• Title/Summary/Keyword: oedometer

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Experimental study of the effect of the glass fibers on reducing collapse of a collapsible soil

  • Bakir, Nassima;Abbeche, Khelifa;Panczer, Gerard
    • Geomechanics and Engineering
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    • v.12 no.1
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    • pp.71-83
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    • 2017
  • Collapsible soil presents a porous unsaturated structure, its sudden settlement after humidification, without supplementary charge, can be of a big nuisance for the foundations and therefore for the constructions built on it. To improve its structure and limit its instability, samples of laboratory reconstituted soil, with different percentages of water contents and compacted at different compaction energies, were treated with glass-fiber. The study of the mechanical behavior was performed by oedometer tests. The microstructure was explored by the Scanning Electron Microscope (SEM). The results obtained show clearly the efficiency of the treatment with glass fiber on reducing the collapsibility of such soil.

Dielectric and Electrical Resistivity Characteristics of Saturated Clay Subjected to Consolidation (포화된 점토의 압밀과정에 따른 유전상수와 전기전도도의 변화)

  • Kim, Yong-Sung;Oh, Myoung-Hak;Bang, Sun-Young;Park, Jun-Boum
    • Proceedings of the Korean Geotechical Society Conference
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    • 2004.03b
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    • pp.791-798
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    • 2004
  • 압밀현상에 따른 포화된 점토의 유전특성과 전기비저항 특성을 분석하기 위해서 전기적 측정이 가능한 Oedometer 압밀시험기를 준비하였다. 포화된 카올리나이트 시료에 대해서 실시한 압밀시험 결과, 압밀현상에 따른 직류 전기비저항과 1MHz (저주파대) 유전상수는 간극수의 소산에 따라 선형으로 증가하는 경향을 보였다. 점토의 전기비저항 특성은 압밀 현상 시 발생하는 흙의 함수량 및 공극비의 감소, 즉 흙의 구조적 특성에 의하여 변하는 것으로 나타났다. 반면, 포화된 점토의 유전 특징은 불포화 점토와는 달리 흙 표면에서 발생하는 분극현상에 의하여 크게 영향을 받는 것으로 나타났다.

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Fast Consolidation Test Using Seepage Forces : Method and Validation (침투압을 이용한 급속압밀시험 : 방법 및 검증)

  • Lee, Kang-Il;Kim, Tae-Hyung;Znidarcic, Dobroslav
    • Journal of the Korean Geotechnical Society
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    • v.25 no.4
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    • pp.31-38
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    • 2009
  • A continuous, fast, and convenient experimental method, replacing recent tests such as standard oedometer or self weight consolidation test, is needed for the determination of the consolidation behavior of unformed soft soils. This study introduced the seepage induced fast consolidation test using the flow pump technique. It can obtain the consolidation characteristics of unformed soft soils conveniently and fast. The seepage induced consolidation test apparatus consists of a modified triaxial cell, differential pressure transducer, flow pump, and displacement transducer. The test continuously proceeds with starting seepage forces induced consolidation, loading consolidation, and permeability test on the same sample. In addition, this test result was compared with the standard oedometer test result to make this method valid. From this study it was found that this method is a convenient and time saving effective method for obtaining data required for calculation of consolidation settlement of unformed soft soils.

Permeability Characteristics of Soft Clay using the Piezocone Test and a Laboratory Test (피에조 콘 시험과 실내시험을 이용한 점토지반의 투수특성 연구)

  • Gu, Nam-Sil;Kim, Young-Min;Park, Jae-Hwhan;Jang, Ji-Guen
    • The Journal of Engineering Geology
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    • v.21 no.4
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    • pp.349-359
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    • 2011
  • The consolidation behavior of soft clay is controlled mainly by its compressibility and deformation characteristics. Soil permeability depends on various soil characteristics, including the soil type and anisotropy. The coefficient of permeability of soft clay is determined by using a laboratory test (the Oedometer test) or a piezocone test. The latter test is useful for estimating the permeability characteristics from $c_h$ and $k_h$ by performing an excess pore-pressure dissipation test. This study seeks to validate an existing theoretical formula in applying it to marine clay, and to assess the relation between $k_h/k_c$ and the mechanical properties of soft clay. Piezocone tests and laboratory tests were performed using sediment from the Yellow Sea and from the South Sea near Korea. We compared $k_h/k_v$ values obtained using the piezocone test and using laboratory consolidation tests. The obtained values are similar to the values obtained by Jamiolkowski et al. (M application); therefore, the latter values are recommended to be used as $k_h/k_v$.

Shear Strength and One-dimensional Compression Characteristics of Granitic Gneiss Rockfill Dam Material (화강편마암 댐 축조재료의 전단강도 및 일차원 압축특성)

  • Kim Bum-Joo;Kim Yong-Seong;Shin Dong-Hoon
    • Journal of the Korean Geotechnical Society
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    • v.21 no.7
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    • pp.31-42
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    • 2005
  • In this study, a rockfill-dam material was investigated on its shear strength and compressibility by performing large-scaled triaxial and oedometer tests. The rockfill material was compacted at two different compaction levels and sheared in triaxial compression at three different confining stresses. Also, rockfill samples were prepared to have three different grain size distributions but the same dry density. Each sample with a given grain size distribution was then compressed one-dimensionally in a large-scaled oedometer cell with and without soaking. The rockfill samples exhibited slightly different shear behaviors with the varying compaction and confining stress levels. The increase in the compaction level changed the behavior from contractive to dilative. Dilation decreased gradually with increasing confining stress, resulting in reduction in the peak shear strength. The large-scaled oedometer test results showed that particle breakages increased with increasing average particle sizes of the samples. Comparing the samples with different gradations, a relatively well-graded sample exhibited lower compressibility. For saturated samples, slightly higher deformations were observed, compared to dry samples. The values of tangent constrained modulis for the dry samples were larger by about 10 to 20$\%$, on the average, than those for the saturated samples.

Evaluation of Permeability Characteristics of Yangsan Clay using Piezocone Penetration Tests and Laboratory Tests (피에조 콘 시험과 실내시험을 이용한 양산점토의 투수특성 평가)

  • Gu, Namsil;Kim, Youngmin;Park, Jaehwhan
    • Journal of the Korean GEO-environmental Society
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    • v.12 no.12
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    • pp.47-54
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    • 2011
  • Consolidation behavior of soft clay is generally to be affected by its compressibility and deformation characteristics. Especially, soil permeability depends on soil characteristics including its type of anisotropy. Coefficient of permeability of soft clay is mostly estimated by using laboratory(Oedometer test) and in-stiu piezocone test. The permeability characteristics of soft clay is estimated by excess pore pressure dissipation test results. In this study, the tests were performed to find out the validity of the existing theoretical formula in clay by pore pressure dissipation test and laboratory test results. After grasping of variation the coefficient of permeability ratio(${k_{h}/k_{v}}$) in different clay soils, it was found out adequate solution of in-stiu permeability ratio(${k_{h}/k_{v}}$). Piezocone tests and laboratory tests were performed at the site of pilot project of ground improvement at Yangsan-Mulgeum, Gyeongsangnam-do. Comparisons of the estimated values of ${k_{h}/k_{v}}$ using piezocone tests results and those from laboratory consolidation tests were carried out. Test results show that values of ${k_{h}/k_{v}}$ by piezocone test result(5.85) is similar of it's laboratory test(5.28).

Evaluation of Consolidation Properties in Soft Soils Using Elastic and Electromagnetic Waves (전단파와 전자기파를 이용한 연약 지반의 실내 압밀 특성 평가)

  • Lee, Chang-Ho;Yoon, Hyung-Koo;Kim, Joon-Han;Lee, Jong-Sub
    • Journal of the Korean Geotechnical Society
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    • v.24 no.8
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    • pp.25-34
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    • 2008
  • A new hybrid oedometer cell is designed and manufactured to investigate a behavior of soft soils by using elastic and electromagnetic waves during consolidation test. Bender elements, which generate and detect shear waves, are placed in the top cap and the bottom plate and mounted on the oedometer wall. Double wedge type electrical resistance probe, which measures local void ratio change, is positioned onto the top cap of the oedometer cell. The bender elements and the electrical resistance probe are anchored into a nylon set screw with epoxy resin. The nylon set screw with epoxy resin minimizes directly transmited elastic waves through the oedometer cell due to impedence mismatch and allows for easy replacement of defected bender elements and electrical resistance probe. Primary consolidation time can be estimated from the slope of electrical resistance versus log time curve and the evolution of shear wave velocity. The shear wave velocity can be used to assess inherent anisotropy when disturbance effects are minimized because particle alignment affects the shear wave velocity. The void ratios evaluated by the electrical resistance probe are similar to those by the settlement during consolidation. This study suggests that the shear wave velocity and the electrical resistance can provide complementary imformations to understand consolidation characteristics such as primary consolidation, anisotropy, and void ratio.

The Prediction Method of the Small Strain Shear Modulus for Busan Clay Using CPT and DMT (CPT와 DMT를 이용한 부산점토의 최대전단탄성계수 추정방법에 관한 연구)

  • Hong, Sung-Jin;Yoon, Hyung-Ko;Lee, Jong-Sub;Lee, Woo-Jin
    • Journal of the Korean Geotechnical Society
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    • v.25 no.6
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    • pp.5-16
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    • 2009
  • The is study is to evaluate the small strain shear modulus ($G_{max}$) of Busan clay using in-situ penetration tests. A series of dilatometer tests (DMT) and piezocone penetration tests (CPTu) are performed at Busan newport and Noksan sites, and hybrid oedometer tests are also carried out on the specimens obtained from both sites. The $G_{max}$ is evaluated from the shear wave velocity ($V_s$) measured by the bender elements installed at the boundary of oedometer cell. By analyzing these data, the relationship of $G_{max}$ and state variables, such as confined stress and void ratio, is developed. The analysis of lab and in-situ test results reveals that the ratio of $G_{max}$ to $q_t$ is inversely proportional to the plasticity index while the ratio of $G_{max}$ to $E_D$ has a linear relationship with ($I/I_D$)$(p_a/{\sigma}'_v)^{0.5}$. Two correlations suggested in this study, based on CPT and DMT results, appear to provide reasonable predictions of the small strain shear modulus.

Approximate Prediction of Soil Deformation Caused by Repeated Loading (반목하중으로 인한 지반의 변형 예측)

  • 도덕현
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.30 no.3
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    • pp.69-81
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    • 1988
  • The Repeated Load Triaxial and Oedometer Tests to the weathered granite & silty clay soil have been fulfilled to investigate their dynarnic characteristics. The results obtained are summarized as follows ; 1. In the relation between the repeated triaxial compression and the oedometer test, the recoverable strain of weathered granite soil showed a tendency to decrease by the increase of the repeated loads number(N), and that of silty clay showed approximately constant values while the total strain increased continuously. 2. The changes of plastic strain was dependent to the level of deviator stress which is the most important element in the calculation of soil deformation under repeated load condition. And there was a significance of 10% between the level of stress and plastic strain. 3. When the soil was aimost dried or saturated to 100%, the deformation by the repeated loads was small. However the deformation showed peak around the saturation of 50%. 4. When the deformation was predicted by the repeated triaxial load tests of a laboratory, it is desirable to introduce the threshold stress concept in the calculation of deformation of subgrade of the pavement. 5. The improved design equation (Eq. 16) introducing the modulus of conversion(Fo), which is based on the Boussineq' s theory, is considered to be rational in the design of flexible pavement. From the above results, the deformation to the repeated traffic loads could be predicted by the repeated triaxial tests on the pavement materials or undisturbed soil layers, therefore it is think that the durable and econornic pavement could be constructed by reflecting that to the design.

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Time-dependent behaviour of interactive marine and terrestrial deposit clay

  • Chen, Xiaoping;Luo, Qingzi;Zhou, Qiujuan
    • Geomechanics and Engineering
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    • v.7 no.3
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    • pp.279-295
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    • 2014
  • A series of one-dimensional consolidation tests and triaxial creep tests were performed on Nansha clays, which are interactive marine and terrestrial deposits, to investigate their time-dependent behaviour. Based on experimental observations of oedometer tests, normally consolidated soils exhibit larger secondary compression than overconsolidated soils; the secondary consolidation coefficient ($C_{\alpha}$) generally gets the maximum value as load approaches the preconsolidation pressure. The postsurcharge secondary consolidation coefficient ($C_{\alpha}$') is significantly less than $C_{\alpha}$. The observed secondary compression behaviour is consistent with the $C_{\alpha}/C_c$ concept, regardless of surcharging. The $C_{\alpha}/C_c$ ratio is a constant that is applicable to the recompression and compression ranges. Compared with the stage-loading test, the single-loading oedometer test can evaluate the entire process of secondary compression; $C_{\alpha}$ varies significantly with time and is larger than the $C_{\alpha}$ obtained from the stage-loading test. Based on experimental observations of triaxial creep tests, the creep for the drained state differs from the creep for the undrained state. The behaviour can be predicted by a characteristic relationship among axial strain rate, deviator stress level and time.