• Journal of the Korean Society for Railway
• /
• v.20 no.2
• /
• pp.257-264
• /
• 2017

The PC (Precast Concrete) construction method is a technique where concrete members that have been produced in a plant are constructed on site. Thus, continuity and secure integration of a structure that can be obtained by connecting rebars at splicing joint for PC members are the main areas of concern for this method. To evaluate the splicing and bonding performance according to application of a splice sleeve for connecting rebar in this research study, the diameter of rebar, development length, grouting strength etc. were set as variables. The performance and stiffness of splicing according to the development length of grout strength were measured and evaluated. In addition, by conducting comparative analysis on each of the variables, the factors that affected the splice sleeve for connecting rebar were discussed. The results confirmed that the strength and stiffness of the splice sleeve for connecting rebar were significantly affected by the development length while the increase in performance according to grout strength was not as significant.

• Journal of the Korean Geosynthetics Society
• /
• v.16 no.2
• /
• pp.121-129
• /
• 2017

There have been a number of water and sewer pipe breakdown reports followed by ground subsidence. Also, the excavating works for construction due to overcrowding of city have been common. Particularly, in urban areas ground becomes unstable because of the lowered lifeline sinkage followed excavation and backfilling. In order to solve the problem, some reinforcement works for ground by rod tamping or grouting have been applied. However, it is hard to predict when the buried utilities in underground will be damaged. Also, there is a limit for the underground exploration and investigation methods. Therefore, in this study, the estimated about the water soluble polymer pouch including poor mixed admixture which is designed to eliminate the dangerous factors. The reinforcement strength of this method was confirmed by verifying three points: meltiness in a certain period, water solubility in the ground water level, and characteristics of the pouch, which can be stored in daily conditions. It is also proved that this method allows to keep the ground from getting weakened in the installation of water and sewer pipe along with back filling materials.

• Journal of the Korean Geosynthetics Society
• /
• v.18 no.1
• /
• pp.67-77
• /
• 2019

The grouting method is utilized to reinforce and waterproof poor grounds, enhance the bearing capacity of structures damaged resulting from settlement due to elevation and vibration or differential settlement, and for cutoff. The purpose of this research is to enhance the compressive strength of grout materials by using aramid fiber and develop a high-strength ground improvement method by using blast furnace slag powder. In this regard, this study has conducted a uniaxial compression test after checking the high charge (higher than 50%) of the ratio of blast furnace slag powder and cement at 100:0, 70:30 and 40:60%, adding the aramid mixture based on 0, 0.5 and 1.0% of the cement and furnace slag powder weight and creating sand gels based on surface oiling rate of 0.7 and 1.2%. For the environmental review evaluation, a heavy metal exudation test and a pH test measurement have been conducted. The experiment results showed that 1% increase of aramid fiber led to 1.3 times greater uniaxial compression intensity. As for the hexavalent chrome, a 30% increase in blast furnace slag powder led to approximately 50% decrease in heavy metal exudation. However, the pH test revealed that a 30% increase in blast furnace slag powder resulted in approximately 0.5 increase in pH. Further research on the pH part is needed in the future.

• The Journal of the Convergence on Culture Technology
• /
• v.8 no.5
• /
• pp.469-475
• /
• 2022

As the recent structure construction is constructed as a large-scale and deep underground excavation in close proximity to the building, the installation of retaining wall and supporters (Struts) has become complicated, and the number of supporters to avoid interference of the structural slab has increased. This construction process becomes a factor that causes an increase in construction joints of a structure, leakage and an increase in wall cracks. In addition, this reduced the durability and workability of the structure and led to an increase in the construction period. This study planned to dismantle the two struts simultaneously as a plan to reduce the construction joints, and corrected the earth pressure by assuming the reaction force value by the initial earth pressure and the measured data as the response ratio. After recalculating the corrected earth pressure through the iterative trial method, it was verified by numerical analysis that simultaneous disassembly of the two struts was possible. As a result of numerical analysis applying the final corrected earth pressure, the measured value for the design reaction force was found to be up to 197%. It was analyzed that this was due to the effect of grouting on the ground and some underestimation of the ground characteristics during design. Based on the result of calculating the corrected earth pressure in consideration of the response ratio performed in this study, it was proved analytically that the improvement of the brace dismantling process is possible. In addition, it was considered that the overall construction period could be shortened by reducing cracks due to leakage and improving workability by reducing construction joints. However, to apply the proposed method of this study, it is judged that sufficient estimations are necessary as there are differences in ground conditions, temporary facilities, and reinforcement methods for each site.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.11 no.2
• /
• pp.131-140
• /
• 2009

It has been repeatedly reported that a drainage system of a drained tunnel is deteriorated. And consequently the water pressure on the lining increases with time. However, little research on the watertight tunnel was found in the literatures. According to field measurements, leakage of the undrained tunnel has increased with time, which is completely opposite to the behavior of the drained tunnel. It is evident that the hydraulic deterioration of the tunnel lining changes the water pressure on the lining and the amount of leakage, thus the design coneept in terms of groundwater is not maintained tightly throughout the life time of the tunnel. The Segment lining is generally constructed as watertight. However, it is frequently reported that the leakage in the segment tunnel increases with time. It is also reported that the leakage is generally concentrated at the joints of the segments. In this study structural and hydraulic interaetion of the segment lining due to the hydraulic deterioration of the segments and the joints is investigated using the numerical modeling method. An electric utility tunnel below groundwater table is considered for the analyses. The effects of hydraulic deterioration of the segment lining are identified in terms of ground loading, water pressure and lining behavior. A remedial grouting measure for leakage is also numerically simulated, and its appropriateness is evaluated.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.11 no.1
• /
• pp.11-22
• /
• 2009

Tunnel excavation with several sections and appropriate auxiliary measures such as face bolt and pre-grouting are widely used in case of weak and less rigid ground for the stability of a tunnel face during excavation. This papers first described the evaluation methods proposed in technical literature to maintain the tunnel face stable, and then studied by FEM analysis whether face reinforcement is need in what degree of ground deformation and strength features for the stability of a tunnel face when excavating by full excavation with sub-bench. Lastly, a three dimensional FEM analysis was performed to study how the tunnel face itself and the ground around the tunnel behave depending on different bolt layouts, length of bolts, number of bolts. There were relative differences in comparison of results on the stability of a tunnel face by a theoretical evaluation methods and FEM analysis, but the same in reinforced effect of face. It was found that the stability of a tunnel face can be obtained with face bolt installed longer than 1.0D (tunnel width), bolt density of about 1 bolt per every $1.5\;m^2$ (layout of grid type), and reinforcement area of $120^{\circ}$ arch area of upper section.

• Journal of the Korean GEO-environmental Society
• /
• v.25 no.6
• /
• pp.5-12
• /
• 2024

Currently, a grouting method that minimizes damage to the reservoir embankment by injecting solidification agent at low pressure is commonly used to ensure waterproofing and safety of the embankment, but the use of solidification agents can cause issues, such as a decrease in durability and a lack of clear method for determining the mixing ratio. In this study, when the base ground and solidification agent were stirred and mixed at various weight mixing ratios, the permeability coefficient and strength of the mixture were confirmed through laboratory tests, and the optimal mixing ratio was suggested through analysis of the test results. The specimen for the laboratory test was produced considering the mixing ratio of the solidification agent. The specimen for the permeability coefficient test was tested by producing one each of cohesionless and cohesive soil for a mixing amount of 1.5 kN/m³ of solidification agent, and the permeability test results confirmed that the water barrier performance was secured below the permeability coefficient value required by various design criteria. A total of 24 specimens for the strength test were produced, 3 for each of 5 mixing amounts for cohesive soil and 3 mixing amounts for cohesionless soil. The strength test results showed that the uniaxial compressive strength tends to increase linearly with increasing curing time for both cohesionless soil and cohesive soil when the mixing amount is less than 2.0 kN/m³. Therefore, the optimal mixing ratio applied to the site is determined to be mixing amount of 1.5 kN/m³ and 2.0 kN/m³. Finally, numerical analysis reflecting test results was conducted on design case for improvement projects for aging reservoirs embankment to verify the water barrier performance and safety improvement effects.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.20 no.3
• /
• pp.543-560
• /
• 2018

With the increased development in downtown underground space facilities that vertically cross under a railway at a shallow depth, the demand for non-open cut method is increasing. However, most construction sites still adopt the pipe roof method, where medium and large diameter steel pipes are pressed in to form a roof, enabling excavation of the inside space. Among the many factors that influence the loosening region and loads that occur while pressing in steel pipes, the size of the pipe has the largest impact, and this factor may correspond to the magnitude of load applied to the underground structure inside the steel pipe roof. The super equilibrium method (SEM) has been developed to minimize ground disturbance and loosening load, and uses small diameter pipes of approximately 114 mm instead of conventional medium and large diameter pipes. This small diameter steel pipe is called an SEM pile. After SEM piles are pressed in and the grouting reinforcement is constructed, a crossing structure is pressed in by using a hydraulic jack without ground subsidence or heaving. The SEM pile, which plays the role of timbering, is a fore-poling pile of approximately 5 m length that prevents ground collapse and supports surface load during excavation of toe part. The loosening region should be adequately calculated to estimate the spacing and construction length of the piles and stiffness of members. In this paper, we conducted a comparative analysis of calculations of loosening load that occurs during the press-in of SEM pile to obtain an optimal design of SEM. We analyzed the influence of factors in main theoretical and empirical formulas applied for calculating loosening regions, and carried out FEM analysis to see an appropriate loosening load to the SEM pile. In order to estimate the soil loosening caused by actual SEM-pile indentation and excavation, a steel pipe indentation reduction model test was conducted. Soil subsidence and soil loosening were investigated quantitatively according to soil/steel pipe (H/D).

• The Journal of Engineering Geology
• /
• v.24 no.2
• /
• pp.261-271
• /
• 2014

An almost permanent anchor (friction type) is resistant to ground deformation due to the friction between the soil and grout at a fixed length from the anchor body. The purpose of this study is to calculate the force of bearing resistance for a bearing anchor in enlarged boreholes. We conducted analytical and numerical analyses, along with laboratory testing, to find the quantities of bearing resistance prior to grouting in EBA (Enlarged Bearing Anchor) construction. The force of bearing resistance from the analytical method was defined as a function of general borehole diameter, expanded borehole diameter, and soil unconfined compressive strength. We also employed the Flac 3D finite difference numerical modeling code to analyze the bearing resistance of the soil conditions. We then created a laboratory experimental model to measure bearing resistance and carried out a pull-out test. The results of these three analyses are presented here, and a regression analysis was performed between bearing resistance and uniaxial compression strength. The laboratory results yield the strongest bearing resistance, with reinforcement 28.5 times greater than the uniaxial compression strength; the analytical and numerical analyses yielded values of 13.3 and 9.9, respectively. This results means that bearing resistance of laboratory test appears to be affected by skin friction resistance. To improve the reliability of these results, a comparison field study is needed to verify which results (analytical, numerical, or laboratory) best represent field observations.

• The Journal of Engineering Geology
• /
• v.26 no.4
• /
• pp.485-495
• /
• 2016

To reinforce and improve the soft ground under a breakwater while using materials efficiently, the replacement ratio and leaving periods of surcharge load are optimized probabilistically. The results of Bayesian updating of the random variables using prior information decrease uncertainty by up to 39.8%, and using prior information with more samples results in a sharp decrease in uncertainty. Replacement ratios of 15%-40% are analyzed using First Order Reliability Method and Monte Carlo simulation to optimize the replacement ratio. The results show that replacement ratios of 20% and 25% are acceptable at the column jet grouting area and the granular compaction pile area, respectively. Life cycle costs are also compared to optimize the replacement ratios within allowable ranges. The results show that a range of 20%-30% is the most economical during the total life cycle. This means that initial construction cost, maintenance cost and failure loss cost are minimized during total life cycle. Probabilistic analysis for leaving periods of shows that three months acceptable. Design optimization with respect to life cycle cost is important to minimize maintenance costs and retain the performance of the structures for the required period. Therefore, more case studies that consider the maintenance costs of soil structures are necessary to establish relevant design codes.