• Tunnel and Underground Space
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• v.8 no.2
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• pp.139-145
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• 1998

The reliable estimation of the system parameters and the accurate prediction of the system behavior are important to design underground structures safely and economically. Especially, the elastic modulus and the in-situ stresses are very important parameters in predicting the behavior of the underground structure. Therefore, the back analysis using the field measurement data is developed to determine accurately the elastic modulus and the in-situ stresses of the underground structural system in this study. A back analysis using the combined finite and boundary element is developed. It can consider the far field boundary condition and is efficient in computation. In this study, a back analysis is performed to predict behaviors of underground structures for the real construction site. The comparison between the results of the back analysis with field measurement data and the obtained material properties from the field test shows good agreement for the real construction site.

• Tunnel and Underground Space
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• v.7 no.4
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• pp.323-333
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• 1997

A rock mass is usually classified by the results of geological survey and laboratory tests on rock specimens in order to obtain the adequate properties for the numerical analysis. For these purposes a rock mass strength is estimated based on the empirical criterion proposed by Hoek and Brown and a modulus of deformation is taken with the empirical relations developed by Bieniawski, Serafim and Pereira. In addition, the $K_o$ value which is the ratio of the horizontal stress to the vertical stress is one of the most important input data in the numerical analysis. Its role on a tunnel stability analysis could be verified with the numerical results taken by a finite difference code or a distinct element code. However, a deduced value used to be applied for the $K_o$ value in most of tunnel designs, even though the patterns of stress tensor are variable with regions and depths. Thus in situ stresses were measured by a hydraulic fracturing technique on several tunnel sites and applied directly to the tunnel design for the enhancement of its precision. With those informations on in situ stresses, the safe design should be obtained economically on the road or subway tunnels.

• Geotechnical Engineering
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• v.12 no.3
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• pp.83-98
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• 1996

In this paper, the results of back analysis based on, the inverse method are presented. Using the field measurements obtained from the two different underground storage caverns in Korea during their construction, the deformation modulus and the initial in-situ stresses of the rock masses around the access tunnels are calculated. The finite element analysis is carried out by usinB these results as input parameters. The calculated displacements are compared with the measured ones.

• Tunnel and Underground Space
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• v.1 no.2
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• pp.204-217
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• 1991

In this study, the elastic modulus and the initial stresses of the rock were calculated through back analysis of in-situ displacements measured during excavation of the underground caverns. Results from back analysis were employed to determine the redistributed stresses the displacements and relaxed zone in the rock around the caverns, which supplement the geological characterization results. To verify the reliability of the back analysis program the elastic modulus and the initial stresses were obtained from inputting the displacements calculated by FEM. These were compared with the assumed normalized stresses in FEM and were in a reasonable agreement with an error of more or less than 3%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.4
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• pp.697-703
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• 2006

In this research, model tests for in-situ Top-Base Foundation are carried out in other to investigate the load delivering mechanism and the incremental effect of bearing capacity. According to the result of model tests, the load-settlement curves of both in-situ Top-Base(In-situ TBF) and Precast Top-Base Foundation(PC-TBF) showed similar results in term of the ground movement and effect of bearing capacity. Also, the range of vertical stresses delivered into ground was decreased with Top-Base method regarding other types foundations.

• Tunnel and Underground Space
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• v.1 no.2
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• pp.218-228
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• 1991

Natural stress measurements have been made at two sites at the depth of 280m from surface by means of stress relief overcoring methods using three directonal deformation gage. Attempts have been made to determine the state of natural stress in the rock and provide useful basic data to investigate the stress distribution and the determination of yield zone around powerhouse cavern. The magnitude and the direction of the miximum principal stress obstained from in-situ stress measurements is -96.1kgf/$\textrm{cm}^2$ and N38$^{\circ}$W, N35$^{\circ}$W respectively. Vertical stresses are in approximately agreement with the theoretical value. The ratio of measured to theoretical stresses are 85% at two sites. The ratio of average horizontal to vertical stresses(k=($\sigma$h)ave/$\sigma$v is 1.07.

• Journal of Industrial Technology
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• v.23 no.A
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• pp.69-81
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• 2003

Numerical analysis is important for the design, construction and maintenance of large caverns. The rock mass contains generally discontinuities such as faults, joints and fissures. The mechanical behavior and geometric characteristics of these discontinuities would have a significant impact on the stability of the caverns. In this research the Distinct Element Method(DEM) was used to analyze the structural stability of the large cavern. The Barton-Bandis Joint Model (B-B J.M) was used as a constitutive model for the joint. In addition, two different cases 1) analysis with a support system and 2) analysis with no support system, were analyzed to optimize a support system and to investigate reinforcing effects of a support system. The most significant parameters of in-situ stress, JRC of in-situ natural joints, and spatial distribution characteristics of discontinuities were acquired through field investigation. Displacement (horizontal, joint shear), maximum joint opening, maximum and minimum principal stresses, range of relaxed zone, rockbolt axial forces and shotcrete stresses were calculated at each excavation stage. As a result of analysis the calculated values proved to be under the allowable value Rockbolts also proved to be an efficient support measure to control joint shear displacement which had significant effects on extending the relaxed zone. As a consequence, the structural stability of the cavern was assured with an appropriate support system.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.45-53
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• 1991

The underground structure, which has infinite or semi-infinite boundary conditions, is subjected by body forces and in-situ stresses. It also has stress concentration, which causes material nonlinear behavior, in the vicinity of the excavated surface. In this paper, some methods which can be used to transform domain integrals into boundary integrals are reviewed in order to analyze the effect of the body forces and the in-situ stresses. First, the domain integral of the body force is transformed into boundary integral by using the Galerkin tensor and divergence theorem. Second, it is transformed by writing the domain integral in cylindrical coordinates and using direct integration. The domain integral of the in-situ stress is transformed into boundary integral applying the direct integral method in cylindrical coordinates. The methodology is verified by comparing the results from the boundary element analysis with those of the finite element analysis. Coupling the above boundary elements with finite elements, the nonlinear behavior that occurs locally in the vicinity of the excavation is analyzed and the results are verified. Thus, it is concluded that the domain integrals of body forces and in-situ stresses could be performed effectively by transforming them into the boundary integrals, and the nonlinear behavior can be reasonably analyzed by coupled nonlinear finite element and boundary element method. The result of this research is expected to he used for the analysis of the underground structures in the effective manner.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2002.10a
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• pp.78-83
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• 2002

• Tunnel and Underground Space
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• v.4 no.1
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• pp.17-23
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• 1994

This study consists of two procedures on back analysis and forward analysis which is a basic tool of the former. For a safe and economical construction of underground structures, it is required to identify the structural parameters and analyze the structural behavior as exactly as possible. In this paper, a boundary element method to analyze the behavior of multi-alyered underground structures is studied, in which body forces and initial stresses are considered. That is, each layer is discritized into subregions using infinite fundamental solutions, and terms of body forces and initial stresses are transformed into boundary integral where the applied direct integral method is used. And the system of equations containing body forces and initial stresses are considered. That is, each layer is discritized into subregions using infinite fundamental solutions, and terms of body forces and initial stresses are transformed into boundary integral where the applied direct integral method is used. And the system of equations containing body forces and initial stresses are composed, then the method to solve unknowns is used with applying compatibility and equilibrium conditions between interfaces. As well, the direct search method is applied in back analysis problems. By Powell's method as a technique to search unknown parameters, assuming displacements calculated from boundary element analysis as in-situ displacements, elastic moduli and initial stresses are presumed. As consequences of this study, the results of boundary element analysis of the behavior of multilayered structure considering body forces and initial stresses are agreed with those of finite element analysis. And results of back analysis of elastic moduli and initial stresses in each layers are agreed with exact values with a little difference. Therefore, it is known that this study can be efficiently applied for analyzing the behavior of underground structures including back analysis problems.