scholarly journals A Deviatoric Softening Model to Simulate Compressibility Properties of Soft Clays

2021 ◽  
Author(s):  
Cong Shi
Keyword(s):  
Yield Surface ◽  
Soft Clay ◽  
Lateral Spreading ◽  
Excess Pore Pressure ◽  
Soft Clays ◽  
Constant Rate ◽  
Anisotropic Consolidation ◽  
Soil Compressibility ◽  
Stress Ratios ◽  
Pore Pressure Response

Soft clays are often associated with high compressibility due to their high void ratio, low shear strength, and creep behavior. Structures built on top of it can experience excessive settlement issues over a long period of time. The prediction of these settlements has attracted attentions from many researchers for over a century, but accurately predicting them still remains a difficult issue due to complex properties of soft clays, including plasticity, viscosity, anisotropy, soil structure and so forth. Therefore, studying the compressibility of soft clay is of significant importance. This dissertation aims to investigate the influence of plastic deviatoric strains on the compressibility of soft clays. First of all, the dissertation reviews a number of published incremental anisotropic consolidation tests on Finnish clays. The results demonstrate the dependence of soil compressibility on stress ratios. Based on the result, a modified yield surface size deviatoric softening law has been introduced. This softening law describes yield surface softening to be related to plastic deviatoric strain increments. Secondly, a new model named MEVP-DS, has been incorporated into the framework of Yin’s elaso-viscoplastic model to consider deviatoric softening, destructuration, and yield surface anisotropy of soft clay. Furthermore, the verification of MEVP-DS has been done through three phases. Phase one is the simulation of published incremental anisotropic consolidation tests on intact Finnish clay samples. The model results demonstrate MEVP-DS successfully captures the soil compressibility in response to different stress ratios. Phase two is the application of MEVP-DS in modeling 1-D consolidation tests on sensitive Champlain Sea clay. Model results highlight that using MEVP-DS is beneficial for predicting the compressibility and excess pore pressure response of the clay subject to constant rate of strain loading. Phase three is the application of MEVP-DS in simulating a real embankment dam on Champlain Sea clay. MEVP-DS not only simulates 40-year settlement measurements of the dam reasonably well, but also improves the prediction of lateral spreading of the dam. In summary, the MEVP-DS model proposed in this dissertation has shown to improve the simulation of soil compressibility of soft clays subject to 1-D, anisotropic and more complicated loading conditions.

scholarly journals A Deviatoric Softening Model to Simulate Compressibility Properties of Soft Clays

2021 ◽  
Author(s):  
Cong Shi
Keyword(s):  
Yield Surface ◽  
Soft Clay ◽  
Lateral Spreading ◽  
Excess Pore Pressure ◽  
Soft Clays ◽  
Constant Rate ◽  
Anisotropic Consolidation ◽  
Soil Compressibility ◽  
Stress Ratios ◽  
Pore Pressure Response

Soft clays are often associated with high compressibility due to their high void ratio, low shear strength, and creep behavior. Structures built on top of it can experience excessive settlement issues over a long period of time. The prediction of these settlements has attracted attentions from many researchers for over a century, but accurately predicting them still remains a difficult issue due to complex properties of soft clays, including plasticity, viscosity, anisotropy, soil structure and so forth. Therefore, studying the compressibility of soft clay is of significant importance. This dissertation aims to investigate the influence of plastic deviatoric strains on the compressibility of soft clays. First of all, the dissertation reviews a number of published incremental anisotropic consolidation tests on Finnish clays. The results demonstrate the dependence of soil compressibility on stress ratios. Based on the result, a modified yield surface size deviatoric softening law has been introduced. This softening law describes yield surface softening to be related to plastic deviatoric strain increments. Secondly, a new model named MEVP-DS, has been incorporated into the framework of Yin’s elaso-viscoplastic model to consider deviatoric softening, destructuration, and yield surface anisotropy of soft clay. Furthermore, the verification of MEVP-DS has been done through three phases. Phase one is the simulation of published incremental anisotropic consolidation tests on intact Finnish clay samples. The model results demonstrate MEVP-DS successfully captures the soil compressibility in response to different stress ratios. Phase two is the application of MEVP-DS in modeling 1-D consolidation tests on sensitive Champlain Sea clay. Model results highlight that using MEVP-DS is beneficial for predicting the compressibility and excess pore pressure response of the clay subject to constant rate of strain loading. Phase three is the application of MEVP-DS in simulating a real embankment dam on Champlain Sea clay. MEVP-DS not only simulates 40-year settlement measurements of the dam reasonably well, but also improves the prediction of lateral spreading of the dam. In summary, the MEVP-DS model proposed in this dissertation has shown to improve the simulation of soil compressibility of soft clays subject to 1-D, anisotropic and more complicated loading conditions.

Analytical solution for radial consolidation considering soil structure characteristics

2015 ◽  
Vol 52 (7) ◽  
pp. 947-960 ◽  
Author(s):  
Cholachat Rujikiatkamjorn ◽  
Buddhima Indraratna
Keyword(s):  
Ground Improvement ◽  
Soft Soil ◽  
Soft Clay ◽  
Excess Pore Pressure ◽  
Vertical Drains ◽  
South Wales ◽  
Surcharge Load ◽  
Speed Up ◽  
Soil Compressibility ◽  
Conventional Models

A system of surcharge load combined with vertical drains to speed up consolidation of soft soil by reducing the drainage path is one of the most efficient and economical ground improvement techniques. In the field, conventional theories including smear zone have been commonly employed to predict the radial consolidation behaviour induced by vertical drains in soft clay. One of the key parameters in conventional analysis is the use of mean coefficient of volume compressibility and soil permeability, which are often assumed to be constant. The effect of drain installation on the soil compressibility of the in situ clay structure is often ignored. Laboratory testing has shown that the soil compressibility and permeability can vary nonlinearly over a considerable range of applied surcharge pressure, and both these properties can be affected during the drain installation. This study presents a mathematical model of radial consolidation via vertical drains incorporating the variations of soil compressibility and permeability as well as highlighting the effects of drain installation on those parameters. The main differences between the proposed and conventional models are elucidated, in terms of stress history and preloading (surcharge) pressure. The effects of preconsolidation pressure and the magnitude of applied preloading are examined through the dissipation of average excess pore pressure and associated settlement. Supported by experimental observations, the proposed theory is validated with field data of a selected case study in the town of Ballina, New South Wales, Australia.

scholarly journals Effects of sampling disturbance in geotechnical design

2019 ◽  
Vol 56 (2) ◽  
pp. 275-289 ◽  
Author(s):  
Guan Tor Lim ◽  
Jubert Pineda ◽  
Nathalie Boukpeti ◽  
J. Antonio H. Carraro ◽  
Andy Fourie
Keyword(s):  
Soil Mechanics ◽  
Soft Clay ◽  
Excess Pore Pressure ◽  
Soil Parameters ◽  
Test Results ◽  
Sample Quality ◽  
Laboratory Test Results ◽  
Geotechnical Design ◽  
Pore Pressure Response ◽  
Shallow Footing

This paper describes an experimental study of the effects of sampling disturbance in an Australian natural soft clay and the consequences of different sample quality on the representativeness of soil parameters used in geotechnical designs. The paper is divided into three sections. Laboratory test results obtained from specimens retrieved using three different tube samplers as well as the Sherbrooke (block) sampler are first described. Then, the sample quality assessment, using available indices proposed for soft soils, is presented. It is shown that sample quality varies with the stress paths and boundary conditions applied in laboratory tests. Finally, mechanical soil properties derived from specimens retrieved using the different samplers are used in the prediction of two classical problems in soil mechanics: the settlement and excess pore pressure response underneath an embankment as well as the settlement and bearing capacity of a shallow footing. These two examples are used here to highlight the consequences of poor sampling in practice.

Pore Pressure Build-up of Silt Soft Clay under Dynamic Loading at Zhoushan Islands

2012 ◽  
Vol 594-597 ◽  
pp. 460-464
Author(s):  
Qian Shi ◽  
Kui Zhou ◽  
Qiang Li
Keyword(s):  
Pore Pressure ◽  
Dynamic Loading ◽  
Dynamic Load ◽  
Soft Clay ◽  
Test System ◽  
Dynamic Responses ◽  
Minor Effect ◽  
Consolidation Pressure ◽  
Anisotropic Consolidation ◽  
Pore Pressure Build Up

The mechanism of dynamic tri-axial test is introduced in this paper and the dynamic responses of silt soft clay at Zhoushan are studied using a dynamic tri-axial test system. The laws of pore pressure build-up of the silt clay are obtained which are affected by the consolidation pressure and dynamic load. The greater the consolidation pressure and the dynamic loading is, the more the build-up of pore pressure is. However, the dynamic load has minor effect on pore pressure build-up under the anisotropic consolidation.

Experimental Study on the Combined Effect of Cyclic and Static Loads on the Mechanical Properties of the Saturated Soft Clay Material

2016 ◽  
Vol 723 ◽  
pp. 843-848
Author(s):  
Yi Wei ◽  
Ying Zhu ◽  
Jing Ni
Keyword(s):  
Mechanical Properties ◽  
Cyclic Load ◽  
Stress Ratio ◽  
Axial Strain ◽  
Soft Clay ◽  
Cyclic Stress ◽  
Excess Pore Pressure ◽  
Static Loads ◽  
Cyclic Stress Ratio ◽  
Excess Pore

The combined effect of cyclic and static loads on the mechanical properties of the soft clay was experimentally investigated by conducting undrained cyclic triaxial tests on Shanghai clay. The results show that an increment in either static or cyclic load increases excess pore pressures and axial strains. For a given value of combined cyclic and static loads, the mechanical properties of the soft clay are more sensitive to the cyclic load. Furthermore, the accumulated excess pore pressure and axial strain for a larger cyclic stress ratio and a lower combined stress ratio might overcome that for a lower cyclic stress ratio and a higher combined stress ratio. The mechanical properties of the soft clay after the cyclic load was unloaded were also discussed. It was observed that the excess pore pressure and axial strain under the static load alone decrease gradually with time. The trend of them largely depends on the ratio of cyclic load to static load.

Characterization of a smear zone around vertical drains by large-scale laboratory tests

2000 ◽  
Vol 37 (6) ◽  
pp. 1265-1271 ◽  
Author(s):  
J S Sharma ◽  
D Xiao
Keyword(s):  
Large Scale ◽  
Soft Clay ◽  
Excess Pore Pressure ◽  
Laboratory Model ◽  
Clay Layer ◽  
Prefabricated Vertical Drains ◽  
Vertical Drains ◽  
Undisturbed Samples ◽  
Oedometer Tests ◽  
Excess Pore

Installation of prefabricated vertical drains using a mandrel causes disturbance of clay surrounding the drain, resulting in a "smear" zone of reduced permeability. In this paper, an attempt is made to characterize the smear zone using large-scale laboratory model tests. Two tests, simulating the cases of "no smear" and "with smear," were conducted. Excess pore-water pressures were monitored at seven different locations along the radial direction. In addition, undisturbed samples were collected at various locations in the clay layer for conducting oedometer tests. The distribution of excess pore pressure due to drain installation gave a clear indication of the extent of the smear zone. The effect of reconsolidation on the properties of clay was found to be much greater than that of the remoulding of the clay. The extent of the smear zone was also confirmed from the change in permeability of the clay layer in the smear zone obtained from oedometer tests. The radius of the smear zone is about four times that of the mandrel, and the horizontal permeability of the clay layer in the smear zone is approximately 1.3 times smaller than that in the intact zone.Key words: consolidation, permeability, smear zone, soft clay, vertical drains.

scholarly journals Assessing the undrained strength of very soft clays in the SPT

2021 ◽  
Vol 44 (4) ◽  
pp. 1-6
Author(s):  
Francisco Lopes ◽  
Osvangivaldo Oliveira ◽  
Marcio Almeida
Keyword(s):  
Standard Procedure ◽  
Soft Clay ◽  
Test Procedure ◽  
State Theory ◽  
Technical Note ◽  
Construction Site ◽  
Soft Clays ◽  
Design Engineers ◽  
Present Information ◽  
Undrained Strength

The log of a SPT in very soft clay may simply indicate a zero blow-count, or present information on the penetration – under self-weight – of the composition (sampler, rods and hammer) as recommended by some standards. The second type of information is often disregarded by design engineers due to the lack of a standard procedure for measuring these penetrations or because the test is regarded as not sensitive enough to give an indication on the undrained shear strength of soft clays. The penetration under the composition’s selfweight, however, can indicate the magnitude of Su, which, along with other more specific and sensitive tests, can help in assessing the spatial distribution of clay consistency in a large deposit. A proposed test procedure and interpretation had been given in an earlier technical note. This note presents an extended formulation and an evaluation of Su via the SPT at a construction site in Rio de Janeiro, including comparisons with results of piezocone and vane tests. The values of Su obtained with the SPT lie between the profiles given by vane tests, corrected by Plasticity Index, and the Critical State Theory, the latter representing a lower bound to the clay strength.

Behaviour of friction piles in soft sensitive clays

1980 ◽  
Vol 17 (2) ◽  
pp. 203-224 ◽  
Author(s):  
R. Blanchet ◽  
F. Tavenas ◽  
R. Garneau
Keyword(s):  
Precast Concrete ◽  
Soft Clay ◽  
Load Test ◽  
Pile Groups ◽  
Test Program ◽  
Shear Creep ◽  
Soft Clays ◽  
The North ◽  
Effective Stress Analysis

During the construction of heavy structures, such as bridges and overpasses, on soft clays on the north shore of the St. Lawrence Valley, a detailed load test program on friction piles was performed to establish the characteristics of the most suitable type of pile and to study its long-term behaviour. Three types of piles, timber, steel pipe with closed end, and precast concrete Herkules H-420 piles, were tested. Four timber piles driven in a group and submitted to a 712 kN load served to study the long-term settlement of a small group of piles. Three deep settlement gauges were installed in the centre of this group for measuring settlements in clay at various depths.This test program was completed by the instrumentation of two bridge piers in order to verify the behaviour of larger groups of piles.The paper presents the results of the test piles, the long-term behaviour (4 years) of the bridge pier foundations resting on friction piles in soft clay, and the interpretation of the results.This study shows that the pore pressures induced by pile driving are related to the pre-consolidation of the clay and that they are much larger for tapered piles. It is demonstrated that the effective stress analysis method proposed in 1976 by Meyerhof determines adequately the ultimate pile bearing capacity, but that the effect of the timber pile taper doubles the skin friction.The settlement analysis of pile groups shows that settlements are due to the reconsolidation of the clay and shear creep deformations in the clay close to the pile wall.

The Effects of Geosynthetic-Reinforcement on Consolidation Behavior of Soft Clay Embankment under Step Construction

2018 ◽  
Vol 783 ◽  
pp. 46-50
Author(s):  
Yu Cong Gao ◽  
Rong Chen ◽  
Dong Xue Hao ◽  
Myoung Soo Won
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Pore Pressure ◽  
Clay Soil ◽  
Clayey Soil ◽  
Soft Clay ◽  
Excess Pore Pressure ◽  
Calculation Results ◽  
Consolidation Behavior ◽  
Excess Pore

Geosynthetics–reinforced structures are widely used in embankments and walls. This paper presents the simulation of the embankment under load in order to compare the behavior of clay embankment with and without wrapping-facing-geosynthetics-reinforcement using finite element method (FEM) and to analyse the variation of behavior included of displacement and excess pore pressure under the different over-consolidation ratios (OCR). The calculation results show that embankment with higher OCR showing lower displacement compare to embankment with lower OCR. However, OCR isn’t very sensitive to the dissipation of excess pore pressure. Geosynthetics-reinforcements could reduce the displacement of embankment and accelerate dissipation of excess pore pressure after construction and surcharge. Gravel, geosynthetics-reinforcement and clay soil are properly combined, clayey soil is expected to be useful as embankment material.

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