• Geomechanics and Engineering
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• v.29 no.5
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• pp.567-582
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• 2022

In the present study, a series of physical experiments and numerical simulations were conducted to investigate the effects of mode I and mixed-mode I/II cracks on the fracture modes and stability of roadway tunnel models. The experiments and simulations incorporated different inclination angle flaws under both static and dynamic loads. The quasi-static and dynamic testing were conducted by using an electro-hydraulic servo control device and drop weight impact system (DWIS), and the failure process was simulated by using rock failure process analysis (RFPA) and AUTODYN software. The stress intensity factor was also calculated to evaluate the stability of the flawed roadway tunnel models by using ABAQUS software. According to comparisons between the test and numerical results, it is observed that for flawed roadways with a single radical crack and inclination angle of 45°, the static and dynamic stability are the lowest relative to other angles of fractured rock masses. For mixed-mode I/II cracks in flawed roadway tunnel models under dynamic loading, a wing crack is produced and the pre-existing cracks increase the stress concentration factor in the right part of the specimen, but this factor will not be larger than the maximum principal stress region in the roadway tunnel models. Additionally, damage to the sidewalls will be involved in the flawed roadway tunnel models under static loads.

• Smart Structures and Systems
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• v.15 no.2
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• pp.299-314
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• 2015

Submersed rock-berm structures are frequently used for protection of underwater lifelines such as pipelines and power cables. During the service life, the rock-berm structure can experience several accidental loads such as anchor collision. The consequences can be severe with a certain level of frequency; hence, the structural responses should be carefully understood for implementing a proper structural health monitoring method. However, no study has been made to quantify the structural responses because it is hard to deal with the individual behavior of each rock. Therefore, this study presents a collision analysis of the submersed rock-berm structure using a finite element software package by facilitating the smoothed-particle hydrodynamics (SPH) method. The analysis results were compared with those obtained from the Lagrange method. Moreover, two types of anchors (stock anchor and stockless anchor), three collision points and two different drop velocities (terminal velocity of each anchor and 5 m/s) were selected to investigate the changes in the responses. Finally, the effect of these parameters (analysis method, anchor type, collision point and drop velocity) on the analysis results was studied. Accordingly, the effectiveness of the SPH method is verified, a safe rock-berm height (over 1 m) is proposed, and a gauge point (0.5 m above the seabed) is suggested for a structural health monitoring implementation.

• Tunnel and Underground Space
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• v.20 no.5
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• pp.318-324
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• 2010

Dynamic properties of materials by shock loads such as rock blasting and earthquake are recently attracted in the design of aboveground and underground structures. The advance of measuring devices enables to obtain the whole histories of stress and strain in rock specimen of which the failure is completed in several hundred microseconds. The SHPB has been a popular and promising technique to study the dynamic behavior of rock. And the dynamic compressive, tensile and other test with this experiment system are planned to be Suggested Methods of ISRM. This technical paper is to introduced one study article which focuses the design of 3S (special shaped striker) to produce the half-sine wave to eliminate the problems of the rectangular wave. This article is also describing the advantage of half-sine incident wave and size effect of rock dynamic strength.

• International Journal of Highway Engineering
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• v.17 no.6
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• pp.27-32
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• 2015

PURPOSES : It is difficult to estimate tunnel stability because of lack of timely information during tunnel excavation. Tunnel deformability refers to the capacity of rock to strain under applied loads or unloads during tunnel excavation. This study was conducted to analyze a methods of pre-evaluation of stability during tunnel construction using the critical strain concept, which is applied to the results of tunnel settlement data and unconfined compression strength of intact rock or rock mass at the tunnel construction site. METHODS : Based on the critical strain concept, the pre-evaluation of stability of a tunnel was performed in the Daegu region, at a tunnel through andesite and granite rock. The critical strain concept is a method of predicting tunnel behavior from tunnel crown settlement data using the critical strain chart that is obtained from the relationship between strain and the unconfined compression strength of intact rock in a laboratory. RESULTS : In a pre-evaluation of stability of a tunnel, only actually measured crown settlement data is plotted on the lower position of the critical strain chart, to be compared with the total displacement of crown settlement, including precedent settlement and displacement data from before the settlement measurement. However, both cases show almost the same tunnel behavior. In an evaluation using rock mass instead of intact rock, the data for the rock mass strength is plotted on the lower portion of the critical strain chart, as a way to compare to the data for intact rock strength. CONCLUSIONS : From the results of the pre-evaluation of stability of the tunnel using the critical strain chart, we reaffirmed that it is possible to promptly evaluate the stability of a tunnel under construction. Moreover, this research shows that a safety evaluation using the actual instrumented crown settlement data with the unconfined compression strength of intact rock, rather than with the unconfined compression strength of a rock mass in the tunnel working face, is more conservative.

• Journal of the Korean Geotechnical Society
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• v.25 no.8
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• pp.77-93
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• 2009

The load distribution and deformation of rock socketed drilled shafts subjected to axial loads were evaluated by a load transfer approach. The emphasis was laid on quantifying the end bearing load transfer characteristics of rock socketed drilled shafts based on 3D Finite Difference (FD) analysis performed under varying rock strength and rock mass conditions. From the results of FD analysis, it was found that the ultimate unit toe resistance ($q_{max}$) was influenced by both rock strength and rock mass conditions, while the initial tangent of end bearing load transfer curve ($G_{ini}$) was only dependent on rock strength. End bearing load transfer function of drilled shafts socketed in rock was proposed based on the FD analysis and the field loading tests which were performed on weathered rock in South Korea. Through the comparison with the results of the field loading tests, it is found that the load transfer curve by the present study is in good agreement with the general trend observed by field loading tests, and thus represents a significant improvement in the prediction of load transfer behavior of drilled shaft.

• Journal of the Korean Geotechnical Society
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• v.22 no.12
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• pp.45-55
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• 2006

This paper presents the results of full-scale uplift load tests performed on 30 passive anchors grouted to various lengths at Taean site in Korea. Various rock types were tested, ranging from highly weathered to sound gneiss. Rock anchors were installed over a wide range of rock types and qualities with a fixed anchored depth of $1{\sim}4m$. The majority of installations used SD4O-D51 no high grade steel rebar to induce rock failure prior to rod failure. In many tests, rock failure was reached and the ultimate loads were recorded along with observations of the shape and extent of the failure surface. The test results, the failure mechanisms as well as uplift capacities of rock anchors depend mostly on rock type and quality, embedded fixed length, and the strength of rebar. Based on test results, the main parameters governing the uplift capacity of the rock anchor system were determined.

• Tunnel and Underground Space
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• v.12 no.2
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• pp.107-114
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• 2002

It is the common practice to over design the reinforcement for the secondary tunnel lining due to the lack of rational insight into the ground loosening loads. and due to the conservative application of the empirical design methods. The main loads of the secondary lining are the ground Loosening loads and the ground water pressure, and the ground load is critical in the reinforcement design of the secondary lining in the case of drained tunnel. If the external load is absent around a tunnel, the reasons of the load far secondary tunnel lining are the deterioration of the primary supports such as shotcrete, steel rib, and rockbolts. Accordingly, the analysis method considering the ground-primary supports-secondary lining interaction should be required tar the rational design of the secondary tunnel lining. In this paper, the interaction was conceptually described by the simple mass-spring model and the load transfer from the ground and primary supports to the secondary lining is showed by the ground-primary supports-secondary lining reaction curves fur the theoretical solution of a circular tunnel. And also, the application of this proposed model to numerical analysis is verified in order to check the potential far the tunnel with the complex analysis conditions.

• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.143-154
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• 1999

In this study, the load transfer mechanism of tendon-grout interface of rock anchors has been examined through a series of static pull-out tests conducted on the model rock anchors constructed in the natural and artificial rock masses of granite and concrete, respectively. Several rock masses with horizontal discontinuities have been prepared to study the effects of weak planes on the shear stress distribution in tendon-grout interface. As a result, for the rock anchors constructed in the rock mass without discontinuities, stress concentration occurs on the upper part of the tendon-grout interface. On the contrary, as the frequency or the number of discontinuities increases, the shear stress distribution along the depth tends to be uniform. Also, an experimental equation about shear stress distribution between tendon-grout interface can be made by the regression of test results. The shear stresses computed from the experimental results between the rock surface and the depth of 2~3 times the tendon diameter are smaller than those from theory. Below the depth, the reverse can be observed.

• Geomechanics and Engineering
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• v.34 no.1
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• pp.103-113
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• 2023

This study focused on understanding the relationship between the design of a tunnel boring machine disc cutter ring and its rock-breaking efficiency, as well as the applicable conditions of different cutter ring types. The discrete element method was used to establish a numerical model of the rock-breaking process using disc cutters with different ring types to reveal the development of rock damage cracks and variation in cutter penetration load. The calculation results indicate that a sharp-edged (V-shaped) disc cutter penetrates a rock mass to a given depth with the lowest load, resulting in more intermediate cracks and few lateral cracks, which leads to difficulty in crack combination. Furthermore, the poor wear resistance of a conventional V-shaped cutter can lead to an exponential increase in the penetration load after cutter ring wear. In contrast, constant-cross-section (CCS) disc cutters have the highest quantity of crack extensions after penetrating rock, but also require the highest penetration loads. An arch-edged (U-shaped) disc cutter is more moderate than the aforementioned types with sufficient intermediate and lateral crack propagation after cutting into rock under a suitable penetration load. Additionally, we found that the cutter ring wedge angle and edge width heavily influence cutter rock-breaking efficiency and that a disc cutter with a 16 to 22 mm edge width and 20° to 30° wedge angle exhibits high performance. Compared to V-shaped and U-shaped cutters, the CCS cutter is more suitable for soft or medium-strength rocks, where the penetration load is relatively small. Additionally, two typical case studies were selected to verify that replacing a CCS cutter with a U-shaped or optimized V-shaped disc cutter can increase cutting efficiency when encountering hard rocks.

• Journal of Industrial Technology
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• v.26 no.A
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• pp.109-117
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• 2006

This study is an numerical study of predicting the behavior of anchor embedded in weathered rocks, subjected to uplift loads, about ultimate pullout capacity and the failure mechanism. Factors influencing the behavior of anchors were investigated by reviewing the data about in-situ anchor tests performing numerical modelling with changing the bondage length of anchor, diameter of anchor body and diameter of tenden, and by Correlations between those factors were evaluated to apply them to predict the behavior of anchors. As results of numerical analysis, a linear relationship between bondage length, diameter of anchor body and diameter of tenden with ultimate pullout capacity was obtained on the one hand, from the result of numerical analysis changing the Young's modulus of weathered rock, this parameter was found to inflence to load-displacement and ultimate pullout capacity within the range of 10%, which was mot so significant to affect.