continental scale salt tectonics on mars and the origin of valles marineris and associated outflow channels a synthesis of deformation patterns within and around the thaumasia plateau mars points to a new interpretation for regional deformation and the origin of valles marineris and associated outflow channels the morphology of the thaumasia plateau is typical of thin skinned deformation akin to a mega slide in which extensional deformation in syria planum and noctis labyrinthus connects via lateral zones of transtension and strike slip claritas fossae and valles marineris to a broad zone of compressional uplift and shortening defined by truncated craters and thrust faults along the coprates rise and thaumasia highlands however the low regional slope 1 results in gravitational body forces that are too small to deform the basaltic lava flows conventionally thought to compose the flanks of the tharsis volcanic province instead we conclude that geothermal heating and topographic loading of extensive buried deposits of salts and or mixtures of salts ice and basaltic debris would allow for weak detachments and large scale gravity spreading we propose that the generally linear chasmata of valles marineris reflect extension collapse and excavation along fractures radial to tharsis either forming or reactivated as part of one lateral margin of the thaumasia gravity spreading system the other dextral lateral margin is a massive splay of extensional faults forming the claritas fossae which resembles a trailing extensional imbricate fan the compressional mountain belt defined by the coprates rise and thaumasia highlands forms the toe of the mega slide topographic observations and previous structural analyses reveal evidence for a failed volcanic plume below syria planum that could have provided further thermal energy and topographic potential for initiating regional deformation either intrusively through inflation or extrusively through lava flow and or ash fall emplacement higher heat flow during noachian time or geothermal heating due to burial by tharsis derived volcanic rocks would have contributed to flow of salt deposits as well as formation of groundwater from melting ice and dewatering of hydrous salts we further propose that connection of overpressured groundwater from aquifers near the base of the detachment through the cryosphere to the martian surface created the outflow channels of echus coprates and juventae chasmata at relatively uniform source elevations along the northern margin of the mega slide where regional groundwater flow would have been directed toward the surface our hypothesis provides a unifying framework to explain perplexing relationships between the rise of the tharsis volcanic province deformation of the thaumasia plateau and the formation of valles marineris and associated outflow channels

permeability characteristics of mudstone cap rock and interlayers in bedded salt formations and tightness assessment for underground gas storage caverns abstract permeability of nonsaline cap rock and interlayers is a key parameter for the assessment of the tightness of gas storage caverns in bedded salt formations x ray diffraction permeability tests scanning electron microscope studies and theoretical analyses have been performed for the mudstone cap rock and interlayers of a potential cavern in a bedded salt formation the results show that the permeability of cap rock and interlayers is in the range of 10 18 10 20 m2 whereas the interface in between salt and interlayer behaves as if impervious applied confinement conditions significantly affect the permeability the higher the applied hydrostatic pressure the lower the permeability permeability decreases more than one order of magnitude with hydrostatic pressure increases up to a certain compression threshold pressure permeability remains virtually constant at an extremely low magnitude once the hydrostatic pressure exceeds this compression threshold pressure the intrinsic reasons for the low permeability have been revealed by sem studies and are as follows 1 the grains making up the bulk of the mudstone are very small and extremely tightly cemented secondary minute clay minerals completely fill the pores and fissures between grains of quarts and feldspar etc resulting in very little residual void space and reducing connectivity for fluid penetration and 2 the boundaries between quartz feldspar and other grains are mainly plate shape cracks that are poorly interconnected while the finer matrix is very tight and crack free the mechanical compaction investigation shows that the plate shape cracks are much easier to be compacted than sphere shape pores which contributes significantly to the decrease in permeability a capillary tube model suggests that permeability decreases very rapidly in the initial stages of compaction but decreases extremely slowly in subsequent stages so the permeability obviously behaves differently before and after the compression threshold pressure by comparison with previous studies the research we launched demonstrates that the cap rock and interlayers are characterized by extremely low permeability in compression regions hence the requirements of tightness except for the possible presence of excavation disturbed zones are basically guaranteed also a recommendation is expressed as to ensure higher tightness and safety reasonable design and operating programs should be adopted to reduce the edzs as much as possible

compression behavior of canadian oil sands the compression behavior of canadian oil sands was investigated by running high stress oedometer compression tests up to 65 mpa an x ray microtomography investigation confirmed the significant disturbance affecting the core samples showing large pores located between dense intact clusters made up of angular sand grains compression tests confirmed the significant effects of disturbance on the com pression characteristics providing a much softer response without any memory of the significant load applied by the 3 to 4 km thick ice sheet during the quaternary period high stress compression allowed us to bring back the samples close to the in situ estimated porosity providing compression characteristics estimated fromaloading cycle close totheintact ones despiteobviousdifferencesinfabric includingtheeffects attributable to grain crushing at high stress creep behavior was also observed and an estimate of the order of magnitude of the creep strain corresponding to the quaternary period is provided doi 10 1061 asce gt 1943 5606 0000808 2013 american society of civil engineers ce database subject headings oils compression sand soil type x rays canada author keywords heavy oil oil sand high stress compression x ray microtomography core disturbance

parametric assessment of salt cavern performance using a creep model describing dilatancy and failure abstract the present paper discusses a systematic approach to study the time dependent performance of underground storage caverns in rock salt an elasto viscoplastic constitutive model capable of describing dilatancy short term failure and long term failure during creep of rock salt was implemented in a lagrangian finite element formulation using the finite element formulation a series of numerical analyses was performed to investigate the influence of the cavern geometry and non salt interbeds on the performance of underground storage caverns excavated in rock salt in the framework of large displacements the attained results demonstrated the capability of the proposed approach in performance assessment of the underground caverns

the campanian ignimbrite southern italy geochemical zoning insight on the generation of a super eruption from catastrophic differentiation and fast withdrawal more than ca 100 km3 of nearly homogeneous crystal poor phonolite and ca 100 km3 of slightly zoned trachyte were erupted 39 ka during the campanian ignimbrite super eruption the most powerful in the neapolitan area partition coefficient calculations equilibrium mineral assemblages glass compositions and texture were used to reconstruct compositional thermal and pressure gradients in the pre eruptive reservoir as well as timing and mechanisms of evolution towards magma chamber overpressure and eruption our petrologic data indicate that a wide sill like trachytic magma chamber was active under the campanian plain at 2 5 kbar before ci eruption thermal exchange between high liquidus 1199 c trachytic sill and cool country rocks caused intense undercooling driving a catastrophic and fast 102 years in situ fractional crystallization and crustal assimilation that produced a water oversaturated phonolitic cap and an overpressure in the chamber that triggered the super eruption this process culminated in an abrupt reservoir opening and in a fast single step high decompression sanidine phenocrysts crystal size distributions reveal high differentiation rate thus suggesting that such a sill like magmatic system is capable of evolving in a very short time and erupting suddenly with only short term warning

influence of the leaching phase on the mechanical behavior of salt caverns abstract big caverns can be leached out from salt formations during the leaching process cold water is injected in the cavern through tubing warmer brine is withdrawn through an annular space thermal balance is relatively intricate because salt dissolution is an endothermic process whereas brine and water exchange heat through the steel tubing inside the well as a whole the rock mass is cooler around the cavern after leaching than before resulting in a small reduction of cavern creep

landslide reconstruction using seismic signal characteristics and numerical simulations case study of the 2017 6 24 xinmo landslide abstract landslide modeling based on seismic signal characteristics is an effective method to study landslide evolution the scientific challenge lies in how to systematically characterize and reconstruct the entire landslide evolution process using the recorded seismic data we selected the 2017 6 24 xinmo landslide as a case study empirical mode decomposition emd is used to analyze the seismic signals from 14 seismic stations near the landslide area numerical simulations using two dimensional discrete element methods dem are performed to simulate landslide dynamics using the calculated kinetic energy profile after analyzing the short time fourier transform stft and fast fourier transform fft characteristics of the signal the landslide process is reconstructed and compared with the dem simulation the landslide process is observed to consist of a stationary stage slipping stage transition stage entrainment transportation stage and a deposition stage this is the first study that uses seismic signals to identify a transition stage which is a feature that is difficult to constrain from field survey and analysis alone landslide development and movement in the transition stage are discussed considering the sedimentology of the study area this study provides improved theoretical guidance for the reconstruction and characterization of landslide processes by seismic signals

the age of the neapolitan yellow tuff caldera forming eruption campi flegrei caldera italy assessed by 40ar 39ar dating method abstract the neapolitan yellow tuff nyt is the product of the largest known trachytic phreatoplinian eruption it covered an area larger than 1000 km2 with an estimated volume of about 40 km3 of erupted magma during the course of the eruption a caldera collapsed within the previously formed campanian ignimbrite caldera the resulting nested structure strongly influenced the following volcanic activity in the campi flegrei caldera as previous dating of the nyt does not converge toward a unique result a new set of 40ar 39ar age determinations has been carried out to better constrain the age of the eruption two variants of the 40ar 39ar dating method were applied to determine the age of the nyt eruption 1 single crystal total fusion sctf on an individual phenocryst of feldspar and 2 laser incremental heating lih on bulk aliquots of feldspar phenocrysts the results of the sctf analyses show that the overall sample weighted mean age derived from the conventional age calculation is 15 6 0 8 ka a weighted mean of the isochron age is 15 3 1 2 ka 2 and has been assumed as the best indicator of age to be derived from the sctf analyses the lih analyses results show that plateau ages vary from 15 4 0 5 to 14 5 0 5 ka the overall weighted mean age of the isochron results is 14 9 0 4 ka 2 this result has been assumed as the reference age for the nyt eruption and agrees with the sctf age the new age obtained for the nyt deposits is of great relevance for the understanding of the evolution and the present state of the campi flegrei caldera and collocates the nyt in a crucial stratigraphical position to date the climatic oscillations that occurred between the late glacial and the holocene

geomechanical model test for stability analysis of high arch dam based on small blocks masonry technique abstract rock mass deformation and strength property simulation plays a key role in the rupture tests of arch dam geomechanical model subject to the limit of geometry scale usually the simulation of tectonic discontinuities such as faults disturbed belts crush belts and weak interlayer were ignored as safety buffer which may yield overstated safety factors in this paper small block masonry technique and low strength binder invented make the simultaneous simulation of the rock mass and tectonic discontinuities available which is more coincident with real engineering conditions based on the material test of blocks and binder the small blocks masonry technique has been successfully applied in the rupture test of xiluodu arch dam with the assistance of high accuracy monitoring and measuring system the stress strain and displacement distribution of the dam abutments and rock foundations are obtained by analyzing these monitoring results the failure process mode and mechanism of the dam body and abutments are derived for further identification of weakness at last the comparative analysis with other arch dam geomechanical rupture test results yields the evaluation of the dam s global stability and necessary reinforcement measures

deformation characteristics of rock salt with mudstone interbeds surrounding gas and oil storage cavern abstract this paper discusses the deformation differences that occur due to the presence of thin mudstone layers in underground storage caverns in rock salt both plasticity and viscosity are considered in the displacement calculations the results show that both creep deformation and deformation distinction i e the differences in the creep behavior between the salt rock and the mudstone are very large under the condition of high effective stresses when the inner diameters of salt caverns are 40 60 m the maximum radial convergence can reach 24 m and the deformation distinction can reach up to 6 m 30 years after the completion of cavern by solution mining the affected areas are however are restricted to the vicinity of the cavern the tightness of the cavern may not be violated if the distance between the caverns is greater than this amount the extension of plastic and dilatancy zones in rock salt is limited to three times the cavern diameter when elasto plastic mudstone interbeds are included tensile failure zones are present in the vicinity of the cavern and the plasticity zone stretches through the entire layer this could cause a loss of cavern tightness or stability if the mudstone interbeds creep although the creep rate is 2 orders lower than that of rock salt yielding is strongly de escalated but the deformation distinction is not affected

evidences for disruption of a crystallizing front in a magma chamber during caldera collapse an example from the breccia museo unit campanian ignimbrite eruption italy abstract this work is focused on juvenile components and some cognate xenoliths of the breccia museo bm unit the bm is a coarse grained proximal unit of the caldera forming phase of the ignimbrite campana ic eruption southern italy the bm products show some peculiar characteristics that distinguish them from the other ic deposits in particular different types of pumice fragments constitute the juvenile fraction and their crystal contents are remarkably higher than the other ic units slightly porphyritic and highly porphyritic trachytic to phonolitic pumices were distinguished in each sample and investigated separately for mineralogy matrix glass composition melt and fluid inclusion studies most feldspar crystals may have formed at the margins of the magma chamber and the crystal content of both types of pumice fragments can be ascribed to variable entrainment of these crystals from the solidification front by the melt variably porphyritic

effects of dilatancy and yield criteria on displacements around tunnels analytical elastoplastic solutions for stresses and displacements around a circular opening have been developed using two different yield criteria and a nonassociated flow rule the effects of dilatancy and postpeak decrease in strength are included in these solutions it is shown that the two different yield criteria lead to practically identical results while the dilatancy angle plays an important role in controlling radial displacement four case histories one in soft fractured rock and three in a heavily overconsolidated stiff clay are analyzed the calculated radial displacements along the crown line are consistent with results of field measurements key words tunnels elastoplastic analysis stress strain dilatancy yield criteria postpeak strength nonassociated flow rule soft rock stiff clay

oxygen isotope geochemistry of pyroclastic clinopyroxene monitors carbonate contributions to roman type ultrapotassic magmas the oxygen isotope geochemistry and chemical composition of clinopyroxene crystals from alban hills pyroclastic deposits constrain the petrological evolution of ultrapotassic roman type rocks volcanic eruptions in the 560 35 ka time interval produced thick pyroclastic deposits bearing clinopyroxene phenocrysts with recurrent chemical characteristics clinopyroxenes vary from si mg rich to al fe rich with no compositional break indicating that they were derived from a continuous process of crystal fractionation based on the 18o and trace element data no primitive samples were recovered monomineralic clinopyroxene cumulates set the oxygen isotope composition of primary magmas in the range of uncontaminated mantle rocks 5 5 but their ree composition resulted from extensive crystal fractionation departing from these mantle like 18ocpx values the effects of crustal contamination of clinopyroxene o isotope composition were identified and used to monitor chemical variations in the parental magma 18o values in si mg rich clinopyroxene are slightly higher than typical mantle values 5 9 6 2 and the low ree contents are representative of early stages of magmatic differentiation 18o values as high as 8 2 are associated with al fe3 rich clinopyroxene showing high ree contents these 18o values are characteristic of crystals formed during the late magmatic stages of each main eruptive phase geochemical modelling of 18o values vs trace element contents indicates that these ultrapotassic magmas were derived from fractional crystallization plus assimilation of limited amounts of carbonate wall rocks starting from a primary melt and from interaction with co2 derived from country rocks during crystal fractionation

a geotechnical study of evaporitic lacustrine sediments in the saline environment of the dead sea area this paper is the third by the authors relating to the geotechnical properties of the evaporitic lacustrine sediments of the saline environment in the dead sea area the earlier papers identified difficulties involved in establishing the water content of sediments in a saline environment a different approach was adopted whereby fluid content rather than water content was used to define geotechnical properties the present paper expands on the geological background presented in the previous papers and discusses additional geotechnical aspects of the materials behavior the three major sediment types encountered in the region are fluvial granular soil cohesive lime carbonate deposits and granular to massive halite sediments the granular soils composed predominantly of sand and pebbles of dolomite with minor chert and limestone have gradations which vary widely both with depth and laterally shear wave velocities are higher than those estimated from common existing correlations with standard penetration test spt blow counts while compression indices cc and cyclic shear response of the saturated lime carbonates are consistent with behavior of clay soils their effective friction angle of about 34 on average is significantly higher than that of clays the geotechnical properties of the rock salts encountered in the region are shown to be intimately related to the extent of diagenesis and burial with very significant difference between the younger more porous deposits of holocene age and the older mt sdom diapiric salt wall of upper miocene age the latter are seen to have properties consistent with those of older rock salt deposits at greater depths reported in the literature

physical model test and numerical simulation for the stability analysis of deep gas storage cavern group located in bedded rock salt formation abstract the stability of gas storage cavern complex constructed in bedded salt rock formation might be influenced by multiple factors during the operation process in order to assess these effects three dimensional rheological model tests were conducted in this study physical model with four ellipsoid caverns were constructed with scaled in situ stresses applied through independent sets of hydraulic jacks and internal pressure applied by digital controlled latex balloons influences of different factors on the deformation properties of surrounding rock were systematically evaluated including the gas recovery and injection rate the loss of pressure the extremely low and high gas pressure and the pillar width and pressure difference between adjacent caverns test results revealed that the deformation of the cavern wall was accelerated when the gas extraction injection rate exceeds 0 65 mpa d loss of internal pressure dramatically promoted the deformation tertiary creep stage arose when the internal pressure was too low 3 mpa or too high 22 mpa internal pressure difference and pillar width worked together to affect the deformation properties tests results obtained in this study provided physical evidence for the safety analysis of cavern group as well as the optimization of design and operation scheme these results can also serve as benchmark for the validation of numerical models

pore structure characteristics of debris flow source material in the wenchuan earthquake area abstract wide grading loose soils wgls are a special slope deposit that often serve as a source for debris flows in the western mountainous area of china previous research indicated that rainfall infiltration induced the migration of fine particles within soil slopes and lead to the initiation of shallow failure and subsequent debris flows clearly soil pore structure exerts a profound influence on seepage during rainfall infiltration which is closely related to soil permeability and corresponding internal erosion the current understanding of the mechanisms of fine particle migration is limited because of the complexity of wgls micropore structure the challenge lies in how to systematically characterize wgls pore structure so that it provides a foundation for future numerical simulations of fine particle migration induced debris flows in this study the characteristics of wgls pore structure were analyzed quantitatively using scanning electron microscopy the results revealed that wgls predominantly contained micropores and mesopores the pore size distribution exhibited a bimodal nature with one peak occurring at a pore diameter of 12 m and another at 72 m the pore complexity of all samples exceeded 0 75 which indicates a low aspect ratio for each pore the average diameter of the fine particles that migrated was then determined with a laboratory seepage test a preliminary jamming probability analysis based on three dimensional micropore reconstruction and average fine particle diameter indicate that jamming is most prevalent along the slope

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

clinopyroxene liquid trace element partitioning in natural trachyte trachyphonolite systems insights from campi flegrei southern italy trace element partition coefficients between clinopyroxenes and associated glassy matrix cpx l d have been determined for 13 ree hfse4 5 u th sr pb sc and v from combined la icp ms emp analyses in selected trachytes and trachyphonolites from campi flegrei composition of clinopyroxene and glass is pretty homogeneous in the trachyphonolites pointing to an overall attainment of the equilibrium conditions in trachytes conversely phases show some compositional heterogeneity due to the presence of clinopyroxene xenocrysts that requested a more careful petrographic and geochemical inspection of the samples to assess the equilibrium clinopyroxene composition in the trachyte clinopyroxenes ree are compatible from nd to lu cpx l d up to 2 9 like y ti sc and v the cpx l d for eu is lower than those of the adjacent ree highlighting eu2 contribution high d values are also shown by u th pb zr hf nb and ta relatively to basaltic and andesitic systems whereas the d sr is roughly similar to that found for less evolved magmas trachyphonolites are characterized by an overall decrease of the cpx l d for highly charged cations with the exception of v and by a slight increase of d sr ree are still compatible from nd to lu cpx l d up to 2 1 like ti y sc and v this variation is also predicted for ree and y by models based on the elastic strain theory being consistent with the slightly lower polymerization degree estimated for the trachyphonolites however the observed cpx l d ree y are matched by the modelled ones only considering very low t 825 c which are believed unlikely this mismatch cannot be attributed to effects induced by the water rich composition of the trachyte trachyphonolite suite since they would lower the observed cpx l d ree y moreover the anomalous inflections of measured cpx l d for hree suggests some crystal chemical control such as the entrance of these elements in a site distinct from m2 it is concluded that the large cpx l d determined for trachytes and trachyphonolites are likely induced by hitherto unconstrained changes of the z3 activities related to the composition of melt and or solid all these considerations strongly highlight the importance of a direct characterization of trace element partitioning in natural samples from magmatic systems poorly characterized by experimental studies

application of proton microprobe data to trace element partitioning in volcanic rocks abstract in situ proton microprobe analyses are used to calculate partition coefficients d for mn fe cu zr ga rb sr y zr ba and pb and more restricted data for ni ge nb and as in pyroxenes olivines biotites hornblendes feldspars and fe ti oxides from 32 volcanic rocks all with glassy matrices these range from leucitite and picritic basalt to high silica and peralkaline rhyolites data for pigeonite aenigmatite allanite and leucite are included where these occur as additional phases coefficients have also been rayleigh fractionation corrected this correction being significant for those elements with high coefficients in specific mineral phases and where pronounced crystallisation has occurred partition coefficients are presented as plots vs nbo t ratios of coexisting glasses melts negative correlations are observed based on log transformed data for mn zn fe and y pyroxenes mn zn and fe olivines mn and zn fe ti oxides nb y sr and zr hornblendes sr plagioclase and ba cu zn and fe feldspars these element partition coefficients are not correlated with bulk mineral compositions zr and ga are not correlated with either glass or mineral compositions except zr in hornblende the correlations support the role of melt polymerisation in controlling element partitioning at least for those elements listed although possible effects of temperature cannot be uniquely isolated in the present data set the coefficients presented here are generally consistent with published values for equivalent rock compositions one difference being that some of the higher published coefficients e g sr in plagioclase are not matched in the present data set from a practical viewpoint the relative regularity of the coefficient data presented does facilitate choice of relevant coefficient values that are required for petrogenetic modelling procedures

true triaxial strength and deformability of the siltstone overlying the chelungpu fault chi chi earthquake taiwan 1 we conducted true triaxial compression tests to examine the effect of the intermediate principal stress 2 on brittle failure and deformability of the siltstone overlying the chelungpu fault taiwan for constant minimum stress 3 a pattern of increased strength 1 as a function of 2 unpredicted by common strength criteria was observed strength data are well fitted by a mogi modified nadai criterion relating the octahedral shear stress at failure to the mean normal stress on the induced shear fracture or fault the induced fault strikes subparallel to 2 and dips steeply in the direction of 3 significantly fault dip angle steadily increases as 2 rises for unchanged 3 sem inspection of tested specimens reveals only sporadic localized intergranular microcracks associated with the creation of the fault the modulus of elasticity and the onset of dilatancy exhibit a similar behavior to that of 1 as they increase with 2 when subjected to a constant 3

physical modelling of subsidence from sequential extraction of partially overlapping longwall panels and study of substrata movement characteristics field examples of subsidence from sequential extraction of overlapping coal longwall panels have shown that complex and unexpected subsidence effects can occur physical models comprising sand and plaster obeying relevant similarity rules were used to investigate the subsidence mechanisms displacements within the models were measured using a combination of optical transducers photogrammetry and laser scanning the observed results were compared with finite element models the models demonstrate that the incremental subsidence and substrata movement profiles after lower seam extraction can be separated into three different zones these zones undergo different horizontal and vertical movement characteristics the zone of overlap of the two longwall panels undergoes greater total subsidence compared to a single seam of equivalent thickness the limit angle of the subsidence also differs at the two ends of the lower extraction as a result of the effects of the previously mined out area above

a numerical characterization workflow for assessing the strength and failure modes of heterogeneous oil sands understanding the strength and failure modes of overburden and reservoir are critical components in safety assessments for oil sands surface mining and in situ thermal recovery operations currentl

high internal pressure induced fracture patterns in rock masses surrounding caverns experimental study using physical model tests abstract this research has experimented with artificial rock specimens that contain a circular or oblong hole using a novel physical modeling approach to investigate the failure behavior of rock masses surrounding a cavern with high internal pressure the knowledge of fracture initiation and propagation in rock masses is crucial to the selection of underground storage construction sites and a stability evaluation method specifically this research attempts to investigate the fracture initiation and propagation direction of the rock mass that encloses an underground gas air storage cavern with high internal pressure under varying control conditions the experiments are carried out with 200 time scaled down artificial rock specimens under varying stress ratio k i overburden stress vi and the joint s dip angle the internal pressure applied to the hole is gradually increased until the fracture is initiated and propagates photogrammetric analysis is utilized to identify the rock mass response induced by increasing internal pressure and the occurrence of failure path the experimental results indicate that the fracture initiation point and propagation direction of failure path are strongly influenced by the in situ stress ratio k the findings also reveal that the site with an initial in situ stress ratio greater than one is suitable for use as a high internal pressure underground cavern in addition in the presence of a nearby joint the site with a smaller dip angle joint is more desirable for the same in situ stress ratio an oblong shaped cavern is more stable than a circular cavern tunnel of similar size although both cavern configurations exhibit the similar failure patterns

rock mechanics for gas storage in bedded salt caverns abstract liquefied petroleum gases and natural gas have been stored in caverns solution mined in domal and bedded salt for many years the majority of the natural gas storage caverns in the united states have been developed in domal salt this paper is a case history of three caverns that were developed specifically for natural gas storage in bedded salt in an area that has historically known only lpg storage in similar caverns coring and rock mechanics studies indicated that the salt could be divided into two distinctive types one of which could not support an underground excavation rock mechanics testing was limited to salt cores but insoluble ledges and intercalated redbed clay played a great part in the ultimate cavern shapes and spans based upon development of storage space in the three caverns conclusions have been reached that will simplify future cavern development

geomechanical investigation of roof failure of china s first gas storage salt cavern abstract jk a cavern is the first operating cavern of jintan underground gas storage which is also the first operating salt cavern gas storage in china in 2015 the sonar survey carried out under working conditions indicated that a massive roof collapse of the jk a cavern had taken place to prevent similar accidents from happening again finding the causes and the collapse time of jk a cavern would be valuable by using the target salt formation information rock properties and monitored gas pressure a 3d geomechanical model of jk a cavern has been built the responses of the rock mass around jk a cavern under leaching sealing tests debrining and gas injection delivery have been investigated a safety evaluation system consisting of cavern volume shrinkage dilatancy safety factor displacement vertical stress and equivalent strain is proposed to find the likely collapse time and the reason for the jk a cavern roof collapse results show that there are two main causes for the cavern roof failure 1 a large span flat roof detrimental for bearing loads once local damage takes place massive collapse may be triggered by the self weight of the loosened rock 2 the decrease speed of the internal gas pressure is too fast the loads applied to the cavern roof cannot be transferred in a timely fashion which causes a stress concentration zone to form and local damage develops the roof collapse of jk a cavern took place 1 3 years after its gas injection delivery started numerical analysis results show that dilatancy safety factor and vertical stress have high accuracy and sensitivity in the prediction of the cavern roof collapse there is a high potential for a roof collapse of jk a cavern to happen again we propose that the gas pressure and pressure decrease rate are to be controlled strictly in the later operating period to prevent any collapses in the future

differences in the acoustic emission characteristics of rock salt compared with granite and marble during the damage evolution process rock salt cavities for energy storage are important elements of energy supply management and sustainability the mechanical properties of other common rocks have already been adequately investigated but a systematic characterization of the differences in acoustic emission ae characteristics among rock salt and other common rocks is needed in this study the ae characteristics of the full regime uniaxial compression of rock salt and common rocks such as granite and marble were determined a damage variable based on ae parameters and a methodology for its determination were established including an analysis of the characteristics of the ae time space evolution the ae amplitude distribution and the damage evolution based on ae parameters clear differences were observed in the ae characteristics of rock salt compared with granite and marble during the damage evolution process the ae activity and energy release of rock salt with coarse grains and nonuniform structures decreased gradually with increasing stress level the ae activity of rock salt appeared in a continuous group occurring form the ae spatial distribution of rock salt was relatively uniform without a definite rupture surface the ae amplitude distribution varied slowly and the proportion of ae events with small amplitudes increased gradually during compression in rock salt moreover the damage in rock salt predominantly occured during the pre peak period resulting in a large damage variable of 0 9 at peak stress by contrast the damage variables of granite and marble are only 0 5 and 0 1 respectively at peak stress rock salt exhibited less damage when approaching failure resulting in a gentler and steadier process and the plastic characteristics of rock salt are relatively obvious these properties to some extent ensure the safety of underground storage engineering when rock salt is chosen as the medium

deformation and permeability evolution of coals considering the effect of beddings abstract coal belongs to sedimentary rock with obvious bedding planes the existence of bedding weakens the continuity and integrity of coal deformation and permeability anisotropy of coals to a certain extent is attributed to the bedding planes we performed experiments of deformation and permeability evolution of coals under true triaxial stress conditions the experimental results indicate that the volumetric strain and bedding jointly affect permeability an analytical model for stress strain relationship of coals containing beddings is developed to quantify the bedding effects under true triaxial stress conditions in the model the deformation and permeability of the bedding and non bedding are separated through bedding ratio and bedding elastic modulus the bedding ratio is defined as the ratio of the total length of bedding to the total length of coal normal to bedding planes which is a parameter closely related to the porosity the elastic modulus is divided into four parts a bedding elastic modulus and a non bedding elastic modulus in the direction normal to bedding planes and two elastic moduli in the direction parallel to bedding planes the four elastic moduli are calculated by the analytical model the bedding elastic modulus is relatively small which shows that the bedding effect cannot be ignored the permeability is highly sensitive to the bedding of coal with low stress in the direction normal to the bedding the bedding ratio always affects the volumetric strain the permeability of the coal is divided into bedding and non bedding permeability the ratio of the bedding permeability to the total permeability is different due to different stresses in the direction normal to bedding planes which is linking with the compression of bedding a permeability model which can reflect the different effects of beddings and non beddings to the total permeability is proposed and verified

failure analysis of thick interlayer from leaching of bedded salt caverns abstract a mathematical model is proposed to calculate the critical collapse span of a thick interlayer during the leaching of a gas storage salt cavern in bedded rock salt in the proposed model the ratio of the height of the damaged zone to the interlayer thickness is introduced this approach overcomes the negative effects on the calculation accuracy of the fact that the damaged rock does not fall off from the thick interlayer but is linked to it by contact forces brine immersion tests have been carried out to obtain the solution characteristics and the influence of brine immersion on tensile strength and on elastic modulus of interlayer samples of a salt formation from yingcheng city hubei province china experimental results show that these mechanical parameters decrease with immersion in brine and more so with decreasing brine density to validate the proposed model a 3d geomechanical model has been built of a salt cavern under construction in a bedded rock salt formation of yingcheng city the stresses and deformations of the thick interlayer obtained by the analytical solution and by the numerical simulation are compared and show good agreement the critical collapse span of the thick interlayer decreases greatly with a decrease of the ratio of damaged zone height to interlayer thickness and interlayer depth increases with increasing tensile strength and thickness of interlayer and is independent of the elastic modulus of the interlayer the proposed model has been used in the planning of the leaching of the underground salt cavern gas storage of yingcheng city hubei province china

trends in large deformation analysis of landslide mass movements with particular emphasis on the material point method traditional geotechnical analyses for landslides involve failure prediction i e onset of failure and the design of structures that can safely withstand the applied loads the analyses provide limited information on the post failure behaviour modern numerical methods are able to simulate large mass movements and there is an opportunity to utilise such methods to evaluate the risks of catastrophic damage if a landslide occurs in this paper various large deformation analysis methods are introduced and their applicability for solving landslide problems is discussed since catastrophic landslides often involve seepage forces consideration of the coupled behaviour of soil and pore fluid is essential two approaches to model soil pore fluid coupling in large deformation analysis using the material point method mpm are introduced an example simulation is presented for each approach one on a model levee failure and the other on a natural cut slope failure the selborne experiment conducted by cooper and co workers in 1998 in the levee failure case mpm simulation was able to capture a complex failure mechanism including the development of successive shear bands the simulation was also able to predict excess pore pressure generation during the failure propagation and the subsequent consolidation stage the simulations demonstrated the importance of the dilation characteristics of soil as well as changes in geometry for the post failure behaviour in the selborne case mpm was able to simulate the progressive failure of brittle overconsolidated clay the evolution of shear stresses along the failure surface was also captured by the mpm the changes in the pore pressure and the actual shape of the failure surface were simulated by the mpm the importance of accurately modelling the shear band within the mpm framework is highlighted

the crystallization of shoshonitic to peralkaline trachyphonolitic magmas in a h2o cl f rich environment at ischia italy with implications for the feeder system of the campania plain volcanoes abstract bulk rock and mineralogical characterization of massive samples lava flows lava domes scoria spatter chosen to be representative of different activity periods and of the whole known compositional range of ischia island roman magmatic province campanian district is reported in this paper the rocks vary in composition from shoshonites to peralkaline trachyphonolites crystallization started with al rich chromite inclusions and their host magnesian olivine in shoshonites and latites and ended with lavenite rinkite kochite hiortdahlite hainite mn aenigmatite britholite and ti zr rich aegirine in the groundmass of the peralkaline trachyphonolites removal of feldspar bearing assemblages with calcic to sodic plagioclase in shoshonites and latites sodic sanidine and anorthoclase in trachytes and trachyphonolites is established throughout the compositional range and is accompanied by interaction between variably evolved magmas with their differing phenocryst assemblage mostly in mafic and intermediate compositions this led to enrichment in mn alkalis zr nb ree rb th u cl and f and depletion in mg fe v ca ba sr and eu in the most evolved magmas the ischian rocks have a tendency to sodic affinity and by peculiar mineral compositions and compositional trends which do not indicate extremely oxidizing conditions the ischian rocks thus differ from the phlegrean fields analogues and the ultrapotassic more silica undersaturated rocks of somma vesuvius overall variations in the chemical compositions of the rocks and their trends imply unrelated feeding systems and thus are inconsistent with the hypothesis of a common magma reservoir beneath the main volcanic areas of the campanian plain

engineering properties of rock salt and simplified closed form deformation solution for circular opening in rock salt under the true triaxial stress state abstract underground structures and storage caverns are increasingly being constructed in rock salt due to its unique self healing ability and impervious nature rock salts are likely to experience and develop time dependent behavior deformation hence the characterization of rock salt for its properties including viscosity are pertinent for design of these structures in addition the material in underground openings experiences true triaxial stresses and hence it is vital to study the behaviour of such structures under true triaxial loading conditions this paper presents results of extensive laboratory testing carried out on specimens of khewra rock salt for its physico mechanical properties physical and engineering properties such as mineralogy density sonic wave velocity resistivity point load index and shear strength properties were measured a simplified closed form solution which deploys three dimensional strength criterion mogi coulomb with maxwell viscoelastic behaviour is developed to assess the stress and deformation behaviour of circular opening in plane strain condition the closed form solution assumes that the material exhibits the maxwell behavior when the stresses are lower than the yield stress and the material behavior is the combination of maxwell and mogi coulomb elastoplastic material when the stresses are equal to the yield stress in addition a cylindrical wellbore problem is solved with the proposed closed form solution and the deformation of the wellbore was estimated for the different time intervals

determination of mechanical properties of flysch using laboratory methods abstract the paper deals with the determination of the mechanical properties of heterogeneous rocks in the laboratory and proposes a methodology for predicting the rock mass strength of flysch formations consisting of siltstone sandstone alternations in different proportions in order to simulate such formations composite specimens comprising superimposed disks of intact sandstone and siltstone material with different thickness ratios were prepared wave velocity p and s uniaxial and triaxial compressive strength and young s modulus of the composite samples were determined in the laboratory according to the laboratory results the uniaxial compressive strength and young s modulus decrease with the increase of the siltstone percentage in the specimens and yield the strength of siltstone when the siltstone percentage in the rock is equal to 37 additionally the triaxial compression tests on composite samples revealed a significant decrease of the m i parameter for a siltstone percentage of only 17 a comparison is made between the results of the present study with similar laboratory and empirical references from literature finally it was possible to suggest how the relation between uniaxial compressive strength ci and siltstone percentage sl may differ according to the ratio of the compressive strength of the two main rocks weak and strong which comprise the heterogeneous rock

experimental investigation of mechanical behavior of bedded rock salt containing inclined interlayer abstract uniaxial and triaxial compression tests have been carried out on specimens of rock salt interlayers and composite rock salt containing inclined interlayers in combination with failure mechanism analysis of the stratified rock structures the variation and impact factors of bonding stresses between the layers have been investigated and the fracture properties and failure mechanisms of inclined bedded rock salt have been revealed the research demonstrated that the inclined interlayer influences the deformation and fracture properties of rock salt due to the composite mechanical characteristics cracks primarily initiate near the interface region and then propagate to the interlayer and the rock salt adjacent to it the thickness of the interlayer affects the entire performance of the composite specimen and governs the development of the local fractures macro cracks tend to form more easily in the test specimens that contain a medium thick interlayer than in the ones containing only a thin interlayer increasing confining pressure gradually changes the overall mechanical behaviors from brittle to more ductile at higher confining pressure the ductile behavior is characterized by differences of strain hardening behaviors and also the geometry of cracks at different locations in the interlayer as compared to the results of uniaxial compression tests

experimental investigation of the mechanical properties of synthetic magnesium sulfate hydrates implications for the strength of hydrated deposits on mars 1 we have carried out uniaxial compression experiments to determine the mechanical properties of three crystalline magnesium sulfate hydrates that may be present in the near surface environment of mars our synthetic samples of kieserite mgso4 h 2o epsomite mgso4 7 h2o and meridianiite mgso4 11h2o have mean values of unconfined compressive strength of 6 3 0 7 12 9 1 8 and 30 1 4 5 mpa respectively young s modulus of 0 8 0 1 2 9 0 4 and 5 9 0 8 gpa respectively and mean porosity values of 47 8 0 5 11 1 0 6 and 2 9 0 2 respectively although our tests cannot quantify a systematic relationship between hydration state and mechanical properties the different porosities produced by consistent sample preparation methods suggest that the addition of non cation coordinated water molecules likely reduces the strength of individual sulfate hydrate phases however the bulk mechanical properties of our synthetic specimens are instead controlled predominantly by the sample porosity generally the strength increases as the porosity decreases we expect the mechanical properties of sulfate hydrate deposits on mars to be governed by the bulk porosity rather than the strength of the pure solid phase we have performed cyclic stressing tests replicating possible periodic depositional and erosional periods on mars resulting from obliquity changes a gradual compaction and reduction in sample porosity rather than an increase in crack damage is observed with each loading cycle suggesting that the evolution of mechanical properties will depend on local factors such as bulk density in addition to the overall stress history

surface diffusivity of cleaved nacl crystals as a function of humidity impedance spectroscopy measurements and implications for crack healing in rock salt 1 rock salt offers an attractive host rock for geological storage applications because of its naturally low permeability and the ability of excavation induced cracks to heal by fluid assisted diffusive mass transfer however while diffusive transport rates in bulk nacl solution are rapid and well characterized such data are not directly applicable to storage conditions where crack walls are coated with thin adsorbed water films to reliably predict healing times in geological storage applications data on mass transport rates in adsorbed films are needed we determined the surface diffusivity in such films for conditions with absolute humidities ah ranging from 1 to 18 g m3 relative humidities rh of 4 78 by measuring the surface impedance of single nacl crystals we use the impedance results to calculate the effective surface diffusivity s d cusing the nernst einstein equation thes values obtained lie in the range 1 10 27 m3 s 1 at very dry conditions to 1 10 19 m3 s 1 for the deliquescence point at 296 k which is in reasonable agreement with existing values for grain boundary diffusion under wet conditions estimates for the diffusivity d made assuming a film thickness of 50 90 nm and no major effects of thickness on the solubility c lie in the range of 1 10 14 to 8 10 12 m2 s 1 for the highest humidities studied 14 18 g m3 ah 60 78 rh for geological storage systems in rock salt we predict s values between 1 10 22 8 10 18 m3 s 1 these imply crack healing rates 6 to 7 orders of magnitude lower than expected for brine filled cracks

constraining the recent plumbing system of vulcano aeolian arc italy by textural petrological and fractal analysis the 1739 a d pietre cotte lava flow 1 the 1739 a d pietre cotte lava flow is part of a sequence of low explosive to weak effusion events occurred at la fossa cone the active vent on vulcano island aeolian arc italy this lava is rhyolitic texturally heterogeneous and contains lati trachytic enclaves these compositions are recurrent in the la fossa volcanic products and are representative of the recent vulcano plumbing system the host lava is vesicular relatively phenocryst free and locally contains microlites and millimeter sized spherulites the enclaves are up to 10 cm in size display angular to spherical shapes and can form the core of spherulites enclaves mostly consist of plagioclase and augitic phenocrysts set in a weakly vesicular groundmass characterized by variable abundance of glass and feldspar microlites field textural and fractal data allow us to constrain the rheological features of the rhyolitic and lati trachytic magmas in situ major trace and volatile element analyses provide evidence for heterogeneities in the glassy matrix and zoning of phenocrysts processes of magma evolution have been quantitatively constrained by using the apparent distribution ratios of trace elements measured between mineral phases and glassy matrices the collected data in combination with petrological and fluid inclusion data from the literature provides evidence for 1 a genetic relationship between the two magmas through assimilation fractional crystallization process 2 a mingling mechanism between an uprising rhyolitic magma and a shallower partly crystallized lati trachytic magma plug 3 the desegregation enclaves at variable scales of the lati trachyte within the rhyolite and 4 the possible eruptive scenarios consequent to a future magmatic unrest

volatile element zonation in campanian ignimbrite magmas phlegrean fields italy evidence from the study of glass inclusions and matrix glasses the distribution of h2o f cl and s in the campanian ignimbrite ci magma chamber was investigated through study of primary glass inclusions and matrix glasses from pumices of the plinian fall deposit the eruption fed by trachytic to phono trachytic magmas mainly produced a trachytic non welded to partially welded tuff underlain by a minor cogenetic fallout deposit the entire chemical variability of the eruptive products is well represented in the pumices of the plinian fall deposit which we divide into a basal lower fall unit lfu and an overlying upper fall unit ufu primary glass inclusions were only found in clinopyroxenes associated with the lfu pumice and contain a mean of 1 60 0 32 wt h2o analysed by ftir 0 11 0 08 wt f 0 37 0 03 wt cl and 0 08 0 04 wt so3 emp analysis co2 concentrations were below the ftir detection limit 10 20 ppm the coexisting matrix glasses contain similar amounts of halogens and sulfur but less water 0 60 wt partially degassed matrix glasses from ufu pumices contain a mean of 0 30 0 02 h2o 0 28 0 10 f 0 04 0 02 so3 and 0 80 0 04 wt cl to reconstruct the total amount of volatiles dissolved in the most evolved trachytes we have used experimental solubility data and mass balance calculations concerning the amount of crystal fractionation required to produce the most evolved trachyte from the least evolved trachyte these yield an estimated pre eruptive magma volatile content h2o cl f of 5 5 wt for the most evolved magmas on the basis of new determinations of cl solubility limits in hydrous trachytic melts coexisting with an aqueous fluid phase hydrosaline melt brine we suggest that the upper part of the magma chamber which fed the ci eruption was fluid s saturated and at a minimum depth of 2 km variations in eruptive style plinian fallout pyroclastic flows do not appear to be related to significant variations in pre eruptive volatile contents

timing of magma extraction during the campanian ignimbrite eruption campi flegrei caldera a core drilled within the northern part of the city of napoli has offered the unique opportunity to observe in one single sequence the superposition of the four pyroclastic flow units emplaced during the campanian ignimbrite ci eruption such a stratigraphic succession has never been encountered before in natural or in man made exposures therefore the ci sequence was reconstructed only on the basis of stratigraphic correlations and compositional data in literature the occurrence of four superposed ci flows together with all the data available in literature allowed us to better constrain the chemical stratigraphy of the deposit and the compositional structure of the ci magma chamber the ci magma chamber includes two cogenetic magma layers separated by a compositional gap the upper magma layer was contaminated by interaction with radiogenic fluids the two magma layers were extruded either individually or simultaneously during the course of the eruption in the latter case they produced a hybrid magma but no evidence of input of new geochemically and isotopically distinct magma batches just prior or during the eruption has been found comparison with the exposed ci deposits has permitted reconstruction of variable eruption phases and related magma withdrawal and caldera collapse episodes the eruption was likely to have began with phreatomagmatic explosions followed by the formation of a sustained plinian eruption column fed by the simultaneous extraction from both magma layers towards the end of this phase the upward migration of the fragmentation surface and the decrease in magma eruption rate and or activation of fractures formed an unstable pulsating column that was fed only by the most evolved magma layer this plinian phase was followed by the collapse of the eruption column and the beginning of caldera formation at this stage expanded pyroclastic flows fed by the upper magma layer in the chamber generated during the following major caldera collapse episode the maximum mass discharge rate was reached and both magma layers were tapped generating expanded pyroclastic flows towards the end of the eruption only the deeper and less differentiated magma layer was tapped producing more concentrated pyroclastic flows that traveled short distances

scale of experiment and rock physics trends because rock is heterogeneous at all scales it is often invalid to assign a single porosity permeability resistivity or velocity to a volume in the subsurface well data demonstrate that these properties can vary appreciably between two points just a foot apart the same happens at the pore scale consider for example a ct scan of a 1 3 mm berea sandstone cube figure 1 the porosity of this sample as calculated by counting the blue pore space pixels is 0 164

post yield plastic frictional parameters of a rock salt using the concept of mobilized strength abstract salt slabbing spalling and fallout surrounding underground salt storage cavern are closely associated with the nonlinear deformability and post yield property of rock salt a better understanding of the pre and post yield behavior of rock salt helps the designer in predicting displacements and failure zones around the salt cavity more accurately as well as in the optimizing design and operation in the present study an approach to determine young s modulus and poisson s ratio from triaxial test plots has been discussed a series of compression tests was performed to explore the nonlinear deformability and post yield strength properties of a rock salt the rock salt specimens were prepared from jintan salt deposit china it is found that the error in modulus obtained by directly computing the gradient of stress strain curve is relatively small and can be used in analysis however error in poisson s ratio is large the post yield strength characteristics were described by nonlinear empirical evolution law of mobilized strength components with maximum principal strain during the process of strain softening hardening the proposed generalized mohr coulomb strength criterion with cohesion weakening and frictional strengthening was proved effective to capture the post yield behavior of rock salt

trace element partitioning in pantellerites and trachytes abstract in order to investigate the effect of increasing melt peralkalinity on partitioning partition coefficients have been determined using neutron activation analyses of coexisting phenocrysts and glass of five samples from pantelleria spanning the range trachyte to pantellerite alkali feldspar partition coefficients for fe rb ba sr and eu vary with melt peralkalinity due to changes in melt polymerization and to the systematic increase in xor and decrease in xan of the feldspar in going from trachyte to pantellerite fe partition coefficients increase from 0 04 to 0 10 presumably because fe 3 increasingly substitutes in the feldspar tetrahedral site as melt activity of al declines and fe concentrations increase partition coefficients for trivalent light rees decrease and the partitioning pattern becomes flatter the most evolved samples having some of the lowest published values for feldspar the hundredfold decline in eu partition coefficients 2 5 to 0 024 and the decrease in the size of the positive partitioning anomaly are attributed to increasing eu3 eu2 in the melt as it becomes more peralkaline as well as to concomitant decrease in the ca content of feldspar as a result the behavior of eu during fractional crystallization of peralkaline suites is fundamentally different from that in metaluminous suites absolute abundances rise and the size of the negative eu anomaly changes little with fractionation beyond pantelleritic trachyte barium and strontium do not decline to extremely low concentrations in pantellerites as they do in highly evolved metaluminous rhyolites because the feldspar partition coefficients drop precipitously with peralkalinity similarly rb contents do not get large because the partition coefficient increases slightly 0 11 to 0 25 with peralkalinity and is sufficient to make rb only weakly incompatible in the feldspar dominated assemblage partition coefficients calculated for sr and ba from natural phenocryst matrix pairs can be gross over estimates in these feldspar rich felsic rocks if phenocrysts are zoned this effect is severe for assemblages with bulk distribution coefficients d greater than 4 even at very small crystal contents and for 4 d 2 it is significant if crystal contents exceed about 25 some of the very high values and much of the variability reported in the literature for ba and sr feldspar partition coefficients may be a result of this effect in contrast to feldspar partition coefficients for apatite and mafic phases change little with peralkalinity partition coefficients for rees and the compatible elements sc co and cr are all less than half those in fe rich clinopyroxene and olivine of similar composition in high silica rhyolite although absolute levels of partition coefficients are a function of melt polymerization the shapes of the ree partitioning patterns appear to be related to the composition of the clinopyroxene scandium is most strongly concentrated in clinopyroxene partition coefficient 27 60 having larger values in more fe rich compositions apatite shows a wide range in composition within the suite the concentrations of si fe rees and y increasing and mg ca and p decreasing in more evolved samples these trends however parallel those in coexisting glasses so that partition coefficients are essentially constant in peralkaline suites cs is the most incompatible of commonly analyzed elements but its great mobility during alteration and weathering limits its use as a differentiation index next in order of incompatibility are th u hf zr and ta which have small but finite values of d due to the partitioning of th and u into apatite 2 the accommodation of zr and hf by clinopyroxene 0 4 and titanomagnetite 0 2 and relatively high concentrations of ta in cossyrite and fe ti oxides the next most incompatible are the lightest and the heaviest rees and finally the middle trivalent rees and rb plots of pairs of relatively incompatible elements form straight line trends over large compositional ranges in peralkaline suites because the replacement of olivine titanomagnetite by cossyrite as the melt becomes more peralkaline causes little change in d the ree patterns of titanomagnetite and cossyrite are both approximately flat at values less than 0 1 and the relatively high titanomagnetite partition coefficients for ta 2 zr and hf when combined with the very low partition coefficients for these elements for olivine approximate the moderate partition coefficients for cossyrite

in situ gas permeability measurements to delineate damage in rock salt in situ gas permeability measurements can be used to distinguish regions within rock salt formations which have experienced disturbance or damage high resolution hydrologic testing reveals rock salt well removed from an excavation i e undisturbed is a low permeability low porosity porous medium with a significant pore brine pressure in this region rock salt is effectively impermeable to gas due to threshold capillary pressures which preclude gas from displacing the resident brine in a region confined to a depth of less than about one effective radius of an excavation rock salt is typically permeable to gas the measured gas permeabilities are consistent with a partially saturated dilated zone developing adjacent to the excavation the extent and nature of the damaged region interpreted from gas permeability measurements is consistent with other measurements and analyses thus gas permeability measurements serve as effective means for detecting and delineating the damaged region

large scale geomechanical model testing of an underground cavern group in a true three dimensional 3 d stress state the stability of a large cavern group at great depth is discussed on the basis of large scale three dimensional 3 d geomechanical model tests and numerical simulations the model tests are described in detail improvements in the tests were made in terms of experimental techniques and advanced measurement methods the model tests utilized active loading on six sides of a rock mass in a true 3 d stress state during the model construction precast blocks were fabri cated and monitoring holes were defined prior to test initiation newly developed combination ball sliding walls were in stalled on each of the major loading surfaces to reduce the friction induced by model deformation a unique grouting and installation technique employing prestressed cables was adopted in the tests a digital photogrammetric technique dis placement sensing bars using fiber bragg grating fbg technology and mini multipoint extensometers were developed for measuring deformation overloading tests were then conducted for different overburden depths and 3 d numerical analyses were performed to simulate the testing procedures conclusions regarding the stability of the cavern group were developed based on a comparison between the experimental and numerical results resume la stabilited un groupe de grandes cavernes profondes est discutee en utilisant des essais en modele geomeca nique 3 d agrande echelle et des simulations numeriques les essais sont decrits en details dans l article des ameliora tions ont eteapportees aux essais par rapport aux techniques experimentales et aux methodes de mesures les essais comportent des chargements actifs sur 6 faces d une masse de roche de facon a representer un etat des contraintes en 3 d durant la construction du modele des blocs pre moules ont etefabriques et des ports de suivi ont etedefinis avant le de but des essais sur chacune des surfaces majeures de chargement des murs en combinaison bille glissement recemment de veloppes ont eteinstalles afin de reduire la friction induite par les deformations du modele une technique de scellement et d installation unique utilisant des cables precontraints a eteutilisee durant les essais une technique photogrammetrique digitale des sondes de deplacements munies de la technologie d un reseau de fibre bragg et de minis extensiometres multi points ont etedeveloppes afin de mesurer les deformations des essais en surcharge ont eteeffectues pour des pro fondeurs de mort terrain differentes ensuite des analyses numeriques en 3 d ont eteeffectuees dans le but de simuler les procedures de l essai des conclusions en lien avec la stabilitedu groupe de cavernes ont etedeveloppees selon des com paraisons entre les resultats experimentaux et numeriques mots cles essai en modele geomecanique simulation numerique groupe de grandes cavernes souterraines etat des contraintes 3 d reel analyse de stabilite traduit par la redaction

experimental study of mechanical properties of gypsum soaked in brine abstract gypsum glauberite and mudstone are common interlayers in bedded salt deposits during subterranean cavern development by leaching methods they will be exposed to saline brines of different concentrations and temperatures over periods of time of at least 18 36 months to investigate the relevant mechanical properties of gypsum under these conditions a series of laboratory tests including uniaxial compression tensile and shear strength was carried out the soak time for gypsum in different brines was as long as 80 days and its ucs strength is reduced to different extents with increases in brine concentration and temperature the strength weakening coefficient of wet gypsum can be as low as 0 1 after being soaked in saturated brine for 60 days with increase of temperature and concentration of the soaking brine the elastic modulus of the gypsum and the tensile strength decrease the time dependent mechanical weakening of wet gypsum is also documented a damage parameter based on rigidity is defined to quantify gypsum deterioration it drops from 704 4 gpa for dry gypsum to 19 5 gpa for wet gypsum soaked in saturated brine at 70 c and the failure style also changes from brittle to ductile the mechanical properties of gypsum can be severely degraded by exposure to warm brine for long times and consequently the study has significance for evaluation of interlayer stability and leakage security of storage caverns in bedded salt deposits

time dependent geochemistry of clinopyroxene from the alban hills central italy clues to the source and evolution of ultrapotassic magmas abstract we investigated chemical and isotopic compositions of clinopyroxene crystals from well age constrained juvenile scoria clasts lava flows and hypoabyssal magmatic ejecta representative of the whole eruptive history of the alban hills volcanic district the alban hills is a quaternary ultra potassic district that was emplaced into thick limestone units along the tyrrhenian margin of italy alban hills volcanic products even the most differentiated are characterised by low sio2 content we suggest that the low silica activity in evolving magmas can be ultimately due to a decarbonation process occurring at the magma limestone interface according to the liquid line of descent we propose the differentiation process is driven by crystallisation of clinopyroxene leucite apatite magnetite coupled with assimilation of a small amount of calcite and or with interaction with crustal co2 by combining age chemical data strontium and oxygen isotopic compositions and ree content of clinopyroxene we give insights into the evolution of primitive ultrapotassic magmas of the alban hills volcanic district over an elapsed period of about 600 kyr geochemical features of clinopyroxene crystals consistent with data coming from other italian ultrapotassic magmas indicate that alban hills primary magmas were generated from a metasomatized lithospheric mantle source in addition our study shows that the 87sr 86sr and lree hree of alban hills magmas continuously diminished during the 600 35 ka time interval of the alban hills eruptive history possibly reflecting the progressive depletion of the metasomatized mantle source of magmas

crystal mush reactivation by magma recharge evidence from the campanian ignimbrite activity campi flegrei volcanic field italy abstract processes of crystal mush remobilization by mafic magma recharges are often related to the outpouring of large volumes of silicic melt during caldera forming eruptions this occurred for the campanian ignimbrite ci eruption campi flegrei italy which produced a voluminous trachy phonolitic ignimbrite in southern central italy about 40 ka ago we focussed on the proximal ci deposits at san martino that are composed of a main sequence of early erupted crystal poor units and a late erupted post caldera collapse crystal rich upper pumice flow unit upfu detailed micro analytical geochemical data were performed on glasses and crystals of pyroclasts from these deposits and coupled with sr nd isotopic measurements on glasses results show that the ci eruption was fed by two distinct melts for the early erupted units and the late upfu respectively the glasses of the early erupted units have negative eu anomalies and show more evolved compositions and higher nd isotope ratios than those of the upfu which have positive eu eu the magmas of the early units formed the main volume of eruptible melt of the ci reservoir and are interpreted as having been extracted from cumulate crystal mush without a vertical geochemical gradient within the magma reservoir the data indicate that the generation of the distinctive upfu melts involved the injection of a new batch of mafic magma into the base of the ci reservoir the mafic magma allowed heating and reactivation of the ci crystal mush by melting of low or sanidines low an plagioclases leaving high an plagioclases and high mg clinopyroxenes as residual phases and a crystal mush melt made of 20 of the initial mush interstitial melt with a composition similar to the early erupted units and 80 of sanidine melt when the mush crystallinity was sufficiently reduced the mafic magma was able to penetrate into the reactivated crystal mush mixing with variable proportions of crystal mush melt and generating cooler hybrid melts which underwent further crystallization of high or sanidine at variable degrees 10 25 finally possibly a short time before the eruption the upfu magmas were able to mix and mingle with the crystal poor eruptible melts still persisting in the ci reservoir at the time of upfu emission we suggest that the complex mechanisms described for the magma evolution feeding the ci eruption may occur whenever a crystal mush is reactivated by new mafic magma inputs

a chemostratigraphic study of the campanian ignimbrite eruption campi flegrei italy insights on magma chamber withdrawal and deposit accumulation as revealed by compositionally zoned stratigraphic and facies framework abstract petrochemical analyses of juvenile samples from twenty stratigraphic sections of the campanian ignimbrite medial deposits located from 30 to 79 km from the vent are presented here sampling has accurately followed a well defined stratigraphic framework and the new component facies scheme the campanian ignimbrite succession is formed by a basal plinian pumice fall deposit overlain by a complex architecture of pyroclastic density current deposits emplaced from a single sustained pyroclastic density current through a mechanism of vertical and lateral accretion the deposit is broadly zoned from more evolved trachyte at its base to less evolved trachyte at its top and is similarly less evolved with increasing distance from the area of emission irregular chemical trends are locally observed and interpreted to represent only a limited patchy record of the entire vertical geochemical trend the petrochemical variation observed horizontally was ascribed to changes in the flow dynamics and interaction between the advancing flow and the underlying topography the results of this study were used to propose a unified volcanological petrological model for the campanian ignimbrite eruption taking into account the emplacement of both the proximal i e the breccia museo formation and medial deposits

petrogenesis and tectonic setting of the roman volcanic province italy abstract the volcanism in the roman province of italy can be modelled by the partial melting of heterogeneously enriched mantle sources the heterogeneity was created by materials derived from a subducted slab which can still be traced geophysically beneath the central apennines new petrographical and chemical data are presented for the high k calc alkaline and the shoshonitic volcanics of the campania region primary magmas are present only locally the existence of spatial zonation in the volcanism of campania is documented for the first time the shoshonitic leucite basanitic and leucititic volcanics of the phlegraean fields procida ischia and the somma vesuvius areas are at similar degrees of evolution about two times richer in nb and ba than those of northwestern campania and the latium part of the roman province accordingly distinct north western and south eastern subprovinces can be defined the evaluation of enrichment factors that is the abundance ratio between the average contents of each element in the relatively primitive lavas of the low k and the high k suites shows that the mantle sources prior to k metasomatism were different in the two sub provinces of the roman province in the north western one they resembled the sources of ocean island tholeiites and moderately enriched mor basalts in the south east they were similar to those of ocean island alkaline lavas and enriched morb s modelling based on k p ce sr rb ba th sm eu gd y nb and 87 sr 86 sr was carried out it indicates that the range of mantle sources of the volcanics in northwestern campania and latium can be modelled by the addition of 3 to 20 of materials derived by partial melting of carbonaceous pelites to a sr enriched mantle wedge comparable to the honolulu mantle source least enriched in nb the production of sr enriched mantle wedge requires either the action of fluids produced by dehydration of subducted oceanic crust or a small amount of metasomatism caused by the presence of carbonatite melts the near absence of ti ta nb yb and the highly fractionated ree in the metasomatizing component requires the presence of residual garnet and accessory ti rich minerals during the partial melting of the subducted sediments the writers propose that the mantle wedge overlying the subducted slab was hybridized by melts produced by partial fusion of subducted material derived from the continental crust probably sediments this process played a dominant role in the generation of the mantle sources from which the high k calc alkaline shoshonitic leucite basanitic and leucititic magmas of the roman province were derived

evidence of crystallization in residual cl f rich agpaitic trachyphonolitic magmas and primitive mg rich basalt trachyphonolite interaction in the lava domes of the phlegrean fields italy the lava domes in the northwestern cuma northern punta marmolite and central accademia parts of the phlegrean fields are the subject of this study the cuma and punta marmolite trachyphonolitic lava domes are among the oldest phlegrean products cropping out the cuma rocks have an agpaitic groundmass with early alkali feldspar fe rich clinopyroxene fe edenite and sodalite and late rosenbuschite fluorite baddeleyite pyrochlore britholite monazite aegirine often zr rich and exceptionally fe mn rich olivine the bulk rock compositions at cuma have some of the highest concentrations of zn mn zr nb th u and lanthanides among the phlegrean fields rocks and some of the lowest mgo p 2 o 5 sr eu and ba the punta marmolite dome is chemically less evolved and lacks characteristic agpaitic minerals but features alkali feldspar sodalite nepheline and relatively na poor fe rich hedenbergite with rare ca rich plagioclase xenocryst cores the accademia dome belonging to the recent activity is latitic to trachytic in composition has highly forsteritic olivine with chromiferous spinel inclusions calcic plagioclase and mg rich diopside phlogopite xenocrysts in an evolved host rock with phenocrysts and microlites of alkali feldspar fe rich clinopyroxene fe rich amphibole magnetite fe rich olivine and accessory baddeleyite zirconolite and fluorite there is clear evidence of open system magma crystallization in the form of interaction between a crystallizing primitive shoshonitic basalt in a reservoir already filled by rather evolved trachytic magma the magmatic evolution towards the evolved compositions is dominated by crystallization of more and more na rich alkali feldspar in a cl f rich and relatively h 2 o poor environment input of mafic magma is evident in many trachytic eruptions of the phlegrean fields and even in the products of the campanian ignimbrite but eruptions having mineral assemblages rich in xenocryst phases as well as eruptions virtually free of mafic magma input are also frequently observed throughout the history this suggests a variable pattern of open and closed system crystallization which may or may not be linked to explosive activity and that can be caused by intermittent supply of basaltic magma from depth

safety evaluation of salt cavern gas storage close to an old cavern abstract uniaxial compression tests triaxial compression tests brazilian disk splitting tests direct shear tests and triaxial creep tests have been carried out on samples cored from jintan mining district to determine their mechanical parameters based on the formation characteristic and the sonar survey data of an old cavern a 3d geomechanical model has been built of a cavern close to an old brine cavern the effects of the distance between new and old caverns on the safety of the rock mass around the caverns are investigated deformation plastic areas and volumes effective strains safety factors and volume shrinkages are selected as the indexes to assess the safety of the caverns the width of the pillar between the new and old caverns is optimized based on the calculated results experimental results show that the interlayer has large effects on the mechanical parameters of jintan bedded rock salt and should be considered in the numerical simulations numerical calculations indicate that the distance between the new and old caverns has large influences on the deformations effective strains and safety factors but has little effect on the plastic areas and volumes and volume shrinkages of the rock mass around the caverns although the dimensions of these old brine caverns are much smaller than those of the new ones a distance between the new and old caverns of no less than two times the maximum diameter of the new cavern is proposed as the shape of the old cavern is poor

estimation of the physical petrophysical and mineralogical properties of messinian salt rocks sicily implications for multidisciplinary applications abstract the messinian salinity crisis msc was a short term 5 96 5 33ma and dramatic paleoenvironmental event which led to the deposition of a thick evaporitic layer throughout mediterranean area however several studies have demonstrated that messinian evaporites have different characteristics and properties from east to west in the mediterranean area and the caltanissetta basin sicily west mediterranean provides an excellent messinian onshore record for investigating evaporitic succession given the scarcity of representative halite samples and at the same time widespread research and scientific drilling in the mediterranean area new physical mechanical petrophysical mineralogical and thermal characterization of messinian halite could provide useful information for several disciplines and applications hence 50 samples of messinian halite were obtained from a sicilian mine italkali analyzed and tested using different instruments ultrasound velocities measured under hydrostatic confining pressure up to 120 mpa ranged from 4210 to 4780 m s and 2510 2650 m s respectively for p and s waves the results further showed that the halite samples had low porosity 2 5 8 5 and negligible permeability demonstrating the weak presence of pores and the total lack of interconnection among them which is typical of rock salt units densities of the halite determined with the hydrostatic weighing method and gas porosimeter were low and ranged from 2 14 to 2 23 g cm3 while high values were obtained for thermal conductivity 17 0 and 32 0 c it is significant that the mineralogical heterogeneity of the halite was due to the presence of clay bearing veins although this work was performed mainly using onshore data and observations the results have wider applications for offshore studies of the msc and its deposits furthermore the study provides important insights for future mediterranean drilling projects geological modelling hydrocarbon exploration and or fluids storage and the understanding of salt rheology under different conditions of pressure and temperature

the influence of shortening and sedimentation on rejuvenation of salt diapirs a new discrete element modelling approach abstract this study employs a novel discrete element modelling approach to investigate the interplay of sedimentation with rejuvenation of diapirs by shortening the inherent complexity of salt tectonics the complications encountered when imaging structures beneath salt and the lack of outcrop analogues coupled with its importance to petroleum systems make salt tectonics one of the most interesting and debated topics in basin studies model results successfully reproduce the geometric and dynamic behaviour of active diapirism and show the effects of sedimentation thickness rate and timing on the generation of distinct diapir geometries including i salt tongues and ii squeezed upright diapirs models with late sedimentation or a lower sedimentation rate relative to salt mobility show development of asymmetric diapirs with allochthonous salt tongues whereas models with earlier sedimentation or a faster sedimentation rate generate upright squeezed diapirs early sedimentation at a moderate rate results in a symmetrical hour glass shaped structure resembling a tear drop diapir results are fully reproducible and comparable with many natural examples and include overburden deformation which is difficult to simulate using other numerical techniques extending this approach to different problems and basinal contexts could improve our understanding of deformation mechanisms and sediment distribution around salt structures

evolution of stress induced borehole breakout in inherently anisotropic rock insights from discrete element modeling the aim of this study is to better understand the mechanisms controlling the initiation propagation and ultimate pattern of borehole breakouts in shale formation when drilled parallel with and perpendicular to beddings a two dimensional discrete element model is constructed to explicitly represent the microstructure of inherently anisotropic rocks by inserting a series of individual smooth joints into an assembly of bonded rigid discs both isotropic and anisotropic hollow square shaped samples are generated to represent the wellbores drilled perpendicular to and parallel with beddings at reduced scale the isotropic model is validated by comparing the stress distribution around borehole wall and along x axis direction with analytical solutions effects of different factors including the particle size distribution borehole diameter far field stress anisotropy and rock anisotropy are systematically evaluated on the stress distribution and borehole breakout propagation simulation results reveal that wider particle size distribution results in the local stress perturbations which cause localization of cracks reduction of borehole diameter significantly alters the crack failure from tensile to shear and raises the critical pressure rock anisotropy plays an important role on the stress state around wellbore which lead to the formation of preferred cracks under hydrostatic stress far field stress anisotropy plays a dominant role in the shape of borehole breakout when drilled perpendicular to beddings while a secondary role when drilled parallel with beddings results from this study can provide fundamental insights on the underlying particle scale mechanisms for previous findings in laboratory and field on borehole stability in anisotropic rock

the breccia museo formation campi flegrei southern italy geochronology chemostratigraphy and relationship with the campanian ignimbrite eruption the breccia museo is one of the most debated volcanic formations of the campi flegrei volcanic district the deposit made up of six distinctive stratigraphic units has been interpreted by some as the proximal facies of the major caldera forming campanian ignimbrite eruption and by others as the product of several more recent independent and localized events new geochemical and chemostratigraphical data and ar ar age determinations for several units of the breccia museo deposits 39 ka correlate well with the campanian ignimbrite forming eruption the chemical zoning of the breccia museo deposits is interpreted here to be a consequence of a three stage event that tapped a vertically zoned trachytic magma chamber

application of 3d laser scanner optical transducers and digital image processing techniques in physical modelling of mining related strata movement a physical testing protocol for modelling mining related problems has been presented a new method for monitoring fracture propagation pattern has been introduced laser based and optical devices have been used for physical modelling of subsidence multiple seam subsidence has been measured by photogrammetry dic analysis optoncdt and 3d tls

experimental determination of ree partition coefficients between amphibole and basaltic to andesitic liquids at high pressure abstract amphibole liquid partition coefficients for the ree damph liqree obtained from natural rocks increase systematically with bulk rock compositional change from basalt to rhyolite and are higher for the middle to heavy ree five new experimentally determined sets of dree la sm eu2 ho lu and 4 published sets are similar to these data and provide values for use in geochemical modelling of magmatic processes involving amphibole over a range of temperature pressure and oxygen fugacity the partition coefficients increase significantly with decreasing temperature and increase slightly with increasing oxygen fugacity pressure does not appear to have a major effect although one data set suggests increased pressure lowers damph liqree in a basaltic composition

a study of isolated draw zones in block caving mines by means of a large 3d physical model block caving methods rely on gravity to break and transport large amounts of ore and waste despite the importance of gravity flow there is debate within the literature about the influence that the height of draw particle size and particle size distribution has on the geometry of extraction and movement zones this paper presents the results of an experimental programme conducted in the largest three dimensional 3d physical model to investigate the mechanisms of flow of cohesionless materials when drawing from a single drawpoint experimental results showed that isolated draw zones are mainly influenced by mass drawn and height of draw particle size was found to have a slight effect on extraction zones and no significant effect on movement zone width particle size composition wide or narrow distributions and drawpoint width were found not to have a major role on drawzone geometry those conclusions were based on statistical analysis of experimental data to define the controlling parameters in isolated draw model theory principles were used to investigate within the physical modelling framework the possibility of directly scaling the geometry of the extraction zones which indicated that flow zones could be scaled in cohesionless materials under a set of assumptions a mechanistic model of isolated draw is also postulated from experimental data from observations of stresses and the imz s geometry

experimental investigation of mechanical properties of bedded salt rock abstract because of salt cavern utilization for liquid gas and solid waste storage salt rock mechanical properties are needed for assessments of facility stability and safety bedded salt deposits are widespread and used as much or more than diapiric salt bodies as storage facility hosts but experimental data on the mechanical properties of bedded salt rock with impurities are far less common than data available on relatively pure diapiric salt rocks through laboratory uniaxial and triaxial compression experiments on rock salt halite interlayers anhydrite and bedded composite specimens anhydrite halite and mudstone halite differences in mechanical properties of the various lithologies are explored in the composite specimens the weakest or the most deformable component governs the behavior also the properties of bedded composite lithology specimens tend to be in between the property ranges of the pure lithologies the elastic modulus of the bedded salt rock increases from 5 3 to 24 1 gpa with an increase in the confining stress from 0 to 15 mpa with some evidence of sample damage the ductile transition for halite at the strain rates used is at about 3 10 mpa with increasing 3 the anhydrite halite composite lithology deformation showed strain hardening and a strong trend to ductile behavior as the halite bands tended to dominate the behavior strain incompatibility effects exist along interfaces between creeping and non creeping phases in anhydrite halite composite lithologies mudstone halite rocks tended to be extremely weak compared with all other specimens