanic source area that was probably ast of south carolina the interval between the k bentonite beds also thickens toward the southeast owing to increased rates of carbonate deposition between the two volcanic episodes the areal extent of known correlatives of the deicke and millbrig is minimally estimated to be 600 000 sq km and at least 1122 cu km of pre compaction deicke k bentonite accumulated as ash in eastern north america the volume of both beds suggests they rank among the largest air fall ash deposits documented in the stratigraphic record

late ordovician chatfieldian catastrophic volcanism and abrupt carbonate platform interior subsidence a tectonic link across a taconian foreland basin quebec embayment due to inherited crustal weakness the late ordovician trenton group of new york state and equivalent strata in south central canada peripheral to the quebec embayment form a regional carbonate platform succession within the taconian foreland basin the upper and lower group boundaries record geodynamically controlled changes in regional subsidence whereas a higher order allocyclic stratigraphy traced south along the foreland interior of the eastern united states may identify shorter term eustatic controls a tectonomagmatic event extending across the foreland basin is recorded a few million years prior to the regional collapse of the foreland platform in the quebec embayment within the lower c spiniferus graptolite zone platform margin retreat 50 km in southern quebec is contemporaneous with a shale rich limestone succession that thins 30 10 m westward over 300 km into the ottawa embayment eastern ontario west of the appalachian structural front this stratigraphic record coincides with catastrophic volcanism within the once distant volcanic arc terranes as recorded by a bentonite traced geophysically from the platform margin to the michigan basin core from the ottawa embayment demonstrates western directed transport of lithic bearing ash the lithic material representing reworked deep water sedimentary and or volcaniclastic sediment was entrained by eruption of calc alkaline felsic to basaltic andesitic and trachyandesitic magmatic sources the above geological history documents a short period of diminishing influence of subsidence moving into the platform interior an event that enhanced briefly cross platform oceanographic circulation as recorded by elevated shale abundance and change in macrofaunal assemblages short lived differential subsidence of the continental crust in this region in response to distal tectonism may have been predicated by inherited weakness of a shallowly buried intracratonic 400km precambrian fault system manifest today by the ottawa bonnechere graben the resulting thin 10 to 30 m stratigraphic record of the tectonomagmatic event is of similar thickness to high order allostratigraphic patterns within the taconic foreland interior of the eastern united states because there is a heterogeneous distribution of precambrian fault systems underlying the taconian foreland interior of eastern laurentia differential structural response of the foreland interior can be anticipated the apparent regional allostratigraphy may contain subtle facies differences along the strike of the foreland basin that reflect this tectonic component

40ar 39ar and nd sr isotopic characteristics of mid ordovician north american k bentonites a test of early paleozoic laurentia gondwana interactions highly altered tephra layers k bentonites of mid ordovician age are widespread throughout the midcontinent region of the united states and the appalachian taconic foreland basin the numerous ash layers their wide areal extent and their large volume provide evidence that extensive volcanic activity accompanied taconic orogenesis the mineralogical and geochemical characteristics of these widespread ordovician tephra layers can be used to constrain the nature of their source region and thereby help test recent hypotheses that gondwana collided with laurentia in mid ordovician time initial 143nd 144nd and 87sr 86sr ratios of two k bentonites that occur traced throughout the midcontinent are 0 51183 0 51187 and 0 7101 0 7120 respectively isotopic ratios for k bentonites within the taconic basin are 0 51178 0 51201 and 0 70564 0 70905 the isotopic composition of the tephra layers and the ubiquitous presence of proterozoic zircon xenocrysts within the k bentonites is consistent with an origin by crustal anatexis the cooling history of the source is constrained by 842 996 ma 40ar 39ar apparent ages of hornblende xenocrysts contained within two taconic basin k bentonites a possible south american source region of the k bentonites is the arequipa massif of peru this region contains early paleozoic arc related rocks many of which contain mid proterozoic zircon xenocrysts and early proterozoic gneisses which were affected by grenville age granulite grade metamorphism gneisses within the adirondack highlands of the grenville province have similar end 450 ma values and hornblende cooling ages to the k bentonites consistent with this region as a source caradocian k bentonites in sweden have sr isotopic ratios similar to the north american beds if the swedish and north american k bentonites were produced from the same source then baltica and laurentia were proximal in ordovician time precluding a gondwana laurentia link if caradocian k bentonites with north american characteristics are found in western south america support for a laurentia gondwana link would be established if such k bentonites cannot be found considerable doubt would be cast on this model

trace element chemistry of individual apatite phenocrysts as a tool for fingerprinting altered volcanic ash beds assessing interbed and intrabed variation at local and regional scales trace element analyses of groups of single apatite microphenocrysts separated from k bentonites define the intrabed homogeneity and interbed variability of apatites in a set of k bentonites from the gaspe peninsula and the regional scale homogeneity of the tioga b k bentonite by analyzing many single grains from each bed it is possible to quantify the homogeneity of beds for statistical comparisons of similarity and differences this approach leads directly to tests that can be used to chemically correlate or distinguish k bentonite beds the results from multiple k bentonite beds from gaspe demonstrate that many of them may be distinguished from one another the results from the tioga b k bentonite demonstrate that there is little variation in apatite chemistry over distances of several hundred kilometers this technique is advantageous for use in k bentonite correlation because it provides a direct test of sample contamination as well as the necessary data on variance of each sample allowing for robust statistical analysis

characteristic microseismicity during the development process of intermittent rockburst in a deep railway tunnel abstract during deep tunnel excavation more than one rockburst sometimes occur in a particular area which seriously threatens construction safety in this work the characteristic microseismicity occurring during the development process of intermittent rockburst more than one rockburst occurring in a particular area and single rockburst only one rockburst occurring in a particular area and the associated mechanism of formation are studied data was collected during the construction of a railway tunnel in southwestern china microseismicity was recorded and analyzed before and after each rockburst for both intermittent and single rockbursts the schmidt number declines heavily with time the cumulative apparent volume rises sharply with time and the seismic activity is high before the rockburst however this characteristic microseismicity can also be found with no rockburst occurrence between each rockburst in an intermittent rockburst the ms events mostly have low ms energy i e whose logarithm measured in joules is smaller than 3 5 and the energy stored in the rockmass of the rockburst zone is not adequately released therefore there is likely to be another rockburst after the blast when high in situ stress is present after the last rockburst of an intermittent rockburst and the single rockburst some ms events of high ms energy i e whose logarithm measured in joules is larger than 3 5 occur in the deep surrounding rockmass and the energy stored in the rockmass of the rockburst zone is gradually released to a certain degree the stress is transferred to the deep surrounding rockmass whose stability is relatively high as a result a subsequent rockburst is hardly likely to occur again

microseismic monitoring of a controlled collapse in field ii at ocnele mari romania several decades of faulty exploitation of salt through solution mining led to the creation of an underground cavern containing several million cubic meters of brine to eliminate the huge hazard near a densely inhabited area a technical solution was implemented to resolve this instability concern through the controlled collapse of the roof while pumping the brine out and filling the cavern with sterile to supervise this an area of over 1 km2 was monitored with a staggered array of 36 one component 15 hz geophones installed in 12 boreholes about 160 360 m deep a total of 2 392 seismic events with mw 2 6 to 0 2 occurred from july 2005 to march 2006 located within an average accuracy of 18 m the b value of the frequency magnitude distribution exhibited a time variation from 0 5 to 1 and from there to 1 5 suggesting that the collapse initiated as a linear fracture pattern followed by shear planar fragmentations and finally a 3 d failure process the brunching ratio of seismicity is indicative of a super critical process except for a short period in mid february when temporary stability existed event relocation through the use of a collapsing technique outlines that major clusters of seismicity were associated with the main cavern collapse whereas smaller clusters were generated by the fracturing of smaller size nearby caverns it is shown that one component recordings allow for stable and reliable point source event mechanism solutions through automatic moment tensor inversion using time domain estimates of low frequency amplitudes with first polarities attached detailed analysis of failure mechanism components uses 912 solutions with conditional number cn 0 5 the largest pure shear dc components characterize the events surrounding the cavern ceiling which exhibit normal and strike slip failures the majority of mechanism solutions include up to 30 explosional failure components which correspond to roof caving under gravitational collapsing the largest vertical deformation rate relates closely to the cavern roof and floor as well as the rest of the salt formation whereas the horizontal deformation rate is most prominent in areas of detected collapses

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

local acceleration monitoring and its application in physical modelling of underground mining abstract a micro electro mechanical systems mems inertial sensor was introduced to perform local acceleration monitoring lam in a physical model to showcase mining induced strata movements to prove the feasibility of lam a physical model experiment was performed using four sensors mounted on the roof strata acquired acceleration signals were processed by a moving average and median filter analysed with respective trend variation and fluctuation along with excavation sequence to identify the movement of roof strata a key reference was the mid span section that characterized by adjacent sensors with opposite acceleration change direction to assess the stability of strata a clear evidence is the synchronicity loss of two adjacent sensors in terms of acceleration change in the presented experiment the first weighting and the fracture position can be predicted 1 5 h prior to final failure this study represents a novel attempt to apply lam in a physical modelling experiment and tentatively interpret signals in accordance with strata movement the proposed lam based approach succeeded in identifying the movement and assessing the stability of the strata results presented in this paper verify the validity of lam in terms of noise analysis sensibility and rationality this lam technique is capable of serving as an easy to implement high precision and low cost method in mining and geotechnical related physical modelling research

petrology and geochemistry of ordovician k bentonites in new york state constraints on the nature of a volcanic arc altered volcanic ashes k bentonites in the late ordovician caradocian utica shale of new york state are the product of explosive arc volcanism most of the 30 k bentonites examined in this investigation contain fragmental crystals and rock fragments microliths up to 600 mu m in diameter that generally are neither detrital contamination from the surrounding black shale nor igneous phenocrysts the dominant phases are garnet two groups gr sub 15 20 alm sub 45 75 py sub 35 0 sp sub 2 5 gr sub 2 5 alm sub 55 85 py sub 10 40 sp sub 1 plagioclase feldspar an sub 80 10 alkali feldspar or sub 99 0 clinopyroxene wo sub 50 40 en sub 50 30 fs sub 0 30 and orthopyroxene wo sub 1 2 en sub 77 32 fs sub 32 66 accompanied by lesser quantities of hornblende aluminosilicate quartz sphene fe ti oxides apatite and zircon most of the fragmental crystals appear to be derived from the same source as the metamorphic microliths which possess minerals with similar compositions both crystals and microliths are interpreted as xenocrysts and xenoliths from the ancient continental crust on which the ordovician arc was constructed they became entrained in the volcanic plume during explosive eruptions a precambrian age acquired on k feldspars from one k bentonite using the sup 40 ar sub 39 ar method shows that these xenocrysts were derived from depths of less than 5 10 km in the microcontinent at the time of late ordovicianmore volcanism the occurrence of xenocrysts and xenoliths in these k bentonites underscores the importance of performing detailed petrology on ash layers prior to the onset of more sophisticated tasks e g isotopic age determinations regional stratigraphic correlations of k bentonites based upon chemical compositions less

chronology of late cenozoic volcanic eruptions onto relict surfaces in the south central sierra nevada california early twentieth century geologists ob served extensive areas of subdued topography in the otherwise strongly dissected landscape of the southern sierra nevada that they ascribed to periods of stability following episodes of orogenic uplift from this evidence they developed an uplift history for the sierra nevada this conceptual model for landscape evolution of the sierra has largely been rejected or ignored since the middle of the twentieth century based in considerable part on observations indicating that these surfaces can be explained as dynamic landforms actively developing in response to conditions of the relatively recent geological past and that long term erosion rates are much too high to permit pre quaternary surfaces to be preserved we investigated the chronology of basaltic flows and ejecta on several such apparent relict surfaces located west of bishop california most of the basalt cones and flows that were sampled are nearly concordant with the present topography generally showing no more than 50 m of landscape inversion the 40 ar 39 ar ages of the basalts fall into two groups 11 76 0 05 ma and 3 40 0 06 ma these ages demonstrate that paleosurfaces dating back to at least the miocene can be preserved close to the summits of the sierra nevada with minimal erosion the elevations and relative sequences of these surfaces do indeed appear to preserve a topographic history of the sierra nevada encouraging continued investigation of their significance within the tectonic history of the sierra nevada

quantification and interpretation of seismicity abstract methods based on acoustic emission and microseismicity ae ms have proven to be valuable for monitoring microcracking at the underground research laboratory url in canada the source locations of the seismic events induced by the excavation have helped to map out the extent of the excavation damage disturbed zone edz around tunnels this paper describes methods for advanced processing and interpretation of ae ms data and the quantification of changes in material properties using velocity interferometry examples of methods that are generally not used routinely in the analysis of ae ms data are given these include 1 long term spatial and temporal source parameter trends and magnitude frequency studies 2 source mechanism analysis and 3 source location refinement by the use of relative location and clustering techniques results from these studies are shown to aid in the understanding of the effect of confining pressure on ae ms activity around tunnels and the mechanics of rock failure in the edz also the reduction of source location error is shown to be critical for delineating structures that may exist in clusters of ae ms data finally examples of the use of seismic sources to produce repeat measurements of seismic velocity along raypaths in 3d orientations through a rock mass are given this is found to be a highly sensitive method for quantifying changes in rock properties such as young s modulus as well as for modelling the change in crack density and saturation occurring in a rock mass with time

correlation of north american ordovician bentonites by using apatite chemistry middle ordovician bentonites in the central and southeastern united states have been correlated on the basis of rare earth element ree concentrations of primary apatite phenocrysts ratios of light to heavy ree such as la tb or ce yb produce the best separation of the four studied bentonites the deicke bentonite has been correlated over a distance of more than 1000 km from southern minnesota to central tennessee and the millbrig bentonite has been correlated over 750 km from central minnesota to central missouri the successful discrimination of closely spaced bentonites over a long distance demonstrates that apatite chemistry is a powerful correlation tool on a continental scale

correlation of ordovician mohawkian k bentonites in the upper mississippi valley using apatite chemistry implications for stratigraphic interpretation of the mixed carbonate siliciclastic decorah formation abstract four ordovician k bentonites have been chemically fingerprinted using trace element content of apatite phenocrysts contained within the altered ash layers trace element analysis was performed using electron microprobe on individual crystals the bentonites include the deicke millbrig elkport and dickeyville beds these beds lie within the decorah formation of the northern mississippi valley outcrop area all four k bentonite beds are believed to have a taconic source whereas volcanic ash was transported by wind and deposited in the ordovician north america epeiric sea the decorah is a marine unit shaly to the north and west and carbonate rich to the south and east thirteen k bentonite samples were collected from six localities only one locality dickeyville wi contains all four beds in succession one hundred seventy one apatite crystals were handpicked and analyzed for major minor and trace elements using an electron microprobe each crystal was analyzed at three to six separate spots to ascertain compositional variation the most discriminating and diagnostic elements were mg and mn plotting mg vs mn content produces data clusters characteristic for each k bentonite clusters show only minimal change between localities allowing individual k bentonites to be identified and used for stratigraphic correlation time slices provided by the k bentonite horizons show that the decorah formation is composed of reciprocal wedges stratigraphic sequences of shale and carbonate shale was deposited in deeper water within the hollandale embayment but pinched out southeastward onto the flank of the wisconsin dome carbonates were formed largely in shoal water on the arch prograding northwestward and shaling out downramp into the embayment

stress estimated using microseismic clusters and its relationship to the fracture system of the hijiori hot dry rock reservoir a method for estimating the in situ stress state by analyzing microseismic clusters induced by hydraulic injections is proposed the method is based on focal mechanism analysis supplemented with microseismic doublet analysis the latter is used to discriminate between the fault plane and the auxiliary planes of the focal mechanism solution the method was applied to estimate the stress field within the hijiori hot dry rock geothermal reservoir and yielded results which were consistent with other estimates the mechanics of permeability creation within the reservoir during major hydraulic injections was then examined by evaluating the interaction of the inferred stress field with the natural fracture system the characteristics of the latter were determined by integrating information obtained from core samples acoustic borehole televiewer images and pressure temperature and spinner logs the results indicated that the observed microseismicity and orientation dependent permeability characteristics of the fracture population are well explained by shear failure inferred from coulomb s friction theory it is also shown that the growth direction of the reservoir is strongly controlled by the distribution of favorably oriented pre existing fractures and their interaction with the stress field

studies on temporal and spatial variation of microseismic activities in a deep metal mine abstract aiming at forecasting techniques of ground pressure hazards in deep metal mines a microseismic monitoring system was established at a deep stope in hongtoushan copper mine in china based on theories of geophysics and rock mechanics a forecasting approach was introduced using microseismic multi parameters including cumulative apparent volume energy index spatial correlation length fractal dimension and b value the approach was used to predict large scale fractures and ground pressure hazards in rock masses the results showed that microseismic activities were very weak before mining commenced however activities became significant when mining started when mining finished microseismic activities remained at a higher level for about one week then became weakened before large scale fractures occurred all microseismic multi parameters behaved differently the apparent volume and spatial correlation length were continually increasing while energy index fractal dimension and b value were gradually dropping to their minimum values therefore these parameters could be used as precursory indicators for great ground pressure hazards comprehensive analysis on microseismic multi parameters changes could improve reliability of forecasting which is of great significance to deep metal mines in managing ground pressure failure risks

source parameters of mining induced seismic events an evaluation of homogeneous and inhomogeneous faulting models for assessing damage potential source parameter estimates based on the homogeneous and inhomogeneous source models have been examined for an anomalous sequence of seven mine induced events located between 640 and 825 m depth at strathcona mine ontario and having magnitudes ranging betweenmn 0 8 and 2 7 the derived brune static stress drops were found to be similar to those observed for natural earthquakes 30 bars whereas dynamic stress drops were found to range up to 250 300 bars source radii derived from madariaga s model better fit documented evidence of underground damage these values of source radii were similar to those observed for the inhomogeneous model the displacement at the source based on the observed attenuation relationship was about 60 mm for three magnitude 2 7 events this is in agreement with slip values calculated using peak velocities and assuming the asperity as a brune source within itself 72 mm by using madariaga s model for the asperity the slip was over 3 times larger than observed peak velocity and acceleration scaling relations with magnitude were investigated by incorporating available south african data appropriately reduced to canadian geophysical conditions the dynamic stress drop scaled as the square root of the seismic moment similar to reported results in the literature for crustal earthquakes this behavior suggests that the size of the asperities responsible for the peak ground motion with respect to the overall source size follow distributions that may be similar over a wide range of magnitudes measurements of source rupture complexity ranging from 2 to 4 were found to agree with estimates of overall source to asperity radii suggesting together with the observed low rupture velocities 0 3 to 0 6 that the sources were somewhat complex validation of source model appropriateness was achieved by direct comparison of the predicted ground motion level to observed underground damage in creighton mine located within the same regional stress and geological regime as strathcona mine close to the source 100 m corresponding to relatively higher damage levels a good agreement was found between the predicted peak particle velocities for the inhomogeneous model and velocities derived based on established geomechanical relationships the similarity between asperity radii and the regions of the highest observed damage provided additional support for the use of the inhomogeneous source model in the assessment of damage potential

source parameters of seismic events at heinrich robert mine ruhr basin federal republic of germany evidence for nondouble couple events abstract a three component digital seismic station is in operation at heinrich robert coal mine in the ruhr basin at a depth of 890 m a cluster of seismic events occurred at the beginning of 1987 at a distance of about 5 km from the station and continued in 1988 source parameters of 46 tremors selected from the cluster with local magnitude from 1 2 to 2 3 are studied the ratio of p wave to s wave corner frequency is variable implying its dependence on the angle of observation and in turn the variability of focal mechanism with time the scaling relations indicate that characteristic tremors with a fault length of about 200 m are possibly generated in the area but the evidence is not conclusive the seismic energy for a given seismic moment can vary by a factor of 20 and the ratio of s wave to p wave energy ranges from 1 5 to 30 stress release estimates show low values not exceeding a few bars typical for tremors induced by mining a comparison of the apparent stress with the static stress drop divides the selected tremors into high and low apparent stress events the latter events are characterized by high p wave energy and almost constant and large ratio of p wave to s wave corner frequency which differs from the lower ratios of other events implying similar focal mechanism these high p wave energy tremors are the most likely candidates for nondouble couple events

upper wenlock bentonites from wren s nest hill dudley comparisons with prominent bentonites along wenlock edge shropshire england the upper wenlock series homerian stage of the northern midland platform england contains numerous volcanic bentonite clay layers at wren9s nest hill dudley 15 bentonites have been investigated and comparisons with the type wenlock have been made by means of two key sections along wenlock edge shropshire in total 22 bentonites have been investigated and their clay and sand grade mineralogies determined rare earth element ree and yttrium concentrations of apatite grains contained within ten of the bentonites have been established allowing geochemical fingerprinting as an indication of provenance of source magmas and identification of geochemical marker beds based on the analysis of ree and yttrium concentrations it seems likely that the majority of these bentonites originated from a granodiorite magmatic source comparisons with published llandovery and lower wenlock age bentonites indicate generally more enrichment in light rees relative to heavy rees in addition close geochemical similarities between bentonites along wenlock edge and at wren9s nest hill strongly argue for their presence as precise stratigraphic equivalents within the upper much wenlock limestone formation these correlations are further supported by geophysical data from borehole wire line logs across the west midlands finally a chemically distinct mid homerian episode of volcanism is identified and represents a potentially important marker interval between the study area and other similarly aged bentonites reported from the island of gotland sweden

estimation of rock mass properties in excavation damage zones of rock slopes based on the hoek brown criterion and acoustic testing abstract when slopes are excavated in rock masses with the blasting method blasting and stress relaxation will produce an excavation damage zone edz in the remaining rock mass this study presents an estimation of the rock mass properties in the edz based on the generalized hoek brown failure criterion and the varying disturbance factor in this estimation the disturbance factor is quantified by using the acoustic p wave velocities tested in undamaged and damaged rock masses instead of a single constant value chosen from the descriptive guidelines statistical analysis of the acoustic test data shows that with an increase in depth behind the slope face the disturbance factor declines from 1 0 to 0 almost in a linear manner for blasting excavation of slopes in weaker rock masses the zone in the immediate vicinity of the slope face is fully damaged and thus over this range the disturbance factor remains the constant value of 1 0 as the disturbance factor linearly decreases within the edz the deformation modulus uniaxial compressive strength and equivalent cohesive strength of the damaged rock mass linearly increase to the undamaged values by assigning the varying parameters to the rock mass in the edz a numerical calculation based on the flac program is conducted to assess the slope stability it is found that using the varying rock mass parameters within the edz will yield completely different failure surfaces and factors of safety from that uses the constant parameters therefore it is significant to develop such an approach to quickly estimate the varying rock mass properties in the edz particularly when in situ tests are not available

stratigraphic and chemical correlation of volcanic ash beds in the terminal proterozoic nama group namibia at least twenty silicified volcanic ash beds have been identified in the kuibis and schwarzrand subgroups of the terminal proterozoic nama group of namibia nineteen of the nama ash beds are in the schwarzrand subgroup in the witputs subbasin two of these are in the siliciclastic dominated lower part of the subgroup which consists of the nudaus formation and nasep member of the urusis formation and comprises two depositional sequences identification and correlation of these ash beds are very well known based on stratigraphic position sixteen ash beds are contained within the carbonate dominated strata of the huns feldschuhhorn and spitskop members of the urusis formation these strata comprise four large scale sequences and eighteen medium scale sequences ash beds have been found in three of the large scale sequences and seven of the medium scale sequences correlations are proposed for these ash beds that extend over large changes in facies and stratal thickness and across transitions between the seaward margin depocentre and landward margin of the huns spitskop carbonate shelf a study of whole rock and in situ phenocryst compositions was conducted to evaluate the feasibility of independently testing sequence stratigraphic correlations by geochemically identifying individual ash beds whole rock abundances of al fe mg k and ti vary inversely with si reflecting variations in phenocryst concentration due to air fall and hydrodynamic sorting these sorting processes did not substantially fractionate whole rock rare earth element abundances ree which vary more widely with si ree abundances are higher in samples of the nudaus ash bed than in samples of the nasep ash bed independent of position in bed phenocryst abundance or grainsize providing a geochemical means for discriminating between the two beds variations in the position of chondrite normalized whole rock ree plots similarly support suspected correlations of ash beds between widely separated sections of the spitskop member abundances of fe mg and mn in apatite plot in distinct clusters for spitskop ash beds that are known to be different and in clusters that overlap for ash beds suspected of correlating between sections abundances of ree in monazites differ for the nudaus nasep and spitskop ash beds in which these phenocrysts were identified multivariate statistical analysis provided a quantitative analysis of the discriminating power of different elements and found that whole rock abundances of ge nb cs ba and la discriminate among the whole rock compositions of the nudaus and nasep ash beds and the spitskop ash beds that are thought to correlate between sections each of the above geochemical signatures by itself is not definitive because the differences between beds are comparable to the variability within beds and because some signatures are shared by beds known to be different taken together however weight of evidence arguments based on multiple components and phases can successfully discriminate among nama ash beds results from this study support sequence stratigraphic correlations of spitskop ash beds that document stratal truncations and gaps in the record related to onlap and erosion

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

deformation forecasting and stability analysis of large scale underground powerhouse caverns from microseismic monitoring abstract to assess the stability of the underground powerhouse caverns and analyse the failure mechanism of the surrounding rock mass at the baihetan hydropower station in southwest china a high resolution microseismic ms monitoring system was implemented in the left bank underground powerhouse caverns based on the temporal and spatial distribution of ms events the correlation between ms activities and construction was established and three damage regions for the surrounding rock mass during excavation were identified ms clusters were found to occur most often in stress concentration regions of the underground powerhouse caverns and to result from various factors including excavation induced unloading and geological structure activation the seismic source parameters i e moment magnitudes and s wave to p wave energy ratios e s e p of the three ms clusters demonstrate the different failure modes and risks of the surrounding rock mass the temporospatial evolution of the ms activities apparent stress and cumulative apparent volume in localized rock mass during the period of a typical large deformation were used to develop a comprehensive analytical method for forecasting the deformation of the surrounding rock mass thus this comprehensive analytical method which incorporates ms monitoring conventional monitoring geological survey and construction is promising for identifying the damage zones and forecasting the macro deformation of the surrounding rock mass in underground powerhouse caverns subjected to excavation

u pb zircon age constraints on the timing and duration of wenlock silurian paleocommunity collapse and recovery during the big crisis high precision isotope dilution u pb zircon dating was conducted on three volcanic ash fall bentonite samples from the swedish island of gotland and on a fourth bentonite from the west midlands england zircons from the ireviken grotlingbo djupvik gotland and wren s nest hill 15 west midlands bentonites yielded weighted mean pb 206 u 238 ages of 431 83 0 23 0 67 ma 428 45 035 0 73 ma 428 06 0 2110 66 ma and 427 86 032 0 71 ma respectively analytical total uncertainties these biostratigraphically well controlled age dates effectively bracket the wenlock epoch of the silurian period and provide control for the duration of one of the major paleozoic biotic events and associated perturbations to the global carbon cycle the big crisis or lundgreni event graptolites the niulde event conodonts the mulde excursion carbon isotopes these new data suggest an older and shorter duration for the recalibration of the wenlock series and demonstrate that the cascade of biological and chemical events that took place during the big crisis happened on time scales of tens to hundreds of thousands of years less

space time clustering of seismic events and hazard assessment in the zabrze bielszowice coal mine poland the results of the statistical analysis of seismic activity recorded in the zabrze bielszowice coal mine in poland are presented in this article the monitoring was conducted by a small network consisting of four triaxial geophones deployed in vertical holes in the roof for over 1000 seismic events recorded during the two month s experiment the location of sources was realized the seismic sources were mostly located ahead of the active face of the longwall since the first day of the monitoring cluster analysis was sequentially performed for increasing number of sources at the end of the experiment 31 clusters were identified they consisted of different numbers of events and were separated in space about 40 of the events were not included in the clusters for each large cluster hazard analysis was separately performed the hazard function evaluated for the largest cluster was compared with hypocenters of high energy tremors e 1000 j recorded by the geophones in that area for some cases recorded tremors occurred after an abrupt decrease of hazard function but only one of them was located in the vicinity of the appropriate cluster we concluded that for the analyzed cluster a correlation between evaluated hazard function and time occurrences of the high energy tremors existed except for one case there is no space correlation between analyzed clusters and high energy tremors

stratigraphic correlations using trace elements in apatite from late ordovician sandbian katian k bentonites of eastern north america the early late ordovician sedimentary rocks of eastern north america contain a relatively large number 100 of widespread heavily altered tephra layers k bentonites these beds represent an intense period of subaerial volcanism that occurred from ca 455 to 449 ma the sedimentary rocks that contain these k bentonites display complex regional lithostratigraphic relationships ranging from clastic foreland basin facies to cratonic carbonate platform facies accurate correlation of these ancient ash fall beds is essential for testing chronostratigraphic hypotheses that attempt to connect these different tectono sedimentary provinces despite the relatively thorough study of a few of these k bentonites over the past several decades the full stratigraphic potential of these beds has yet to be realized to test the utility of the apatite trace element k bentonite correlation method on a larger scale we studied over 200 k bentonite samples from the mohawkian stage of eastern north america and statistically compared our results with previous studies on the same suites of k bentonites electron microprobe epma and laser ablation inductively coupled plasma mass spectrometry la icp ms results show that apatite trace element data provide unique bed discriminators each of the k bentonite layers exhibits unique and reproducible trends in mg cl mn fe ce y and other trace element concentrations in apatite statistical evaluation of results from our apatite analyses suggests correlations for 12 k bentonite beds providing a significant improvement in stratigraphic resolution the stratigraphic relations indicated by these new k bentonite fingerprints provide a rigorous means by which to evaluate some previous interpretations of biostratigraphic chemostratigraphic and sequence stratigraphic studies in eastern north america

excavation induced damage studies at the underground research laboratory the underground research laboratory url is situated in the lac du bonnet granite batholith in southeastern manitoba canada the url was developed to study issues related to the deep geologic disposal of used fuel from nuclear reactors and has developed into an international atomic energy agency recognized geotechnical center of excellence extensive rock mechanics research has been conducted including work to understand the character and extent of excavation damage experience at the url has shown that damage exists around underground openings and that the damage develops from the energy imparted to the rock by the excavation method and by redistribution of the in situ stress field around the excavated openings subsequent near by excavations removal of loose material from the existing tunnel thermal loads and pore pressure changes will all influence the development and extent of rock damage as does the rock type and its fabric studies at the url have shown that in highly stressed rock damage will develop around underground openings even when a low energy excavation method is used and that properly designing the excavation geometry and orientation plays a major role in constructing stable openings two zones of excavation affected rock have been shown to exist from studies at the url 1 a zone of irreversibly damaged rock surrounding the excavation which may include failed zones inner and outer damage zones and 2 a zone of excavation disturbance where the in situ stresses are influence by the excavation no damage is measurable measurements of the properties of the damaged rock ultrasonic velocity transmissivity using a variety of instruments have shown that a less intensively damaged outer zone surrounds a more highly damaged inner zone the inner damage zone may have zones of failed rock depending on stress concentrations relative to rock strength and damage imparted by excavation method the inner damage zone is attributed to the effects of the excavation method and stress redistribution and the outer damage zone is attributed to the effects of stress redistribution alone in lower stressed rock the extent of the outer zone is much less than for an opening in highly stressed rock with the same excavation shape and orientation relative to in situ stresses the excavation disturbed zone describes the volume of rock surrounding the damage zone where the stress redistribution is too small to permanently change rock properties unless some other stress increase such as thermal loading is added and it is also characterized non permanent but potentially long term changes in hydraulic head

microseismicity monitoring and failure mechanism analysis of rock masses with weak interlayer zone in underground intersecting chambers a case study from the baihetan hydropower station china abstract a weak interlayer zone wiz is a rock mass system with poor mechanical properties large scale random distribution water softening causing an adverse effect on the safety of the construction and project progress to investigate the fracture process and the mechanism of rock masses with wizs in the intersecting chambers during the excavation process in situ microseismic ms monitoring was carried out in the underground powerhouse on the right bank of the baihetan hydropower station china during the monitoring the spatio temporal evolution process of the microseismicity of the rock masses around the intersecting chambers was obtained during the excavation unloading of multiple working faces the spatial evolution of ms events illustrates the dynamic progressive characteristics of ms activities as they propagate and accumulate along the wiz and finally form a cluster zone the fracture mechanism of moment tensor inversion reveals the distribution and evolution of ms events with respect to different fracture types tensile fracture events are distributed near the free surface while non tensile fracture events are far from the free surface finally the study proposes support measures restraining fracture development in surrounding rock masses with wiz the effectiveness of reinforced support measures is verified by ms events and the deformation of surrounding rocks the results of the study are particularly valuable for the stability analysis excavation and support optimization of similar engineering studies