The role of pore water plays in coal under uniaxial cyclic loading

2019 ◽  
Vol 257 ◽  
pp. 105125 ◽  
Author(s):  
Chunlin Zhong ◽  
Zhenyu Zhang ◽  
Pathegama Gamage Ranjith ◽  
Yiyu Lu ◽  
Xavier Choi
Keyword(s):  
Cyclic Loading ◽  
Pore Water

TIME TO THE END OF PRIMARY CONSOLIDATION (EOP) OF SOFT CLAYEY SOILS: CONCERNING THE EFFECT OF ATTERBERG’S LIMIT AND CYCLIC LOADING HISTORY

2019 ◽  
Vol 128 (2B) ◽  
pp. 29-41
Author(s):  
Trần Thanh Nhàn
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Clayey Soils ◽  
Loading History ◽  
Cyclic Shear ◽  
Wide Range ◽  
Primary Consolidation ◽  
Time Required

In order to observe the end of primary consolidation (EOP) of cohesive soils with and without subjecting to cyclic loading, reconstituted specimens of clayey soils at various Atterberg’s limits were used for oedometer test at different loading increments and undrained cyclic shear test followed by drainage with various cyclic shear directions and a wide range of shear strain amplitudes. The pore water pressure and settlement of the soils were measured with time and the time to EOP was then determined by different methods. It is shown from observed results that the time to EOP determined by 3-t method agrees well with the time required for full dissipation of the pore water pressure and being considerably larger than those determined by Log Time method. These observations were then further evaluated in connection with effects of the Atterberg’s limit and the cyclic loading history.

scholarly journals Mechanical response and pore pressure generation in granular filters subjected to uniaxial cyclic loading

2018 ◽  
Vol 55 (12) ◽  
pp. 1756-1768
Author(s):  
Jahanzaib Israr ◽  
Buddhima Indraratna
Keyword(s):  
Cyclic Loading ◽  
Pore Pressure ◽  
Pore Water ◽  
Mechanical Response ◽  
Pore Water Pressure ◽  
Axial Strain ◽  
Water Pressure ◽  
Internal Erosion ◽  
Excess Pore Water Pressure ◽  
Excess Pore

This paper presents results from a series of piping tests carried out on a selected range of granular filters under static and cyclic loading conditions. The mechanical response of filters subjected to cyclic loading could be characterized in three distinct phases; namely, (I) pre-shakedown, (II) post-shakedown, and (III) post-critical (i.e., the occurrence of internal erosion). All the permanent geomechanical changes such, as erosion, permeability variations, and axial strain developments, took place during phases I and III, while the specimen response remained purely elastic during phase II. The post-critical occurrence of erosion incurred significant settlement that may not be tolerable for high-speed railway substructures. The analysis revealed that a cyclic load would induce excess pore-water pressure, which, in corroboration with steady seepage forces and agitation due to dynamic loading, could then cause internal erosion of fines from the specimens. The resulting excess pore pressure is a direct function of the axial strain due to cyclic densification, as well as the loading frequency and reduction in permeability. A model based on strain energy is proposed to quantify the excess pore-water pressure, and subsequently validated using current and existing test results from published studies.

scholarly journals Medial migration in cephalomedullary nail fixation of pertrochanteric hip fractures

2019 ◽  
Vol 8 (7) ◽  
pp. 313-322 ◽  
Author(s):  
G. W. Law ◽  
Y. R. Wong ◽  
A. K-S. Yew ◽  
A. C. T. Choh ◽  
J. S. B. Koh ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Hip Fractures ◽  
Tensile Loading ◽  
Biomechanical Analysis ◽  
Cephalomedullary Nail ◽  
Compression Loading ◽  
Medial Migration ◽  
Group 3 ◽  
Group 2

Objectives The paradoxical migration of the femoral neck element (FNE) superomedially against gravity, with respect to the intramedullary component of the cephalomedullary device, is a poorly understood phenomenon increasingly seen in the management of pertrochanteric hip fractures with the intramedullary nail. The aim of this study was to investigate the role of bidirectional loading on the medial migration phenomenon, based on unique wear patterns seen on scanning electron microscopy of retrieved implants suggestive of FNE toggling. Methods A total of 18 synthetic femurs (Sawbones, Vashon Island, Washington) with comminuted pertrochanteric fractures were divided into three groups (n = 6 per group). Fracture fixation was performed using the Proximal Femoral Nail Antirotation (PFNA) implant (Synthes, Oberdorf, Switzerland; n = 6). Group 1 was subjected to unidirectional compression loading (600 N), with an elastomer (70A durometer) replacing loose fracture fragments to simulate surrounding soft-tissue tensioning. Group 2 was subjected to bidirectional loading (600 N compression loading, 120 N tensile loading), also with the elastomer replacing loose fracture fragments. Group 3 was subjected to bidirectional loading (600 N compression loading, 120 N tensile loading) without the elastomer. All constructs were tested at 2 Hz for 5000 cycles or until cut-out occurred. The medial migration distance (MMD) was recorded at the end of the testing cycles. Results The MMDs for Groups 1, 2, and 3 were 1.02 mm, 6.27 mm, and 5.44 mm respectively, with reliable reproduction of medial migration seen in all groups. Bidirectional loading groups showed significantly higher MMDs compared with the unidirectional loading group (p < 0.01). Conclusion Our results demonstrate significant contributions of bidirectional cyclic loading to the medial migration phenomenon in cephalomedullary nail fixation of pertrochanteric hip fractures. Cite this article: G. W. Law, Y. R. Wong, A. K-S. Yew, A. C. T. Choh, J. S. B. Koh, T. S. Howe. Medial migration in cephalomedullary nail fixation of pertrochanteric hip fractures: A biomechanical analysis using a novel bidirectional cyclic loading model. Bone Joint Res 2019;8:313–322. DOI: 10.1302/2046-3758.87.BJR-2018-0271.R1.

The Role of Agarose Mechanical Response on the Matrix Synthesis of Nucleus Pulposus Cells: A Pilot Study

2009 ◽  
Author(s):  
Arzu Tasci ◽  
Ladina Ettinger ◽  
Stephen Ferguson ◽  
Philippe Büchler
Keyword(s):  
Cyclic Loading ◽  
Mechanical Response ◽  
Low Back ◽  
Limited Capacity ◽  
Nucleus Pulposus Cells ◽  
Matrix Synthesis ◽  
Biosynthetic Activity ◽  
The Matrix ◽  
Ivd Degeneration

Low back pain is the most common spinal disorder and its main cause is intervertebral disc (IVD) degeneration. IVD has a major role of withstanding loads generated in the spine during daily activities. However, it has a limited capacity for self-repair. Since it has an avascular structure, the pathways it uses for regeneration is quite complex and not yet well understood. The mechanical stimulation studies on the cell seeded constructs revealed that cells regulate their biosynthetic activity with cyclic loading [1,2]. The mechanical properties of the scaffold might play an important role in the transmission of mechanical signals to the embedded cells. The objective of this study is to investigate the effect of agarose concentration on the amount of extracellular matrix synthesis in IVD cell seeded constructs under static culture and cyclic loading conditions.

Influence of cycling pore-water pressures and principal stress ratios on drained deformations in clay

1992 ◽  
Vol 29 (2) ◽  
pp. 326-333 ◽  
Author(s):  
K. D. Eigenbrod ◽  
J. Graham ◽  
J.-P. Burak
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Seasonal Changes ◽  
Triaxial Tests ◽  
Strain Rates ◽  
Natural Clay ◽  
Groundwater Levels ◽  
Deviator Stress ◽  
Pore Water Pressures ◽  
Stress Ratios

Seasonal changes in groundwater levels affect the rate of downhill creep movements in slopes. This process has been studied in triaxial tests on undisturbed specimens of a natural clay from Bluefish Lake, 50 km north of Yellowknife, N.W.T. Specimens were first anisotropically consolidated to low stresses that correspond to conditions at shallow depths in creeping slopes. Pore-water pressures (back pressures) in the specimens were then cycled systematically (over periods lasting 4–48 h) with the drainage leads open. Resulting axial and volumetric strains were measured, and shear and lateral strains deduced from them. Strain rates decreased with increasing total times of testing. They increased with increasing values of the ratio Δu/Δuf, with increasing values of deviator stress q, and with decreasing values of [Formula: see text]. Systematically increasing the pore-water pressures in the specimens produced clear estimates of failure at low stresses. Key words : slope, clay, creep, cyclic loading, ground water, triaxial.

Disc Mechanics With Trans-Endplate Partial Nucleotomy are not Fully Restored Following Cyclic Compressive Loading and Unloaded Recovery

2006 ◽  
Vol 128 (6) ◽  
pp. 823-829 ◽  
Author(s):  
Edward J. Vresilovic ◽  
Wade Johannessen ◽  
Dawn M. Elliott
Keyword(s):  
Cyclic Loading ◽  
Stress Relaxation ◽  
Nucleus Pulposus ◽  
Time Constant ◽  
Annulus Fibrosus ◽  
Compressive Loading ◽  
Magnetic Resonance Images ◽  
Mechanical Behaviors ◽  
Short Time

Mechanical function of the intervertebral disc is maintained through the interaction between the hydrated nucleus pulposus, the surrounding annulus fibrosus, and the superior and inferior endplates. In disc degeneration the normal transfer of load between disc substructures is compromised. The objective of this study was to explore the mechanical role of the nucleus pulposus in support of axial compressive loads over time. This was achieved by measuring the elastic slow ramp and viscoelastic stress-relaxation mechanical behaviors of cadaveric sheep motion segments before and after partial nucleotomy through the endplate (keeping the annulus fibrosus intact). Mechanics were evaluated at five conditions: Intact, intact after 10,000cycles of compression, acutely after nucleotomy, following nucleotomy and 10,000cycles of compression, and following unloaded recovery. Radiographs and magnetic resonance images were obtained to examine structure. Only the short time constant of the stress relaxation was altered due to nucleotomy. In contrast, cyclic loading resulted in significant and large changes to both the stiffness and stress relaxation behaviors. Moreover, the nucleotomy had little to no effect on the disc mechanics after cyclic loading, as there were no significant differences comparing mechanics after cyclic loading with or without the nucleotomy. Following unloaded recovery the mechanical changes that had occurred as a consequence of cyclic loading were restored, leaving only a sustained change in the short time constant due to the trans-endplate nucleotomy. Thus the swelling and redistribution of the remaining nucleus pulposus was not able to fully restore mechanical behaviors. This study reveals insights into the role of the nucleus pulposus in disc function, and provides new information toward the potential role of altered nucleus pulpous function in the degenerative cascade.

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