state of the art of modelling two phase flow in fractured rock two phase flow in fractured rock is an important phenomenon for a range of practical problems not the least of which is non aqueous phase liquid napl contamination of groundwater although multiphase systems have long been studied in the petroleum field in the hydrogeological field progress has only just reaches the point where models are being developed scale effect is one of the main issues of concern although models presented in this paper have the potential to provide useful predictions they can only be used to investigate a variety of possible scenarios with parameters being specified in the form of distribution of values the calibration and validation of all but the simplest of these models poses a formidable task with great demands on hydrogeologists and geophysicists to provide adequate data

a constitutive model for water flow in unsaturated fractured rocks a conceptual model for describing effective saturation in fractured hard rock is presented the fracture network and the rock matrix are considered as an equivalent continuum medium where each fracture is conceptualized as a porous medium of granular structure and the rock matrix is assumed to be impermeable the proposed model is based on the representation of a rough walled fracture by an equivalent porous medium which is described using classical constitutive models a simple closed form equation for the effective saturation is obtained when the van genuchten model is used to describe saturation inside fractures and fractal laws are assumed for both aperture and number of fractures the relative hydraulic conductivity for the fractured rock is predicted from a simple relation derived by liu and bodvarsson the proposed constitutive model contains three independent parameters which may be obtained by fitting the proposed effective saturation curve to experimental data two of the model parameters have physical meaning and can be identified with the reciprocal of the air entry pressure values in the fractures of minimum and maximum apertures effective saturation and relative hydraulic conductivity curves match fairly well the simulated constitutive relations obtained by liu and bodvarsson copyright 2008 john wiley sons ltd

a model for flow in the chalk unsaturated zone incorporating progressive weathering summary groundwater from unconfined chalk aquifers constitutes a major water resource in the uk the unsaturated zone in such systems plays a crucial role in the hydrological cycle determining the timing and magnitude of recharge and the transport and fate of nutrients however despite more than three decades of study our physical understanding of this system is incomplete in this research state of the art instrumentation provided high temporal resolution readings of soil moisture status rainfall and actual evaporation from two sites in the pang and lambourn catchments berkshire uk for a continuous two year period 2004 5 a parsimonious physically based model for the flow of water through the chalk unsaturated zone including a novel representation of the soil and weathered chalk layers was developed the parameters were identified by inverse modelling using field measurements of water content and matric potential the model was driven by rainfall and evaporation data and simulated fluxes throughout the profile including the discrete matrix and fracture components down to the water table but not the water table response results showed that the model was able to reproduce closely the observed changes in soil moisture status recharge was predominantly through the matrix and the recharge response was strongly attenuated with depth however the activation of fast recharge pathways through fractures in the chalk unsaturated zone was highly sensitive to rainfall intensity relatively modest increases in rainfall led to dramatically different recharge patterns with potentially important implications for groundwater flooding the development and migration of zero flux planes with time and depth were simulated the simulations also provided strong evidence that for water table depths greater than 5 m recharge fluxes persist throughout the entire year even during drought conditions with important implications for the calculation of specific yield from baseflow estimates and the representation of recharge in groundwater models

a continuum model for water movement in an unsaturated fractured rock mass the movement of fluids in a fractured porous medium has been the subject of considerable study this paper presents a continuum model that may be used to evaluate the isothermal movement of water in an unsaturated fractured porous medium under slowly changing conditions this continuum model was developed for use in evaluating the unsaturated zone at the yucca mountain site as a potential repository for high level nuclear waste thus its development has been influenced by the conditions thought to be present at yucca mountain a macroscopic approach and a microscopic approach are used to develop a continuum model to evaluate water movement in a fractured rock mass both approaches assume that the pressure head in the fractures and the matrix are identical in a plane perpendicular to flow both approaches lead to a single flow equation for a fractured rock mass the two approaches are used to calculate unsaturated hydrologic properties i e relative permeability and saturation as a function of pressure head for several types of tuff underlying yucca mountain using the best available hydrologic data for the matrix and the fractures rock mass properties calculated by both approaches are similar

influence of transitional volcanic strata on lateral diversion at yucca mountain nevada 1 natural hydraulic barriers exist at yucca mountain nevada a potential high level nuclear waste repository that have been identified as possible lateral diversions for reducing deep percolation through the waste storage area historical development of the conceptual model of lateral diversion has been limited by available field data but numerical investigations presented the possibility of significant lateral diversion due to the presence of a thin porous rock layer the paintbrush nonwelded tuffs analytical analyses of the influence of transitional changes in properties suggest that minimal lateral diversion is likely at yucca mountain numerical models to this point have not accounted for the gradual transition of properties or the existence of multiple layers that could inadvertently influence the simulation of lateral diversion as an artifact of numerical model discretization analyses were made of subsurface matric potential measurements and comparisons were made of surface infiltration estimates with deeper percolation flux calculations using chloride mass balance calculations and simulations of measured temperature profiles these analyses suggest that insignificant lateral diversion has occurred above the repository horizon and that water generally moves vertically through the paintbrush nonwelded tuffs

is enso a cycle or a series of events 1 after early ideas that saw el ninos as isolated events the advent of coupled models brought the conception of enso as a cycle in which each phase led to the next in a self sustained oscillation twenty two years of observations that represent the el nino and la nina peaks east pacific sst and the memory of the system zonal mean warm water volume suggest a distinct break in the cycle in which the coupled system is able to remain in a weak la nina state for up to two years so that memory of previous influences would be lost similarly while the amplitude of anomalies persists from the onset of a warm event through its termination there is no such persistence across the la nina break these observations suggest that el ninos are in fact event like disturbances to a stable basic state requiring an initiating impulse not contained in the dynamics of the cycle itself

a note on unsaturated flow in two dimensional fracture networks 1 although considerable progress has been made in understanding unsaturated flow processes in a single fracture our knowledge of unsaturated flow in fracture networks remains incomplete in this study we present a numerical investigation of steady flow behavior in two dimensional fracture networks containing thousands of fractures within a 10 m 10 m domain simulation results indicate that flow paths are generally vertical as a result of gravity dominated flow behavior with subhorizontal fractures providing pathways for communications between vertical flow paths inducing horizontal spreading of these paths although many fractures with small trace lengths do not contribute to the global flow through a fracture network some of them are still connected to the major flow paths and thus contribute to the overall connectivity of the network they may also considerably affect the interaction between fractures and the matrix on the basis of our simulation results we hypothesize that average spacing between flow paths in a layered system tends to increase with depth as long as flow is gravity driven we also discuss the concept of an influence zone of a capillary barrier to describe seepage from fracture networks to underground openings drifts our simulation results imply that three dimensional fracture network models are needed for providing a more realistic evaluation of capillary barrier effects

constitutive relations for unsaturated flow in a fracture network abstract modeling water flow in unsaturated fractured rocks is of interest to many areas of active research including geological disposal of nuclear waste and subsurface contaminant transport a commonly used approach for modeling water flow in unsaturated fractured rocks is the continuum approach in which the constitutive relation models originally developed for porous media have often been borrowed to represent constitutive relations for the fracture continuum while these models have been successfully used for soils and other porous media their usefulness and limitations have not been investigated for the fracture continuum the objectives of this study are 1 to present an evaluation of the commonly used van genuchten vg and brooks corey models by mainly comparing these models with constitutive relations simulated from two dimensional fracture networks and 2 to develop improved constitutive relation models based on the evaluation results we find that the vg model can reasonably well match the simulated water retention curves except for a range of high saturations but both the vg and brooks corey models generally underestimate relative permeability values simulation results also indicate that a combination of a modified brooks corey relative permeability saturation relation obtained by introducing a new expression for tortuosity and the vg capillary pressure saturation relation can generally represent the simulated curves with no additional parameters for this combination needed other than those used in the vg model

a comparison of sea surface salinity in the equatorial pacific ocean during the 1997 1998 2012 2013 and 2014 2015 enso events sea surface salinity sss variability during the 1997 1998 el nino event and the failed 2012 2013 and 2014 2015 el nino events is explored using a combination of observations and ocean reanalyses previously studies have mainly focused on the sea surface temperature sst and sea surface height ssh variability this analysis utilizes salinity data from argo and the simple ocean data assimilation soda reanalysis to examine the sss variability advective processes and evaporation minus precipitation e p variability is understood to influence sss variability using surface wind surface current evaporation and precipitation data we analyze the causes for the observed sss variability during each event barrier layer thickness and upper level salt content are also examined in connection to subsurface salinity variability both advective processes and e p variability are important during the generation and onset of a successful el nino while a lack of one or both of these processes leads to a failed enso event

side resistance of large diameter bored piles socketed into decomposed rocks the design of large diameter bored piles socketed into rock has received considerable attention in sedimentary rocks but has only occasionally been addressed in igneous and metamorphic rocks design methods based on the performance of sockets in sedimentary rocks have been proposed in literature but it is uncertain how applicable they are to other rock types large diameter 600 mm rock socketed piles were used in several recent developments in hong kong which involved 13 large scale pile load tests in various decomposed rocks the test piles varied in length from 20 to 60 m and in diameter from 1 0 to 1 3 m the test loads were as high as 30 mn this provides a golden opportunity for a study of the performance of piles socketed in igneous volcanic and metasedimentary rocks decomposed as a result of subtropical weathering in total 35 pile tests including 13 in hong kong in decomposed rocks together with 44 other tests in sedimentary rocks are reviewed side resistance is analyzed with regard to rock type and is compared to the findings and correlations published by others the rate of mobilization of side resistance was generally scattered in the test results as were the general shapes of the resistance displacement relationships a trend line was established relating the unconfined compressive strength to side resistance for granitic rocks during bidirectional multistage tests a reduction in the socket stiffness was observed with the second test stage for a given displacement the side resistance mobilized in the second stage was less than in the first

numerical analysis of laterally loaded 3 3 to 7 3 pile groups in sands the coupled bridge foundation superstructure finite element code flpier was employed to predict the lateral response of the single piles and 3 3 to 7 3 pile groups founded in both loose and medium dense sands the p multiplier factors suggested by mcvay et al for laterally loaded pile groups with multiple pile rows were implemented for the predictions the soil parameters were obtained through a back analysis procedure based on single pile test results the latter as well as the numerical predictions of both the single and group tests are presented it was found that the numerical code flpier did an excellent job of predicting the response of both the single piles and the 3 3 to 7 3 pile groups the latter involved the predictions of lateral load versus lateral deflection of the group the shears and bending moments developed in the individual piles and the distributions of the lateral loads in each pile row which were all in good agreement with the measured results

phase transition of the el nino southern oscillation a stationary sst mode a stationary sst mode is proposed to understand the physical mechanisms responsible for the phase transition of the el nino southern oscillation this stationary sst mode differs from the original delayed oscillator mode and the slow sst mode in the sense that it considers both balanced and unbalanced thermocline depth variations and does not take into account the zonal propagation of sst within this mode the walker circulation acts as a positive feedback mechanism to amplify and maintain an existing interannual sst anomaly whereas the hadley circulation acts as a negative feedback mechanism that dismisses the original anomaly and causes the phase shift from a warm cold to a cold warm episode the key to the cause of interannual oscillations in the stationary sst mode lies in the zonal mean thermocline depth variation that is not in equilibrium with the winds because of the nonequilibrium this part of the thermocline depth anomaly tends to have a phase lag with the wind or sst anomaly and therefore holds a key for the interannual oscillation the zonally asymmetric part of the thermocline depth anomaly on the other hand is always in sverdrup balance with the winds such a phase relationship agrees well with observations and with gcm simulations the stationary sst mode strongly depends on the basin width on the air sea coupling strength and on the seasonal cycle basic state for a reasonable parameter regime it depicts an interannual oscillation with a period of 2 7 years this stationary sst mode is also season dependent it has a maximum growth rate during the later part of the year and a negative growth rate during the northern spring which may explain the occurrence of the mature phases of the el nino in the northern winter and a rapid drop of the lagged correlation of the southern oscillation index in the boreal spring

upscaling of constitutive relations in unsaturated heterogeneous tuff matrix when numerical models are used for modeling large scale flow and transport processes in the subsurface upscaling is generally needed to determine large scale hydraulic properties from small scale measurements this study is focused on the upscaling of constitutive relations among relative permeability capillary pressure and saturation for unsaturated tuff matrix or a porous medium with a large air entry value unsaturated flow in tuff matrix is of interest at a number of existing and proposed waste disposal sites as well as in connection with environmental contamination in arid and semiarid regions based on the notion that a large air entry value corresponds to a spatially uniform capillary pressure distribution even at a relatively large scale for steady state unsaturated flow we present an upscaling approach for constitutive relations of tuff matrix numerical experiments were used to verify and demonstrate the usefulness of the approach

behavior of laterally loaded large section barrettes a barrette is a large cross section rectangular pile due to dependence of the flexural stiffness of the rectangular section on its orientation and the nonlinear behavior of barrette materials loading direction affects the lateral resistance of the barrette recently full scale lateral load tests were conducted on two barrettes in hong kong one db1 with a cross section of 2 8 m by 0 86 m and a length of 51 m and the other db2 with a cross section of 2 7 m by 1 2 m and a length of approximately 30 m this paper aims to investigate the response of laterally loaded large section barrettes based on the load tests to simulate the response of the two test barrettes and to study the influence of loading direction on the lateral response of barrettes nonlinear p y curves for soils and nonlinear stress strain relations for barrette concrete and reinforcement are used to simulate the lateral response of the test barrettes considering five loading directions the simulations were able to capture the apparently different behaviors before and after cracking of the barrette section sudden increases of displacement and rotation under a small lateral load increment and reduced depths of load transfer in the ground are predicted when the barrette section cracked based on this study the direction of the resultant horizontal displacement is different from the loading direction if the barrette is not loaded along the major or minor axis of the cross section

a variable aperture fracture network model for flow and transport in fractured rocks a three dimensional variable aperture fracture network model for flow and transport in fractured rocks was developed the model generates both the network of fractures and the variable aperture distribution of individual fractures in the network before solving for the flow and transport of the whole network a library of single fracture permeabilities and particle transport residence time spectra is first established the spatially varying aperture field within an individual fracture plane is constructed by geostatistical methods then the flow pattern the fracture transmissivity and the residence times for transport of particles through each fracture are calculated the library of transmissivities and frequency distributions of residence times is used for all fractures in the network by a random selection procedure the solution of flow through the fracture network and the particle tracking calculation of solute transport for the whole network are derived from one side of the network to the other the model thus developed can handle flow and transport from the single fracture scale to the multiple fracture scale the single fracture part of the model is consistent with earlier laboratory tests and field observations the multiple fracture aspect of the model was verified in the constant aperture fracture limit with an earlier code the simulated breakthrough curves obtained from the model display dispersion on two different scales as has been reported from field experiments

analysis of some laboratory tracer runs in natural fissures tracer tests in natural fissures performed in the laboratory are analyzed by means of fitting two different models in the experiments sorbing and nonsorbing tracers were injected into a natural fissure running parallel to the axis of a drill core the models take into account advection dispersion diffusion into the rock matrix and sorption onto the surface of the fissure and on the microfissures inside the matrix for the second mechanism one of the models considers hydrodynamic dispersion while the other model assumes channeling dispersion the models take into account time delays in the inlet and outlet channels the dispersion characteristics and water residence time were determined from the experiments with nonsorbing tracers surface and volume sorption coefficients and data on diffusion into the rock matrix were determined for the sorbing tracers the results are compared with values independently determined in the laboratory good agreement was obtained using either model when these models are used for prediction of tracer transport over larger distances the results will depend on the model the model with channeling dispersion will show a greater dispersion than the model with hydrodynamic dispersion assuming constant dispersivity

on two phase relative permeability and capillary pressure of rough walled rock fractures this paper presents a conceptual and numerical model of multiphase flow in fractures the void space of real rough walled rock fractures is conceptualized as a two dimensional heterogeneous porous medium characterized by aperture as a function of position in the fracture plane portions of a fracture are occupied by wetting and nonwetting phase respectively according to local capillary pressure and accessibility criteria phase occupancy and permeability are derived by assuming a parallel plate approximation for suitably small subregions in the fracture plane for log normal aperture distributions a simple approximation to fracture capillary pressure is obtained in closed form it is found to resemble the typical shape of leverett s j function wetting and non wetting phase relative permeabilities are calculated by numerically simulating single phase flows separately in the wetted and non wetted pore spaces illustrative examples indicate that relative permeabilities depend sensitively on the nature and range of spatial correlation between apertures it is also observed that interference between fluid phases flowing in a fracture tends to be strong with the sum of wetting and nonwetting phase relative permeabilities being considerably less than 1 at intermediate saturations

seasonal propagation of sea level along the equator in the atlantic in the equatorial atlantic the sea surface height ssh anomaly field is dominated by an annual signal propagating eastward this signal has been previously interpreted in terms of propagating waves in this article it is argued that this propagating signal is not a free equatorial kelvin wave because the phase velocity observed is too small compared to first second or third baroclinic mode kelvin waves and is not the result of an equatorial forced wave because the zonal wind stress does not show a similar propagation rather it is suggested that the eastward propagation in ssh is due to the sum of two independent modes of variability one mainly driven by the wind stress curl off the equator and the other driven by the zonal wind stress along the equator these two modes are uncorrelated in time and space and therefore can be conveniently separated by an empirical orthogonal function analysis of the equatorial atlantic sea surface height the first mode explains 74 of the variance is one signed in longitude and is interpreted as the variability of the warm water volume above the thermocline the second mode explains 24 of the variance consists of an east west tilt along the equator and is driven by variations of the zonal equatorial wind stress

tropical pacific variability in the ncar climate system model a 300 yr simulation with the ncar climate system model csm version 1 captured only 60 of the observed enso signal and exaggerated the interannual variability of sst in the western tropical pacific here a simulation with a new version of the csm which significantly improves the spatial and temporal patterns of tropical pacific variability is described maximum sst variability is shifted to the central and eastern pacific a better simulation of the equatorial pacific thermocline structure results in nino 3 and nino 4 statistics com parable to the observed estimates for the last century the evolution of sst and subsurface temperature anomalies is in excellent agreement with observed events the majority of events evolve as a standing mode with weak sst anomalies occurring in the northern spring in the eastern tropical pacific and maximum anomalies covering the eastern tropical pacific ocean to the date line by the following northern winter at the same time subsurface temperature anomalies spread eastward and upward along the tropical thermocline the delayed oscillator and wyrtki s buildup hypothesis are consistent with aspects of the csm simulation on the equator a westerly wind stress anomaly in the central pacific forces off equatorial upwelling anomalies which propagate westward reaching the western boundary about one half year later this upwelling signal then propagates eastward along the equator arriving 2 months before cooling in the eastern pacific basin the tropical pacific atmospheric response to warm oceanic events also agrees with observational analyses with a negative southern oscillation pattern in sea level pressure wind stress anomalies and low level convergence to the west of the maximum sst anomalies and enhanced deep convection and precipitation in the central and eastern tropical pacific

assessing the validity of the channel model of fracture aperture under field conditions in recent investigations of fluid and solute movement in discrete fractures spatial heterogeneity of the fracture aperture has been conceptualized as a series of noninterconnecting constant aperture flow paths or channels two methods of estimating the distribution of the aperture sizes are presented using information from a single hole pumping test and a radially converging tracer test the first method uses the transmissivity of the fracture and mean arrival time of the tracer while the second method uses the mean and variance of the solute arrival time if the fracture can be conceptualized as a series of nonintersecting flow paths of constant aperture the two methods should yield identical estimates for the parameters of the distribution the validity of the channel model can be assessed by comparing the parameters of the distribution that are estimated by the two methods this technique was demonstrated using hydraulic and tracer tests conducted in a discrete areally extensive horizontal fracture in the silurian dolomite in the northeastern illinois a lognormal and a truncated gamma distribution were used to describe the distribution of constant aperture flow paths the lognormal distribution could not reproduce the abrupt rising limb and maximum rate of mass arrival that characterized the tracer tests the gamma distribution more accurately predicted the shape of the breakthrough curves however the two methods of estimating the parameters of the distribution provided significantly different estimates of the variances of the aperture sizes the mean aperture as estimated by the two methods was similar the difference in the variance of the aperture as estimated by the two methods indicates that alternative conceptual models of aperture heterogeneity are required to more accurately describe both fluid and solute movement in this field situation

field studies of well instrumented barrette in hong kong over the last 15 years barette foundations have become increasingly popular in parts of asia such as hong kong and malaysia for many civil engineering structures and tall buildings a large excavated rectangular pile barette with lateral earth pressure and pore water pressure cells was successfully constructed and tested in a sequence of marine alluvial and weathered granite soils a soft base formed beneath the bottom of the barette permitted over 100 mm of vertical settlement completely mobilizing the shaft friction at the barette soil interface during the vertical load tests an unusual and complex response of pore water pressures and earth pressures at the barrette soil interface was measured during each vertical loading cycle except the last one and before interface slippage of the barrette occurred excess positive pore water pressures were recorded in all soil layers upon the initiation of slip at the barrette soil interface a sudden drop in the measured pore pressures as well as a substantial drop in lateral earth pressures generally resulted subsequent loading and unloading slippage events did not show the same dramatic behavior unless a period of consolidation recovery was allowed first this implies that caution must be used in design of barrettes relying heavily on skin friction when shearing induces contractive soil behavior the current test results indicated that the empirical uncorrected n value measured by standard penetration tests spt n approach and the deduced shaft friction coefficient beta value based on the effective stress principle effective stress beta method were inconsistent

hydrologic mechanisms governing fluid flow in a partially saturated fractured porous medium in contrast to the saturated zone within which fluid moves rapidly along fractures the fractures with apertures large relative to the size of matrix pores will desaturate first during the drainage process and the bulk of fluid flow would be through interconnected pores in the matrix within a partially drained fracture the presence of a relatively continuous air phase will produce practically an infinite resistance to liquid flow in the direction parallel to the fracture the residual liquid will be held by capillary force in regions around fracture contact areas where the apertures are small normal to the fracture surfaces the drained portion of the fractures will reduce the effective area for liquid flow from one matrix block to another matrix block a general statistical theory is constructed for flow along the fracture and for flow between the matrix blocks to the fractures under partially saturated conditions results are obtained from an aperture distribution model for fracture saturation hydraulic conductivity and effective matrix fracture flow areas as functions of pressure the effects of distortion of flow paths by the air pockets are taken into account by a phase separation constriction factor in a generalized cubic law for fracture flow under a partially saturated condition the reduction of matrix fracture flow area is taken into account by summing the aperture distribution function to a saturation cutoff aperture which is inversely proportional to the suction head drainage from a column of fractured tuff is simulated using available parameters for the densely welded tuff of the topopah spring member at yucca mountain southern nevada the column is bounded by discrete vertical fractures and dissected by horizontal fractures with the fracture spacings determined by the frequencies and orientations of fractured cores the fraction of fracture surfaces with coatings is assumed to correspond to the fraction of in situ fracture contact area the characteristic curves for the matrix are based on laboratory measurements of tuff samples from the cases simulated for the fractured porous columns with discrete vertical and horizontal fractures and porous matrix blocks explicitly taken into account it is observed that the highly transient changes from fully saturated conditions to partially saturated conditions are extremely sensitive to the fracture properties however the quasi steady changes of the fluid flow of a partially saturated fractured porous system could be approximately simulated without taking the fractures into account

wind stress curl and enso discharge recharge in the equatorial pacific discharge and recharge of the warm water volume wwv above the 20 c isotherm in an equatorial pacific ocean box extending across the pacific from 156 e to the eastern ocean boundary between latitudes 5 s and 5 n are key variables in enso dynamics a formula linking wwv anomalies zonally integrated wind stress curl anomalies along the northern and southern edges of the box and flow into the western end of the box is derived and tested using monthly data since 1993 consistent with previous work a wwv balance can only be achieved if the 20 c isotherm surface is not a material surface that is warm water can pass through it for example during el nino part of the wwv anomaly entering the box is cooled so that it is less than 20 c and therefore passes out of the bottom of the box the 20 c isotherm surface the observations suggest that the anomalous volume passing through the 20 c isotherm is approximately the same as t the anomalous wwv entering the western end of the box therefore the observed wwv anomaly can be regarded as being driven by the anomalous wind stress curl along the northern and southern edges of the box the curl anomaly changes the wwv both by divergent meridional flow at the edges of the box and vortex stretching that is the sverdrup balance does not hold in the upper ocean a typical amplitude for the rate of change of wwv for the 5 s 5 n box is 9 6 sv sv 10 6 m 3 s 1 the wind stress curl anomaly and the transport anomaly into the western end of the box are highly correlated with the el nino index nino 3 4 the average sea surface temperature anomaly ssta over the region 5 s 5 n 170 120 w and nino 3 4 leads minus the wwv anomaly by one quarter of a cycle based on the preceding results a simple discharge recharge coupled enso model is derived only water warmer than about 27 5 28 c can give rise to deep atmospheric convection so unlike past discharge recharge oscillator models the west central rather than eastern equatorial sstas are emphasized the model consists of two variables t the ssta averaged over the region of strong enso air sea interaction in the west central pacific equatorial strip 5 s 5 n 156 e 140 w and d the 20 c isotherm depth anomaly averaged over the

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

scale dependence of continuum models for fractured basalts numerical simulations are carried out to determine the scale above which an equivalent porous medium epm model can be used to represent flow through the dense interiors of fractured basalts steady laminar flow is assumed to occur through the interconnected network of conduits formed by the intersecting column defining fracture patterns of the basalt dense interiors the basalt rock matrix is considered to be impermeable a porous medium equivalence is established in terms of fluid darcian fluxes a polar plot for the equivalent hydraulic conductivity is used to test whether a given fractured basalt system can be approximated as an epm for interconnected colonnade network models of filled or unfilled fractures with uniform apertures and a column diameter of 1 m epm models are appropriate at a length scale of approximately 6 times the column diameter for network models of filled or unfilled fractures with a lognormal aperture b millimeters distribution mean in b 1 945 and ln b 0 896 epm models can be justified at length scales of approximately 22 and 27 times the column diameter respectively the computed equivalent k values for clay filled fractures compare favorably with the field measured data this suggests that a model comprised of an interconnected network of filled fractures may not be an unlikely representation of flow through the dense interiors at the small scales considered in this study several limitations of the study are noted

numerical investigation of steady liquid water flow in a variably saturated fracture network numerical simulation was used to study steady liquid water movement in a 5 m by 5 m vertical section containing a hypothetical fracture network under conditions of variable saturation the fracture network was assumed to be embedded within an impermeable rock matrix three variations of a network were considered the mixed network consisted of two fracture sets a subvertical set containing five 125 m average aperture fractures and a subhorizontal set containing four 25 m average aperture fractures the other two networks had identical fracture orientation and contained either all 125 m or all 25 m average aperture fractures the tough simulator was used to calculate the total steady liquid water flux through the network the flux through individual fracture segments and the pressure head at each fracture segment a unit hydraulic gradient was imposed on the network by applying fixed pressure head boundaries ranging from 0 25 to 0 0 m of water of equal value to the top and bottom saturation and permeability versus pressure head relations for the two sets of fractures were determined with the vsfrac model which assumed that aperture was variable within an individual fracture results showed that the spatial distributions of pressure head and flux within the network as well as the location of the dominant pathways depended strongly on the prescribed boundary pressure head for the mixed network both pressure head and flux tended to become more spatially uniform when the boundary pressure head approached the pressure head at which the permeability thickness products of the large and small aperture fractures are equal the crossover pressure head these results imply that for systems similar to the one considered here interpretation of actual measurements of pressure head and flux may be quite complex and that representation of variably saturated fracture networks as an equivalent continuum may be more valid for some ranges in pressure head than for others equivalent permeability as a function of pressure head was calculated for the fracture network illustrating how information collected on individual fractures may be used to estimate the flow properties of rock at larger scales

infiltration of a liquid front in an unsaturated fractured porous medium we consider liquid infiltrating by gravity flow into a system of parallel regularly spaced fractures in an unsaturated porous medium the position of the fracture liquid front as a function of time under some simplifying assumptions is shown to obey a nonlinear integrodifferential equation approximate analytic solutions are developed showing that the movement of the liquid front exhibits three major flow periods 1 at early time the frontal position is determined by the fracture inlet boundary condition and the gravity driven flow behavior of the fracture with negligible influence by the matrix 2 at intermediate time matrix imbibition retards the frontal advance against the pull of gravity 3 at late time the matrix approaches saturation and the frontal velocity approaches a limiting value a two dimensional numerical model is used to confirm the approximate solutions implications of the model for nuclear waste storage are discussed the analysis is applicable not only to fractured rock but also to lateral infiltration into coarse grained sediments lying between layers of fine grained soil

a fractal constitutive model for unsaturated flow in fractured hard rocks abstract a physical conceptual model for water retention in self similar fractured hard rocks is presented the geometric pattern of the fracture network is described using a classical fractal object known as the sierpinski carpet assuming this type of geometry a relatively simple closed form expression for the water content is obtained all model parameters can be calculated from the density of the main fractures the maximum and minimum values of the fracture aperture and the residual water content the resulting water content expression is then used to estimate the unsaturated hydraulic conductivity of the fractured medium based upon the well known model of burdine it is found that for large enough ranges of fracture apertures the new constitutive model converges to the empirical brooks corey model

transient simulations of flow and transport in the chalk unsaturated zone chalk is a fractured porous medium composed of matrix blocks bounded by interconnected fractures furthermore there are a number of commonly observed and apparently contradictory phenomena these include a fast water table response slow solute migration and very little solute dispersion to the authors knowledge no unified physically based numerical model has been able to reconcile all of these points in this paper these issues were addressed through the development of a transient dual permeability model of flow and transport the behaviour of the model was explored through a hypothetical scenario the one dimensional model featured a fixed water table at 10 m depth a recharge time series derived using the penman grindley model in conjunction with daily precipitation and monthly potential evaporation data from the kennet valley berkshire was applied at the top of the model a conservative solute that could be tritium chloride or nitrate was applied to the recharge for 1 year subsequent years involved the input of clean water the simulations suggested that although transient effects have been previously neglected overlying soil and gravelly chalk layers are likely to cause significant attenuating effects on flow such that most flow occurs through the matrix fracture flow was found to be episodic and infrequent and represented between 17 and 30 of the annual recharge

field observation of flow in a fracture intersecting unsaturated chalk flow through a natural fracture crossing unsaturated chalk in an arid region was investigated in a field experiment using a specially designed experimental setup the setup allowed complete control of the flow domain inlet and outlet water flux into and out of the fracture was measured in small segments of the fracture openings and flow trajectories were identified using seven fluorobenzoic acid tracers a 5 day percolation experiment on a 5 3 m long fracture showed significant spatial and temporal variability of the flow regime flow through fracture openings did not reach a steady state either in individual segments or across the entire flow domain although the boundary conditions were kept relatively steady for the entire duration of the experiment flow trajectories within the fracture plane varied over time however most of the flow was confined to small sections of the fracture over 70 of the flux was transmitted through 20 of the studied fracture openings observations from the tracer tests suggest that flow paths can coexist near each other without water mixing probably because the fracture fill generates unconnected flow paths across the main fracture void

lateral load behavior of full scale pile group in clay a static lateral load test was performed on a full scale pile group to determine the resulting pile soil pile interaction effects the 3 3 pile group at three diameter spacing was driven into a profile consisting of soft to medium stiff clays and silts underlain by sand the piles were instrumented with inclinometers and strain gages the load carried by each pile was measured a single pile test was conducted for comparison the pile group deflected over two times more than the single pile under the same average load group effects significantly reduced load capacity for all rows relative to single pile behavior trailing rows carried less than the leading row and middle row piles carried the lowest loads maximum moments in the group piles were 50 100 higher than in the single pile p multipliers were 0 6 0 38 and 0 43 for the front middle and back row piles respectively good agreement between the measured and computed pile group responses was obtained using the p multiplier approach design c

an examination of some enso mechanisms using interannual sea level at the eastern and western equatorial boundaries and the zonally averaged equatorial wind abstract theory suggests that the interannual equatorial kelvin wave sea level w in the western pacific should be directly proportional to the interannual western australian sea level and the interannual equatorial kelvin wave sea level e in the eastern pacific should be directly proportional to the equatorial interannual sea level at the south american coast forced equatorial kelvin wave dynamics implies approximately that e t t w t b t t where t b and are respectively a lag corresponding to equatorial kelvin wave propagation zonally averaged equatorial interannual eastward wind stress a forcing coefficient and a number between 0 and 1 a regression analysis of the sea level difference above using western australian and south american sea levels against shows that the correlation is high and is highest 0 83 when deltat 3 months and deltat 1 month the values for deltat and b are reasonable for they are appropriate for a signal dominated by the first

on thermohydrologic conditions near high level nuclear wastes emplaced in partially saturated fractured tuff 2 effective continuum approximation this paper presents an effective continuum approximation for modeling of fluid and heat flow in fractured porous media the approximation is based on the thermohydrologic behavior observed in detailed simulations with explicit consideration of fracture effects see the companion paper part 1 the crucial concept in the development of an effective continuum approximation is the notion of local thermodynamic equilibrium between rock matrix and fractures where applicable it provides a substantial simplification of the description of fluid and heat flow in fractured porous media we derive formulas for effective continuum characteristic curves relative permeabilities and capillary pressures in terms of the properties of fracture and matrix continua respectively numerical simulations demonstrate that under favorable conditions the effective continuum approximation closely matches predictions obtained from an explicit modeling of fracture effects it is also demonstrated that the approximation breaks down under unfavorable conditions very tight rock matrix a simple criterion for the applicability of an effective continuum approximation is derived from consideration of diffusive processes a quantitative evaluation shows the criterion to be consistent with results of our numerical simulations

on thermohydrologic conditions near high level nuclear wastes emplaced in partially saturated fractured tuff 1 simulation studies with explicit consideration of fracture effects we have performed modeling studies on the simultaneous transport of heat liquid water vapor and air in partially saturated fractured porous rock formation parameters were chosen as representative of the potential nuclear waste repository site in the topopah spring unit of the yucca mountain tuffs the presence of fractures makes the transport problem very complex both in terms of flow geometry and physics the numerical simulator used for our flow calculations takes into account most of the physical effects believed to be important in multiphase fluid and heat flow it has provisions for handling the extreme nonlinearities that arise in phase transitions component disappearances and capillary discontinuities at fracture faces we model a region around an infinite linear string of nuclear waste canisters taking into account both the discrete fractures and the porous matrix thermohydrologic conditions in the vicinity of the waste packages are found to depend strongly on relative permeability and capillary pressure characteristics of the fractures which are unknown at the present time if liquid held on the rough walls of drained fractures is assumed to be mobile strong heat pipe effects are predicted under these conditions the host rock will remain in two phase conditions right up to the emplacement hole and formation temperatures will peak near 100 c if it is assumed that liquid cannot move along drained fractures the region surrounding the waste packages is predicted to dry up and formation temperatures will rise beyond 200 c a substantial fraction of waste heat can be removed if emplacement holes are left open and ventilated as opposed to backfilled and sealed emplacement conditions comparing our model predictions with observations from in situ heater experiments reported by zimmerman and coworkers some intriguing similarities are noted however for a quantitative evaluation additional carefully controlled laboratory and field experiments will be needed

application of the discrete fracture network concept with field data possibilities of model calibration and validation the uneven flow distribution observed in a migration experiment in the stripa research mine is analyzed with a discrete fracture network model data on the measured inflow distribution and trace geometry in the experimental drift are the basic sources for estimation of the model parameters direct estimates cannot provide a unique definition of input data to the model thus different combinations of input data need to be analyzed in the network model detailed measurements of the inflow distribution in the experimental drift provided an opportunity to determine the model parameters through calibration in the network model calibration was performed on the mean inflow distribution of flow and trace geometry observed in the roof of the experimental drift the simulation results show that the model can be calibrated to produce an areal flow distribution that is consistent with the measured one the uncertainties in the input parameters are thus reduced but different combinations of input data are still possible the calibration simulations show that the length of conductive fractures per area might be used as a calibration parameter simulations based on different combinations of fracture size and density but with the same length of conductive fracture traces produced similar flow distributions the validity of the calibrated model is explored by predicting the flow into the boreholes at the experimental site the resulting inflow distributions accord well with those measured in two of the three boreholes the properties of the third borehole which differ substantially from the other two could not be explained by the simulation results

evidence of boundary reflection of kelvin and first mode rossby waves from topex poseidon sea level data the topex poseidon sea level data lead to new opportunities to investigate some theoretical mechanisms suggested to be involved in the el nino southern oscillation phenomenon in the tropical pacific ocean in particular we are interested in studying the western boundary reflection a process crucial for the delayed action oscillator theory by using the topex poseidon data from november 1992 to may 1995 we first projected the sea level data onto kelvin and first mode rossby waves then we estimated the contribution of wind forcing to these waves by using a single baroclinic mode simple wave model forced by the ers 1 wind data wave propagation was clearly observed with amplitudes well explained by the wind forcing in the ocean interior evidence of wave reflection was detected at both the western and eastern boundaries of the tropical pacific ocean at the eastern boundary kelvin waves were seen to reflect as first mode rossby waves during the entire period the reflection efficiency in terms of wave amplitude of the south american coasts was estimated to be 80 of that of an infinite meridional wall at the western boundary reflection was observed in april august 1993 in january june 1994 and later in december 1994 to february 1995 although the general roles of these reflection events in the variability observed in the equatorial pacific ocean are not clear the data suggest that the reflections in january june 1994 have played a role in the onset of the warm conditions observed in late 1994 to early 1995 indeed during the january june 1994 period as strong downwelling first mode rossby waves reflected into downwelling kelvin waves easterly wind and cold sea surface temperature anomalies located near the date line weakened and eventually reversed in june july 1994 the presence of the warm anomalies near the date line then favored convection and westerly wind anomalies that triggered strong downwelling kelvin waves propagating throughout the basin simultaneously with the beginning of the 1994 1995 warm conditions

study of soil layering effects on lateral loading behavior of piles this paper presents results of the finite element study on the behavior of a single pile in elastic plastic soils pile behavior in uniform sand and clay soils as well as cases with a sand layer in a clay deposit and a clay layer in a sand deposit were analyzed using finite element modeling finite element results were used to generate p y response curves which were cross compared to investigate the soil layering effects