• The Journal of Engineering Geology
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• v.18 no.3
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• pp.339-347
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• 2008

This study was carried out to assess quantitatively the safety of a tunnel by using critical strains in the ground. Critical strain is a new material property of the ground. It can be applied as deformation limits in the ground due to excavation using the measured displacement at the tunnel construction site. To achieve this purpose, the critical strain concept was reviewed and applied to assess the tunnel safety. First of all, the calculated excavation displacements of a circular tunnel by commercial programs were investigated and inputted into a feedback analysis module to calculate strains in the ground. Then the safety of tunnels was evaluated based on the critical strain concept. Subsequently the measured displacements obtained in the field are utilized practically to assess the safety of tunnels using the critical strain concept. Through this study, it was confirmed that the critical strain concept is useful to assess the safety of tunnels quantitatively.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.571-576
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• 2010

In this study, an application method of critical strains concept for tunnels' safety by using the values of measured displacements which are obtained in the field is discussed. The aim is to: (1) study on the engineering meanings of critical strains concept by reviewing the previous researches and application examples with measured displacement values; (2) study on the engineering reasonability of critical strains concept with the view point of a tunnel engineering and a geotechnical engineering; (3) study on the features of ground deformation due to tunneling and reciprocal relation between total displacement and measured displacement; (4) evaluate a tunnel safety by using domestic measurements collected in the field; and (5) re-evaluate the control criteria which were previously used in the field, with the view point of critical strains concept. Consequently, it was confirmed that critical strains in the ground has a reasonability and a possibility of unified or common concept with the view point of a tunnel engineering.

• International conference on construction engineering and project management
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• 2009.05a
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• pp.432-439
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• 2009

This research project was carried out to develop the technique to assess quantitatively and rapidly the stability of a tunnel by using the measured displacement at the tunnel construction site under excavation. To achieve this purpose, a critical strain concept was introduced and applied to an assessment of a tunnel under construction. The new technique calculates numerically the strains of the surrounding ground by using the measured displacements during excavation. A numerical practical system was developed based on the proposed analysis technique in this study. The feasibility of the developed analysis module was verified by incorporating the analysis results obtained by commercial programs into the developed analysis module. To verify the feasibility of the developed analysis module, analysis results of models both elastic and elasto-plastic grounds were investigated for the circular tunnel design. Then the measured displacements obtained in the field are utilized practically to assess the safety of tunnels using critical strain concept. It was verified that stress conditions of in-situ ground and ground material properties were accurately assessed by inputting the calculated displacement obtained by commercial program into this module for the elastic ground. However for the elasto-plastic ground, analysis module can reproduce the initial conditions more closely for the soft rock ground than for the weathered soil ground. The stability of tunnels evaluated with two types of strains, that is, the strains obtained by dividing the crown displacement into a tunnel size and the strains obtained by using the analysis module. From this study, it is confirmed that the critical strain concept can be fully adopted within the engineering judgment in practical tunnel problems and the developed module can be used as a reasonable tool for the assessment of the tunnel stability in the field.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.4
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• pp.337-347
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• 2008

Critical strain is a new material property of the ground. Critical strain concept which was established in tunnel engineering can be applied to deformation limits in the ground due to tunneling by using the measured displacement at the tunnel construction site. In this study, quantitative evaluations for the tunnel stability are conducted by analysing the displacement results obtained at the construction field. Especially, critical stain concept was reviewed from a total displacement point of view using the displacements occurring before excavation. As a results, the variation characteristics of the tunnel stability are presented on the critical strain diagram with or without the preceeding displacements.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.11 s.116
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• pp.1172-1178
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• 2006

Measurement of blade strain with sensors directly installed on the blade has one critical issue, how to send the sensor signal to the ground. Strain-gauges have been dominantly used to directly measure stress of a blade and either a slip ring or a telemetry system has to be used to send measured signal to the ground. However, both systems have many inherent problems and sometimes very severe limitations to be practically used. In this paper, new on-line strain monitoring method using. FBG(Fiber Bragg Grating) sensors and a beam coupler is introduced. Measurement of rotor stress using FBG sensors is nothing new, but unlike other system which installs all necessary instruments on the rotor and use telemetry system to send data to the ground, this system makes use of light's unique characteristic - light travels through space. In this new approach, single optical fiber with many FBG sensors is installed on the blade and all other necessary instruments can be installed at ground thereby giving tremendous advantages over slip ring or telemetry system. A reference sensor is also introduced to compensate the beam coupler's transmission loss change due to rotation. The suggested system's good performance is demonstrated with experiments.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.6
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• pp.637-652
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• 2013

After studying the characteristics of three different evaluation methods of rock load; namely theoretical method, empirical method and numerical method, there were too many limitations for them to be applied on tunnels. Therefore, in this research paper, the method based on numerical analysis is selected to use as this method is the most reasonable one since it considers all parameters that are necessary for rock load estimations, and it also considers the interaction between ground and tunnel support. The critical shear strain concept formulated by Sakurai (1981) was used in order to measure exact rock load values based on numerical analysis. Evaluation on a Level 1 rock load height, which is depicted by the stable region in the graph shows that rock load is not affecting between ground grade 1~3, and it was evaluated that the fourth and fifth grades show less values of rock load height which led to the conclusion of a more economical design of concrete lining.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.6
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• pp.577-587
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• 2021

Room and Pillar method is an underground facility construction method that maximizes the strength of the in-situ ground. In order to secure the safety of the underground space, it is necessary to secure the safety of the room actually used in addition to the safety of pillar of the room and Pillar method. In this study, the evaluation method for the safety of the room and rock pillar in the room and pillar method was studied through numerical analysis. Numerical analysis was performed for a total of 125 cases using ground conditions, pillar width, and room width as parameters, and the results were derived. As for the safety factor of the pillar, it was confirmed that the safety factor increased when the strength of the ground increased, and it was confirmed that the increment in the safety factor decreased when the width of the pillar was widened. The room strain was evaluated by applying the Critical strain. As the width of the pillar became narrower, the Critical strain was higher, and as the width of the room became smaller, the Critical strain was smaller. As a result of the correlation analysis between the safety factor of the pillar and the room strain, it was possible to derive the upper limit of the room strain that can secure the standard safety factor of the pillar according to the width of the pillar. It is judged that the results derived from this study can be used as a guideline to secure the safety of the room when the actual design is performed in consideration of the ground conditions and room width.

• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.6
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• pp.501-517
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• 2011

In general, the tunnel stability during excavation is assessed by comparing measured displacements at roof and sidewall to control criteria. The control criteria were established based on the past experience that considered ground conditions, size of the tunnel cross section, construction method, supports, etc. Therefore, a number of researches on the control criteria using the critical strain have been conducted. However, the critical strain obtained from uniaxial compression tests have drawbacks of not taking damage in rock mass due to increase of stress level and longitudinal arching into account. In this paper, damage-controlled tests simulating stress level and longitudinal arching during tunnel excavation were carried out in addition to uniaxial compression tests to investigate the critical strain characteristics of granite and gneiss that are most abundant rock types in Korean peninsula. Then, the critical strains obtained from damage-controlled tests were compared to those from uniaxial compression tests; the former showed less values than the latter. These results show that the critical strain obtained from uniaxial compression tests has to be reduced a little bit to take stress history during tunnel excavation into account. Moreover, the damage critical strain was proposed to be used for assessment of the brittle failure that usually occurs in deep tunnels.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.4
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• pp.403-410
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• 2009

This paper discusses an application method of critical strains concept for tunnels' safety by using the values of measured displacements which are obtained in the field. The aim of this paper is to: (1) study on the engineering meanings of critical strains concept by reviewing the previous researches and application examples with measured displacement values; (2) study on the engineering reasonability of critical strains concept with the view point of a tunnel engineering and a geotechnical engineering; (3) study on the features of ground deformation due to tunneling and reciprocal relation between total displacement and measured displacement; (4) evaluate a tunnel safety by using domestic measurements collected in the field; and (5) re-evaluate the control criteria which were previously used in the field, with the view point of critical strains concept. Consequently, it was confirmed that critical strains in the ground has a reasonability and a possibility of unified or common concept with the view point of a tunnel engineering.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.9
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• pp.38-45
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• 2003

This research is concerned with the dynamic modeling of the multi-purpose satellite with deployable solar arrays equipped with strain energy hinges(SEH). To this end, we proposed the use of the equivalent torsional spring for the SEH and derived the equations of motion assuming that the satellite and solar arrays are being rigid. We also considered the effect of the support string for the ground experiment model, which has been observed as a critical factor affecting the deployment in the ground experiments. From the numerical simulation results, it is found that solar arrays are deployed in a similar pattern but the hub motions are different because of the support strings. It was concluded that the non-gravity deployment of the solar arrays can be approximately simulated by the ground experimental facility. The effects of the support string are also investigated by varying the length of the string. It was found that the current length of the string is adequate for the ground experiment. Ground experimental results will follow.