Softening of the Clayey Seabed Foundation due to Earthquakes

1988 ◽  
Vol 110 (1) ◽  
pp. 17-23 ◽  
Author(s):  
N. Mori ◽  
Y. Ishikawa ◽  
A. Hirayama ◽  
K. Tamaoki ◽  
H. Kobayashi
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Confining Pressure ◽  
Offshore Structures ◽  
Model Tests ◽  
Shaking Table ◽  
Earthquake Response ◽  
Response Analysis ◽  
Earthquake Response Analysis

Offshore structures are subjected to repeated loads from earthquakes and waves which may cause softening of the clayey seabed foundation. Carrying out a series of model tests on a shaking table, the following results are obtained. Settlement and inclination of a model of the base-part of the structure occur when the excess pore water pressure beneath the model rises to about 5 percent of the initial confining pressure. The earthquake response analysis even taking the nonlinearity of the soil into account cannot predict the results of the model test when the pore water pressure does generate and accumulate. Model tests show that the values of the pore water pressure are about twice as large as those predicted by calculation. From these results, rough evaluation of earthquake stability of the clayey seabed under offshore structures are obtained.

Dynamic Experimental Study on Highly Weathered Granite

2014 ◽  
Vol 518 ◽  
pp. 132-137
Author(s):  
Lei Niu ◽  
Quan Jie Song ◽  
Shuang Xu ◽  
Xiao Ming Guo
Keyword(s):  
Shear Modulus ◽  
Shear Strain ◽  
Pore Water ◽  
Effective Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Damping Ratio ◽  
Confining Pressure ◽  
Response Analysis ◽  
Weathered Granite

The shear modulus and damping ratio are two important index in equivalent nonlinear model which is widely used in seismic response analysis. GDS resonant-column is used to study the shear modulus and damping ratio of highly weathered granite by controlling the consolidation confining pressure and pore water pressure. Variation of resonant frequency, shear modulus and damping ratio can be observed when different effective stress which is changed with confining pressure and pore water pressure applied on the sample. Hadin-Drnevich fitting curves are given on the basis of experimental data, and damping mechanism of highly weathered granite is discussed by making use of frictional theory. We can conclude from the results that there is a positive correlation between resonance frequency and shear strain, while there is a negative correlation between samples damping ratio and shear strain. The effective stress impact both samples shear modulus and damping ratio. However, pore water pressure can only act on damping ratio.

scholarly journals Effect of Variable Confining Pressure on Cyclic Triaxial Behavior of K0-consolidated Soft Marine Clay

2018 ◽  
Vol 4 (4) ◽  
pp. 755
Author(s):  
Lei Sun
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Axial Strain ◽  
Water Pressure ◽  
Confining Pressure ◽  
Stress Path ◽  
Cyclic Stress ◽  
Marine Clay ◽  
Stress Ratios ◽  
Variable Confining Pressure

The effect of variable confining pressure (VCP) on the cyclic deformation and cyclic pore water pressure in K0-consolidated saturated soft marine clay were investigated with the help of the cyclic stress-controlled advanced dynamic triaxial test in undrained condition. The testing program encompassed three cyclic deviator stress ratios, CSR=0.189, 0.284 and 0.379 and three stress path inclinations ηampl=3,1 and 0.64. All tests with constant confining pressure (CCP) and variable confining pressure (VCP) have identical initial stress and average stress. The results were analyzed in terms of the accumulative normalized excess pore water pressure rqu recorded at the end of each stress cycle and permanent axial strain, as well as resilient modulus. Limited data suggest that these behavior are significantly affected by both of the VCP and CSR. For a given value of VCP, both of the pore water pressure rqu and permanent axial strains are consistently increase with the increasing values of CSR. However, for a given value of CSR, the extent of the influence of VCP and the trend is substantially depend on the CSR.

scholarly journals Effect of Seismic Loading on Variation of Pore Water Pressure During Pile Pull-Out Tests in Sandy Soils

2021 ◽  
Vol 27 (12) ◽  
pp. 1-12
Author(s):  
Haider N. Abdul Hussein ◽  
Qassun S. Mohammed Shafiqu ◽  
Zeyad S. M. Khaled
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Seismic Loading ◽  
Shaking Table ◽  
Dense Sand ◽  
Pressure Transducers ◽  
Pull Out ◽  
Pullout Tests ◽  
Pile Model

Experimental model was done for pile model of L / D = 25 installed into a laminar shear box contains different saturation soil densities (loose and dense sand) to evaluate the variation of pore water pressure before and after apply seismic loading. Two pore water pressure transducers placed at position near the middle and bottom of pile model to evaluate the pore water pressure during pullout tests. Seismic loading applied by uniaxial shaking table device, while the pullout tests were conducted through pullout device. The results of changing pore water pressure showed that the variation of pore water pressure near the bottom of pile is more than variation near the middle of pile in all tests. The variation of pore water pressure after apply seismic loading is more than the variation before apply seismic loading near the middle of pile and near the bottom of pile and in loose and dense sand. Variation of pore water pressure after apply seismic loading and uplift force is less than the variation after apply seismic loading in loose sand at middle and bottom of pile.

scholarly journals Experimental Study on the Variation Law of Excess Pore Water Pressure at the Bottom of the Foundation Pit for Excavation

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Qizhi Hu ◽  
Qiang Zou ◽  
Zhigang Ding ◽  
Zhaodong Xu
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Confining Pressure ◽  
Deep Foundation ◽  
Foundation Pit ◽  
Excess Pore Water Pressure ◽  
Accurate Expression ◽  
Excess Pore

The excavation unloading of deep foundation pits in soft soil areas often produces negative excess pore water pressure. The rebound deformation of soil on the excavation surface of the foundation pit can be predicted reliably through the accurate expression of relevant variation laws. In combination with the principle of effective stress and the general equation of unidirectional seepage consolidation, an equation for calculating the rebound deformation from the bottom in the process of foundation pit excavation unloading was obtained. Additionally, a triaxial unloading test was adopted to simulate the excavation unloading processes for actual foundation pit engineering. After studying the variation law of the excess pore water pressure generated by excavation unloading, it was found that the negative excess pore water pressure increased with increasing unloading rate, while the corresponding peak value decreased with increasing confining pressure. The equation for rebound calculation was verified through a comparison with relevant measured data from actual engineering. Therefore, it is considered that the equation can reliably describe the rebound deformation law of the base. This paper aims to guide the design and construction of deep foundation pits in soft soil areas.

Experimental Study of the Influence of the Pore Water Pressure Evolution and the Shear Band Formation on the Extraction Resistance of Submerged Anchor Plates

2018 ◽  
Author(s):  
Manuela Kanitz ◽  
Juergen Grabe
Keyword(s):  
Experimental Study ◽  
Shear Band ◽  
Pore Water ◽  
High Speed ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Offshore Structures ◽  
Shear Band Formation ◽  
Band Formation ◽  
Anchor Plates

Floating offshore structures used to generate wind energy are founded on submerged foundations such as anchor plates. Their extraction resistance is of major importance during and at the end of the lifetime cycle of these offshore structures. During their lifetime cycle, the foundation is suspended to complex loading conditions due to waves, tidal currents and wind loads. To guarantee a stable structure, the extraction resistance of the anchor plates has to be known. At the end of the lifetime cycle of the offshore structures, the extraction resistance is mainly influencing the removal of the anchor plates. This resistance is a lot higher than the sum of its self-weight and hydrostatic and earth pressure acting on the structure. With initiation of a motion of the anchor plate, the volume underneath this structure is increased leading to negative pore water pressure until inflowing pore water is filling the newly created volume. In order to investigate this effect, an extensive experimental study at model scale with a displacement-driven extraction is performed. Pore pressure measurements are carried out at various locations in the soil body and underneath the plate. The soil movement is tracked with a high-speed camera to investigate the shear band formation with the particle image velocimetry method (PIV). The experiments will be conducted considering different packing densities of the soil body and at different extraction velocities to investigate their effect on the extraction resistance of anchor plates.

scholarly journals Numerical Evaluation of The Nonlinear Behavior of Soil-Pile Interaction Under The Effect of Coupled Static-Dynamic Loads

2021 ◽  
Author(s):  
Duaa Al-Jeznawi ◽  
ISMACAHYADI Mohamed Jais ◽  
Bushra S. Albusoda
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Three Dimensional ◽  
Ground Surface ◽  
Frictional Resistance ◽  
Saturated Soil ◽  
Shaking Table ◽  
Physical Models ◽  
Soil Layers

Abstract Liquefaction of saturated soil layers is one of the most common causes of structural failure during earthquakes. Liquefaction occurs as a result of increasing pore water pressure, whereby the rise in water pressure occurs due to unexpected change in stress state under short-term loading, i.e., shaking during an earthquake. Thus, general failure occurs when the soil softens and eliminates its stiffness against the uplift pressure from the stability of the subsurface structure. In this case, the condition of soil strata is considered undrained because there is not enough time for the excess pore water pressure to dissipate when a sudden load is applied. To represent the non-linear characteristics of saturated sand under seismic motions in Kobe and Ali Algharbi earthquakes, the computational model was simulated using the UBCSAND model. The current study was carried out by adopting three-dimensional-based finite element models that were evaluated by shaking table tests of a single pile model erected in the saturated soil layers. The experimental data were utilized to estimate the liquefaction and seismicity of soil deposits. According to the results obtained from the physical models and simulations, this proposed model accurately simulates the liquefaction phenomenon and soil-pile response. However, there are some differences between the experiment and the computational analyses. Nonetheless, the results showed good agreement with the general trend in terms of deformation, acceleration, and liquefaction ratio. Moreover, the displacement of liquefied soil around the pile was captured by the directions of vectors generated by numerical analysis, which resembled a worldwide circular flow pattern. The results revealed that during the dynamic excitation, increased pore water pressure and subsequent liquefaction caused a significant reduction in pile frictional resistance. Despite this, positive frictional resistance was noticed through the loose sand layer (near the ground surface) until the soil softened completely. It is worth mentioning that the pile exhibited excessive settlement which may attribute to the considerable reduction, in the end, bearing forces which in turn mobilizing extra end resistance.

scholarly journals Progressive Failure and Fracture Mechanism of Sandstone under Hydraulic-Mechanical Coupling

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Yingming Li ◽  
Gang Liu ◽  
Tao Qin ◽  
Zhupeng Jin ◽  
Chengxing Zhao ◽  
...  
Keyword(s):  
Pore Water ◽  
Fracture Mechanism ◽  
Pore Water Pressure ◽  
Progressive Failure ◽  
Water Pressure ◽  
Confining Pressure ◽  
Experimental Results ◽  
Type I ◽  
Volume Deformation ◽  
Mechanical Coupling

Hydraulic coupling often leads to progressive rock failure accidents. Mechanical tests were performed over a range of combined pore water pressure and confining pressure stress path conditions to study the progressive failure characteristics of sandstone under hydraulic-mechanical coupling and explore the crack initiation and pore water fracture mechanism. The closure stress and damage stress were determined by the axial deformation stiffness and volume deformation stiffness. The experimental results indicate that confining pressure is the main controlling factor in the crack propagation stage, and pore water pressure enhances crack evolution. With increasing effective confining pressure, the effective peak deviatoric stress strongly increases and the characteristic stress increases linearly. The initiation stress and damage stress decrease with increasing pore water pressure. The moduli in stages I, II, and III are similar to the law of the transverse and radial deformation ratio with notable differences in stage IV. The fracture trend angle was determined by the ratio of axial crack strain and radial crack strain. Compared with the experimental results, the internal cracks in the sandstone samples are mainly type-II cracks, and type-I cracks are also locally present. After stress damage, the cracks expand and extend at an angle close to the real fracture.

Numerical Investigations of the Extraction of Submerged Foundations by Coupled CFD-DEM

2017 ◽  
Author(s):  
Manuela Kanitz ◽  
Juergen Grabe ◽  
Alice Hager ◽  
Christoph Goniva ◽  
Christoph Kloss
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Solid Phase ◽  
Water Pressure ◽  
Discrete Element ◽  
Offshore Structures ◽  
Spherical Particles ◽  
Embedment Depth ◽  
Sea Bed ◽  
Element Method

Offshore structures are founded on submerged foundations. The excavation of submerged foundations in the sea bed is a difficult task to accomplish when it comes to the decommissioning of these offshore structures. The extraction resistance is a lot higher than the pressure acting on the structure due to hydrostatic pressure, earth pressure and its self-weight. Once the extraction begins, a negative pore water pressure is created until inflowing pore water compensates this negative pore water pressure. This depression is hindering the extraction of the submerged foundation. Additionally, the resistance is dependent on the embedment depth of the structure, the soil properties as well as the extraction velocity, which influences the dimension of the negative pore water pressure. The numerical investigation of this dynamic problem is a limitation for continuum based approaches like the Finite Element Method (FEM) due to the occurring large deformations. These results from the soil bed failing under the movement of the structure and hence starting to flow. Additionally, in order to estimate the created depression, the investigation of the water-soil-interaction is crucial, as the change of the pore water pressure plays a significant role. Therefore, it is necessary to analyze the behavior of the soil particles and the pore water pressure. In order to do this, a coupled Euler-Lagrange approach, namely the combination of Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM), is used. In these simulations on one hand, the liquid phase, e.g. the water, is considered as a continuum, while on the other hand, for the solid phase, e.g. the soil, a particle representation is chosen. Hence, it is possible to compute the particle-particle — as well as the fluid-particle-interactions. The calculations are carried out with the open source software package CFDEMcoupling®, which combines the discrete element code LIGGGHTS® with CFD solvers based on OpenFOAM®. This paper introduces the coupled CFD-DEM approach to simulate the extraction of a submerged plate in the soil bed. In this work, the soil grains are idealized by spherical particles of different diameters. In order to consider effects of dilatancy and contractancy in the soil bed, different relative densities are investigated. Additionally, a variation of the extraction velocity of the plate is carried out to examine the dependence on the creation of negative pore water pressure. For each case, the extraction resistance is calculated. The flow velocity and the pressure distribution in the vicinity of the structure are analyzed.

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