Stability of unsupported tunnels in clay

An overall long-term stability of unsupported shallow tunnels in overconsolidated clays which is directly related to the stand-up time is investigated. A new approach that combines finite element methods and the limit equilibrium theory is used to overcome limitations of current design practice. A more realistic initial stress field, unloading due to excavation, and variation of strength and modulus with depth are used. The pore-pressure change is analysed using a finite element model that incorporates an uncoupled consolidation theory. These pore pressures along with the previously obtained stress field are utilized to predict the variation of stability with time for given soil parameters such as strength and coefficient of earth pressure at rest. The results obtained employing a simple mechanism are presented using non-dimensional quantities. These results relate time, stability of the tunnel, and soil strength. The analysis showed that, under certain circumstances, the initial undrained stability may be of no practical value and may only be used as a starting point for more practical long-term stability. This procedure explains the stand-up time phenomenon in tunnels and may also be used in design as a direct tool for its evaluation. Key words : overconsolidated clay, long-term stability, stand-up time, shallow tunnels, finite elements, limit equilibrium.

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The Influence of Operation Pressure on the Long-Term Stability of Salt-Cavern Gas Storage

Advances in Mechanical Engineering ◽

10.1155/2014/537679 ◽

2014 ◽

Vol 6 ◽

pp. 537679 ◽

Cited By ~ 1

Author(s):

Jianjun Liu ◽

Qiang Xiao

Keyword(s):

Internal Pressure ◽

Element Model ◽

Gas Storage ◽

Salt Cavern ◽

Term Stability ◽

Long Term Stability ◽

Rock Creep ◽

Operation Pressure ◽

Salt Cavern Gas Storage

The operation pressure of underground salt-cavern gas storage directly affects its stability. Because of seasonal demand and other emergency reasons, the gas storage working pressures always change from high to low or from low to high cyclic variation. In order to analyze the effect of gas storage pressure changing on its long-term stability, considering the salt rock creep, a 3D finite element model was built using the software Abaqus. Moreover, the deformation and analyzed results of the storage under 0 MPa, 4 MPa, 6 MPa, 8 MPa, 10 MPa, and 12 MPa and also circulating changes pressure operation were given in the 10-year creep. It concluded that how working pressures have effect on long-term stability of salt-cavern gas storage. The research results indicated that the long-term creep performance of underground salt cavern gas storage is affected by internal pressure, the smaller the internal pressure creep is, the more obvious the creep and the greater deformation of gas storage are. The greater the internal pressure is, the smaller the deformation of the gas storage is. The low pressure and excessive high pressure must be avoided during the operation of gas storage. These results have an important significance on determining the reasonable pressure of gas storage operation and ensure the long-term stability of gas storage.

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Towards the Optimal Crown-to-Implant Ratio in Dental Implants

Volume 3: 19th International Conference on Advanced Vehicle Technologies; 14th International Conference on Design Education; 10th Frontiers in Biomedical Devices ◽

10.1115/detc2017-67889 ◽

2017 ◽

Author(s):

T. J. Sego ◽

Yung-Ting Hsu ◽

Tien-Min Gabriel Chu ◽

Andres Tovar

Keyword(s):

Dental Implants ◽

Strain Distribution ◽

Mechanical Stability ◽

Element Model ◽

Equivalent Strain ◽

Skeletal Tissue ◽

Term Stability ◽

Long Term Stability ◽

Clinical Scenarios

Short dental implants are commonly recommended to be implemented with small crown-to-implant (C/I) ratios due to their mechanical stability — decreasing C/I ratios cause less deformation in skeletal tissue under occlusal force. However, the long-term stability of short implants with high C/I ratios remains a controversial issue due to biomechanical complications. This study evaluates the strain distribution and functional implications in an implant-supported crown with various C/I ratios using a high-fidelity, nonlinear finite-element model. Several clinical scenarios are simulated by loading implants with various implant lengths (IL) and crown heights (CH). Strain distribution and maximum equivalent strain are analyzed to evaluate the effects and significance of CH, IL, and the C/I ratio. The study shows underloading for certain implant configurations with high C/I ratio. Increasing IL and decreasing C/I in moderation demonstrates a positive effect in long-term stability.

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