the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

equivalent discrete fracture networks for modelling fluid flow in highly fractured rock mass fracture flow is the dominant flow in many cases in a fractured rock mass which behaves more heterogeneous anisotropic and irregular than porous flow because of the complexity of the fracture networks rock mass with fracture networks is commonly represented by homogenized continuous models to reduce the impractical computational complexity in this paper a density reduced equivalent discrete fracture network e dfn method is proposed to simplify the original highly dense target dfn t dfn models an equivalent permeability factor is derived for the fracture sets in the simplified e dfn models a number of t dfns with different fracture patterns are stochastically generated and fluid flow is simulated in both t dfn and corresponding e dfn to test the effectiveness of the proposed method results show the permeability similarity of the two dfn systems and high accuracy of the proposed e dfn method the proposed method takes the advantage of permeability similarity of dfn systems and it significantly reduces the computational complexity and cost while the characteristics of the fluid flow such as heterogeneity irregularity and discontinuity in highly fractured rock mass are well retained because of the statistical equivalence of the two dfn systems monte carlo simulations can be used to optimize the equivalent permeability factor and to achieve more accurate and reliable results

the late devensian glaciation along the western margin of the cheshire shroshire iowland the glacial succession in the western part of the cheshire shropshire lowland records the advance coalescence and subsequent uncoupling of irish sea and welsh ice sheets during the late devensian stage during advance a discontinuous sheet of basal till was emplaced across the floor of the region by subglacial lodgement on retreat compression of the irish sea ice sheet against bedrock obstruction generated a zone of supraglacial sedimentation resulting in the creation of the wrexham ellesmere wem whitchurch moraine system and the formation of a wide range of sedimentary environments including ice marginal sandur troughs ice front alluvial fans proglacial ribbon sandur and subglacial ice contact and proglacial lakes the geometry of sedimentary units and their lithologic and geomorphic characteristics display spatially ordered patterns of sediment landform assemblage which show that the statigraphic succession is a response to rapidly changing depositional conditions at a retreating supraglacial ice margin punctuated by minor still stands and ice front oscillations

marine geophysical evidence for ice sheet extension and recession on the malin shelf new evidence for the western limits of the british irish ice sheet multibeam swath bathymetry and backscatter data collected as part of the irish national seabed survey and integrated mapping for the sustainable development of ireland s marine resource programmes is used to investigate the glacial geomorphology of the malin shelf the data provides direct evidence that the former british irish ice sheet was grounded as far out as the shelf break in this sector on more than one occasion drumlins on the outer shelf indicate the region was a zone of confluence where ice flowing onto the shelf from northwest ireland converged with ice flowing across the shelf from western scotland ice berg furrows located on the outer shelf record ice sheet break up by a calving event that may have been triggered by rising sea levels and northwest southeast aligned moraines indicate the ice retreated north eastwards across the shelf towards scotland the absence of direct dating control from moraines on the malin shelf precludes a definitive assessment of the timing of ice sheet events however consideration of the stratigraphic relationship of the glacial landforms on the shelf with age constrained ice sheet events in the wider region indicates that the former british irish ice sheet reached the outer shelf in this region on at least two occasions during the last cold stage moraines that have been overprinted by drumlins may possibly belong to an early phase of glaciation that occurred c 45 ka b this was subsequently followed by another episode of shelf extensive glaciation where converging ice flow from northwest ireland and western scotland reached the shelf break during the lgm that subsequently retreated from the shelf edge around 23 ka bp

fluvial development and the sediment regime of the lower calder ribble catchment northwest england in the lower reaches of the calder lancashire tributary of the ribble catchment northwest england five river terraces set into the surrounding glacial terrain have been mapped and their underlying sediments radiocarbon dated the earliest terrace t1 reflects sandur style deposition during deglaciation and it aggraded in a reach cut into glacial diamict and glaciolacustrine muds incision below t1 spanned the start of the holocene driven by a combination of reduced sediment supply under a stabilising landscape and lower base levels t2 had aggraded and was being abandoned by 4000 bc its formation latterly involving a period of comparative stability in terms of channel migration perhaps a function of extensive forest cover and sea levels reaching above present day levels the last 3000 years were marked by substantial changes in the sedimentary regime with increased and varying sediment supply driving cycles of cut and fill and greater lateral channel migration these changes coincided with the first widespread and substantial reductions in forest cover and a progression towards an agricultural landscape between the aggradation of terraces t3 and t4 there was a substantial increase in sediment supply which is broadly in keeping with the erosion history in the surrounding uplands this sediment slug appears to have induced a switch from highly sinuous meandering to lower sinuosity channels characterised by lateral scroll style migration late holocene vegetation changes particularly woodland removal driven by anthropogenic land pressure appear to have rendered the floodplain prone to channel migration and the landscape more susceptible to erosion

the last glacial maximum in the north sea basin micromorphological evidence of extensive glaciation despite a long history of investigation critical issues regarding the last glacial cycle in northwest europe remain unresolved one of these refers to the extent timing and dynamics of late devensian weichselian glaciation of the north sea basin and whether the british and scandinavian ice sheets were confluent at any time during this period this has been the result of the lack of the detailed sedimentological data required to reconstruct processes and environment of sediments recovered through coring this study presents the results of seismic sedimentological and micromorphological evidence used to reconstruct the depositional processes of regionally extensive seismic units across the north sea basin thin section micromorphology is used here to provide an effective means of discriminating between subglacial and glacimarine sediments from cored samples and deriving process based interpretations from sediment cores on the basis of micromorphology critical formations from the basin have been reinterpreted with consequent stratigraphic implications within the current stratigraphic understanding of the north sea basin a complex reconstruction is suggested with a minimum of three major glacial episodes inferred on at least two occasions during the weichselian devensian the british and scandinavian ice sheets were confluent in the central north sea whilst micromorphology can provide much greater confidence in the interpretation of late quaternary offshore stratigraphic sequences it is noted that a much better geochronology is required to resolve key stratigraphic issues between the onshore and offshore stratigraphic records copyright 2006 john wiley sons ltd

the relationship of the degree of interconnection to permeability in fracture networks the problem of determining the permeability of a rock mass containing a system of finite fractures is highly dependent on both the degree of interconnection between fractures and the heterogeneity of individual fracture characteristics this paper examines how degree of interconnection affects both magnitude and nature of the fracture permeability the interconnection between given fracture sets is a complex function of 1 fracture density i e the number of fractures per unit volume and 2 the fracture extent or size unfortunately neither the density nor the extent of fractures is easily determined from borehole data however fracture frequency can be directly measured in a borehole because it is simply the number of fractures intersected per unit length of the borehole the frequency is a measure of the product of fracture density and size because the probability of a fracture intersecting a borehole is proportional to this product the effect of the degree of interconnection was investigated by numerically simulating flow in fracture networks where fracture size and density varied inversely while the product of these two parameters was held fixed directional permeabilities of a number of such networks were determined and the hydraulic behavior of each fracture system was compared to that of an ideal porous medium the permeability of the rock matrix between the fractures was assumed to be low enough to be negligible the results show that as fracture length increases the degree of interconnection increases thus for a given fracture frequency as measured in a borehole the permeability of the system increases as fracture length is increased and density is proportionally decreased also fracture systems with shorter but more dense fractures behave less like porous media than do systems with longer but less dense fractures knowledge of fracture frequency and orientation alone is inadequate when determining permeability or deciding the important question of whether a given system behaves like a porous medium for many cases where these parameters can be measured in the borehole it is critical to know fracture length in order to predict the degree of fracture network interconnection however for certain cases where fractures are larger than some critical size it may not be necessary to know fracture lengths exactly

robust chronologies for landform development obtaining chronological control for geomorphological sequences can be problematic due to the fragmentary and non sequential nature of sediment and landform archives the robust analysis of 14c ages is often critical for the interpretation of these complicated sequences this paper demonstrates a robust methodology for the 14c dating of geomorphological sequences using a case study from the lower ribble valley northwest england the approach adopted incorporates using greater numbers of ages targeting plant macrofossils obtaining replicate measurements from single horizons to assess the extent of reworking and the use of bayesian approaches to test models of the relative order of events the extent of reworking of organic materials and space time dynamics of fluvial change means that it is critical that chronological control is sufficiently resourced with 14c measurements as a result bayesian approaches are increasingly important for the evaluation of large data sets assessing the conformability of relative order models informed by interpretation of the geomorphology can identify contexts or materials that are out of sequence and focuses attention on problem materials reworking and errors in interpretation outlier ages these relative order models provide a framework for the interrogation of sequences and a means for securing probability based age estimates for events that occur between dated contexts this approach has potential value in constraining the sequence of geomorphological development at scales that vary from individual sites to a catchment or region furthering understanding of forcing and change in geomorphological systems copyright 2008 john wiley sons ltd

a continuum approach for estimating permeability in naturally fractured rocks abstract many models for predicting permeability in rock masses have been proposed however most of these models do not relate the conductivity closure behavior to fracture geometry parameters and geostati stresses in this study an attempt is made to estimate the permeability tensor as well as the relation between permeability and depth on naturally jointed rocks the new model includes effects of hydromechanical coupling normal closure and fracture geometry the fracture tensor related only to the fracture geometry aperture size and orientation is introduced to formulate a permeability tensor fracture aperture estimated by a simple field investigations is defined as a function of joint roughness coefficient jrc joint wall compression strength jcs and geostatic stress an actual rock mass of jointed andesite rock on the lan yu site taiwan was studied to predict the permeability and conducting aperture with depth through a comparison of the presented model with three existing models 1 the simple one parallel fracture set model 2 the three orthogonal fracture set model and 3 the random disc fracture model it was shown that permeability depth relations for the three orthogonal fracture set model and the new model are almost the same

morphological and sedimentary responses to ice mass interaction during the last deglaciation during decline of the last british irish ice sheet biis down wasting of ice meant that local sources played a larger role in regulating ice flow dynamics and driving the sediment and landform record at the last glacial maximum glaciers in north western england interacted with an irish sea ice stream isis occupying the eastern irish sea basin isb and advanced as a unified ice mass during a retreat constrained to 21 17 3 ka the sediment landform assemblages lain down reflect the progressive unzipping of the ice masses oscillations of the ice margin during retreat and then rapid wastage and disintegration evacuation of ice from the ribble valley and lancashire occurred first while the isis occupied the isb to the west creating ice dammed lakes deglaciation complete after 18 6 17 3 ka was rapid 50 25 m a 1 but slower than rates identified for the western isis 550 100 m a 1 the slower pace is interpreted as reflecting the lack of a calving margin and the decline of a terrestrial grounded glacier ice marginal oscillations during retreat were probably forced by ice sheet dynamics rather than climatic variation these data demonstrate that large grounded glaciers can display complex uncoupling and realignment during deglaciation with asynchronous behaviour between adjacent ice lobes generating complex landform records

seepage analysis in a fractured rock mass the upper reservoir of pushihe pumped storage power station in china abstract a numerical simulation model of seepage in a fractured rock mass was constructed based on the hydrogeological conditions of the upper reservoir of pushihe pumped storage power station in china which is currently under construction in addition an analysis was conducted of groundwater movement in the reservoir rock system and calculations were made of the leakage rate and distribution of seepage under various operating conditions during the simulation the most important but most difficult problem was the determination of the hydraulic conductivity tensor of a fractured rock mass this paper modifies the method of determining the hydraulic conductivity tensor so that it not only reflects the permeability characteristics of the fractured rock mass but also improves the calculation precision the principal values and directions of the hydraulic conductivity tensor were first determined with a statistical method based on measurements of the spatial spreading of the fractures and were then modified using estimates of isotropic hydraulic conductivity that were calculated by the babushkin formula according to the water permeability rate from a field water pressure test and finally were verified using an inversion analysis with a mathematical model the simulation results show that the total leakage rate is estimated to be 5832 92 m3 d under the operating conditions of a normal pool level and no anti seepage treatment results of the analysis of various seepage control scenarios suggest that the preferred scenario is grouting curtain only in the dam foundation with the curtain depth 5 m below the line where the water permeability rate equals 3 lu thus reducing the leakage rate by 3571 27 m3 d the above results provide a basis and reference for designing seepage control structures and facilitating decision making

structural evolution triggers a dynamic reduction in active glacier length during rapid retreat evidence from falljokull se iceland over the past two decades iceland s glaciers have been undergoing a phase of accelerated retreat set against a backdrop of warmer summers and milder winters this paper demonstrates how the dynamics of a steep outlet glacier in maritime se iceland have changed as it adjusts to recent significant changes in mass balance geomorphological evidence from falljokull a high mass turnover temperate glacier clearly shows that between 1990 and 2004 the ice front was undergoing active retreat resulting in seasonal oscillations of its margin however in 2004 2006 this glacier crossed an important dynamic threshold and effectively reduced its active length by abandoning its lower reaches to passive retreat processes a combination of ice surface structural measurements with radar lidar and differential global navigation satellite systems data are used to show that the upper active section of falljokull is still flowing forward but has become detached from and is being thrust over its stagnant lower section the reduction in the active length of falljokull over the last several years has allowed it to rapidly reequilibrate to regional snowline rise in se iceland over the past two decades it is possible that other steep mountain glaciers around the world may respond in a similar way to significant changes in their mass balance rapidly adjusting their active length in response to recent atmospheric warming

modeling spatial fracture intensity as a control on flow in fractured rock spatial fracture intensity p 32 fracture area by volume is an important characteristic of a jointed rock mass although it can hardly ever be measured p 32 can be modeled based on available geological information such as spatial data of the fracture network flow in a mass composed of low permeability hard rock is controlled by joints and fractures in this article models were developed from a geological data set of fractured andesite in lanyu island taiwan where a site is investigated for possible disposal of low level and intermediate level radionuclide waste three different types of conceptual models of spatial fracture intensity distribution were generated an enhanced baecher s model ebm a levy lee fractal model llfm and a nearest neighborhood model nnm modeling was conducted on a 10 10 10 m synthetic fractured block simulated flow was forced by a 1 hydraulic gradient between two vertical x z faces of the cube from north to south with other boundaries set to no flow conditions resulting flow vectors are very sensitive to spatial fracture intensity p 32 flow velocity increases with higher fracture intensity p 32 r squared values of regression analysis for the variables velocity v v max and fracture intensity p 32 are 0 293 0 353 and 0 408 in linear fit and 0 028 0 08 and 0 084 in power fit higher r 2 values are positively linked with structural features but the relation between velocity and fracture intensity is non linear possible flow channels are identified by stream traces in the levy leefractal model

a large arthropod trackway from the gaspe sandstone group middle devonian of eastern canada a large arthropod trackway from the cap aux os member of the battery point formation gaspe sandstone group middle devonian from the baie de gaspe eastern canada is described and assigned to the ichnotaxon palmichnium paleohelcura antarcticum gevers et al 1971 a large stylonurid eurypterid or scorpion is considered the most likely producer a shallow water marginal fluvial environment is inferred as the setting the animal making a transition from walking to swimming along the course of the trackway resume la trace d une piste d un grand arthropode dans le membre de cap aux os de la formation de battery point groupe gres de gaspe devonien moyen dans la baie de gaspe dans l est du canada est decrite et assignee a l ichnotaxon palmichnium paleohelcura antarcticum gevers et al 1971 il semble que la trace ait ete produite par un grand eurypteride stylonuride ou un scorpion on presume que c est dans un environnement fluviatile marginal sous une mince tranche d eau que l animal a creuse cette empreinte en marchant vers un lieu de nage traduit par la redaction braddy and milner 1122 a large arthropod trackway was discovered in 1988 milner 1992 along the northern shore of the baie de gaspe grid reference 20u lk 993112 approximately 5 km east of the town of gaspe near the village of cap aux os on the forillon peninsula in the province of quebec eastern can ada fig 1 the locality is within the cap aux os member of the battery point formation gaspe sandstone group approximately 750 m above the base of the formation in the lower part of unit 4 lawrence and rust 1988 fig 7 the battery point formation comprises a coarsening upwards clastic sequence ranging in age from early emsian to early eifelian middle devonian based on abundant spores oc curring throughout the formation mcgregor 1977 the cap aux os member approximately 640 m thick consists mainly of interbedded sandstones and mudstones which were deposited in a meandering fluvial system the prevail ing palaeocurrent direction varied from the north northwest to the west northwest lawrence and rust 1988 sand was deposited in the river channels and finer grained silts and muds on the extensive vegetated floodplain lawrence 1986

extent and timing of the last glacial maximum lgm in britain and ireland a review the last glacial maximum lgm of marine isotope stage mis 2 is defined here as the period either of maximum global ice volume or in which major ice sheets reached their maximum extent both definitions lack clarity as there is no reason to suppose that maximum volumes or limits were reached simultaneously at either all ice sheets or around the margins of individual ice sheets here we review the traditional terrestrial limits of the biis british irish ice sheet examine developments in understanding the offshore record and attempt a redefinition of the extent and timing of the mis 2 maximum as a working chronological model the build up of the biis is assigned to after 35 32 ka the maximum to the period 27 21 ka and a more limited readvance after 19 ka as marginal oscillations driven by ice sheet dynamics appear to have characterised much of the advance and especially the retreat of the biis caution should be exercised in assigning climatic significance to the many identified ice limits or still stands while much of the terrestrial limit in britain remains relatively unaltered significant revision is required offshore around britain and ireland to portray an extensive ice advance to the shelf edge and a period when the biis was conjoined with the adjacent fenno scandinavian ice sheet although there appears to be a broad synchrony between the biis and other major ice sheets local controls have produced some variation in the timing of advance to and retreat from maximum limits for particular ice streams or lobes but much of the offshore limit remains very poorly age constrained consequently a key objective in future research should be to improve and refine the chronological control for all portions of the maximum margin of the biis and its subsequent retreat stages copyright 2010 john wiley sons ltd

glaciology of the british isles ice sheet during the last glacial cycle form flow streams and lobes abstract the last ice sheet over the british isles together with other mid latitude pleistocene ice sheets and in contrast to the modern ice sheets of greenland and antarctica had a relatively low profile low summit elevation and extensive elongated lobes at its margin a thermo mechanically coupled numerical ice sheet model driven by a proxy climate has been used to explore the properties that would have permitted these characteristics to develop the approach the key to quantitative palaeoglaciology is to determine the boundary conditions that permit the simulated ice sheet to mimic the evolution of the real ice sheet through the last glacial cycle simulations show how a british ice sheet may have been confluent with a scandinavian ice sheet during some parts of its history and how unforced periodic and asynchronous oscillations could occur in different parts of its margins marginal lobes are a reflection of streaming within the ice sheet such streams can be ephemeral dynamic streams located because of ice sheet properties or fixed streams whose location is determined by bed properties the simulations that best satisfy constraints of extent elevation and relative sea levels are those with major fixed streams that strongly draw down the ice sheet surface in these the core upland areas of the ice sheet were cold based at the last glacial maximum basal streaming velocities were between 500 and 1000 ma 1 compared with surface velocities of 10 50 ma 1 in inter stream zones shear stresses were as low as 15 25 kpa in streams compared with 70 110 kpa in upland areas and 60 84 of the ice flux was delivered to the margin via streams

geomorphological criteria for identifying pleistocene ice streams ice streams are critical regulatory mechanisms in contemporary ice sheets it has been inferred that they also had a significant effect on the dynamics of former ice sheets subsequently many people have invoked their widespread occurrence from a variety of formerly glaciated areas hypothesised locations however have often outweighed meaningful evidence this paper addresses the problem using the characteristics of contemporary ice streams as a basis for their identification from former ice sheet beds a convergence of knowledge gained from contemporary ice stream research coupled with theories of glacial geomorphology allows several geomorphological criteria to be identified as suggestive signatures of ice stream activity it is envisaged that the geomorphological criteria developed here will introduce a more objective approach to the study of former ice streams the criteria are used to construct conceptual land system models of the beds of former ice streams and it is hoped such models can provide an observational template upon which hypotheses of former ice streams can be better based

scale up of two dimensional conductivity tensor for heterogenous fracture networks abstract an approach is developed to scale up the two dimensional conductivity tensor for highly heterogenous fracture networks based on a numerical modelling approach that was proposed previously by zhang et al j rock mech min sci 33 17 37 1996 in that approach it was assumed that the fractured rock mass was statistically uniform and only a unit square of sample rock was needed to work out the conductivity tensor hence its application was limited where the heterogenous characteristics of a fracture network was not negligible in the present paper the local conductivity tensors both magnitude and direction either calculated based on small fracture networks or samples measured on separate exposures are scaled up to estimate the overall nature of conductivity for a relatively large region the approach developed is used to estimate the two dimensional conductivity tensor of naturally fractured rock masses for two types of fracture networks constant aperture and variable aperture under stress the effects of sample number and sample size of local sub areas were examined against the totally sampled area finally field data were used to predict the overall conductivity tensor of a large region based on four fracture networks sampled on separate exposures within the region

radiocarbon constraints on the age of the maximum advance of the british irish ice sheet in the celtic sea reconstructions of the british irish ice sheet biis during the last glacial maximum lgm in the celtic sea and southern ireland have been hampered by a paucity of well dated stratigraphic records as a result the timing of the last advance of the largest outlet of the biis the irish sea ice stream to its maximum limit in the celtic sea has been variously proposed as being pre last glaciation early devensian and lgm the irish sea till was deposited by the irish sea ice stream during its last advance into the celtic sea we present 26 stratigraphically well constrained new ams radiocarbon dates on glacially transported marine shells from the irish sea till in southern ireland which constrain the maximum age of this advance the youngest of these dates indicate that the biis advanced to its overall maximum limit in the celtic sea after 26 000 20 000 14c yr bp thus during the last glaciation the most extensive phase of biis growth therefore appears to have occurred during the lgm at least along the celtic sea and irish margins these data further demonstrate that the uppermost inland glacial tills from the area of supposed older drift in southern ireland a region previously regarded as having been unglaciated during the lgm also date from the last glaciation thus most of southern ireland was ice covered at the lgm advance of the biis to its maximum southern limit in the celtic sea may have been a short lived glaciodynamic response facilitated by subglacial bed conditions rather than a steady state response to climate forcing alone

evaluation of the representative elementary volume rev of a fractured geothermal sandstone reservoir the objective of this study is to evaluate a representative elementary volume rev in a fractured geothermal sandstone reservoir in germany using the discrete fracture network dfn model approach due to the lack of in situ data from the deep geothermal reservoir field measurements of outcrop reservoir analogues were conducted to get a quantitative description of the dfn field measurements reveal that the geometry of the dfn is largely influenced by the lithological layering e g relationship between joint spacing and bed thickness thus dfn models have to be completed individually for each layer since each bed is distinct compared to its neighbouring beds various dfns were generated using statistical derived fracture input data the two dimensional universal distinct element code udec was used for fracture flow simulations in order to determine the minimum rev the equivalent average conductivity tensors were obtained with increasing block size plots of conductivity tensor coefficients versus block size exhibit only minor variation of the hydraulic properties with increasing block size hence an rev size of 10 m 10 m could be determined for all studied stochastically derived discrete fracture networks

a critical review of the glaciomarine model for irish sea deglaciation evidence from southern britain the celtic shelf and adjacent continental slope in support of their glaciomarine model for the deglaciation of the irish sea basin eyles and mccabe cited the occurrence of distal glaciomarine mud drapes onshore in the isles of scilly and north devon and of arctic beach face gravels and sands around the shores of the celtic sea glacial and sea level data from the southern part of the irish sea in the terminal zone of the ice stream and the adjacent continental slope are reviewed here to test this aspect of the model the suggestion that the glacial sequences of both the isles of scilly and fremington in north devon are glaciomarine mud drapes is rejected an actively calving tidewater margin only occurred early in the deglacial sequence close to the terminal zone in the south central celtic sea relative sea levels were lower and therefore glacio isostatic depression less than envisaged in the glaciomarine model geochronological sedimentological and biostratigraphical data indicate that the raised beach sequences around the shores of the celtic sea and english channel were deposited at or during regression soon after interglacial eustatic highstands evidence for ice rafting at a time of high relative sea levels is restricted to a phase s earlier than the late devensian these data indicate that the raised beach sequences have no bearing on the style of irish sea deglaciation copyright 2001 john wiley sons ltd

ice marginal depositional responses to readvance episodes in the late devensian deglaciation of the isle of man abstract remapping of the quaternary geology of the isle of man and consequent revision of the stratigraphic succession identifies three glacigenic formations each separated by a major unconformity the oldest formation the shellag represents an extensive ice advance beyond the island limits to the last glacial maximum lgm the overlying formation the orrisdale represents a major readvance episode during retreat from the lgm and is associated with the construction of the bride moraine and the deposition of extensive proglacial subaqeous sediment examination of the sedimentology and micropalaeontology of these sediments indicates that the water body was most likely lacustrine and not marine application of sequence stratigraphy to the overlying jurby formation identifies evidence for three further phases of readvance each off lapping one another into the margin of the lake basin via a complex system of ice contact subaqueous fans and outwash fan deltas the jurby formation is dated by organic sediments overlying it as older than 18 5 14 4 kyr bp and provides an ice marginal correlative for heinrich event 1 readvance limits identified 50 km to the west in eastern ireland

accelerating ice loss from the fastest greenland and antarctic glaciers 1 ice discharge from the fastest glaciers draining the greenland and antarctic ice sheets jakobshavn isbrae ji and pine island glacier pig continues to increase and is now more than double that needed to balance snowfall in their catchment basins velocity increase probably resulted from decreased buttressing from thinning and for ji breakup of their floating ice tongues and from reduced basal drag as grounding lines on both glaciers retreat ji flows directly into the ocean as it becomes afloat and here creep rates are proportional to the cube of bed depth rapid thinning of the pig ice shelf increases the likelihood of its breakup and subsequent rapid increase in discharge velocity results from a simple model indicate that ji velocities should almost double to 20 km a 1 by 2015 with velocities on pig increasing to 10 km a 1 after breakup of its ice shelf these high velocities would probably be sustained over many decades as the glaciers retreat within their long very deep troughs resulting sea level rise would average about 1 5 mm a 1

widespread rapid grounding line retreat of pine island thwaites smith and kohler glaciers west antarctica from 1992 to 2011 we measure the grounding line retreat of glaciers draining the amundsen sea sector of west antarctica using earth remote sensing ers 1 2 satellite radar interferometry from 1992 to 2011 pine island glacier retreated 31 km at its center with most retreat in 2005 2009 when the glacier ungrounded from its ice plain thwaites glacier retreated 14 km along its fast flow core and 1 to 9 km along the sides haynes glacier retreated 10 km along its flanks smith kohler glaciers retreated the most 35 km along its ice plain and its ice shelf pinning points are vanishing these rapid retreats proceed along regions of retrograde bed elevation mapped at a high spatial resolution using a mass conservation technique that removes residual ambiguities from prior mappings upstream of the 2011 grounding line positions we find no major bed obstacle that would prevent the glaciers from further retreat and draw down the entire basin 2014 american geophysical union all rights reserved

ice sheet retreat dynamics inferred from glacial morphology of the central pine island bay trough west antarctica abstract pine island glacier drains portions of the west antarctic ice sheet into the amundsen sea during the last glacial maximum the glacier extended nearly 500 km from its present location onto the outer continental shelf unusually restricted sea ice cover during the austral summer of 2010 allowed for a systematic multibeam swath bathymetric and chirp sonar survey of the mid shelf section of pine island trough the mapped glacial landforms reveal new information about the paleo pine island ice stream s dynamic retreat from the mid shelf area and confirm previous suggestion of a retreat in distinct steps the periods of grounding line stability during the overall retreat phase are marked by sediment accumulations i e grounding zone wedges these wedges are here mapped in sufficient detail to characterize spatial dimensions and estimate the volume of deposited sediment considering a range of sediment flux rates from the paleo pine island ice stream we estimate that the largest and most clearly defined grounding zone wedge located at about 73 s in the surveyed area took between 600 and 2000 years to form the ice stream retreated landward of this wedge before 12 3 cal ka bp the swath bathymetric imagery of landforms in pine island trough includes glacial features that suggest that retreat between periods of grounding line stability may be associated with episodes of ice shelf break up the depths of grounding line wedges decrease in a landward direction from 740 to 670 m and record elevation of the grounding line as it stepped landward in all the grounding line elevation varied by only 80 m over a distance of just over 100 km implying a low ice sheet profile during retreat finally we revisited seismic reflection profile nb9902 acquired along pine island trough in 1999 in combination with the newly acquired swath bathymetric imagery from 2010 together these data show that the ice stream paused during its retreat to form grounding zone wedges at an area in central pine island trough where a high in dipping bedrock strata exists and the glacial trough is narrow forming a bathymetric bottle neck

flow pattern evolution of the last british ice sheet we present a 10 stage reconstruction of the evolution in ice flow patterns of the last british ice sheet from build up to demise derived from geomorphological evidence 100 flowsets identified in the subglacial bedform record drumlins mega scale glacial lineations and ribbed moraine are combined with ancillary evidence erratic transport paths absolute dates and a semi independently reconstructed retreat pattern to define flow patterns ice divides and ice sheet margins during build up maximum glaciation and retreat overprinting and cross cutting of landform assemblages are used to define the relative chronology of flow patterns and a tentative absolute chronology is presented based on a collation of available dates for ice advance and retreat the ice flow configuration of the last british ice sheet was not static some ice divides were remarkably stable persisting through multiple stages of the ice sheet evolution whereas others were transient features existing for a short time and or shifting in position 10s km the 10 reconstructed stages of ice sheet geometry capture two main modes of operation first as an integrated ice sheet with a broadly n s orientated ice divide and second as a multi domed ice sheet orientated parallel with the shelf edge a thick integrated ice sheet developed as ice expanded out of source areas in scotland to envelop southerly ice caps in northern england and wales and connect with the irish ice sheet to the west and the scandinavian ice sheet across the north sea following break up of ice over the north sea ice streaming probably drove mass loss and ice sheet thinning to create a more complex divide structure where ice flow patterns were largely controlled by the form of the underlying topography ice surface lowering occurred before separation of and retreat to multiple ice centres centred over high ground we consider this 10 stage reconstruction of the evolution in ice sheet configuration to be the simplest palaeo glaciological interpretation of the flowsets identified from the geomorphological record and their relative timing this empirically based reconstruction of flow pattern geometry provides a framework for more detailed local and regional studies and numerical modelling to provide robust explanations of the observed changes in ice sheet structure in terms of climate and glacial dynamics as a minimum numerical model outputs should be able to reproduce the identified flowset patterns in space and satisfy their chronological order

structural and depositional evidence for repeated ice marginal oscillation along the eastern margin of the late devensian irish sea ice stream abstract late devensian glacigenic sediments and landforms along the north west coast of wales document the advance and subsequent retreat of the eastern margin of an irish sea ice stream that met coalesced and ultimately uncoupled from ice radiating outwards from the adjacent welsh ice cap centred over snowdonia across the boundary between the two former ice masses is a set of sediment landform assemblages that reflect rapidly changing erosional and depositional conditions during ice interaction from the inner part of the ice stream the assemblages range outwards from a subglacial depositional assemblage characterised by drumlin swarms through a subglacial erosional assemblage marked by prominent bedrock scours and large subglacial rock channels through an ice marginal assemblage identified by closely spaced glaciotectonised push moraines and intervening marginal sandur troughs into a freely expanding proglacial sandur and lacustrine delta assemblage the ice marginal assemblage provides evidence for numerous oscillatory episodes during retreat and at least 20 ice marginal limits can be identified at least 11 of these display multiple criteria for identifying readvance and in the ideal case is characterised by a moraine form built by localised tectonic stacking of diamict to the rear fronted by a clastic wedge of ice front alluvial fan gravel and intercalated flow till the distribution of sediment landform assemblages suggests a highly dynamic convergent ice stream flow pattern with high ice velocity a sharply delineated lateral shear margin pervasive ice marginal glaciotectonic deformation and a tightly focused ice marginal sediment delivery system all signature characteristics of contemporary ice streams

a review of existing methods used to evaluate the hydraulic conductivity of a fractured rock mass we review the existing methods for evaluating the hydraulic conductivity of a rock mass rock mass permeability may be assessed using empirical analytical and numerical approaches empirical methods use data from in situ field tests to derive the relationship between depth and permeability by applying a curve fitting method and establishing the relationship between hydraulic conductivity and a geological index analytical methods rely on darcy and cubic laws to estimate the permeability of a rock mass by taking into account the geometrical characteristics of the joint sets analytical equations of the flow rate into underground excavations are also developed by solving the laplace equation for homogeneous and isotropic aquifers under various boundary conditions numerical modeling can evaluate the outcomes of both empirical and analytical approaches and vice versa and can provide a sensitivity analysis of the parameters that affect rock mass permeability the importance of stress and joint set characteristics is often investigated via numerical modeling as are the scale effect and directional permeability in this review paper we provide a comprehensive review of these approaches for studying rock mass permeability we summarize the advantages and disadvantages of existing methods and highlight potential future research directions

a continuum approach for modeling mass transport in fractured media a continuum approach has been developed for modeling mass transport in fractured rocks it involves a new application of a particle tracking method in which physical transport is simulated in terms of velocity and the variations in velocity statistics describing the particle motion come from observing the actual pattern of particle motion in a discrete subdomain this subdomain is a small but representative piece of the much larger continuum in effect particle motion in the continuum is forced to mimic that in the discrete subdomain the model successfully duplicates patterns of anisotropic dispersion predicted by de josselin de jong 1972 and breakthrough curves simulated with a discrete fracture model applications demonstrate that the de josselin de jong approach for estimating dispersivities for idealized networks cannot generally be applied to networks formed from sets of finite irregularly spaced fractures in addition this study reinforces indications from earlier studies about the complexity of dispersion in fractured media factors that contribute to spreading in the major and minor principal directions change with the orientation of the network relative to the mean hydraulic gradient

submarine glacial landforms record late pleistocene ice sheet dynamics inner hebrides scotland we use 7000 km2 of high resolution swath bathymetry data to describe and map the submarine glacial geomorphology and reconstruct late pleistocene ice sheet flow configurations and retreat dynamics within the inner hebrides western scotland frequently dominated by outcrops of structurally complex bedrock the seabed also comprises numerous assemblages of well preserved glacigenic landforms typical of grounded ice sheet flow and punctuated ice margin retreat the occurrence and character of the glacially streamlined landforms is controlled in part by the shallow geology and topography however these factors alone cannot account for the location orientation and configuration of the observed landforms we attribute the distribution of these elongate streamlined landforms to the onset zone of the former hebrides ice stream his part of a major ice stream system that drained 5 10 of the last british irish ice sheet biis we suggest this geomorphic signature represents the transition from slow sheet flow to streaming flow as ice accelerated out from an environment characterized by numerous bedrock obstacles e g islands headlands towards the smooth sediment dominated shelf the majority of streamlined landforms associated with the his indicate ice sheet flow to the southwest with regional scale topography clearly playing a major role in governing the configuration of flow during maximal glacial conditions 29 23 ka we infer that the his merged with the north channel malin shelf ice stream to form a composite ice stream system that ultimately reached the continental shelf edge at the barra donegal trough mouth fan taken collectively however the pattern of landforms now preserved at seabed e g convergent flow indicators cross cutting flow sets is more indicative of a thinning ice mass undergoing reorganization during overall ice sheet retreat during latter stages of late weischselian glaciation suites of moraines overprinting the streamlined landforms suggest partial stabilization of the his prior to the ice sheet retreating to more isolated topographically confined troughs and basins retreat from the shelf towards and back into the inner hebrides may have been rapid due the prevalence of overdeepened troughs within the near shore fjord like troughs and deeps basin aligned streamlined landforms indicate the subsequent flow of thinner topographically partitioned ice masses and overprinted moraines record further ice margin retreat potentially along tide water margins this work provides the first geomorphological constraints for this large marine influenced sector of the former biis we also shed new light on the glacial geomorphic record found at the transition from terrestrial to marine continental shelf settings and examine the interplay between substrate geology bed topography bathymetry and grounding line positions relationships which are important for characterizing contemporary marine ice sheet margins

drumlin evolution and ice sheet oscillations along the ne atlantic margin donegal bay western ireland abstract satellite imagery of donegal bay northwestern ireland reveals two streamlined subglacial bedform sets produced during the late devensian glaciation ca 22 000 15 000 yrs b p the first bedform set trends northeast southwest and records fast ice flow from inland ice domes onto the eastern atlantic continental shelf the second bedform set trending east west crosscuts and partially reorientates the first morphological and sedimentary evidence show that the second set corresponds to the last phase of fast ice flow drumlinization in northwestern ireland morphological characteristics of the donegal bay drumlin field and sedimentary characteristics of the mullinasole drumlin donegal bay support a two stage interpretation of drumlin evolution these are the following 1 deposition of glaciomarine mud and diamict facies at a tidewater glacier margin stratified diamicts record debris flow events and sediment reworking this facies sequence is erosionally truncated 2 deposition of subglacial diamict and sand facies recording ice readvance and drumlinization drumlinization sediment streamlining reflects ice mass balance destabilization episodic fast ice flow and ice marginal oscillation and may be correlated with millennial time scale climate changes in the circum north atlantic

application of fracture network model with crack permeability tensor on flow and transport in fractured rock article i nfo very efficient and practical models that use a crack tensor in terms of fracture geometry parameters for field rock mass are proposed a framework of the crack tensor approach combined with the identifying fracture controlled characteristics was successively used in a hypothetical hydro geological field for determining the dynamics of flow and transport of nuclides in fractured rock the modeling results and site specific data of lan yu island in taiwan reveal the characteristics associated with the geometry of fracture networks under the prescribed boundaries the simulated fracture networks were transformed into a grid based simulation procedure under consideration of the delaying effect in matrix owing to particle migration synthetic flow results indicate that the flowing vector is very sensitive to fracture intensity p32 high fracture intensity leads to high velocity heterogeneity generated by fractures field will result in the shortest and the longest transmission distance of 12 fold difference while taking into consideration of the ingrowth decay transport the plumes of the daughter product were relatively tortuous and anomalous to predict

sediment transmission and storage the implications for reconstructing landform development the late holocene last 3000 years development of the lower ribble valley northwest england displays evidence for a complex response to a sediment recharge event forced by land use change induced increases in erosion and sediment delivery the deposition of fluvial sediments during the late holocene was restricted to a series of reaches or depocenters separated by zones with no sediment accumulation constrained by older glacial and fluvial terrain apparent reach wide correlations of fluvial terraces break down under the scrutiny applied by comprehensive and extensive radiocarbon control bayesian testing of relative order models show that large scale geomorphological changes e g the progression from one terrace level to another were time transgressive between different depocenters the different histories of sediment delivery and storage are probably a function of local and process scale variations in these depocenters and reflect dis connectivity relationships within a reach in propagating a basin scale change superslug in the sediment regime disconnectivity in the depositional regime through a fluvial reach limits what we can reconstruct in terms of sediment budgets but radiocarbon dating of multiple palaeochannels offers considerable potential for landform based research to uncover rates of change within individual depocenters copyright 2009 john wiley sons ltd

pattern and timing of retreat of the last british irish ice sheet during the last glacial the ice sheet that subsumed most of britain ireland and the north sea attained its maximum extent by 27 ka bp and with an ice volume sufficient to raise global sea level by ca 2 5 m when it melted we reconstruct the demise of this british irish ice sheet biis and present palaeo glaciological maps of retreat stages between 27 and 15 ka bp the whole land area was investigated using remote sensing data and we present maps of moraines meltwater channels eskers and drumlins and a methodology of how to interpret and bring them together for the continental shelf numerous large moraines were discovered recording an extensive pattern of retreat stretching from sw ireland to the shetland isles from an integration of this new mapping of glacial geomorphology 26 000 landforms with previously published evidence compiled in the britice database we derive a pattern of retreat for the whole biis we review and compile relevant dates 881 examples that constrain the timing of retreat all data are held within a geographic information system gis and are deciphered to produce a best estimate of the combined pattern and timing of retreat pattern information reveals an ice sheet mainly comprised of a shelf parallel configuration from sw ireland to ne scotland but it spread far enough to the south to incorporate outlying ice domes over wales the lake district and kerry final disintegration was into a number of separate ice caps rather than reduction as a single mass and paradoxically retreat was not always back to high ground by 23 ka bp ice withdrew along its northern boundaries at the same time as the southern margins were expanding including transient ice streaming down the irish sea and advances of lobes in the cheshire basin vale of york and east coast of england ice divides migrated south by 19 ka the ice sheet was in crisis with widespread marine based ice losses particularly in the northern north sea and the irish sea considerable dynamic thinning occurred during this phase final collapse of all marine sectors occurred by 17 ka bp and with most margins beginning to back step onshore disintegration of the north sea ice bridge between britain and norway remains loosely constrained in time but the possibility of catastrophic collapse of this sector is highlighted the north channel and irish sea ice streams had finally cleaved the ice sheet into separate irish and scottish ice sheets by 16 ka bp rates of ice loss were found to vary widely over space and time e g 65 260 km3 per year the role of ice streams and calving losses of marine based sectors are examined retreat rates of up to ca 150 ma 1 were found for some ice stream margins that large parts 2 3 of the biis were marine based drained by ice streams and possibly with fringing ice shelves in places makes it a useful analogue for the west antarctic ice sheet wais this is especially so because the biis deglaciated in response to rising temperatures and a rising sea level driven by melting of other ice masses which are the current forcings that might cause collapse of the wais our reconstruction when viewed from the opposite perspective documents when fresh land became exposed for exploitation by plants animals and man and records for how long such land has been available for soil and geochemical development and ecological succession

estimation of permeability for the rock mass around the shiplocks of the three gorges project china changes in the bulk permeability of the fractured rock mass around the shiplocks of the three gorges project china during excavation have been investigated using a numerical modelling technique the numerical model took into account both the effect of fractures on the in situ bulk permeability and the increase in permeability resulting from the stress relief and opening of the fractures caused by excavation fracture patterns were estimated on the basis of field exposures in three orthogonal planes the numerical model was calibrated for the in situ condition by varying the fracture stiffness until a close match in terms of both magnitude and direction was obtained with the equivalent permeabilities estimated on the basis of field pumping tests excavation of the shiplocks both with and without the use of temporary supports was modelled and the resulting changes in stress and permeability in the surrounding rock mass calculated in both cases the opening of fractures subparallel to the shiplock channels resulted in an increase in the permeability of the ground but when the vertical sidewalls were supported during excavation the increase in permeability was less marked the results of the analyses highlight the effects of engineering activities on the permeability of fractured rock masses and demonstrate that these effects can be controlled through the judicious choice of construction techniques and procedures

sedimentation at the margins of a late pleistocene ice lobe terminating in shallow marine environments dundalk bay eastern ireland late pleistocene morainic sequences around dundalk bay eastern ireland were deposited in a variety of shallow glaciomarine environments at the margins of a grounded ice lobe the deposits are essentially ice proximal delta fan and apron sequences and are divided into two lithofacies associations lithofacies association 1 occurs as a series of morainal banks formed at the southern margin of the ice lobe in a body of water open to influences from the irish sea the morainal banks consist mainly of diamictic muds deposited from turbid plumes and by ice rafting with minor occurrences of turbidites cross bedded gravels subaqueous outwash and massive boulder gravels high density debris flows lithofacies association 2 was deposited in a narrow arm of the sea at the north eastern margin of the ice lobe the deposits consist mainly of a series of coalescing ice proximal gilbert type fan deltas which are interbedded distally with tabular and lens shaped subaqueous deposits the latter are mainly ice rafted diamictons debris flow deposits and subaqueous sands and gravels both lithofacies associations are draped by diamictons formed by a combination of rain out debris flow and traction current activity at a few localities the upper parts of the sequence have been sheared by minor oscillations of the ice sheet margin these sequences form part of an extensive belt of glaciomarine deposits which border the drumlin swarms of east central ireland lithostratigraphic variability is partially related to the arrival of large volumes of debris at the ice lobe margin when the main lowland ice sheet surged during drumlin formation complex depositional continua of this type lack any major erosional breaks and should not be used either as climatic proxies or for stratigraphic correlations

a model of subaqueous sedimentation at the margin of the late midlandian irish ice sheet connemara ireland and its implications for regionally high isostatic sea levels abstract the geomorphology and sedimentology of a series of late midlandian glacigenic sites in connemara western ireland are described and a set of commonly occurring sedimentary assemblages identified these form components of a simple model of ice contact subaqueous sedimentation involving progressive down current transition from subglacial esker tunnel fill through proximal tunnel mouth fans proximal and distal subaqueous fans into basin floor sediments in two of the sites aggradation to the water line passes into fan delta topsets and foresets all sites abut into inferred water bodies to their west and imply minimum water surface heights of between 35 and 65 m irish od or in the case of the two deltaic sites shoreline heights of between 75 and 80 m these high water levels very close to and facing directly into the immediately adjacent open atlantic ocean are difficult to explain as ice dammed glaciolacustrine water bodies without invoking improbable ice sheet marginal geometries they may however be explained as a set of successive fjord head grounding line depositional systems that trace temporary still stands in the phased retreat of the irish ice sheet from its offshore maximum this possibility not yet confirmed by the discovery of in situ marine fauna implies a degree of late midlandian isostatic depression and subsequent response unexplained by currently applied crustal response models but supported by previously constructed glacio sedimentary models

palaeoglaciology of the welsh sector of the british irish ice sheet this palaeoglaciological reconstruction based on the distribution of glacial lineations interpreted from satellite imagery considers the extent thickness and dynamics of the welsh ice cap and its interaction with the british irish ice sheet two major ice flow events were identified the oldest phase of ice flow event i is characterized by ice flowing from an ice dispersal centre situated over the higher terrain in north central wales and by ice thick enough to cover the mountain summits at this time the interior of the ice cap is inferred to have been dominated by cold based ice during the growth of the welsh ice cap it became confluent with the british irish ice sheet the welsh ice cap at this time was again sufficiently thick to submerge the highest mountain summits the youngest detected phase of ice flow event ii was marked by an abrupt change in the dynamics of the welsh ice cap during event ii the welsh ice cap was drained by at least four ice streams which followed major troughs in northern and eastern wales

investigation of the permeability anisotropy of 2d fractured rock masses abstract a hydro geometric anisotropy factor is derived for better correlation with the permeability anisotropy of field scale fractured rock masses the hydro geometric anisotropy factor considers the orientation length spacing and hydraulic aperture properties of a discrete fracture network numerical simulations are carried out by using a pipe network method which simulates the fractures as connected and directed pipes obeying darcy s law to validate the correlation between the hydro geometric anisotropy factor and the permeability anisotropy of fracture networks fracture patterns from simple to complex with a scale of 10 m by 10 m are generated to study the effects of different fracture distributions on the hydro geometric anisotropy of fracture networks and thus on the permeability anisotropy it is found that the aperture size and distribution have a significant effect on the permeability anisotropy that affects the main permeable direction of the fracture networks the permeability anisotropy varies following a power relation with the change of the intersection angle between two fracture sets varying the number and length ratio of the fracture sets also alters the permeability anisotropy in all fracture patterns the hydro geometric anisotropy factor gives an accurate correlation with the permeability anisotropy an anisotropic conductivity index is further defined to evaluate the directional hydraulic connectivity of the fracture system based on this approach the permeability anisotropy of a fracture network system can be quickly assessed through the correlation with the hydro geometric anisotropy factor and the anisotropic conductivity index

an equivalent continuum model for coupled stress and fluid flow analysis in jointed rock masses to provide a set of governing equations for solving the coupled stress and fluid flow a rock mass which commonly contains a large number of geological discontinuities is treated as an anisotropic elastic porous medium with the corresponding elastic compliance and permeability tensors hydro mechanical equivalents to the discontinuous mass the hydromechanical equivalents with the special emphasis on the permeability tensor are formulated on the assumption that any crack can be replaced by a set of parallel planar plates connected by two springs two dimensional numerical analyses on seepage flow networks support the validity of the permeability tensor some field evidence is analyzed to examine the applicability of the present model for the practical purpose of rock hydraulics

study of the hydrogeological characteristics and permeability of the xinli seabed gold mine in laizhou bay jiaodong peninsula china this paper presents a case study investigation into the hydrogeological characteristics and permeability of rock mass in a seabed mine following an introduction to the geology and hydrogeological conditions in the xinli mine area we reveal the features of the preferred structural planes dynamic characteristics of mine water seepage and the permeability of the fractured rock mass in the pit the permeability of the pit rock mass shows varied characteristics at different geotectonic locations because of the different degrees to which the structural planes developed the fractured rock mass generally shows low permeability and the main composition of water seepage is high salinity brine future large scale undersea mining may induce rock mass movement destroy water resistant layers and enhance water transmissibility and the probability of water gushing into the pit thus strengthening the quality of the filling mass protecting the stope roof and the water resistant layers as well as regular monitoring of water seepage discharge and identification of water sources are critical to work safety and the prevention of seawater gushing in the mine