• 한국지반공학회논문집
• /
• 제36권9호
• /
• pp.5-20
• /
• 2020

2017년 발생한 포항지진에서는 계기지진 이래 처음으로 액상화 현상이 목격되었다. 본 연구에서는 액상화 현상이 목격된 포항시 (1) 송림공원, (2) 흥해읍 망천리, (3) 흥안리를 대상으로 다양한 지반조사 및 실내실험을 수행하였다. 액상화 발생위치의 동적특성을 파악하기 위해 지반조사 항목으로는 표준관입시험(SPT), 콘관입시험(CPT), 표면파탐사(MASW), 밀도검층, 다운홀테스트, 전기비저항탐사를 수행하였고, 현장에서 채취한 시료를 바탕으로 진동삼축압축 시험기를 통해 액상화실험을 수행하였다. 그 결과 세 곳 모두 지하수위가 높고 얕은 심도에 연약한 모래층이 존재하며, 송림공원에서 채취한 모래는 주문진 표준사, Toyoura 모래, Ottawa 모래에 비해 액상화 저항강도가 작은 것을 확인하였다.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
• /
• pp.1431-1437
• /
• 2008

The small-strain shear modulus ($G_{max}$) of uncemented sand is affected by the the mean principal stress and void ratio, and it has been known that the cementation and aging also affect to $G_{max}$ of sand. For extensive understanding about the effect of cementation on the $G_{max}$ of sand, a series of bender element tests was conducted on the cemented specimens prepared in a large calibration chamber by pluviation of the sand-gypsum mixture. It was observed from the experimental results that the $G_{max}$ of cemented sand is higher above 10 times than value of uncemented one, and it increases exponentially with the gypsum content increases. Whereas, the increase of the vertical stress from 50kPa to 200kPa and the relative density from 40% to 80% result in 20~30% and 2 times increase of $G_{max}$, respectively. It means that the gypsum content, that is cementation level, is the most influential factor on the $G_{max}$ of cemented sand. In addition, the effect of relative density on $G_{max}$ was more apparent on cemented sand than uncemented one.

• 한국건축시공학회지
• /
• 제8권4호
• /
• pp.45-51
• /
• 2008

Recently, the demand of ultra high-rise building is on the increase in korea due to the rapidly changing movement in economic growth and the expansion of national infrastructure. At the same time, the tendency toward the amount used of concrete has greatly increased every year. In addition, as the seriousness of quantity demanded of aggregate is gathering strength, the active areas of research proceeds to do actively in every place in order to review the usability of crushed sand as a part of the countermeasures. And, it needs to establish the quality standard and service guide, etc. for the practical use. Accordingly, this study was to establish the ratio of water-binder materials as three levels like 23.5, 27.5, and 31.5%, and the replacement ratio as three levels like 0, 50, and 100% in order to define the engineering properties of ultra high-strength concrete using the crushed sand. This study was to examine it after establishing the combined condition by the substitute of the fine aggregate percentage and admixture. From the result of this research above, it may be summed up as follows. 1) The more the replacement ratio of crushed sand and the ratio of water-binder materials increased, the mon the fluidity decreased due to the decrease of irregular grain shape of sand and unit combined discretion. 2) This study found out that 100% of replacement ratio of crushed sand was almost similar level to the compressive strength of concrete using the natural sand.

• International Journal of Concrete Structures and Materials
• /
• 제3권1호
• /
• pp.3-9
• /
• 2009

This paper examines the incorporation of the crushed sand (CS) and desert sand (DS) in the formation of self compacting concrete (SCC). These sands have been substituted for the rolled sand (RS), which is currently the only sand used in concretes and which is likely to run out in our country. DS, which comes from the Tunisian Sahara in the south, is characterized by a tight distribution of grains size. CS, a by-product of careers containing a significant amount of fines up to 15%, is characterized by a spread out granulometry having a maximum diameter of around 5mm. These two sands are considered as aggregates for the SCC. This first part of the study consists in analyzing the influence of the type of sand on the parameters of composition of the SCC. These sands consist of several combinations of 3 sands (DS, CS and RS). The method of formulation of the adopted SCC is based on the filling of the granular void by the paste. The CS substitution to the RS made it possible, for all the proportions, to decrease the granular voids, to increase the compactness of the mixture and to decrease the water and adding fillers proportioning. These results were also obtained for a moderate substitution of DS/CS (< 40%) and a weak ratio of DS/RS (20%). For higher proportions, the addition of DS to CS or RS did not improve the physical characteristics of the SCC granular mixture.

• 한국지반공학회논문집
• /
• 제24권11호
• /
• pp.91-100
• /
• 2008

본 연구에서는 Mohr-Coulomb 파괴기준에 따라 고결모래의 전단강도를 유도하고, 삼축 및 일축압축시험으로 검증하였다. 모래의 마찰각은 고결의 영향을 받지 않으며, 일정구속압 이하에서 고결모래의 점착력은 고결정도에 따라 일정하다. 따라서 고결모래의 전단강도는 미고결 모래의 전단강도와 고결모래의 일축압축강도의 합으로 표현되며, 고결모래의 점착력은 마찰각과 일축압축강도의 함수로 표현되었다. 또한 고결결합 파괴구속압 이후인 전이구간에서 고결모래의 전단강도는 비교적 일정하게 유지된다고 가정하여 전이구간에서 고결모래의 전단강도와 점착력을 유도하였다. 추정된 고결모래의 전단강도와 점착력은 실험결과와 잘 일치하였다. 실험 결과는 또한 고결모래의 점착력 변화에 큰 영향을 미치는 고결결합 파괴구속압이 일축압축강도와 선형비례관계임을 보여준다.

• 한국지형학회지
• /
• 제23권1호
• /
• pp.17-33
• /
• 2016

Samples from newly exposed outcrop of sedimentary layers forming Jeongdongjin coastal terrace in Gangreung area are collected and analyzed to find the sedimentary environment. The site are located at the gentle hillslope of the terrace surface area. The height of the outcrop is about 8m and the altitude of it's highest part is 68~73m MSL. The lowest part of this out crop is the partly consolidated sand layer with gravel veneer within it. It is found that this part is not in-situ weathered sand stone through the OSL method. This sand layer is overlain by the gravel layer with sand matrix. The shapes of the gravels from this part are mainly 'platy', 'elongated', and 'bladed' by the index of Sneed and Folk(1958). In addition, mean roundness is not so high. It is sceptical to regard this part as marine sediments which are continuously exposed to erosional processes. The boundary between the lowest sand layer and gravel layer showing the abrupt change in forming material without any mixture or transitional zone, so gravels are seemed to deposited after some degree of consolidation of the lowest sand layer. In addition, the hight of the boundary between layers are changed by the place, so the surface of the partly consolidated sand layer is not flat and has irregularity on topography when it buried by gravels. Main part of this out crop is the poorly sorted coarse gravel(22.4mm) with sand matrix($1.36{\phi}$) layer with at least 2m thick covering the relatively fine gravels discussed above. Over 20% of particles have 'very platy', 'very elongated' and 'very bladed' shape and only less than 5% of particles have 'compact' shape, So this particles are also very hard to be regard as marine gravels which are abraded by marine processes. It can be concluded that this gravel layer formed by fluvial processes rather than coastal processes base on the form of the clast and sedimentary structure. The gravel layer is covered by fine($3{\sim}4{\phi}$) material layers of psudo-gleization which showing inter-bedding of red and white layers. Chemical composition of matrix and other fine materials should be analyzed in further studies. It is attempted to fine the burial ages of the sediment using OSL method, but failed by the saturation. So it can be assumed that these sediments have be buried over 120ka.

• 한국지반공학회논문집
• /
• 제23권6호
• /
• pp.103-114
• /
• 2007

제주도 해안지역에 분포하고 있는 모래는 화산암류가 풍화되어 형성된 모래와 조개 등의 어패류가 풍화되어 탄산염 $(CaCO_3)$ 함유량이 많은 모래, 그리고 이들 두 가지 특징이 혼재한 모래로 분류할 수 있었다. 분류된 모래들 중 삼양, 김녕, 제주외항 지역의 모래에 압축 특성을 알고자 압축시험을 수행한 결과, 삼양인 경우 초기압축이 다른 모래에 비해 큰 것으로 나타났으며 김녕, 제주외항 모래인 경우 초기압축외의 추가적인 압축도 상당히 발생하였으며, 이는 압축시험 전·후의 모래의 입도분포 분석 결과 입자의 파쇄와 재배열에 의한 것으로 나타났다. 또한 현재 제주외항 항만시설 축조공사에 따른 지반의 침하특성을 분석한 결과 초기 압축 외에도 모래의 파쇄성과 재배열에 의해 상당시간동안 압축이 일어난 것을 알 수 있으며, 파쇄성과 재배열이 고려되지 않은 기존 탄성침하량 산정법을 이용한 침하량과 기존의 침하시간 산정 시 과소평가 될 우려가 있는 것으로 나타났다.

• 한국주조공학회지
• /
• 제12권6호
• /
• pp.435-441
• /
• 1992

• 상하수도학회지
• /
• 제21권4호
• /
• pp.485-491
• /
• 2007

The fluctuation of inlet flow to a water treatment plant makes a serious problem that it can change the filtration rate abruptly, and ultimately occur the breakthrough of the detained particles inside filter media. Also, since it takes very short time (about 10 minutes) for the surface wave occurred from the fluctuation of inlet flow to reach the filtration process, it is impossible to control the filtration rate stably. Therefore, this study was conducted to evaluate the effect of daily flow-rate fluctuation on the performance of sand filtration process, and to suggest the dual media composition for coping with that effect. Comparative column tests have been carried out for various dual media (sand and anthracite) compositions. From the results of column tests, dual media, especially in the case of sand 45cm/anthracite 30cm, is more effective to cope with the effect of flow-rate fluctuation on the performance of filtration than single media (only sand). In addition, irrespective of dual media composition, managing ability to cope with that fluctuation tends to be weak at the end of allowable filtration duration time,

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2005년도 춘계 학술발표회 논문집
• /
• pp.974-981
• /
• 2005

Because general laboratory tests for sand compaction pile method including unit-cell test device have fixed outside diameter, as area replacement ratio increase, diameter of sand pile increase. These condition can bring about overestimation of stiffness of composite ground. In addition, existing large soil box which consist of bellows type loading plate can occur serious mistake in checking the amount of drained water because there are additional drainage along the inside wall in device. Overcoming these shortcoming, this paper developed modified large scale soil box consist of piston type load plate. In this study, using this device, series of modified large scale soil box tests were performed, and investigated the settlement and stress transportation characteristics with area replacement ratio in sand compaction pile method.