• Journal of the Korean GEO-environmental Society
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• v.10 no.1
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• pp.25-34
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• 2009

Since the particle sizes of the coarse materials used in dam or harbor constructions are much larger than those of typical soils, it is desirable that large shear testing apparatuses are used when performing shear tests on the coarse materials to obtain as accurate results as possible. Two large-scale shear testing apparatuses, large direct shear testing apparatus and large triaxial shear testing apparatus, are commonly used. Currently in Korea, however, there have not been many cases in which shear tests were done using the large apparatus due to mainly difficulties in manufacturing, diffusing, and operating them. In present study, both large direct shear tests and large triaxial shear tests were performed on the coarse materials, which are used as dam fill materials, for 6 test cases in which particle sizes, specimen sizes, vertical pressure (confining pressure) conditions were little different, and then, the shear strength characteristics of the materials were compared with the two different shear tests. The test results showed that, by the Mohr-Coulomb failure criterion, overall the shear strength obtained by the large direct shear tests was larger than that by the large triaxial shear tests. Moreover, the shear strength under the normal stress of 1,000 kPa was about 10 to 70% larger for the large direct shear tests than for the large triaxial shear tests, revealing the larger differences in the coarse materials, compared to typical soils.

• Geotechnical Engineering
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• v.20 no.5
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• pp.58-65
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• 2004

일반적으로 토압, 사면안정, 기초의 지지력 계산 등에 이용하는 강도정수를 결정하기 위한 시험법으로는 일축$.$삼축시험과 직접전단시험이 많이 이용되고 있다. 일축$.$삼축시험은 흙 공시체를 축방향으로 압축 또는 신장 파괴시켜서 압축강도를 구하는 것으로, 활동면의 응력을 Mohr-Coulomb의 파괴 기준으로부터 간접적으로 구하기 때문에 간접전단시험으로 불리고 있다. 특히. 삼축시험은 공시체의 주응력 상태가 명확하기 때문에 연구$.$실용면에서 폭넓게 이용되고 있다. (중략)

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.109-112
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• 2008

In this study, Assessment of bond property of HSC with the rate of Blust-furnace(0, 12, and 25 percent by weight cement) and Evaluation of the relationship of the compressive strength coefficient (${\beta}$) between compressive strength with 40${\sim}$120MPa were performed. Design and Test of Bond specimens were carried out based on the ASTM C-234. Test results are follows, most specimens showed that the splitting failure in all specimens, except for B-40 series which showed that the pull-out failure. For the B-40 Series, the relation of compressive strength versus bond stress has well converged that of the proposed equation with the variation(${\beta}$=2/3) in UCB/E.E.R.C-83. The crack strength of concrete in splitting was proportioned to the compressive strength of concrete, and was the highest on the contents of blast furnace slag to 12 percent by weight of cement in each series, except for B-60 series. In the relation of admixture replacement rate versus maximum bond stress, The maximum bond stress was the highest in 12 percent by weight of cement according to less than 40MPa, and was the highest in 25 percent by weight of cement according to 80MPa.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2010.05a
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• pp.115-116
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• 2010

방사성농축폐액처리를 위한 Polymer-Modified-portlandcement 고화체는 Polymer 및 시멘트, 물을 혼합매질로 제조되며 농축폐액처리를 위해 Emulsion Polymer를 사용하였으며 PMC 고화체의 물성을 평가하기위한 고화체의 제조에서 이들 매질의 최적혼합비를 찾기 위해 Polymer 및 물, 시멘트의 혼합비를 1/1/2,1/2/4,1/3/9 등 혼합비에 따른 시편 및 Polymer 첨가량의 증가에 따라 함유비를 달리하는 시편을 제조하여 경화시간별 압축강도를 측정하였으며 매질의 최적혼합비 및 폴리머의 투입비를 구하고자하였다. 특성평가시험을 위한 시편으로는 직경 50, 높이 100mm(L/D=2) 인시편을 제조하여 압축강도를 측정하였으며 폴리머와 시멘트의 결합상태를 확인하기위해 SEM사진을 통한 미세구조를 관찰하였으며 시험결과 P/W/C의비가 1/3/9인 혼합비시편의 압축강도가 $343.36Kg_f/cm^2$로 가장 높았으며 폴리머의 함유량을 달리한 시험에서는 7%폴리머 함유시편은 $397.24Kg_f/cm^2$, 20% 폴리머함유시편은 $175.36Kg_f/cm^2$으로 폴리머의 함유량이 7~15% 이내의 폴리머함유고화체가 적합한 것으로 판단되었으며 폴리머의 투입양이 증가할수록 압축강도가 감소하였으며 경화시간도 최소4주이상 되어야하는 것으로 판단되었다.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.519-520
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• 2009

The purpose of this research was to develop a very-early-strength dry-mix shotcrete without accelerator using a rapid-setting cement, to analyze the correlationship of test results among cube test, core test, pullout test and maturity

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.965-968
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• 2008

The KS F 2403 method used on domestic sites for checking the compressive strength of a structure, sets the compressive strength of the concrete used in structural specimens as the compressive strength of testing specimens. Under this regulation, the curing method used for testing the specimens must be the standard ponding curing method (20$\pm$2$^{\circ}$C). However, because in-placed concrete is exposed to open air and cured under the seasonal temperature changes, the compressive strength of a real structure is different from the tested compressive strength. (Therefore,) This thesis first identifies the distinct characteristics of the strength development by applying the curing method listed under the KS and used for testing specimens on compressive strength tests; the atmospheric curing method, the sealed curing method, and the structural specimen core strength testing methods used for the in-sites quality checks including reckoning of the compressive strength of the structural specimens and form-demolding period; and the curing method suggested in this research, which sets the internal conditions of the structural specimens as the conditions of the applied curing method. Then, the thesis suggests the specimen curing method that most closely reenacts the compressive strength of the concrete used on the structural specimens

• Journal of the Korean Geotechnical Society
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• v.40 no.2
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• pp.19-28
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• 2024

This study explores the long-term decline in the uniaxial compressive strength of Controlled Low Strength Material (CLSM) by preparing a sample with a 1:1 mixing ratio of CLSM and water. Uniaxial compressive strength tests were conducted after 7 and 28 days of curing. The results revealed that the compressive strength at 28 days was reduced by a factor of 2.85 compared to that at 7 days. Additionally, when expansion was introduced under the same mixing conditions, there was a significant reduction in compressive strength. Point load strength tests based on 7 and 28 days of curing indicated a disparity of 29.27 to 58.76 and 48.19 to 95.13 times, respectively, between the point load strength and the uniaxial compressive strength at 7 days. The differences observed in the findings of this study compared to previous studies may be attributed to variations in the precision of the test method and the sample production process. Therefore, it is essential to establish clear testing methods to accurately evaluate CLSM.

• Journal of the Korean Geotechnical Society
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• v.19 no.1
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• pp.93-102
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• 2003

Unconfined compression test (UC) has been widely used to determine the undrained shear strength ($c_u$) of clay, because it is convenient and economical. However, UC can not represent the behaviour of in-situ stress condition and the strength obtained by the test is generally underestimated compared to that of triaxial compression, due to no confining pressure. Therefore, a simple and practical method to correct the ($c_u$) for sample disturbance and to be used in geotechnical practice is needed. This study is aimed at proposing the method to estimate in-situ undrained shear strength from UC with suction measurement. The proposed method is based on theoretical shear strength equation of perfect sample (Noorany & Seed, 1965), and effective overburden stress and analysis results ($A_f,\phi'$) of effective stress behaviour by UC are needed for the equation. The shear resistance angle ($\phi'$) can be simply estimated through the result that $K_f$-line slope of the UC is 1.6 times higher than that of triaxial compression test. The result of this study shows that the measured strength by this method is very similar to that of the undrained shear strength by triaxial compression test (CK$_0$UC).

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.833-840
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• 2004

Among non-destructive tests for compressive strength, rebound number test and pulse velocity test are the most widely used methods. However, the non-destructive tests mostly used in Korea was developed by foreign country. Therefore, it is unreasonable to directly apply them to concrete structures in Korea. In accordance with the suggestion of Institute of Architecture in Japan for rebound number test, a compressive strength is calculated by the mean value of 20 hit points without being considered standard deviation. Furthermore, there is no regulation on the number of measurements required for measuring compressive strength by pulse velocity test. This study, therefore, reviewed the rebound number test and pulse velocity test by chi-square, and suggested the minimum number of each test. As a result, the minimum number that falls within range of reliability for rebound number test and pulse velocity test are 11 and 7, respectively. If abnormal values are processed as missing and test groups are assumed to be arrayed in cross by considering changes in quality of actual concrete structures, 20 times and 9 times are appropriate for rebound number test and pulse velocity test, respectively.

• Journal of the Korean Geotechnical Society
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• v.17 no.4
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• pp.259-267
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• 2001

실내시험으로 구한 점토의 공학적 성질은 샘플링, 운반, 저장, 그리고 성형과정 동안에 발생하는 시료의 교란으로 인해 원지반의 성질과 다르게 측정된다. 본 연구에서는 양산점토에 대한 삼축압축시험($CK_{o}$ UC) 결과를 이용하여 샘플링 방법에 따른 교란의 정도를 평가하였다. 실험에 사용된 시료는 76mm 튜브샘플러, 76mm 피스톤샘플러, 블록샘플러로 채취되었으며, 시료의 교란정도를 평가하기 위해 각 시료에서 측정된 체적변형률, 비배수 전단강도, Secant Youngs modulus, 그리고 파괴시 간극수압계수를 비교하였다. 시료의 교란정도를 평가하는 것 이외에도 SHANSEP 방법을 이용하여 수행한 $CK_{o}$ U 삼축압축시험 결과를 이용하여 양산점토에 대한 정규화 전단강도($C_{u}$ /$\sigma$$_{vc}$ )와 OCR 관계를 규명하였다. 또, 피에조콘 관입시험, 딜라토메타 시험, 그리고 현장 베인시험결과를 이용하여 구한 양산점토의 비배수 전단강도를 삼축압축시험 결과와 비교하였다.