scholarly journals Pore pressure coefficient in frozen soils

Géotechnique ◽  
2021 ◽  
pp. 1-35
Author(s):  
Chuangxin Lyu ◽  
Gustav Grimstad ◽  
Satoshi Nishimura
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Solid Phase ◽  
Pressure Coefficient ◽  
Fluid Pressure ◽  
Frozen Soil ◽  
Theoretical Research ◽  
Porous System ◽  
B Values ◽  
Study Results

The Skempton pore pressure coefficient, B, is defined as the variation in pore pressure with the unit change in confining pressure under undrained conditions. The B-parameter is an essential parameter to consider the coupled effects of solid-fluid compressibility and skeleton compressibility in the porous system. It is a key factor in exploring a possible definition of effective stress in frozen soil. However, limited experimental and theoretical research is available in the literature to give insight to the problem. Therefore a series of B tests on frozen clay was conducted in this study. Results from these tests along with tests on Ottawa sand, available in the literature, are analyzed considering the effect of the ice crystallization mode on the skeleton stiffness. The measured B values were lower than expected compared with B-value using models which consider single grain bulk stiffness. However, when the difference in bulk stiffness of ice and of soil grains is considered, even an increase in pore volume, for an increase in fluid pressure, at constant Terzaghi effective stress is possible. The “pore stiffness”, different from the solid phase stiffness, can take a negative value and can be used to explain the low measured B values.

DESTRUCTION OF POROSITY THROUGH PRESSURE SOLUTION

Geophysics ◽  
1977 ◽  
Vol 42 (4) ◽  
pp. 726-741 ◽  
Author(s):  
Eve S. Sprunt ◽  
Amos Nur
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Fluid Pressure ◽  
Confining Pressure ◽  
Pressure Solution ◽  
Porous System ◽  
Point Counts ◽  
Grain Crushing ◽  
Porosity Reduction ◽  
Confining Pressures

A stressed fluid‐filled porous system was modeled by hollow cylinders of St. Peter sandstone subjected to various combinations of pore and confining pressure at 270° to 280°C for up to four weeks. Large reductions in porosity, up to more than 50 percent, were produced purely by pressure solution without grain crushing. Most of the porosity reduction occurred early in the experiments and in samples with the finer of two grain sizes. Experiments with the same pore pressure, but different confining pressures, and experiments with the same effective stress, but different stress magnitudes showed that a simple effective stress law does not hold for pressure solution, and that the amount of porosity reduction depends on pore fluid pressure. However, nonhydrostatic stress appears to be necessary for rapid porosity reduction because experiments with hydrostatic pressure produced very little change in porosity. Also, experiments with the same confining pressure but different pore pressures showed that the amount of porosity loss is dependent on both pore pressure and effective stress. Pore pressure appears to place an upper limit on the rate of porosity reduction, while nonhydrostatic stress appears to be necessary for rapid porosity reduction. A dry control experiment showed that fluid must be present for porosity reduction at the temperatures and pressures in our study. The porosities of many of the samples in this study were determined both gravimetrically and by point counts on cathodoluminescent micrographs. Cathodoluminescence is useful in studying pressure solution because the intergranular relationships and pore spaces are very distinct. However, in examining natural samples caution is required when relying solely on the luminescence to determine pressure solution, because luminescent characteristics change with time.

Fluid pressure response to undrained compression in saturated sedimentary rock

Geophysics ◽  
1986 ◽  
Vol 51 (4) ◽  
pp. 948-956 ◽  
Author(s):  
Douglas H. Green ◽  
Herbert F. Wang
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Wave Attenuation ◽  
Fluid Pressure ◽  
Confining Pressure ◽  
Pressure Response ◽  
Additional Parameter ◽  
Seismic Wave Velocity ◽  
Specific Storage ◽  
Order Of Magnitude

The pore pressure response of saturated porous rock subjected to undrained compression at low effective stresses are investigated theoretically and experimentally. This behavior is quantified by the undrained pore pressure buildup coefficient, [Formula: see text] where [Formula: see text] is fluid pressure, [Formula: see text] is confining pressure, and [Formula: see text] is the mass of fluid per unit bulk volume. The measured values for B for three sandstones and a dolomite arc near 1.0 at zero effective stress and decrease with increasing effective stress. In one sandstone, B is 0.62 at 13 MPa effective stress. These results agree with the theories of Gassmann (1951) and Bishop (1966), which assume a locally homogeneous solid framework. The decrease of B with increasing effective stress is probably related to crack closure and to high‐compressibility materials within the rock framework. The more general theories of Biot (1955) and Brown and Korringa (1975) introduce an additional parameter, the unjacketed pore compressibility, which can be determined from induced pore pressure results. Values of B close to 1 imply that under appropriate conditions within the crust, zones of low effective pressure characterized by low seismic wave velocity and high wave attenuation could exist. Also, in confined aquifer‐reservoir systems at very low effective stress states, the calculated specific storage coefficient is an order of magnitude larger than if less overpressured conditions prevailed.

The effect of pore pressure depletion and injection cycles on ultrasonic velocity and quality factor in a quartz sandstone

Geophysics ◽  
2007 ◽  
Vol 72 (2) ◽  
pp. E43-E51 ◽  
Author(s):  
P. Frempong ◽  
A. Donald ◽  
S. D. Butt
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Axial Strain ◽  
Fluid Pressure ◽  
Porous Rocks ◽  
Confining Stress ◽  
Viscoelastic Deformation ◽  
Experimental Conditions ◽  
Pore Pressures ◽  
Pressure Depletion

Passing seismic waves generate transient pore-pressure changes that influence the velocity and attenuation characteristics of porous rocks. Compressional ultrasonic wave velocities [Formula: see text] and quality factors [Formula: see text] in a quartz sandstone were measured under cycled pore pressure and uniaxial strain conditions during a laboratory simulated injection and depletion process. The objectives were to study the influence of cyclical loading on the acoustic characteristics of a reservoir sandstone and to evaluate the potential to estimate pore-fluid pressure from acoustic measurements. The values of [Formula: see text] and [Formula: see text] were confirmed to increase with effective stress increase, but it was also observed that [Formula: see text] and [Formula: see text] increased with increasing pore pressure at constant effective stress. The effective stress coefficient [Formula: see text] was found to be less thanone and dependent on the pore pressure, confining stress, and load. At low pore pressures, [Formula: see text] approached one and reduced nonlinearly at high pore pressures. The change in [Formula: see text] and [Formula: see text] with respect to pore pressure was more pronounced at low versus high pore pressures. However, the [Formula: see text] variation with pore pressure followed a three-parameter exponential rise to a maximum limit whereas [Formula: see text] had no clear limit and followed a two-parameter exponential growth. Axial strain measurements during the pore-pressure depletion and injection cycles indicated progressive viscoelastic deformation in the rock. This resulted in an increased influence on [Formula: see text] and [Formula: see text] with increasing pore-pressure cycling. The value [Formula: see text] was more sensitive in responding to the loading cycle and changes in pore pressures than [Formula: see text]; thus, [Formula: see text] may be a better indicator for time-lapse reservoir monitoring than [Formula: see text]. However, under the experimental conditions, [Formula: see text] was unstable and difficult to measure at low effective stress.

scholarly journals Pore-water pressure development in a frozen saline clay under isotropic loading and undrained shearing

2021 ◽  
Author(s):  
Chuangxin Lyu ◽  
Satoshi Nishimura ◽  
Seyed Ali Ghoreishian Amiri ◽  
Feng Zhu ◽  
Gudmund Reidar Eiksund ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Water Pressure ◽  
Frozen Soil ◽  
Hydraulic Pressure ◽  
Physical Analysis ◽  
Rate Dependency ◽  
Frozen Soils ◽  
Unfrozen Water Content ◽  
Pressure Development

AbstractA systematical testing program on frozen Onsøy clay under isotropic loading and undrained shearing at different temperatures (− 3 ~ − 10 °C), strain rates (0.2~5%/h) and initial Terzaghi effective stress (20~400 kPa) was conducted with the focus on pore pressure development. It is meant to increase the understanding and facilitate the development of an ‘effective stress’-based model for multi-physical analysis for frozen soils. This study adopted the pore pressure measurement method suggested by Arenson and Springman (Can Geotech J 42 (2):412–430, 2005. https://doi.org/10.1139/t04-111) and developed a new testing procedure for frozen soils, including a ‘slow’ freezing method for sample preparation and post-freezing consolidation for securing hydraulic pressure equilibrium. The B-value of frozen soils is less than 1 and significantly dependent on temperature and loading history. The dilative tendency or pore pressure development in an undrained shearing condition is found to be dependent on both unfrozen water content and mean stress, which is consistent with unfrozen soils. Besides, the experimental results reported in the literature regarding uniaxial tests show that the shear strength does not share the same temperature- and salinity-dependency for different frozen soil types. The rate dependency of frozen soils is characterized between rate dependency of pure ice and that of the unfrozen soil and is therefore highly determined by the content of ice and the viscous behavior of ice (through temperature dependency). This paper also explains the pore pressure response in freezing and thawing is dependent on volumetric evolution of soil skeleton.

Response of Pore Pressure and Effective Stress in Seabed to Waves Around a Permeable Submerged Breakwater

2015 ◽  
Author(s):  
Hao Chen ◽  
Jinhai Zheng ◽  
Qianzhen Li ◽  
Naiyu Zhang ◽  
Hanyi Chen ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Fluid Pressure ◽  
Wave Model ◽  
Pore Fluid Pressure ◽  
Submerged Breakwater ◽  
Great Ability ◽  
Wave Induced ◽  
Foundation Failure ◽  
Dynamic Wave

As the unexpected wave-induced seabed instability may cause foundation failure, the evaluation of wave-induced pore pressure and effective stress in seabed plays an important role in the design of the foundation of marine structures. In this study, a two-dimensional integrated mathematical model, based on COBRAS wave model and SWANDYNE seabed model is developed to numerically investigate the mechanism of wave-induced seabed response in the vicinity of a permeable submerged breakwaters. Numerical results indicate that this model has a great ability in predicting the dynamic response of the pore pressure and effective stress around the breakwater. Both the pore fluid pressure and effective stress in seabed largely changes with an increasing water depth. It is also found that the responses of the pore pressure and effective stress of different locations to the dynamic wave loading are significantly different in the cases with variable top width of the breakwater.

Constitutive model for rate-independent behavior of saturated frozen soils

2016 ◽  
Vol 53 (10) ◽  
pp. 1646-1657 ◽  
Author(s):  
S.A. Ghoreishian Amiri ◽  
G. Grimstad ◽  
M. Kadivar ◽  
S. Nordal
Keyword(s):  
Constitutive Model ◽  
Mechanical Behavior ◽  
Solid Phase ◽  
Fluid Pressure ◽  
Frozen Soil ◽  
Reverse Direction ◽  
State Variables ◽  
Soil Behavior ◽  
Frozen Soils ◽  
Strain Behavior

The mechanical behavior of frozen soils is strongly affected by the amount of ice. The amount of ice depends on the temperature and the applied mechanical stresses. The influence of ice content and temperature on the mechanical behavior and the coupling effects on the reverse direction can be mentioned as the main difference between frozen and unfrozen soils. In the light of this difference, an elastoplastic constitutive model for describing the stress–strain behavior of saturated frozen soils is proposed. By dividing the total stress into fluid pressure and solid phase stress, in addition to consideration of the cryogenic suction, the model is formulated within the framework of two-stress state variables. The proposed model is able to represent many of the fundamental features of the behavior of frozen soils, such as ice segregation phenomenon and strength weakening due to pressure melting. In the unfrozen state the model becomes a conventional critical state model. Typical predictions of the model for simulating the characteristic trends of the frozen soil behavior is described qualitatively. Model predictions are also compared with the available test results and reasonable agreement is achieved.

scholarly journals Modelling debris flows down general channels

2005 ◽  
Vol 5 (6) ◽  
pp. 799-819 ◽  
Author(s):  
S. P. Pudasaini ◽  
Y. Wang ◽  
K. Hutter
Keyword(s):  
Debris Flow ◽  
Pressure Distribution ◽  
Pore Pressure ◽  
Debris Flows ◽  
Volume Fraction ◽  
Solid Phase ◽  
Fluid Pressure ◽  
Solid Particles ◽  
Simulation Results ◽  
Model Equations

Abstract. This paper is an extension of the single-phase cohesionless dry granular avalanche model over curved and twisted channels proposed by Pudasaini and Hutter (2003). It is a generalisation of the Savage and Hutter (1989, 1991) equations based on simple channel topography to a two-phase fluid-solid mixture of debris material. Important terms emerging from the correct treatment of the kinematic and dynamic boundary condition, and the variable basal topography are systematically taken into account. For vanishing fluid contribution and torsion-free channel topography our new model equations exactly degenerate to the previous Savage-Hutter model equations while such a degeneration was not possible by the Iverson and Denlinger (2001) model, which, in fact, also aimed to extend the Savage and Hutter model. The model equations of this paper have been rigorously derived; they include the effects of the curvature and torsion of the topography, generally for arbitrarily curved and twisted channels of variable channel width. The equations are put into a standard conservative form of partial differential equations. From these one can easily infer the importance and influence of the pore-fluid-pressure distribution in debris flow dynamics. The solid-phase is modelled by applying a Coulomb dry friction law whereas the fluid phase is assumed to be an incompressible Newtonian fluid. Input parameters of the equations are the internal and bed friction angles of the solid particles, the viscosity and volume fraction of the fluid, the total mixture density and the pore pressure distribution of the fluid at the bed. Given the bed topography and initial geometry and the initial velocity profile of the debris mixture, the model equations are able to describe the dynamics of the depth profile and bed parallel depth-averaged velocity distribution from the initial position to the final deposit. A shock capturing, total variation diminishing numerical scheme is implemented to solve the highly non-linear equations. Simulation results present the combined effects of curvature, torsion and pore pressure on the dynamics of the flow over a general basal topography. These simulation results reveal new physical insight of debris flows over such non-trivial topography. Model equations are applied to laboratory avalanche and debris-flow-flume tests. Very good agreement between the theory and experiments is established.

Sorption-Induced Permeability Change of Coal During Gas-Injection Processes

2008 ◽  
Vol 11 (04) ◽  
pp. 792-802 ◽  
Author(s):  
Wenjuan Lin ◽  
Guo-Qing Tang ◽  
Anthony R. Kovscek
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Gas Adsorption ◽  
Gas Production ◽  
Co2 Injection ◽  
Permeability Reduction ◽  
Permeability Change ◽  
Gas Composition ◽  
Adsorption Equilibria ◽  
Study Results

Summary Our study has two features. First, laboratory experiments measured the change of the permeability of coal samples as a function of pore pressure and injected-gas composition at constant effective stress. Second, adsorption-solution theory described adsorption equilibria and aided interpretation. The gases tested include pure methane (CH4), nitrogen (N2), and carbon dioxide (CO2), as well as binary mixtures of N2 and CO2 of different compositions. The coal pack was initially dry and free of gas, then saturated by each test gas at a series of increasing pore pressures at a constant effective stress until steady state was reached. Thus, the amount of adsorption varied, while the effective stress was held constant. Results show that, (i) permeability decreases with an increase of pore pressure at fixed injection-gas composition, and, (ii) permeability change is a function of the injected-gas composition. As the concentration of CO2 in the injection gas increases, the permeability of the coal decreases. Pure CO2 leads to the greatest permeability reduction among all the test gases. However, 10 to 20% by mole of N2 helps to preserve permeability significantly. According to the mixed-gas adsorption isotherms, adsorption and the selectivity of a particular gas species on coal surfaces is a function of pressure and the gas composition. Therefore, we conclude that loading coal surfaces with adsorbed gas at constant effective stress causes permeability reduction. Finally, gas adsorption and permeability of coal are correlated, simply to extend the usefulness of study results. Introduction Coalbed methane (CBM) has grown to supply approximately 10% of US natural-gas production and is becoming important worldwide as an energy source (EIA 2006). Conventional CBM-recovery procedures stimulate wells and produce CH4 by depressurizing the coalbed. A full understanding of the mechanisms underlying CBM production has yet to be established. Injection of CO2, N2, or mixtures of the two gases enhances CBM recovery significantly (Stevens et al. 1998; Stevens 2001). Coalbeds also present a potential sink for greenhouse gases (GHGs), such as CO2. One issue of particular interest for CO2 injection, and the subject of our study, is the sensitivity of coal permeability to the partial pressure of CO2 in the injection gas.

Dynamic effective pressure coefficient calibration

Geophysics ◽  
2015 ◽  
Vol 80 (1) ◽  
pp. D65-D73 ◽  
Author(s):  
Hua Yu
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Oil And Gas ◽  
Pressure Coefficient ◽  
Oil And Gas Industry ◽  
Velocity Variation ◽  
Effective Pressure ◽  
Overburden Pressure ◽  
Gas Industry ◽  
Pore Pressure Prediction

Pore pressure prediction provides an important risk assessment in the oil and gas industry. Most predrill pore-pressure prediction methods from seismic and/or well-log sonic velocities are based on the effective stress principle, which relates velocity variation to the combined effect of overburden stress and pore pressure. In the current practice of pore pressure prediction, the effective stress coefficient [Formula: see text] is often assumed as unity, which is not always the case, especially when sediments are deeply buried and consolidated. To understand the variation of [Formula: see text] with depth, I analyzed density and velocity trends from more than 100 Gulf of Mexico wells near the Louisiana continental shelf edge. In the study area, overpressure zones are present in most wells and compaction disequilibrium is the dominant overpressure mechanism. Normal compaction trends for velocity and density were built. The overburden pressure model was refined by taking into account that the density gradient approaches zero at the onset depth of overpressure. Based on the effective pressure principle, values for [Formula: see text] in the overpressure intervals were estimated in the study area. The average [Formula: see text] values varied from 0.6 to 0.9 inclusive of errors associated with assuming the gradient of mud weight and pore pressure is the same.

A comparative study on methods for determining the hydraulic properties of a clay shale

2020 ◽  
Vol 224 (3) ◽  
pp. 1523-1539
Author(s):  
Lisa Winhausen ◽  
Alexandra Amann-Hildenbrand ◽  
Reinhard Fink ◽  
Mohammadreza Jalali ◽  
Kavan Khaledi ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Ion Beam ◽  
Applied Pressure ◽  
Pressure Oscillation ◽  
Stress Conditions ◽  
Data Set ◽  
Clay Shale ◽  
Permeability Coefficients ◽  
Effective Stresses

SUMMARY A comprehensive characterization of clay shale behavior requires quantifying both geomechanical and hydromechanical characteristics. This paper presents a comparative laboratory study of different methods to determine the water permeability of saturated Opalinus Clay: (i) pore pressure oscillation, (ii) pressure pulse decay and (iii) pore pressure equilibration. Based on a comprehensive data set obtained on one sample under well-defined temperature and isostatic effective stress conditions, we discuss the sensitivity of permeability and storativity on the experimental boundary conditions (oscillation frequency, pore pressure amplitudes and effective stress). The results show that permeability coefficients obtained by all three methods differ less than 15 per cent at a constant effective stress of 24 MPa (kmean = 6.6E-21 to 7.5E-21 m2). The pore pressure transmission technique tends towards lower permeability coefficients, whereas the pulse decay and pressure oscillation techniques result in slightly higher values. The discrepancies are considered minor and experimental times of the techniques are similar in the range of 1–2 d for this sample. We found that permeability coefficients determined by the pore pressure oscillation technique increase with higher frequencies, that is oscillation periods shorter than 2 hr. No dependence is found for the applied pressure amplitudes (5, 10 and 25 per cent of the mean pore pressure). By means of experimental handling and data density, the pore pressure oscillation technique appears to be the most efficient. Data can be recorded continuously over a user-defined period of time and yield information on both, permeability and storativity. Furthermore, effective stress conditions can be held constant during the test and pressure equilibration prior to testing is not necessary. Electron microscopic imaging of ion-beam polished surfaces before and after testing suggests that testing at effective stresses higher than in situ did not lead to pore significant collapse or other irreversible damage in the samples. The study also shows that unloading during the experiment did not result in a permeability increase, which is associated to the persistent closure of microcracks at effective stresses between 24 and 6 MPa.

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