• Journal of the Korea Institute of Building Construction
• /
• v.14 no.2
• /
• pp.118-126
• /
• 2014

The establishment of the technology for evaluating friction resistance and pipe pressure and the relation of the fluid characteristics and pumpability of concrete is essential for concrete pumping performance for the rapid construction of super-tall buildings. In this study, a quantitative evaluation of concrete fluid characteristics and surface friction resistance was performed, applying different concrete mix proportions and pumping conditions. To achieve this, we developed a temporary horizontal pumping evaluation system to measure pipe pressure and surface friction characteristics, and performed an experiment to investigate the relations between concrete rheology characteristics and friction resistance in pipe. The experiment found that in terms of the rheology characteristics, plastic viscosity was reduced remarkably after pumping. As well, high regression between the surface friction and pressure gradient was confirmed. This means that it is possible to evaluate the friction resistance between concrete and pipe by means of a pumping system that includes a frictional resistance testing pipe. In addition, high regression between the plastic viscosity of concrete after pumping and friction resistance coefficient was confirmed. Finally, it is considered that pumping pressure can be predicted using the friction resistance coefficient derived in this study, and it has high regression.

• Journal of the Korea Institute of Building Construction
• /
• v.10 no.2
• /
• pp.97-104
• /
• 2010

This study evaluated the energy efficiency of a windows system using built-in blinds, with regard to their insulation performance and their blocking of solar radiation. The study took advantage of the "Physibel Voltra" program as a physical simulation of heat transfer. To simulate the "Physibel Voltra" program, I practiced a mock-up test to determine heating quality and translation condition. I analyzed the propensity to annual energy consumption, the annual quantity of heat transfer, and the annual cooling and heating cost through a computer simulation for one general household in an apartment building. In the test, it was found that compared to a general windows system, a windows system with built-in blinds reduced the annual heat transfer by 10% in cooling states and by 11% in heating states when the blind was up. When the blind was down, the windows system with built-in blinds reduced the annual heat transfer by 25% in cooling states and 30% in heating states. When a windows system with built-in blinds is compared with a general windows system, the quantity of cooling and heating loads is reduced by 283.3kw in cooling states and 76.3kw in heating states. This leads to a reduction in the required cooling and heating energy of 359.6kw per house. It is thus judged that the use of a windows system with built-in blinds is advantageous in terms of reducing greenhouse gas emissions, because the annual TOE (tons of oil equivalent) per house is reduced by 0.078TOE, while $tCO_2$ is reduced by $0.16tCO_2$. In addition, compared with a general windows system, the cost of cooling and heating loads in the system reduces the annual cooling cost by 100,000won, and the annual heating cost by 50,000won. Ultimately, this means that cooling and heating loads are cut by 150,000won per year.

• Tunnel and Underground Space
• /
• v.20 no.5
• /
• pp.352-359
• /
• 2010

Stability of twin tunnels depends on the pillar width and the ground condition. In this study, large scale model tests were conducted for investigating the influence of the pillar width of twin tunnels on their behavior in the regular horizontal jointed rock mass. Jointed rocks was composed of concrete blocks. Pillar width of twin tunnels varied in 0.29D, 0.59D, 0.88D and 1.18D, where D is the tunnel width. During the test, pillar stress, lining stress, tunnel distortion, and ground displacement were measured. Lateral earth pressure coefficient was kept in a constant value 1.0. As a result, it was found that the pillar stress and the displacement of the ground and tunnel were increased by decreasing pillar width. The maximum displacement rate was measured just after the upper excavation in each construction sequence. And the maximum influence position was the right shoulder of the preceeding tunnel at the pillar side. It was also found that for the stability assessment the inner displacement was more critical than the crown displacement. The influence zone was formed at the pillar width 0.59D~0.88D that was smaller than 0.8D~2.0D, which was proposed by experience for a good ground condition. And it would be concluded that horizontal joints could also influence on the stability of the twin tunnels.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.24 no.6
• /
• pp.553-581
• /
• 2022

Shortly after tunnel boring machine (TBM) was introduced in the tunneling industry, the use of TBM has surprisingly increased worldwide due to its performance together with the benefit of being safely and environmentally friendly. One of the main cost items in the TBM tunneling in rock and soil is changing damaged or worn cutters. It is because that the cutter change is a time-consuming and costly activity that can significantly reduce the TBM utilization and advance rate and has a major effect on the total time and cost of TBM tunneling projects. Therefore, the importance of accurately evaluating the cutter life can never be overemphasized. However, the prediction of cutter wear in soil, rock including mixed face is very complex and not yet fully clarified, subsequently keeping engineers busy around the world. Various prediction models for cutter wear have been developed and introduced, but these models almost usually produce highly variable results due to inherent uncertainties in the models. In this study, a case study of design and construction of disc cutter change is introduced and analyzed, rather than proposing a prediction model of cutter wear. As the disc cutter is strongly affected by the geological condition, TBM machine characteristic and operation, authors believe it is very hard to suggest a generalized prediction model given the uncertainties and limitations therefore it would be more practical to analyze a real case and provide a detailed discussion of the difference between prediction and result for the cutter change. By doing so, up-to-date idea about planning and execution of cutter change in practice can be promoted.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.5
• /
• pp.32-39
• /
• 2021

Recently, necessities of steel form for reinforced concrete beam and girder have been emphasized in building structures for the reduction of the construction period and the labor cost. SY Beam was developed for the these purposes and is roll-formed using thin steel plate. On this research, we tried to evaluate and verify the performance and behavior of SY Beam under construction loading stage as like pouring in situ concrete. For the standard shape of SY beam, structural modelling with various steel thicknesses has carried out using MIDAS GEN program. From results of modelling, the width and height of SY Beam were determined 600mm and 400mm respectively. For 3 SY Beams, the loading experiment was performed to measure vertical and horizontal displacement under stacking sand, concrete block, and bundle of rebar. As a result, the vertical deflection showed a tendency to decrease as the thickness increased. In the horizontal displacement, the trend according to the thickness was not clearly observed. From the evaluation on the loading experiment, it is considered that the SY Beam can secure both workability and structural safety. In particular, the SY Beam(1.2mm) hardly generates horizontal displacement, so it has excellent load-bearing capacity. So, we judged that the SY Beam with 1.2mm steel plate has excellent performance and consider to be immediately commercially available.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.11
• /
• pp.750-757
• /
• 2018

The mechanically stabilized earth wall abutment is an earth structure using a mechanically stabilized earth wall and it uses in-extensional steel reinforcements having excellent friction performance. In order to analyze the pullout behavior of in-extensional steel reinforcements usually applied on the mechanically stabilized earth wall abutment, effects of stiffness and particle-size distributions of backfills and also horizontal spacings were considered in this study. As a result of parametric analyses, the highest pulling force acted on the uppermost reinforcement, and the stiffness and the particle-size distributions of the backfill significantly affected the pulling resistance of the reinforced soils. The internal friction angle of backfills should be at least 25 degrees, the coefficient uniformity factor should be at least 4, and the horizontal spacing of the uppermost steel reinforcement should be less than 25cm. Therefore, in order to secure the pullout resistance of the reinforced soil, it is necessary a properly spacing of reinforcement and more strict quality control for the backfill.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.21 no.3
• /
• pp.347-362
• /
• 2019

Underground excavation using TBM machines has been increasing to reduce complaints caused by noise, vibration, and traffic congestion resulted from the urban underground construction in Korea. However, TBM excavation design and construction still need improvement because those are based on standards of the technologically advanced countries (e.g., Japan, Germany) that do not consider geological environment in Korea at all. Above all, although TBM performance is a main factor determining the TBM machine type, duration and cost of the construction, it is estimated by only using UCS (uniaxial compressive strength) as the ground parameters and it often does not match the actual field conditions. This study was carried out as part of efforts to predict penetration rate suitable for Korean ground conditions. The effective parameters were defined through the correlation analysis between the penetration rate and the geotechnical parameters or TBM performance parameters. The effective parameters were then used as variables of the multiple regression analysis to derive a regression model for predicting TBM penetration rate. As a result, the regression model was estimated by UCS and joint spacing and showed a good agreement with field penetration rate measured during TBM excavation. However, when this model was applied to another site in Korea, the prediction accuracy was slightly reduced. Therefore, in order to overcome the limitation of the regression model, further studies are required to obtain a generalized prediction model which is not restricted by the field conditions.

• Journal of the Korea Institute of Building Construction
• /
• v.19 no.3
• /
• pp.201-207
• /
• 2019

In this study, the direct tensile properties of amorphous metallic fiber-reinforced cement based composites according to the strain was evaluated. A thin plate-shape amorphous metallic fiber with 15mm and 30mm in length was used. And fiber-reinforced cement based composites were prepared with contents of 1.0, 1.5, 2.0%. The direct tensile test was conducted under the conditions of $10^{-6}/s(static)$ and $10^1/s(dynamic)$ strain rate. As a results, amorphous metallic fiber with a length of 15mm was observed in pull-out behavior from the cement matrix because of the short fiber length and large portion of mixed fiber. On the other hand, amorphous metallic fiber with a length of 30mm were not pulled out from matrix because the bonding force between the fiber and matrix was large due to rough surface and large specific surface area. However, fracture occurred because thin plate shape fibers were vulnerable to shear force. Tensile strength, strain capacity and toughness were improved due to the increase in the fiber length. The dynamic increase factor of L15 was larger that of L30 because the bonding performance of the fiber-matrix interface is significantly affected by the strain rate.

• Journal of the Society of Disaster Information
• /
• v.17 no.3
• /
• pp.454-464
• /
• 2021

Purpose: There is a need to construct an evacuation passageway for the 2-Arch tunnel, which has been constructed and is in operation. Therefore, it aims to analyze tunnel and center wall behaviour and stability due to excavation of the center wall. Method: We describe the theoretical background of 2-Arch tunnel and evacuation passageway, and focused on analyzing the behaviour of tunnel and wall using 3-dimensional finite element analysis. Parametric analysis according to rock rating was performed with various ground conditions, and the displacement and stress of the center wall were intensively analyzed. Result: With the center wall excavation, the largest amount of settlement was shown in the center of the opening, and the stress was greatest during the first excavation. In addition, it was shown that stress concentration occurred at the top of both openings, and stability reviews considering the concept of allowable stress showed that it exceeded the allowable stress. Conclusion: Although the displacement of the tunnel has secured stability within the allowable standard, the generated stress is found to exceed the allowable standard, so it is necessary to prevent sudden stress release by applying appropriate reinforcement methods during construction.

• Journal of the Korean Geosynthetics Society
• /
• v.20 no.1
• /
• pp.35-44
• /
• 2021

This research studies the stabilization method for improved soil sloped through the on-site application of Paper Flyash ground stabilizers. The target strength required for improved soil is 500 kPa, and the compressive strength for the slope surface needs to be less than 1,000 kPa after the improvement in order to plant vegetation. To meet this condition, we mixed soil from the site and the ground stabilization material, which is the main material for surface improvement material, performed mixing design and conducted various tests including strength test, permeability test and plantation test. After analyzing the results of the compression test on improved soil slope, we proposed soil constants for the improved soil. In order to evaluate the applicability of the improved soil on the slope, the site construction was carried out on the collapsed slope and the reinforcement evaluation of the surface of the improvement soil was conducted. The stability was not secured before the reinforcement, but the test shows after the reinforcement with improved soil, the safety rate is secured up to 48 hours during the raining period. In addition, the compressive strength of the improved soil at the site was secured at more than 200 kPa adhesion as planned, and the soil hardness test result was also found to be within the specified value of 18-23 mm, which increased the resistance to rainfall and ability to grow plant on the surface for improved soil.