• Structural Engineering and Mechanics
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• 제83권3호
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• pp.377-386
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• 2022

This paper considers dynamic impedance functions and presents a detailed analysis of the soil plasticity influence on the pile-group foundation dynamic response. A three-dimensional finite element model is proposed, and a calculation method considering the time domain is detailed for the nonlinear dynamic impedance functions. The soil mass is modeled as continuum elastoplastic solid using the Mohr-Coulomb shear failure criterion. The piles are modeled as continuum solids and the slab as a structural plate-type element. Quiet boundaries are implemented to avoid wave reflection on the boundaries. The model and method of analysis are validated by comparison with those published on literature. Numerical results are presented in terms of horizontal and vertical nonlinear dynamic impedances as a function of the shear soil parameters (cohesion and internal friction angle), pile spacing ratio and frequencies of the dynamic signal.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2017년도 9th Asian Crop Science Association conference
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• pp.321-321
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• 2017

Water availability in rainfed lowlands (RFL) is strongly affected by climate change. In RFL, rice plants are exposed to soil moisture fluctuations (SMF) but rarely to simple progressive drought as widely believed. Typical RFL field is characterized by a about 5-cm thick high bulk density hardpan layer underneath the cultivated layer at about 20 cm depth that impedes deep root development. Root system has the ability to develop in response to changes in SMF, known as phenotypic plasticity. We hypothesized that genotypes that can adapt to RFL have root plasticity. The roots can sharply respond to re-wetting after drought period and thus penetrate the hardpan layer when the hardpan is wet and so becomes relatively soft, and thus access water under the hardpan. This study aimed to identify CSSLs derived from a cross between Sasanishiki and Habataki which adapted to such RFL conditions. We used 39 CSSLs together with the parent Sasanishiki, which were grown in hydroponics and pot under transient soil moisture stresses (drought and then rewatering), and compared with continuously well-watered (WW) (control) up to 14 days after sowing (DAS), and 20 DAS, respectively. Based on the results of hydroponics and pot experiments, we selected a few lines, which were grown in the soil-filled rootbox with artificial hardpan layer and without artificial hardpan. For the rootbox without artificial hardpan, plants were grown under WW and transient soil moisture stresses for 49 DAS. While the rootbox with artificial hardpan, the plants were grown under WW (control) and SMF (WW up to 21 DAS, 1st drought (22-36 DAS), rewatering (37-44 DAS), and followed by 2nd drought (45-58 DAS)). Among the 39 CSSLs, only CSSL439 (SL39) consistently showed significantly higher shoot dry weight (SDW) than Sasanishiki under transient soil moisture stress conditions as well as SMF conditions in all the experiments. Furthermore, under WW, SL39 consistently showed no significant differences from Sasanishiki in shoot and root growth in most of traits examined. SL39 showed significantly greater total root length (TRL) than Sasanishiki under transient soil moisture stress, which is considered as phenotypic plasticity in response to rewatering after drought period. Such plastic root development was the key trait that effectively contributed to root elongation and branching during the rewatering period and consequently enhanced the root to penetrate hardpan layer when the soil penetration resistance at hardpan layer reduced. In addition, using the rootbox with artificial hardpan layer ($1.7g\;cm^{-3}$, heavily compacted), SL39 showed greater root system development than Sasanishiki under SMF, which was expressed in its significantly higher TRL, total nodal RL, and total lateral RL at hardpan layer as well as at below the hardpan layer. These results prove that SL39 has plasticity that enables its root systems to penetrate hardpan layer in response to rewatering. Under SMF, such root plasticity contributed to its higher gs and Pn.

• Geomechanics and Engineering
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• 제16권3호
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• pp.217-231
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• 2018

Clayey soils with swelling and shrinkage characteristics have been major causes for many problems in roads, buildings and other civil engineering infrastructure in various areas of Pakistan, particularly where there are several patches of such soils on either side of Indus River. As the consistency characteristics are directly related with the variation of moisture content; therefore, this study was explicitly focused to investigate the effect of lime and wheat straw on the consistency characteristics of clayey soils with relatively high swelling and shrinkage characteristics. The consistency test results indicate that by the increase in lime content there is a decrease in the plasticity index of soil; for instance, 10% lime content resulted to 59% decrease in the plasticity index value. On the other hand; the addition of wheat straw resulted in a significant increase in the plasticity index; for instance, 10% wheat straw content resulted to a 120% increase in the plasticity index. This study has further shown that the shrinkage and swelling of clayey soils which resulting to several problems in the civil engineering infrastructures may adequately be managed through mixing an appropriate amount of lime and wheat straw as soil stabilizing agent for both immediate and long-term effects.

• 한국지반신소재학회논문집
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• 제16권3호
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• pp.31-39
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• 2017

국내 해성 점성토의 강도증가율 평가시, 흙의 물리적 특성인 소성지수 및 액성한계만을 이용해서 비교적 쉽게 구할 수 있으므로 연약 지반 설계 실무에서 폭넓게 적용되어온 경험식, Skempton(1954, 1957) 및 Hansbo(1957)의 적용성을 분석하였다. Scandinavia 반도지역의 해성 점성토 지반에서 수행된 현장베인시험(FVT) 결과를 이용하여 제안된 두 식은 소성지수와 점토 함유량의 비례관계를 나타내는 국내 지반 조건에서는 적용성이 떨어지므로, 압밀 및 강도 산정을 위한 역학시험을 통해서 강도증가율을 평가하는 것이 적절한 것으로 분석되었다. 일축압축강도 저평가 경향의 인천, 화성 및 군산 저소성 토질의 결과를 제외하면, 소성지수에 관계없이 국내 해성 점성토 지반의 강도증가율은 대략 0.25~0.35 사이에서 분포하는 것으로 나타났다.

• 한국지반신소재학회논문집
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• 제16권1호
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• pp.73-83
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• 2017

모래 및 실트 함유량이 우세한 서해안 저소성 지반(인천, 화성, 군산)에서 실시된 실내 및 현장시험으로부터 얻어진 비배수전단 강도를 이용하여 피에조콘계수(Nkt)를 분석한 후, 이에 대한 적용성을 평가하였다. 인천, 화성 및 군산지역에서 얻어진 일축압축 강도에 의한 콘계수(Nkt)는 19~23, 간이 CU 강도에 의한 값은 13~13.8, 현장베인강도에 의한 값은 11.6~13.1로 평가되었다. 이는 저소성 실트 지반조건에서 일축압축강도가 과소평가되는 원인에 의한 것으로 간이 CU 강도 적용조건과 비교했을 때 콘계수(Nkt)가 약 1.8배 전후로 커지며 분산되는 경향을 나타냈다. 저소성 실트 지반에서 수행된 CPTU 데이터를 이용하여 콘계수(Nkt)를 평가할 때에는 지반의 입도분포, 액소성한계 등의 물리적 특성, 지층 내의 sandseam 분포 등으로 인한 콘선단저항(qt) 및 주면마찰력(fs)의 불규칙한 분포, 간극수압계수(Bq)를 종합적으로 분석하여 수행하는 것이 바람직할 것으로 판단된다.

• Environmental Engineering Research
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• 제24권2호
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• pp.289-297
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• 2019

Indiscriminate disposal of waste and citation of open dumpsites are some of the key factors affecting the various soil geotechnical properties. Atterberg limit and consolidation tests were conducted to determine the effects of two open waste dumpsites (Uselu Market and New Benin) on geotechnical properties of their underlying soils. Soil sample collected from Uselu Market dumpsite in Benin City metropolis showed slightly lower hydraulic conductivity (K) of $1.0{\times}10^{-6}$ with plasticity index of 18.53% compared to sample collected 1.6 m from the same dumpsite which had high K value of $2.42{\times}10^{-3}$ with plasticity index of 6.9%. Soil sample collected from New Benin dumpsite in Benin City metropolis showed slightly lower K of $1.45{\times}10^{-6}$ with plasticity index of 13.8% than sample collected 1.6 m from the same dumpsite which had high K value of $2.14{\times}10^{-2}$ with plasticity index of 6.0%. X-ray florescent analyser (X-MET 7000) and direct soil pH meter were used to determine the composition of the aforementioned soil samples. The result of samples collected from both dumpsites indicated a low hydraulic conductivity compared to samples collected 1.6 m from both dumpsites. Also, the chemical composition and pH of both dumpsite underlying soils indicated high level of soil contaminants with pH of 3.3 and 3.5 which is very acidic unlike pH of other samples which were in the neutral range (6.8-7.1). Hence, a liner is recommended for all dumpsites or engineered landfill systems to mitigate against the challenges associated with open waste dumping system in the environment.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회 2차
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• pp.68-75
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• 2010

Around the Nakdong River which is one part of the repairing business of 4 Grand Rivers currently being constructed, sandy ground is distributed throughout the wide area. Many civil engineering structures such as small and medium sized dams, flood control basins, and redevelopment of reservoirs and retention reservoirs are scheduled to be constructed, so the prevention measures for liquefaction are surely needed. To identify such liquefaction, a lot of factor affecting the strength of liquefaction were studied through laboratory investigation. Most of the conducted study was about clean sands, but in the case of the real ground the sand can exist not in the clean conditions but in the conditions mostly including sand of fine grained soil. The sand of fine grained soil has become a significant factor to assess liquefaction because many cases of liquefaction happened in the silty and clayer soil. In this study, un-drained tests of plasticity index of fine grained particles were conducted with the sands from Nakdong River. In result, the study shows that dynamic shear strength characteristics differ according to the plasticity index.

• Structural Engineering and Mechanics
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• 제22권4호
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• pp.511-515
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• 2006

• 한국유체기계학회 논문집
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• 제19권3호
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• pp.29-32
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• 2016

A series of laboratory tests were conducted to investigate the geotechnical engineering characteristics of muskeg soil for construction machinery widely distributed in cambridge region in Canada which makes problems in construction works. Physical characteristics of cambridge region muskeg soil were measured in terms of such categories as nature water content, organic content, specfic gravity, liquid limit, and plasticity index. As the test result, it was found that nature water content, organic content, specific gravity, liquid limit, plasticity index, and compression strength were 50.8~343.8%, 12.1~42.5%, 1.76~2.57, 46.6~440.2%, 25.6~280.5, $0.665{\sim}1.537kg/cm^2$, respectively.

• Geomechanics and Engineering
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• 제4권2호
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• pp.135-150
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• 2012

This paper presents the study of the effect of microorganism Bacillus pasteurii on the properties such as Atterbergs' limit and unconfined compressive strength of cohesive soils. The results of this study reveal that the liquid limit and plasticity index for all clay soils decreased and the unconfined compressive strength increased. Decrease in plasticity index is very high for Kuttanad clay followed by bentonite and laterite. The unconfined compressive strength increased for all the soils. The increase was high for Kuttanad soil and low for laterite soil. After 24 h of treatment the improvement in the soil properties is comparatively less. Besides the specific bacteria selected Bacillus pasteurii, other microorganisms may also be taking part in calcite precipitation thereby causing soil cementation. But the naturally present microorganisms alone cannot work on the calcite precipitation.