• Earthquakes and Structures
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• 제26권2호
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• pp.97-115
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• 2024

In this paper, a database consisting of the dynamic shear modulus ratio and damping ratio test data of clay obtained from 406 groups of triaxial tests is constructed with the starting area of Xiong'an New Area as the research background. The aim is to study the nonlinear dynamic properties of clay in this area under cyclic loading. The study found that the effective confining pressure and plasticity index have certain influences on the dynamic shear modulus ratio and damping ratio of clay in this area. Through data analysis, it was found that there was a certain correlation between effective confining pressure and plasticity index and dynamic shear modulus ratio and damping ratio, with fitting degree values greater than 0.1263 for both. However, other physical indices such as the void ratio, natural density, water content and specific gravity have only a small effect on the dynamic shear modulus ratio and the damping ratio, with fitting degree values of less than 0.1 for all of them. This indicates that it is important to consider the influence of effective confining pressure and plasticity index when studying the nonlinear dynamic properties of clays in this area. Based on the above, prediction models for the dynamic shear modulus ratio and damping ratio in this area were constructed separately. The results showed that the model that considered the combined effect of effective confining pressure and plasticity index performed best. The predicted dynamic shear modulus ratio and damping ratio closely matched the actual curves, with approximately 88% of the data falling within ±1.3 times the measured dynamic shear modulus ratio and approximately 85.1% of the data falling within ±1.3 times the measured damping ratio. In contrast, the prediction models that considered only a single influence deviated from the actual values, particularly the model that considered only the plasticity index, which predicted the dynamic shear modulus ratio and the damping ratio within a small distribution range close to the average of the test values. When compared with existing prediction models, it was found that the predicted dynamic shear modulus ratio in this paper was slightly higher, which was due to the overall hardness of the clay in this area, leading to a slightly higher determination of the dynamic shear modulus ratio by the prediction model. Finally, for the dynamic shear modulus ratio and damping ratio of the engineering site in the starting area of Xiong'an New Area, we confirm that the prediction formulas established in this paper have high reliability and provide the applicable range of the prediction model.

• Geomechanics and Engineering
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• 제32권4호
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• pp.411-426
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• 2023

Soft clay is widely distributed in the southeast coastal areas of China. Many large underground structures, such as subway stations and underground pipe corridors, are shallow buried in the soft clay foundation, so the dynamic characteristics of the soft clay must be considered to the seismic design of underground structures. In this paper, the dynamic characteristics of saturated soft clay in Shanghai under the bidirectional excitation for earthquake loading are studied by dynamic triaxial tests, comparing the backbone curve and hysteretic curve of the saturated soft clay under different confining pressures with those under different vibration frequencies. Considering the coupling effects of the confining pressure and the vibration frequency, a fitting model of the maximum dynamic shear modulus was proposed by the multiple linear regression method. The M-D model was used to fit the variations of the dynamic shear modulus ratio with the shear strain. Based on the Chen model and the Park model, the effects of the consolidation confining pressure and the vibration frequency on the damping ratio were studied. The results can provide a reference to the earthquake prevention and disaster reduction in soft clay area.

• 한국농공학회논문집
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• 제47권6호
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• pp.59-70
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• 2005

A series of resonant column test was performed to investigate the dynamic deformation characteristics of silty sand soils mixed with polypropylene fibrillated type fiber. Results show that optimum mixing ratios were $0.2\%$ for 19mm of cut fiber for shear modulus and $0.1\%$ for 60mm cut fiber fur damping ratio. As shear strain was increased, normalized values of shear modulus (G(Reinforced)/ G(Unreinforced)) of fiber reinforced soil were increased up to $10^{-3}\%\~10^{-1}\%$ ranges. However, normalized damping ratio (D(Reinforced/D(Unreinforced)) was diminished with an increase in strain beyond $10^{-3}\%\~10^{-1}\%$ for the damping capacity of soils mixed with fiber. Normalized shear modulus $(G/G_{max})$ obtained from the test was plotted in the chart suggested by Seed and Idriss. The shear modulus of silty sand was located between sand and gravel curves.

• 한국지반환경공학회 논문집
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• 제12권5호
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• pp.59-63
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• 2011

전단탄성계수와 감쇠비와 같은 동적지반계수는 반복하중과 동적하중을 받는 지반구조물 설계에서 중요한 요소이다. 선형 한계변형률 내에서 미소변형률에 관한 전단탄성계수와 감쇠비는 변형률과 관계없이 일정하다. 전단탄성계수는 최대전단탄성계수로 감쇠비는 최소 감쇠비로 고려하였다. 동적변형특성 범주내의 최대선형탄성계수에 관련된 많은 시험들이 수행됨과 동시에 간극비, 과압밀비, 구속압, 지질이력, PI 그리고 하중주기수에 관련된 많은 인자들이 동적지반특성에 영향을 미친다. 그러나 그라우팅에 의해 향상된 지반동적특성에 관한 연구는 지하연속벽시공, 심층혼합처리공법, 강관다단그라우팅과 같이 미비한 실정이다. 본 논문에서는 그라우팅에 의해 향상된 동적지반특성을 연구하기 위하여 함수비(20%, 25%, 30%), 그라우트 주입율(5%, 10%, 15%),양생기간(7일, 28일)을 변화시키면서 공진주시험을 실시하였다. 그 결과, 밀크 그라우트의 주입율과 재령, 함수비에 따라 동적계수인 전단탄성계수와 감쇠비가 영향을 받는 것으로 나타났다.

• Geomechanics and Engineering
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• 제10권1호
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• pp.77-94
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• 2016

Cyclic triaxial and resonant column tests were conducted to understand the beneficial effects of various grouted sands on liquefaction resistance and dynamic properties. The test procedures were performed on a variety of grouted sands, such as silicate-grouted sand, silicate-cement grouted sand and cement-grouted sand. For each type of grout, sand specimen was mixed with a 3.5% and 5% grout by volume. The specimens were tested at a curing age of 3, 7, 28 and 91 days, and the results of the cyclic stress ratio, the maximum shear modulus and the damping ratio were obtained during the testing program. The influence of important parameters, including the type of grout, grout content, shear strain, confining pressure, and curing age, were investigated. Results indicated that sodium silicate grout does not improve the liquefaction resistance and shear modulus; however, silicate-cement and cement grout remarkably increased the liquefaction resistance and shear modulus. Shear modulus decreased and damping ratio increased with an increase in the amplitude of shear strain. The effect of confining pressure on clean sand and sodium silicate grouted sand was found to be insignificant. Furthermore, a nonlinear regression analysis was used to prove the agreement of the shear modulus-shear strain relation presented by the hyperbolic law for different grouted sands, and the coefficients of determination, $R^2$, were nearly greater than 0.984.

• Geomechanics and Engineering
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• 제7권3호
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• pp.297-316
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• 2014

This paper presents a detailed study focused on investigating the effects of silt content on the static and dynamic properties of sand-silt mixtures. Specimens with a low-plastic silt content of 0, 15, 30 and 50% by weight were tested in static triaxial, cyclic triaxial, and resonant columns in addition to consolidation tests to determine such parameters as compression index, internal friction angle, cohesion, cyclic stress ratio, maximum shear modulus, normalized shear modulus and damping ratio. The test procedures were performed on specimens of three cases: constant void ratio index, e = 0.582; same peak deviator stress of 290 kPa; and constant relative density, $D_r$ = 30%. The test results obtained for both the constant-void-ratio-index and constant-relative-density specimens showed that as silt content increased, the internal friction angle, cyclic stress ratio and maximum shear modulus decreased, but cohesion increased. In testing of the same deviator stress specimens, both cohesion and internal friction angle were insignificantly altered with the increase in silt content. In addition, as silt content increased, the maximum shear modulus increased. The cyclic stress ratio first decreased as silt content increased to reach the threshold silt content and increased thereafter with further increases in silt content. Furthermore, the damping ratio was investigated based on different silt contents in three types of specimens.

• 한국지반공학회지:지반
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• 제3권2호
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• pp.7-16
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• 1987

흙의 동적 특성은 공극비, 구속압력, 입도 등의 여러가지 요인에 의해서 변화한다. 본 연구에서는 모래의 입도가 그 동적 특성에 미치는 영향을 구속압력과 공극비의 영향과 함께 실험적으로 살펴 보았다. 실험 결과, 전단탄성계수(Shear Modulus)와 감쇠비 (Damping Ratio)는 공극비가 감소 함에 따라, 그리고 구속압력이 증가함에 따라 각카 증가 및 감소하였다. 한펀, 실트 크기의 석영분말을 섞어 입도를 변화시켰을 때, 시료의 전단탄성계수와 감쇠비는 석영 분말의 함유량이 증가함에 따라 각각 감소 및 증가하였다. 여기서는 이 현상을 "유효 접촉수"와 "사공간"의 개념을 써서 미시적으로 살펴보았다. 개념을 써서 미시적으로 살펴보았다.

• 한국지반공학회지:지반
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• 제2권1호
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• pp.55-66
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• 1986

유효구속추력, 초기전단응력, 응력비 및 반복회수등의 영향을 고려하면서 비배수조건하에 있는 연약점토시료의 동력학적 전단탄성계수 및 감쇠비의 변화특성을 파악하기 위하여 일련의 삼축롱륜시험을 수행하였다. 그 결과, 초기전단응력 및 구속압력이 동력학적 토성치에 미치는 영향은 크지 않았지만, 축방향 변형의 증가에 따라 전단탄성계수는 감소하고 감쇠하는 증가하는 영향을 나타낸다. 또한, 전단탄성 계수는 Marcuson et al(3)과 Kokusho et al.(4)에 의해 제안된 경험식으로 얻어진 범위내에 분포되었고, 감쇠비는 Kokusho et al.(4)과 Ishihara et al.(9)에 의해 얻어진 범위에 분포됨을 보이고 있다.

• 한국지반공학회논문집
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• 제19권5호
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• pp.69-78
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• 2003

화강풍화토의 동결-융해 전후의 동적 거동을 구명하기 위하여 반복삼축압축시험을 수행하였다. 화강풍화토의 실트 함유량 20%이내에서 동결-융해를 받지 않은 공시체와 동결-융해를 받은 공시체를 구속압력을 변화시켜 동적 물성치인 전단탄성계수와 감쇠비의 변화 특성을 고찰하였다. 또한 점성토의 함유량을 각각 다르게 하여 소성지수의 변화에 따른 동결-응해 후의 동적 거동의 변화를 고찰하였다. 연구결과, 화강풍화토의 실트함유량이 증가할수록 전단탄성계수는 감소하였다. 그러나 동일한 밀도, 구속압력의 조건에서 동결-융해를 받은 화강풍화토의 전단탄성계수는 실트함유량에 관계없이 전단탄성계수에 큰 차이가 없었다. 점토를 함유한 소성지수 20이내의 화강풍화토의 전단탄성계수는 소성지수가 클수록 증가하였으며 동결-융해를 받게되면 전단탄성계수의 감소가 뚜렷하게 나타났다.

• 한국철도학회논문집
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• 제3권1호
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• pp.34-41
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• 2000

The analysis of static and dynamic characteristics of reinforced roadbed materials was performed through model and laboratory tests. The strength characteristic of reinforced roadbed materials such as HMS-25 and soil were investigated through the unconfined axial compression test, the model soil box test and the combined resonant column and torsional shear test. The unconfined axial compression strength of HMS-25 shows a steady increasement in strength due to the chemical hardening reaction between HMS-25 and water. The result of model soil box test reveals that railroad roadbed of HMS-25 is better than that of soil in several aspects, such as, bearing capacity and settlement. The combined resonant column and torsional shear test result indicates that shear modulus of HMS-25 and soil increase with the power of 0.5 to the confining pressure and linear relationship to normalized shear modulus and damping ratio.