continuum discontinuum analysis of failure mechanisms around unsupported circular excavations in anisotropic clay shales abstract the stability of circular excavations in clay shales is a key issue in the drilling and tunnelling industries as well as in the field of deep geological waste storage a large body of experimental evidence indicates that the damaged zone around these cavities is influenced by strong mechanical anisotropy induced by the layered material structure the vast majority of numerical models adopted to date to analyse the stability of openings in layered rocks have been based on continuum mechanics principles using classic shear failure theory for elasto plastic materials however a number of experimental observations demonstrate that clay shales may fail in a brittle manner under low confinement conditions such as those characterizing the near field of the excavation therefore an alternative numerical approach based on non linear fracture mechanics principles and the discrete element method is adopted to gain new insight into the failure process of this class of geomaterials in order to account for the influence of clay shale microstructure on its mechanical behaviour a newly developed approach to capture the anisotropy of strength is proposed with this numerical approach the cohesive strength parameters of the fracture model are assumed to be a function of the relative orientation between the element bonds and the layering orientation the effectiveness of the numerical technique is quantitatively demonstrated by simulating standard rock mechanics tests on an indurated claystone namely opalinus clay emergent strength and deformation properties together with the simulated fracture mechanisms are shown to be in good agreement with experimental observations the modelling technique is then applied to the simulation of the excavation damaged zone edz around a circular tunnel in horizontally bedded opalinus clay the simulated fracturing process is mainly discussed in the context of the damage mechanisms observed at the mont terri url furthermore the influence of in situ stress on resulting edz geometry is analysed together with possible implications for ground support and tunnel constructability modelling results highlight the importance of shear strength mobilization along bedding planes in controlling the edz formation process in particular slippage of bedding planes is shown to cause rock mass deconfinement which in turn promotes brittle failure processes in the form of spalling the numerical technique is currently limited to two dimensional analyses without any thermo hydro mechanical coupling

archaeomagnetism of burnt cherts and hearths from middle palaeolithic amud cave israel tools for reconstructing site formation processes and occupation history abstract apart from magnetostratigraphy archaeomagnetism is rarely used in middle and late pleistocene sites here we present detailed palaeomagnetic analyses of cemented hearths and burnt chert items from amud cave israel 68 55 ka two types of materials common in levantine middle palaeolithic cave sites both materials are shown to be recorders of the geomagnetic field and were used to reconstruct either the ancient field direction for cemented hearths or intensity palaeointensity for chert at the time of the last burning or shortly after we test the utility of palaeomagnetic data to further our understanding of temporal aspects of occupations in the cave by comparing the dispersion of the palaeomagnetic data to the known characteristics of geomagnetic secular variation in the holocene we show that divergent palaeointensities can help identify diachronic burning events suggesting different activity patterns in two areas of the cave additionally we used palaeomagnetic directional vectors to distinguish between a well preserved hearth and one that had been mixed prior to cementation using rock magnetic investigations we demonstrate that magnetic methods can be used as a relatively fast and inexpensive method to identify burning of cherts in antiquity above 500 c the palaeomagnetic results are in agreement with results of previous studies at amud cave obtained by other independent methods this study shows that palaeomagnetic methods can serve as a powerful tool in the study of palaeolithic sites

ash deposits in hayonim and kebara caves israel macroscopic microscopic and mineralogical observations and their archaeological implications abstract a study of the hearths and ash layers preserved in hayonim and kebara caves israel showed that they are composed of one or several different minerals these include the polymorph of caco3 calcite a variety of phosphate minerals and a suite of siliceous minerals the major component of the latter are siliceous aggregates that are present in wood detailed studies of the mineral associations in these fossil ash layers as well as in fresh wood ash using optical and scanning electron microscopy in the back scattered electron mode together with elemental analyses showed that ash in these caves undergoes a series of diagenetic changes the best preserved ash layers resemble fresh ash and are composed mainly of calcite with minor amounts of siliceous minerals the calcite reacts with phosphate rich solutions to form carbonated apatite and with time the latter dissolves and a variety of other phosphate containing minerals form with each diagenetic change some of the more soluble minerals are lost and ultimately only the ash derived siliceous minerals remain in both caves there are local accumulations of such siliceous minerals that are metres thick in fact ash derived minerals in general are major components of the sediments in both kebara and hayonim caves their diagenesis involves a hugh reduction in volume which in turn may have important effects on the geological structures and stratigraphy of the sediments the changing mineralogy of the sediments due to diagenesis complicates the use of present day estimates of radiation content of the sediments for correcting age estimates by thermoluminescence and electron spin resonance finally the presence of the relatively stable ash derived siliceous minerals in a sedimentary layer in other caves could be a useful means of identifying the presence of ash in other archaeological sites where macroscopic hearth features are absent

geological and hydraulic characterisation of the excavation disturbed zone in the opalinus clay of the mont terri rock laboratory abstract the fracture network in the excavation disturbed zone edz of an argillaceous formation the opalinus clay in the mont terri rock laboratory in northwest switzerland is characterised using structural and hydrogeological techniques sampling of unloading fractures is done by analysing resin injected overcores taken from the edz resulting in a structural data set of fracture orientations frequencies and extent of the edz these parameters are derived in tunnel sections which were excavated by blasting pneumatic hammering and road header techniques pneumatic and hydrogeological tests are subsequently carried out to derive hydraulic parameters such as permeability and transmissivity distributions of the fracture network synthesis of the structural and hydrogeological data led to a conceptual model of the edz in the mont terri rock laboratory which is defined by a 2 m plastically deformed zone around the tunnel this plastic zone is further divided into an inner 1 m zone consisting of an air filled fracture network and an outer zone with mostly saturated and isolated fractures transmissivities in the inner zone are orders of magnitude higher than those of the undisturbed opalinus clay finally a methodology is proposed for the structural and hydrogeological characterisation of the edz this methodology is not site specific and is thus applicable at any argillaceous underground facility

different mechanisms of magnetisation recorded in experimental fires archaeomagnetic implications abstract we present here the archaeomagnetic and rock magnetic results obtained from the experimental recreation of prehistoric fires on a clayish soil substratum by using a system of thermocouples that allows the control of temperatures and heat penetration with depth the magneto mineralogical transformations as well as the ability to acquire magnetic remanences are studied a detailed set of rock magnetic analyses carried out both on surface and depth with a millimetre scale resolution shows the creation of post burn magnetite over the entire surface of the hearth thus promoting a distinguishable magnetic enhancement on the basis of a detailed control of temperatures interesting differences between areas centre vs periphery were observed and two different mechanisms of magnetisation have been recorded the central area which exceeded 600 c acquired a thermal remanent magnetisation trm and the periphery which was heated up to 300 c recorded a thermo chemical tcrm remanent magnetisation the most noticeable mineralogical changes are focused to the first centimetre of the central area where single domain magnetite has been created the implications of these results for archaeomagnetic and palaeointensity studies as well as their utility for the detection of fire in archaeological sites are discussed

isotopic and rock magnetic expression of environmental change at the pleistocene holocene transition in the central great plains abstract in a region too dry for the effective use of the traditional palynological approach loess deposits of the central great plains offer a source of proxy information for the reconstruction of past climates the brady soil a ubiquitous feature developed within the uppermost late pleistocene peoria loess recorded the character of vegetation change associated with climate shifts during the pleistocene holocene transition stable carbon isotope ratio analysis and two room temperature magnetic parameters were used to examine the nature of the change during this period 13 c values derived from soil organic matter indicate that in the late pleistocene minor populations of drought tolerant c4 plants were interspersed among the dominant cool season grasses c3 in the west while c3 grasses were accompanied by trees in the east by the early holocene c4 grasses were the dominant vegetation in the west and contributed substantially to the 13 c signal in the east magnitude of the 13 c shift suggests an increase in july mean daily temperature of 8 10 c according to existing models magnetic susceptibility and frequency dependence signal the cessation of loess deposition and development of the brady soil and indicate a spatial pattern in the intensity of weathering across the region

estimating the approximate firing temperature of burnt archaeological sediments through an unmixing algorithm applied to hysteresis data abstract estimating the temperature to which burnt archaeological sediments and soils have been exposed in antiquity is of interest as it may well elucidate the interpretation of specific features certain semi industrial activities such as metal working or the production of pottery are often associated with the controlled use of intense high temperature processes 500 c exposure to such high temperatures will inevitably lead to the thermal alteration of commonly found iron minerals within the soil magnetic measurements made on a series of soil samples subjected to controlled laboratory heating confirms both the sensitivity of iron minerals to thermal alteration and also suggests a correlation between the maximum exposure temperature and the hysteresis properties from this data a method for estimating the maximum exposure temperature of burnt archaeological samples recovered from similar soil types is proposed based on the application of a linear unmixing model this model compares hysteresis data from the archaeological samples to an end member data set created from the laboratory heated soil the maximum exposure temperature for the archaeological samples is estimated from the relative proportion of known temperature end members present within the final model describing the experimental hysteresis data the validity of the model is demonstrated through application to samples recovered from a series of actualistic fire experiments and a range of burnt archaeological features recovered during excavation of a multi period site at yarnton near the city of oxford uk a further application of the method to determine the fidelity of samples collected for archaeomagnetic dating is presented from the excavation of a large hearth type features at whitby north yorkshire uk

rock magnetic analyses as a tool to investigate archaeological fired sediments a case study of mirador cave sierra de atapuerca spain summary here we report a detailed mineral magnetic study of neolithic burnt levels in the mirador cave sierra de atapuerca burgos spain to reconstruct the burning history and to investigate their suitability for archaeomagnetic purposes as a consequence of the ancient burning a characteristic facies sequence was developed along the holocene stratigraphy from top to bottom it includes i 2 10 cm ash layers ii 2 cm underlying rubefied layers and iii clay mainly unburnt and of variable thickness in some cases a thermally altered facies 2 6 cm with a heterogeneous texture was identified facies tf usually between rubefactions and the unburnt levels 126 oriented samples from 4 units mir12 15 18 and 21 and a 2 m section all comprised between units mir21 6380 40 14c bp and mir9 5090 40 14c bp were analysed with rock magnetic methods in addition bulk sediment from each facies that comprise the neolithic sequence was investigated measurements included stepwise alternating field and thermal demagnetization of natural remanent magnetization nrm viscosity experiments determination of the anisotropy of the magnetic susceptibility ams the susceptibility frequency dependence at room temperature and determination of the temperature dependence of the susceptibility additional experiments consisted in the determination of the behaviour of anhysteretic and isothermal irm remanences magnetic hysteresis loops first order reversal curve diagrams and thermal demagnetization of three axial irm it appeared that the facies all show a fairly similar magnetic mineralogy and grain size dominated by low titanium magnetite that is often partially maghaemitized main differences constitute the amount of superparamagnetic particles that is higher in unburnt strata concurring with a less well defined nrm behaviour the magnetic mineral concentration is notably higher in ashes this homogeneity strongly suggests that similar sources and burial conditions prevailed during neolithic times agreeing with archaeological observations and favoured by rapid burial conditions very limited alterations have been deduced ams data revealed the absence of fluid flow in the ash lenses sampled demagnetization revealed a stable single nrm component in ashes a single or two component nrm in rubefactions and less stable multicomponent behaviour in clays in ashes magnetic minerals are likely secondary in origin formed by low temperature oxidization soon after burning although this thermochemical nature of the nrm invalidates the use of these sediments for palaeointensity studies archaeomagnetic directional data can be successfully obtained because the burning and oxidation are closely confined in time

in situ monitoring of tunnel deformation evolutions from auxiliary tunnel in deep mine abstract deformation caused by excavation is of great effects on tunnel stability and tunnel support design monitoring using instruments that are installed in place within the examined tunnel cannot record a large amount of surrounding rock deformation that usually takes place ahead and close to the tunnel face for this important reason the overall deformation process was observed using instruments installed prior to excavation from auxiliary tunnel in a 900 m deep coal mine tunnel two monitoring methods i e multipoint extensometers and wave velocity tomography were used at two monitoring sections with different rock lithology the results showed that a large amount of deformation at both monitoring sections had already been occurred when the excavation face passed the monitoring sections at a very small distance the size of the plastic zone at monitoring section 1 is identified as 1 8 m 0 36 d d denotes the diameter of the examined tunnel and the velocities within this zone decreased from 4 5 km s to 2 km s the primary deformation was generated in a distance from 0 8 d ahead the excavation face to 2 3 d behind the excavation face the induced deformation was also observed after the primary deformation period and some additional deformation was still occurred in the plastic zone although the size of plastic zone remains constant the displacements and p wave velocities at the two monitoring sections showed little differences

magnetic prospection on prehistoric sites in western canada prehistoric sites in western canada present unusual conditions for magnetic prospection archaeological features are few and difficult to discern using standard prospection procedures however by addressing specific types of features particularly fire hearths and fired rock and pottery useful information about the cultural content of an archaeological site can be obtained to secure comparative data a number of replicative studies were conducted with specific reference to determining a typical anomaly produced by the features a small fire pit was kindled several times and repeatedly monitored with surveys using a single proton magnetometer fired rock received similar treatment an in situ collection of local aboriginal pottery was also assayed the experimental results indicated that fired rock will produce a detectable magnetic field after one firing but a hearth must be rekindled at least three times to produce a significant anomaly pottery fragments also generate a small magnetic field which r

contributions of wood ash magnetism to archaeomagnetic properties of fire pits and hearths magnetic studies were conducted on a variety of plant ash and ash material from fire pits to investigate the possible contribution of ash to the magnetic signature of hearths the measurements included magnetic susceptibility remanence acquisition to saturation sirm alternating field demagnetization of sirm and remanent coercivity brc we conclude from these studies that wood ash produces fine grained magnetic iron oxides these oxides are probably magnetic that is concentrated enough to add to the magnetic signature of hearths and fire pits at one site ellicottville new york the ash layer exhibits a magnetic susceptibility that is 22 times greater than a control soil sample from the site we attribute this large enhancement to repeated burns at the site which continued to add ferromagnetic material to the fire pit the source of the magnetic material is probably phytoferritin from plants the variation in the intensity of magnetic anomalies over ancient hearths and fire pits may in part be caused by the magnetic contribution from ash

are burnt sediments reliable recorders of geomagnetic field strength abstract this study tests if burnt soils and sediments can provide reliable records of geomagnetic field strength at the time of burning by carrying out an experiment to reproduce the prehistoric use of fire on a clayish soil substratum rock magnetic experiments showed that in the upper 0 1 cm of the central part of the burnt surface remanence is a thermoremanent magnetization carried by single domain magnetite and that samples are thermally stable fourteen specimens from that area were subjected to paleointensity experiments with the coe method 1967 an intensity of 42 9 5 7 t was estimated below 440 c whereas at higher temperatures magneto mineralogical alterations were observed corresponding successful microwave intensity determinations from two specimens gave a mean value of 47 6 t both results are in reasonable agreement with the expected field value of 45 2 t burnt soils of archeological fires thus have the potential to record accurately the paleofield strength and may be useful targets for archeointensity investigations coincident results obtained from two different paleointensity determination methods support this conclusion

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

predictions and observations of convergence in shallow tunnels case histories in greece abstract convergence of shallow tunnels 30 120 m overburden thickness constructed in greece in different types of rock masses has been assessed as a function of the geological strength index gsi classification predictions of maximum vertical and horizontal convergence during or shortly after tunnel excavation were made using finite element modeling fem and the characteristic line theory and were found to be in good agreement with geodetic observations of convergence collected during a period of approximately 2 months after the section excavation the results from fem were found to adequately and reliably predict the expected deformation during tunnel excavation the theory of the characteristic line on the other hand seems to offer a realistic and reliable upper bound estimate of the convergence

archaeomagnetism and magnetic anomalies in the american southwest magnetic surveying is probably the most widely used geophysical technique at archaeological sites weymouth and huggins 1985 it is useful for locating features in which the magnetic susceptibility contrasts with the magnetic susceptibility of the surroundings because of induced and or remanent magnetization a contrast in magnetic induction can arise for example when the disturbed soil fill inside a formerly occupied room has a different magnetic susceptibility from the subsoil outside the room tite and mullins 1971 a contrast in magnetic remanence most commonly occurs when a baked clay artifact or feature such as a hearth has acquired a thermoremanent magnetization after being heated to several hundred degrees celsius

new directional archeomagnetic data of burned cave sediments from switzerland and geomagnetic field variations in central europe this paper presents new directional archeomagnetic data from nine meso neolithic fireplaces sampled in a cave shelter at arconciel in western switzerland rock magnetic measurements indicate a homogenous magnetic mineralogy in all fireplaces with magnetite as the main magnetic carrier the remanent magnetization is stable and generally shows one characteristic directional component nine new directions which were obtained from arconciel are combined with 356 other archeomagnetic data from a circular area with a radius of 700 km around this site to obtain a penalized least square spline fit for the past 9000 yr we found in general good agreement with other local compilations such as the balkan curve the regional scha dif 8k model and with lake sediments from uk fennoscandia and switzerland nevertheless a time lag of several centuries is observed for a declination maximum between the archeomagnetic spline fit and the other european data records around 5900 bc this time lag is also observed in the swiss lake sediment record therefore we interpret this shift as a local feature of the earth s magnetic field

coulomb stress changes from earthquakes to underground excavation failures abstract evidence from shallow tunnels and mines indicates that in certain cases deformation and failure are not confined to the vicinity of the excavation front as is widely believed this situation has recently been described as lateral strain propagation from a source to remote parts of the excavation through low strength rocks a similar situation is observed in deep excavations mainly expressed by rock bursts and micro earthquakes we suggest that slow propagation or seismic radiation of deformation away from the excavation front can be explained on the basis of the theory of coulomb failure stress changes in analogy to faulting in large earthquakes local increase of stresses due to the excavation or failure in a certain point leads to a slight increase of stresses around this point if adjacent points are already at a critical level for failure this slight increase triggers a laterally domino style propagating new failure yet in contrast to earthquakes triggered deformation in mining can in principle be predicted and counteracted

geohydromechanical processes in the excavation damaged zone in crystalline rock rock salt and indurated and plastic clays in the context of radioactive waste disposal abstract the creation of an excavation disturbed zone edz or excavation damaged zone edz is expected around all man made openings in geologic formations macro and micro fracturing and in general a redistribution of in situ stresses and rearrangement of rock structures will occur in this zone resulting in drastic changes of permeability to flow mainly through the fractures and cracks induced by excavation the edz may have significant implications for the operation and long term performance of an underground nuclear waste repository various issues of concern need to be evaluated such as processes creating fractures in the edz the degree of permeability increase and the potential for sealing or healing with permeability reduction in the zone in recent years efforts along these lines have been made for a potential repository in four rock types crystalline rock salt indurated clay and plastic clay and these efforts have involved field laboratory and theoretical studies the present work involves a synthesis of the ideas and issues that emerged from presentations and discussions on edz in these four rock types at a cluster conference and workshop held in luxembourg in november 2003 first definitions of excavation disturbed and edzs that may be applicable to all four rock types are proposed then an approach is suggested for the synthesis and intercomparison of geohydromechanical processes in the edz for crystalline rock salt indurated clay and plastic clay comparison tables of relevant processes associated factors and modelling and testing techniques are developed a discussion of the general state of the art and outstanding issues is also presented a substantial bibliography of relevant papers on the subject is supplied at the end of the paper

records of geomagnetic secular variation since 1200 ad and the potential for chronological control of lake sediments in northern alberta we assess whether absolutely aged declination changes can be used to date recent massive lake sediments at the sub century scale three issues limiting such studies are addressed recovery of undisturbed recent lake sediments assessment of the reliability of the geomagnetic record and the comparison of lake sediment records with historic re cords a 793 year long geomagnetic chronology was obtained from the annually laminated sediment of rainbow lake a sediment disturbance was minimized by freezing the sediment in situ and maintaining this state for geomagnetic analyses geomagnetic chronologies ca 600 years long from the massive sediments of fariya lake and ninisith lake were collected in removable plastic tubes using a piston corer sediment disturbance was minimized by ex situ draining of water from the plastic tubes the reliability of the geomagnetic record was assessed using a measure of internal co herence with an absolute cutoff of 15 by further separating the samples at coherence values of 5 and 7 5 it was possible to identify zones of disturbance and reduced compaction the most reliable samples had a high magnetic in tensity due to high inputs of magnetic minerals sediment compression and inputs of stable magnetic minerals neither freezing nor dewatering of the sediments appeared to decrease reliability of the geomagnetic record the declination chronology from the annually laminated sediments was significantly correlated with a 230 year long historical record from churchill manitoba and with the massive lake sediment chronology from fariya lake geomagnetic dating was not possible however because of the large amplitude in the annually laminated sediment declination record the large number of years of sediment in many specimens and the lack of reliability for samples that contain few years of sedi ment per specimen

tunnelling through the young himalayas a case history of the maneri uttarkashi power tunnel abstract a 8 56 km long circular tunnel with a finished diameter of 4 75 m has been constructed for the maneri hydel hydro electric project on the river bhagirthi the tunnel passes through quartzitic and metabasic rock formations of the young himalayas the tunnel excavation was accomplished from four headings one from the upstream end at maneri two from an intermediate adit at heena and one from the downstream end near uttarkashi where an 80 mw power house is located problems of tunnel face collapse with or without heavy ingress of water cavity formation and large tunnel closures leading to buckling of steel ribs on account of squeezing ground conditions were encountered methods to combat these problems are described the absence of advance knowledge of the frequently chanigng rock mass and ground water conditions and therefore the inability of the tunnelling engineers to modify the construction method and the support system was responsible for these problems predic values of support pressure obtained from the empirical methods of terzaghi barton et al and the one proposed by singh et al have been compared with the observed values of checking the reliability of various methods particularly for poor rock masses

considerations and observations of stress induced and construction induced excavation damage zone in crystalline rock abstract bsed on the recent observations from two underground laboratories the construction induced excavation damage zone edz ci caused by explosion or by mechanical excavation and stress induced excavation damage zone edz si are distinguished the key location for in situ testing of edz and method development has been the tbm tunnel in aspo hard rock laboratory in sweden since the 1990s the research and development has been continued between 2010 and 2012 with in situ stress measurement campaign and in 2013 with ground penetrating radar investigations with new gpr edz method the new gpr edz method based on frequency analysis of the reflected signal indicates mean depth for edz ci of 120 mm the same zone is indicated also by various other geophysical and laboratory methods and is distinguished as construction induced and continuous around the tunnel perimeter fracture mechanics modelling suggests a lowered hydraulic conductivity of 1 8 10 13 m s in edz si and 4 0 10 11 m s in edz ci biaxial testing suggests a zone in which young s modulus values are lowered and which is not continuous around the tunnel this zone is distinguished as an observable part of stress induced edz si

the contribution of termites to the microgranular structure of soils on the uasin gishu plateau kenya abstract the structure of many clay soils in tropical africa is composed of microaggregates that range in size from 0 03 to 1 mm these structural units are often very stable and known as pseudo sand or pseudo silt their presence is detected from the loamy feel of the soil this paper tests the hypothesis that termites contribute to a stable microgranular i e finely aggregated soil structure a termite mound was selected on pedologically unaffected clayey weathering material derived from phonolite the fate of microaggregates produced by termites has been followed through the various stages of mound building field evidence was supplemented with microscopic analysis development of the mound begins when lumps of soil are detached from the subsoil by termites and carried as microaggregates up to the surface in the next stage the microaggregates are cemented to form the nest breakdown begins when the nest is abandoned and disintegrates by splash and runoff producing colluvium or is demolished by ants in the final stage this material is integrated in the soil of the mound soil aggregates produced by splash ants and soil forming processes have different size characteristics but the original microaggregates produced by the termites are preserved in the matrix throughout it is assumed that they owe their stability to impregnation with saliva or other body fluid excreted by the termites termites produce also microaggregates in the form of fecal pellets but these appear to be unstable and are found only in the voids of the soil developed during the last stage

a preliminary magnetic study of soil samples from west central minnesota abstract various rock magnetic techniques were applied to characterize magnetically the samples of a soil profile taken from west central minnesota there is a marked change in magnetic properties as a function of depth in the core x ray analysis and curie temperature measurements carried out on the magnetic fractions indicate that magnetite is the dominant iron oxide in both the top soil and the subsoil the intensity of anhysteretic remanent magnetization arm decreases sharply as the depth increases in contrast the stability of arm was found to be higher for the subsoil the surface soil sample was capable of acquiring a significant amount of viscous remanent magnetization vrm the vrm acquisition coefficient s a of the subsoil s a 3 18 10 6 emu g 1 3 18 10 6 a m 2 kg 1 was about ten times weaker than that of the top soil sample s a 3 868 10 7emu g 1 3 868 10 7 a m 2 kg 1 the magnetic domain state indicator the ratio of coercivity of remanence to coercive force h cr h c was 1 5 and 3 85 for the top soil and subsoil respectively it appears that the observed variations in magnetic properties down the present soil core is due only to a difference in grain size we conclude that the magnetic grains in surface soil samples were more single domain sd like whereas the magnetite grains in the subsoil samples were more likely in pseudo single domain psd or small multidomain md range the observed lower stability for the surface soil samples is attributed to the presence of superparamagnetic grains whose presence was confirmed by transmission electron micrographs

a numerical study of the mechanical response to excavation and ventilation around tunnels in clay rocks abstract as an attempt to more accurately model the nonlinear elastic response and excavation damaged zone edz behavior induced by excavation and ventilation in clay shale we have incorporated and implemented a recently developed stress strain relationship called the two part hooke s model tphm within the tough flac3d code tphm is based on a macroscopic scale approximation using a natural strain based hooke s law to describe elastic deformation for a fraction of pores subject to a large degree of deformation an engineering strain based hooke s law is used for the other part we carried out a series of numerical verification tests on the deformation behavior of small scale clay and shale samples based on tphm a comparison with an elastic model described by the conventional hooke s law the single part hooke s model sphm indicates that the tphm can more accurately capture observed mechanical deformation in the low stress region of clay shale rocks furthermore based on numerical simulations of elastic response and edz behavior around a tunnel opening in opalinus clay induced by excavation and ventilation we found a larger radial elastic deformation on the roof and floor of the tunnel and considerably different stress distributions than were found with sphm although desaturation was influenced by ventilation only and occurred within a narrow zone around the tunnel opening a suction state in the rock mass developed over quite a long radial distance which had a substantial effect on the macroscopic behavior of the rock matrix during the desaturation process throughout the tunnel the mode and extension of damage zones calculated by tphm showed clear differences from those calculated by sphm the results based on tphm are more consistent with observations indicating the need and importance of incorporating more accurate constitutive models for modeling coupled processes

linking site formation processes to magnetic properties rock and archeomagnetic analysis of the combustion levels at riparo gaban italy this study focuses on archeomagnetic directional data that are obtained from combustion levels in the riparo gaban rock shelter northern italy in order to assess the degree of disturbance in the sediments and to provide new information to evaluate evolution of the geomagnetic field in the mid holocene combustion levels consist of ash rubefied levels or partially burned material and mixtures of these or polygenic material rock magnetic investigations show that superparamagnetic to single domain magnetite is the main carrier of the remanent magnetization but small amounts of hematite and maghemite may also be present in the different materials rock magnetic parameters e g the koenigsberger ratio q or the reversibility of thermomagnetic can be related to the degree of burning and the dispersion parameter k to the degree of preservation the grouping of archeomagnetic directions of a specific level is strongly dependent on the degree of physical disturbances directional means from thirteen levels can be compared with reference curves for paleosecular variation based on geomagnetic field models and other archeomagnetic data the data from this study are in agreement with other archeomagnetic data from the balkans in the time period 4900 bc to 4600 bc

induced deformation during tunnel excavation evidence from geodetic monitoring abstract during tunnel excavation convergence i e a tendency for reduction of the section area of the void formed is observed due to the stress redistribution around the excavation free surface this deformation accumulates with a gradually decreasing rate until an equilibrium level is obtained its amplitude depends on the rock mass conditions the support system and the excavation procedure as well as on the state of stress and is usually recognized as a two dimensional effect i e a deformation confined to a plane normal to the tunnel axis not affecting neighboring sections in the last years electronic theodolites a new generation of geodetic instruments which can describe in detail the 3 d changes in the shape of tunnels during their excavation stage relative to fixed reference frames became available making possible the understanding of the detailed pattern of such changes especially the effect of rejuvenation of deformation in previously stabilized sections while tunnel excavation is progressing analysis of geodetic monitoring records of certain recently constructed tunnels indicates that occasionally large deformation from specific source sections is transferred along the tunnel axis to host neighboring sections causing additional time delayed deformation of previously stabilized sections and necking of the tunnel this induced deformation is not due to effects such as nearby excavations changes in the hydrological conditions etc and to tertiary creep its distribution along the tunnel axis seems to depend on the potential of host sections to accommodate additional stresses from neighboring deformation source sections and it may lead to a progressive domino type failure the overall process is reminiscent of the triggering of new earthquakes by coulomb static stress changes caused by a certain earthquake on the condition that the stress level in the epicentral areas of the new events was close to the rupture limit

a method for assessment of excavation damaged zone edz of a rock mass and its application to a dam foundation case abstract excavation of slope is an unloading process and also an energy releasing process when the stress in the rock mass is unloaded leading to the rebounding deformation towards the free face and then a zone namely excavation damaged zone edz will be formed near the excavation boundary where the rock is damaged or disturbed and its physical mechanical and hydraulic properties are greatly changed this paper is to put forward a new method to quantify the extent and damage degree of the edz according to the unloading strain energy which is released in the process of excavation a simple relationship between unloading strain e and accumulative opening displacement t of cracks d t d h is proposed to describe the damage degree of rock mass in the edz where h is the depth variable in normal direction of the open cracks this method is used to assess the edz of the dam foundation at xiaowan hydropower station in southwestern china by the accumulative opening displacement curves of cracks along boreholes based on boreholes camera photos we find that the edz can be naturally divided into two sub zones i e the excavation heavily disturbed sub zone ehdz and excavation slightly disturbed sub zone esdz according to the variation of unloading strain e two inflexions of the accumulative opening displacement curve indicate the lower limits of ehdz and esdz respectively

rock magnetic signature of the cretaceous tertiary boundary black magnetic microspherules commonly found in cretaceous tertiary k t boundary sediments and believed to be of an impact melt origin were found to be responsible for a strong magnetic anomaly at the k t boundary in petriccio italy and in almost all deep sea drilling project dsdp sediment cores investigated in which the k t boundary was present the enriched concentrations of magnetic minerals have been detected by measurements of the magnetic susceptibility which is in a good approximation proportional to the magnetic microspherule content a rock magnetic characterization of extracted microspherules by hysteresis isothermal remanent magnetization acquisition demagnetization and thermomagnetic measurements describes the magnetic minerals in the microspherules as ferrites with a near magnetite composition and soft i e multidomain magnetic behavior in agreement with earlier nonmagnetic studies on the contrary volcanic ash from hawaii has distinctively harder magnetic properties an important finding with regard to the proposed alternative a volcanic origin of the well known ir anomaly at the k t boundary it is suggested here that from magnetic susceptibility scanning of numerous cross sections of the k t boundary a distinct worldwide pattern might evolve that can potentially reveal the impact volcano site because of a presumed higher microspherule concentration near the source the advantage of mapping the microspherule distribution over the previous unsuccessful attempt using ir concentrations lies in the large size hundreds of microns of the microspherules with relatively short airborn life times while the iridium might have adhered to small dust particles that circled the globe several times before settling

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