laser probe 40ar 39ar studies of the peace river shocked l6 chondrite abstract samples of matrix and melt glass from the shocked l6 chondrite peace river have been subjected to 40ar 39ar analysis using both stepped heating and localised outgassing by a laser probe stepped heating studies of three distinct samples of matrix gave indistinguishable and unusually well defined low temperature 40ar 39ar plateaux corresponding to an age of 450 30 ma in an attempt to investigate whether or not this plateau age is meaningful i e the time of a major collision event involving the parent body or is an artefact resulting from partial degassing during the fragmentation of the parent body which commenced the exposure of peace river to cosmic rays 40 ma ago we have used a laser probe to analyse ar from single 80 m diameter laser pits which release gas from a few micrograms of sample on this scale no areas have ages younger than the plateau age supporting the view that it is not an artefact measurements on the melt glass gave variable and meaningless ages in some cases greater than the age of the solar system due to retention of 40ar and loss of k during melting followed by rapid quenching this observation indicates the danger of attempts to date impact melt glass directly the observation that argon has been retained by the glass and lost by the matrix can be understood in terms of a range of plausible annealing histories

quantifying the effects of scale and heterogeneity on the confined strength of micro defected rocks abstract a numerical study was performed to develop a framework for estimating the confined strength of rock blocks considering scale effects and in situ heterogeneity i e intensity of structural microdefects and degree of weathering grain boundary models using the voronoi tessellation scheme within udec have been used to simulate the results of small lab and large field scale compression unconfined and triaxial and indirect tensile brazilian tests on a series of progressively larger in size and degrading in quality numerical specimens accordingly relationships that link rock block strength with its volume and in situ condition were developed for the preliminary estimation of scaled mohr coulomb and hoek brown parameters the results from the scaling analysis generally suggest that cohesion decreases with both increasing scale and degrading sample condition in a manner similar to the scale condition dependant reduction of uniaxial compression strength ucs while the friction angle shows only minor variation with no apparent trend the measured peak confined strength values were also fitted to the generalized hoek brown criterion and a new block scale geological strength index parameter is introduced named micro gsi mgsi which was also linked to the scale condition dependant reduction of ucs by using the proposed linear and non linear approaches once the ucs reduction due to scaling effects is known the confined strength of rock blocks could be then defined and can be used to carry out preliminary rock engineering calculations and to run discontinuum numerical models in which rock blocks are simulated explicitly

triaxial strength and deformability of intact and increasingly jointed granite samples abstract triaxial strength tests were performed on artificially jointed standard size granite specimens with two sub vertical and three sub horizontal 2 3 joints a fully servo controlled press was used to load the samples and attain residual strength these tests add to an existing test database for intact and artificially jointed 1 2 joints samples of the same rock the main parameters from each test were used to analyse tendencies in particular changes in elasticity and peak and residual strength in line with increased jointing peak strength and apparent young s modulus decreased from the intact to the jointed specimens reflecting a tendency analogous to that deriving from the use of classification systems to characterize rock masses mohr coulomb and hoek brown failure criteria were fit to peak and residual strength tests results in the case of the hoek brown criterion it seems that an equivalent of the geological strength index gsi which reflects structure at the specimen scale could be of use in estimating the decrease in strength of increasingly jointed samples residual strength envelopes were practically the same for the intact and jointed specimens our results for granite would suggest that the so called rock mechanics scale effect at large i e the relevant change in material properties from rock samples at lab scale to that of the rock mass including the occurrence of natural discontinuities at the engineering work scale is more due to structure number orientation spacing and features of occurring joints than to sample scale effect i e the variation in properties when testing different size from a few mm to some decimetres unjointed intact rock samples at the laboratory

paired lunar meteorites mac88104 and mac88105 a new fan of lunar petrology abstract new lunar meteorite mac88104 5 represents an exciting new opportunity to study a potentially unsampled region of the moon we have analyzed six thin sections by electron microprobe and three bulk samples by instrumental neutron activation ina in order to determine the chemical characteristics of this new lunar sample lunar meteorite macs 8104 5 is dominated by lithologies of the ferroan anorthosite fan suite and contains abundant granulitized highland clasts devitrified glass beads of impact origin and two small clasts which appear to be of basaltic origin one of these asaltic clasts clast e in mac88105 84 is probably mesostasis material whereas the second larger clast clast g may be similar to the very low ti vlt or low ti high alumina mare basalts impact melt clasts mac88105 69 and 72 have major and trace element compositions similar to the bulk meteorite there is little evidence of any lkfm low k fra mauro or low k kreep contribution to this meteorite as mac88104 5 and other brecciated lunar meteorites are fe rich and poor in the incompatible elements relative to apollo 16 regolith and feldspathic breccias while the exact site of origin for the lunar meteorites cannot be pinpointed it is evident that they were derived from a relatively kreep free ferroan anorthosite terrain

geochemistry and petrography of the macalpine hills lunar meteorites abstract macalpine hills 88104 and 88105 are anorthositic lunar meteorites recovered from the same area in antarctica which are demonstrated to be paired samples of the same fall petrographic studies of matrix and clasts show that mac88104 5 is a polymict breccia dominated by impact melt clasts it contains a small amount of highland impact glass and very few regolith glass spherules it is better classified as a fragmental breccia than a regolith breccia the bulk composition is ferroan mg 63 and highly aluminous al 2 o 3 28 ree and other incompatible element concentrations are very low compositions of anorthositic granulitic and impact melt breccia clasts are very similar to but distinct from matrix composition mac88104 5 is very similar in composition to the other anorthositic lunar meteorites but each of the meteorites is distinct the anorthositic lunar meteorites especially mac88104 5 and y82192 3 86032 are very similar to north ray crater feldspathic fragmental breccias in compositon and petrography these fragmental lunar meteorites may have been ancient deeply buried breccias from the megaregolith comparisons of chemical petrographic features and exposure histories suggest that the twelve lunar meteorites were derived from two to nine but probably four to seven impacts onto the lunar surface discrepancies between the proportions of lunar meteorites and results of apollo missions may be due to unrepresentative sampling lunar meteorites provide valuable new information on the nature of the lunar crust

mineralogy and geochemistry of lunar meteorite queen alexandra range 93069 queen alexandra range que 93069 is a glass rich regolith breccia derived from the lunar highlands the high abundance of glassy fragments the presence of agglutinates the small size of all mineral and glass fragments the presence of mostly melt rocks and the low abundance of pristine lunar crustal rocks all indicate that que 93069 is derived from a mature regolith this conclusion is also supported by its high siderophile element content the most common mafic mineral is pyroxene with compositions that indicate derivation from ferroan ant suite rocks rare gabbro differentiation products may be indicated by the presence of silica fayalitic olivine and one pyroxferroite grain lithic fragments are mostly meta melt rocks of ant composition the glass compositions are dominated by troctolitic anorthosite compositions followed by gabbroic anorthosite and noritic anorthosite most glasses are ol normative in composition some rare basic glasses of noritic composition were observed glass fragments and matrix glasses are alkali poor except for some rare alkali rich shards the bulk chemical composition of que 93069 as well as the rare earth element ree abundance pattern is very similar to that of other highlands meteorites such as mac 88105 and y 86032 and to average lunar highlands crust one small porous clast was found to be very rich in volatile elements as well as in most lithophile and siderophile elements as this sample also contains abundant sulfides the enrichments could be related to element mobilization and redistribution by volatile sulfur species

geochemistry and 40ar 39ar geochronology of impact melt clasts in feldspathic lunar meteorites implications for lunar bombardment history we studied 42 impact melt clasts from lunar feldspathic regolith breccias macalpine hills mac 88105 queen alexandra range que 93069 dar al gani dag 262 and dag 400 for texture chemical composition and or chronology although the textures are similar to the impactmelt clasts identified in mafic apollo and luna samples the meteorite clasts are chemically distinct from them having lower fe ti k and p thus representing previously unsampled impacts the 40ar 39ar ages on 31 of the impact melts the first ages on impact melt samples from outside the region of the apollo and luna sampling sites range from 4 to 2 5 ga we interpret these samples to have been created in at least six and possibly nine or more different impact events one inferred impact event may be consistent with the apollo impact melt rock age cluster at 3 9 ga but the meteorite impact melt clasts with this age are different in chemistry from the apollo samples suggesting that the mechanism responsible for the 3 9 ga peak in lunar impact melt clast ages is a lunar wide phenomenon no meteorite impact melts have ages more than 1 older than 4 0 ga this observation is consistent with but does not require a lunar cataclysm

challenges in the characterisation of intact rock bridges in rock slopes abstract intact rock bridges have been recognised as of critical importance in the stability of rock slopes but still remain a poorly understood and challenging engineering problem both in respect to their measurement and their incorporation into design analyses the objective of this paper is not to provide conclusive answers as to the definition and measurement of rock bridges and the manner that they can be accounted for in rock slope stability analysis rather we highlight important and as yet unanswered questions to allow review of fundamental rock bridge concepts and then proceed to provide new insight into how rock bridges may be incorporated into slope stability analysis early definitions of what constitute a rock bridge are somewhat limited and the authors suggest that they could be improved by including important constraints such as block forming potential and block kinematics in this context this paper introduces an improved terminology rbij commonly used by the discrete fracture network dfn community to define rock bridge intensity relative to the sampling region in rock engineering the measurement of rock bridges is exacerbated by the fact that rock bridges are not visible unless the rock mass is exposed by human activities or by natural events such as rockfalls this constitutes a major problem for engineering design scenarios since it would not be possible to validate any assumption made with respect to extent of rock bridges without performing some form of field testing or back analysis the results of a of the finite discrete numerical analysis are presented to support our conclusions with respect to the limitations current methods used to characterise rock bridge strength the role of scale effects block theory kinematics and what we term negative rock bridges in stability analysis is discussed

the influence of structure on the behaviour of london clay an intensive investigation is described into the london clay units from heathrow terminal 5 intrinsic properties and composition were established and relating the behaviour of intact and reconsti

applicability of the seismic response analysis using multiple yield model for discontinuous rock abstract the stability deformation behavior permeability and other properties of discontinuous rocks are greatly influenced by the geometrical distribution of discontinuities in rock mass and extremely important infrastructures such as nuclear power plants large scale underground excavations long span bridges etc built on or in discontinuous rock mass are also influenced by these same effects however a seismic analytical method such as for earthquake response to correctly evaluate discontinuous conditions of rock mass has not been developed this paper describes a new seismic response analytical method using the multiple yield model as a kind of fem the applicability of this method was verified by making comparisons between the seismographic records obtained with several underground deaths at the 2005 offshore miyagi prefecture earthquake m w 7 2 and the 2011 offshore the pacific coast of tohoku earthquake m w 9 0 both of which seismic motions were obtained at the same large and very important nuclear power plant and the results of the response analyses using the seismic motions recorded at the deepest earth level of seismographs the geological condition of the foundation ground is one of strongly folded hard sedimentary rocks from this study we have confirmed that the multiple yield model is an effective method for seismic response analysis

incorporating scale effect into a failure criterion for predicting stress induced overbreak around excavations abstract the evaluation of the depth of brittle failure around excavations is of major importance in order to optimize the design of underground excavations and ensure the safety of workers and equipment the current proposed approaches to evaluate it are related to a single scale of study intact rock or rock mass scale therefore they are scale dependent and cannot be applied for all excavation diameter in this paper a generalized failure criterion including the scale effect for predicting stress induced overbreak around excavations is developed this failure criterion is based on the damage initiation relation 1 a 3 b c the scale effect is included into it through a relation proposed to evaluate the b parameter and depending on the scale of study the fit parameters of the relation proposed have been defined considering a database at both rock mass and intact rock scales arising from a literature review for intact rock scale the b parameter is defined as a function of the diameter of the excavation expressed following a potential form for rock mass scale the b parameter is defined equal to 0 35 regardless the diameter of the excavation based on the proposed b parameter relation the depth and extension of the brittle failure around excavations can be evaluated for any scale of study

practical determination of mechanical design parameters of intact rock considering scale effect as a rule the change in mechanical properties of rock by specimen size is regarded as scale effect a rock mass basically consists of two components intact rock and discontinuities each of which has different scale effects in order to numerically analyze the behavior of discontinuous rock masses sufficient mechanical properties must be determined not only for discontinuities but also for intact rock taking into consideration the different scale effects this paper reviews the scale effect on strength and deformation characteristics of intact rock and also discusses the possibility of using standard specimens to estimate strength and deformation characteristics of actual scale rock finally we propose an adequate method for the practical determination of mechanical design parameters based on the above discussions

geological applicability of critical wedge thrust belt models critical wedge models for foreland thrust belts although popular paradigms for thrust mechanics also predict definite progressive changes within the orogenic belt the most important constraint on critical wedge models is the need for deformation of the interior of the wedge when new sheets are accreted to its front well dated foreland thrust belts have sequential formation of new thrust sheets in the front of the belt thus they also require continued superimposed deformation within the wedge geologic mapping and fabric studies provide evidence of only minor later intra wedge shortening severely reducing the acceptability of an accreting critically tapered wedge model to apply critically tapered wedge models to foreland fold and thrust belts one must relax requirements for constant wedge strengths and basal sliding laws the wedge will need to strengthen after initial thrust emplacement and the fault zones will probably need to progressively weaken it is most likely that critical wedge models which apply well to accretionary wedges do not apply in simple ways to foreland fold and thrust belts

geochemical comparison of impact glasses from lunar meteorites alha81005 and mac88105 and apollo 16 regolith 64001 abstract most glasses that occur in lunar highland regolith are quenched droplets of impact melt the chemical compositions of these glasses are equivalent in the absence of volatile losses to the original target materials the compositional range of impact glasses in a regolith reflects the chemical diversity that existed throughout the region up to the time of system closure e g breccia formation since these glasses are a product of widespread and random sampling both in terms of space and time they can be used for geochemical exploration of the moon the major element compositions of impact glasses occurring in three samples of lunar feldspathic regolith alha81005 mac88105 apollo 16 64001 have been determined by electron microprobe the glass populations among these three unrelated samples are compositionally distinct while most of the impact glasses within each of these three samples are compositionally similar to the regolith in which they are found up to 40 of the impact glasses are different some of the compositionally exotic glasses were ballistically transported from other areas of the moon and thereby provide information about the compositional range of regoliths that exist elsewhere since the geological setting of the apollo 16 region is well known compared to the source areas of the lunar meteorites the apollo 16 glasses provide a ground truth for interpretations the thirty four impact glasses in meteorite alha81005 overlap the compositional range of feldspathic regoliths represented by all of the lunar highland meteorites i e y86031 y82192 y791197 mac88105 alha81005 and are compositionally distinct from highland regoliths sampled by apollo 14 apollo 16 apollo 17 and luna 20 a small proportion of alha81005 glasses contain a mare component no kreep glasses were observed due to their scarcity only ten impact glasses in lunar meteorite mac88105 were analyzed the spherules occur in two broadly defined compositional groups one group of glasses is similar to the bulk composition of mac88105 whereas the other group is more mafic all of these glasses are distinct from highland regoliths sampled by apollo 14 apollo 16 and apollo 17 and luna 20 a low ti mare glass was also analyzed in mac88105 no kreep glasses were observed the two hundred and fifty three aluminous impact glasses analyzed in apollo 16 regolith 64001 display a prominent grouping of compositions equivalent to the local regolith in addition about 10 of the glasses in 64001 are distinct from the local regolith and chemically resemble the lunar highland meteorites alha81005 mac88105 these glasses may record the chemical composition of an ancient regolith that occurred in the apollo 16 region prior to the arrival of kreep and mare components twentythree percent of the glasses in 64001 have high ti mare affinities these mare glasses are clearly exotic to the apollo 16 site and have been transported from distances of at least 300 km

compositional variation in apollo 16 impact melt breccias and inferences for the geology and bombardment history of the central highlands of the moon abstract high precision data for the concentrations of a number of lithophile and siderophile elements were obtained on multiple subsamples from 109 impact melt rocks and breccias mostly crystalline from the apollo 16 site compositions of nearly all apollo 16 melt rocks fall on one of two trends of increasing sm concentration with increasing sc concentration the eastern trend lower sm sc mg fe and sm yb ratios consists of compositional groups 3 and 4 of previous classification schemes these melt rocks are feldspathic poor in incompatible and siderophile elements and appear to have provenance in the descartes formation to the east of the site the western trend higher sm sc mg fe and sm yb ratios consists of compositional groups 1 and 2 these relatively mafic kreep bearing breccias are a major component 35 of the cayley plains west of the site and are unusual compared to otherwise similar melt breccias from other sites in having high concentrations of fe ni metal 1 2 the metal is the carrier of the low ir au 0 3 chondritic siderophile element signature that is characteristic of the apollo 16 site four compositionally distinct groups 1m 1f 2db and 2nr of western trend melt breccias occur that are each represented by at least six samples compositional group 1 of previous classification schemes the poikilitic or lkfm melt breccias can be subdivided into two groups group 1m represented by six samples including 60315 is characterized by lower al2o3 concentrations higher mgo and alkali concentrations and higher mg fe and cr sc ratios than group 1f represented by fifteen samples including 65015 group 1m also has siderophile element concentrations averaging about twice those of group 1f and ir au and ir ni ratios that are even lower than those of other western trend melt rocks ir au 0 24 0 03 ci normalized at the mafic extreme of group 2 vha melt breccias the melt lithology occurring as clasts in feldspathic fragmental breccias from north ray crater group 2nr is compositionally distinct from the melt lithology of dimict breccias from the cayley plains group 2db in having higher concentrations of sc cr and heavy rare earth elements and lower concentrations of siderophile elements the distinct siderophile element signature high absolute abundances low ir au ratio suggest that the four groups of mafic melt breccia are all somehow related ratios of some lithophile elements also suggest that they are more closely related to each other than they are to melt breccias from other apollo sites however none of the breccia compositions can be related to any of the others by any simple process of igneous fractionation or mixing involving common lunar materials thus the origin of the four groups of mafic melt breccia is enigmatic if they were produced in only one or two impacts then a mechanism exists for generating regimes of impact melt breccia in a single impact that are substantially different from each other in composition for various reasons including the problem of delivering large volumes of four different types of melt to the apollo 16 site it is unlikely that any of these breccias were produced in basin forming impacts if they were produced in as many as four crater forming impacts then the unusual siderophile element signature is difficult to explain possible explanations are 1 1 the four groups of melt breccia all contain metal from a single earlier impact 2 2 they were each formed by related metal rich meteoroids or 3 3 some common postimpact process has resulted in metal of similar composition in each of four melt pools within a compositional group most intrasample and intersample variation in lithophile element concentrations is caused by differences among samples in the proportion of a component of normative anorthosite or noritic anorthosite in most cases this compositional variation probably reflects variation in clast abundance for group 2db and probably 2nr differences in abundance of a component of ferroan anorthosite estimated al2o3 32 accounts for the compositional variation for groups 1m and 1f the anorthositic component is more mafic estimated al2o3 26 some group 2 samples may be related by a troctolitic component of varying abundance

very low strengths of interplanetary meteoroids and small asteroids we have assembled data on thirteen cases of meteorite falls with accurate tracking data on atmospheric passage in all cases we estimate the bulk strength of the object corresponding to its earliest observed or inferred fragmentation in the high atmosphere and can compare these values with measured strengths of meteorites in the taxonomic class for that fall in all thirteen cases the strength corresponding to earliest observed or inferred fragmentation is much less than the compressive or tensile strength reported for that class of stony meteorites we find a more random relation between bulk sample strength and sample mass than is suggested by a commonly used empirical power law we estimate bulk strengths on entry being characteristically of the order of 10 1 to 10 2 times the tensile strengths of recovered samples

the great lunar hot spot and the composition and origin of the apollo mafic lkfm impact melt breccias thorium rich mafic impact melt breccias from the apollo 14 17 missions that is those breccias identified with the composition known as lkfm are regarded largely as products of basin forming impacts that penetrated the feldspathic crust and sampled underlying mafic material and magma ocean residuum carrying the compositional signature of kreep potassium rare earth elements phosphorous despite considerable compositional variation among such breccias compositions of all of them correspond to mixtures of only four components 1 a norite with composition generally similar to that of apollo 15 basalt mean abundance 58 range 30 95 2 fo 90 dunite mean 13 range 1 27 3 feldspathic upper crust mean 29 range 4 50 and feni metal 0 1 1 7 petrographic evidence has shown that much of the feldspathic component but none of the kreep component is clastic this observation and the high proportion of kreep norite component in the breccias suggest that the melt zone of the impact or impacts forming the breccias contained little feldspathic material but consisted predominantly of material with the average composition of kreep norite the dunite component probably derives ultimately from the upper mantle these conclusions support the hypothesis that the breccias were not formed in typical feldspathic crust but instead by one or more impacts into what is designated here the great lunar hot spot that is the anomalous th rich terrane in the imbrium procellarum area identified by the apollo and lunar prospector gamma ray spectrometers the lkfm composition is a special product of the great lunar hot spot and is not the average composition of the lower crust in typical feldspathic highlands similarly mg suite and alkali suite plutonic rocks of the apollo collection are likely all differentiation products of the hot spot not of plutons that might occur in typical feldspathic crust

application of synthetic rock mass modeling to veined core size samples abstract rock masses of the primary copper ore at the el teniente mine fail mainly through the infill of preexisting veins during the caving processes especially through those composed of less than 35 hard minerals quartz and pyrite in this study the synthetic rock mass srm approach is used to reproduce the results of ten uniaxial compression tests on veined core size samples of el teniente mafic complex cmet lithology from el teniente mine codelco chile at the scale of the tested samples it is observed that veins composed mostly of quartz dominate the failure process the developed methodology considers generating a deterministic discrete fracture network dfn based on the veins mapped at the surface of each core sample then the micro parameters of the bonded particle model bpm are calibrated to represent the macro parameters of the average block of intact rock within all samples next the micro parameters of the smooth joint contact model sjcm which represent the mechanical properties of veins are calibrated to reproduce the stress strain curves and the failure modes of the veined core size samples measured during the laboratory tests results show that the srm approach is able to reproduce the behavior of the veined rock samples under uniaxial loading conditions the strength and stiffness of veins as well as the vein network have an important impact on the deformability and global strength of the synthetic samples contrary to what was observed in the laboratory tests synthetic samples failed mainly through weak veins this result is expected in the modeling given that anhydrite veins are considered weaker than quartz veins further research is required to completely understand the impact of veins on the behavior of rock masses

transversely isotropic creep behavior of phyllite and its influence on the long term safety of the secondary lining of tunnels abstract phyllite which is a low grade metamorphic rock with well developed foliations is encountered frequently during the construction of tunnels in western china first uniaxial compressive creep tests were performed to study the time dependent behavior of phyllite specimens from zhegu mountain tunnel then a numerical approach was put forward based on the particle discrete element method to describe the typical creep behavior of phyllite including its decay steady accelerated creep stages and its transverse isotropy finally the numerical model was adopted to investigate the failure process of secondary tunnel lining in the phyllite stratum the following results were obtained ai et al 2014 1 the creep behavior of phyllite was affected significantly by the weak plane loading angles and water content its creep strength decreased as the water content increased and the maximum and minimum values occurred at 90 and 30 respectively carrillo et al 2016 2 the fractal dimension of fracture surface for 0 was the smallest due to the shear and tensile failure along foliations for each angle fractal dimension increased with the increase of water content chen et al 2018 3 micro cracks were initiated at the initial loading stage and propagated during the entire loading process at 0 while they appeared at a higher stress level after specimens had accumulated sufficient energy at 30 or 90 chen et al 2019 4 the evolution of micro cracks was affected jointly by the inclination angle of foliations and the geo stress field and the cluster of cracks shows evidently asymmetric features the results revealed the transversely isotropic creep behavior of phyllite and proposed a method which can aid more accurate predictions for design and construction with respect to geotechnical engineering structures related to layered rock mass

nail penetration test for determining the uniaxial compressive strength of rock abstract we offer a new and practical index test method the nail penetration test npt to estimate the ucs of intact rocks to be used as alternative to the point load test plt or schmidt rebound hammer test srh the major tools used in the investigation include a gasnailer with 130 j power and its nails ranging from 25 to 60 mm in length the study material covers 65 rock blocks of gypsum tuff ignimbrite andesite sandstone limestone and marble for the npt five nail shots were performed on each block sample and the average value was obtained two to three uniaxial compression tests were carried out on each specimen ten impacts were applied on rock blocks by using both the l and n types of srh regarding the plt either 10 axial or 10 block tests was applied on each rock type the average nail penetration depths were correlated with the ucs is 50 and rebound number for both types of the srh also the measured ucs values were compared with those obtained from the empirical relationships using the data from the npt plt and srh it was found that the npt provides better estimates for ucs than the plt or srh particularly applicable to weak to very weak rocks the npt is capable of indirectly estimating the ucs of intact rocks up to 100 mpa the test is proposed for use in mainly in situ applications