prandtl s mixing length concept modified for equilibrium sediment laden flows the prandtl von karman mixing length concept for clear water flows is generalized for sediment laden flows the new model is applied for the analysis of dilute equilibrium sediment laden flows down an inclined flat bed composed of mobile suspendable sediment particles the derivation and the features of the modified formulation are discussed in detail the model incorporates the effect of density stratification and accounts for the presence of a solid phase in the flow computational results are compared with experimental data the model successfully explains the observed characteristics of these flows

effects of borehole stress concentrations on dipole anisotropy measurements we show both experimentally and theoretically how stress concentrations affect the velocity field around a borehole and how the velocity field influences dipole anisotropy measurements at low frequencies the dipole mode is sensitive to the far field stresses primarily so standard sonic log interpretation correctly yields the direction of maximum stress at higher frequencies the dipole mode is sensitive to near field stress concentrations such that the fast polarization direction is aligned with the direction of minimum tectonic stress these effects combine to produce a crossover in the dipole dispersion curves measured in the fast and slow directions with broad band dipole data the dispersion crossover can be used as an indicator of stress induced anisotropy dominating over weak intrinsic anisotropy

subsurface settlement profiles above tunnels in clays designers assessing the possible effect of tunnelling on structures relatively close to the tunnel crown need to know how subsurface settlement profiles develop and how these relate to surface settlement profiles the effect on piled foundations or existing tunnels depends on the width of the subsurface settlement profile and on the magnitude of the settlement this note uses available field measurements and centrifuge model test data to determine how the widths of the settlement profiles and the magnitudes of settlement vary with depth above tunnels constructed in clays the results reveal a fairly consistent pattern of behaviour the width of the subsurface settlement troughs at depth is significantly greater than would be predicted by assuming a constant trough width parameter k of 0 5 smaller more realistic subsurface settlements and strains will be predicted if account is taken of the proportionally wider trough widths at depth

simulation of the effect of stress induced anisotropy on borehole compressional wave propagation abstractformation elastic properties near a borehole may be altered from their original state due to the stress concentration around the borehole this can lead to an incorrect estimation of formation elastic properties measured from sonic logs previous work has focused on estimating the elastic properties of the formation surrounding a borehole under anisotropic stress loading we studied the effect of borehole stress concentration on sonic logging in a moderately consolidated berea sandstone using a two step approach first we used an iterative approach which combines a rock physics model and a finite element method to calculate the stress dependent elastic properties of the rock around a borehole subjected to an anisotropic stress loading second we used the anisotropic elastic model obtained from the first step and a finite difference method to simulate the acoustic response of the borehole although we neglected the effects of rock failure and stress induced crack opening our modeling results p

fluid and sediment dynamics of upper stage plane beds to understand more fully the fluid and sediment dynamics of upper stage plane beds laboratory experiments were conducted using mobile and fixed beds where turbulent motions of fluid and sediment were measured using laser anemometry bed elevation fluctuations on mobile upper stage plane beds reveal millimeter high bed waves vertical profiles of flow velocity mixing length and eddy viscosity diffusivity are represented well by the law of the wall for the mobile bed von karman s 0 33 and equivalent sand roughness to mean bed grain size varies from 9 to 17 because of the presence of bed load and low relief bed waves for fixed beds with no sediment transport 0 41 and equivalent sand roughness is equal to the mean bedgrain size the decrease in for mobile beds is related to the relative motion of grains and fluid mobile bed turbulence intensities are greater than those for sediment free fixed beds because of enhanced wake formation from the lee side of near bed grains and low relief bed waves sediment diffusivities es calculated in a similar way to fluid diffusivities e indicate that es e sediment diffusivities calculated using the equilibrium balance between upward diffusion and downward settling of sediment are similar to e in near bed regions y d 0 3 suggesting that larger more energetic turbulent eddies are responsible for sediment suspension higher in the flow

analytical approach for estimating ground deformation profile induced by normal faulting in undrained clay although theoretical models have been developed to predict the location of the failure surface in soil induced by bedrock faulting no analytical tool is available to estimate subsurface ground deformation in this paper a newly developed semi empirical approach is introduced and developed for calculating surface and subsurface deformations induced by normal faulting in undrained clay based on observations from centrifuge model tests the ground deformation mechanisms are identified by three regions namely a stationary zone a shearing zone and a rigid body zone by using an error function to represent vertical displacement continuously the ground deformation profile can be described quantitatively it is revealed that the ground deformation profile depends on vertical displacement of the bedrock hanging wall soil thickness dip angle of the bedrock fault plane and a shape parameter that is a function of the undrained shear modulus normalized by the undrained shear strength validation and consist

an approach for predicting stress induced anisotropy around a borehole abstractformation elastic properties near a borehole may be altered from their original state due to the stress concentration around the borehole this could result in a biased estimation of formation properties but could provide a means to estimate in situ stress from sonic logging data to properly account for the formation property alteration we propose an iterative numerical approach to calculate stress induced anisotropy around a borehole by combining a rock physics model and a finite element method we tested the validity and accuracy of our approach by comparing numerical results to laboratory measurements of the stress strain relation of a sample of berea sandstone which contains a borehole and is subjected to a uniaxial stress loading our iterative approach converges very fast and can be applied to calculate the spatially varying stiffness tensor of the formation around a borehole for any given stress state

crustal stress determination from boreholes and rock cores fundamental principles abstract obtaining quantitative information on the state of stress in the crust can only be accomplished by accessing the zone of interest by drilling the borehole cavity however disrupts the virgin stress state by concentrating stresses in predictable patterns with a number of consequences at sufficiently low stress magnitudes the concentrated stresses amplify the elastic anisotropy azimuthally around the borehole because the elastic properties of most rocks depend nonlinearly on stress at higher levels the stresses damage then fracture the rock near the wellbore wall or within a growing core stub indeed almost all of the borehole techniques indirectly measure stress through these manifestations of the concentrated stresses this contribution reviews at a fundamental level the concentration of stresses by the borehole the effects on the materials in the borehole s vicinity and how these are used to infer stress states stress concentrations applied to rocks which are generally nonlinear elastic materials induce both radial and azimuthal variations in elastic wave speeds near the borehole that can be used to infer stress directions from advanced acoustic logging methods hydraulic fractures initiate propagate and remain propped open by measured pressures that can be interpreted with knowledge of the stress concentrations to obtain quantitative stress magnitudes at higher stress levels the rock fails producing borehole breakouts or drilling induced tensile fractures both of which are indicative of stress directions and can be used to constrain stress magnitudes similarly the various styles of drilling induced core fractures indicate both stress directions and the faulting environment encountered unfortunately no method currently allows for complete determination of the stress tensor using a number of different but complementary techniques is necessary to best constrain in situ stress states

three dimensional deformation behavior of the taipei national enterprise center tnec excavation case history the taipei national enterprise center tnec excavation project was constructed using the top down construction method in which a diaphragm wall was supported by the concrete floor slab previous

transport equation for suspended sediment based on two fluid model of solid liquid two phase flows most theoretical and numerical studies employ diffusion theory to investigate suspended sediment distributions in fluvial rivers yet diffusion theory based descriptions are strictly valid only in the limit of small particle inertia and low concentrations this paper presents a transport equation for sediment in suspension based on a two fluid model of solid liquid two phase flows the transport equation is derived from the consideration of mass conservation for solid particles the velocity of the solid phase is obtained from an asymptotic solution of the momentum conservation equation for solid phase moreover this transport equation is a typical convection diffusion equation that includes the conventional diffusion equation as a special case when particle inertia is small and concentrations are low retaining the essential features of two fluid models the transport equation is applicable to sediment laden flows with a wide range of particle inertia and sediment concentrations comparisons of the results with available experimental observations are presented and fairly good agreement is obtained doi 10 1061 asce hy 1943 7900 0000331 2011 american society of civil engineers ce database subject headings suspended sediment two phase flow open channels solids flow author keywords suspended sediments sediment concentration two phase flow open channels

applications of perturbation theory to acoustic logging to study the normal modes generated during acoustic logging the authors have developed a method to calculate 1 phase velocities when the formation has slight general anisotropy 2 partial derivatives of either the wave number or frequency with respect to either an elastic modulus or density 3 group velocities and 4 phase velocities when the cross section of the borehole is slightly irregular the method which is based upon perturbation theory relates first order perturbations in frequency wave number elastic moduli densities and locations of interfaces for a general model with many fluid and solid layers which have any cross sectional shape and any type of anisotropy to demonstrate the use of this method formulas for the four applications are developed for a relatively simple model consisting of a fluid filled borehole through a transversely isotropic solid with its symmetry axis parallel to the borehole and some sample calculations are performed using these examples formulas for more complicated borehole models that may be appropriate for some field situations could readily be developed the significance of this work is that three applications can be used to study the normal modes when the borehole environment is complicated and the other can be used in anmore inversion for formation properties less

predicting stress induced velocity anisotropy in rocks a simple transformation using measured isotropic vp and vs versus hydrostatic pressure is presented for predicting stress induced seismic velocity anisotropy in rocks the compliant crack like portions of the pore space are characterized by generalized compressional and shear compliances that are estimated from the isotropic vp and vs the physical assumption that the compliant porosity is crack like means that the pressure dependence of the generalized compliances is governed primarily by normal tractions resolved across cracks and defects this allows the measured pressure dependence to be mapped from the hydrostatic stress state to any applied nonhydrostatic stress predicted p and s wave velocities agree reasonably well with uniaxial stress data for barre granite and massillon sandstone while it is mechanically similar to methods based on idealized ellipsoidal cracks the approach is relatively independent of any assumed crack geometry and is not limited to small crack densities

is the von karman constant affected by sediment suspension 1 is the von karman constant affected by sediment suspension the presence of suspended sediment in channels and fluvial streams has been known for decades to affect turbulence transfer mechanism in sediment laden flows and therefore the transport and fate of sediments that determine the bathymetry of natural water courses this study explores the density stratification effects on the turbulent velocity profile and its impact on the transport of sediment there is as yet no consensus in the scientific community on the effect of sediment suspension on the von karman parameter two different theories based on the empirical log wake velocity profile are currently under debate one supports a universal value of 0 41 and a strength of the wake that is affected by suspended sediment the other suggests that both and could vary with suspended sediment these different theories result in a conceptual problem regarding the effect of suspended sediment on which has divided the research area in this study a new mixing length theory is proposed to describe theoretically the turbulent velocity profile the analytical approach provides added insight defining as a turbulent parameter which varies with the distance to the bed in sediment laden flows the theory is compared with previous experimental data and simulations using ak eturbulence closure to the reynolds averaged navier stokes equations model the mixing length model indicates that the two contradictory theories incorporate the stratified flow effect into a different component of the log wake law the results of this work show that the log wake fit with a reduced is the physically coherent approximation

static and dynamic pressure sensitivity anisotropy of a calcareous shale optimizing the productivity of nonconventional low permeability shale reservoirs requires detailed knowledge of the mechanical properties of such materials these rocks elastic anisotropy is acknowledged but usually ignored due to difficulties in obtaining such information here we study in detail the dynamic and static elastic properties of a suite of calcareous mudstones from the nonconventional duvernay reservoir of alberta canada the complete set of transversely isotropic elastic constants is obtained from strategically oriented ultrasonic transducers to confining pressures of 90 mpa wave speed anisotropies of up to 35 are observed at even the highest confining pressures furthermore the stress sensitivity of the wave speeds and hence moduli is itself highly dependent on direction with speeds taken perpendicular to the bedding plane being highly nonlinearly dependent on pressure whereas those along the bedding plane show unexpectedly nearly no pressure dependence these observations are in qualitative agreement with the preferentially oriented porosity and minerals seen in scanning electron microscope images these results may be significant to the interpretation of sonic logs and azimuthal amplitude versus offset for principal stress directions for the concentration of stress within such formations and for estimation of static engineering moduli from sonic log wave speeds

effect of particle concentration on sediment and turbulent diffusion coefficients in open channel turbulent flow to achieve a complete knowledge about the effect of particle concentration on sediment and turbulent diffusion coefficients in open channel turbulent flow is a long standing problem for the community of researchers the effect of particle concentration is investigated on the sediment and turbulent diffusion coefficients through the inverse of turbulent schmidt number or which is defined by the ratio of sediment diffusion coefficient to turbulent diffusion coefficient it is observed that with increasing particle concentration the sediment diffusion coefficient decreases more in comparison with the turbulent diffusion coefficient for both dilute and non dilute sediment laden flows the physical characteristics of observed are expressed mathematically in terms of normalized settling velocity reference level and reference concentration the applicability of the mathematical formulae is confirmed by the agreement analysis between experimental data and particle concentration profile computed from the rouse equations modified through the newly proposed expression of apart from the better agreement between dilute particle concentration data and the developed rouse equation the striking observation is that the modified rouse equation shows reasonable computational accuracy for non dilute particle concentration data also minimum error is obtained from the present model when it is compared with the models proposed by the previous researchers

drift velocity concept for sediment laden flows the vertical distribution of suspended sediment concentration in open channel flows is usually described by the advection diffusion equation hence only the mechanisms of advection and diffusion affect the movement of sediment particles however recent publications show that the equation could not describe fully the sediment concentration distribution in open channels a new model for particle migration in sediment laden turbulent flow is presented the model assumes there is an additional mechanism influencing the particle movement in sediment laden flows a new mechanism which is called the drift acts independently of advection and turbulent diffusion based on all three mechanisms a new equation for the concentration distribution is derived the equation describes the vertical distribution of sediment concentration more accurately than the advection diffusion equation

the disturbance of drilling mud on rock formation and a method for error elimination on acoustic log curves errors in acoustic logs have a significant influence on the assessment of formations the description of oil deposits and modelling using synthetic seismograms the elimination of these errors is a problem that many researchers have been trying to solve for many years we derive theoretical formulae for calculating the radial depth of investigation of acoustic logging and analyse the relationship between the error in acoustic interval transit time and the altered zone thickness we explain in detail how mud affects the acoustic interval transit time we also describe the variation of altered zone thickness with time and a method for calculating the altered zone thickness finally we present a set of new methods that can be directly applied to correct the disturbing influence on acoustic curves our results are obtained based on the fact that acoustic velocities in the altered zone show a small lateral variation examples are given of analysing the acoustic log data which are collected from a bs well at three different times this paper is significant both for selection of the acoustic logging device with proper transmitter to receiver distance spacing and improvement of the device

mapping the mechanical properties of rocks using automated microindentation tests a microindentation scanner is constructed that measures the spatial fluctuation in the elastic properties of natural rocks this novel instrument performs automated indentation tests on the surface of a rock slab and outputs 2 d maps of the indentation modulus at submillimeter resolution maps obtained for clean well consolidated sandstone are presented and demonstrate the capabilities of the instrument we observe that the elastic structure of sandstones correlates well with their visual appearance further we show that the probability distribution of the indentation modulus fluctuations across the slab surfaces can be modeled using a lognormal probability density function to illustrate possible use of the data obtained with the microindentation scanner we use roughly 10 cm 10 cm scans with millimeter resolution over four sandstone planar slabs to numerically compute the overall drained elastic moduli for each sandstone sample we show that such numerically computed moduli are well modeled using the multicomponent form of the hashin shtrikman lower bound that employs the observed lognormal probability distribution for the mesoscopic scale moduli the geometric mean works almost the same we also compute the seismic attenuation versus frequency associated with wave induced fluid flow between the heterogeneities in the scanned sandstones and observe relatively small values for the inverse quality factor q 1 10 2 in the seismic frequency band 102 hz f 104 hz the numerically computed frequency dependence in the attenuation varies from one type of sandstone to another and we observe significant anisotropy in the attenuation associated with waves propagating in different directions

azimuthal velocity variations caused by borehole stress concentrations in laboratory experiments borehole stress concentrations caused by far field uniaxial stress produce measurable variations in compressional wave velocities near the borehole uniaxial stress was applied perpendicular to the axis of a borehole drilled through a sandstone block inside the fluid filled borehole refracted compressional waves were propagated in the rock parallel to the borehole axis at discrete azimuths producing a scan of velocity versus azimuth as uniaxial stress increased significant variations of compressional wave velocity with azimuth developed of the order of 10 variation the azimuth of velocity minima provides an excellent indicator of the direction of maximum far field uniaxial stress accurate to 5 the detailed variation of velocity with azimuth while approximately sinusoidal has sufficient character to provide new information about the rock one interpretation yields the curvature of the velocity versus stress curve of the rock

seismic anisotropy in sedimentary rocks part 2 laboratory data part one of this paper presents a method for measuring seismic velocities and transverse isotropy in rocks using a single core plug this method saves at least two thirds of the time for preparing core samples and measuring velocities in transversely isotropic ti rocks using this method we have measured velocity and anisotropy of many shale and reservoir rocks from oil and gas fields around the world we present some of the data in this paper which include seismic velocity and anisotropy in 17 brine saturated shale samples 1 gas and brine saturated coal sample 8 brine saturated sands 12 gas saturated sands 32 gas saturated carbonate samples and 25 brine saturated carbonate samples the results show that clays and fine layering in sedimentary rocks are the main causes of seismic anisotropy very little intrinsic anisotropy exists in unfractured reservoir rocks such as sands sandstones and carbonates under reservoir conditions in contrast all shales were found seismically anisotropic anisotr

sensitivity and inversion of borehole flexural dispersions for formation parameters propagation characteristics of borehole flexural waves are functions of five borehole fluid and formation parameters uncertainties in any of these model parameters may introduce errors in the estimate of formation shear wave speed other sources of error in the estimate may be caused by deviations from the assumed circular borehole cross section or heterogeneity in the material properties of formation in the vicinity of a borehole from the usually assumed homogeneous properties the influence of uncertainties in model parameters on borehole flexural dispersion has been calculated from a general perturbation model based on hamilton s principle a sensitivity analysis of the flexural dispersion to small variations in the model parameters shows that the formation shear speed has by far the most dominant influence in a slow formation in contrast the flexural dispersion in a fast formation is significantly influenced by three of the five model parameters the formation shear speed the borehole fluid compressional speed and the borehole diameter the frequency dependence of these sensitivity functions indicates that the inversion of flexural dispersion for formation shear speed is optimal in the range 2 4 khz for a borehole of diameter 25 4 cm the range of validity of the perturbation model has been estimated by comparing results of concentric annuli of different thicknesses and shear wave speeds different from that of the formation with those from exact numerical solutions from a modal search program generally the perturbation results for altered annuli of thicknesses up to 15 cm are accurate to within 1 per cent for a shear wave speed 10 per cent lower than that of the formation this difference between the perturbation and exact results increases to approximately 1 to 3 per cent for a shear wave speed 20 per cent lower than that of the formation

shape of ground surface settlement profiles caused by excavation there are two general types of settlement profiles induced by excavation the spandrel type and the concave type based on a regression analysis of the field observations of settlement curves with

turbulence measurements in open channel flows over artificial bed forms measurements of mean and turbulence characteristics in uniform open channel flows of constant mean depth over artificial fixed one dimensional periodic bed features were obtained using two component laser doppler velocimetry two types of bed forms based on triangular elements of the same height n 20 of the flow depth and wavelength n 12 5 times the height but of different shape were studied 1 45 triangle ridges separated by a flat region and 2 triangular elements approximating dunes with a mildly sloping upstream face instead of a flat region the role of the total shear velocity based on the mean energy slope and the mean flow depth as a possible velocity scale is studied velocity defect and the reynolds shear stress profiles were generally well approximated by the flat bed profiles for regions of flow far from the bed sufficiently far from the recirculation and reattachment zones turbulence characteristics collapsed fairly well when scaled with the total shear velocity over most of the depth but do not follow the flat bed behavior in the lower part of the flow possible implications of the clear water measurements for the description of suspended sediment concentration profiles and total suspended load computations are explored

ultrasonic velocities acoustic emission characteristics and crack damage of basalt and granite acoustic emissions ae compressional p shear s wave velocities and volumetric strain of etna basalt and aue granite were measured simultaneously during triaxial compression tests deformation induced ae activity and velocity changes were monitored using twelve p wave sensors and eight orthogonally polarized s wave piezoelectric sensors volumetric strain was measured using two pairs of orthogonal strain gages glued directly to the rock surface p wave velocity in basalt is about 3 km s at atmospheric pressure but increases by 50 when the hydrostatic pressure is increased to 120 mpa in granite samples initial p wave velocity is 5 km s and increases with pressure by 20 the pressure induced changes of elastic wave speed indicate dominantly compliant low aspect ratio pores in both materials in addition etna basalt also contains high aspect ratio voids in triaxial loading stress induced anisotropy of p wave velocities was significantly higher for basalt than for granite with vertical velocity components being faster than horizontal velocities however with increasing axial load horizontal velocities show a small increase for basalt but a significant decrease for granite using first motion polarity we determined ae source types generated during triaxial loading of the samples with increasing differential stress ae activity in granite and basalt increased with a significant contribution of tensile events close to failure the relative contribution of tensile events and horizontal wave velocities decreased significantly a concomitant increase of double couple events indicating shear suggests shear cracks linking previously formed tensile cracks

dipole dispersion crossover and sonic logs in a limestone reservoir analyses of sonic logs in a horizontal well provide new information about mechanical properties of rocks made possible by recent developments in our understanding of acoustic wave propagation in prestressed formations most sections of this horizontal well exhibit azimuthal shear isotropy indicating isotropic stresses in the plane perpendicular to the well trajectory leading to stable wellbore conditions however two sections show dipole dispersion crossovers that confirm the presence of stress induced shear anisotropy caused by a difference between the maximum and minimum stresses in the plane perpendicular to the well trajectory the two dipole dispersions are obtained by processing the recorded waveforms by a modified matrix pencil algorithm the fast shear direction is estimated from alford rotation of the cross dipole waveforms one section of the well exhibits the fast shear direction parallel to the overburden stress as the maximum stress direction whereas the other section has the fast shear direction parallel to the horizontal stress that is larger than the overburden stress the cause of this change in the fast shear direction is believed to be the well s penetration into a 3 ft thick bed with lower porosity and permeability and significantly higher elastic stiffnesses than those in the other part of the homogeneous high permeability reservoir a stiff bed is likely to have greater stresses in its plane than perpendicular to it which would make the horizontal stresses greater than the vertical

stress induced borehole elongation a comparison between the four arm dipmeter and the borehole televiewer in the auburn geothermal well the nature and origin of borehole elongation recorded by the four arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in auburn new york a preferred orientation n10 w s10 e 10 and a less prominant e w orientation of borehole elongation was observed on two runs of the dipmeter comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures obtained from hydrofracturing tests and televiewer data show that the n10 w s10 e borehole elongations 1 are axisymmetric 2 are aligned with the minimum horizontal stress sh and 3 are not associated with natural fractures intersecting the well these elongations are interpreted as stress induced well bore breakouts the e w elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts this asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter this study demonstrates that the dipmeter can be used to determine the orientation of sh by mapping breakouts confirming the results of earlier less detailed studies and provides a firm basis for mapping regional stress patterns using existing dipmeter data

ultrasonic borehole velocity imaging we describe a new technique for making high resolution velocity images of rocks using refracted ultrasonic waves the use of refracted waves makes this technique potentially suitable for imaging borehole walls in the laboratory we use a single transmitter two receiver first arrival method for making velocity measurements with a spatial resolution on the order of 1 cm our acoustic pulses are centered near 200 khz scans of a borehole wall reveal dipping thin layers and fractures when external stress is applied perpendicular to the borehole stress concentrations appear on our images as axial bands of high and low velocities breakouts created by high stress also can be imaged on a planar sample a velocity image reveals shale laminations and carbonate stringers for field applications this technique offers the potential for imaging in both conductive and nonconductive muds and provides images based on a physical property velocity that currently is not used for fine scale borehole imaging

turbulence characteristics of sediment laden flows in open channels the turbulence characteristics of sediment laden flows in open channels are investigated using two component laser doppler velocimetry suspensions of well sorted sands with diameters ranging from 0 15 mm to 0 24 mm flowing over nominally flat beds both fixed and erodible are studied in a tiltable recirculating flume various conceptual models that have been proposed to explain the mean field profiles are examined for consistency with respect to their implications for higher order characteristics no evidence is found to support either the traditional model associated with a decrease in the von karman constant or the more recently proposed models based on simple analogies to slightly stably stratified wall bounded flows a model based on small scale fluid particle interaction is suggested as more promising

resistance in flat bed sediment laden flows the effect on flow resistance in uniform flat bed open channel flows due to suspended sediment is investigated flows with and without an equilibrium sand bed are studied in a laboratory channel three well sorted natural sands are used point velocity measurements as well as estimates of local wall shear are obtained with a laser doppler anemomentry system and are used to evaluate friction factors the results indicate that contrary to recent models the presence of suspended sediment does not necessarily lead to a reduction in flow resistance but will generally result in an increase the relation between changes in the velocity profile and changes in friction factors is discussed

three dimensional responses observed in an internally braced excavation in soft clay several three dimensional effects were observed in the performance monitoring data collected during excavation for the ford engineering design center in evanston illinois the elevations of the soil around the excavation varied and the excavator removed the soil in a nonuniform excavation process both of which contributed to the observed three dimensional 3d effects this paper describes the excavation support system and subsurface conditions at the site summarizes the construction procedures and presents the lateral soil movements measured by inclinometers ground surface movements measured by an automated total station tilt of components of an adjacent structure and forces in internal braces these responses are compared with expected responses from current design methods the 3d nature of the excavation resulted in smaller movements on the side of the excavation where the retained soil was lowest an unexpected pattern of axial strut loads and very slight damage to an exterior wall that paralleled one of the excavation walls

stratification effects by cohesive and noncohesive sediment this study focuses on stratification effects induced by the interaction between suspensions of fine grained cohesive and noncohesive sediment and the turbulent flow in estuarine and coastal environments a concise literature review reveals that this interaction may cause an appreciable modification of the vertical profiles of velocity vertical eddy viscosity diffusivity and reynolds stresses this interaction is further studied with a one dimensional vertical 1dv numerical model which includes the standard k turbulence model with buoyancy destruction terms application of this model to the experimental results by coleman 1981 shows that the measured changes in the velocity profile can be explained entirely by sediment induced buoyancy effects it is argued that capacity for cohesive sediment is cc e a fluid mud layer is formed upon the deposition of the cohesive sediment flocs contrary to the case with noncohesive sediment where the depositing grains immediately form a rigid bed thus a two layer fluid system develops causing significant damping of the vertical mixing processes decreasing the carrying capacity further this positive feed back results in a catastrophic collapse of the turbulence field and the concentration profile a scaling law for this saturation behavior is derived from classical stratified flow theory this law is sustained with a series of numerical experiments with the 1dv model it also predicts the suspended sediment concentrations observed in the yellow river to the right order of magnitude it is concluded that sediment induced buoyancy yields appreciable stratification effects at already moderate suspended sediment concentrations in the case of cohesive sediment these stratification effects can result in a catastrophic collapse of the turbulent flow field and the vertical profile of suspended sediment concentration

borehole wave propagation in three dimensions in this paper the three dimensional finite difference method is used to simulate borehole wave propagations in an isotropic as well as an anisotropic formation the finite difference results agree excellently with the analytic solutions of a point force source in the transversely isotropic medium the finite difference synthetics are also in very good agreement with the discrete wave number solutions for fluid filled borehole wave propagation the finite difference synthetics are compared with ultrasonic lab measurements in a scaled borehole model the borehole is drilled along the x axis in an orthorhombic phenolite solid both monopole and dipole logs agree well the observations of the shear wave splitting in the dipole logs are confirmed by the finite difference simulations the 3 d finite difference method is applied to the fluid filled borehole wave propagation in the tilted isotropic formation and in the orthorhombic phenolite formation in a borehole drilled along the z axis in a phenolite formati

high resolution velocity field imaging around a borehole excavation damaged zone characterization the excavation of a deep underground structure induces stress field redistribution that creates an excavation damaged zone edz the study of edz physical properties is of prime importance in the framework of nuclear waste geologic storage where edz constitutes a preferential pathway for storage materials toward the biosphere a probe for measuring the ultrasonic velocity field around a cylindrical excavation zone has been developed the probe uses pzt transducers operating at 150 khz to collect all required data with high accuracy and minimum effort the probe is fully monitored for automatic data acquisition also a numerical inversion method reconstructs a stress field using the measured velocity field this method was partially validated in the laboratory on a multilayer test bed following laboratory tests and probe development an in situ experiment was performed in the meuse haute marne underground research laboratory france to assess the safety of nuclear waste storage in the callovo oxfordian argillaceous layer the damaged zone extends up to 0 175 diameter of depth with an anisotropic damage pattern oriented according to the regional stress field the results show the potential of the method to forecast damage of similar larger structures

a similarity approach to turbulent sediment laden flows in open channels a basis is developed for a similarity treatment of the coupled mean fields in turbulent open channel flows over a flat sand bed in equilibrium with a suspension of sand hypotheses involving multiple scales asymptotic similarity and matching over an overlapping region are made instead of the traditional dependence on eddy diffusion and reynolds analogies velocity measurements using the laser doppler technique in experiments with well sorted natural sands showed that contrary to the implications of previous models the effect of suspended sediment on the mean velocity profile may over a variety of laboratory conditions be confined to a layer adjacent to the bed this is interpreted within the similarity framework in terms of the existence of an inner lengthscale differing from either the viscous or the grain scale associated with the presence of sediment the suggested lengthscales and concentration scales are examined in light of the experimental results

a numerical investigation of lutocline dynamics and saturation of fine sediment in the oscillatory boundary layer 1 understanding the state of the muddy seabed is critical to sediment transport hydrodynamic dissipation and seabed properties however this endeavor is challenging because the availability and settling velocity of sediment in muddy environments are highly variable for a given reynolds number typical of fine sediment settling in a moderately energetic muddy shelf recent 3d numerical simulations have revealed four distinct regimes of wave induced fine sediment transport these regimes depend on the availability or concentration of sediment and range from well mixed condition to the formation of lutocline and eventually a complete flow laminarization by keeping the sediment availability unchanged this study further demonstrates the existence of these flow regimes for a range of sediment settling velocities simulation results suggest that when settling velocity is larger the location of the lutocline becomes lower closer to the bed and the flow eventually laminarizes when there is further increase in the settling velocity hence the dynamics of lutocline is clearly related to the transition between these flow regimes the vertical flow structure in the presence of lutocline is revealed through the budgets of sediment flux and turbulent kinetic energy the suppressed mixing in the lutocline layer is further illustrated from a new perspective i e the budgets of turbulent suspension and concentration fluctuation variance the concept of saturation commonly used for tidal boundary layer is extended here for wave boundary layer

multipole acoustic waveforms in fluid filled boreholes in biaxially stressed formations a finite difference method a finite difference method is developed to simulate elastic wave propagation in a borehole surrounded by a biaxially stressed solid formation the linear elastic formation is altered by such tectonic stresses that cause significant changes in the characteristics of wave propagation in a borehole the 2 5 dimensional problem addressed in this work concerns the three dimensional wave propagation in a medium inhomogeneous in two spatial coordinates transverse to the borehole axis a second order finite difference method is developed to solve the partial differential equations arising from a published acoustoelastic model for borehole acoustic wave propagation in prestressed formations the algorithm is validated and applied to model both the borehole flexural and axisymmetric stoneley waves the computed waveforms are processed by a variation of prony s algorithm that yields dispersion curves for flexural waves polarized both parallel and perpendicular to the stress direction the flexural dispersion crossover in a uniaxially stressed formation is quantitatively confirmed the stoneley dispersion in the presence of such stresses exhibits approximately a uniform shift toward lower slownesses over the entire bandwidth of interest this implies that azimuthal averaging of formation stiffnesses approximately yields the same effective stoneley stiffness at different radial positions

detection of formation s wave in a slow formation using a monopole acoustic logging while drilling tool acoustic logging while drilling lwd is a technology that is used to measure the formation elastic properties during drilling when the formation shear slowness is smaller than the borehole fluid slowness i e fast formation monopole logging can be used to obtain both formation compressional and shear slownesses by measuring the corresponding refracted waves in a slow formation where the shear slowness is larger than the borehole fluid slowness other logging methods such as quadrupole lwd is used instead for shear slowness measurement due to the missing of fully refracted shear wave through modeling analysis we find that the transmitted shear wave generated by a monopole lwd tool in a slow formation can be detected and used to measure the formation shear slowness this phenomenon can be explained by huygens principle which states that every point on a wave front can be considered as a secondary source that induces particle motion it is hard to discern the transmitted shear wave in monopole w

borehole damage indicator from stress induced velocity variations i develop a simple technique to indicate the onset of stress induced mechanical damage near a wellbore stress concentrations near a wellbore can cause the yield strength of the rock to be exceeded the resulting mechanical damage causes a decrease in acoustic velocity that precedes the development of breakouts with laboratory experiments on stressed boreholes i show that high resolution shallow acoustic measurements made inside the borehole can detect these stress induced velocity changes the onset of damage can be predicted by comparing these shallow measurements to a deep velocity measurement in undamaged rock when the maximum shallow velocity is decreased by damage and approaches the deep velocity i infer that damage has occurred and breakouts and or borehole failure are imminent if implemented in the oilfield this technique could form the basis for a real time damage warning for drillers that allows for preventive action

determination of in situ attenuation from full waveform acoustic logs method for the determination of in situ p and s wave attenuation from full waveform acoustic logs are developed for p waves the peak amplitude ratios of the refracted p waves from two different receivers can be used with geometrical spreading taken into account for s waves owing to the contamination by the guided waves its attenuation cannot be determined directly instead s wave attenuation is determined from the attenuation of the guided waves using the partition coefficients normalized partial derivatives of the phase velocity with respect to the body wave velocities analytical forms of these partition coefficients are presented here along with examples for a number of different rock formations granite limestone sandstone and soft sediments the results show that in high velocity rocks the fluid attenuation controls the guided wave attenuation except near the cut off frequency of the pseudo rayleigh wave for low velocity rock formations especially in the case where the s wave velocity is lower than the fluid velocity the s wave attenuation is the main contributor to the guided wave attenuation synthetic microseisgmogram calculated with the measured body wave attenuation agrees well with the actual microseismograms

building response and ground movements induced by a deep excavation this paper presents building responses and ground movements induced by an excavation using the top down construction method the ground surface settlement and lateral wall displacement for each excavation stage were observed the displacement performances of the soil were further studied by examining the strain field and displacement vector developing in a soil mass behind the wall the centre of the vertical strain concentration area was found to be consistent with the location of the maximum ground surface settlement for a given distance from the wall the maximum vertical soil movement occurred at a certain depth below the ground surface the soil behind the wall had a non zero volume change during excavation both consolidation and soil creep behaviour might contribute towards the volume change of the soil factors such as the type of foundation the size of foundation the length of the side of the excavation and the shape of the settlement profile may affect the building performance during excavati

modes of noncircular fluid filled boreholes in elastic formations dispersion curves for4 the modes of noncircular fluid filled boreholes in homogeneous elastic formations are calculated with a boundary integral formulation results are displayed for the propagatory modes of several borehole shapes in both fast and slow formations any departure from circularity reduces the tube wave speed agreement with exact analytical results is obtained for elliptical boreholes while a simple approximate relation involving borehole perimeter and area is verified for arbitrary cross sections higher order surface modes such as the flexural and screw modes split into two distinct branches distinguished by their orientation with respect to the principal axes of the borehole cross section modal dispersion characteristics in elliptical boreholes may be approximately by scaled circular borehole results in fast formations the effective scaled radii are related to transverse dimensions of the borehole but in slow formations they are more closely related to local radii of curvature of the borehole for more complex cross sections with a single axis of symmetry dispersion of the flexural mode is well modeled by that in elliptical boreholes of similar dimensions while that of stoneley and screw modes is not in asymmetrical boreholes significant torsional and out of phase motion may occur

effects of stratification by suspended sediments on turbulent shear flows sediments suspended in turbulent flows of water over plane beds are known to influence the structure of the flows by which they are carried past attempts to model this effect have been based almost exclusively on a theoretical framework in which the dense solid particles stratify the flow and have an influence analogous to that of a downward heat flux in the stably stratified atmospheric surface layer we compare results from a model based on this theoretical framework with laboratory measurements of ensemble averaged velocity and ensemble averaged particle concentration obtained by previous investigators in order to test the applicability of the theoretical approach to dilute suspensions of sand in turbulent flows of water we find that the stratification effect can be observed qualitatively in measured velocity profiles except in one series of experiments in which systematic measurement errors may have obscured the effect estimates of model constants based on measured velocity profiles are overall roughly consistent with expectations based on measurements in thermally stratified flows although there is substantial variability in individual profiles some of this variability is explainable as a consequence of a parameter range in which stratification effects are too weak to be detected accurately other variability is explainable as a consequence of approximations in the model and still other variability is possibly a consequence of weak dependence of model constants on sediment grain size which was not expected from the theoretical development the stratification effect is not observed in individual particle concentration profiles but must instead be observed in experiments in which the flow conditions and particle properties are held fixed while the particle load is increased

assessing rock brittleness and fracability from radial variation of elastic wave velocities from borehole acoustic logging rock brittleness and fracability of subsurface formations are two important parameters for hydraulic fracturing in hydrocarbon reservoir production this paper presents an effective technique to assess these parameters using the radial variation of compressional and shear velocities from borehole acoustic logging our technique is based on a rock mechanic phenomenon that a brittle rock with high fracability tends to leave a significant amount of drilling induced cracks at the borehole wall resulting in radial elastic wave velocity variation away from borehole by determining the velocity variation the combined effects of brittleness and fracability of formation rocks can be assessed the compressional wave travel time tomography and flexural shear wave inversion methods are respectively used to obtain compressional and shear velocity variations well log data analysis examples demonstrate the practicability and effectiveness of this technique

acoustic evidence of mechanical damage surrounding stressed boreholes laboratory experiments demonstrate that acoustic waveforms recorded in a borehole provide evidence of stress induced mechanical damage in surrounding rock in the experiments external uniaxial stress was applied perpendicular to the borehole stress concentrations near the borehole wall caused velocities of refracted compressional wave to vary with azimuth low velocities occurred in zones of tensile stress and high velocities occurred in zones of compressive stress velocity variations are on the order of 10 at high values of externally applied uniaxial stress rock exceeded its yield strength and permanent damage developed this damage decreased the measured velocities by approximately 10 especially in the zones of compressive stress concentration the heterogeneous nature of the velocities surrounding the borehole resulted in low velocity channels parallel to the borehole wall caused either by tensile stress concentrations or by mechanical damage these low velocity channels may be responsible for high amplitude bright spots that appear on variable density plots of azimuthal waveform scans the amplitude increases can be on the order of 500 and are associated with low velocity zones not with decreased attenuation the hypothesized mechanism is acoustic focusing whereby velocity gradients refract acoustic waves back towards the borehole

elastic wave propagation in a fluid filled borehole and synthetic acoustic logs the propagation and dispersion characteristics of guided waves in a fluid filled borehole are studied using dispersion curves and modeling full wave acoustic logs by synthetic microseismograms the dispersion characteristics of the pseudo rayleigh reflected and stoneley waves in a borehole with and without a tool in the center are compared effects of different tool properties are calculated the effect of a rigid tool is to make the effective borehole radius smaller as an approximation dispersion characteristics of the guided waves in a borehole with a tool can be calculated as a purely fluid filled borehole with a smaller effective radius theoretical waveforms microseismograms of elastic waves propagating in a borehole are calculated using a discrete wavenumber integration with an appropriate choice of parameters our results look similar to the acoustic waveforms recorded in a limestone and a shale formation several factors affect the shape of an acoustic log microseismogram the effective rad

centimeter scale heterogeneities and microstratifaction in sedimentary rocks two dimensional acoustic images of sedimentary rocks were generated in order to characterize centimeter scale heterogeneities and microstratigraphy the images are based on dense sampling of the compressional phase velocity at frequencies near 1 mhz the acoustic observations are compared to visual and x ray images of the same samples the results are intrepreted in terms of microscopic compositional variations sedimentary rocks are more variable on the scale of a centimeter than we expected the homogeneous berea sandstone exhibits a 3 random variation in velocity heterogeneous rocks show 20 and 30 velocity variations in the particular case where porosity is the sole compositional inhomogeneity the acoustic and radiographic images agree in general however the acoustic images yield different information from the visual and radiographic images

investigation of borehole cross dipole flexural dispersion crossover through numerical modeling crossover of the dispersion of flexural waves recorded in borehole cross dipole measurements is interpreted as an indicator of stress induced anisotropy around a circular borehole in formations that are isotropic in the absence of stresses we have investigated different factors that influence flexural wave dispersion through numerical modeling we determined that for a circular borehole surrounded by an isotropic formation that is subjected to an anisotropic stress field the dipole flexural dispersion crossover is detectable only when the formation is very compliant this might happen only in the shallow subsurface or in zones having high pore pressure however we found that dipole dispersion crossover can also result from the combined effect of formation intrinsic anisotropy and borehole elongation we found that a small elongation on the wellbore and very weak intrinsic anisotropy can result in a resolvable crossover in flexural dispersion that might be erroneously interpreted as borehole stress induced anisotropy a thorough and correct interpretation of flexural dispersion crossover thus has to take into account the effects of stress induced and intrinsic anisotropy and borehole cross sectional geometry

velocity profiles for particles and liquid in open channel flow with suspended sediment experiments were performed to measure the mean velocity and turbulence characteristics in open channel flows with and without suspended sediment alluvial sand of nearly uniform size velocity measurements were obtained by using a newly developed technique the discriminator laser doppler velocimeter dldv which can distinguish both liquid and sediment particle velocities the mean velocity of sediment particles was found to be lower than that of the water while the velocity fluctuations in the water were not changed with the addition of sediment those of the sediment were diminished for the range of concentrations considered the friction velocity and the free surface slope increased with sediment concentration unlike other bulk flow parameters which were practically constant a uniform method of analysis was developed to facilitate data interpretation and comparison between similar studies

distributions of ground movements parallel to deep excavations in clay an empirical procedure for fitting a complementary error function erfc to settlement and lateral ground movement data in a direction parallel to an excavation support wall is proposed based on extensive optical survey data obtained around a 12 8 m deep excavation in chicago the maximum ground movement and the height and length of an excavation wall define the erfc fitting function the erfc fit is shown to apply to three other excavation projects where substantial ground movement data were reported key words excavations clays ground movements performance data