scholarly journals Effect of Deep Mixing Grid Spacing On The Settlement of Liquefied Soil, Using Numerical Approach

2022 ◽  
Author(s):  
Fereshteh Rahmani ◽  
Seyed Mahdi Hosseini
Keyword(s):  
Pore Pressure ◽  
Ground Improvement ◽  
Pressure Ratio ◽  
Soil Layer ◽  
Excess Pore Pressure ◽  
Analysis Model ◽  
Liquefaction Mitigation ◽  
Deep Mixing ◽  
Liquefiable Soil ◽  
Excess Pore

Abstract Liquefaction occurs in a loose and saturated sand layer, induces quite large damages to infrastructures, the importance of liquefaction mitigation has been emphasized to minimize earthquake disasters for many years. Many kinds of ground improvement techniques based on various improvement principles have been developed for liquefaction mitigation. Among them, deep mixing method with grid pattern was developed for liquefaction mitigation in the 1990s, where the grid of stabilized column walls functions to restrict the generation of excess pore pressure by confining the soil particle movement during earthquake. In this study, a parametric study of the grid-form deep mixing wall is performed using numerical modeling with GID+OpenSees interface V2.6.0. The finite element method with a three-dimensional analysis model can be used to estimate the foundation settlement over liquefiable soil layer. The validity of the developed model was evaluated by comparing the results obtained from the model with the results of numerical studies and the experimental centrifuge test to investigate the effect of deep mixing grid wall on the settlement and generation of excess pore pressure ratio of liquefiable soil. Based on the analysis, the settlement for improved soil was 69% smaller than the settlement for unimproved soil. The results also indicated that the grid wall space, relative density, and stiffness ratio between soil-cement columns and enclosed soil plays an important role in the occurrence of liquefaction and volumetric strains.

scholarly journals Experiment and Analysis of Submarine Landslide Model Caused by Elevated Pore Pressure

2019 ◽  
Vol 7 (5) ◽  
pp. 146 ◽  
Author(s):  
Tao Liu ◽  
Yueyue Lu ◽  
Lei Zhou ◽  
Xiuqing Yang ◽  
Lei Guo
Keyword(s):  
Pore Pressure ◽  
Soil Layer ◽  
Initial Crack ◽  
Excess Pore Pressure ◽  
Deep Soil ◽  
Hydrate Decomposition ◽  
Dynamic Relationship ◽  
Geological Conditions ◽  
Shear Slip ◽  
Excess Pore

Hydrate decomposition is an important potential cause of marine geological disasters. It is of great significance to understand the dynamic relationship between hydrate reservoir system and the overlying seabed damage caused by its decomposition. The purpose of this study is to understand the instability and destruction mechanisms of a hydrated seabed using physical simulations and to discuss the effects of different geological conditions on seabed stability. By applying pressurized gas to the low permeability silt layer, the excess pore pressure caused by the decomposition of hydrate is simulated and the physical appearance process of the overlying seabed damage is monitored. According to the test results, two conclusions were drawn in this study: (1) Under the action of excess pore pressure caused by hydrate decomposition, typical phenomena of overlying seabed damage include pockmark deformation and shear–slip failure. In shallower or steeper strata, shear-slip failure occurs in the slope. The existence of initial crack in the stratum is the main trigger cause. In thicker formations or gentler slopes, the surface of the seabed has a collapse deformation feature. The occurrence of cracks in the deep soil layer is the main failure mechanism. (2) It was determined that the thickness and slope of the seabed, among other factors, affect the type and extent of seabed damage.

Liquefaction Mitigation Using Stone Columns Around Deep Foundations: Full-Scale Test Results

2000 ◽  
Vol 1736 (1) ◽  
pp. 110-118 ◽  
Author(s):  
Scott A. Ashford ◽  
Kyle M. Rollins ◽  
S. Case Bradford V ◽  
Thomas J. Weaver ◽  
Juan I. Baez
Keyword(s):  
Pore Pressure ◽  
Ground Improvement ◽  
Full Scale ◽  
Stone Columns ◽  
Excess Pore Pressure ◽  
Deep Foundations ◽  
Laterally Loaded Piles ◽  
Before And After ◽  
Laterally Loaded ◽  
Excess Pore

The results presented were developed as part of a larger project analyzing the behavior of full-scale laterally loaded piles in liquefied soil, the first full-scale testing of its kind. Presented here are the results of a series of full-scale tests performed on deep foundations in liquefiable sand, both before and after ground improvement, in which controlled blasting was used to liquefy the soil surrounding the foundations. Data were collected showing the behavior of laterally loaded piles before and after liquefaction. After the installation of stone columns, the tests were repeated. From the results of these tests, it can be concluded that the installation of stone columns can significantly increase the density of the improved ground as indicated by the cone penetration test. Furthermore, it was found that the stone column installation limited the excess pore pressure increase from the controlled blasting and substantially increased the rate of excess pore pressure dissipation. Finally, the stone columns were found to significantly increase the stiffness of the foundation system by more than 2.5 to 3.5 times that in the liquefied soil. This study provides some of the first full-scale quantitative results on the improvement of foundation performance due to stone columns in a liquefiable deposit.

scholarly journals A semi-empirical model to predict excess pore pressure generation in partially saturated sand

2020 ◽  
Vol 195 ◽  
pp. 02026
Author(s):  
Mousavi Sayedmasoud ◽  
Majid Ghayoomi
Keyword(s):  
Pore Pressure ◽  
Empirical Model ◽  
Pressure Ratio ◽  
Pore Fluid ◽  
Excess Pore Pressure ◽  
Saturated Soils ◽  
Partial Saturation ◽  
Liquefaction Resistance ◽  
Semi Empirical ◽  
Excess Pore

Past studies revealed that excess pore pressure generation due to cyclic loading is highly governed by induced strains, volumetric deformation potential of soil, number of cycles, and bulk stiffness of pore fluid. It is well established that partial saturation can significantly reduce bulk stiffness of pore fluid and consequently excess pore pressure generation during seismic loading. On the basis of that, a number of researchers have investigated induced partial saturation as an effective soil improvement technique to increase the liquefaction resistance of fully saturated soils. This paper focuses on development of a semi- empirical model to interpret the effects of partial saturation on the excess pore pressure generation in sands. In this regard, an existing strain based excess pore pressure ratio (ru) prediction model originally developed for fully saturated soils was modified to incorporate the effect of partial saturation on the excess pore pressure generation. The literature data as well as data from a series of strain-controlled direct simple shear test were used to evaluate the reliability of the proposed equation in predicting the excess pore pressure ratio in partial saturation condition.

HHT Analysis on Pore Pressure Dissipation of Wave-Induced Fluidization in a Sandy Bed

2011 ◽  
Author(s):  
Shiaw-Yih Tzang ◽  
Yung-Lung Chen ◽  
Shan-Hwei Ou
Keyword(s):  
Pore Pressure ◽  
Soil Layer ◽  
Excess Pore Pressure ◽  
Pressure Measurements ◽  
Flume Tests ◽  
Dissipation Mechanism ◽  
Frequency Components ◽  
Excess Pore Pressures ◽  
Wave Induced ◽  
Excess Pore

Wave-induced pore pressure variations during the stage of increasing excess pore pressure consist of the mechanism of generation of fluidization. Moreover, in post-fluidization stage, pore pressure variations not only reveal the dissipation mechanism of fluidization but also the wave-fluidized bed interactions. Past results from a series of lab flume tests have further illustrated that pore pressure variations in a fluidized response are nonlinear and nonsataionary. Hence, the HHT method was further applied to analyze the pore pressure measurements in this study. The results demonstrate that after the dissipation of excess pore pressures the amplitudes of fundamental and higher-frequency components begin to decay. Meanwhile, the amplified amplitudes of fundamental and higher-frequency components during fluidization response would decrease with decreasing thickness of fluidized soil-layer in consecutive tests.

Liquefaction potential of silts from CPTu

2007 ◽  
Vol 44 (1) ◽  
pp. 1-19 ◽  
Author(s):  
Dawn A Shuttle ◽  
John Cunning
Keyword(s):  
Finite Element ◽  
Pore Pressure ◽  
Earthquake Engineering ◽  
Critical State ◽  
Pressure Ratio ◽  
Excess Pore Pressure ◽  
Liquefaction Potential ◽  
Triaxial Cell ◽  
Excess Pore

Silt tailings (slimes) are difficult materials to test in that, like sands, it is extremely difficult to obtain undisturbed samples and subsequently re-establish them in a triaxial cell for element testing in a laboratory in anything approaching their in situ condition. Evaluation of silt tailing behaviour has to depend on in situ tests, and the piezocone (CPTu) in particular. However, CPTs in silt generate substantial excess pore pressure and there is no established methodology to evaluate the measured responses in terms of soil properties, as drained sand-based CPT interpretation is inapplicable. A case history of particularly loose silt tailings is reported in which the National Center for Earthquake Engineering Research (NCEER) liquefaction assessment method would lead to uncertainty in the liquefaction potential. However, the extremely high CPTu excess pore pressure ratio, Bq, and low dimensionless CPT resistance, Qp, at this site indicates liquefaction is likely occurring during pushing of the CPT. Detailed finite element simulations of the CPT using a critical state model provided an effective stress framework to evaluate the in situ state parameter of the silt from the measured CPT data. This framework shows that the group of dimensionless CPT variables Q(1 – Bq) + 1 is fundamental for the evaluation of undrained response during CPT sounding. And, despite the high silt content, the interpretation indicates that the tailings are indeed liquefiable.Key words: liquefaction, CPT, silt, finite element, critical state.

scholarly journals The Use of Ground Motion Parameters to identify the Liquefaction during a Strong Earthquake in Northern Thailand

2021 ◽  
Vol 27 (1) ◽  
pp. 1-8
Author(s):  
Lindung Zalbuin Mase
Keyword(s):  
Pore Pressure ◽  
Amplification Factor ◽  
Pressure Ratio ◽  
Excess Pore Pressure ◽  
Response Analysis ◽  
Ground Response ◽  
Ground Response Analysis ◽  
Northern Thailand ◽  
Motion Parameters ◽  
Excess Pore

This paper presents a ground response analysis to simulate the liquefaction phenomenon during the 2011 Tarlay Earthquake in northern Thailand. The site investigation data and geophysical measurements on 7 sites in northern Thailand were collected. The multi-springs element model was implemented in finite element ground response analysis. Several parameters, such as peak ground acceleration, peak ground velocity, amplification factor, excess pore pressure ratio, were observed. Furthermore, the correlation from the ground motion parameters was generated to estimate liquefaction potential, which was represented by excess pore pressure ratio. The result showed that the excess pore pressure ratio was relatively well correlated with several ground parameters, such as amplification factor, velocity-acceleration ratio, and factor of safety against liquefaction. The results could be also used for the engineering practice in predicting liquefaction potential in Northern Thailand.

Excess Pore Pressures Around Underground Structures Following Earthquake Induced Liquefaction

2012 ◽  
Vol 3 (2) ◽  
pp. 25-41 ◽  
Author(s):  
Siau Chen Chian ◽  
Santana Phani Gopal Madabhushi
Keyword(s):  
Pore Pressure ◽  
Underground Structure ◽  
Unit Weight ◽  
Excess Pore Pressure ◽  
Earthquake Loading ◽  
Underground Structures ◽  
Floating Structure ◽  
Centrifuge Tests ◽  
Liquefiable Soil ◽  
Excess Pore

Underground structures located in liquefiable soil deposits are susceptible to floatation following an earthquake event due to their lower unit weight relative to the surrounding saturated soil. This inherent buoyancy may cause lightweight structures to float when the soil liquefies. Centrifuge tests have been carried out to study the excess pore pressure generation and dissipation in liquefiable soils. In these tests, near full liquefaction conditions were attained within a few cycles of the earthquake loading. In the case of high hydraulic conductivity sands, significant dissipation could take place even during the earthquake loading which inhibits full liquefaction from occurring. In the case of excess pore pressure generation and dissipation around a floating structure, the cyclic response of the structure may lead to the reduction in excess pore pressure near the face of the structure as compared to the far field. This reduction in excess pore pressure is due to shear-induced dilation and suction pressures arising from extensile stresses at the soil-structure interface. Given the lower excess pore pressure around the structure; the soil around the structure retains a portion of this shear strength which in turn can discourage significant uplift of the underground structure.

Excess Pore Pressure Dissipation Characteristics of Different Soil by CPTU on Pearl River Delta

2011 ◽  
Vol 71-78 ◽  
pp. 4606-4609
Author(s):  
Yan Chun Tang ◽  
Gao Tou Meng
Keyword(s):  
Pore Pressure ◽  
Pearl River Delta ◽  
Clay Soil ◽  
Soil Layer ◽  
River Delta ◽  
Excess Pore Pressure ◽  
Pearl River ◽  
Silty Clay ◽  
Sand Soil ◽  
Excess Pore

Through a lot of CPTU excess pore pressure dissipation tests on Pearl River Delta in China, excess pore pressure dissipation characteristics of different soil layer on Guangzhou-Zhuhai section of Beijing-Zhuhai Expressway and Taishan section of Guangdong West Coast Expressway has been analyzed. The dissipation time of 50% dissipation degree t50 of excess pore pressure dissipation curve by CPTU can be used as the auxiliary method to determine the type of soil, and through CPTU excess pore pressure dissipation tests, the t50 value of sand soil, silt, silty clay, clay soil and silt soil has been obtained; through comparison with the t50 value of different soil, the difference of sand soil, silt and clay soil can be roughly distinguished; the obvious boundary value between the t50 value of clay soil, silty clay and silt soil is not existed, so the t50 value can not be direct to determine the type of these clay type of soil. The achieved results can provide a research foundation for CPTU application research on Pearl River Delta in China.

Consolidation of a soil layer subsequent to cessation of deposition

2005 ◽  
Vol 42 (2) ◽  
pp. 678-682
Author(s):  
Guofu Zhu ◽  
Jian-Hua Yin
Keyword(s):  
Pore Pressure ◽  
Soil Layer ◽  
Average Degree ◽  
Excess Pore Pressure ◽  
Triangular Distribution ◽  
Pressure Distributions ◽  
Pore Pressures ◽  
Degree Of Consolidation ◽  
Excess Pore Pressures ◽  
Excess Pore

It is necessary in certain cases to estimate the progress of consolidation in a soil layer that has ceased increasing in thickness over time. In this paper, the existing excess pore pressures for two time–thickness relations are used as the "initial" pore pressures for analysing the consolidation of soil subsequent to the cessation of deposition. Average degrees of consolidation of the soil layer are presented for one-way drainage and two-way drainage boundary conditions. The average degrees of consolidation are compared with those for uniform and triangular initial excess pore pressure distributions. It is found that the average degree of consolidation for one-way drainage boundaries can be estimated using the value for the triangular distribution. The average degree of consolidation for two-way drainage boundaries is bound by the averages for both the uniform and the triangular initial excess pore pressure distributions.Key words: consolidation, deposition, drainage, settlement, soil.

Interaction mechanism between deep mixing column and surrounding clay during installation

2003 ◽  
Vol 40 (2) ◽  
pp. 293-307 ◽  
Author(s):  
Shui-Long Shen ◽  
Norihiko Miura ◽  
Hirofumi Koga
Keyword(s):  
Pore Pressure ◽  
Tensile Failure ◽  
Excess Pore Pressure ◽  
Laboratory Model ◽  
Strength Increase ◽  
Test Field ◽  
Shearing Force ◽  
Deep Mixing ◽  
Short Period ◽  
Excess Pore

Laboratory and field investigation has shown that the shear strength of the surrounding clay increased in the vicinity of a deep mixed (DM) column in the short period following installation. Field observations indicated that significant excess pore pressure, which may be higher than the hydraulic fracture pressure, was generated during installation.The behaviour between a DM column interacting with the surrounding clay during installation can be simulated as the shearing-expanding process of a cylindrical cavity. A simple approach is proposed to calculate the excess pore pressure around a DM column during installation. The proposed method of calculation considers the effect of a shearing force caused by rotating blades during mixing. In the proposed approach, the excess pore pressure is expressed in terms of undrained strength of clay, shearing force, injection pressure, and a pore pressure parameter. An approach is developed to analyze clay fracturing using a tensile failure mechanism. Analytical results indicate that the rotation of the mixing blades has a significant effect on the generation of excess pore pressure and clay fracturing in a close region around the column. The proposed approach has been verified against laboratory model tests and in situ DM column installation in clay ground at two construction sites. Clay fracturing around a DM column was observed in the laboratory and is analyzed based on field data. This paper reveals that clay fracturing is the major factor behind the strength increase and property changes of the surrounding clay in a short period.Key words: soft clay, deep mixing column, shearing-expanding process, excess pore pressure, clay fracturing, laboratory test, field tests.

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