A Numerical Investigation on Time-Dependent Failure of Tunnels Based on the Long-Term Strength Characteristics of Rocks

2014 ◽  
Vol 580-583 ◽  
pp. 1315-1320
Author(s):  
Lian Chong Li ◽  
Meng Xing
Keyword(s):  
Numerical Model ◽  
Model Test ◽  
Failure Modes ◽  
Physical And Mechanical Properties ◽  
Time Dependent ◽  
Rock Mechanic ◽  
Long Term Stability ◽  
Numerical Experimentation ◽  
Accelerated Creep

How to establish the proper rheological model to describe and simulate the relationship between rock mechanic characteristics and time is one of the difficulties in the tunnel long-term stability analysis. In this paper, a numerical model to replicate the time-dependent deformation of rock mass was presented. In the model, the time-dependent deformation is described in terms of degradation of intrinsic physical and mechanical properties of rock and accumulation of mesoscopic damage inside the rock. Based on the model, uniaxial numerical experimentation and tunnel numerical model test are numerically constructed and investigated respectively. The model well reflects the initial creep, steady creep of rock and accelerated creep, which preliminary prove the validity of the proposed model. The results of the tunnel numerical model test show that the displacement curves from the numerical simulation were generally consistent with those from physical model tests. Furthermore, the macroscopic failure modes and local mesoscopic damage evolution of the tunnels were simulated.

Safety Assessment of Long Term Serviced Pressure Vessels: A Case Study of Typical Refining and Chemical Plants in China

2021 ◽  
Author(s):  
Zhiyuan Han ◽  
Guoshan Xie ◽  
Haiyi Jiang ◽  
Xiaowei Li
Keyword(s):  
Pressure Vessel ◽  
Safety Assessment ◽  
Failure Modes ◽  
Pressure Vessels ◽  
Time Dependent ◽  
Chemical Plants ◽  
Safety Specification ◽  
Detailed Assessment

Abstract The safety and risk of the long term serviced pressure vessels, especially which serviced more than 20 years, has become one of the most concerned issues in refining and chemical industry and government safety supervision in China. According to the Chinese pressure vessel safety specification TSG 21-2016 “Supervision Regulation on Safety Technology for Stationary Pressure Vessel”, if necessary, safety assessment should be performed for the pressure vessel which reaches the design service life or exceeds 20 years without a definite design life. However, the safety and risk conditions of most pressure vessels have little changes after long term serviced because their failure modes are time-independent. Thus the key problem is to identify the devices with the time-dependent failure modes and assess them based on the failure modes. This study provided a case study on 16 typical refining and chemical plants including 1870 pressure vessels serviced more than 20 years. The quantitative risk and damage mechanisms were calculated based on API 581, the time-dependent and time-independent failure modes were identified, and the typical pressure vessels were assessed based on API 579. Taking the high pressure hydrogenation plant as an example, this study gave the detailed assessment results and conclusions. The results and suggestions in this study are essential for the safety supervision and extending life of long term serviced pressure vessels in China.

Numerical Investigation on Factors Influencing the Time-Dependent Stability of the Rock Slopes with Weak Structure Planes

2013 ◽  
Vol 353-356 ◽  
pp. 177-182
Author(s):  
Lian Chong Li ◽  
Shao Hua Li
Keyword(s):  
Rock Mass ◽  
Rock Slope ◽  
Failure Time ◽  
Time Dependent ◽  
Catastrophic Failure ◽  
Long Term Stability ◽  
Stability Of Slopes ◽  
Factors Influencing ◽  
Weak Structure

Under the combined effects of various external factors, such as temperature, seepage, alternate wetting and drying and so on, the mechanical properties of rock mass are susceptible to be deteriorated, and its strength characteristics are significantly degraded with time. The mesoscopic damage accumulated inside the rock, contributing the rock slope instability with weak structure planes, generate the time-dependent deformation, and eventually lead to the slope failure. Given the time-dependent deformation of the rock, numerical simulations are conducted to investigate the key factors influencing the long-term stability of slopes. Numerical results show that the catastrophic failure time of slopes is linear to its cohesion, and the bigger cohesion and friction angle increase catastrophic failure time, i.e., the stability of rock slope increase. In addition, the configuration of the intact rock bridge can also influence the time-dependent slope stability. Slope height can significantly affect the slope stability and the maximum horizontal displacement. Differences in rock mass storage environment play an important role in the long-term stability of slopes.

scholarly journals Design Study of Steel Fibre Reinforced Concrete Shaft Lining for Swelling Ground in Toronto, Canada

2021 ◽  
Vol 11 (8) ◽  
pp. 3490
Author(s):  
Min Seong Kim ◽  
Sean Seungwon Lee
Keyword(s):  
Reinforced Concrete ◽  
Steel Fibre ◽  
Time Dependent ◽  
Fibre Reinforced Concrete ◽  
Swelling Behaviour ◽  
Steel Fibre Reinforced Concrete ◽  
Long Term Stability ◽  
Shaft Lining ◽  
Installation Time

Reinforced concrete (RC) is a widely used construction material around the world. RC has many advantages in terms of structural stability. However, the reinforcement of RC requires extensive labour costs. Steel fibre reinforced concrete (SFRC) has been widely studied to replace steel bars in concrete structures over the decades. However, most underground structures, such as tunnel lining, are usually designed using conventional RC for long-term stability due to unexpected geotechnical characteristics, such as directional and depth-dependent varied lateral pressure, earthquakes, groundwater, and time-dependent swelling behaviour. In this paper, an alternative design of shaft structure using SFRC, based on the original RC designed data in the Toronto region, was studied to evaluate the feasibility of SFRC replacing conventional RC. A key geological feature of the site is that the bedrock is comprised of Georgian Bay shale, which exhibits long-term time-dependent deformation (TDD). The capacities of RC and SFRC for the shaft lining were calculated based on the Canadian concrete design codes CSA A23.3 and RILEM TC 162-TDF, to assess the benefit of adding steel fibre, and several analytical solutions were used to calculate the applied load on the lining. A specialised TDD constitutive model in Fast Lagrangian Analysis of Continua (FLAC) 2D was developed to estimate whether the optimum installation time of the shaft lining, based on the geological reports, is appropriate under swelling behaviour, and evaluate the resultant long-term stability. The calculated hoop thrust and bending moment for several loading cases were within the capacity of the SFRC shaft lining. The numerical analysis demonstrated that the proposed lining installation time could be reduced, despite consideration of the long-term TDD behaviour.

scholarly journals A Nanoindentation Approach for Time-Dependent Evaluation of Surface Free Energy in Micro- and Nano-Structured Titanium

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 287
Author(s):  
Serena De Santis ◽  
Edoardo Rossi ◽  
Marco Sebastiani ◽  
Simona Sennato ◽  
Edoardo Bemporad ◽  
...  
Keyword(s):  
Tissue Engineering ◽  
Free Energy ◽  
High Resolution ◽  
Sample Preparation ◽  
Surface Free Energy ◽  
Time Dependent ◽  
Long Term Stability ◽  
Titanium Surfaces ◽  
Non Destructive

Surface free energy (SFE) of titanium surfaces plays a significant role in tissue engineering, as it affects the effectiveness and long-term stability of both active coatings and functionalization and the establishment of strong bonds to the newly growing bone. A new contact–mechanics methodology based on high-resolution non-destructive elastic contacting nanoindentation is applied here to study SFE of micro- and nano-structured titanium surfaces, right after their preparation and as a function of exposure to air. The effectiveness of different surface treatments in enhancing SFE is assessed. A time-dependent decay of SFE within a few hours is observed, with kinetics related to the sample preparation. The fast, non-destructive method adopted allowed for SFE measurements in very hydrophilic conditions, establishing a reliable comparison between surfaces with different properties.

Investigation on time-dependent behaviour and long-term stability of underground water-sealed cavern

2015 ◽  
Vol 19 (sup1) ◽  
pp. s119-s139 ◽  
Author(s):  
Huan-ling Wang ◽  
Wei-ya Xu ◽  
Long Yan ◽  
Qing-xiang Meng ◽  
Ru-bin Wang ◽  
...  
Keyword(s):  
Underground Water ◽  
Time Dependent ◽  
Term Stability ◽  
Long Term Stability ◽  
Time Dependent Behaviour ◽  
Dependent Behaviour

Effect of TiO2 Nanofillers on Mechanical Properties of PVC/ENR/TiO2 Nanocomposites

2014 ◽  
Vol 911 ◽  
pp. 105-109 ◽  
Author(s):  
Nur Azrini Ramlee ◽  
C.T. Ratnam ◽  
N.H. Alias ◽  
T.A. Tengku Mohd
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Uv Light ◽  
Research Work ◽  
Physical And Mechanical Properties ◽  
Shore Hardness ◽  
Long Term Stability ◽  
Insignificant Difference ◽  
Irradiation Dose Rate

Addition of nanoparticles currently in polymer blends has brought tremendous transformation in polymer engineering field. Incorporation of TiO2 nanofillers is believed to enhance the physical and mechanical properties of PVC/ENR blends due to its excellent characteristics including non-toxicity, long term stability and UV light discoloration resistance. The main objective of this research work is to introduce titanium dioxide (TiO2) nanofillers in a range of 0 - 6 phr into polyvinyl chloride (PVC) and epoxidized natural rubber (ENR) blends. Modification on mechanical properties of PVC/ENR blends has successfully been carried via irradiation crosslinking technique. The addition of TiO2 nanofillers has improved the tensile strength and hardness of the nanocomposites. Nevertheless, at higher loading of 6 phr, the results obviously showed an insignificant difference of performances for both tensile strength and shore hardness properties. Upon radiation of 50 kGy, the increase in Ts of the PVC/ENR blends with addition of 4 phr TiO2 was found to be optimum before the Ts value drops with higher exposure to irradiation dose rate. Gel fraction of irradiated PVC/ENR/TiO2 nanocomposites indicates the nanocomposites are crosslinked upon electron beam irradiation. Degree of crosslink was also increased with the addition of 4 phr and 6 phr TiO2.

scholarly journals Long-Term Slope Stability of Abandoned Mine Lake—Numerical Modelling and Risk Assessment

2021 ◽  
Vol 5 (1) ◽  
pp. 88
Author(s):  
Vincent Renaud ◽  
Marwan Al Heib ◽  
Roxane Muller ◽  
Jan Burda
Keyword(s):  
Numerical Model ◽  
Slope Stability ◽  
Large Scale ◽  
Geometric Model ◽  
Open Pit ◽  
Lidar Data ◽  
Open Pit Mines ◽  
Long Term Stability ◽  
Almost All

Almost all post exploitation open pit mines in the world are shaped as a final reservoir intended to be filled with water. In Europe, the creation of water lakes is the most common way of reclaiming post open pit mines. The safety and the security of mine lakes is one of the priorities of mine regions. One of the main hazards identified is the slope stability of lake banks. To develop a reliability methodology for assessing the long-term stability of flooded open pit mines, a large-scale numerical model of the lake was carried out and was applied on Lake Most, which is one of the largest mining lakes in Europe (Czech Republic). The large-scale numerical model was built, based on the site observations, large scale LiDAR data and geotechnical data. The results highlighted the reliability of the methodology to combine the geometric model with the geological model to create a large-scale numerical model, and to identify local and potentially instable zones.

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