• Title/Summary/Keyword: Granular soils

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Numerical modeling of dynamic compaction process in dry sands considering critical distance from adjacent structures

  • Pourjenabia, Majid;Hamidi, Amir
    • Structural Engineering and Mechanics
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    • v.56 no.1
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    • pp.49-56
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    • 2015
  • Dynamic compaction (DC) is a useful method for improvement of granular soils. The method is based on falling a tamper (weighting 5 to 40 ton) from the height of 15 to 30 meters on loose soil that results in stress distribution, vibration of soil particles and desirable compaction of the soil. Propagation of the waves during tamping affects adjacent structures and causes structural damage or loss of performance. Therefore, determination of the safe or critical distance from tamping point to prevent structural hazards is necessary. According to FHWA, the critical distance is defined as the limit of a particle velocity of 76 mm/s. In present study, the ABAQUS software was used for numerical modeling of DC process and determination of the safe distance based on particle velocity criterion. Different variables like alluvium depth, relative density, and impact energy were considered in finite element modeling. It was concluded that for alluvium depths less than 10 m, reflection of the body waves from lower boundaries back to the soil and resonance phenomenon increases the critical distance. However, the critical distance decreases for alluvium depths more than 10 m. Moreover, it was observed that relative density of the alluvium does not significantly influence the critical distance value.

Behavior of Shear Zone by Improved Direct Shear Test (개선된 직접전단시험을 이용한 전단영역의 거동)

  • Byeon, Yong-Hoon;Truong, Q. Hung;Tran, M. Khoa;Lee, Jong-Sub
    • Proceedings of the Korean Geotechical Society Conference
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    • 2010.03a
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    • pp.607-614
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    • 2010
  • Shear behavior of granular soils largely affects the safety and stability of underground and earth structures. This study presents the characteristics of shear zone in a direct shear test using shear wave and electrical resistivity measurements. An innovative direct shear box made of transparent acrylic material has been developed to prevent direct electric current. Bender elements and electrical resistivity probe are embedded in the wall of direct shear box to estimate the shear wave velocities and the electrical resistivity at the shear and non-shear zones. Experimental results show that the void ratio and shear wave velocity at shear zone increase during shearing while the values remain constant at non-shear zone. The results demonstrate correlation among the contact force, small strain shear modulus, and void ratio at shear zone. This study suggests that the application of the modified direct shear box including shear wave and electrical resistivity measurements may become an effective tool for analyzing soil behavior at shear zone.

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Heading Failure Modes during Underground Excavation (지하공간 건설에 따른 굴착전면의 파괴모드)

  • Kwon, Oh-Yeob;Cho, Jae-Wan;Shin, Jong-Ho;Choi, Ypng-Ki;Shin, Yong-Suk
    • Proceedings of the Korean Geotechical Society Conference
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    • 2005.03a
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    • pp.409-416
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    • 2005
  • Design analysis for underground spaces requires evaluating stability related to tunnel collapses. A failure mode is one of the critical factors in the conventional methods of stability analysis. Therefore identification of failure modes is essential in securing safe construction in the phase of design analysis, instrumentation planning and implementation of reinforcing measures. In this study failure modes at the tunnel heading in granular soils are investigated using physical model tests and numerical simulation for various tunnel depths and ground surface inclinations. Test results indicated that the effect of depth and inclination of ground surface on a failure mode are significant. It is identified that, with an incase in depth, failure modes become localized in a region close to the tunnel. It is also known that an increase in the inclination of ground surface results in inclined and wide failure modes.

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Nonlinear Subgrade Model-Based Comparison Study between the Static and Dynamic Analyses of FWD Nondestructive Tests (노상의 비선형 모델에 근거한 비파괴 FWD 시험에 있어 정적과 동적 거동의 비교연구)

  • Mun, Sungho
    • International Journal of Highway Engineering
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    • v.19 no.1
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    • pp.73-80
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    • 2017
  • PURPOSES : This paper presents a comparison study between dynamic and static analyses of falling weight deflectometer (FWD) testing, which is a test used for evaluating layered material stiffness. METHODS: In this study, a forward model, based on nonlinear subgrade models, was developed via finite element analysis using ABAQUS. The subgrade material coefficients from granular and fine-grained soils were used to represent strong and weak subgrade stiffnesses, respectively. Furthermore, the nonlinearity in the analysis of multi-load FWD deflection measured from intact PCC slab was investigated using the deflection data obtained in this study. This pavement has a 14-inch-thick PCC slab over fine-grained soil. RESULTS: From case studies related to the nonlinearity of FWD analysis measured from intact PCC slab, a nonlinear subgrade model-based comparison study between the static and dynamic analyses of nondestructive FWD tests was shown to be effectively performed; this was achieved by investigating the primary difference in pavement responses between the static and dynamic analyses as based on the nonlinearity of soil model as well as the multi-load FWD deflection. CONCLUSIONS : In conclusion, a comparison between dynamic and static FEM analyses was conducted, as based on the FEM analysis performed on various pavement structures, in order to investigate the significance of the differences in pavement responses between the static and dynamic analyses.

Advanced Evaluation of In-situ Strength using CPT results (콘관입시험을 이용한 지반강도의 상세평가해석)

  • Lee, Jun-Hwan;Kang, Byung-Jun;Kyung, Doo-Hyun;Hong, Jung-Mu
    • Proceedings of the Korean Geotechical Society Conference
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    • 2008.10a
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    • pp.111-116
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    • 2008
  • 콘관입시험(CPT)은 의사정적상태로 수행되는 현장시험방법으로서, 각종 기초구조물의 설계와 더불어 지반조사를 위한 대표적 방법으로 널리 적용되고 있다. 본 논문에서는 콘관입시험결과를 이용하여 사질토 지반에 있어서 지반강도의 상세평가법을 제안하고자 한다. 사질토의 강도는 상대밀도와 응력상태에 따라 변하는 상태의존적 성질을 나타내고 있으나, 이러한 역학적 성질은 실험실 내에서만 측정이 가능한 상태이며, 현장강도의 경험식이나, 대표강도의 평가만이 제안되어 있는 실정이다. 따라서 본 연구에서는 대표적 현장시험방법인 CPT를 이용하여 다이러턴시 특성 평가가 가능하며, 다양한 지반특성치가 반영될 수 있는 현장강도의 상세평가법을 제안하고자 한다. 이를 위해 실내삼축압축시험을 통해 얻어진 강도특성과 역학특성치들을 분석하였으며, 이를 토대로 수정 다일러턴시 평가법을 제안하였다. 제안된 방법의 검증을 위해 가압토조를 이용한 콘관입시험을 수행하였으며, 측정값과의 비교분석을 수행하였다.

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Deformation Characteristics of Granular Ark Shell-Loess Mixtures due to the Cyclic Loading (반복재하에 의한 고막껍질-황토 혼합토의 변형 특성)

  • Chang, Yong-Chai;Seo, Ji-Woong;Lee, Seung-Eun;Lee, Kang-Il
    • Proceedings of the Korean Geotechical Society Conference
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    • 2008.10a
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    • pp.1377-1388
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    • 2008
  • In our country where over 80% of land is mountainous, decomposed granite soils are often used as building materials for civil engineering works. Seashores are having great difficulties in management and treatment of marine byproducts that are left vulnerable. It is necessary to find a way to efficiently utilize such vulnerable marine byproducts. For this reason, shell and ocher were mixed together in order to efficiently utilize ocher that is being used frequently as a building material in civil works and shell that is a type of marine byproducts being thrown away. The purpose of this study is to examine the extent to which shell-ocher mixture can reduce liquefaction through cyclic triaxial test. The author of this study aims to provide the possibility for application at construction site of shell-ocher mixture.

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Evaluation of Compaction Properties of Subgrade Soil by Gyratory Compaction Curve (선회다짐곡선특성을 이용한 노상토의 다짐도 평가)

  • Lee, Kwan-Ho;Cha, Min-Kyung;Lim, Yu-Jin
    • Journal of the Korean Society of Hazard Mitigation
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    • v.9 no.1
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    • pp.33-40
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    • 2009
  • Compacted soil are used in almost roadway construction with compaction of soil. The direct consequence of soil compaction is densification, which in turn results in higher strength, lower compressibility, and lower permeability. The standard and modified Proctor tests are the most common methods. Both of these tests utilize impact compaction, although impact compaction shows no resemblance to any type of field compaction and is ineffective for granular soils. It has been dramatic advances in field compaction equipment. Therefore, the Proctor tests no longer represent the maximum achievable field density. The main objectives of this research are a survey of current field compaction equipment, laboratory investigation of compaction characteristics, and field study of compaction characteristics. The findings from the laboratory and compaction program were used to establish preliminary guidelines for suitable laboratory compaction procedures.

Effect of arbitrarily manipulated gap-graded granular particles on reinforcing foundation soil

  • Xin, Zhen H.;Moon, Jun H.;Kim, Li S.;Kim, Kab B.;Kim, Young U.
    • Geomechanics and Engineering
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    • v.17 no.5
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    • pp.439-444
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    • 2019
  • It is generally known that high strength soil is indicative of well-graded particle size distribution. However, there are some special cases of firm ground despite poor grade distribution, especially a specific gap-graded soil. Based on these discoveries, this study investigated the development of an additive of gap-graded soils designed to increase soil strength. This theoretical concept was used to calculate the mixed ratio required for optimal soil strength of the ground sample. The gap-graded aggregate was added according to Plato's polyhedral theory and subsequently calculated ratio and soil strength characteristics were then compared to characteristics of the original soil sample through various test results. In addition, the underground stress transfer rate was measured according to the test conditions. The test results showed that the ground settlement and stress limit thickness were reduced with the incorporation of gap-graded soil. Further field tests would confirm the reproducibility and reliability of the technology by using gap-graded soil to reinforce soft ground of a new construction site. Gap-graded soil has the potential to reduce the construction cost and time of construction compared to other reinforcing methods.

Changes in bound water and microstructure during consolidation creep of Guilin red clay

  • Zhang, Dajin;Xiao, Guiyuan;Yin, Le;Xu, Guangli;Wang, Jian
    • Geomechanics and Engineering
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    • v.30 no.5
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    • pp.471-478
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    • 2022
  • Creep of soils has a significant impact on mechanical properties. The one-dimensional consolidation creep test, thermal analysis test, scanning electron microscope (SEM) test, and mercury compression test were performed on Guilin red clay to study the changes in bound water and microstructure during the creep process of Guilin red clay. According to the results of the tests, only free and weakly bound water is discharged during the creep of Guilin red clay. When the consolidation pressure p is in the 12.5-400.0 kPa range, it is primarily the discharge of free water; when the consolidation pressure p is in the 800.0-1600.0 kPa range, the weakly bound water is converted to free water and discharged. After consolidation creep, the microstructure of soil changes from granular overhead contact structure to flat sheet-like stacking structure, with a decrease in the number of large and medium pores, an increase in the number of small and micro pores, and a decrease in the fractal dimension of pores. The creep process of red clay is the discharge of weakly bound water as well as the compression of large pores into small pores and the transition of soil particles from loose to dense.

An Experimental Study for Suggestion of Simple Method of Determining the Maximum Relative Density (최대상대밀도 산정 간편법 제안을 위한 실험연구)

  • Lee, Jong-Jin;Kim, Myong-Mo;Lee, Seung-Hyun;Kim, Byoung-Il
    • Journal of the Korean Geotechnical Society
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    • v.23 no.10
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    • pp.23-31
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    • 2007
  • Although the relative density is an important factor showing mechanical properties of granular soils, the methods for its estimation have not been satisfactorily standardized. Many researchers have proposed various methods to determine max, and min, dry density, but the results, especially for max, dry density, show significant differences. In this study, a simple and practical method of evaluating the max, relative density was proposed, which could give reliable results in comparison with conventional methods. The experiment was carried out by varying the number of blows and the layers of the sample for each mold and the results were compared with those of Bowles method.