variations of hydraulic properties of granular sandstones during water inrush effect of small particle migration the evaluation of the hydraulic properties evolution of granular sandstones in relation with groundwater inrush within faults is an important issue for mining engineering applications this paper presents the results of an experimental investigation of small particle migration from granular sandstone samples under different original porosities particle size compositions and water flow pressures a new rock testing system has been setup to carry out the tests based on the results it is observed that the overall permeability evolution during the tests can be divided into four different phases including i re arrangement of large rock fragments ii water inrush with substantial particle migration iii continued moderate particles seepage and iv steady state water flow the crushing of edges and corners of large rock fragments and the evolution of the fracture network has mainly been observed in the first two phases of the tests the results indicate that the migration of small particles has an essential effect on permeability and porosity increase during water inrush through fractured sandstone the samples with higher original porosity higher percentage of fine particles in their formation and under higher water flow pressures achieve higher permeability and porosity values when the test is complete furthermore using the measured data the performances of a number of empirical models for permeability evolution in fractured porous media have been studied the prediction results indicate that not all of the fractures in a sample domain contribute in small particle migration there are parts of the fracture network that are not effective in particle flow a sample with less original porosity more fine particles and under lower water pressure shows less ineffective fractures therefore using the concept of the effective porosity fracture is sufficient enough for the flow calculation

mechanical behavior of groundwater seepage in karst collapse pillars abstract groundwater inrush has an impartible relationship with geological structures such as karst collapse pillars kcps which are widely distributed in north china in order to study the mechanism of groundwater inrush from coal seam floor the variable mass dynamics and nonlinear dynamics were introduced a mechanical model plug model is established to describe the behavior of water seepage flow in coal seam floor containing kcp the study shows that 1 if the mass of the kcp keeps steady the water seepage velocity in the kcp and the surrounding rocks will reach a constant value soon 2 if the mass of the kcp and the surrounding rocks increases by grouting etc the seepage velocity in the kcp and the surrounding rocks will reach its minimum value gradually and 3 if the mass of the kcp and the surrounding rocks decreases by scouring the flow velocity in the kcp and the surrounding rocks shows a monotone increase the water flow may change into pipe flow especially when a large number of the mass of the kcp and the surrounding rocks enters into goaf road which may lead to instable flow and cause groundwater inrush

application of brillouin optical time domain reflectometry to dynamic monitoring of overburden deformation and failure caused by underground mining abstract brillouin optical time domain reflectometry botdr a fully distributed optical fiber sensing technology was applied to monitoring the deformation behavior of overlying strata during underground mining three types of optical cables metal kieso sensing optical cable mks glass fiber reinforced sensing optical cable gfrs and 10 m interval fixed point sensing optical cable 10 m ifs were embedded vertically into two boreholes that are located 582 m and 1746 m from the open off cut respectively the strain distribution characteristics of the cables and variations of the mechanical and hydraulic properties in the overburden were analyzed with consideration of the lithology and mining positions the results show that mks cable has better performance in strength and accuracy than the gfrs and 10 m ifs cables the strata in front of the panel provided front bearing loads and were compressed in the vertical direction as the panel passed the cables to approximately 90 m the tensile stress increased and the peak value moved up gradually with the occurrence and development of the caved zone the strains of the lower optical drill were negative and in the compression state throughout the monitoring process the upper cable showed a process from compression to tension while the lower cable showed a process from compression through tension to compression in addition the strain distribution of the cables corresponded well with the strata the vertical compression of the strata appears to be inversely proportional to their young s modulus tensile failure dominates in the overlying strata during the mining process with the advancing of the panel the tensile failure zone moved upward episodically and the height of the fractured zone reached the maximum where the distance between the face and cable was approximately 90 or 100 m compared with the traditional monitoring methods botdr monitoring provided more accurate data on the dynamic height of the fractured zone the research results are of practical significance for monitoring overburden deformation under mining and they are helpful to prevent or mitigate water inrush and surface ecological geological disasters

the height of fractured water conducting zone in undermined rock strata the height of fractured water conducting zone is of significant importance for the safety of underground mining because of the conspicuous discrepancy of the height of fractured water conducting zone in bulianta coal mine as predicted by the traditional method with those observed in practice a systematic research has been carried out the study indicates that two aspects should be taken into account firstly the traditionally proposed empirical formula in prediction of the height of fractured zone was based on the conditions of single slice mining where the mining height was less than 3 m and the total slice mining height was limited within 15 m in such a case it would not be suitable to predict the maximum fractured zone height for the conditions where a single mining height is larger than 3 m secondly the stratum structure such as the thick and strong rock layer termed as key stratum plays an important role in controlling of the height of movement in the overburden physical model tests by making use of a similar material illustrate that if the vertical distance from the primary key stratum to the coal seam is shorter than a certain value then the developing fracture zone will extend above the key stratum into the top of bedrock resulting in a larger height of water conducting zone than is calculated by the empirical method the outcome of the work presented will be helpful in practice to prevent the overburden aquifer inrush and to avoid mine water hazard

height of water conducting fractured zone in a coal seam overlain by thin bedrock and thick clay layer a case study from the sanyuan coal mine in north china the accurate determination of the height of the water conducting fractured zone hwcfz in a coal seam covered by thin bedrock and thick clay layer is crucial for aquifer protection mine safety and eco environmental conservation using the sanyuan coal mine in north china as a case study theoretical analysis numerical simulation and field measurements were used to analyze the regularity of the hwcfz in this area per mechanical theory a geometrical model for calculating rock bending and subsidence was established two arcs of equal curvature and lengths and opposite curvature direction were used to fit the curve section of intermediate rock layer after bending the theoretical method for solving the hwcfz was given by calculating the rock layer s tensile ratio in addition rock failure process analysis rfpa software was used to simulate the development of the water conducting fractured zone wcfz during the mining process and the hwcfz was measured by the drilling fluid loss measurement both which verified the feasibility of the theoretical calculation to determine the primary controlling factors affecting the hwcfz the seepage characteristics and plastic properties of the quaternary clay layer were also analyzed using laboratory tests results show that the quaternary clay with a depth greater than 130 m has a permeability coefficient of e 10 m s a liquidity index less than 0 25 and a plasticity index more than 17 indicating the clay layer is impermeable and of great importance to inhibiting the development of wcfz the research can provide significant theoretical insights for effectively preventing water hazards on mine roofs

bulking factors and extents of caved zones in weathered overburden of shallow abandoned underground workings abstract a comparison between the bulking factor and height of the caved zone for different weathered subsurface rocks over shallow abandoned mines and for strong rocks at intermediate and large depths of longwall mining is performed in this study vertical boreholes drilled from the ground surface have been used to detect the height of caving in weathered w and very weathered vw rock mass overlying abandoned underground workings at a shallow depth and then to calculate the bulking factor it is found that key parameters that control the bulking factor k and the ratio between the heights of caving and mining h h are different for w and vw rocks in w rocks such parameters are the rock strength of immediate roof and rock porosity whereas those for vw rocks are rock quality designation rqd and standard linear fracture intensity p10 it is argued that h h in vw rocks increases according to linear logarithmic law with an increasing ratio p10 rqd in the immediate roof and p10 in four rock layers over the immediate roof observations show that vw rocks exhibit smaller values of k 1 06 1 165 and larger h h 6 07 15 6 compared to w rocks having 1 09

the fault pattern in the northern negev and southern coastal plain of israel and its hydrogeological implications for groundwater flow in the judea group aquifer abstract on the basis of a broadly expanding data base the hydrogeological properties of the judea group sequence in the northern negev and southern coastal plain of israel have been reassessed the updated subsurface model is based on data derived from water and oil wells and on recent large scale geophysical investigations a new regional pattern of the reassessed geological through the subsurface of the study area has been revealed in view of the reassessed geological and hydrological subsurface setting it appears that the judea group aquifer should not be regarded as one continuous and undisturbed hydrological unit owing to the occurrence of regional faults its subaquifers are locally interconnected these subaquifers which contain mainly high quality water are juxtaposed as a result of faulting against kurnub group sandstones containing brackish paleowater the latter group is faulted against late jurassic formations containing highly saline groundwater in the beer sheva area the judea group aquifer is vertically displaced against the senonian and eocene mt scopus and avdat groups which also contain brackish and saline water in the southern coastal plain major faults locally dissect also the pleistocene kurkar group facilitating inflow of mg rich groundwater deriving from judea group dolomites the new geological evidence and its hydrogeological implications provide new solutions for previously unexplained salinization phenomena

upward slicing longwall roadway cemented backfilling technology for mining an extra thick coal seam located under aquifers a case study many water inrush disasters have occurred in mines that were attempting to recover extra thick coal seams located under aquifers this paper presents a technology known as upward slicing longwall roadway cemented backfilling uslcb which can provide a safe and effective solution to extract these seams the fundamentals of the technology are to divide a coal seam into several slices and extract each slice sequentially from bottom to top using longwall roadway mining technology gobs are filled with cemented backfill which then act as a new floor allowing the overlying slices to be mined similar to the overhand cut and fill method this paper also presents the compressive properties of cemented backfill material with various mixing ratios and curing times moreover a physical simulation was conducted to verify the effects of uslcb the results of the simulation indicate that uslcb can be used to control strata movement as well as the height of the water conducting zone hwcz the uslcb was applied at gonggeyingzi coal mine in inner mongolia china the results indicate that the recovery ratio has increased from 39 2 to 95 the backfill ratio reached 95 water inflow decreased from 245 to 120 m3 h and the maximum hwcz was 39 2 m after extracting the entire 21 m of the coal seam the conclusions of this research show that implementing uslcb can significantly improve productivity and safety when extra thick coal seams are mined which are located under aquifers

numerical analysis of the dynamic evolution of mining induced stresses and fractures in multilayered rock strata using continuum based discrete element methods abstract in this study the continuum based discrete element method cdem was adopted to simulate the evolution of mining induced stress and fracturing during roadway tunnelling and mining in multilayered heterogeneous rock strata the cdem integrates the finite element method fem and the discrete element method dem to characterize the mining induced stress evolution the discontinuous fractures separations and caving that occur in the interfaces between multilayered rock strata the maximum tensile stress criterion and the mohr coulomb strength criterion were used to evaluate the tensile and shear failure of the material elements the cdem model for rock strata was constructed by employing image processing and reconstruction approaches using the geometrical and physical parameters that were measured from a real coal mining site the stress evolution and compression deformation of the roof and floor strata were computed to evaluate the criticality of mining induced disasters the constructed model was employed to simulate and analyse the immediate roof collapse immediate floor bulges and the compaction of the collapse blocks as well as the large deformation separation and collapse between the immediate roof and the main roof during coal seam mining it was shown that the proposed method could predict ranges for the caving zone and fracture zone in the rock roofs that were in good agreement with the observation results from the real coal mining site

void fraction distribution in overburden disturbed by longwall mining of coal voids in overburden disturbed by coal mining provide channels for transfer of heat methane groundwater oxygen exhaust gas and fire fighting materials in the underground environment based on expressions of strata and ground subsidence a group of void fraction distribution models are proposed including porosity in the caved zone the fracture ratio in the bed separation zone and the fissure ratio in the ground subsidence zone combined with a case study of the antaibao coal mine china theoretical calculation and numerical simulation indicate that porosity distribution in the caved zone is u type and the transverse void fractions in the bed separation zone and ground subsidence zone have m type distributions additionally the longitudinal void fraction distribution changes from type to m type along the strike and dip of the coalbed after the complete subsidence of ground the distribution of fractures in the disturbed overburden of the goaf presents a fractured arch and fracture density gradually decreases from arch foot to crown fire prone zones propagating paths of coalbed fires areas prone to water influx and outlets of boreholes used for fire fighting all usually appear around the perimeter of disturbed overburden the transverse void fractions distribution in the bed separation zone changes from type to m type with an increase in the size of the goaf it is suggested that the inlets of gob vent boreholes should be arranged near the center of the bed separation zone in the early stages of longwall mining and around the perimeter in middle to late stages of mining

measuring streambank erosion due to ground water seepage correlation to bank pore water pressure precipitation and stream stage limited information exists on one of the mechanisms governing sediment input to streams streambank erosion by ground water seepage the objective of this research was to demonstrate the importance of streambank composition and stratigraphy in controlling seepage flow and to quantify correlation of seepage flow erosion with precipitation stream stage and soil pore water pressure the streambank site was located in northern mississippi in the goodwin creek watershed soil samples from layers on the streambank face suggested less than an order of magnitude difference in vertical hydraulic conductivity ks with depth but differences between lateral ks of a concretion layer and the vertical ks of the underlying layers contributed to the propensity for lateral flow goodwin creek seeps were not similar to other seeps reported in the literature in that eroded sediment originated from layers underneath the primary seepage layer subsurface flow and sediment load quantified using 50 cm wide collection pans were dependent on the type of seep intermittent low flow lf seeps flow rates typically less than 0 05 l min 1 persistent high flow hf seeps average flow rate of 0 39 l min 1 and buried seeps which eroded unconsolidated bank material from previous bank failures the timing of lf seeps correlated to river stage and precipitation the hf seeps at goodwin creek began after rainfall events resulted in the adjacent streambank reaching near saturation i e soil pore water pressures greater than 5 kpa seep discharge from hf seeps reached a maximum of 1 0 l min 1 and sediment concentrations commonly approached 100 g l 1 buried seeps were intermittent but exhibited the most significant erosion rates 738 g min 1 and sediment concentrations 989 g l 1 in cases where perched water table conditions exist and persistent hf seeps occur seepage erosion and bank collapse of streambank sediment may be significant copyright 2007 john wiley sons ltd

weathering of a gypsum calcareous mudstone under semi arid environment at tabernas se spain laboratory and field based experimental approaches the weathering of a late miocene gypsum calcareous mudstone outcropping in large badland areas of se spain under a semi arid mediterranean climate was studied by means of two experimental approaches field and laboratory experiments were carried out to reproduce though in accelerated form some of the weathering conditions of the consolidated mudstone in the laboratory three sequences of 5 10 and 20 wetting drying cycles were produced on undisturbed blocks of fresh mudstone samples at the end of the three sequences samples were analysed for their micromorphology elemental and soluble salt chemistry and total mineralogy unweathered dry samples as blanks and permanently wet samples were also analysed in the field two small plots of freshly exposed mudstone were monitored over 3 years for their response to natural weathering in terms of morphological changes and sediment output the porosity was increased by a few wetting drying cycles as assessed by significant increases in water absorption capacity of the mudstone a combination of three factors is responsible for mudstone weathering repeated cycles of wetting drying the presence of geologically induced cracks and fissures and dissolution crystallisation of relatively soluble minerals gypsum being the most abundant within this category a few wetting drying cycles were sufficient to reveal ion migration specially na ca mg so4 hco and cl within the mudstone explaining mineral dissolution in the field surface weathering rates from 0 7 to 8 mm year 1 were measured weathering rates were found to be proportional to the number of rainfall events during the sampling periods confirming what was found in laboratory conditions namely that the number of wetting drying cycles has the greatest influence on weathering these weathering rates might be considered as the probable range of incision rates under present semi arid conditions

prediction of water inrush risk areas in process of mining under the unconsolidated and confined aquifer a case study from the qidong coal mine in china the unconsolidated cenozoic formation is well developed in the qidong coal mine water inrushes from the bottom unconsolidated cenozoic aquifer which is the confined aquifer have happened several times during mining in the north mining area of the qidong coal mine to predict the water inrush risk areas in the south mining area of the qidong coal mine where some working faces have just begun to mine the engineering analogy method is used on basis of the fisher s discriminant model from the actual mining situation in the north mining area six main influence factors including the effective thickness the specific yield and the load transfer coefficient of the aquifer the effective thickness of the protective bedrock layer the fractal dimensional value of bedrock faults and the distance between the key hard stratum and the primary mineable coal seam are selected as discriminant indexes and their corresponding data in the north mining area of the qidong coal mine are served as training samples on this basis the fisher s discriminant model for water inrush is established and water inrush risk areas including the safety the medium risk and the risk areas of no 61 82 and 9 primary mineable coal seams in the south mining area of the qidong coal mine are predicted by the model the model s accuracy is 90 4 the scatter diagram of training samples shows obviously classified effect and the field verification indicates that the predicted type is consistent with the actual type results show that the discriminant model is well applied in the engineering analogy method and the water inrush risk areas predicted by the discriminant model contribute to the subsequent mining in the south mining area in the qidong coal mine

effect of sand grain size on simulated mining induced overburden failure in physical model tests abstract to investigate the influence of sand grain size sgs on mining induced overburden failure in physical model tests uniaxial compressive experiments on rock like material with various sgss were performed and two sgss 0 0 5 and 0 5 1 mm were selected the young s modulus uniaxial compressive strength and tangent modulus were larger in rock like material samples with finer sgs and the failure mode changed from mostly shear failure to tensile failure with rising sgs as the mechanical characteristics of coarser sand samples are weaker the overburden breakage distance was shorter in the coarser sand model and the ratio of the average breakage distance between the two models was 1 688 the extent of the overburden fracture was heavier in the coarser sand model and closer pattern to that of the actual coal mine a large database of the heights of the overburden caved zone hcz and fractured zone hfz values with various mining height hm based on previous studies was compiled to obtain best fit parabolic empirical formulas the hcz hm and hfz hm ratios measured in the field were similar to those estimated by the proposed empirical formulas the discrepancy between the physical model test and field measurement may be explained by the fracture pattern in the overburden of the caved zone in the form of layered rectangles unlike the polygonal forms in the coal mine we propose four recommendations to optimize the physical model for such tests from the perspective of sgs the results and recommendations presented here can provide a useful guide for coal mining scientists and engineers designing models for testing of coal mining conditions

model experimental research on deformation and subsidence characteristics of ground and wall rock due to mining under thick overlying terrane abstract based on the prototype of a mine a physical simulation test is conducted the characteristics of the deformation and failure of the ground surface and the wall rock around a goaf as well as the creep behavior of the wall rock deformation and the failure mechanism are analyzed the simulation test has greatly improved our understanding on the wall rock s deformation and failure characteristics for the first time digital close range photogrammetry was used to measure the displacements in a sectional model test the measurements by this technique agreed very well with those obtained by other methods such as using dial gauges

soil pipe collapses in a loess pasture of goodwin creek watershed mississippi role of soil properties and past land use little is known about the association of soil pipe collapse features with soil properties or land use history three loess covered catchments in northern mississippi usa were characterized to investigate these relationships soil pipe collapses were characterized for their size type feature and spatial location along with soil properties across the three catchments although mapped as the same soil one of the catchments did not contain pipe collapse features while the other two had 29 4 and 15 4 pipe collapses per hectare these loess soils contained fragipan layers that are suspected of perching water thereby initiating the piping processes pipe collapses associated with subsurface flow paths were not always consistent with surface topography the surface layer tended to be non erodible while layers below even the upper fragipan layers were susceptible to erosion by pipeflow soil properties of the lowest fragipan layer were highly variable but tended to prevent further downward erosion of soil pipes and thus formed a lower boundary for gullies middle to lower landscape positions in one of the piped catchments contained anthropic soils that were highly erodible these anthropic soils were previously gullies that were filled in in the 1950s when forested areas assumed to have been established when land was previously converted from crop to forest land were converted to pasture three decades after this land use change from forest to pasture pipe collapses became evident in contrast the adjacent catchment that does not exhibit pipe collapse features experienced severe sheet and rill erosion prior to the 1930s while in cotton production the surface horizons above the lower fragipan layer were completely removed during this period thus the top soil layer that tends to form a bridge above soil pipes in the more erodible subsoil layers was removed this study showed that knowledge of soil characteristics or topography alone do not explain the distribution of soil pipe collapses as past land use can play a definitive role copyright 2015 john wiley sons ltd

salt accumulation in the loessial sequence in the be er sheva basin israel evidence of climatic changes is recorded in the salt content of the surface sediments in arid zones in wetter periods airborne salts are removed downward by leaching to the groundwater whereas in drier periods they accumulate the period of salt accumulation in the loessial sediments of the northern negev is about 10 000 yr this period represents the recent aridification phase the beginning of this stretch of time followed the last humid period in the region top paleo soil calcic horizon found in the region and dated 12 000 yr b p is an indicator of this humid period

characterising the multi seam subsidence due to varying mining configuration insights from physical modelling abstract multi seam mining induced subsidence profile is observed to be different from that of single seam mining understanding the characteristics of multi seam subsidence is the first step in achieving reliable subsidence predictions characteristics of multi seam subsidence are investigated by means of several sand plaster physical models geological and site specific parameters are kept constant in all the models in order to compare the multi seam subsidence parameters for different mining configurations based on observations from the physical models it is concluded that the panel configurations of the two seams have significant impact on the multi seam subsidence development based on the relative location of the panels the multi seam mine area can be divided into different zones to which suitable subsidence characteristics can be assigned dividing the mine area into different zones enables characterisation of the strata movement and multi seam subsidence for various multi seam configurations the proposed characterisation of the multi seam subsidence can also be utilised in subsidence prediction methods in order to achieve reliable prediction results

characteristics and controlling factors of bank gullies in two semi arid mediterranean environments abstract bank gullies are gullies that are formed due to a height drop caused by a terrace or a river bank which develop by headward retreat in erodible hillslopes this study aims i to investigate the morphology of actively eroding bank gullies i e geometrical characteristics resulting from past erosion and active erosion processes shaping the gully and ii to find relationships with environmental site characteristics such as topographical parameters material properties and climate the ultimate goal is to identify the most important controlling factors of past and present bank gully erosion fifty five active bank gullies formed in different lithologies by various erosion processes have been selected in the guadalentin basin and the surroundings of guadix southeast spain for each bank gully site geometrical and topographical parameters of both the channel and the drainage basin were measured erosion features indicating activity at the gully head such as tension cracks plunge pools undercutting fluting piping and rill or sheet erosion on sloping side walls were mapped and samples were taken from distinct lithological layers that were considered to influence the type and intensity of erosion processes a relationship could be shown between the presence of piping and fluting and a number of material characteristics including particle size distribution dispersion behaviour and electrical conductivity on the other hand lithology appeared not to be a differentiating factor on gully development in the long run as expressed by the total eroded volume v this parameter was most strongly related to the drainage basin area in which the entire bank gully had been formed a o explaining 66 of the variance the relationship is v 1 75 a o 0 59 no significant difference was found between regression lines through sub datasets of different soil textural classes finally multiple regression was used to include both topographical parameters and material characteristics in an explanatory and or predictive equation for the total eroded bank gully volume the results of the analyses using the entire dataset including the sites in the guadalentin as well as in the guadix area have been compared with the results for the separate study areas differences are not only related to topographical and lithological characteristics but may also be the consequence of a different climate in the two areas

variations in soil dispersivity across a gully head displaying shallow sub surface pipes and the role of shallow pipes in rill initiation a small bifurcating gully head displaying shallow pipe development was surveyed to explore how far three dimensional patterns of geochemistry and sediment size can be related to hydraulic gradients in the local marl bedrock almeria se spain the crust sub crust and parent materials were sampled every 20 cm across a 2 m by 3 m grid and then analysed for dispersive and granulometric characteristics spatial patterns of sodium adsoption ratio sar for each layer were plotted separately in situ material at depths of 5 10 cm was only weakly dispersive and the thin 0 2 cm depth crust is also found to be mostly non dispersive paralleling ndings from other eld sites in almeria however the signature relating sar to electrical conductivity for each layer shows that in places the immediate sub crust layer 2 5 cm is highly dispersive the pattern is not random rather the sar of this sub crust layer follows inferred hydraulic gradients the dispersive hot spots being located in the most incised part of the small gully exacerbating the erodibility of that position patterns of sediment particle size and sorting do not correlate with inferred hydraulic gradients but surface material is slightly siltier than the sub crust clay fraction increased with depth and sar is shown to have a weak inverse relationship to particle size this association between sar and the increased clay fractions in the lower layers supports the inference that massive pipe enlargement in the messinian rich unit is suppressed by sub surface swelling since a reduction in in ltration capacity fc with depth can be inferred from these results in ltrating water must be de ected into the already vulnerable sub crust layer during rainfall events explaining the development of shallow pipe forms at preferential depths it is concluded that calcium replaces sodium in the crust during leaching leaving a calcic crust and a sub crust that is sodic and prone to subsequent pipe enlargement rill morphology in these materials also suggests that rills develop from these pipes when pipe roofs collapse i e rill discontinuity bridges steep headwalls and rills with excessively high depth to width ratios copyright 2004 john wiley sons ltd

seepage weathering impacts on erosivity of arid stream banks a new conceptual model field observations have indicated the formation of horizontal pipe shape cavities along gully and dry stream channel banks in the semi arid region of the northern negev desert israel piping is a well known phenomenon in humid regions due to subsurface water flow and seepage weathering however in dry environments where rain events are scarce and subsurface water flow is rare it is proposed here that capillary flow of saline water in the vadose zone leads to similar processes it is suggested that where saline and shallow ground water persists capillary flow may result in salt accumulation and precipitation at the top of the capillary fringe consequently rendering this zone to be more susceptible to erosion a conceptual model is presented and field observations laboratory experiments and a physically based model are used to prove the feasibility of the proposed conceptual model and to explain why salts accumulate at the top of the capillary fringe even though evaporation acts all along the vertical stream channel or gully banks it is suggested that the low evaporative flux in comparison to the liquid water flux disables salt accumulation along the profile to the top of the capillary fringe where the liquid water flux is minimal the presented findings strengthen the conceptual model but thorough field studies are needed to estimate the impact of the proposed mechanism on erosion processes on a field scale

investigation of movement and damage of integral overburden during shallow coal seam mining abstract most prediction methods used to calculate mining induced subsidence are empirical which cannot explain the mechanism of fundamental rock strata movement in this paper based on key stratum theory and the mechanical analysis of overburden a new analytical solution the analogous hyperbola subsidence model ahsm was proposed to describe the movement and damage of inner burden mining induced rock strata movement was verified using the distinct element method udec to assess the performance of the theoretical model three subsidence parameters smax t sgoaf smax d h generally used to describe surface subsidence trough agree with statistical field measurements of the south coalfield in australia the surface subsidence and the movement boundary in the overburden are very close to the theoretical predictions additionally the primary key stratum damages the least in the overlying strata its broken length is the smallest the width of subsidence trough and maximum surface subsidence increase as the primary key stratum drops

the role of some site geochemical processes in the development and stabilisation of three badland sites in almeria southern spain samples of both surface and subsurface soils were collected on various surfaces in three badland areas of differing ages tabernas vera and mocatan in almeria province southern spain data were explored with the aim of identifying any diagnostic geochemical relationships between site ec ph sediment size and sar which might constitute typical signatures for site materials with some success data for the three sites are further used to explore the hypothesis that changes in site geochemistry through time are involved in badland stabilisation it was found that 1 the physico chemical properties of the three sites can be differentiated by the functional relationship between ec and sar and this may represent a useful tool in characterising sites where piping predominates 2 there is some equivocal evidence that sediment size distribution may play an additional role in site diagnosis and evolution and 3 surfaces appear to lose sodium over time the suggestion being that sodium is either progressively buffered by calcium during leaching or exchanges with hydrogen on the cation exchange sites under a vegetation cover since other research suggests that smectite can also relocate down the profile on some marl sites reducing hydraulic conductivity and suppressing pipes we argue that the surface at tabernas may be capable of long term autostabilisation in which piping intensity progressively reduces however this possibility really applies only to fine grained densely structured materials and evidence from the silty triassic rich unit in the mocatan basin suggests that without a high clay content piping may be expected to increase through time from this standpoint contemporary badland morphology at mocatan does not represent an early stage of the forms seen in vera and tabernas

on prevention and mechanism of bed separation water inrush for thick coal seams a case study in china bed separation can occur in overlying strata especially in hard and soft interbedded roof strata if these strata prone to form bed separation are rich aquifers water can accumulate into bed separation and maybe cause a serious water hazard under the condition of water inflow passages existence therefore studying these types of roof water inrush mechanisms forecasting roof water inrush and formulating preventive and control measures in advance are extremely important to a mine in this paper we takes the typical case of water inrush in the workface number 1121 at hongliu coal mine as an example and study the mechanism of water inrush in detail primarily field drilling with water leakage and color tv observations showed that the maximum height of the water conducting fractured zone was 12 50 times the thickness of the coal seams which spread to the overlying coarse grained sandstone aquifer secondly the numerical simulation indicated that bed separation storage space was prone to form under the combination of coarse grained sandstone and mudstone geological structure the detection using uwtem revealed that the groundwater accumulated in this bed separation and formed a water bag bed separation water when the water bag reached a certain degree water bursting happened with the main roof collapsing finally prevention effective drainage methods and successful experiences with bed separation water have been summarized and it will have a major significance to coal mines suffering from bed separation water inrush

height of the mining induced fractured zone above a coal face abstract the development height of a gas conducting fracture zone gfz in the gob overlying strata is crucial to the gas drainage and safe production of a coal mine in order to address the issues of excessive gas concentration and uncertain gfz height in no 7435 face overlying strata of kongzhuang coal mine china the caving characteristics of overlying strata were explored using both physical experiments on similar materials and numerical simulations of particle flow code pfc software and verified each other the relationship of cracks development to porosity changing characteristics was introduced to quantitatively determine the height of the local gfz the quantified gfz heights were compared with those measured using the in situ drilling flow method the results showed that 1 pfc software could accurately simulate the overlying strata caving behaviors thus saving manpower materials and financial resources needed for related physical experiments and 2 the temporospatial distribution characteristics of porosity could be used to forecast gfz height and are of significant importance for determination of gfz overall the conclusions are of engineering significance for accurate arrangement of boreholes for gas drainage and reduction of mine gas disasters

soil properties controlling seepage erosion contributions to streambank failure the majority of sediment leaving catchments may be from streambank failure seepage erosion of unconsolidated sand above a restrictive layer is an important erosion process in incised streams that leads to streambank failure by undercutting banks the objective of this study was to determine the impact of soil properties on seepage erosion and the resulting streambank failure seepage flow and sediment concentrations were measured in situ at eight locations along the banks of a deeply incised stream in northern mississippi using field observations as a guide the soil profile conditions of a shallow 45 cm streambank consisting of 30 cm of topsoil a 10 cm conductive layer and a 5 cm restrictive layer were mimicked in laboratory lysimeter experiments to quantify the hydrologic properties controlling seepage erosion and bank failure under a 40 cm head the time to flow initiation and the flow rate were linearly related to the slope of the restrictive layer seepage erosion began within minutes of flow initiation and resulted in substantial 3 to 34 cm undercutting of the bank sediment concentrations of seeps were as high as 660 g l 1in situ and 4500 g l 1 in the lysimeters sediment concentrations were related to the layer slope thereby indicating the importance of detailed site characterization the usda ars streambank stability model demonstrated the increase in instability of banks due to undercutting by seepage erosion but failed to account for the sediment loss due to sapping for stable banks and overestimated the sediment loads for failed banks published in 2006 by john wiley sons ltd

large scale infiltration experiments into unsaturated stratified loess sediments monitoring and modeling summary two large scale field experiments were conducted to track water flow through unsaturated stratified loess deposits in the experiments a trench was flooded with water and water infiltration was allowed until full saturation of the sediment column to a depth of 20 m was achieved the water penetrated through a sequence of alternating silty sand and sandy clay loess deposits the changes in water content over time were monitored at 28 points beneath the trench using time domain reflectometry tdr probes placed in four boreholes detailed records were obtained from a 21 day period of wetting followed by a 3 month period of drying and finally followed by a second 14 day period of re wetting these processes were simulated using a two dimensional numerical code that solves the flow equation the model was calibrated using pest the simulations demonstrate that the propagation of the wetting front is hampered due to alternating silty sand and sandy clay loess layers moreover wetting front propagation is further hampered by the extremely low values of the initial unsaturated hydraulic conductivity thereby increasing the water content within the onion shaped wetted zone up to full saturation numerical simulations indicate that above hydrostatic pressure is developed within intermediate saturated layers enhancing wetting front propagation

evolution mechanism of water flowing zones and control technology for longwall mining in shallow coal seams beneath gully topography the height and evolution mechanism of fractured water flowing zones are of great importance for prevention of water inrush disasters and protection of immediate environments particularly in ecological vulnerable areas in this paper comparative approaches including empirical formula calculation physical simulation numerical simulation and protem transient electromagnetic analysis are employed to identify the development of the fracture zones caused by water flowing so as to ensure mining safety and protection of groundwater in shallow coal seams beneath gully topography an empirical formula was used to calculate the height of the water flowing fracture zone and an experimental study utilizing a model based on a similar material was adopted to analyze the movement and fracture development of the overlying strata results provide a reasonable basis from which a rational mining height may be determined the protem transient electromagnetic apparatus was employed to detect the water flowing structure conductivity of the overlying strata induced by mining beneath gully topography in the field the water flowing fracture of the overlying strata can be estimated according to comprehensive analysis of the apparent resistivity changes of the field gully surface crack development and aquifer water level accordingly the control technologies in the field were implemented and discussed regarding preventing gully water from rushing into underground mining spaces through water flowing fracture zones results indicate that safe and efficient mining of shallow seams beneath gully topography can be achieved by prevention of gully accidents and protecting the surface water resources of the ecological environment

geomorphological chemical and physical study of calanchi landforms in nw sicily southern italy abstract this work deals with an integrated geomorphological and chemical physical study of calanchi landforms in two sites ottosalme and catalfimo of nw sicily southern italy developed on dominant silty clay deposits the calanchi fronts are characterized by different morphological features and dominant geomorphic processes sharp knife edged ridges and concentrated water runoff dominate at ottosalme and smoother landforms affected by mass movements mud flows and translational slides prevail at catalfimo we focused on some geochemical and physical parameters such as ph total dissolved salts sodium adsorption ratio sar porosity plastic and liquid limits as possible causes of the above differences with special emphasis on their role in discriminating the behavior of peculiar microforms such as a weathered outer crust and the corresponding inner massive portion unweathered substrate our results show that the main chemical physical features of calanchi morphologies and microforms often display no clear correlations with respect to those reported in the existing literature pointing to a higher complexity of patterns and behaviors in particular all samples consist of dispersive material sar values 10 but a more plastic and liquid behavior at catalfimo can explain a higher occurrence of landslides and smoother morphology than at ottosalme higher sar values at ottosalme well explain the dominance of concentrated water erosion the chemical behavior of the studied microforms is better described by ph being alkaline with higher values in the inner substrate than the outer crust and appears to minimize the effects of all other parameters and their responses to other external controlling factors lower sar values in the crust suggest that clay dispersivity is not the prominent factor controlling its surface detachment and mobility downslope which is more likely promoted by its higher porosity and consequent water absorption than the inner portion with changes in the saturation state shear strength and water pressure

geo chronological context of the open air acheulian site at nahal hesi northwestern negev israel abstract the open air site of nahal hesi located on northwestern negev desert fringe of israel is one of the few primary context late acheulian localities in the levant late acheulian sites in the levant rarely provide faunal assemblages and radiometric ages leaving large gaps in our knowledge of the lower paleolithic palaeoenvironment ecology subsistence and chronology here we present a new geo chronological study conducted at the nahal hesi site the major objectives were to describe the geological and archaeological stratigraphy assign a numerical age to the acheulian artifact bearing deposit by tt osl and pir ir290 dating and reconstruct the local palaeoenvironment during the human occupation at the site geological and microfaunal observations suggest that late acheulian hominins at nahal hesi exploited marshy environments the limited spatial and vertical extent of the artifact bearing deposit and the presence of artifacts only in context of marsh like sediments highlight the utilization of short lived water bodies by the hominins the combined tt osl and pir ir290 methods provide an average age of 430 35 ka for the studied marsh like deposits the study indicates that the middle pleistocene in the area of the nahal hesi site is characterized by lengthy cycles of deposition and erosion of fine grained sediments associated with the semi arid nahal shiqma drainage system marshy sediments could be the result of full or partial blockage of the shiqma system probably by coastal dune ridges that led to formation of standing water bodies during the middle pleistocene

field investigation of fractures evolution in overlying strata caused by extraction of the jurassic and carboniferous coal seams and its application case study abstract in multiple seam coal mining the fractures induced by the mining of the lower coal seam may propagate to the goaf of the upper coal seam that is mined earlier the fracture connection leads to the leakage of hazardous gas to fully understand the gas leakage due to fracture evolution the electromagnetic based measurement system and the borehole televiewer were adopted in the panel no 8100 in tongxin coal mine datong coalfield china the coal seam thickness is 15 m and it was mined by top coal caving method the resistivity and fracture pattern in distinct zones of rock stratum were detected and the correlation between them was explained clearly we found that the fracture evolves in two stages as the panel working face advances i e fracture propagation and fracture re closure the maximum height of fracture propagation is 150 m in which the height of the caved and the fractured zones are 80 m and 70 m respectively these fractures start to be compacted and are re closed at the distance of 80 m behind the working face the extraction of the panel no 8100 results in the formation of a gas bearing zone gbz with separations and shear fractures rather than connecting the goafs of the carboniferous coal seam ccs and the jurassic coal seam jcs the gbz is located in a region from 80 m to 150 m above the goaf and 80 m behind the working face based on the above findings effective gas drainage approach is proposed to reduce the concentrations of the hazardous gases consisted of ch4 and co after gas drainage the maximum concentrations of ch4 and co drop to 0 5 and 16 63 ppm with reductions of 53 7 and 33 9 respectively

impact of particle transfer on flow properties of crushed mudstones karst collapse pillar kcp is widespread in north china coalfields where coal extraction above the ordovician limestone aquifer is threatened by the abundant supply of water and a very high hydraulic pressure kcp is composed of rock skeleton and fine fillings which can be transferred under the effect of water flow thus kcp usually functions as a channel for groundwater inrush in order to investigate the mechanism of mining induced groundwater inrush of kcp which was caused by fine fillings transfer a self designed particle transfer permeability testing system was used to test the crushed mudstones flow properties which included fine filling particle transfer rate porosity increase rate and permeability under the conditions of varying pore pressure particle size mixture and compaction level initial porosity the tests indicate fine fillings transfer is the essential reason for mining induced groundwater inrush flow instability of kcp the flow properties changeability during fine particle transfer could be divided into four stages i e initial flow stage flow inrush stage continued particle flow stage and stable flow stage and flow inrush stage which is the key point to cause water inrush due to the crushing of edges and corners and the adjustment of the structure the fluctuation of permeability time relationship mainly distributed in the first two stages which make a change to flow channel moreover with the increasing of pore pressure particle size mixture and initial porosity the water inrush time and stable seepage time decreased more rapidly the fine fillings porosity and permeability increased gradually the efficiency criteria analysis between measurement and calculation permeability shows an empirical equation can fit the relationship between porosity and permeability well and not all of the pore structures were in flow this means there was a part of pores that were invalid but the effective porosity in flow can be treated as calculation value approximately

tracking changes in the specific storage of overburden rock during longwall coal mining the hydraulic properties of geologic formations such as specific storage and hydraulic conductivity are known to vary spatially due to formation heterogeneity however they may also change temporally if the formation undergoes mechanical disturbance such as occurs during mining characterising changes in hydraulic properties is important for groundwater systems that are disturbed by mining conventional hydrogeological investigations rely on literature derived values or limited programs of field testing e g pumping test to define specific storage but these approaches do not consider the change in compressibility that may occur due to mechanical disturbance this paper presents for the first time direct in situ measurements of the changes in compressibility and consequently specific storage as a result of mechanical disturbance within geologic formations overlying underground mining operations the in situ measurements of compressibility are derived in this study from the pore pressure response to barometric loading or strains induced by earth tides even prior to disturbance the compressibility obtained from in situ measurements was found to be an order of magnitude lower than that measured on core samples by unconfined strength test in the laboratory the differences in compressibility for the intact formation are likely due to sample disturbance and the differences in strain level imposed by the field and laboratory methods the increase in compressibility of the overburden rock varied with the location of the monitoring site relative to longwall extraction and the level of strain the formation sustained the study found that quantifying the changes in compressibility and consequently specific storage as a result of mine induced disturbance is critical to our understanding of subsidence the extent of depressurization and the impact that mining may have on regional groundwater flow systems

mechanisms of the development of water conducting fracture zone in overlying strata during shortwall block backfill mining a case study in northwestern china in this work a shortwall block backfill mining sbbm technique is proposed for the recovery of residual corner coal pillars and irregular blocks left behind during the exploitation of coal mines and a solution is provided for the risks associated with gangue piling and the loss of water resources owing to coal mining based on the theory of beams on elastic foundations a mechanical analysis model was established for calculating the height of a water conducting fracture zone wcfz in the overlying strata of coal mines exploited using the sbbm technique it was found that the key factors influencing the development of the wcfz are the mining height width of the protective coal pillars backfill percentage block length and number of mining blocks the relationships between these factors and the height of the wcfz were obtained by incorporating the relevant parameters in the above mentioned model in the field experiment site it was discovered that the minimum coal pillar width and goaf backfill percentage required to prevent the development of water conducting fractures that could reach an aquifer are 5 m and 65 respectively based on this result the protective pillars of the site were designed to be 5 m wide while the goaf backfill percentage was set as 80 the borehole fluid method was used to measure the height of the wcfz which was found to be 26 8 m this is consistent with the theoretical calculations 27 0 m of this study and thus validates the reliability of the proposed mechanical model the findings of this work will improve the recovery rate of residual coal resources in coal mining areas and they are significant for the refinement of water conservation mining theories

sampling statistic limitations on benthic foraminifera chemical and isotopic data abstract analyses of benthic foraminiferal isotopic and chemical properties are typically done on a small number of individuals often 5 10 because benthic sediment mixing produces a mix of individuals whose properties were determined at times encompassing several thousand years a sampling of several individuals does not adequately represent the average mixture a quantitative statistical analysis shows that this effect places a fundamental limit on measurement precision in cores especially where rapid environmental changes occur over short vertical distances the fundamental parameters defining this limit are the rate of change of the property per unit distance and the effective mixing depth in cores found in the vema channel rio grande rise region where sedimentation rates are about 1 cm ka 1 and mixing depths are about 3 cm a single sampling of six individuals can produce a result that has an expected one sigma standard deviation of 6 25 of the observed range precision can be improved by using more individuals or running more replicate analyses but the result only improves as the square root of the number of individuals or replicates this effect is illustrated by cd ca and isotopic data from low 0 7 cm ka 1 and moderate 1 5 cm ka 1 sedimentation rate cores although precision is compromised the most in low sedimentation rate cores this effect contributes to imprecision in high sedimentation rate cores as well