Initiation and failure mechanism of base instability of excavations in clay triggered by hydraulic uplift

2015 ◽  
Vol 52 (5) ◽  
pp. 599-608 ◽  
Author(s):  
Y. Hong ◽  
C.W.W. Ng ◽  
L.Z. Wang
Keyword(s):  
Failure Mechanism ◽  
Simple Shear ◽  
Triaxial Compression ◽  
Soft Clay ◽  
Constitutive Models ◽  
Model Parameters ◽  
Hydraulic Pressure ◽  
Percentage Increase ◽  
Basal Resistance ◽  
Dimensionless Groups

Excavations in clay overlying an aquifer may cause catastrophic basal failure due to hydraulic uplift. Although case histories with hydraulic uplift failures are reported worldwide from time to time, the initiation and failure mechanism of the base instability are not well studied and understood. To address these two issues, dimensional analysis is firstly conducted to propose dimensionless groups (DGs) possibly relevant to this subject. Effects of these DGs on the initiation and failure mechanism of base instability are then investigated, by carrying out a series of finite element analyses, in which constitutive models and model parameters have been previously validated against centrifuge test results. It is revealed that the initiation and failure mechanism of base instability due to hydraulic uplift is mainly governed by a ratio of excavation width over the thickness of soft clay inside excavation (B/D). As excavation becomes narrower (i.e., B/D decreases), the hydraulic pressure (Pi) required to initiate uplift movement of clay inside excavation increases significantly (maximum percentage increase = 50%), due to increased effect of downward shear stress acting along soil–wall interface on basal resistance. Based on the parametric study, a calculation chart is developed for estimating Pi of excavations with varied B/D and undrained shear strength of clay. At basal failure caused by hydraulic uplift, the dominant failure mode changes from simple shear in relatively narrow excavations (i.e., B/D < 4) to combined modes of triaxial compression, triaxial extension, and simple shear in relatively wide excavations (i.e., B/D > 4).

Evaluation of the predictive ability of two elastic-viscoplastic constitutive models

2005 ◽  
Vol 42 (6) ◽  
pp. 1675-1694 ◽  
Author(s):  
Sean D Hinchberger ◽  
R Kerry Rowe
Keyword(s):  
Finite Element ◽  
Triaxial Compression ◽  
Soft Clay ◽  
Constitutive Models ◽  
Field Performance ◽  
Predictive Ability ◽  
Coupled Analysis ◽  
Element Analysis ◽  
Finite Element Program ◽  
Case Record

Two elastic-viscoplastic constitutive formulations are evaluated using laboratory and field data from Sackville, New Brunswick and Gloucester, Ontario. Both constitutive models have been implemented in a finite element program and formulated for undrained analysis and fully coupled analysis based on Biot consolidation theory. A laboratory study of the rate-sensitive behaviour of Sackville clay is described. The response of Sackville clay during consolidated anisotropic undrained (CAU) triaxial creep, CAU triaxial compression, and incremental oedometer consolidation is compared with the calculated behaviour. The comparisons demonstrate the general ability of three-parameter elastic-viscoplastic constitutive models to satisfactorily describe the rate-dependent behaviour of Sackville clay. The measured response of Gloucester clay during long-term Rowe cell consolidation tests is compared with the calculated behaviour, and the predictive ability of both constitutive formulations is evaluated using the field performance of the Gloucester case record. In undertaking the present study, the predictive ability of two elastic-viscoplastic constitutive models is examined for two soft clays. A new method of overstress measurement is introduced for elliptical yield surfaces and the importance of adopting a scalable yield surface for the constitutive modeling of soft clay is demonstrated. A model that is suitable for the study of reinforced and unreinforced embankments on soft rate-sensitive clay foundations is identified.Key words: elastic-viscoplastic, finite element analysis, overstress viscoplasticity, case study, rate-sensitive, coupled analysis.

Microscopic Failure Mechanism Analysis of Sandstone Under Triaxial Compression

2018 ◽  
Vol 37 (2) ◽  
pp. 683-690 ◽  
Author(s):  
Guibin Zhang ◽  
Wenquan Zhang ◽  
Hailong Wang ◽  
Chuanyang Jia ◽  
Keming Liu ◽  
...  
Keyword(s):  
Failure Mechanism ◽  
Triaxial Compression ◽  
Mechanism Analysis

scholarly journals Researches on the Constitutive Models of Artificial Frozen Silt in Underground Engineering

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Yugui Yang ◽  
Feng Gao ◽  
Hongmei Cheng ◽  
Yuanming Lai ◽  
Xiangxiang Zhang
Keyword(s):  
Mechanical Characteristic ◽  
Stress Level ◽  
Strain Softening ◽  
Triaxial Compression ◽  
High Stress ◽  
Constitutive Models ◽  
Confining Pressure ◽  
Frozen Soil ◽  
Conventional Triaxial Compression ◽  
Shear Process

The researches on the mechanical characteristic and constitutive models of frozen soil have important meanings in structural design of deep frozen soil wall. In the present study, the triaxial compression and creep tests have been carried out, and the mechanical characteristic of frozen silt is obtained. The experiment results show that the deformation characteristic of frozen silt is related to confining pressure under conventional triaxial compression condition. The frozen silt presents strain softening in shear process; with increase of confining pressure, the strain softening characteristic gradually decreases. The creep curves of frozen silt present the decaying and the stable creep stages under low stress level; however, under high stress level, once the strain increases to a critical value, the creep strain velocity gradually increases and the specimen quickly happens to destroy. To reproduce the deformation behavior, the disturbed state elastoplastic and new creep constitutive models of frozen silt are developed. The comparisons between experimental results and calculated results from constitutive models show that the proposed constitutive models could describe the conventional triaxial compression and creep deformation behaviors of frozen silt.

State of the Art of Constitutive Model of Concrete Materials Based on Damage Mechanics

2011 ◽  
Vol 194-196 ◽  
pp. 848-852
Author(s):  
Duo Xin Zhang ◽  
Qing Yun Wang
Keyword(s):  
Constitutive Model ◽  
Damage Mechanics ◽  
State Of The Art ◽  
Constitutive Models ◽  
Experimental Tests ◽  
Constitutive Relationship ◽  
Model Parameters ◽  
Softening Effect ◽  
Volumetric Expansion ◽  
Concrete Materials

This study centered on the development of constitutive model of the material based on damage mechanics. Volumetric expansion, unilateral behavior and softening effect have been pointed out as three difficulties during setting constitutive model of concrete, the applicable and deficiency of the existed constitutive relationship been reviewed, and the methods used to deal above difficulties were overviewed, Meanwhile, the background of existed model has been summarized and listed systematically. The development of a thermodynamic approach to constitutive model of concrete, with emphasis on the rigorous and consistency both in the formulation of constitutive models and in the identification of model parameters based on experimental tests has been potential direction of the future study, and hoped furnished basement for the elastic to plastic coupled damage mechanics constitutive model of concrete.

An Improved Method of Determining the Disturbed State Concept Model Parameters

2014 ◽  
Vol 919-921 ◽  
pp. 1345-1349
Author(s):  
Wei Lu ◽  
Jia Jun Pan
Keyword(s):  
Triaxial Compression ◽  
Model Parameters ◽  
Improved Method ◽  
Stress Strain ◽  
Material Parameters ◽  
Concept Model ◽  
Strain Relation ◽  
Stress Strain Relation ◽  
Disturbed State Concept

The method of postulate of relatively intact model in the disturbed concept model is reached. Because it is more difficult to assume relatively intact curve by observed experimental data, a method which could automatically calculate the stress strain relation curve of relative intact by triaxial compression test data is raised, so that the determination of material parameters becomes easier, and the improved method is verified by numerical calculation. The results show that this method can effectively determine the stress strain relation curve of relative intact.

Design of a Scaled Model for a High Rise, High Speed Elevator

2001 ◽  
Author(s):  
W. D. Zhu ◽  
L. J. Teppo
Keyword(s):  
High Speed ◽  
Scaling Laws ◽  
Sufficient Accuracy ◽  
Model Parameters ◽  
Minimal Effect ◽  
Model Design ◽  
Scaled Model ◽  
Lateral Dynamics ◽  
High Rise ◽  
Dimensionless Groups

Abstract A novel scaled model is developed to simulate the linear lateral dynamics of a hoist cable with variable length in a high rise, high speed elevator. The dimensionless groups used to formulate the scaling laws are derived through dimensional analysis. The model parameters are selected based on the scaling laws subject to space and hardware constraints. It is demonstrated that while it is almost impossible to obtain a fully scaled model unless the model is extremely tall, a reasonably sized model can be constructed with sufficient accuracy. The scaling laws that are not satisfied can be rendered to have a minimal effect on the scaling between the model and prototype. In conjunction with the model design, an analysis of model tension in a closed cable loop is developed. A new movement profile, which ensures a continuous jerk function during the entire period of motion, is derived. Practical considerations that occur in the design of the model are addressed. The methodology can be used to investigate the vibration of a very long cable in other applications.

Evolution of Anand Parameters With Elevated Temperature Aging for SAC Leadfree Alloys

2020 ◽  
Author(s):  
Pradeep Lall ◽  
Vikas Yadav ◽  
Jeff Suhling ◽  
David Locker
Keyword(s):  
Experimental Data ◽  
High Strain ◽  
Constitutive Models ◽  
Tensile Tests ◽  
Model Parameters ◽  
Strain Rates ◽  
Automotive Electronics ◽  
High Strain Rates ◽  
Operating Temperatures ◽  
Electronic Assemblies

Abstract Electronic equipment in automotive, agricultural and avionics applications may be subjected to temperatures in the range of −55 to 200°C during storage, operation and handling in addition to high strain-rates. Strain rates in owing to vibration and shock may range from 1–100 per sec. Temperature in electronic assemblies depends typically on location, energy dissipation and thermal architecture. Some investigators have indicated that the required operating temperature is between −40 to 200°C for automotive electronics located underhood, on engine, on transmission. Prior data indicates the evolution of mechanical properties under extended exposures to high temperatures. However, the constitutive models are often only available for pristine materials only. In this paper, effect of low operating temperatures (−65°C to 0°C) on Anand-model parameters at high strain rates (10–75 per sec) for aged SAC (SAC105 and SAC-Q) solder alloys has been studied. Stress-Strain curves have been obtained at low operating temperatures using tensile tests. The SAC leadfree solder samples were subjected to isothermal-aged up to 4-months at 50°C before testing. Anand Viscoplastic model has been used to describe the material constitutive behavior. Evolution of Anand Model parameters for SAC solder has been investigated. The computed parameters of the experimental data were used to simulate the tensile test and verified the accuracy of the model. A good correlation was found between experimental data and Anand predicted data.

Numerical Studies of the Effect of Constitutive Model Parameters as Reflecting Polymer Molecular Structure on Extrudate Swell

2002 ◽  
Vol 12 (5) ◽  
pp. 252-259 ◽  
Author(s):  
Nattapong Nithi-Uthai ◽  
Ica Manas-Zloczower
Keyword(s):  
Molecular Weight ◽  
Constitutive Model ◽  
Full Range ◽  
Constitutive Models ◽  
Model Parameters ◽  
Extrudate Swell ◽  
Relaxation Spectra ◽  
Shear Rates ◽  
Swell Ratio ◽  
Numerical Predictions

Abstract PolyFlow, a software package based on the finite element method was employed to simulate the extrudate swell for polybutadiene of various molecular weight (Mw) and molecular weight distribution (MWD). We calculated the relaxation spectra for the different samples and then inserted the spectra into a standard K-BKZ constitutive model used in the numerical simulations. Accurate predictions of MWD confirm the completeness of frequency range in the oscillatory shear experimental data. In turn, the wholeness of relaxation spectra as substantiated by MWD predictions, sustain the level of confidence when using constitutive models based on these spectra. We demonstrate the importance of using the full range of relaxation spectrum rather than a short range around typical shear rates for the accuracy of the numerical predictions. We found extrudate swell ratio (ESR) to be strongly dependent on MWD and stress conditions at the die exit.

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