낙동강 모래의 실트함유량 변화에 따른 반복전단응력비 특성

김영수(Kim Young-Su),김대만(Kim Dae-Man) 대한토목학회 2009 대한토목학회논문집 C Vol.29 No.6

실트함유량 변화에 따른 낙동강 모래의 반복전단강도 특성을 살펴보고자 낙동강 유역에 분포하는 모래와 실트를 채취하여 실트함유량 0~50%의 범위로 실내에서 재성형된 실트질 모래시료에 대하여 일련의 비배수 반복삼축실험을 실시하였다. 실험 결과, 실트함유량 변화에 따른 반복횟수(N) 10에서의 반복전단응력비(CSR)는 모든 상대밀도에서 실트함유량 5%에서 최대였고,20%에서 최소를 보였다. 반복비(N/N<SUB>L</SUB>)에 따른 간극수압비 (Δu/p') 관계로 부터 분석된 간극수압의 발달 경향은 실트함유량에 따른 CSR 크기변화와는 무관하였다. 압밀 후 간극비(e)와 skeleton 간극비(e<SUB>s</SUB>)를 비교해 본 결과, 전반적으로 실트함유량에 따른 CSR의 변화 경향과 일치하여 실트함유량에 따른 CSR은 실트질 모래의 전단거동에 영향을 미치는 모래만의 간극비인 skeleton 간극비 (e<SUB>s</SUB>)에 큰 영향을 받는 것으로 나타났다. A series of undrained cyclic triaxial tests were carried out to investigate the cyclic shear stress strength characteristics of sands with respect to the silt content. Silty sand was collected around the basin of Nak-Dong River and remolded in laboratory with the range of silt content 0~50% in sand located. As results, with the change of silt content cyclic shear stress ratio (CSR) at N=10 showed the maximum value at 5% and the minimum at 20% in all relative density. The development tendency of the pore water pressure analyzed by the relationship cyclic ratio and pore water pressure ratio is unrelated the change of CSR varying silt content. Comparing the results of the void ratio and skeleton void ratio after consolidation, CSR varying silt content was much affected by skeleton void ratio which is known to affect shear behavior of silty sand.

모래-실트 혼합토의 구속압력에 따른 전단특성 파악

김욱기,장 리 한국지반공학회 2015 한국지반공학회논문집 Vol.31 No.3

Triaxial tests on sand-silt mixture specimens under low and high confining pressures were performed to understandtheir shear behaviors. The fines content in the mixture is lower than the threshold value. A series of tests under differentconditions including fines contents (0%, 9.8%, 14.7%, 19.6%), density of specimen (controlled by different compactionenergies of Ec = 22 kJ/m3, Ec = 504 kJ/m3), confining pressure (100 kPa, 1 MPa, 3 MPa, 5 MPa) were performed toinvestigate influences of these factors. Based on the test results, the threshold fines content, where the dominant structureof mixture changes from sand-matrix to fines-matrix, decreases with the increase of confining pressure. Under very highconfining pressures, as a result of sand particle crushing, the behavior of the dense specimen is similar to that of theloose specimen which shows hardening, compression behavior, and shear strength increases with increase of fines content. In conclusion, silt is granular material like sand, and its influence on shear behavior of sand-silt mixture is very differentfrom that of plastic fines on sand-fines mixture.

실트질 함유량에 따른 낙동강 모래의 비배수 반복전단거동 특성

김영수,김대만,Kim, Young-Su,Kim, Dae-Man 한국지반공학회 2008 한국지반공학회논문집 Vol.24 No.11

In this study, a series of undrained cyclic triaxial tests were performed with three different consolidation stress ratios ($K_c$=1.0, 1.5, 2.0) to investigate the undrained shear strength characteristics of sands with respect to the amount of contained silt located around the basin of Nak-dong River. The test results show that the more the sand has silt, the lower is cyclic shear stress ratio (CSR) in all $K_c$ and that the higher $K_c$ goes, the larger CSR decreases due to the increase of contained silt. The excessive pore pressure caused during shearing has an influence on the decrease of CSR by the high initial pore pressure in proportion to the amount of contained silt regardless of the $K_c$ value. After consolidation, the analysis of the skeleton void ratio of the sample reveals that the main cause of the decrease of CSR as well as the increase of the initial excessive pore pressure is the increase of the skeleton void ratio in proportion to the amount of contained silt.

전단속도와 소성지수를 달리한 재생성 점성토의 응력-변형률 거동

이용희(Lee Yonghee),강권수(Kang Kwon-Soo),정상국(Jung Sang-Guk),강진태(Kang Jintae),김대현(Kim Daehyeon) 한국지반환경공학회 2011 한국지반환경공학회논문집 Vol.12 No.1

직접전단시험이나 삼축압축시험 시 하중재하속도가 증가할수록 시료의 전단강도는 증가하는 것으로 알려져 있다. 본 연구에서는 점성토 지반의 거동특성에 영향을 미치는 중요한 두 가지 요인, 즉 전단속도와 실트함유량에 따른 점성토의 응력-변형률 거동특성을 규명하기 위하여 광양지역의 재생성 점성토를 대상으로 완속재하 상태로부터 급속재하 상태까지 재현함과 동시에 실트 함유량 변화 시 그 거동 특성이 어떻게 변화되는지에 대한 연구를 수행하였다. 연구결과 동일변형률에서의 전단속도 증가에 따른 축차응력의 변화, 즉 등변형률선의 기울기는 양의 기울기를 가지며 일정변형률 이상에서는 기울기의 변화가 거의 없는 것으로 나타났다. 그리고 기울기 변화가 없는 지점의 값은 흙의 종류에 따라 달라지므로 그 흙이 가지는 고유 특성인 것으로 판단된다. In general, the shear strength of a clay specimen under the direct shear test and the triaxial compression test increases with an increase in the shear rate. This study investigates the effects of shear rate and silt content on the stress-strain behavior of remolded Gwangyang clay, by changing the shear rate and the silt content. Based on the results of the triaxial compression tests, the equi-strain line of remolded Gwangyang clay shows initially positive slope and then becomes flat at certain strain level. As the strain level where the equistrain becomes flat is different depending on the soil with different silt contents, this can be considered as the inherent property of soil.

Silt fraction effects of frozen soils on frozen water content, strength, and stiffness

Kim, Sang Yeob,Hong, Won-Taek,Lee, Jong-Sub Elsevier 2018 Construction & building materials Vol.183 No.-

<P><B>Abstract</B></P> <P>The strength and stiffness of soil mixtures vary with regard to the particle composition and the properties of soil mixtures that critically change when water, which is a component in soils, is frozen. The objective of this study is to evaluate silt fraction effects of frozen sand-silt mixtures on the frozen water content, shear strength, and stiffness. The sand-silt mixtures are prepared in a shear box at a fixed relative density of 60% and a fixed degree of saturation of 15% with various silt fractions ranging from 0 to 100% in weight (W<SUB>silt</SUB>/W<SUB>sand</SUB> × 100%). A time domain reflectometry (TDR) probe, bender elements, and thermocouple are installed in the shear box, and the direct shear apparatus is placed in the freezing chamber. After the sand-silt mixtures are frozen at −5 °C, the direct shear tests are conducted. The TDR signals and shear waves are monitored before and after the freezing phases for the estimation of the volumetric water content and stiffness, respectively. Test results show that the void ratio, volumetric frozen water content, shear strength, and shear wave velocity are at a minimum near a silt fraction of 30%. As the relationships between the volumetric frozen water content and peak shear strength, as well as between the volumetric frozen water content and shear wave velocity after freezing, are linear, the peak shear strength correlates well with the shear wave velocity after freezing. Furthermore, as the residual shear strength and shear wave velocity before freezing are related to the silt fraction, the residual shear strength is bi-linearly proportional to the shear wave velocity before freezing. This study suggests that the void ratio and frozen water content of sand-silt mixtures are affected by the silt fraction. Thus, the silt fraction effects should be considered for the characterization of the strength and stiffness of frozen soils.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Strength and stiffness of frozen soils with different silt fractions are evaluated. </LI> <LI> Freezing temperature and frozen water content vary according to silt fraction. </LI> <LI> Strength and stiffness are minimum at the silt fraction of ∼30%. </LI> <LI> Peak shear strength is linearly proportional to Vs owing to ice-bonding. </LI> <LI> Residual shear strength is bi-linearly proportional to Vs owing to the silt effect. </LI> </UL> </P>

The influence of soil aggregation induced by water content variation on the engineering behaviors of cement-treated silt subgrade

Sai Zhang,Jian-Wen Ding,Zhenyuan Lai,Qinying Guo,Xing Wan 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.10

Water content is an important indicator of highway subgrade compaction, which has an impact on the engineering behaviors of pavement structures significantly. To study the influence of soil aggregation induced by water content variation on the engineering behaviors of silt subgrade, a series of laboratory experiments, including sieving analysis, unconfined compression tests and hydraulic conductivity tests, were conducted on the cement-treated silt subgrade. The influence of water content on the soil aggregation, unconfined compressive strength (UCS) and hydraulic conductivity were examined, respectively. The distribution range of UCS index (IUCS) and hydraulic conductivity index (Ik) were expressed accordingly. Test results demonstrate that when the water content lower than the optimum water content (wopt), the specimens are more homogeneous, the UCS increases regularly with the increase of curing time and water content, the hydraulic conductivity decreases regularly with curing time and water content increased. When the water content is higher than the wopt, the silt aggregation leads to the structural inhomogeneity of specimens, the strength decreases irregularly with the increase of curing time and water content, the hydraulic conductivity increases irregularly with the increase of curing time and water content accordingly. The soil aggregation induced by water content variation is proved to be a major reason for the ununiformly distribution of the UCS and hydraulic conductivity, the influence of which is more significant than that of binders when the water content higher than the wopt. Hence, controlling water content within 2% lower the wopt is strongly suggested to forming a more homogeneous structure of the subgrade.

실트함유율에 따른 낙동강 모래의 불포화 함수특성곡선

문홍득(Moon Hongduk),김대만(Kim Daeman) 한국지반환경공학회 2011 한국지반환경공학회논문집 Vol.12 No.2

본 연구에서는 낙동강 모래를 상대밀도 40%, 60%, 80%, 실트 함유율 0%, 10%, 20%, 30%에 대한 함수특성곡선을 구하였다. 시험결과, 동일 실트함유율에 대해서는 상대밀도가 커질수록 그리고 동일 상대밀도에서는 실트함유율이 커질수록 체적함수비의 변화가 작게 나타났다. 기존의 경험식을 통해 구한 함수특성곡선과 시험에서 구한 결과를 비교하여 보면, van Genuchten(1980), Fredlund와 Xing(1994) 경험식에 의한 함수특성곡선은 시험결과의 경향과 비슷한 S자형 곡선을 나타내어 비교적 시험결과와 잘부합하였다. 특히 Fredlund와 Xing 경험식의 경우 상관계수(R²)가 모두 0.99로 나와 거의 일치하는 결과를 보였다. In this paper, we got soil-water characteristic curve(SWCC) of Nak-Dong River's sand respectively as relative density 40%, 60%, 80% and content of silt 0%, 10%, 20%, 30%. As a result, the more the sand densify in the same silt content and the more the sand has silt in the same relative density, the change of volume water content was decreased. we have known effect of silt contents for SWCC and verified existing empirical formula of SWCC. As experiment results of soil-water characteristic curves compared to the empirical solutions, the results of van Genuchten(1980) and Fredlund & Xing(1994) were well-matched showing S type curves with experiment results. Especially the empirical solution of Fredlund & Xing showed almost same results of the coefficient of correlation(R²) equal to 0.99.

서해중부연안 조간대 퇴적물내 중금속 분포 및 특성

황갑수,김강주,이장훈 한국환경보건학회 2003 한국환경보건학회지 Vol.29 No.5

Heavy metal contents and distributional characteristics in sediments from the tidal flats along the middle west coast of Korea were investigated. The averages of heavy metal contents in sediments from 12 sampling sites range from 10.54 to 47.41 mg/kg for Zn, from 6.17 to 19.14 mg/kg for Cr, from 3.53 to 12.03 mg/kg for Ni, from 1.80 to 7.79 mg/kg for Cu, from 0.004 to 0.040 mg/kg for Cd, and from 5.46 to 13.19 mg/kg for Pb(on dry weight basis). The literatural comparative study showed that the study area has been little affected by heavy metal contamination. On the whole, heavy metal content, ignition loss rate(%) and clay+silt content(%) in sediments were higher in the southern part area than in the northern part area, regionally divided by S6 and S7 sites(Osikdo). In the present study, it is suggested that methodological selection of acid digestion, particle size fraction for analysis and normalization should be carefully deliberated to make the comparative study of heavy metal contamination more objective.

Cyclic liquefaction and pore pressure response of sand-silt mixtures

Dash, H.K.,Sitharam, T.G. Techno-Press 2011 Geomechanics & engineering Vol.3 No.2

The effect of non-plastic fines (silt) on liquefaction and pore pressure generation characteristics of saturated sands was studied through undrained stress controlled cyclic triaxial tests using cylindrical specimens of size 50 mm diameter and height 100 mm at different cyclic stress ratios and at a frequency of 0.1 Hz. The tests were carried out in the laboratory adopting various measures of sample density through various approaches namely gross void ratio approach, relative density approach, sand skeleton void ratio approach, and interfine void ratio approach. The limiting silt content and the relative density of a specimen were found to influence the undrained cyclic response of sand-silt mixtures to a great extent. Undrained cyclic response was observed to be independent of silt content at very high relative densities. However, the presence of fines significantly influenced this response of loose to medium dense specimens. Combined analyses of cyclic resistance have been done using the entire data collected from all the approaches.

저소성실트를 이용한 시멘트 혼합토의 강도 예측

박종찬(Jongchan Park),박민철(Minchul Park),전제성(Jesung Jeon),정상국(Sangguk Jeong),박경한(Kyunghan Park),이송(Song Lee) 한국지반환경공학회 2014 한국지반환경공학회논문집 Vol.15 No.7

소일 시멘트 혼합토의 역학적 성질을 파악할 수 있는 인자로서는 일축압축강도로 기존 연구사례에서 제시되었다. 본 연구에서는 저소성실트를 이용한 시멘트 혼합토의 일축압축강도 시험을 통해 실트함수비, 재령일, 시멘트 함유율에 대한 역학적 변화를 분석하였으며, Abrams가 제안한 B계수에 대한 변화를 기존연구사례와 비교?분석 및 시멘트 혼합토의 일축압축강도 예측식도 제안하였다. 상수 B계수값은 토질의 특성 및 재령일 등에 따라 변화였으며, B계수 변화의 적정성 여부를 일축압축강도로 분석한 결과 변수형태의 고려가 적정한 것으로 나타났다. Abrams 방정식을 적용하고 재령일, 시멘트 함유율과 재령일을 고려한 저소성실트 혼합토의 일축압축강도 예측식을 제안하였다. For analysis of mechanics properties of soil cement, unconfined compressive strength has been proposed by existing case studies. In this study, mechanical changes with water content of silt, curing time and cement content were analyzed through unconfined compressive strength test. In addition, the changes for B factor by Abrams were compared with existing case studies after the prediction equations could be proposed about the unconfined compressive strength of admixed cement soil. Especially, the B constant factor was changed with soil characteristics and curing time. For analysis results of appropriateness status and unconfined compressive strength, consideration of variable form was titrated. The prediction equations at low plasticity silt admixed using the uniaxial compressive strength with applying Abrams’s equation and considering cement content, curing time is proposed.