• Geotechnical Engineering
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• v.14 no.6
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• pp.17-32
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• 1998

The Bakun hydroelectric project includes the construction of a hydroelectric power plant with an installed capacity of 2,520MW and a power transmission system connecting to the existing transmission networks in Sarawak and Western Malaysia, The power station will consist of a 210m height concrete faced rockfill dam. During the construction of the dam and the power facilities the Balui river has to be diverted by three diversion tunnels with a length of some 1,400m each. The inner diameter of the tunnels is 12m and the tunnel width is 16m at the portal area. This paper describes the stability analysis and design methods for the open cut rock slopes in the inlet and outlet area of the diversion tunnels. The geotechnical parameters employed in stability calculations were given as a function of four. defined Rock Mass Types (RMT) which were based on RMR system from Bieniawski. The stability calculations procedure of the rock slopes are divided into two stages. In the first stage, it is calculated for the stability of each 'global' slope without any rock support and shotcrete system. In the second stage, it is calculated for each 'local'slope stability with berms and supported with rock bolts and shotcrete. The monitoring instrumentation was performed continuously and some of the design modification was carried out in order to increase the safety of failed area based on the unforeseen geological risks during the open cut excavation.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.1 no.1
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• pp.41-51
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• 2002

As Advanced Traveler Information System(ATIS) is the kernel of the Intelligent Transportation System, it is very important how to manage data from traffic information collectors on a road and have at borough grip of the travel time's change quickly and exactly for doing its part. Link travel time can be obtained by two method. One is measured by area detection systems and the other is estimated by point detection systems. Measured travel time by area detection systems has the limitation for real time information because it Is calculated by the probe which has already passed through the link. Estimated travel time by point detection systems is calculated by the data on the same time of each. section, this is, it use the characteristic of the various cars of each section to estimate travel time. For this reason, it has the difference with real travel time. In this study, Artificial Neural Networks is used for estimating link travel time concerned about the relationship with vehicle detector data and link travel time. The method of estimating link travel time are classified according to the kind of input data and the Absolute value of error between the estimated and the real are distributed within 5$\~$15minute over 90 percent with the result of testing the method using the vehicle detector data and AVI data of Namsan Tunnel $\#$1. It also reduces Time lag of the information offered time and draws late delay generation and dissolution.

• The KIPS Transactions:PartC
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• v.15C no.1
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• pp.37-44
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• 2008

In order to minimize the signaling delay for a resource reservation on the new routing path after the handover of Mobile Node(MN) is completed, it is important to discover the crossover node where the old and new routing paths meet. With the 크로스오버 노드 being found, the signaling messages only need to be transferred on the changed part of the end-to-end path. The crossover node is generally discovered using the end-to-end Session ID(SID) of the established session between MN and Correspondent Node(CN). However, in the Hierarchical Mobile IPv6(HMIPv6) network, if the Mobile Anchor Point (MAP) reserves the resource by aggregate with the Home Agent(HA), the crossover node discovery cannot be performed in the general way since the aggregate SID that has established between the previous MAP and HA is different from the that of the current MAP and HA after MN's handover. In this paper, we propose a mechanism to discover the crossover node within the tunnel between the MAP and the HA in an HMIPv6 network, assuming that the Next Steps in Signaling(NSIS) is deployed for the resource reservation and the aggregate reservation is applied over the MAP and HA tunnel. The local repair required for the change of path is performed upon the crossover node discovery. The simulation results show that the proposed scheme reduces the signaling delay for the reservation and outperforms the existing scheme with respect to throughput during the handover.

• Journal of KIISE:Information Networking
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• v.34 no.1
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• pp.62-72
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• 2007

Mobile Virtual Private Network (MVPN) provides VPN services without geographical restriction to mobile workers using mobile devices. Coexistence of Mobile IP (MIP) protocol for mobility and IPsec-based VPN technology are necessary in order to provide continuous VPN service to mobile users. However, Problems like registration failure or frequent IPsec tunnel re-negotiation occur when IPsec-based VPN Gateway (GW) and MIP are used together. In order to solve these problems, IETF proposes a mechanism which uses external home agent (x-HA) located external to the corporate VPN GW. In addition, based on the IETF proposal, a mechanism that assigns x-HA dynamically in the networks where MN is currently located was also proposed with the purpose to reduce handover latency as well as end-to-end delay. However, this mechanism has problems such as exposure of a session key for dynamic Mobility Security Association (MSA) or a long latency in case of the handover between different networks. In this paper, we propose a new MVPN protocol in order to minimize handover latency, enhance the security in key exchange, and to reduce data losses cause by handover. Through a course of simulation, the performance of proposed protocol is compared with the existing mechanism.

• Tunnel and Underground Space
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• v.30 no.6
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• pp.573-590
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• 2020

This study presents the current status of DECOVALEX-2023 project Task G and our research results so far. Task G, named 'Safety ImplicAtions of Fluid Flow, Shear, Thermal and Reaction Processes within Crystalline Rock Fracture NETworks (SAFENET)' aims at developing a numerical method to simulate the fracture creation and propagation, and the coupled thermohydro-mechanical processes in fracture in crystalline rocks. The first research step of Task G is a benchmark simulation, which is designed for research teams to make their modelling codes more robust and verify whether the models can represent an analytical solution for displacements of a single rock fracture. We reproduced the mechanical behavior of rock and embedded single fracture using a three-dimensional grain-based distinct element model for the simulations. In this method, the structure of the rock was represented by an assembly of rigid tetrahedral grains moving independently of each other, and the mechanical interactions at the grains and their contacts were calculated using 3DEC. The simulation results revealed that the stresses induced along the embedded fracture in the model were relatively low compared to those calculated by stress analysis due to stress redistribution and constrained fracture displacements. The fracture normal and shear displacements of the numerical model showed good agreement with the analytical solutions. The numerical model will be enhanced by continuing collaboration and interaction with other research teams of DECOVALEX-2023 Task G and validated using various experiments in a further study.

• Tunnel and Underground Space
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• v.22 no.2
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• pp.93-105
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• 2012

This paper compares the two- and three-dimensional (2D and 3D) approaches for the numerical determination of the equivalent mechanical properties of fractured rock masses. Both orthogonally-fractured model and discrete fracture networks (DFN) were used for the geometry and 2D models were cut in various directions from 3D model to compare their mechanical properties. Geological data were loosely based on the data available from Sellafield, UK. Analytical method based on compliance tensor transformation was used for investigation in orthogonally fractured rock and numerical experiments were conducted on fractured rock mass with DFN geometry. It is shown that 2D approach always overestimates the elastic modulus of fractured rock masses by a factor of up to around two because fractures are assumed to be perpendicular to the model plane in 2D problems. Poisson ratios tend to have larger values in 2D analysis while there is opposite trend in some sections. The study quantitatively demonstrates the limitation of the 2D approach that uses the simplified model from true 3D geometry.

• Journal of KIISE:Information Networking
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• v.35 no.4
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• pp.301-310
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• 2008

In the existing literature, the handover process reveals numerous problems manifested by high movement detection latency. FMIPv6 can reduce packet loss using a tunnel-based handover mechanism. However, this mechanism may cause performance degradation due to the out-of-sequence packets. Recently. Proxy Mobile IPv6 is proposed for network-based mobility management to reduce overhead in mobile node. PMIPv6 can decrease handover latency which related overhead in MN by using network agent. In this paper, we proposed optimized fast handover scheme called Fast Proxy Mobile IPv6 (EF-PMIPv6). The proposed EF-PMIPv6 can support fast handover using fast IAPP and ND schemes. Further, a mathematical analysis is provided to show the benefits of our scheme. In the analysis, various parameters are used to compare our scheme with the current procedures, while our approach focuses on the reduction of handover latency.

• Tunnel and Underground Space
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• v.12 no.1
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• pp.19-30
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• 2002

Rock joint orientation is one of important geometric attributes that have an influence on the stability of rock structures such as rock slopes and tunnels. Especially, statistical models of the geometric attributes of rock joints can provide a probabilistic approach of rock engineering problems. The result from probabilistic modeling relies on the choice of statistical model. Therefore, it is critical to define a representative statistical model for joint orientation data as well as joint size and intensity and build up a series of modeling procedure including analytical validation. In this paper, we have examined a theoretical methodology for the statistical estimate and hypothesis analysis based upon Fisher distribution and bivariate normal distribution. In addition, we have proposed the algorithms of random number generator which is applied to the simulation of rock joint networks and risk analysis.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.11
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• pp.2920-2939
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• 2012

Enterprises that develop online games have to deploy supporting infrastructures, including hardware and bandwidth resources, in order to provide a good service to users. First Person Shooter games generate high rates of small UDP packets from the client to the server, so the overhead is significant. This work analyzes a method that saves bandwidth, by the addition of a local agent which queues packets, compresses headers and uses a tunnel to send a number of packets within a multiplexed packet. The behavior of the system has been studied, showing that significant bandwidth savings can be achieved. For certain titles, up to 38% of the bandwidth can be saved for IPv4. This percentage increases to 54% for IPv6, as this protocol has a bigger overhead. The cost of these bandwidth savings is the addition of a new delay, which has an upper bound that can be modified. So there is a tradeoff: the greater the added delays, the greater the bandwidth savings. Significant reductions in the amounts of packets per second generated can also be obtained. Tests have been deployed in an emulated scenario matching an access network, showing that if the number of players is big enough, the added delays can be acceptable in terms of user experience.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.6
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• pp.837-847
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• 2019

Korea's long underground roads are being promoted around the metropolitan city center to realize advanced transportation networks. Many disaster prevention facilities are applied to secure fire safety of the closed and long-distance underground roads. As the facility response and fire suppression subjects are unclear, additional human and material damages from fire spread are inevitable. Therefore, in this study, we developed a remote automatic fire extinguishing system that uses the fire extinguishing water inside the fire hydrant to monitor the CCTV in the management room and sprays it directly to the fire site through automatic control. The design application method was studied through the performance improvement that can be put into practical use.