The Influence of Dynamic Properties of Ground Soil on Vibration Characteristics of Rigid Body on Sand Ground

Yoon-Sang Kim,Tae-Gyun Ha,Jae-Jin Choi,Choong-Ki Chung 대한토목학회 2007 KSCE journal of civil engineering Vol.11 No.2

This study aims to investigate the influence of dynamic properties of the ground soil on vibration properties of a rigid body placed on the sand ground surface to clarify the vibration behavior of a structure in terms of the interaction between the structure and the ground. A series of cyclic triaxial tests and three types of model vibration tests were performed. The dynamic properties of ground soil were clarified using cyclic triaxial tests. It was found that the equivalent shear modulus markedly depends on confining pressure and relative density, and that the hysteresis-damping ratio also depends on confining stress but not upon relative density. In model vibration tests, rigid body models with variable masses, inertial moment, base size and base shape were prepared and their vibration behaviors were observed. Vibration characteristics were estimated from the observed behavior, and the period and damping ratio were examined. It was found that the period depends on not only the mechanical properties of the rigid body and the relative density of ground, but also upon the magnitude of the vibration amplitude. A simple model of a spring and a dashpot was used to correlate period and damping ratio of ground soil in a model vibration test with equivalent shear modulus and hysteresis damping ratio by cyclic triaxial testing. The relationship between normalized inverse squares of the period and rotation amplitude was similar to the relationship between the normalized equivalent shear modulus and the shear strain amplitude. Normalized damping ratio also showed good agreement with the normalized hysteresis-damping ratio. The calculated equivalent shear modulus from the simple model linearly increased with increased average contact pressure, as the equivalent shear modulus of the cyclic triaxial test linearly increased with effective confining pressure on a log-log scale.

대형 직접전단시험과 대형 삼축압축시험에 의한 조립재료의 전단강도 비교

서민우(Seo Minwoo),김범주(Kim Bumjoo),하익수(Ha Iksoo) 한국지반환경공학회 2009 한국지반환경공학회논문집 Vol.10 No.1

댐이나 항만 건설시 재료로 사용되는 조립재는 입자크기가 일반 토사에 비해 매우 크기 때문에 이러한 재료에 대해서 전단시험을 수행할 때에는 가급적 대형 전단시험장치를 사용하는 것이 보다 정확한 결과를 얻기 위해 바람직하다. 대형 전단시험장치로는 일반적으로 대형 직접전단시험장치와 대형 삼축압축시험장치가 있으나 일반 토질시험장치와 비교해 제작과 보급, 운영 등의 어려움 때문에 현재까지 국내에서 두 시험장치를 사용하여 시험을 수행한 실적은 많지 않은 편이다. 본 연구에서는 댐 축조재로 사용되는 입경이 큰 조립재료를 대상으로 시료의 평균 입자크기와 공시체 크기, 연직응력(구속압) 조건 등에 차이가 있는 총 6개 case에 대해서 대형 직접전단시험과 대형 삼축압축시험을 수행하고 두 시험간 전단강도 특성의 차이를 비교하였다. Mohr-Coulomb 강도규준에 의한 전단강도를 기준으로, 대형 직접전단시험을 통해 산정된 전단강도가 대형 삼축압축시험을 통해 산정된 전단강도보다 전체적으로 크게 나타났으며 또한, 1,000㎪ 수직응력에 대해 두 시험간 산정된 전단강도를 비교한 결과 대형 직접전단시험에 의한 전단강도가 대형 삼축압축시험에 의한 전단강도보다 약 10∼70% 크게 나타나 입경이 작은 일반 토사와 비교해 그 차이가 크고, 대형 직접전단시험결과의 분산도가 상대적으로 높은 것으로 나타났다. Since the particle sizes of the coarse materials used in dam or harbor constructions are much larger than those of typical soils, it is desirable that large shear testing apparatuses are used when performing shear tests on the coarse materials to obtain as accurate results as possible. Two large-scale shear testing apparatuses, large direct shear testing apparatus and large triaxial shear testing apparatus, are commonly used. Currently in Korea, however, there have not been many cases in which shear tests were done using the large apparatus due to mainly difficulties in manufacturing, diffusing, and operating them. In present study, both large direct shear tests and large triaxial shear tests were performed on the coarse materials, which are used as dam fill materials, for 6 test cases in which particle sizes, specimen sizes, vertical pressure (confining pressure) conditions were little different, and then, the shear strength characteristics of the materials were compared with the two different shear tests. The test results showed that, by the Mohr-Coulomb failure criterion, overall the shear strength obtained by the large direct shear tests was larger than that by the large triaxial shear tests. Moreover, the shear strength under the normal stress of 1,000 ㎪ was about 10 to 70% larger for the large direct shear tests than for the large triaxial shear tests, revealing the larger differences in the coarse materials, compared to typical soils.

A Review of Advances in Triaxial Tests: Instruments, Test Techniques and Prospects

Jitao Bai,Yu Diao,Chenhang Jia,Chongyang Liu,Menghan Zhang,Chu Wang 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.8

Triaxial test is approved to be the most suitable method for studying the mechanical properties of rocks and soils in lab. Through conventional triaxial tests, parameters like the strength of rocks and soils can be obtained, thus providing guidance for the design and construction of geotechnical engineering. With the development of geotechnical engineering, more and more new problems that can hardly be solved by conventional triaxial tests have arisen, which can be classified into two categories: one is the mechanical properties of special soils (rocks), and the other is the mechanical properties of the soils (rocks) under special conditions like geologic hazards and multi-field coupling. The paper introduced several new types of triaxial instruments and test techniques developed in response to the problems, and prospects have been made for further study of triaxial tests, which may provide reference for the optimization of triaxial tests.

반복삼축압축시험을 이용한 주문진 표준사의 동적변형특성 분석

김유성,고형우,이진광,김재홍 한국지반공학회 2012 한국지반공학회논문집 Vol.28 No.12

In this study, the modified cyclic triaxial tests with Joomunjin standard sand are performed for dynamic deformation characteristics, such as Young’s moduli and damping ratio. The cyclic triaxial test is equipped with Local Displacement Transducer (LDT) on the outside of a cell which has a range from 10-4 to 10-1 of shear strains,  (%), instead of conventional cyclic triaxial test which has linear variable displacement transducer (LVDT) with low precision. With the small strain control, tests were carried out at various loading rates, void ratios, and effective confining pressures. Based on the test results, such as dynamic deformation characteristics, shear modulus, and damping ratio, it is found that the test can measure more range of medium strains (0.02-0.2%) than results obtained from conventional test (resonant column test). For the medium strain range, dynamic deformation characteristics investigated by the cyclic triaxial test are also different from those predicted by nonlinear model in conventional test.

대형직접전단시험과 대형삼축시험을 통한 석산골재의 전단거동 특성 비교

이대수,김경열,오기대 한국지반공학회 2008 한국지반공학회논문집 Vol.24 No.2

Shear characteristics of quarry blasted rocks were compared using large scale direct shear tests and triaxial tests. For comparison purpose, similar test conditions were simulated as much as possible and three types of relative density (50%, 70%, 90%) were employed for the test. Results indicate that stress-strain behavior shows the same trend for two tests, but the measured shear strengths differ for the different test ms and depends on the relative density. At low relative density, the internal friction angles from direct shear test are smaller than those from triaxial tests. However, at high relative density, this phenomenon is reversed.

DMT를 이용한 부산신항 점토의 비배수 전단강도 추정

홍성진,신동현,김동휘,정상진,이우진 한국지반공학회 2007 한국지반공학회논문집 Vol.23 No.7

A series of dilatometer test, field vane test, and CK0U triaxial test were performed for clayey soils of Busan new port site to develop the relationships between undrained shear strength and the DMT results. Normalized undrained shear strength is turned out to be su(CKU)/σ'v=0.30~0.35 for CK0U triaxial test and μsu(VST)/σ'v=0.20~0.22 for vane shear test. By comparing the undrained shear strength estimated from DMT indices with the results measured by in-situ vane test or CK0U triaxial test, two methods to predict the undrained shear strength from DMT results are suggested. One is based on the relationship between su/σ'v and horizontal stress index (KD) while another method comes from Nc-ID and Nc-ED correlation. It was observed that the method based on Nc-ID or Nc-ED relation shows slightly better accuracy than the one based on KD although all of the methods suggested in this study provided comparable values of predicted undrained shear strength. Since the definitions of ID and ED contain p1-p0, in which soil condition is reflected, it is believed that the prediction method using Nc is capable of taking a material type into consideration.

준설토-저회-폐타이어 혼합경량토의 전단 및 CBR 특성

김윤태(Yun-Tae Kim),강효섭(Hyo-Sub Kang) 한국해양공학회 2011 韓國海洋工學會誌 Vol.25 No.3

This study investigated the shear and CBR characteristics of dredge soil-bottom ash-waste tire powder-mixed lightweight soil, which was developed to recycle dredged soil, bottom ash, and waste tire powder. Test specimens were prepared with various contents of waste tire powder ranging from 0 to 100% at 50% intervals by the weight if the dry dredged soil. Several series of triaxial compression tests and CBR tests were conducted. The shear strength characteristics if the lightweight soil were compared using two different shear tests (triaxial compression test and direct shear test). The experimental results indicated that the internal friction angle if the lightweight soil obtained by the direct shear tests was greater than that by the triaxial shear tests. However, the cohesion value obtained by the triaxial shear tests was greater than that by the direct shear tests. The CBR value if the lightweight soil decreased from 35% to 15% as waste tire powder content increased

Behaviors of Soft Bangkok Clay behind Diaphragm Wall Under Unloading Compression Triaxial Test

Nghia Trong Le,Wanchai Teparaksa,Toshiyuki Mitachi,Takayuki Kawaguchi 한국지반공학회 2007 한국지반공학회논문집 Vol.23 No.9

The simple linear elastic-perfectly plastic model with soil parameters su, Eu and n of undrained condition is usually applied to predict the displacement of a constructed diaphragm wall (DW) on soft soils during excavation. However, the application of this soil model for finite element analysis could not interpret the continued increment of the lateral displacement of the DW for the large and deep excavation area both during the elapsed time without activity of excavation and after finishing excavation. To study the characteristic behaviors of soil behind the DW during the periods without excavation, a series of tests on soft Bangkok clay samples are simulated in the same manner as stress condition of soil elements happening behind diaphragm wall by triaxial tests. Three kinds of triaxial tests are carried out in this research: K0 consolidated undrained compression (CK0UC) and K0 consolidated drained/ undrained unloading compression with periodic decrement of horizontal pressure (CK0DUC and CK0UUC). The study shows that the shear strength of series CK0DUC tests is equal to the residual strength of CK0UC tests. The Young’s modulus determined at each decrement step of the horizontal pressure of soil specimen on CK0DUC tests decreases with increase in the deviator stress. In addition, the slope of Critical State Line of both CK0UC and CK0DUC tests is equal. Moreover, the axial and radial strain rates of each decrement of horizontal pressure step of CK0DUC tests are established with the function of time, a slope of critical state line and a ratio of deviator and mean effective stress. This study shows that the results of the unloading compression triaxial tests can be used to predict the diaphragm wall deflection during excavation.

Behaviors of Soft Bangkok Clay behind Diaphragm Wall Under Unloading Compression Triaxial Test

Le, Nghia Trong,Teparaksa, Wanchai,Mitachi, Toshiyuki,Kawaguchi, Takayuki Korean Geotechnical Society 2007 한국지반공학회논문집 Vol.23 No.9

The simple linear elastic-perfectly plastic model with soil parameters $s_u,\;E_u$ and n of undrained condition is usually applied to predict the displacement of a constructed diaphragm wall(DW) on soft soils during excavation. However, the application of this soil model for finite element analysis could not interpret the continued increment of the lateral displacement of the DW for the large and deep excavation area both during the elapsed time without activity of excavation and after finishing excavation. To study the characteristic behaviors of soil behind the DW during the periods without excavation, a series of tests on soft Bangkok clay samples are simulated in the same manner as stress condition of soil elements happening behind diaphragm wall by triaxial tests. Three kinds of triaxial tests are carried out in this research: $K_0$ consolidated undrained compression($CK_0U_C$) and $K_0$ consolidated drained/undrained unloading compression with periodic decrement of horizontal pressure($CK_0DUC$ and $CK_0UUC$). The study shows that the shear strength of series $CK_0DUC$ tests is equal to the residual strength of $CK_0UC$ tests. The Young's modulus determined at each decrement step of the horizontal pressure of soil specimen on $CK_0DUC$ tests decreases with increase in the deviator stress. In addition, the slope of Critical State Line of both $CK_0UC$ and $CK_0DUC$ tests is equal. Moreover, the axial and radial strain rates of each decrement of horizontal pressure step of $CK_0DUC$ tests are established with the function of time, a slope of critical state line and a ratio of deviator and mean effective stress. This study shows that the results of the unloading compression triaxial tests can be used to predict the diaphragm wall deflection during excavation.

퇴적연암의 비선형특성 조사.시험기법에 관한 연구

김유성 한국지반공학회 1996 지반 : 한국지반공학회지 Vol.12 No.5

퇴적연암의 변형특성을 조사하기 위하여 여러 종류의 실내시험과 원위치시험결과를 비교검토 하였다. 초음파측정시험 등의 실내시험에서 불구속 시료의 탄성계수는 원위치유효토피압에 해당하는 압밀구속압으로 구속한 시료의 탄성계수 보다 현저히 작았다. 또 삼축압축시험에서 재하피 스톤의 축변위로 부터 구한 축변형률은 시료 상.하단에서의 오차(bedding error)로 인하여 정확히 측정할 수 없고, 전체적으로 신뢰할 수 없다. 따라서 시료측면에서 직접 변형률을 측정하는 국소변형측정장치를 이용하여 0.001% 이하에서 약 1%까지 연속적으로 위와 같은 오차를 제거한 축변형률을 얻을 수 있었고, 0.00% 이하 축변형률에서 정의된 탄성계수 Emax는 원위치탄성 파속도시험으로 얻어진 탄성계수 Er와 거의 일치하였다. 변형률이 0.01%에 도달하기 이전에 변형은 비선형성을 보이기 시작하고, 실제 원위치 작용하중 범위에서 예상할 수 있는 최대변형률 0.1%에서의 할선탄성계수 Esec는 Emax의 1/2보다 여전히 큰 값을 보인다. 위와 같은 내용을 골자로 하여 정밀측정실내시험 결과에 따른 변형특성과 현장거동 및 원위치측정결과의 비교검토를 통해 변형률레벨을 고려한 원위치 탄성계수 추정법을 제안하였다. Various type of in-situ and laboratary tests were performed in order to evaluate the stiffness of sedimentary soft rock. In triaxial compression tests of sedimentary soft rocks, axial strains from the axial displacement of the loading piston or specimen cap conventionally were considerably larger than those measured. tocally on the lateral surfaces of specimen, due to the bedding errors at the top and bottom ends of a specimen. A local deformation transducer was used to measure axial strains free from the bedding error ranging from 0.001% to about 1%. In ultra-sonic wave tests, the elastic modulus of unconfined spec imens was smaller than that of confined specimens, due probably to microfracks. Young's modulus Ed from ultra-sonic wave tests and those at small local strains from triaxial tests were similar, both of which agreed very well with Young's modulus Er from field shear wave velocities. Young'a modulus from the field behaviour was virtually similar to that obtained by reducing Er based on the strain level-dependency of stiffness evaluated by the triaxial tests.