scholarly journals Effective stresses in a porous seabed of finite thickness: inertia effects

2000 ◽  
Vol 37 (6) ◽  
pp. 1383-1392 ◽  
Author(s):  
D S Jeng ◽  
M S Rahman
Keyword(s):  
Pore Pressure ◽  
Finite Thickness ◽  
Relative Difference ◽  
Inertia Force ◽  
Soil Conditions ◽  
Inertia Effects ◽  
Effective Stresses ◽  
Present Solution ◽  
Wave Induced ◽  
Inertia Forces

The evaluation of wave-induced pore pressure and effective stresses is an important factor in the design of offshore installations. However, to simplify a complicated problem, most previous investigations have ignored the effects of inertia forces. This paper presents a new semi-analytical solution to the equations governing the wave-induced seabed response, including inertia terms for the whole problem. The numerical results show that the inertia forces cannot always be ignored. The relative difference between the present solution (with inertia items) and the previous solution (without inertia items) may reach 17% of po under certain combinations of wave and soil conditions. Key words: inertia force, pore pressure, effective stresses.

scholarly journals Effects of the Soil Property Distribution Gradient on the Wave-Induced Response of a Non-Homogeneous Seabed

2019 ◽  
Vol 7 (8) ◽  
pp. 281 ◽  
Author(s):  
Titi Sui ◽  
Yu Jin ◽  
Zhaojun Wang ◽  
Chi Zhang ◽  
Jian Shi
Keyword(s):  
Numerical Model ◽  
Dynamic Response ◽  
Soil Properties ◽  
Pore Pressure ◽  
Soil Property ◽  
Induced Response ◽  
Property Distribution ◽  
Effective Stresses ◽  
Soil Distribution ◽  
Wave Induced

The seabed is usually non-homogeneous in the real marine environment, and its response to the dynamic wave loading is of great concern to coastal engineers. Previous studies on the simulation of a non-homogeneous seabed response have mostly adopted a vertically layered seabed, in which homogeneous soil properties are assumed in the governing equations for one specified layer. This neglects the distribution gradient terms of soil property, thus leading to an inaccurate evaluation of the dynamic response of a non-homogeneous seabed. In this study, a numerical model for a wave-induced 3D non-homogeneous seabed response is developed, and the effects of the soil property distribution gradient on the wave-induced response of a non-homogeneous seabed are numerically investigated. The numerical model is validated, and the results of the present simulation agree well with those of previous studies. The validated model is applied to simulate an ideal two-dimensional (2D) vertical non-homogeneous seabed. The model is further applied to model the practical wave-induced dynamic response of a three-dimensional (3D) non-homogeneous seabed around a mono-pile. The difference in pore pressure and soil effective stresses due to the soil distribution gradient is investigated. The effects of the soil distribution gradient on liquefaction are also examined. Results of this numerical study indicate that (1) pore pressure decreases while soil effective stresses increase (the maximum difference of the effective stresses can reach 68.9 % p 0 ) with a non-homogeneous seabed if the distribution gradient terms of soil properties are neglected; (2) the effect of the soil property distribution gradient terms on the pore pressure becomes more significant at the upper seabed, while this effect on the soil effective stresses is enhanced at the lower seabed; (3) the effect of the soil distribution gradient on the seabed response is greatly affected by the wave reflection and diffraction around the pile foundation; and (4) the soil distribution gradient terms can be neglected in the evaluation of seabed liquefaction depth in engineering practice.

Experimental Study for Wave-Induced Oscillatory Pore Pressures in a Sandy Seabed

2014 ◽  
Author(s):  
Bo Liu ◽  
Dong-Sheng Jeng ◽  
Guanlin Ye
Keyword(s):  
Experimental Study ◽  
Pore Pressure ◽  
Vertical Cylinder ◽  
Soil Conditions ◽  
Soil Parameters ◽  
Pore Pressures ◽  
Sandy Deposit ◽  
Dimensional Facility ◽  
Set Up ◽  
Wave Induced

In this paper, an experimental study for wave-induced pore pressures in marine sediments was reported. In the experiment, a one-dimensional facility was set up with a vertical cylinder and a 1.8 m thick sandy deposit and 0.2 m thick water above the deposit. Unlike the previous experiments [1], additional static water pressures were added on the harmonic dynamic wave pressure and more pore pressure gauges were buried in the deposit, which allowed us to simulate the case with larger water depth and better describe the distribution of pore pressure trend. A series of experiments with 3000 cycles in each test were conducted under numerous different wave and soil conditions, which allowed us to examine the influence of wave and soil parameters on the wave-induced pore pressures as well as liquefaction. The experimental results show the significant influence of liquefaction on sandy seabed in shallow water. Furthermore, some new experimental phenomenon was observed. The depth of sandy deposit was usually considered to be unchanged in theoretical calculation, while the depth of which was indeed changed periodic with wave loading, which was observed and recorded in the experiments.

Pore pressure on a submarine pipeline in a cross-anisotropic nonhomogeneous seabed under water-wave loading

1999 ◽  
Vol 36 (3) ◽  
pp. 563-572 ◽  
Author(s):  
D S Jeng ◽  
Y S Lin
Keyword(s):  
Pore Pressure ◽  
Element Model ◽  
Relative Difference ◽  
Soil Characteristics ◽  
Pipe Surface ◽  
Pressure Pipeline ◽  
Submarine Buried Pipeline ◽  
Anisotropic Soil ◽  
Soil Behaviour ◽  
Wave Induced

Conventional investigations for the wave–seabed–pipe interaction problem have dealt with a uniform and isotropic seabed, despite the influences of anisotropic soil behaviour and variable soil characteristics. This paper proposes a finite-element model to investigate the effects of cross-anisotropic soil behaviour and variable soil characteristics (permeability and shear modulus) on the wave-induced oscillatory pore pressures on a submarine buried pipeline. The present model is verified with previous experimental data for the case of a uniform and isotropic seabed. The numerical results indicate that the effects of cross-anisotropic soil behaviour and variable soil characteristics on the pore pressure around the pipe surface cannot always be ignored. The maximum relative difference of pore pressure may reach 10% of the amplitude of the wave pressure at the seabed surface.Key words:pore pressure, pipeline, cross-anisotropic, nonhomogeneous

Wave-Induced Pore Pressure and Effective Stresses in a Porous Seabed With Variable Permeability

1997 ◽  
Vol 119 (4) ◽  
pp. 226-233 ◽  
Author(s):  
D. S. Jeng ◽  
B. R. Seymour
Keyword(s):  
Pore Pressure ◽  
Offshore Structures ◽  
Soil Permeability ◽  
Soil Response ◽  
Mathematical Procedure ◽  
Effective Stresses ◽  
Variable Permeability ◽  
Seabed Interaction ◽  
Wave Induced ◽  
Interaction Problem

An evaluation of wave-induced soil response is particularly important for marine geotechnical engineers involved in the design of foundations for offshore structures. To simplify the mathematical procedure, most theories describing the wave-seabed interaction problem have assumed a porous seabed with uniform permeability, despite strong evidence of variable permeability. This paper presents an analytical solution for the wave-induced soil response in a porous seabed with variable permeability. Verification is available through a reduction to the simple case of uniform permeability. The results indicate that the effect of variable soil permeability on pore pressure and effective stresses is significant.

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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