behavior of transversely isotropic shale observed in triaxial tests and brazilian disc tests abstract shale rock is widely distributed in nature and must be taken into account in some rock engineering applications in this research three kinds of experiments namely the conventional triaxial compression test reducing confining pressure test and brazilian test were conducted on a type of shale rock specimen with a horizontal bedding plane and a vertical bedding plane collected from lushan city jiangxi province china to further investigate the bedding effect on the mechanical properties of shale rock an acoustic emission ae monitoring system was used to study the fracture process under the conventional triaxial compression test whereas a digital image correlation dic system was employed to monitor the deformation of disk faces during the failure process under the brazilian test another key issue addressed in this research is the failure process and mechanism of shale specimens with horizontal and vertical bedding planes under the reducing confining pressure test the conventional triaxial compression test shows that the bedding plane could easily affect the elasticity modulus and failure pattern and the failure of the bedding plane can lead to stronger energy release and a higher ae count level the reducing confining pressure test shows that the dissipated energy magnitude of unloading path ii reducing confining pressure and increasing axial stress is much larger than that of unloading path i reducing confining pressure and keeping axial strain constant and that continuous energy input and larger energy dissipation led the specimens under unloading path ii to fail faster than those under unloading path i the brazilian test further revealed that the bedding plane has a significant effect on the tensile strength and failure pattern of shale rock

comparison of the quaternary travertine sites in the denizli extensional basin based on their depositional and geochemical data abstract in the denizli basin turkey located in the western anatolian extensional province travertine and tufa deposition has been an ongoing process for at least 600 000 years travertine bodies which are 30 to 75 m thick and each covers areas of 1 to 34 km2 are up to 1 km3 in volume today spring waters in this area have temperatures of 19 to 57 c are of the ca mg hco3 so4 type in the pamukkale kelkaya and pinarbasi areas and the ca mg so4 hco3 type at cukurbag thermal waters along the northern margin of the basin are generally hotter than those in the east southeast and south the 18o and d values of the spring waters indicate a meteoric origin the average temperatures of the hydrothermal systems in the denizli basin appear to have decreased from pleistocene to holocene travertine which formed from the hotter water is more widespread than the tufa that formed in the cooler spring waters deposition of the travertine which formed largely on slopes in depressions and along fissure ridges mostly on northern basin margins was controlled by the interplay between various intrinsic and extrinsic parameters the travertines are formed largely of calcite with only minor amounts of aragonite in some of the vertically banded crystalline crust raft and pisoid travertines found in some of the northern sites the aragonitic samples rich in sr are typically found around the spring orifices and along the central axis of the fissure ridges the stable isotope values of the travertine found in the northwest and southeast parts of the basin are different the 13c values of the northern travertine deposits are more positive 3 7 to 11 7 vpbd than those found in the south southeast areas 4 to 5 8 vpdb in contrast the travertine and tufa in the southeastern areas have higher 18o values 15 2 to 7 8 vpdb than those of the northern areas 16 6 to 4 8 vpdb available evidence indicates that spring activity and associated travertine precipitation in the denizli basin were controlled largely by tectonic activity rather than by climatic conditions

thermal conductivity and well logs a case study in the paris basin summary the estimation of thermal conductivity from well logs is of great importance for all studies on thermal evolution of sedimentary basins the approach proposed here is to first interpret the well logs in terms of mineralogic composition and porosity and then to estimate the in silu conductivity from a mixing formula the geometric average of individual conductivities weighted by the volumetric proportion of each component the validity of the model has been widely verified by laboratory measurements on isotropic samples however there is a need for validation of such an approach for in situ conditions temperature data recorded at equilibrium in two wells of the paris basin offer a unique possibility of testing this approach in the case of a steady state conductive thermal rcgime fourier s law the conductivity must be proportional to the inverse of the temperature gradient the well logs are quantitatively interpreted in terms of mineralogic composition porosity and then thermal conductivity using a conductivity law calibrated on cuttings and cores laboratory measurements for three examples of well sections the computed thermal conductivity compares reasonably well with the inverse of the gradient for each of the three examples it is possible to define a depth range where the apparent heat flow is almost constant with depth and where the conductive regime seems to prevail this allows a refinement of the conductivity model with emphasis on the contribution of clays assuming that the conductivities of non clay end terms are known it is possible to obtain the conductivity of clay giving the best fit to the temperature measurements in the three cases the conductivity of clay 1 21 4 w m k is found to be lower than the assumed one 1 8 w m k i which probably indicates an anisotropy effect finally an empirical model where the bulk conductivity is expressed directly as a function of well logs is tested in one case the results obtained are quite compatible with the previous one but in the other two sections the stability and the physical meaning of this model are found to be questionable this could be due to the lack of constraints in the underlying implicit mineralogy model

anisotropy rather than transverse isotropy in longmaxi shale and the potential role of tectonic stress abstract in the last few decades the recovery of and exploration for shale gas has increased this has led to increased interest in the mechanical characterization of shale formations as relates to enhancing the conductivity of such formations characterization and modeling of these materials typically assumes transverse isotropy associated with the direction of bedding despite some studies showing anisotropy in these materials in this work we evaluate the validity of transverse isotropy for the longmaxi shale formation which has been targeted for shale gas exploration in china this evaluation is done through analysis of the macro and microstructure distribution confined triaxial tests and compression and shear wave velocity measurements these tests were performed parallel and perpendicular to the bedding and in the directions interpreted as the tectonic principal stresses the effect of tectonic stress on shale anisotropy is also discussed we found that the assumption of transverse isotropy for the mechanical behavior of the longmaxi shale might not be adequate under low confinement stresses the trends in the measured behavior suggest that transverse isotropy might provide adequate estimations as confinement increases the data also suggest that tectonic stresses affected the longmaxi shale rock mass characteristics at the study site in terms of macro and microstructure as well as mechanical properties the results also indicate that isotropic rocks may show anisotropy in subsurface engineering directing more attention to the possible mechanical differences in the field may provide implications for engineering safety

deformation and strength anisotropy of asan gneiss boryeong shale and yeoncheon schist results of deformability and strength anisotropy on three rock types found in korea are reported the experiments were conducted on rock specimen obtained from the directional coring system the anisotropy ratios of elastic modulus were from 1 7 to 4 0 for rock types in this study the applicability of transversely isotropic model was quantitatively investigated

structural characteristics of columnar jointed basalt in drainage tunnel of baihetan hydropower station and its influence on the behavior of p wave anisotropy abstract researches about the structural characteristics of rock mass are the basis for understanding their failure modes mechanism properties as well as evaluation of structural stability during the process of excavation natural columnar jointed basalt has complex structures and exhibits remarkable anisotropy and size effect in this study the observation window method was firstly applied to describe the natural columnar joints and pillar shapes at engineering scale and then the structural characteristics of columnar joints were analyzed the roughness of columnar joints scanned from large size rock core obtained at drainage tunnel 1 1 was secondly investigated based on the 3d scanning method some techniques such as field statistical analysis and ct scanning were used to analyse the characteristics of internal implicit joints in columnar jointed basalt thirdly the large scale columnar jointed basalt cores were tested by p wave which assisted to investigating the anisotropy of columnar jointed basalt the experimental and analytical results indicate that at the engineering scale natural columnar jointed basalt is heterogeneous exhibiting the features of mosaic structure and mainly quadrilateral in shape at the large size rock core scale the roughness of columnar joints is low with the value of 5 558 at the basalt column scale the internal implicit joints are not randomly distributed instead showing obvious tendency the internal implicit joints and columnar joints are important factors contributing to the special failure mode of columnar jointed basalt at the rock core scale with increasing angle between the p wave propagation direction and column the anisotropy of columnar jointed basalt core gradually increases and the degree of anisotropy is proportional to the number of columnar joints the internal implicit joints could also affect the p wave anisotropy of basalt column and the results in this study can provide some references for projects related to columnar jointed rock mass

seismic anisotropy in sedimentary rocks part 2 laboratory data part one of this paper presents a method for measuring seismic velocities and transverse isotropy in rocks using a single core plug this method saves at least two thirds of the time for preparing core samples and measuring velocities in transversely isotropic ti rocks using this method we have measured velocity and anisotropy of many shale and reservoir rocks from oil and gas fields around the world we present some of the data in this paper which include seismic velocity and anisotropy in 17 brine saturated shale samples 1 gas and brine saturated coal sample 8 brine saturated sands 12 gas saturated sands 32 gas saturated carbonate samples and 25 brine saturated carbonate samples the results show that clays and fine layering in sedimentary rocks are the main causes of seismic anisotropy very little intrinsic anisotropy exists in unfractured reservoir rocks such as sands sandstones and carbonates under reservoir conditions in contrast all shales were found seismically anisotropic anisotr

observations and bayesian location methodology of transient acoustic signals likely blue whales in the indian ocean using a hydrophone triplet a notable sequence of calls was encountered spanning several days in january 2003 in the central part of the indian ocean on a hydrophone triplet recording acoustic data at a 250 hz sampling rate this paper presents signal processing methods applied to the waveform data to detect group extract amplitude and bearing estimates for the recorded signals an approximate location for the source of the sequence of calls is inferred from extracting the features from the waveform as the source approaches the hydrophone triplet the source level sl of the calls is estimated at 187 6 db re 1 pa 1 m in the 15 60 hz frequency range the calls are attributed to a subgroup of blue whales balaenoptera musculus with a characteristic acoustic signature a bayesian location method using probabilistic models for bearing and amplitude is demonstrated on the calls sequence the method is applied to the case of detection at a single triad of hydrophones and results in a probability distribution map for the origin

suggestions for a consistent terminology for seismic anisotropy seismic anisotropy is an unfamiliar concept to many geophysicists and the use of misleading and ambiguous terminology has made it more difficult to understand i suggest here a consistent terminology in which simple expressions have specific meanings similar to their colloquial meanings it is hoped that use of such language will help to make the increasing number of papers reporting seismic anisotropy more readily comprehensible to the non specialist this not a manual of anisotropy and it is not intended for theoreticians it is a list of terms which may make anisotropy a little easier to understand for those more familiar with wave propagation in isotropic solids

seismic anisotropy of the upper mantle 1 factors that affect mineral texture and effective elastic properties 1 flow induced mineral alignment in the earth s mantle affects the nature of seismic wave propagation since measurements of seismic travel time and shear wave splitting are a key means by which the structure of the upper mantle can be imaged it is important to understand the factors that contribute to variability in elastic properties seismic anisotropy associated with lattice preferred orientations of minerals in peridotite is the focus of this study one way to better understand anisotropy in a convecting upper mantle is to simulate texture evolution based on certain assumptions simulations of the development of olivine and orthopyroxene alignment along streamlines of a mantle flow field illustrate how continuously varying strain conditions affect the resulting orientation distribution there are various uncertainties in rock texture simulations and the aim here is to investigate how much model assumptions may influence the results a model of upper mantle flow in the vicinity of an oceanic spreading center is used to illustrate these points first we assess how sensitive results are on assumptions of different polycrystal plasticity models specifically lower bounds and viscoplastic self consistent approaches we also investigate how recrystallization during deformation might affect the texture that develops along a streamline the effects of grain growth and nucleation produce as expected textures that are different from the deformation only case however the basic p wave structure of the predicted anisotropy is similar between models for streamlines in a slow spreading passive flow model as is commonly used for simulating flow near this type of plate boundary shear wave splitting patterns are more complex and differ somewhat more between the models in the off axis region we also compare predictions for texture development of olivine only aggregates to that of mixed composition with 70 olivine and 30 orthopyroxene although we consider only one aspect of such polyphase deformation i e plastic deformation on specified crystal slip systems our results are consistent with field observations of the orientation distributions in ophiolitic peridotites finally we determine how simplifying assumptions about the symmetry of the elastic anisotropy can bias interpretations of seismic travel time and shear wave splitting whereas a hexagonal approximation can lead to underestimates of the degree of anisotropy an orthorhombic approximation is found to closely match the results predicted for a general elastic tensor corresponding to an orientation distribution whose symmetry is as low as monoclinic or triclinic

determination of thermal conductivity for deep boreholes two methods for thermal conductivity determinations on rock cores and fragments were tested on a suite of samples from the kontinentales tiefbohrprogramm der bundesrepublik deutschland ktb superdeep drill hole in germany they were also compared with estimates of thermal conductivity using the mineral composition of the rock and physical well logs and with in situ thermal conductivity measurements laboratory methods provide reasonably precise determinations of the thermal conductivities of both solid core 5 and drill cuttings 10 at room temperature and pressure the most common methods presently used for crystalline rocks are the steady state divided bar db technique and the transient half space line source ls sample preparation and measurement times are comparable for the db and ls with sample preparation being more time consuming on average for isotropic rocks there is little to choose from between the two methods which both give reliable values of conductivity in the vertical direction the ls is easier to set up and use in field laboratory situations which renders it the preferred method for field reconnaissance the gneissic crystalline rocks penetrated by the ktb boreholes typically have anisotropy of the order of 10 20 the db provides unambiguous values of conductivity in a given direction so its use is preferable for obtaining both principal conductivities and the vertical component anisotropy can be estimated using ls measurements in many different directions but the potential for large random errors is much greater than with the more straightforward db approach for deep research wells the difficulties of extrapolating laboratory results to in situ conditions particularly temperature present additional obstacles to determining heat flow laboratory measurements of water saturated samples under in situ conditions combined with in situ measurements and judicious use of calculations based on mineralogy and well log derived physical properties can aid in the accurate characterization of thermal conductivity in deep wells the application of different methods helped to link variations of heat flow with depth in the ktb hole to the anisotropy of thermal conductivity or thermal refraction and thus allowed the calculation of background heat flux in this geologically complex area

p and s wave anisotropy and shear wave splitting at pressure and temperature in possible mantle rocks and their relation to the rock fabric the seismic properties and their directional dependence have been measured in three potentially mantle derived rocks peridotite ivrea zone italy lherzolitic xenolith massif central france serpentinite the experimental data include the measurement of elastic wave velocities and densities at confining pressures up to 600 mpa and temperatures up to 600 c 600 mpa and the determination of velocity anisotropy and shear wave splitting the petrophysical data can be related to mineral composition and to microstructural characteristics of the rocks macroscopic anisotropy of p and s wave velocities is strongly controlled in the peridodites by the olivine and in the serpentinite by the serpentine antigorite lattice preferred orientation lpo respectively shear wave splitting was found to be an important characteristic of the anisotropic rocks the study shows that for the interpretation of shear wave splitting the direction of wave propagation in relation to the lpos of the major minerals and to the symmetry of their lattice fabric is of great importance in the ivrea peridotite exhibiting rhombic symmetry there is practically no shear wave splitting to be observed for s waves propagating parallel to the olivine 100 axes and the maximum shear wave splitting is not coupled with the direction of highest p wave velocity in the transversely isotropic massif central xenolith shear waves do not split when propagating parallel to the olivine 010 maximum coinciding with the direction of the radial symmetry axis of the olivine fabric the experimental data are principally in accordance with velocity calculations based on the measured olivine lpo and the olivine single crystal stiffness coefficients implications for the interpretation of seismic data are discussed

coupled reservoir geomechanical analysis of the potential for tensile and shear failure associated with co2 injection in multilayered reservoir caprock systems coupled reservoir geomechanical simulations were conductedto study the potential for tensile and shear failure e g tensilefracturing and shear slip along pre existing fractures associated withunderground co2 injection in a multilayered geological system thisfailure analysis aimed to study factors affecting the potential forbreaching a geological co2 storage system and to study methods forestimating the maximum co2 injection pressure that could be sustainedwithout causing such a breach we pay special attention to geomechanicalstress changes resulting from upward migration of the co2 and how theinitial stress regime affects the potential for inducing failure weconclude that it is essential to have an accurate estimate of thethree dimensional in situ stress field to support the design andperformance assessment of a geological co2 injection operation moreover we also conclude that it is important to consider mechanical stresschanges that might occur outside the region of increased reservoir fluidpressure e g in the overburden rock between the co2 injectionreservoir and the ground surface

anisotropy of elastic moduli p wave velocities and thermal conductivities of asan gneiss boryeong shale and yeoncheon schist in korea abstract this paper presents the anisotropic characteristics of the elastic moduli p wave velocities and thermal conductivities of three types of anisotropic rocks i e asan gneiss boryeong shale and yeoncheon schist occurring in korea the experiments were conducted on rock samples that show clear evidence of transverse isotropy cylindrical core samples with different anisotropy angles were prepared by coring at 15 degree intervals from the transversely isotropic plane using the laboratory directional coring system established for this study elastic moduli p wave velocities and thermal conductivities were determined along the sample axis for different anisotropy angles the anisotropy ratio is defined as the ratio of the properties parallel to the transversely isotropic plane to those perpendicular to the plane and the anisotropy ratios for the thermal conductivities k 90 k 0 of asan gneiss boryeong shale and yeoncheon schist were 1 4 2 1 and 2 5 respectively the p wave velocity anisotropy ratios v p 90 v p 0 for asan gneiss boryeong shale and yeoncheon schist were 1 2 1 5 and 2 3 respectively the elastic moduli p wave velocities and thermal conductivities that were obtained were compared with theoretical predictions by mean prediction error mpe the correlations between the measured properties were evidently correlated with some minor scatter in the data the degree of anisotropy measured in this study suggests that ignoring anisotropy in rock properties may mislead to erroneous results the application of tensorial transformation evaluations revealed that the three types of rocks chosen for this study can be modeled effectively by a transversely isotropic model

possible eastward extension of chinese collision belt in south korea the imjingang belt structural petrological and geochronological data from the middle korean peninsula indicate that the qinling dabie sulu collisional belt of east central china crosses the yellow sea and extends into the imjingang belt the yeoncheon complex first identified as the western imjingang belt comprises primarily north dipping metamorphic sequences 1 the northern jingok unit consisting of barrovian type metapelites and 2 the southern samgot unit consisting of calc silicate and amphibolitic rocks south vergent structures with reverse sense shearing are dominant in the jingok unit whereas late normal sense shearing is pervasive in the samgot unit and the deformed granitoid to the south these structural patterns are interpreted to correspond to extensional deformation associated with uplift following compression in a collisional belt pressure temperature p t estimates from the amphibolites suggest a high p amphibolite facies metamorphism 8 13 kbar and 630 790 c possibly evolving from eclogite facies conditions along a clockwise p t path sm nd and rb sr geochronological data suggest that the amphibolites emplaced in late proterozoic time were metamorphosed during permian triassic time

bonded particle discrete element modeling of mechanical behavior of transversely isotropic rock abstract this paper presents bonded particle discrete element modeling with embedded smooth joints for simulating the mechanical behavior of transversely isotropic rock with systematic verifications and extensions to laboratory and upscaled problems verification was conducted against the analytical solutions in terms of anisotropic elastic and strength behavior the developed model was compared with laboratory observations of three rock types gneiss shale and schist leading to good agreements bonded particle dem modeling successfully captured the failure patterns observed in anisotropic rock in which weak planes play a significant role the model was upscaled to large scale foundation problems subjected to surface line load the study achieved reasonable agreements both for isotropic and anisotropic solutions the results demonstrate that the bonded particle dem with embedded smooth joints can model the equivalent anisotropic medium and it has potential to be applied to problems of larger engineering problems in which anisotropy is important

thermal conductivity anisotropy of metasedimentary and igneous rocks 1 thermal conductivity anisotropy was determined for three sets of metasedimentary and igneous rocks from central utah usa most conductivity measurements were made in transient mode with a half space line source instrument oriented in two orthogonal directions on a flat face cut perpendicular to bedding one orientation of the probe yields thermal conductivity parallel to bedding kpar directly the other orientation of the probe measures a product of conductivities parallel and perpendicular to bedding from which the perpendicular conductivity kperp is calculated some direct measurements of kpar and kperp were made on oriented cylindrical discs using a conventional divided bar device in steady state mode anisotropy is defined as kpar kperp precambrian argillites from big cottonwood canyon have anisotropy values from 0 8 to 2 1 with corresponding conductivity perpendicular to bedding of 2 0 to 6 2 w m 1 k 1 anisotropy values for price canyon sedimentary samples are less than 1 2 with a mean of 1 04 although thermal conductivity perpendicular to bedding for the samples varied from 1 3 to 5 0 w m 1 k 1 the granitic rocks were found to be essentially isotropic with thermal conductivity perpendicular to bedding having a range of 2 2 to 3 2 w m 1 k 1 and a mean of 2 68 w m 1 k 1 the results confirm the observation by deming 1994 that anisotropy is negligible for rocks having kperp greater than 4 0 w m 1 k 1 and generally increases for low conductivity metamorphic and clay rich rocks there is little evidence however for his suggestion that thermal conductivity anisotropy of all rocks increases systematically to about 2 5 for low thermal conductivity rocks

elastic anisotropy in marine sedimentary rocks measurements of four of the five elastic stiffnesses of marine calcareous rocks and estimates of the fifth c13 allow more detailed discussion of elastic wave propagation in these rocks than previously possible the constant c13 which is seldom measured and was not measured in the rocks of this study was derived by equating the gassmann and hashin shtrikman estimates of the bulk moduli of chalk and limestone and then solving for the single unknown c13 for chalk the measured constants in n m2 1010 are c11 1 01 c33 0 94 c44 0 18 and c66 0 21 for limestone the measured constants also in n m2 1010 are c11 2 41 c33 2 09 c44 0 47 and c66 0 60 three physically possible values of c13 were computed for chalk 0 48 0 52 and 0 63 n m2 1010 and for limestone 0 73 1 05 and 1 24n m2 1010 heretofore the only statements which could be made about c13 in these rocks are c13 0 87 1010 n m2 chalk and c13 1 94 1010 n m2 limestone the calculations require the assumption that anisotropy in these rocks is caused by mineral alignment and the simplification of monomineralogy calcite on the basis of these measurements and estimates the effect of elastic anisotropy on seismic reflection determinations of vertical compressional wave speed in calcareous rocks below the earth s surface is small 6 whereas similar determinations of vertically polarized shear wave speeds may be unreliable relationships are provided to convert seismic refraction measurements of horizontal compressional wave velocity to vertical velocity these relationships are independent of the estimated values of c13

evaluation of rock anisotropy using 3d x ray computed tomography abstract the anisotropic nature of fabric and internal structures plays a significant role in fluid flow heat transfer and geomechanical behavior in rock the existence and orientation of anisotropy in various rocks have been evaluated using laboratory experiments and image analyses to characterize anisotropic pore networks micro fractures mineralogy grain fabric and stiffness from micro to macro scales we present an assessment of anisotropy in rock by systematic and planar clustering of three dimensional x ray attenuation values and associated statistical analysis on the basis that x ray ct numbers directly represent the internal density of the mineral fabric in the rock mass variation in voxel values across the slicing plane for a given orientation enables identification of the unique orientation of anisotropy in rock the proposed concept is validated using a 3d virtual structure and is applied to four different rock types the sensitivity of anisotropic features and the image noise effect are further explored to highlight the robustness of the proposed method for evaluating the anisotropy of rock fabrics

seismic anisotropy of shales the seismic properties and preferred clay mineral orientation of a suite of shales are investigated using laboratory velocity measurements as a function of confining pressure x ray diffraction techniques and electron microprobe backscatter bse imaging the velocity measurements indicate that these shales are transversely isotropic with the main symmetry axis perpendicular to bedding anisotropy at elevated pressures caused mainly by preferred orientation of clays illite parallel to bedding ranges from 20 vp and 19 vs for a sample of new albany shale to 30 vp and 35 vs for a sample of chattanooga shale the degree of clay mineral alignment in the shales is constrained by orientation indices produced using simple x ray diffraction techniques a strong positive correlation is found between the degree of preferred orientation as expressed in the orientation indices and seismic anisotropy bse images of the shale fabrics confirm in a qualitative manner the results of the x ray study to investigate wave propagation in the shales elastic constants of each sample are calculated and used to produce phase and group wave velocity surfaces which describe variation in velocity as a function of angle to the bedding normal the calculated velocity surfaces constrained by independent velocity measurements display a lack of shear wave splitting at near normal incidence in even the most anisotropic shales for the highly anisotropic chattanooga shales group velocity surfaces differ significantly from corresponding phase velocity surfaces

thermal conductivity from core and well log data abstract the relationships between thermal conductivity and other petrophysical properties have been analysed for a borehole drilled in a tertiary flysch sequence we establish equations that permit us to predict rock thermal conductivity from logging data a regression analysis of thermal conductivity bulk density and sonic velocity yields thermal conductivity with an average accuracy of better than 0 2 w m k 1 as a second step logging data are used to compute a lithological depth profile which in turn is used to calculate a thermal conductivity profile from a comparison of the conductivity depth profile and the laboratory data it can be concluded that thermal conductivity can be computed with an accuracy of less than 0 3 w m k 1 from conventional wireline data the comparison of two different models shows that this approach can be practical even if old and incomplete logging data are used the results can be used to infer thermal conductivity for boreholes without appropriate core data that are drilled in a similar geological setting

rock structure characterization of a magnetite gneiss with foliation parallel discontinuities for footwall slope design abstract the warramboo magnetite iron ore deposit in south australia is predominantly hosted by gneiss design of the footwall slope requires an assessment of the role of foliation parallel discontinuities as planes of weakness parallel to the slope a review of published studies of joint spacing and joint persistence in gneiss shows spacing and persistence of foliation parallel discontinuities relative to non foliation parallel discontinuities varies greatly foliation parallel discontinuities form a spectrum between simply being one joint set in a blocky rock mass through to being a significant anisotropic weakness based on detailed analysis of the characteristics and frequency of foliation in drill core in the warramboo magnetite deposit it is inferred based on analysis of spacing that foliation parallel discontinuities are no more frequent or persistent than other joints therefore the rock mass is blocky rather than anisotropic and footwall slopes steeper than the foliation dip are viable

the effect of fracture density and stress state on the static and dynamic bulk moduli of westerly granite elastic properties are key parameters during the deformation of rocks they can be measured statically or dynamically but the two measurements are often different in this study the static and dynamic bulk moduli kstatic and kdynamic were measured at varying effective stress for dry and fluid saturated westerly granite with controlled fracture densities under isotropic and differential stress states isotropic fracturing of different densities was induced in samples by thermal treatment to 250 450 650 and 850 c results show that fluid saturation does not greatly affect static moduli but increases dynamic moduli under isotropic loading high fracture density and or low effective pressure results in a low kstatic kdynamic ratio for dry conditions kstatic kdynamic approaches 1 at low fracture densities when the effective pressure is high consistent with previous studies stress induced anisotropy exists under differential stress state that greatly affects kstatic compared to kdynamic as a result the kstatic kdynamic ratio is higher than that for the isotropic stress state and approaches 1 with increasing axial loading the effect of stress induced anisotropy increases with increasing fracture density a key omission in previous studies comparing static and dynamic properties is that anisotropy has not been considered the standard methods for measuring static elastic properties such as poisson s ratio young s and shear modulus involve subjecting the sample to a differential stress state that promotes anisotropy our results show that stress induced anisotropy resulting from differential stress state is a major contributor to the difference between static and dynamic elasticity and is dominant with high fracture density

estimating the transversely isotropic elastic intact rock properties for in situ stress measurement data reduction a case study of the olkiluoto mica gneiss finland abstract an anisotropy in the elastic moduli values of intact rock with a ratio of more than 1 3 1 5 has been reported to have an effect on the calculated magnitudes and orientations of the in situ principal stress components as measured by the overcoring method work related to the on going site investigation for a deep radioactive waste repository at the olkiluoto site in western finland has shown that the migmatic mica gneiss is anisotropic which could therefore affect the interpretation of overcoring stress measurement results this paper includes a summary of the theory of anisotropy concerning the intact rock moduli via the strain compliance matrix a description of the core sample testing methods and interpretation of results for the migmatic mica gneiss from two site investigation boreholes in this case study 19 specimens were tested and the results showed a modulus anisotropy of about 1 4 because such anisotropy is high enough to produce significant errors in the estimation of the in situ principal stresses it is recommended to take this into account in the interpretation of the stress measurement results both in the context of the current work in finland and in other projects where similar anisotropy is encountered

evaluation of the anisotropy and directionality of a jointed rock mass under numerical direct shear tests abstract the characteristics of the anisotropy and directionality of jointed rock masses are the key to simplifying it as a transversely anisotropic material experimental direct shear tests were performed on stratified rocks cored from granulite rocks the influence of normal stresses and joint orientations was tested and the anisotropy and directionality of the shear strength were evaluated numerical shearing tests on stratified rock models and discrete fractures network dfn models were subsequently conducted in addition the shear anisotropy and directionality in the dfn models were tested and discussed the results demonstrate that the peak shear stress was more sensitive to the inclination angles than the normal stress the stratified rocks in the experimental test showed apparent shear anisotropy and directionality the maximum value of directionality coincided with the direction of the strike of the bedding plane the more apparent the anisotropy was the higher the directionality became the failure patterns of stratified rocks exhibited more complex characteristics under higher normal stress significant variation of the shear strength distribution occurred due to the different orientations of fractures relative to the directions of the shear load the failure patterns of dfn models of varied scales differed and no apparent convergence was discovered the shear strength of the dfn model showed an apparent principal direction the numerical results presented in this paper are valuable for evaluating the prediction of the failure behaviour of rock masses and can be further applied to the study of the failure mechanism of surrounding rock in engineering

failure of transversely isotropic rock under brazilian test conditions abstract the behavior of transversely isotropic rock material was studied under brazilian test conditions for nine different rocks two sandstones one shale two slates one schist and three gneiss both the variation of the strength and the final fracture patterns induced by testing were examined as a function of the inclination angle of the weak planes the combination of the observations for both parameters illustrated clearly the complexity of the failure of such rocks which was summarized by assuming four different trends the four trends for the variation of the strength as a function of the inclination angles range from little or no variation trend 1 i e isotropic behavior for strength to a sharp decrease of the strength from very small angles onwards followed by a leveling off trend 4 trend 2 is characterized by a constant value between 0 and about 45 followed by a linear decrease while trend 3 corresponds to a decrease of the strength over the entire interval but a rather systematic decrease approximating a linear variation different variations were observed among these four trends in terms of the relative lengths of the respective fractures along the weak planes and in any other direction for the rocks investigated there is a cross over from dominant fractures in directions other than the weak planes to dominant fractures along the weak planes for the four trends there are systematic changes in the position of this cross over point i e on average at about an inclination angle of 75 for trend 1 and at about 15 for trend 4 for inclination angles larger than the cross over point the rock specimens failed primarily by splitting between both loading lines

microbes in caves agents of calcite corrosion and precipitation abstract diverse biogenic and abiogenic processes produce calcite speleothems from a biogenic perspective cave microbes mediate a wide range of destructive and constructive processes that collectively influence the growth of calcite speleothems and their internal fabrics destructive processes include substrate breakdown by dissolution boring and residue micrite production whereas constructive processes include microbe calcification trapping and binding of detrital particles to substrates and microbial induced calcite precipitation biogenesis can be established from 1 the presence of mineralized microbes 2 fabrics such as stromatolite like structures that can be attributed to microbial activity and or 3 geochemical proxies carbon and oxygen isotopes lipid biomarkers considered indicative of microbe activity such criteria have for example been used to demonstrate microbial involvement in the formation of pool fingers stalactites stalagmites cave pisoliths and moonmilk nevertheless absolute proof of microbial biogenesis in calcitic speleothems is commonly difficult because taphonomic processes and or diagenetic processes commonly mask evidence of microbial activity the assumption that calcitic speleothems are abiogenic which has been tacitly assumed in many studies is dangerous as there is clear evidence that microbes thrive in most caves and can directly and indirectly influence calcite precipitation in many different ways

dolomite formation within microbial mats in the coastal sabkha of abu dhabi united arab emirates microbial mediation is the only demonstrated mechanism to precipitate dolomite under earth surface conditions a link between microbial activity and dolomite formation in the sabkha of abu dhabi has until now not been evaluated even though this environment is cited frequently as the type analogue for many ancient evaporitic sequences such an evaluation is the purpose of this study which is based on a geochemical and petrographic investigation of three sites located on the coastal sabkha of abu dhabi along a transect from the intertidal to the supratidal zone this investigation revealed a close association between microbial mats and dolomite suggesting that microbes are involved in the mineralization process observations using scanning electron microscopy equipped with a cryotransfer system indicate that authigenic dolomite precipitates within the exopolymeric substances constituting the microbial mats in current models microbial dolomite precipitation is linked to an active microbial activity that sustains high ph and alkalinity and decreased sulphate concentrations in pore waters such models can be applied to the sabkha environment to explain dolomite formation within microbial mats present at the surface of the intertidal zone by contrast these models cannot be applied to the supratidal zone where abundant dolomite is present within buried mats that no longer show signs of intensive microbial activity as no abiotic mechanism is known to form dolomite at earth surface conditions two different hypotheses can reconcile this result in a first scenario all of the dolomite present in the supratidal zone formed in the past when the mats were active at the surface in a second scenario dolomite formation continues within the buried and inactive mats in order to explain dolomite formation in the absence of active microbial metabolisms a revised microbial model is proposed in which the mineral template properties of exopolymeric substances play a crucial role

mechanical anisotropy of columnar jointed basalts an example from the baihetan hydropower station china abstract columnar jointed basalts are characterized by a self organized joint network of discontinuities and pose a difficult challenge for geotechnical engineering design due to their inherent anisotropic nature we explore here the anisotropic characteristics of the columnar basalt formation in the chinese baihetan hydropower station including aspects of the geometrical rock structure deformation and strength anisotropy site investigations reveal that a typical cross section of the columnar basalt blocks is mainly quadrangular and pentagonal with an average edge length of 0 152 m three types of joints with different macro and micro characteristics form the columnar jointed rock mass and are identified by scanning electron microscopy in situ ultrasonic tests further confirm that the columnar basalt prisms exhibit transverse isotropy with the plane of isotropy perpendicular to the column axis as can also be observed in the field strength anisotropy is confirmed by point load and uniaxial compression tests the mechanical and anisotropic characteristics of baihetan s jointed basalt mass can be explained by its multi scale joints pattern by means of goodman s stiffness equation we find that the anisotropic coefficients obtained for its deformability and strength are similar for all testing methods employed including in situ p wave velocity point load tests and uniaxial compression tests this result confirms the strong anisotropic effect in these rock masses and facilitates an issue that must be considered when assigning input parameters for various classification and numerical analyses schemes

deposition and diagenesis of mammoth hot springs travertine yellowstone national park wyoming u s a strata forming a 113 m long core through mammoth hot springs record the holocene evolution of this travertine accumulation from deposition as part of a lacustrine to a terraced mound environment the deposit is readily divided into four intervals 113 67 m carbonate cemented volcaniclastic with intercalated layers of travertine 67 60 m moderately pure travertine with some volcaniclastics 60 50 m carbonate cemented volcaniclastic rich interval and 50 0 m essentially pure travertine lithologic composition sedimentary structures and the rare ostracode fossils indicate that the lower 67 m predominantly accumulated in a lacustrine environment whereas the upper 40 m are terraced mound deposits all of the travertine is calcite some after aragonite layers of shrubs oncoids and peloids all bacterial in origin form the dominant allochems within the travertine stable isotopic carbon and oxygen values n 128 are strongly positively correlated and decrease up core 4 and 8 respectively reflec

experimental and theoretical study of the anisotropic properties of shale abstract the effect of bedding plane orientations on shear strength and failure mechanisms of shale is investigated with an emphasis on the shear parameters of the bedding planes this study is based on direct shear tests conducted on directional shale samples obtained from formations which exhibit well developed stratification the tested cylindrical specimens were prepared by coring at 30 intervals from the direction of the bedding planes the results indicate that the anisotropy of the shear strength of shale can be readily observed due to the anisotropic effects of bedding plane orientation and normal stress the shear parameters such as strength cohesion and internal friction angle reach their maximum and the minimum values at 60 and 0 respectively where is the angle between the bedding planes and the coring orientation which is also the direction of normal stress during the laboratory tests it is demonstrated that the bedding planes are weak not only with regards to cementing strength but also with regards to friction three different shear failure modes were built up depending on the shearing angle 1 sliding failure across the bedding planes 2 sliding failure along the bedding planes and 3 sliding failure across the bedding planes combined with tensile splitting along the bedding planes an expression of the shear stress concentration factor of the direct shear model is derived to evaluate the anisotropy of shear strength

what do we really know about early diagenesis of non marine carbonates abstract non marine carbonate rocks including cave spring stream calcrete and lacustrine palustrine sediments are susceptible to early diagenetic processes these can profoundly alter the carbonate fabric and affect paleoclimatic proxies this review integrates recent insights into diagenesis of non marine carbonates and in particular the variety of early diagenetic processes and presents a conceptual framework to address them with ability to study at smaller and smaller scales down to nanometers one can now observe diagenesis taking place the moment initial precipitates have formed and continuing thereafter diagenesis may affect whole rocks but it typically starts in nano and micro environments the potential for diagenetic alteration depends on the reactivity of the initial precipitate commonly being metastable phases like vaterite ca oxalates hydrous mg carbonates and aragonite with regard to the ambient fluid furthermore organic compounds commonly play a crucial role in hosting these early transformations processes like neomorphism inversion and recrystallization cementation and replacement generally result in an overall coarsening of the fabric and homogenization of the wide range of complex primary microtextures if early diagenetic modifications are completed in a short time span compared to the annual to millennial time scale of interest then recorded paleoenvironmental signals and trends could still acceptably reflect original depositional conditions however even compact non marine carbonate deposits may behave locally and temporarily as open systems to crystal fluid exchange and overprinting of one or more geochemical proxies is not unexpected looking to the future relatively few studies have examined the behaviour of promising geochemical records such as clumped isotope thermometry and non conventional stable isotopes in well constrained diagenetic settings ongoing and future in vitro and in situ experimental approaches will help to investigate and detangle sequences of intermediate diagenetic products processes and controls and to quantify rates of early diagenesis bridging a gap between nanoscale molecular lab studies and the fossil field rock record of non marine carbonates