• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.1
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• pp.3-12
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• 2006

The purpose of this study is to describe the Non-Destructive Testing(NDT) of the rockbolt and investigate the applicability of the NDT methods to estimate the integrity of the rockbolt. To examine the rockbolt integrity including rockbolt itself and grouting material, two methods are adopted: numerical and experimental methods. In the numerical method, the numerical code DISPERSE is used to analyze the dispersion of the rockbolt. The dispersion curve shows the effects of the thickness and stiffness of grouted materials on the embedded rockbolt. Therefore, the optimal frequency for the integrity test of the rockbolt is obtained: 20~120kHz in L(1,0) mode. In the experimental methods, destructive and non-destructive tests are carried out in a laboratory. In the non-destructive test, the low frequency mode generated by an impact and t he high frequency mode generated by an ultrasonic transducer seem to characterize the rockbolt condition readily. The experimental results show that the guided waves attenuate more significantly when the stiffness of the grouted material increases and/or the zone of the defect increases. Meanwhile, the ultimate capacity of rockbolt was evaluated through the pull-out tests and is compared to the NDT results. This study demonstrates that the NDT is a valuable tool for the rockbolt integrity evaluation.

• Journal of the Korean GEO-environmental Society
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• v.17 no.12
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• pp.45-54
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• 2016

In this study, the construction method of new underground continuos impervious wall that the bentonite slurry keeps the stability of excavated trench and the mixture of cement and bentonite plays a role as a constituent of impervious wall in the trench. The merit of homogeneity of the method so called as a cement-bentonite slurry wall enables to accurately make an estimation of hydraulic conductivity of the walls compared with that by other general grouting methods and to verify their waterproof efficiency without difficulty at the design stage. The use of cement-bentonite slurry walls for the containment of groundwater flow has also proven a cost-effective impervious wall technology by employing the simple combination of construction equipments and easy and fast construction procedures. The engineering characteristics of cement-bentonite impervious wall obtained by carrying out the laboratory experiments under various conditions. This study reveals the effect of variation of constituent materials and their mixing methods (Water-Cement-Bentonite) on the engineering characteristics of a composition. Also, this study makes some recommendations on the optimum mixing ratio and mixing sequence for the best quality at the site. That is the most important factors to estimate the construction cost and design of the technique. The comparison is lastly made to evaluate the effect of ordinary Portland and blast furnace slag cement as a bonding material on the behavior of impervious walls.

• 한국지구과학회:학술대회논문집
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• 2010.04a
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• pp.98-98
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• 2010

그라우팅은 지반의 공학적인 강도증가를 통한 지지력 향상 및 암반의 투수성 저감을 통해 지하수 유동을 억제하기 위하여 대규모 토목공사 현장의 균열암반 및 댐 또는 제방 등의 지역에서 많이 시행되고 있다. 본 연구는 균열암반지역에서 그라우팅 효과 확인을 위하여 보통 포틀랜드 시멘트(OPC)와 마이크로 시멘트(MC)를 사용하여 그라우팅을 수행하였으며, 그라우팅 전후에 물리검층(시추공영상촬영, 초음파 텔레뷰어검층)을 이용하여 그라우팅 효과 정도를 파악하였다. 연구지역은 경상북도 영주시 평은면 지역으로, 지질은 선캠브리아기 안구상편마암에 시대미상의 흑운모 화강암이 관입을 하였고, 이를 제4기의 충적층이 부정합으로 피복되어 있다. 그라우팅은 일반구간과 단층대구간으로 구분하여 실시하였으며, 두 구간의 이격거리는 서로의 간섭을 피하기 위해 약 40m 간격으로 선정하였다. 주입재(OPC, MC)는 5개의 주입공에서 triangle 방향으로 주입하였으며, 주입정도를 확인하기 위하여 각 구간에 2공씩 확인시추를 하였다. 두 개의 site중 일반구간의 보통 포틀랜드시멘트 주입결과 평균주입량은 48.2kg/공이며 주입 1m당으로 환산하면 Lugeon값 10미만의 지층에서는 1.62kg/m이며, 마이크로시멘트의 평균주입량은 49.6kg/공이며 주입 1m당으로 환산하면 Lugeon값 10미만의 지층에서는 3.86kg/m로 나타났다. 단층대 구간에서는 보통 포틀랜드시멘트의 평균주입량이 40.0kg/공이며, 1m당으로 환산하면 Lugeon값 10미만의 지층에서는 2.75kg/m이며, 마이크로 시멘트는 평균주입량이 56.5kg/공, 주입 1m당으로 환산하면 Lugeon값 10미만의 지층에서는 3.15kg/m로 나타났다. 마이크로시멘트의 주입압은 보통 포틀랜드시멘트에 비해 상대적으로 낮았으며, 그라우팅 개선효과 역시 상대적으로 양호한 것으로 나타났다. 그라우팅 효과확인을 위한 물리검층의 초음파텔레뷰어 해석결과 상대암반강도는 주입전 $250{\sim}750\;kgf/cm^2$, 주입후는 $400{\sim}800\;kgf/cm^2$으로 그라우팅에 의한 암반강도의 상승을 확인할 수 있었고, 시추공영상촬영 분석에서는 시추코어만으로 얻기 힘든 시멘트 충진구간을 직접 확인할 수 있었다. 초음파텔레뷰어의 경우 파쇄대의 분포 및 암반강도 측정을 통한 그라우팅 파악은 가능하였으나 파쇄대 충진물을 확인할 수가 없는 단점이 있었고 이를 시추공영상촬영을 통해 보완할 수 있었다. 다만 물리검층의 경우 그라우팅에 의한 공의 손실로 동일공에 의한 반복 조사가 아닌 경우가 대부분이어서 그라우팅 효과에 대한 정확한 비교가 어려웠으며 추후 이를 보완하기 위한 계속적인 연구가 필요할 것으로 사료된다.

• Resources Recycling
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• v.26 no.2
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• pp.80-88
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• 2017

Globally, there has been a lot of research related to recycling coal ash from power plant stations. This research is happening because there is a considerable shortage of sites for reclamation of increased coal ash every year. In addition, a variety of environmental pollutants have appeared because of mining activity. Abandoned coal mine, pits, and mine tailing piles caused pollutants to come to the surface resulting in serious damage for humans and the environment. Therefore in this study, we investigated whether or not coal ashes have the ability to prevent several environmental problems by mining in Korea and a manageable form recycling coal ashes. In overseas countries, there is a sufficient field of applicable cases where coal ash is used for neutralizing AMD (Acid Mine Drainage), covering of the waste materials, grouting, and soil amendments. However in Korea, since the coal ash is classified as a 'waste', there is an insufficient field applicable cases so far. Therefore it is necessary to establish a specific standard and management system for the utilization of coal ash based on the relevant precedent cases applied abroad in order to prevent environmental pollution caused by mining activity in Korea.

• Journal of the Korean GEO-environmental Society
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• v.22 no.2
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• pp.5-13
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• 2021

In this study, as the production of high-strength steel pipes due to the development of steel materials, the stability and applicability of the soil nailing method using high-strength steel pipes were evaluated. Rebars used as reinforcement in the soil nailing method are the same in order to determine the behavioral characteristics and the effect of increasing the reinforcement when replacing it with a high-strength steel pipe of a diameter, a field test were conducted to confirm the stability. As a result of the tensile test, the measured strain is smaller than the strain in the theoretical equation, so it can be seen that the behavior is similar to that of the soil nailing method using rebars. As a result of the displacement measurement, the displacement of the high-strength steel pipe is larger than that of the rebars is considered to be the effect of the internal grouting effect of the steel pipe and the decrease in the cross-sectional area. In the case of using high-strength steel pipes for the soil nailing method, it is judged that the field applicability is good by improving stability and workability through member performance and weight reduction.

• Journal of the Korean Geosynthetics Society
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• v.20 no.1
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• pp.9-19
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• 2021

This paper deals with the reinforcement performance of acrylate for reinforcing the settled railway roadbed. Concrete tracks have the advantage of reducing track maintenance costs and high resistance to track destruction. However, roadbed settlement is occurring in some construction sections, and the safety of railways is a serious concern because of difficulties in maintenance. Currently, maintenance through the track restoration method is being carried out in Korea as a way of roadbed settlement in concrete tracks, but continuous re-settlement can occur because the roadbed itself cannot be reinforced, and there are very few cases of reinforcement of railway roadbeds and field application. So the development of reinforcement materials and construction methods to reinforce railway roadbeds is required. Therefore, in this paper, acrylate was selected as reinforcement material for railway roadbed, and the reinforcement performance of acrylate was analyzed through experiment. As a result, it was analyzed that the acrylate can penetrate into a permeability coefficient of 1×10^-4 cm/sec, and secure uniaxial compression strength of 0.5 MPa/30min or more and stiffness of 80 MPa or more.

• Journal of the Korean Geosynthetics Society
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• v.20 no.2
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• pp.23-33
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• 2021

In Korea, many reservoirs have been built for the purpose of solving the food shortage problem and supplying agricultural water. However, the current 75.6% of the reservoirs are in serious aged as more than 50 years have passed since the year of construction. In the case of such an aging reservoir, the stability due to scour and erosion inside the reservoir is very reduced, and if concentrated rainfall due to recent abnormal weather occurs, the aging reservoir may collapse, leading to a lot of damage to property and human life. Accordingly, each agency that manages aging reservoirs uses Ordinary Portland Cement (OPC) as an injection material and applies the grouting method. However, in the case of OPC, it may deteriorate over time and water leakage may occur again. And there are environmental problems such as consumption of natural resources and generation of greenhouse gases. So, there is a need to develop new materials and methods that can replace the OPC. In this study, an laboratory test and analysis were performed on the grout material developed to induce a curing reaction similar to that of OPC by recycling power plant byproduct. In addition, test in the field such as electric resistivity survey, Standard Penetration Test (SPT), and field permeability test were performed to analyzed to reinforcement effect and determine the possibility of using instead of OPC. As a results of the test, in the case of recycled power plant byproduct, the compressive strength was 2.9 to 3.2 times and the deformation modulus was 2.3 to 3.3 times higher, indicating that it is excellent in strength and can be used instead of OPC. And it was analyzed that the N value of the reservoir was increased by 1~2, and the coefficient of permeability (k) decreased to the level of 8.9~42.5%. showing sufficient reinforcing effect in terms of order.

• Journal of the Korean Geotechnical Society
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• v.26 no.7
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• pp.117-133
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• 2010

A hybrid system of soil-nailing and compression anchor is proposed in this paper; the system is composed of an anchor bar (installed at the tip) with two PC strands and a steel bar. After drilling a hole, installing proposed hybrid systems, and filling the hole with grouting material, prestress is applied to the anchor bar to restrict the deformation at the head and/or to prevent shallow slope failures. However, since the elongation rate of PC strand is much larger than that of steel bar, yield at the steel bar will occur much earlier than at the PC strand. It means that the yield load of the hybrid system will be overestimated if we simply add yield loads of the two - anchor bar and PC strands. It might be needed to try to match the yielding time of the two materials by applying the prestress to the anchor bar. It means that the main purpose of applying prestress to the anchor bar should be two-fold: to restrict the deformation at the nail head; and more importantly, to maximize the design load of the hybrid system by utilizing load transfer mechanism that transfers the prestress applied at the tip to the head through anchor bar. In order to study the load transfer mechanism in a systematic way, in-situ pullout tests were performed with the following conditions: soil-nailing only; hybrid system with the variation of prestress stresses from 0 kN to 196 kN. It was found that the prestress applied to the anchor system will induce the compressive stress to the steel bar; it will result in decrease in the slope of load-displacement curve of the steel bar. Then, the elongation at which the steel bar will reach yield stress might become similar to that of PC strands. By taking advantage of prestress to match elongations at yield, the pullout design load of the hybrid system can be increased up to twice that of the soil-nailing system.