experimental behaviour of compacted marls jurassic marls from abadia portugal were used in the construction of some motorway embankments large fragments of this evolving material remained after the construction process and their degradation was of concern because of the expected change of the engineering properties of the compacted material the material exhibits a very complex behaviour which is difficult to reproduce with existing constitutive models for unsaturated structured materials this paper focuses on understanding and providing data on the interaction between the pure marls rock and the aggregate behaviour it presents the main results of tests performed to characterise the hydro mechanical behaviour of compacted marls in specimens prepared with different grading size distributions and subjected to oedometer tests where both stress and suction changes were applied the experimental data obtained were analysed considering the presence of fragments and their degradation the marl matrix was characterised to complete the existing

a study of critical state on an unsaturated silty soil critical state models for unsaturated soils have been proposed in recent years however the proposed models have been based on limited experimental data compacted specimens have generally been used for research and the complications of soil fabric resulting from the compaction procedures have brought difficulties into the interpretation of fundamental soil behavior there is a need to undertake further laboratory research studies on unsaturated soils particularly to obtain a fundamental understanding of the shear strength and critical state of unsaturated soils by testing soil specimens with simple soil structures suction controlled triaxial drained shear tests on an unsaturated silt were carried out as part of this research program specimens were prepared by gradually consolidating the initially slurried soil the resulting specimens had a relatively simple soil fabric and stress history the results showed that applying suction to an initially saturated specimen has a similar influence on the stre

introduction to this special section advances in seismic sensors seismic detectors have been around for centuries and seismic prospecting for many decades the variety of seismic sensors in modern surveys is dazzling they can measure particle velocity and acceleration pressure and pressure gradient strain and strain rate and multiple components z h1 h2 yaw pitch roll from near dc to hundreds or thousands of hertz in land marine borehole and extraterrestrial environments

water retention model for compacted bentonites the water retention behaviour of compacted bentonites is strongly affected by multi physical and multi scale processes taking place in these materials experimental data have evidenced major effects of the material dry density the imposed volume constraints and the soil fabric this paper presents a new water retention model accounting for proper retention mechanisms in each structural level of compacted bentonites namely adsorption in the intra aggregate pores and capillarity in the inter aggregate ones the model is calibrated and validated against experimental data on different bentonite based materials showing good capabilities in capturing the main features of the behaviour the model is able to reproduce experimental data on compacted bentonites over a wide range of suction values within a unified framework and using a limited number of parameters some of the parameters introduced are shown to take approximately the same value for several bentonites providing a significant basis for prelimin

measurement and estimation of pore shrinkage and pore distribution in a clayey till during soil water characteristic curve tests the soil water characteristic curve swcc of fine grained soils is usually determined experimentally in many applications such as design of mine waste covers and landfill liners the unsaturated permeability function k h is often derived theoretically from the measured swcc implicit in these derivations is the transformation of the swcc to a pore size distribution psd typically assumed to be constant and mono modal psds of a clayey till compacted at various water contents were measured after compaction after flexible wall permeability testing and during and after swcc tests the measurements show that the psd changes significantly during permeability and swcc testing a method is advanced for predicting the observed changes in psd during swcc testing psds are determined for soil samples subjected to the highest and lowest suctions applied during the swcc test the measured psds are transformed to account for pore trapping the transform assumes that flow occurs through two sets of randomly d

time lapse vsp reservoir monitoring although 3d seismic imaging based on surface sources and receivers has been the primary tool used for geophysical reservoir monitoring to date vertical seismic profiling vsp has characteristics that make this technique particularly suitable for time lapse surveying in particular the use of downhole receivers provides some advantages

a microstructurally based effective stress for unsaturated soils current alternative choices of stress state variables in unsaturated soils are described and compared with a special focus on the use of an effective stress experimental data on stiffness and shear strength evolution with suction suggest that the proportion of suction contributing to the effective stress is often much smaller than predicted by the term suction times degree of saturation generally used in effective stress expressions of the bishop type it is suggested that effective stress in unsaturated soils should be related to soil microstructure an effective degree of saturation is defined as describing the volume of water partially filling the soil macroporosity this effective degree of saturation defines the proportion of the prevailing suction that actually contributes to the effective stress two alternative expressions piecewise linear and non linear are proposed for the effective degree of saturation they offer a similar performance available data on stiffness and shear strength varia

a water retention model for deformable soils the paper presents an experimental study on water retention behaviour of two reconstituted soils a silty clay speswhite kaolin and a sandy clayey silt barcelona silt and two compacted soils a silty clay speswhite kaolin and a silty sandy gravel adige river embankment these soils were used with the aim of encompassing a wide range of soil types and soil fabrics specimens were subjected to drying and wetting hydraulic paths by removing or adding water under zero total stress and to mechanical wetting paths by compressing specimens at constant water content to investigate a broad range of void ratios the reconstituted sandy clayey silt was initially reconstituted from slurry by applying different consolidation vertical stresses whereas the compacted speswhite kaolin and adige river embankment were compacted to a broad range of water contents and compaction energy on the basis of the experimental data a modification to the van genuchten s model is proposed to account for the effect of voi

case history using time lapse vertical seismic profiling data to constrain velocity saturation relations the frio brine pilot co2 injection author s al hosni m caspari e pevzner r daley tm gurevich b abstract 2016 european association of geoscientists a engineers co2 sequestration projects benefit from quantitative assessment of saturation distribution and plume extent for field development and leakage prevention in this work we carry out quantitative analysis of time lapse seismic by using rock physics and seismic modelling tools we investigate the suitability of gassmann s equation for a co2 sequestration project with 1600 tons of co2 injected into high porosity brine saturated sandstone we analyze the observed time delays and amplitude changes in a time lapse vertical seismic profile dataset both reflected and transmitted waves are analyzed qualitatively and quantitatively to interpret the changes obtained from the vertical seismic profile we perform a 2 5d elastic finite difference modelling study the results show a p wave velocity reduction of 750 m s in the proximity of the injection well evident by the first arrivals travel time delays and amplitude change and reflected wave amplitude changes these results do not match with our rock physics model using gassmann s equation predictions even when taking uncertainty in co2 saturation and grain properties into account we find that time lapse vertical seismic profile data integrated with other information e g core and well log can be used to constrain the velocity saturation relation and verify the applicability of theoretical models such as gassmann s equation with considerable certainty the study shows that possible nonelastic factors are in play after co2 injection e g co2 brine rock interaction and pressure effect as gassmann s equation underestimated the velocity reduction in comparison with field data for all three sets of time lapse vertical seismic profile attributes our work shows the importance of data integration to validate the applicability of theoretical models such as gassmann s equation for quantitative analysis of time lapse seismic data

walkaway vsp using multimode optical fibers in a hybrid wireline distributed acoustic sensing das is a novel technology that uses an optical fiber cable as a sensor for acoustic signals and can take almost any downhole fiber optic installation or deployment and turn the fiber optic cable into a large downhole seismic array this array can provide enhanced vertical seismic profile vsp imaging and monitor fluids and pressure changes in the hydrocarbon production reservoir walkaway vsp data acquired over a formerly producing well in northeastern china provided a rich set of high quality das walkaway vsp data a standard vsp data preprocessing workflow was applied followed by prestack kirchhoff time migration in the das preprocessing step we were faced with additional challenges strong coherent noise due to cable slapping and ringing along the borehole casing compared with an earlier offset vsp data set using 327 levels acquired with conventional 3c downhole geophones in the same well the final preprocessed das walkaway vsp has a larger vertical aperture result

failure of soil under water infiltration condition abstract to reduce and mitigate rainfall induced landslide problems there is a need to improve our understanding of the failure mechanism of soil under water infiltration condition this study aimed at understanding the effect of water infiltration on the transformation of shear stress and its eventual failure in unsaturated soil the method of study was via a series of advanced laboratory triaxial test of two specific types 1 constant suction shearing test and 2 shearing infiltration test the shearing infiltration test results indicated that infiltration of water reduced the matric suction of the soil by the generation of excess pore water pressure it however was not accompanied by a reduction in shear strength instead the unsaturated soil failed under a constant shear stress applied prior to the infiltration excessive deformation and the eventual softening of the soil were found to be the main causes of water infiltration induced failure

distributed acoustic sensing of seismic properties in a borehole drilled on a fast flowing greenlandic outlet glacier distributed acoustic sensing das is a new technology in which seismic energy is recorded at high spatial and temporal resolution along a fibre optic cable we show analyses from the first glaciol

a state dependent elasto plastic model for saturated and unsaturated soils a state dependent elasto plastic constitutive model for both saturated and unsaturated soils is presented in this paper the model which is developed under an extended critical state framework uses two independent stress state variables net normal stress and matric suction in addition the influence of a simplified non linear soil water characteristic curve on mechanical behaviour is incorporated in the model by using a bi linear function most importantly a state dependent dilatancy formulation is introduced to account for the effects of stress level or stress ratio internal state density and soil suction in this paper details of the model formulation and the determination of model parameters are described and reported by using the new model numerical simulations of triaxial tests have been carried out on both saturated and unsaturated fine grained sandy silt and coarse grained gravelly sand weathered soils the simulated triaxial tests include undrained shear tests on saturated specimens

quantitative quality of distributed acoustic sensing vertical seismic profile data great advances have been made in distributed acoustic sensing das vertical seismic profile vsp data acquisition hardware and software here we capture a quantitative assessment of the quality of das data at a single point in time we apply comprehensive testing methods to determine the reliability of the data and its suitability as a supplement to geophone data or to gain access to wells where it would be difficult to deploy geophones the test measurements are made on das and geophone data which were collected at the same time and in the same well we analyze the first breaks for waveform consistency signal to noise s n ratio and slowness then we examine the corridor stacks for waveform consistency and s n ratio finally we test the properties of the measurement including linearity repeatability reliability and response as a function of the angle of incidence of a seismic wave to the fiber the results show that the das vsp data provide accurate formation slowness logs and reliable ampl

compaction behaviour of clay this paper presents an experimental study of the compaction behaviour of non active clay one dimensional static compaction tests were carried out at high and medium water content with matric suction monitoring using trento high capacity tensiometers at lower water contents a transistor psychrometer was used to measure post compaction suction samples were compacted on the dry side of optimum to cover a wide range of compaction water contents and vertical stresses three water content regions were identified in the compaction plane depending on whether post compaction suction increased decreased or remained constant as the degree of saturation was increased at constant water content hydraulic paths of specimens subjected to loading unloading cycles at constant water content have clearly shown that post compaction suction may increase as the degree of saturation increases this non intuitive behaviour was demonstrated to be associated with the coupling between mechanical and water retention behaviour to this end a coupled mechanical water retention model was formulated irreversible one dimensional mechanical paths were modelled by a boundary surface in the space average skeleton vertical stress modified suction and void ratio irreversible hydraulic wetting paths were modelled by a boundary surface in the space suction degree of saturation and void ratio this study was completed by investigating the pore size distribution of compacted samples through mip tests

wetting of compacted clays under laterally restrained conditions initial state overburden pressure and mineralogy compacted clay fills are generally placed at the optimum value of water content and immediately after placement they are unsaturated wetting might subsequently occur due for example to rainfall infiltration which can cause volumetric deformation of the fill either swell or collapse with associated loss of shear strength and structural integrity if swelling takes place under partially restrained deformation due for example to the presence of a buried rigid structure or a retaining wall additional stresses will develop in the soil and these can be detrimental to the stability of walling elements and other building assets factors such as dry density overburden pressure compaction water content and type of clay are known to influence the development of stresses this paper investigates these factors by means of an advanced stress path testing programme performed on four different clays with different mineralogy index properties and geological histories specimens of kaolin clay london clay be

experimental analysis of the water retention behaviour of shales shales are among the most commonly considered geomaterials in current energy related geomechanical investigations as they are involved in engineering applications such as the extraction of natural gas co2 sequestration and nuclear waste storage a deep understanding of their behaviour with regard to variations in the degree of saturation is of significance for such applications with the aim to establish a sound protocol for shale retention behaviour analysis this paper presents an experimental methodology that takes into account the specificities of shales such as small pore size dimensions and the large variations in water potential to be applied to induce significant changes in the degree of saturation the technique involves the direct control of the shale water content and the subsequent measurement of the suction at equilibrium by a psychrometer a fluid displacement technique with a non polar liquid is also used to assess the volume changes of the shale and to compute the degree of saturation selected test results are presented for various shale samples that have been cored at different depths the results indicate that important features of the retention behaviour of geomaterials are fundamental aspects to be considered when analysing the retention behaviour of shales such as the existence of main wetting and drying paths the hysteresis domain and the dependency of the air entry value on the void ratio 2014 elsevier ltd all rights reserved

a pore network model for hydromechanical coupling in unsaturated compacted clayey soils the behaviour of deformable unsaturated soils is difficult to characterize with simple relationships unsaturated hydraulic properties namely the soil water characteristic curve and the hydraulic

dual wavefields from distributed acoustic sensing measurements abstractdistributed acoustic sensing das using fiber optic cables is an emerging seismic acquisition technology for the oil and gas industry geothermal resource exploration and underground fluid storage monitoring this technology offers the advantage of improving seismic acquisition by enabling massive arrays for monitoring of seismic wavefields at reduced cost with respect to conventional methods in general it is accepted that this method provides acoustic signals comparable with conventional seismic data however without the multicomponent directional information typical of geophones we have developed a modified data extraction method and found that as a result of the dense spatial distribution of recording points along the optic cable das can provide two linked wavefield components in the axial direction even when using a single 1d cable line these signal pairs consist of dual components that are related to native strain rate or strain and particle acceleration or velocity fields at a

membrane behavior of compacted gmz bentonite and its granite mixture the membrane behavior of gmz bentonite and its granite mixture which consists of 70 gmz bentonite and 30 grinded granite rock in dry weight was quantitatively evaluated in this study specimens with different initial dry densities were subjected to multi stage membrane behavior tests with concentration differences of 0 01 0 05 0 1 and 0 5 m of nacl or cacl2 solutions across the specimen in each stage membrane behavior was evaluated by measuring the chemico osmotic efficiency coefficient results indicate that the membrane behavior of gmz bentonite and its granite mixture decreases with the decrease in initial dry density and bentonite content as well as the increases in solution concentration and cation valence these conclusions could be explained by 1 variations in pore size distribution caused by different initial dry densities and bentonite contents 2 increase in macro pores in quality induced by shrinkage and collapse of ddls resulting from the interactions between clay and solutions 3 decrease in micropores and increase in macro pores induced by cation exchange

evolution of microstructure in compacted london clay during wetting and loading the influence of fabric on mechanical behaviour is explicitly considered in some of the current constitutive models for unsaturated soils these are based on assumptions regarding the interaction b

effects of fractal dimension and water content on the shear strength of red soil in the hilly granitic region of southern china abstract deep residual soil formed by the long term weathering of large granite under the impact of high temperature and abundant rainfall in southern china is prone to instability and deformation which has caused a large number of collapsing gullies in this study five different soil grading ratios and five water contents were employed to systematically investigate the effects of the soil fractal dimension and water content on the red soil shear strength the soil fractal dimension increased with soil fine particle content clay and silt the soil saturated hydraulic conductivity ks decreased with the soil fractal dimension whereas the soil air entry value and residual water content r showed a positive relationship with the fractal dimension shearing tests showed that the soil shear strength increased with normal stress but decreased with the soil water content this reduction in the soil shear strength caused by the increasing water content was more notable for the soil with a lower fractal dimension analyses of the main effect tests showed that the water content presented greater effects on the soil cohesion and friction angle than the soil fractal dimension a stepwise regression analysis showed that a linear relationship occurred between soil matric suction and soil cohesion average r 0 981 and p 004 or friction angle average r 0 951 and p 016 for the same matric suction the soil cohesion and friction angles decreased with the soil fractal dimension and the relationship between the soil fractal dimension with the soil cohesion r 0 951 and p 013 and friction angles r 0 922 and p 026 could be described by logarithmic functions soil fractal dimensions influenced both the soil hydraulic properties and shear strength parameters and the overall effects of fine particles loss would decrease the shear strength of gully red soil

reservoir monitoring of steam assisted gravity drainage using borehole measurements this paper presents the results from a research project focusing on permanent crosswell geophysical methods for reservoir monitoring during steam assisted gravity drainage a feasibility study indicated detectable differences in seismic and electrical reservoir properties based on expected changes in temperature and fluid saturation during the production of extra heavy oil as a result of this a permanent cross well system was installed at the leismer demonstration area located in the athabasca oil sands region in alberta canada baseline data sets including cross well seismic three dimensional vertical seismic profiling and cross well electrical resistivity tomography have been acquired comparisons between conventional surface seismic and downhole seismic data show an increase in resolution and frequency content as expected steam assisted gravity drainage induced time lapse effects are clearly visible in the 3d vertical seismic profiling and electrical resistivity tomography data sets even after a few months of oil production in general the 3d vertical seismic profiling images show a higher resolution than the surface seismic data in particular when dealing with vertical positioning of the time lapse events the electrical resistivity tomography baseline shows clear separation between zones of high and low electrical resistivity and during 23 months of electrical resistivity tomography measurements the maximum reduction of resistivity is 85 time lapse observations from acoustic and electrical borehole data correspond well and are also supported by temperature measurements in the two observation wells emerging technologies updated models improved flexibility and reduced costs will allow future reservoir monitoring with surface and borehole data in combination or even with borehole data exclusively key words borehole geophysics resistivity seismics time lapse

field testing of fiber optic distributed acoustic sensing das for subsurface seismic monitoring distributed acoustic sensing das is a relatively recent development in the use of fiber optic cable for measurement of ground motion discrete fiber optic sensors typically using a bragg diffraction grating have been in research and development and field testing for more than 15 years with geophysical applications at least 12 years old bostick 2000 and summary in keul et al 2005 however developments in recent years have sought to remove the need for point sensors by using the fiber cable itself as a sensor mestayer et al 2011 miller et al 2012

field trial of seismic recording using distributed acoustic sensing with broadside sensitive fibre optic cables distributed acoustic sensing is an emerging technology using fibre optic cables to detect acoustic disturbances such as flow noise and seismic signals the technology has been applied successfully in hydraulic fracture monitoring and vertical seismic profiling one of the limitations of distributed acoustic sensing for seismic recording is that the conventional straight fibres do not have broadside sensitivity and therefore cannot be used in configurations where the raypaths are essentially orthogonal to the fibre optic cable such as seismic reflection methods from the surface the helically wound cable was designed to have broadside sensitivity in this paper a field trial is described to validate in a qualitative sense the theoretically predicted angle dependent response of a helically wound cable p waves were measured with a helically wound cable as a function of the angle of incidence in a shallow horizontal borehole and compared with measurements with a co located streamer the results show a similar behaviour as a function of the angle of incidence as the theory this demonstrates the possibility of using distributed acoustic sensing with a helically wound cable as a seismic detection system with a horizontal cable near the surface the helically wound cable does not have any active parts and can be made as a slim cable with a diameter of a few centimetres for that reason distributed acoustic sensing with a helically wound cable is a potential low cost option for permanent seismic monitoring on land

time lapse 3d vsp using permanent receivers in a flowing well in the deepwater gulf of mexico the vision of smart wells permanently instrumented with geophones has existed for some time such installations would enable opportunities for frequent reservoir monitoring high resolution 3d vsp imaging and illumination of difficult areas for many subsalt fields 3d vsps acquired in such wells may be the best option to illuminate and monitor reservoirs without the need to stop production or enter a well however this technology is not yet widely applied nor perhaps proven

measurements of drying and wetting permeability functions using a new stress controllable soil column direct measurement of a permeability function k where suction of an unsaturated soil is often tedious and time consuming thus researchers have proposed various semiempirical predictive methods to determine k indirectly from a soil water characteristic curve swcc or a particle size distribution also stress effects on k are generally not considered to explore any stress effect on k a new 1 m high stress controllable soil column is developed to measure stress dependent swcc sdswcc and k of soils directly the objectives of this paper are to investigate the effects of 1 two stress state variables matric suction and net normal stress and 2 a drying wetting cycle on both sdswcc and k of a compacted decomposed silty clay each compacted soil column is subjected to an evaporation ponding cycle under various vertical net normal stresses the variations of pore water pressure and volumetric water content vwc w profiles with time are measured instantaneously the k

the effect of gauge length on axially incident p waves measured using fibre optic distributed vibration sensing distributed vibration sensing also known as distributed acoustic sensing is a relatively new method for recording vertical seismic profile data using a fibre optic cable as the sensor the signal obtained from such systems is a distributed measurement over a length of fibre referred to as the gauge length in this paper we show that gauge length selection is one of the most important acquisition parameters for a distributed vibration sensing survey if the gauge length is too small then the signal to noise ratio will be poor if the gauge length is too large resolution will be reduced and the shape of the wavelet will be distorted the optimum gauge length as derived here is a function of the velocity and frequencies of the seismic waves being measured if these attributes vary considerably over the depth of a survey then the use of different gauge lengths is recommended the significant increases in data quality resulting from the use of multiple gauge length values are demonstrated using field data

imaging the aquistore reservoir after 36 kilotonnes of co2 injection using distributed acoustic sensing abstractaquistore is a geologic co2 storage project that is using a deep saline formation as a storage reservoir from april 2015 to february 2016 approximately 36 kilotonnes of co2 were injected into the reservoir at a depth of 3130 3350 m we have developed an analysis of distributed acoustic sensing das 3d vertical seismic profiling data acquired in february 2016 marking the first seismic survey since injection began the vsp data were processed in parallel with baseline preinjection data from a november 2013 survey with the objective of detecting and characterizing the subsurface co2 plume and evaluating the repeatability of das in a reservoir monitoring project a single processing sequence was devised that 1 accurately imaged the reservoir for the baseline and monitor data and 2 attained adequate repeatability to observe time lapse differences related to the presence of co2 repeatability was somewhat compromised by the less advanced noise cancellation methodology of the das system used for

monitoring co2 injection for carbon capture and storage using time lapse 3d vsps carbon capture and storage ccs is the process through which a nearly pure carbon dioxide co2 stream is captured separated from flue gas or other industrial processes compressed transported to an appropriate storage site and injected deep underground into a geological formation where it can be safely stored for long term geologic storage benson 2005 large sedimentary basins such as the illinois michigan and western canadian sedimentary basins are good targets for ccs as they are in close proximity to large co2 emitters and are composed of the appropriate saline formations and overlying nonpermeable formations in 2003 the u s department of energy s national energy technology laboratory doe netl created a nationwide network of federal state and private sector partnerships to determine the most suitable technologies regulations and infrastructure for future ccs in different areas of the north america office of fossil energy 2013

gas flow through clay barriers a model for the simulation of gas flow in clayey rocks and clays is described gas migration is associated with the development of preferential paths along existing or pressure dependent discontinu

a framework for unsaturated soil behaviour a framework is put forward which explains the shear behaviour of an unsaturated soil in terms of the total stresses and suctions acting within the soil it is based on the critical state model for

study of the structure of a sensitive champlain clay and of its evolution during consolidation scanning electron microscopy and mercury intrusion porosimetry are used in parallel to identify the structure of a medium sensitivity champlain clay the clay structure is observed firstly on intact remolded and oven dried soils and secondly on soils consolidated at various levels in one dimensional compression both methods of investigation reveal for the intact soil the existence of an aggregated structure characterized by an interaggregate and an intra aggregate porosity remolding affects interaggregate links but does not destroy aggregates the observation of clay structure at various levels of one dimensional compression shows that the collapse of the structure is progressive the largest interaggregate pores being the first affected as the consolidation proceeds smaller and smaller pores are affected for a given pressure increment only the largest existing pores are affected a structure anisotropy has been seen to develop with increasing compression the scanning electron microscope and the me

the influence of soil structure and stress history on the soil water characteristics of a compacted till the soil water characteristic defines the relationship between the soil suction and gravimetric water content w or the volumetric water content or the degree of saturation s theoretical and

aspects of the behaviour of compacted clayey soils on drying and wetting paths a relatively large number of drying and wetting tests have been performed on clayey soils compacted at the standard or modified proctor optimum water content and maximum density and compared with tests on normally consolidated or overconsolidated soils the results show that drying and wetting paths on compacted soils are fairly linear and reversible in the void ratio or water content versus negative pore water pressure planes on the wet side of the optimum the wetting paths are independent of the compaction water content and can be approached by compaction tests with measurement of the negative pore water pressure correlations have been established between the liquid limit of the soils and such properties as the optimum water content and negative pore water pressure the maximum dry density and the swelling or drying index although based on a limited number of tests these correlations provide a fairly good basis to model the drying wetting paths when all the necessary data are not available key wor

performance of an unsaturated expansive soil slope subjected to artificial rainfall infiltration a major infrastructure project the south to north water transfer project has been proposed to carry potable water from the yangtze river region in the south to many arid and semi arid areas in the northern regions of china including beijing the proposed 1200 km middle route of the project is likely to be an open channel with a trapezoidal cross section at least 180 km of the proposed excavated canal will pass through areas of unsaturated expansive soils an 11 m high cut slope in a typical expansive clay with medium plasticity in zaoyang close to the middle route in hubei was selected for a comprehensive and well instrumented field study of the effects of rainfall infiltration two artificial rainfall events were created during a month of field investigation and monitoring prior to the rainfall events high soil suction was measured within the top 1 m of soil this high initial soil suction created an upward flux of water and moisture the abundant cracks and fissures near the ground surface p

microstructure and soil water retention behavior of compacted and intact silt loess abstract there are an increasing number of mega engineering projects of removing the top of hills to fill in the valley for new land creation in the loess plateau of china which significantly changes the hydrological and geological equilibrium state of the site the formation of a new hydrological equilibrium state is associated with the water movement in the compacted and intact loess layers most disasters occurring in the loess area are related to water the soil water retention curve swrc is the key to the implementation of unsaturated soil mechanics in engineering practice and is required to numerically model the movement of water in the soil in this study the swrcs and microstructure of intact and compacted specimens from lanzhou and yan an two typical cities that have new land creation projects are investigated the swrc is obtained using the filter paper method the mercury intrusion porosimetry mip and scanning electron microscope sem techniques are used to explore the microstructure the results highlight that the intact loess has a higher air occlusion value aov and a similar slope of swrc in the transition zone compared with the remolded specimens that compacted at the natural water content the normalized swrc i e degree of saturation versus suction avo of the intact specimen is approximately the same as the remolded specimens compacted as the natural water content the difference in the microstructure between intact and compacted specimens originates from different existing states of the clay particles and further contributes to the variation of the swrc

water retention and volumetric characteristics of intact and re compacted loess a laboratory testing program was conducted to investigate the effects of microstructure on the water retention curve wrc and wetting drying induced volume change in loess the axis translation an

experimental behaviour and modelling of an unsaturated compacted soil this paper reports the experimental study and modelling of the mechanical response of a silty sand used in the core of the metramo dam italy specimens were prepared by compacting the soil at optimum water content conditions using the modified proctor technique tests were performed under suction controlled conditions by a stress path triaxial cell and an oedometer the experimental program consists of 23 tests carried out in the suction range of 0 400 kpa the findings indicate the strong influence of suction on compressibility stiffness and shear strength the mechanical properties of the soil improve with suction following an exponential law with decreasing gradient furthermore the soil exhibited collapsible behaviour upon wetting even at low stress levels interesting results were also achieved in elastoplastic modelling as well the results led to characterization of soil behaviour with reference to widely accepted modelling criteria for unsaturated soils providing noteworthy suggestions about

model for the prediction of shear strength with respect to soil suction experimental studies on unsaturated soils are generally costly time consuming and difficult to conduct shear strength data from the research literature suggests that there is a nonlinear increas

steam injection monitoring in south oman from single pattern to field scale surveillance downhole seismic monitoring has become an alternative to more conventional surface seismic in cases where the latter has low signal to noise ratio or poor repeatability or when frequent monitoring of a local target is required downhole 3d vsp monitoring has been applied to both onshore o brien et al 2004 kiyashchenko et al 2011 and offshore environments wu et al 2011 in onshore environments surface seismic repeatability often suffers from surface noise and near surface variations caused by water table changes or surface facilities construction for vsp surveys the wavefield separation into downgoing and upgoing fields presents an opportunity to discriminate between near surface and reservoir changes thus making time lapse applications more effective

field testing of modular borehole monitoring with simultaneous distributed acoustic sensing and geophone vertical seismic profiles at citronelle alabama a modular borehole monitoring concept has been implemented to provide a suite of well based monitoring tools that can be deployed cost effectively in a flexible and robust package the initial modular borehole monitoring system was deployed as part of a co2 injection test operated by the southeast regional carbon sequestration partnership near citronelle alabama the citronelle modular monitoring system transmits electrical power and signals fibre optic light pulses and fluids between the surface and a reservoir additionally a separate multi conductor tubing encapsulated line was used for borehole geophones including a specialized clamp for casing clamping with tubing deployment the deployment of geophones and fibre optic cables allowed comparison testing of distributed acoustic sensing we designed a large source effort 64 sweeps per source point to test fibre optic vertical seismic profile and acquired data in 2013 the native measurement in the specific distributed acoustic sensing unit used an idas from silixa ltd is described as a localized strain rate following a processing flow of adaptive noise reduction and rebalancing the signal to dimensionless strain improvement from repeated stacking of the source was observed conversion of the rebalanced strain signal to equivalent velocity units via a scaling by local apparent velocity allows quantitative comparison of distributed acoustic sensing and geophone data in units of velocity we see a very good match of uncorrelated time series in both amplitude and phase demonstrating that velocityconverted distributed acoustic sensing data can be analyzed equivalent to vertical geophones we show that distributed acoustic sensing data when averaged over an interval comparable to typical geophone spacing can obtain signal to noise ratios of 18 db to 24 db below clamped geophones a result that is variable with noise spectral amplitude because the noise characteristics are not identical with vertical seismic profile processing we demonstrate the effectiveness of downgoing deconvolution from the large spatial sampling of distributed acoustic sensing data along with improved upgoing reflection quality we conclude that the extra source effort currently needed for tubing deployed distributed acoustic sensing vertical seismic profile as part of a modular monitoring system is well compensated by the extra spatial sampling and lower deployment cost as compared with conventional borehole geophones

ageing effects in a compacted bentonite a microstructure approach it is suspected that the as compacted state of heavily compacted clays used as possible engineered barriers for nuclear waste disposal is time dependent and that further change may occur in the material even at constant water content and density this paper presents an investigation of the time dependent microstructure changes of an mx80 clay bentonite compacted at various dry densities and water contents microstructure investigation is based on mercury intrusion pore size distribution measurements and scanning electron microscopy sem results obtained by other researchers by using x ray diffraction at low angles are also used statically compacted samples of mx80 were kept at constant volume and water content for various periods of time 1 30 and 90 days prior to mercury intrusion and sem micro structure investigation a significant change in micro structure with time was observed characterised by a decrease in the inter aggregate porosity and an increase in the very thin porosity not intruded by

a field study of stress dependent soil water characteristic curves and permeability of a saprolitic slope in hong kong it is well recognised that field measurements of stress dependent soil water characteristic curves sdswccs and the permeability function coefficient of permeability with respect to the water phase are vital for assessing transient seepage pore water pressure changes and the stability of unsaturated soil slopes in this study sdswccs and the permeability function were measured by using the instantaneous profile method on a saprolitic hillside in tung chung hong kong the ground profile comprises colluvium and completely decomposed tuff cdt a 3 m diameter circular plot was instrumented and subjected to two wetting drying cycles throughout a 48 day monitoring period variations of volumetric water content and matrix suction in the uppermost 3 m of soil were measured continuously using time domain reflectometry moisture probes and jet fill tensiometers respectively the field observations reveal that there is a clear trend of decreasing sizes of hysteretic loops of sdswccs with depth in a compari

effects of repeated hydraulic loads on microstructure and hydraulic behaviour of a compacted clayey silt soils used in earth construction projects are mostly unsaturated and they undergo frequent drying wetting cycles repeated hydraulic loads due to changes in climatic conditions or variations of t

the mechanical behaviour of an unsaturated compacted silty clay a comprehensive experimental study has been carried out to investigate the volumetric and shear strength behaviour of a compacted silty clay which exhibited collapse on wetting behaviour the experiments consisted mainly of suction monitored triaxial tests carried out in a new apparatus the test results are interpreted on the basis of an elasto plastic framework using the conventional stress variable approach net stress and suction as well as an approach that takes into account the degree of saturation within two modified stress variables the evidence for critical states was examined based on the stress dilatancy relationships it was found that a critical state was observed experimentally in cases where the samples contracted over much of their stress paths but was not truly established in other cases relationships between the shear strength and specific volume at the ultimate state were established for samples over a wide range of degrees of saturation from fully saturated to the air dried state

3d vsp technology now a standard high resolution reservoir imaging technique part 1 acquisition and processing abu dhabi company for onshore oil operations adco undertook a two well 3d vsp pilot project in 2007 because it was acquired concurrently with a high resolution wide azimuth surface seismic survey it was at the time the largest 3d vsp ever recorded the project consisted of four main parts acquisition processing interpretation and quantifying value in part 1 of this paper the acquisition and processing of the 3d vsp is described with an emphasis on the lessons learned significant advances in processing are described that demonstrate how larger 3d vsp images with better amplitudes and structural preservation can be produced in part 2 the results of the 3d vsp interpretation and economic evaluation effort are described and illustrate different ways that a vsp image can help characterize a hydrocarbon reservoir

shot clay mx 80 bentonite an assessment of the hydro mechanical behaviour this study presents the results of an experimental study conducted to characterise the hydro mechanical behaviour of shot clay mx 80 bentonite in the shot clay process granular bentonite was mixed continuously with water and shot on the walls of a tunnel section at the grimsel underground research laboratory url in switzerland the shot clay was placed to create a layer of bentonite in direct contact with the host rock to avoid preferential water and or gas flow along the tunnel wall samples for an experimental programme were collected during the shooting the index properties microstructural features swelling potential and water retention properties of the shot clay were analysed an experiment was then conducted under controlled total suction to analyse the hydro mechanical behaviour of the material along a predefined stress path involving suction and confining stress variations based on the results of this test the expected behaviour of the shot clay bentonite when subjected to the environmental conditions in the repository was determined the test results were compared with data on the observed behaviour of compacted mx 80 granular bentonite to assess the effects of the shot clay emplacement technique on the behaviour of shot clay mx 80 bentonite the results highlight the role of the emplacement dry density on the behaviour of bentonite

distributed acoustic sensing for reservoir monitoring with vsp 3d vsp has long been viewed as conceptually attractive for illuminating targets under complex overburden both for exploration purposes and for time lapse monitoring of reservoirs however the widespread use of 3d vsp has been hindered by the cost and risk of deploying geophones in a borehole and by the limited availability of accessible wells these hurdles are largely removed when acquiring downhole seismic with a new measurement called distributed acoustic sensing das

shear strength of a compacted residual soil from consolidated drained and constant water content triaxial tests rainfall induced landslides in unsaturated residual soils can occur slowly under drained conditions or rapidly under undrained conditions consolidated drained cd and constant water content cw

the structure degradation of a silty loess induced by long term water seepage abstract loess is a typical silt sized aeolian soil that is widely deposited and possesses a fragile soil structure susceptible to collapse upon wetting the instability of shallow loess slopes is well documented but deeper failures triggered by rainfall and irrigation can also occur in the case of long term seepage clay particles and salts have been observed to leach out of the loess slopes this paper presents a systematic laboratory study of the effects of water conditions on the mechanical behaviour of silty loess with isotropic compression and bender element tests carried out on natural and reconstituted loess recovered at 10 m depth from a site in china the results show that saturation causes reduction in both the compression yield stress and small strain stiffness of the soil and that after being exposed to seepage they decrease further the possible mechanism of structure degradation is investigated by means of microscopic and chemical analyses and it is found that seepage will cause the pore ions concentration to reduce with a loss of clay mineral bonding strength resulting in the detachment of silt particles from aggregates this work highlights the importance of monitoring the water outflow in the field at the loess slope edge since it may causes large deformation in the long term

coupling of hydraulic and mechanical behaviour in unsaturated compacted clay an experimental study was carried out to investigate the shear strength of a compacted non active clay speswhite kaolin a total of 33 statically compacted specimens were prepared at vertical stresses of 300 600 and 1200 kpa and water contents ranging from 0 24 to 0 34 this made it possible to explore a broad range of initial compaction induced conditions and hence to examine whether differences in water retention characteristics and shear strength are due to differences in initial compaction induced state or are to be attributed to fundamentally different microfabrics a shearbox was modified to allow the direct measurement of negative pore water pressure using trento high suction tensiometers tests were carried out at constant water content by monitoring suction changes in these tests it was possible to investigate the transition from unsaturated to saturated states in the first stage of the test the specimen was compressed at constant water content the specimen was therefore wetted in the s

swelling phenomena and effective stress in compacted expansive clays the central aim of this paper is to discuss the applicability of the effective stress principle as defined by terzaghi total stress minus pore water pressure to predict the behaviour of expansive

coupled water retention and shrinkage properties of a compacted silt under isotropic and deviatoric stress paths although it is generally recognized that unsaturated soil behavior is governed by two constitutive variables matric suction and net normal stress and that the hydromechanical behavior of unsaturated soil is coupled a water retention curve obtained from tests under zero stress and assuming no volume change is still fairly common a relatively limited number of studies on the stress path dependent water retention curve sdwrc particularly under a broader range of stress paths exist in the literature in this paper the sdwrc shrinkage curve and swelling curve of a compacted silt subjected to isotropic and deviatoric stress paths are presented the test results show that the air entry value aev increases but the hydraulic hysteresis loop decreases with an increase in net mean stress furthermore for a given stress level the k0 compressed specimen exhibits higher aev but a smaller hysteresis loop than that of the isotropically compressed specimen a nonlinear shrinkage curve is observed and the

resilient modulus of unsaturated subgrade soil experimental and theoretical investigations the resilient modulus mr of subgrade soil is an important stiffness parameter for analysing fatigue cracking in either the asphalt or concrete layer of a pavement although subgrade soil is often unsaturated and subject to seasonal variations of moisture content and hence suction in the field effects of soil suction on the resilient modulus are generally not accounted for in existing testing methods in this study mr values of a subgrade soil under various stress and suction conditions were investigated using a suction controlled cyclic triaxial apparatus to enhance the accuracy of measurements hall effect transducers were employed to monitor the local axial and radial deformation of each specimen it was found that mr increases with number of load applications when a soil contracts but decreases slightly when a soil dilates when suction increases the soil response tends to change from contractive to dilative due to suction induced dilatancy moreover the measured mr is highly dependent on the s

an experimental study on the compaction and collapsible behaviour of a flood defence embankment fill with renewed interest in the performance of flood embankments globally it is important that the performance of fills in conditions similar to as constructed are scrutinised the fill material investigated in this study was sampled from flood embankments located along the bengawan solo river in east java indonesia the recurrent history of overtopping and stability issues in these embankments provided the motivation for developing a better understanding of the behaviour of this compacted fill under different loading and wetting conditions the site investigation revealed that the embankment fill was compacted at low dry densities and that there was local variation in the dry densities determined a detailed study highlighted that at low compactive efforts this fill material exhibits an irregular double peak compaction curve which can be explained by the tendency of this fill to form aggregates on wetting to cover different plausible operational conditions of these embankments saturated and unsaturated compression oedometer tests and one dimensional collapse tests were performed under different initial conditions specimens compacted at conditions similar to as constructed exhibited significant collapse deformation up to 13 6 on wetting evolution of the microstructure during loading and wetting paths was investigated using mip and esem a physically based framework proposed by romero 2013 was used to explain the changes in the macroscale collapse behaviour observed in the oedometer tests based on the evolution of microporosity using this model the evolution of the microporosity with dry density and water content was presented this microstructural approach could be used as a tool for specifying appropriate compaction conditions for earthworks where fill material is susceptible to volumetric collapse

distributed acoustic sensing for reservoir monitoring with vertical seismic profiling distributed acoustic sensing is a novel technology for seismic data acquisition particularly suitable for vertical seismic profiling it is a break through for low cost on demand seismic monitoring of reservoirs both onshore and offshore in this article we explain how distributed acoustic sensing works and demonstrate its usability for typical vertical seismic profiling applications such as checkshots imaging and time lapse monitoring we show numerous data examples and discuss distributed acoustic sensing as an enabler of seismic monitoring with 3d vertical seismic profiling key words borehole geophysics acquisition seismics time lapse monitoring

effects of wetting drying and stress ratio on anisotropic stiffness of an unsaturated soil at very small strains the very small strain shear modulus of soil g0 is affected by many factors including soil properties current stress state stress history and matric suction very little research has been condu

shear strength and pore water pressure characteristics during constant water content triaxial tests shear strength parameters used in geotechnical design are obtained mainly from the consolidated drained cd or consolidated undrained cu triaxial tests however in many field situations soils are compacted for construction purposes and may not follow the stress paths in cd or cu triaxial tests in these cases the excess pore air pressure during compaction will dissipate instantaneously but the excess pore water pressure will dissipate with time under this condition it can be considered that the air phase is drained and the water phase is undrained this condition can be simulated in a constant water content cw triaxial test the purpose of this paper is to present the characteristics of the shear strength volume change and pore water pressure of a compacted silt during shearing under the constant water content condition a series of cw triaxial tests was carried out on statically compacted silt specimens the experimental results showed that initial matric suction and net confining stress play an important role in affecting the characteristics of the shear strength pore water pressure and volume change of a compacted soil during shearing under the constant water content condition the failure envelope of the compacted silt exhibited nonlinearity with respect to matric suction

making unsaturated soil mechanics accessible for engineers preliminary hydraulic mechanical characterisation and stability assessment the paper presents an accessible approach for preliminary hydraulic and mechanical characterisation of unsaturated soils and stability analysis of geo structures under unsaturated conditions the approach is accessible in the sense that the laboratory investigation and geotechnical analyses can be completed in a relatively short time and at a reasonable cost the overall philosophy behind this approach is that laboratory testing should not be eliminated but kept to a minimum and that any simplification introduced should be conservative the paper illustrates that shear strength can be characterised conservatively by performing constant water content tests with no facilities to control monitor suction and that water retention behaviour can be predicted successfully by performing a single water retention measurement the paper also demonstrates that stability analyses can be carried out within the classical framework of limit analysis we show that a preliminary analysis of the influence of infiltrating rainwater on suction can be carried out using a simple and conservative method that makes use of solutions available in saturated geotechnical textbooks such an approach may be used to assess when it is worthwhile or necessary to conduct further time consuming and costly unsaturated experimental testing field monitoring and numerical analyses when considering the stability of geostructures

effective utilization of seismic reflection technique with moderate cost in uranium exploration abstract in participation with numerous industrial partners the seismic laboratory of the university of saskatchewan has conducted a variety of active seismic reflection experiments both on the west and east sides of the athabasca basin results of the investigations at shea creek mcarthur river and keefe lake illustrate that the seismic investigations deliver effective highly relevant primary structural images of the subsurface with resolution that no other geophysical technique can match correlation of similar seismic signatures on several distant but inter related seismic sections allowed spatial extension of promising exploration target zones previously unrecognized within the three dimensional seismic volume comparable reflectivity patterns defined the complex areal distribution of mineralization related fault systems beyond these novel contributions extended analysis of seismic signal attributes amplitude and frequency optical televiewer and full wave sonic data offer detailed lithological characterization including alteration zones clay content as well as porosity and fracture density information although these structural and geologically relevant anomalies are primary indicators of mineralization presenting novel exploration advantages the seismic method is still not a standard component of the athabasca basin exploration approach due to the negative perception that it is very expensive comparing the costs of all geophysical techniques to the cost of a single logged drill hole illustrates that the results of a properly designed seismic data acquisition program not only leads to more effective planning of a drilling program but also would lead to a much quicker recognition of the major mineralized zone s and a reduction in the number of required exploration boreholes this integrated approach to exploration would then translate into a significant reduction of the total exploration expenditures unquestionably the drilling of boreholes provides the most explicit reliable information to a certain depth but only within a very small area directly connecting the borehole information to seismic results extends the local reliable data permitting reduction of the number of boreholes to create accurate two dimensional or three dimensional subsurface images and reduction of the expenditures of the total exploration program

experimental observation on laterally loaded pile in unsaturated silty soil an experimental study was carried out to investigate the effects of soil partial saturation on the behaviour of laterally loaded piles the proposed study was conducted by means of centrifuge tests

virtual source applications to imaging and reservoir monitoring the virtual source method is a breakthrough that allows us to image and monitor the subsurface in cases where surface seismic or vsp fail to deliver in settings where the overburden is complex or changing traditional time lapse signals are weak or nonrepeatable leading to ineffective seismic input to reservoir modeling and little of value generated by repeated seismic surveys on the other hand the virtual source method allows us to image under complex overburden yields repeatable data for reservoir monitoring enables shear seismic and may help us look ahead as we drill

work input analysis for soils with double porosity and application to the hydromechanical modeling of unsaturated expansive clays a mechanical approach for unsaturated expansive soils considering double porosity has been developed based on the porous media theory in this approach the adsorbed and the capillary water as well as the micropores and macropores are two distinct phases an interaggregate stress considered as the work conjugate of the macrostructural strain increment has been defined both physicochemical and capillary effects of the pore water have been introduced at the macroscopic level other work conjugate variables relevant for the constitutive modeling of double porosity unsaturated media have also been identified consisting of the modified suction as conjugate of the increment of the macrostructural degree of saturation and the microstructural effective stress as conjugate of the microstructural volumetric strain increment a hydromechanical model for unsaturated expansive clays taking into account the interaction between the micro and the macrostructures in expansive clays can thus be built based on the bou

an insight into the water retention properties of compacted clayey soils experimental data from different testing methodologies on different compacted clayey soils with dominant bimodal pore size distribution are presented and analysed to provide a comprehensive picture of the evolution of the aggregated fabric along hydraulic and mechanical paths fabric changes are analysed both from the porous network viewpoint by means of careful mercury intrusion porosimetry investigation and from the soil skeleton viewpoint by quantifying swelling and shrinkage of the aggregates in an environmental scanning electron microscopy study the consequences of the aggregated fabric evolution on the water retention properties of compacted soils are analysed and discussed a new model for water retention domain is proposed which introduces a dependence of the intra aggregate pore volume on water content the model succeeds in tracking correctly the evolution of the hydraulic state of the different soils investigated along generalised hydromechanical paths the proposed approach brings to l

suction stress characteristics in granite red soils and their relationship with the collapsing gully in south china abstract the main goal of this research is to study the relationship between the soil suction stress and soil properties within four different soil profiles of collapsing gullies in the hilly granitic region of southern china large differences were found in the four soil layers between granite red soils which are manifested in terms of soil bulk density porosity particle composition clay minerals micromorphology organic matter cation exchange capacity permeability oxide and hydraulics properties the suction stress of the upper soils increases rapidly and almost linearly monotonously with the increase of matric suction whereas c layers increases rapidly first followed by a slow increase the suction stress of the lower soils is significantly smaller than the upper soils under the same matric suction these findings illustrate that the collapsing gully starts from the lower part of the granite red soil and finally caused the gravity collapse in the upper soils which is the main aspect that is different from the other types of soil erosion furthermore suction stress has a very significant correlation with soil properties with a positive correlation to the fine particle content iron and aluminum oxide and a negative correlation to coarse particles in addition suction stress can also be explained as being directly proportional to weathering degree our research provides a theoretical basis for the mass failures of the granite derived red soil in southern china

experimental investigations of the soil water characteristics of a volcanic soil rain induced landslides are common around the world to analyse transient seepage and to predict pore water pressure distribution in unsaturated slopes subjected to rainfall infiltration it is essential to study soil water char acteristics and water permeability functions the soil water characteristic curve swcc is a relationship between suc tion and water content or degree of saturation conventionally only the drying soil water characteristic curve of soil specimens is determined in a pressure plate extractor without the application of any external stress in this paper the influences of initial dry density and initial water content history of drying and wetting soil structure and the stress state upon the desorption and adsorption soil water characteristics of a completely decomposed volcanic soil in hong kong are examined and discussed the experimental results presented are obtained by using a conventional volumetric pressure plate extractor and a newly modified one dimensional stress controllable pressure plate extractor with deforma tion measurements the swcc of a recompacted specimen is very different from that of a natural specimen with the same initial soil density and initial water content the swcc of the recompacted specimen is highly dependent on the history of drying and wetting the rates of desorption and adsorption are substantially higher at the first drying and wetting cycle than at the second drying and wetting cycle the size of the hysteresis loop of the recompacted specimen is considerably larger than that of the natural specimens the swcc of soil is stress state dependent for recompacted specimens subjected to different stress states the higher the applied stresses the lower the rate of desorption and the smaller the size of the hysteresis loops however for natural specimens the size of the hysteresis loops seems to be independent of the stress state under a higher applied stress natural specimens exhibit lower rates of desorption and adsorption

a source synchronous filter for uncorrelated receiver traces from a swept frequency seismic source abstractwe have developed a novel algorithm to reduce noise in signals obtained from swept frequency sources by removing out of band external noise sources and distortion caused from unwanted harmonics the algorithm is designed to condition nonstationary signals for which traditional frequency domain methods for removing noise have been less effective the source synchronous filter ssf is a time varying narrow band filter which is synchronized with the frequency of the source signal at all times because the bandwidth of the filter needs to account for the source to receiver propagation delay and the sweep rate ssf works best with slow sweep rates and moveout adjusted waveforms to compensate for source receiver delays the ssf algorithm was applied to data collected during a field test at the university of california santa barbara s garner valley downhole array site in southern california at the site a 45 kn shaker was mounted on top of a one story structure and swept from 0 to 10 hz and back over

a field experiment of walkaway distributed acoustic sensing vertical seismic profile in a deep and deviated onshore well in japan using a fibre optic cable deployed inside coiled tubing abstract a two dimensional walkaway vertical seismic profiling survey using distributed acoustic sensing was conducted at an onshore site in japan the maximum depth and the deviation of the observation well were more than 4 000 m and 81 degrees respectively among the several methods for installing fibre optic cables we adopted the inside coiled tubing method in which coiled tubing containing a fibre optic cable is deployed the signal to noise ratio of the raw shot gather was low possibly due to poor coupling between the fibre optic cable and the subsurface formation resulting from the fibre optic cable deployment method and the existence of considerable tubewave noise nevertheless direct p wave arrivals p p reflections and p s converted waves exhibited acceptable signal to noise ratios after careful optimization of gauge length for distributed acoustic sensing optical processing and the application of carefully parameterized tubewave noise suppression one of the challenges in current distributed acoustic sensing vertical seismic profile data processing is the separation of p and s waves using only one component measurements hence we applied moveout correction using two dimensional ray tracing this process effectively highlights only reflected p waves which are used in subsequent subsurface imaging comparison with synthetic well seismograms and two dimensional surface seismic data confirms that the final imaging result has a sufficiently high quality for subsurface monitoring we acquired distributed acoustic sensing vertical seismic profile data under both flowing conditions and closed conditions in which the well was shut off and no fluid flow was allowed the two imaging results are comparable and suggest the possibility of subsurface imaging and time lapse monitoring using data acquired under flowing conditions the results of this study suggest that by adopting the inside coiled tubing method without drilling a new observation well more affordable distributed acoustic sensing vertical seismic profile monitoring can be achieved in fields such as co2 capture and storage and unconventional shale projects where monitoring costs have to be minimized

instability of flood embankments due to pore water pressure build up at the toe lesson learned from the adige river case study a case study is presented of the adige river embankment a segment of which experienced instability of the landside slope due to the development of uplift pressures soil profile and hydromechanica

nineteenth canadian geotechnical colloquium the soil water characteristic curve a historical perspective the constitutive relationship between water content or degree of saturation and suction is called the soil water characteristic curve the soil water characteristic curve provides a conceptual framework in which the behavior of unsaturated soils can be understood a historical review illustrates how the work of early researchers in soil science and geotechnical engineering laid the foundation for our current understanding of this relationship key elements of these early studies were a conceptual understanding of the soil water characteristic curve as a relationship between the mass or volume of water stored within the soil and the energy in the water phase it was on the basis of this conceptual model that current methods of measuring the soil water characteristic curve were developed interpretative models for the distribution and geometry of the water phase in an unsaturated soil based on the capillary model have provided a useful conceptual model for understanding the effects of soil texture gradatio

3d vsp technology now a standard high resolution reservoir imaging technique part 2 interpretation and value this second part of an article about a large 3d vsp survey in abu dhabi describes the interpretation effort which quantifies the value that a 3d vsp seismic image can bring when supplementing even a 640 fold high resolution surface seismic volume