Pore pressures around tunnels in clay

1992 ◽  
Vol 29 (5) ◽  
pp. 819-831 ◽  
Author(s):  
L. Samarasekera ◽  
Z. Eisenstein
Keyword(s):  
Finite Elements ◽  
Pore Pressure ◽  
Earth Pressure ◽  
Dimensionless Time ◽  
Element Analysis ◽  
Initial Stress Field ◽  
Long Term Stability ◽  
Pore Pressures ◽  
Overconsolidated Clays

The pore-pressure generation and dissipation around shallow tunnels excavated in both normally and overconsolidated clays are investigated. The influence of the diameter D, depth of cover to diameter ratio H/D, coefficient of earth pressure at rest K0, and strength and modulus variations with depth on pore-pressure generation are examined. The effects of immediate support on pore pressure are also studied by defining a quantity termed effective stiffness ratio (ESR). A two-dimensional, nonlinear finite element analysis is performed to obtain the pore-pressure generation behav-iour. Strength, modulus, initial stress field, and unloading due to excavation are reflected in this analysis. The pore-pressure dissipation behaviour is investigated by employing an uncoupled consolidation theory using finite elements. A dimensionless time factor is used to present the results of pore-pressure dissipation. These results are presented using nondimensional quantities and in normalized forms. The results are directly applicable to estimation of pore pressures for determining long-term stability of tunnels. Key words : clay, pore pressure, tunnels, uncoupled consolidation, finite elements, stress-strain.

Strain Energy and Behaviour of Overconsolidated Soils

1967 ◽  
Vol 4 (3) ◽  
pp. 326-333 ◽  
Author(s):  
Elmer W Brooker
Keyword(s):  
Mechanical Properties ◽  
Strain Energy ◽  
Large Scale ◽  
Chemical Properties ◽  
Earth Pressure ◽  
Quantitative Evidence ◽  
Physico Chemical ◽  
Overconsolidated Clays ◽  
Overconsolidated Soils

Bjerrum recently presented a strain energy hypothesis which explains qualitatively the behaviour of overconsolidated clays and the phenomena of long-term slope failures in these soils. Quantitative evidence, gathered from a series of large-scale consolidation tests, is presented here which supports the strain energy hypothesis. The coefficient of earth pressure at rest was found to be a function of strain energy at a given value of OCR. It is also shown that the degree of disintegration of overconsolidated soils during a slaking test is related to strain energy. It is inferred from the results that mineralogy and the capacity of a soil to adsorb strain energy are related. The evidence suggests that certain physico-chemical properties may be quantitatively related to mechanical properties through the concept of strain energy.

Effective-Stress Finite Element Analysis of Spudcan Penetration

2012 ◽  
Author(s):  
Jiang Tao Yi ◽  
Fook Hou Lee ◽  
Siang Huat Goh ◽  
Yu Ping Li ◽  
Xi Ying Zhang
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Stress Analysis ◽  
Pore Pressure ◽  
Effective Stress ◽  
Excess Pore Pressure ◽  
Element Analysis ◽  
Pore Pressures ◽  
Excess Pore Pressures ◽  
Excess Pore

The numerical modeling of spudcan penetration involves technical challenges posed by large soil deformation coupled with significant material non-linearity. The Lagrangian approach commonly used for solid stress analysis often does not work well with large deformations, resulting in premature termination of the analysis. Recently, the Arbitrary Langrangian Eulerian (ALE) and the Eulerian methods have been used in spudcan analysis to overcome problems caused by the soil flow and large deformation. However, most of the reported studies are based on total stress analysis and therefore shed no light on the excess pore pressures generated during spudcan installation. As a result, much remains unknown about the long-term behaviour of spudcans in the ground, which is affected by the dissipation of excess pore pressures. This paper reports an effective-stress finite element analysis of spudcan installation in an over-consolidated (OC) soft clay. The Eulerian analysis was conducted using ABAQUS/ Explicit, with the effective stress constitutive models coded via the material subroutine VUMAT. The results demonstrated the feasibility of conducting effective-stress finite element analysis for undrained spudcan penetration in OC clays. The paper discusses the flow mechanism, stable cavity depths and bearing capacity factors when spudcan installation occurs in various OC soils. It was found that the pore pressure build-up concentrates in a bulb-shaped zone surrounding the spudcan. The size of the pore pressure bulb increases with increasing penetration. The maximum excess pore pressure, which is generated near the spudcan tip, is predominantly controlled by the undrained shear strength at the tip level.

scholarly journals Investigation on Creep Behavior and Permeability Evolution Characteristics of Sandstone under Different Pore Pressures

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Hongcai Shi
Keyword(s):  
Pore Pressure ◽  
Creep Behavior ◽  
Mode Analysis ◽  
Permeability Evolution ◽  
Red Sandstone ◽  
Pore Pressures ◽  
Function Relationship ◽  
Fractured Sandstone ◽  
Triaxial Creep Test

To investigate the influence of pore pressure ( σ w ) on the creep behavior and permeability of red sandstone, triaxial creep test with permeability test under different pore pressures was conducted using MTS 815 testing system. The experimental results demonstrate that water has significant weakening effect on the long-term mechanical properties of sandstone, and the long-term strength of sandstone gradually decreases with increase in pore pressures. All permeability-time curves demonstrate a “decreasing-increasing” trend, but two different permeability evolution trends during the steady creep stage are observed, which are related to deviatoric stress. The permeability of both intact ( k 0 ) and fractured sandstone ( k f ) samples increases with the increase in pore pressure, which are in consistent with the failure mode analysis of fractured sandstone samples. However, while the relationship between k 0 and σ w is positive linear, it is a positive exponential function relationship between k f and σ w .

An Investigation on the Effect of Groove Dimensions and Inclination on Cementless Femoral Component in Hip Arthroplasty

2012 ◽  
Author(s):  
B. R. Rawal ◽  
Naresh Bhatnagar
Keyword(s):  
Femoral Stem ◽  
Vital Role ◽  
Surface Shape ◽  
Implant Surface ◽  
Element Analysis ◽  
Term Stability ◽  
Long Term Stability ◽  
Cementless Femoral Stem ◽  
Stress Transmission

The optimal surface for a cementless femoral stem has been the subject of debate for the past several years. Several researchers have stressed the need for research on how an implant surface shape contributes to long-term stability, after implantation, in the field of orthopaedics. The introduction of optimized grooves on an implant surface may enhance long-term stability of an implant. This study thus analyzes the effect of different groove dimensions and angles with a transverse plane on stress transmission by a load at the proximal femur by using finite element analysis. Results suggest that the tendency of stress transmission differs depending on the size, position and angle of the grooves. So, optimized groove size and inclination plays a vital role for long-term stability of cementless femoral stems.

Stability and Change in Emotional Intelligence: Exploring the Transition to Young Adulthood

2005 ◽  
Vol 26 (2) ◽  
pp. 100-106 ◽  
Author(s):  
James D.A. Parker ◽  
Donald H. Saklofske ◽  
Laura M. Wood ◽  
Jennifer M. Eastabrook ◽  
Robyn N. Taylor
Keyword(s):  
High School ◽  
Emotional Intelligence ◽  
Postsecondary Education ◽  
Life Transition ◽  
Full Time ◽  
Major Life ◽  
Long Term Stability ◽  
Time Period ◽  
Transition From High School

Abstract. The concept of emotional intelligence (EI) has attracted growing interest from researchers working in various fields. The present study examined the long-term stability (32 months) of EI-related abilities over the course of a major life transition (the transition from high school to university). During the first week of full-time study, a large group of undergraduates completed the EQ-i:Short; 32 months later a random subset of these students (N = 238), who had started their postsecondary education within 24 months of graduating from high school, completed the measures for a second time. The study found EI scores to be relatively stable over the 32-month time period. EI scores were also found to be significantly higher at Time 2; the overall pattern of change in EI-levels was more than can be attributed to the increased age of the participants.

Multi-Center Calibration of the Second Reference Material for Thromboplastin, Rabbit, Plain, Coded CRM 149R

1991 ◽  
Vol 65 (03) ◽  
pp. 263-267 ◽  
Author(s):  
A M H P van den Besselaar ◽  
R M Bertina
Keyword(s):  
Reference Material ◽  
Standard Error ◽  
Standard Errors ◽  
Sensitivity Index ◽  
Long Term Stability ◽  
Significant Bias ◽  
The Mean ◽  
The Relationship ◽  
International Sensitivity Index

SummaryIn a collaborative trial of eleven laboratories which was performed mainly within the framework of the European Community Bureau of Reference (BCR), a second reference material for thromboplastin, rabbit, plain, was calibrated against its predecessor RBT/79. This second reference material (coded CRM 149R) has a mean International Sensitivity Index (ISI) of 1.343 with a standard error of the mean of 0.035. The standard error of the ISI was determined by combination of the standard errors of the ISI of RBT/79 and the slope of the calibration line in this trial.The BCR reference material for thromboplastin, human, plain (coded BCT/099) was also included in this trial for assessment of the long-term stability of the relationship with RBT/79. The results indicated that this relationship has not changed over a period of 8 years. The interlaboratory variation of the slope of the relationship between CRM 149R and RBT/79 was significantly lower than the variation of the slope of the relationship between BCT/099 and RBT/79. In addition to the manual technique, a semi-automatic coagulometer according to Schnitger & Gross was used to determine prothrombin times with CRM 149R. The mean ISI of CRM 149R was not affected by replacement of the manual technique by this particular coagulometer.Two lyophilized plasmas were included in this trial. The mean slope of relationship between RBT/79 and CRM 149R based on the two lyophilized plasmas was the same as the corresponding slope based on fresh plasmas. Tlowever, the mean slope of relationship between RBT/79 and BCT/099 based on the two lyophilized plasmas was 4.9% higher than the mean slope based on fresh plasmas. Thus, the use of these lyophilized plasmas induced a small but significant bias in the slope of relationship between these thromboplastins of different species.

The Stability of the WHO Reference Thromboplastin NIBS & C 67/40

1979 ◽  
Vol 42 (04) ◽  
pp. 1135-1140 ◽  
Author(s):  
G I C Ingram
Keyword(s):  
Human Brain ◽  
Collaborative Study ◽  
Calibration Constant ◽  
Long Term Stability ◽  
Freeze Dried ◽  
Show Evidence ◽  
Human Material ◽  
Reference Preparation ◽  
The Stability

SummaryThe International Reference Preparation of human brain thromboplastin coded 67/40 has been thought to show evidence of instability. The evidence is discussed and is not thought to be strong; but it is suggested that it would be wise to replace 67/40 with a new preparation of human brain, both for this reason and because 67/40 is in a form (like Thrombotest) in which few workers seem to use human brain. A �plain� preparation would be more appropriate; and a freeze-dried sample of BCT is recommended as the successor preparation. The opportunity should be taken also to replace the corresponding ox and rabbit preparations. In the collaborative study which would be required it would then be desirable to test in parallel the three old and the three new preparations. The relative sensitivities of the old preparations could be compared with those found in earlier studies to obtain further evidence on the stability of 67/40; if stability were confirmed, the new preparations should be calibrated against it, but if not, the new human material should receive a calibration constant of 1.0 and the new ox and rabbit materials calibrated against that.The types of evidence available for monitoring the long-term stability of a thromboplastin are discussed.

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