Accumulation Of Pore Water Pressure Research Articles

Simulation of liquefaction phenomenon in semi-infinite domain under harmonic loading

A fully coupled dynamic computer code in FORTRAN-90 is developed to predict the liquefaction potential of a semi-infinite saturated sandy layer. The saturated soil system is modeled as a two-phase material based on the Biot’s theory for porous media with u–P formulation to determine the responses of pore fluid and soil skeleton. The variational principle is applied to the field equations of fluid flow in a fully saturated porous elastic continuum, and the finite element method is used to numerically solve the resulting continuity equation and equilibrium equation. The mathematical advantage of the coupled finite element analysis is that the excess pore pressure (EPP) and displacement can be evaluated simultaneously without using any empirical relationship. Generalized Newmark-beta method is employed for integration in time. The soil behavior is modeled by Pastor–Zienkiewicz Mark III to describe the inelastic behavior of soils under isotropic cyclic loadings. The effect of the material non-linearity of the soil grain on liquefaction response is investigated by conducting parametric study. The accumulation of pore water pressure and the reduction of mean effective stress are simulated well. It has been observed that soil properties like permeability and shear modulus have significant effect on liquefaction analysis.

Effects of density on cyclic behaviour of anisotropically consolidated Ottawa sand under undrained torsional loading

The undrained response of Ottawa sand to cyclic torsional loading in a hollow cylinder apparatus is assessed at various densities. The cyclic resistance of Ottawa sand is strongly affected by anisotropic consolidation. It is less than half of the cyclic strength of isotropically consolidated material at the loose state; this trend reverses at the dense state. Cyclic strength resistance increases with density irrespective of consolidation path. Anisotropically consolidated specimens develop at all densities a terminal excess pore-water pressure which is less than 40% of the initial effective stress, and fail due to strain rather than pore-water pressure accumulation, contrary to isotropically consolidated specimens reaching pore pressure ratios higher than 70%. The development of excess pore-water pressure is uniquely related to the shear work imparted to the specimen; at the same excess pore-water pressure ratio shear work increases with density, whereas it is not affected by the applied cyclic shear stress amplitude. The phase transformation line is not affected by the consolidation path and appears to be the same under monotonic and cyclic loading conditions.

EXCESS PORE WATER PRESSURE ACCUMULATION AND RECOMPRESSION OF SATURATED SOFT CLAY SUBJECTED TO UNI-DIRECTIONAL AND MULTI-DIRECTIONAL CYCLIC SIMPLE SHEARS

This paper is to investigate the effect of cyclic shear direction (or phase difference) on the accumulation of excess pore water pressure during cyclic shear and on the recompression after cyclic shear. Several series of uni-directional and multi-directional cyclic simple shear tests under undrained condition were carried out for normally consolidated Kaolin. From the test results it is shown that the accumulation of pore water pressure and the post-cyclic settlement increase with the shear strain amplitude and the phase difference. The values of the shear strain amplitude at which the effect of cyclic shear direction is most significant, decrease with the increase of the number of cycles. The change of the void ratio in the recompression stage increases approximately in proportion to the logarithm of the stress reduction ratio and is not affected by the shear strain amplitude. For multi-directional cyclic shear, this change of the void ratio depends on the phase difference and the number of cycles. The cyclic recompression indices in the recompression stage were obtained for uni-directional and multi-directional cyclic shears. The cyclic shear induced settlement can be calculated by using these indices.

Cyclic behaviour of loose anisotropically consolidated Ottawa sand under undrained torsional loading

The behaviour of loose, anisotropically consolidated Ottawa sand was examined under undrained cyclic loading in the hollow cylinder apparatus. The stress level, the cyclic stress level and the consolidation stress ratio were varied. The instability line of anisotropically consolidated loose Ottawa sand, defined under monotonic loading, is shown to form a boundary in the vicinity of which a sudden increase in the rate of excess pore water pressure and strain accumulation is observed, and the sand strain-softens. However, this unstable response is arrested at phase transformation, and the sand specimens show a stable or temporarily stable effective stress cycle at low and high consolidation stress ratios respectively. Similar behaviour is observed for isotropically consolidated sand, which exhibits initial liquefaction after strain-softening. The terminal excess pore water pressure associated with this final stage is described as a function of consolidation stress ratio, while the development of excess pore water pressure during cyclic loading is uniquely defined for all tests as a function of normalised shear work. The cyclic resistance of the sand decreases with decreasing consolidation stress ratio. Anisotropic consolidation significantly affects the stiffness and damping ratio values of loose Ottawa sand.

Cnoidal Water Wave Induced Pore Pressure Accumulation in the Seabed

The pore water pressure accumulation in the seabed soil under cnoidal water waves is examined in detail. The cnoidal water wave theory is employed to calculating the water pressure on the double-layer seabed in shallow water region. The modified Terzaghi consolidation equation is the governing equation. A general analytical solution for the consolidation equation is given in an integral form. And a comparative study is carried out to verify the two previous pore pressure generation models: the linear relation and the hyperbola model. Accordingly, a joint model is presented to analysis the pore pressure accumulation in seabed and the soil liquefaction in a practical accident happened in China Shengli Oil Field. Key words : Cnoidal water wave; Pore pressure accumulation; Hyperbola model; Modified Terzaghi consolidation equation

Prediction of excess pore water pressure and post-cyclic settlement on soft clay induced by uni-directional and multi-directional cyclic shears as a function of strain path parameters

The effects of cyclic shear direction, shear strain amplitude and number of cycles on the accumulation of excess pore water pressure and on the recompression were investigated for a cohesive soil by using the multi-directional cyclic simple shear test apparatus in which the uniform or irregular cyclic shear strain was applied to the specimen from two perpendicular directions in the horizontal plane. It is shown that at the same shear strain amplitude and number of cycles, excess pore water pressure and post-cyclic settlement induced by multi-directional cyclic shear are larger than those generated by uni-directional one. For multi-directional cases, these parameters increase with the phase difference. The unique relations of the excess pore water pressure ratio and the post-cyclic settlement versus cumulative shear strain are obtained for uni-directional and multi-directional cyclic shears and also for multi-directional cyclic shear with various phase differences, and these results lead the effect of cyclic shear direction to be negligible. Furthermore, an estimation method of excess pore water pressure ratio and post-cyclic settlement is presented and the validity of this method is confirmed for both uniform and irregular cyclic shears.

Influence of Intermediate Principal Stress on Undrained Behavior of Intact Clay under Pure Principal Stress Rotation

This study presents the accumulations of the excess pore water pressure and the deformation as well as the noncoaxial behavior of intact soft clay subjected to pure principal stress rotation. Series of tests were carried out by using a dynamic hollow cylinder apparatus to highlight the influence of intermediate principal stress parameterb. It was found that the rate of PWP evolution was greatly influenced byb, but the influence was not monotonous. Specimens under the conditionb= 0.75 had the highest accumulation of pore water pressure while under the conditionb= 0 had the strongest resistance to the pore pressure generation. PWP accumulated mainly in the first cycle. The failure of specimens under principal stress rotation was controlled by the strain other than the pore pressure. The shear stiffness decreased more quickly with higherbvalue. The direction of the principal strain increment was strongly dependent on the principal stress increment orientation and less influenced by thebvalue and the number of cycles.

The Test Study to the Changes of Excess Pore Water Pressure during Precast Pile Construction

The construct to precast pile in thick clayey soil can cause the accumulation of excess pore water pressure. The high excess pore pressure can make soil, buildings and pipes surrounded have large deflection, even make them injured. Combining with actual projects, this paper presents an in-situ model test on the changes of excess pore water pressure caused by precast pile construct. It is found that the radius of influence range for single pile driven is about 15m，the excess pore water pressure can reach or even exceed the above effective soil pressure, and there are two relatively stable stages.

Three-Dimensional Dynamic Response Analysis of Shield Tunnel under Train Loads

The vibration loads will be produced between wheel and rail on the running of the high-speed Train. The vibration energy will be transferred to the ground formation through the rail, guiding bed and tunnel lining structure, thereby causing vibration between the formation and surface and environmental interference effect problems. Thus the research of related issues caused by the high-speed train vibration has the vital great significance. The train design speed of the Shiziyang shield tunnel for Guangzhou-Shenzhen-Hong Kong passenger dedicated line is up to 350km/h. In this paper the research object is located in the segment of the homogeneous formation of the Shiziyang shield tunnel. The analysis of this paper includes the dynamic response rules of the shield tunnel and formation under the single high-speed train loads and the law of the pore water pressure accumulation and dispersion under train cyclic loading.

Performance-Based Assessment of Magnitude (Duration) Scaling Factors

More pronounced at relatively smaller magnitude events, significant variations to an extent of a factor of two in magnitude (duration) scaling factors (MSFs) explain the need to further study this issue, which is also recognized and recommended by the National Center for Earthquake Engineering Research Group. Inspired from this gap, the main motivation of this study is defined as to (1) compa- ratively assess the validity of existing magnitude scaling models and the accuracy of their predictions; (2) develop robust and practical to use semiempirical magnitude scaling models applied on CRR: separate sets for strain (cyclic mobility) or excess pore pressure (cyclic or flow liquefaction) problems. The writers' excess pore water pressure and shear strain accumulation models were used for the assessment of magnitude (duration) scaling factors. On the basis of the proposed framework, it is concluded that (1) MSFs are not only a function of number of equivalent loading cycles but increase with increasing ru or γmax thresholds and decreasing dilational response (i.e., decreasing relative density and/or increasing effective stress states) of soil layers, (2) significantly different set of MSFs than the NCEER recommen- dations can be estimated for different combinations of γmax (or ru), N1;60;CS, σ 0;0 , (3) for the assessment of critical structures (e.g., nuclear power plants), where significantly smaller shear strain performance targets are needed, use of existing models may produce significantly higher MSFs, leading to unconservative estimates of cyclic mobility potential. DOI: 10.1061/(ASCE)GT.1943-5606.0000596. © 2012 American Society of Civil Engineers. CE Database subject headings: Soil liquefaction; Earthquakes; Pore water; Pore pressure; Strain. Author keywords: Liquefaction; Magnitude scaling factor; Earthquake duration; Performance-based design; Pore water pressure; Shear strain; Number of equivalent uniform stress cycle.

Evaluation of Cyclic Behavior of Fine-Grained Soils Using the Energy Method

While seismic waves propagate through soil deposits, a part of their energy dissipates which results in a decrease in the amplitude of the applied shear stresses. To better understand the mechanisms leading to the dissipation of applied energy in fine-grained soils, undisturbed specimens having different geotechnical characteristics obtained from a site investigation after 1999 Kocaeli earthquake, were tested in a series of cyclic triaxial tests. Analysis of cyclic test data suggests that portions of fine-grained soil deposits, i.e., silts and clays could have developed high excess pore pressures and significant shear strains during cyclic loadings which contribute to stability problems. The effects of various factors such as confining stress, dynamic stress amplitude, and pore-water pressure accumulation on the cyclic softening of fine-grained soils were investigated and evaluated using the energy criterion.

On the “elastic” stiffness in a high-cycle accumulation model for sand: a comparison of drained and undrained cyclic triaxial tests

High-cycle accumulation (HCA) models may be used for the prediction of settlements or stress relaxation in soils due to a large number of cycles (N > 103) with a relatively small-strain amplitude (εampl < 10−3). This paper presents a discussion of the elastic stiffness, [Formula: see text], used in the basic constitutive equation of an HCA model, [Formula: see text], where [Formula: see text] is the trend of effective stress, [Formula: see text] is the trend of strain, [Formula: see text] is the rate of strain accumulation, and [Formula: see text] is the plastic strain rate. [Formula: see text] interrelates the “trends” of stress and strain evolution. For the experimental assessment of the bulk modulus, [Formula: see text], the rate of pore-water pressure accumulation, [Formula: see text], in undrained cyclic triaxial tests and the rate of volumetric strain accumulation, [Formula: see text], in drained cyclic tests have been compared. The pressure-dependent bulk modulus, K, was quantified from 15 pairs of drained and undrained tests with different consolidation pressures and stress amplitudes. It is demonstrated that both the curves [Formula: see text] in the drained tests and u(N) in the undrained tests are well predicted by the authors’ HCA model if the elastic stiffness is determined using the method described in the present paper. A simplified determination of K from the unloading and reloading curve in an oedometric compression test is discussed.

Effects of Wave Non-Linearity on Residual Pore Pressures in Marine Sediments

A better understanding of the wave-induced pore pressure accumulations (i.e., residual pore pressure) is a key factor in the analysis of the wave-induced liquefaction in marine sediments. In this paper, the residual mechanism of nonlinear wave-induced pore water pressure accumulation in marine sediments is examined. Unlike previous investigations, the second-order Stokes wave theory is considered in this study. The new model is verified with experimental data and provides a better prediction of pore pressure accumulation than the previous solution with linear wave theory. The parametric study concludes that the influences of wave non-linearity increase as the following parameters increase (i) wave steepness (H/L) and (ii) residual parameter (β). However, an opposite trend is found for (i) wave period (T), (ii) relative water depth (d/L), (iii) seabed thickness (h/L) and (iv) another residual parameter (α). Furthermore, the effect of wave non-linearity becomes more significant in soft seabed (Soil C).

Experiment and Numerical Simulation of Repeated Liquefaction-Consolidation of Sand

Behaviors of a liquefied ground are influenced by many factors, such as density, confining stress, permeability, particle size and grading, etc. Among these factors, the density plays the most significant role. It is known that when subjected to cyclic loading under undrained condition, there exist three types of liquefaction behaviors, i.e., loose sand will fail directly towards zero mean effective stress without cyclic mobility; medium-dense sand will enter into a cyclic mobility before being completely liquefied; very dense sand, however, will not liquefy at all. In liquefaction analysis, it is important to distinguish these three types of liquefaction behaviors according to different densities. In this paper, firstly, a constitutive model proposed by the same authors is briefly introduced. Secondly, experimental results of shaking-table tests on saturated sandy ground with repeated liquefaction-consolidation process are presented. Then, a finite element-finite difference method (FE-FD) based on the constitutive model and two-phase field theory is conducted. Comparisons between the experiment and the numerical simulation show that the numerical simulation is capable of reproducing almost all main characteristics of the repeated liquefaction-consolidation of sandy grounds with different densities, such as the mechanical behavior pre- and during liquefaction, the settlement in post-liquefaction consolidation and the influence of density on the accumulation of excessive pore water pressure (EPWP) in repeated strong motions.

A new approximation for pore pressure accumulation in marine sediment due to water waves

AbstractThe residual mechanism of wave‐induced pore water pressure accumulation in marine sediments is re‐examined. An analytical approximation is derived using a linear relation for pore pressure generation in cyclic loading, and mistakes in previous solutions (Int. J. Numer. Anal. Methods Geomech. 2001; 25:885–907; J. Offshore Mech. Arctic Eng. (ASME) 1989; 111(1):1–11) are corrected. A numerical scheme is then employed to solve the case with a non‐linear relation for pore pressure generation. Both analytical and numerical solutions are verified with experimental data (Laboratory and field investigation of wave– sediment interaction. Joseph H. Defrees Hydraulics Laboratory, School of Civil and Environmental Engineering, Cornell University, Ithaca, NY, 1983), and provide a better prediction of pore pressure accumulation than the previous solution (J. Offshore Mech. Arctic Eng. (ASME) 1989; 111(1):1–11). The parametric study concludes that the pore pressure accumulation and use of full non‐linear relation of pore pressure become more important under the following conditions: (1) large wave amplitude, (2) longer wave period, (3) shallow water, (4) shallow soil and (5) softer soils with a low consolidation coefficient. Copyright © 2006 John Wiley & Sons, Ltd.

Catastrophic failure of submerged slopes in normally consolidated sediments

The application of fracture mechanics methods to shear band growth in granular materials requires careful consideration of the elasto-plastic nature of the material behaviour. In this paper, the Palmer and Rice fracture mechanics approach is applied to the problem of catastrophic shear band propagation in a submerged slope built of normally consolidated sediments. This allows for catastrophic (unstable) and progressive (stable) types of soil failure to be properly distinguished. Many submerged landslides are triggered by earthquakes, via the shear strength degradation, due to the excess pore water pressure accumulation. The conventional analysis assumes that the excess water pressure zone develops simultaneously along the entire landslide length, often reaching several kilometres. When a mechanism of the catastrophic shear band propagation is considered, a much shorter excess water pressure zone (e.g. several hundred metres) can still cause a full-scale landslide (often generating a tsunami wave of considerable height). This mechanism also suggests possible measures for mitigation of the landslide hazard.

Catastrophic failure of submerged slopes in normally consolidated sediments

The application of fracture mechanics methods to shear band growth in granular materials requires careful consideration of the elasto-plastic nature of the material behaviour. In this paper, the Palmer and Rice fracture mechanics approach is applied to the problem of catastrophic shear band propagation in a submerged slope built of normally consolidated sediments. This allows for catastrophic (unstable) and progressive (stable) types of soil failure to be properly distinguished. Many submerged landslides are triggered by earthquakes, via the shear strength degradation, due to the excess pore water pressure accumulation. The conventional analysis assumes that the excess water pressure zone develops simultaneously along the entire landslide length, often reaching several kilometres. When a mechanism of the catastrophic shear band propagation is considered, a much shorter excess water pressure zone (e.g. several hundred metres) can still cause a full-scale landslide (often generating a tsunami wave of considerable height). This mechanism also suggests possible measures for mitigation of the landslide hazard.

Liquefaction characteristics of silts

The paper presents a summary of the results of cyclical triaxial load testing of samples of silt and silty sands. The paper emphasizes differences in behaviour observed between reconstituted triaxial samples of clean sand, of sand containing 10, 20, 30 and 60% silt, pure silt, and undisturbed samples of silt and silty sand. An important observation is that the mechanisms of deformation for sit are different for reconstituted and undisturbed samples, the undisturbed sample having a specific ‘geological’ structure which seems to slow down the excess pore water pressure accumulation, but which still results in cyclic deformations regularly increasing from the very beginning of the test and rapidly reaching high levels. The other important observation is that fine-grained noncohesive soils such as silts and silty sands can be as, or even more, susceptible to liquefaction as clean sands. Test results on samples of sand containing 10, 20 or 30% of silt indicate lesser resistance to liquefaction than pure sand samples. The paper shows the difficulty in identifying a representative parameter to compare the behaviour of silts and silty sands with pure sand, and it seems that more research will be needed in this area.

Landslide induced river bed uplift in the Tal valley of Garhwal Himalaya, India

A large scale landslide occurred in the Tal valley of Garhwal Himalaya in late January, 1990. The most interesting feature associated with this slide was the 4 m uplift of a 200 m long and 25 m wide part of the river bed (at an average rate of 13.8 cm/day) between 28 January and 25 February 1990. Studies revealed that the slide occurred because of complex slope processes consisting of rotation and slump movement attributable to the accumulation of pore water pressure in extremely shattered and pulverized rocks during prolonged surface moistening. The process of movement was triggered by the gravitational force exerted upon the sheared material which dislocated a block at the upper part of the slide along a slip plane which terminated below the river bed. Counter resistance was provided by the rocks below the river bed to subdue the further movement of the slide. This indicates that uplift of the river bed and formation of terraces is also related to the nature of the slide and the volume of slumped material.

Wave-Induced Pore Water Pressure Accumulation in Marine Soils

Wave-Induced Pore Water Pressure Accumulation in Marine Soils