• Geomechanics and Engineering
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• 제36권2호
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• pp.167-181
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• 2024

The soil-structure relative stiffness is a key factor affecting the seismic response of underground structures. It is of great significance to study the soil-structure relative stiffness for the soil-structure interaction and the seismic disaster reduction of subway stations. In this paper, the dynamic shear modulus ratio and damping ratio of an inhomogeneous soft soil site under different buried depths which were obtained by a one-dimensional equivalent linearization site response analysis were used as the input parameters in a 2D finite element model. A visco-elasto-plastic constitutive model based on the Mohr-Coulomb shear failure criterion combined with stiffness degradation was used to describe the plastic behavior of soil. The damage plasticity model was used to simulate the plastic behavior of concrete. The horizontal and vertical relative stiffness ratios of soil and structure were defined to study the influence of relative stiffness on the seismic response of subway stations in inhomogeneous soft soil. It is found that the compression damage to the middle columns of a subway station with a higher relative stiffness ratio is more serious while the tensile damage is slighter under the same earthquake motion. The relative stiffness has a significant influence on ground surface deformation, ground acceleration, and station structure deformation. However, the effect of the relative stiffness on the deformation of the bottom slab of the subway station is small. The research results can provide a reference for seismic fortification of subway stations in the soft soil area.

• Structural Engineering and Mechanics
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• 제45권5호
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• pp.655-676
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• 2013

In this study, strength reduction factors and inelastic displacement ratios are investigated for SDOF systems with period range of 0.1-3.0 s considering soil structure interaction for earthquake motions recorded on soft soil. The effect of stiffness degradation on strength reduction factors and inelastic displacement ratios is investigated. The modified-Clough model is used to represent structures that exhibit significant stiffness degradation when subjected to reverse cyclic loading and the elastoplastic model is used to represent non-degrading structures. The effect of negative strain - hardening on the inelastic displacement and strength of structures is also investigated. Soil structure interacting systems are modeled and analyzed with effective period, effective damping and effective ductility values differing from fixed-base case. For inelastic time history analyses, Newmark method for step by step time integration was adapted in an in-house computer program. New equations are proposed for strength reduction factor and inelastic displacement ratio of interacting system as a function of structural period($\tilde{T}$, T) ductility (${\mu}$) and period lengthening ratio ($\tilde{T}$/T).

• Structural Engineering and Mechanics
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• 제35권2호
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• pp.191-203
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• 2010

To investigate the critical buckling load and post-buckling behavior of an axially loaded pile entirely embedded in soil, the non-linear large deflection differential equation for a pinned pile, based on the Winkler-model and the discretionary distribution function of the foundation coefficient along pile shaft, was established by energy method. Assuming that the deflection function was a power series of some perturbation parameter according to the boundary condition and load in the pile, the non-linear large deflection differential equation was transformed to a series of linear differential equations by using perturbation approach. By taking the perturbation parameter at middle deflection, the higher-order asymptotic solution of load-deflection was then found. Effect of ratios of soil depth to pile length, and ratios of pile stiffness to soil stiffness on the critical buckling load and performance of piles (entirely embedded and partially embedded) after flexural buckling were analyzed. Results show that the buckling load capacity increases as the ratios of pile stiffness to soil stiffness increasing. The pile performance will be more stable when ratios of soil depth to pile length, and soil stiffness to pile stiffness decrease.

• Geomechanics and Engineering
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• 제16권6호
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• pp.577-588
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• 2018

A major concern in deep excavation project in soft clay deposits is the potential for adjacent buildings to be damaged as a result of the associated excessive ground movements. In order to accurately determine the wall deflections using a numerical procedure such as the finite element method, it is critical to use the correct soil parameters such as the stiffness/strength properties. This can be carried out by performing an inverse analysis using the measured wall deflections. This paper firstly presents the results of extensive plane strain finite element analyses of braced diaphragm walls to examine the influence of various parameters such as the excavation geometry, soil properties and wall stiffness on the wall deflections. Based on these results, a multivariate adaptive regression splines (MARS) model was developed for inverse parameter identification of the soil relative stiffness ratio. A second MARS model was also developed for inverse parameter estimation of the wall system stiffness, to enable designers to determine the appropriate wall size during the preliminary design phase. Soil relative stiffness ratios and system stiffness values derived via these two different MARS models were found to compare favourably with a number of field and published records.

• Structural Engineering and Mechanics
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• 제45권6호
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• pp.741-758
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• 2013

In this study, inelastic displacement ratios are investigated for existing systems with known lateral strength considering soil structure interaction. For this purpose, SDOF systems for period range of 0.1-3.0 s with different hysteretic behaviors are considered for a number of 18 earthquake motions recorded on soft soil. The effect of stiffness degradation on inelastic displacement ratios is investigated. The Modified Clough model is used to represent structures that exhibit significant stiffness degradation when subjected to reverse cyclic loading and the elastoplastic model is used to represent non-degrading structures. Soil structure interaction analyses are conducted by means of equivalent fixed base model effective period, effective damping and effective ductility values differing from fixed-base case. For inelastic time history analyses, Newmark method for step by step time integration was adapted in an in-house computer program. A new equation is proposed for inelastic displacement ratio of system with SSI with elastoplastic or degrading behavior as a function of structural period ($\tilde{T}$), strength reduction factor (R) and period lengthening ratio ($\tilde{T}$/T). The proposed equation for $\tilde{C}_R$ which takes the soil-structure interaction into account should be useful in estimating the inelastic deformation of existing structures with known lateral strength.

• 한국재난정보학회 논문집
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• 제10권2호
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• pp.244-252
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• 2014

본 연구에서는 버켓기초로 지지된 해상풍력타워의 지진응답을 지반-구조물 상호작용을 고려하여 해석하였다. 해석프로그램으로는 SASSI를 사용하였으며 연약지반에 대해 생성된 인공지진파를 입력으로 사용하였다. 버켓기초의 형상과 강도를 매개변수로 하여 각 매개변수들의 영향을 파악하였다. 구조물의 응답은 타워의 하부와 나셀위치에서 얻어졌으며 응답스펙트럼으로 비교하였다. 해석결과 형상비, 버켓의 강도, 지반의 강도에 따라서 기초부와 나셀부에서 다른 경향의 응답을 보였다. 그러나 이러한 모든 지반-구조물상호작용의 고려는 암반으로 가정한 거동에 비하여 월등히 큰 응답 값을 보여 이의 고려가 버켓기초를 가진 해상풍력타워의 지진거동에 큰 영향을 미치는 것을 파악할 수 있었다.

• Geomechanics and Engineering
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• 제24권1호
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• pp.57-65
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• 2021

The effects of initial soil fabric and aspect ratio (AR) on the small-strain stiffness (G0) of granular soils are studied by employing discrete element method (DEM) numerical analysis. Elongated clumps composed of subspheres were adopted, and the G0 values were obtained by DEM simulations of drained triaxial tests under different densities and initial confining pressure (p0). The DEM simulations indicate that the initial soil fabric has an insignificant effect on G0. The effect of the AR on G0 is related to the initial density. Namely, for dense specimens, G0 first increases with increasing AR, reaching a plateau value when the AR ≥ 1.5. However, for loose specimens, G0 gradually increases as the AR increases. Microscopic examination reveals that G0 uniquely depends on the coordination number of the particles (CN-particle) rather than the subspheres (CN-sphere) at the particulate level for the effects of initial soil fabric and AR. Finally, Poisson's ratio ν0 is also determined by CN-particle. In addition, based on data in literature and this study, ν0 can be fitted as ν0 = 5.920(G0/(p0)1/3)-0.99, which can be used to predict ν0 of granular soils based on the measured G0.

• Geomechanics and Engineering
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• 제37권4호
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• pp.383-393
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• 2024

Monopile foundations of offshore wind turbines embedded in soft clay are subjected to the long-term cyclic lateral loads induced by winds, currents, and waves, the vibration of monopile leads to the accumulation of pore pressure and cyclic strains in the soil in its vicinity, which poses a threat to the safety operation of monopile. The researchers mainly focused on the hysteretic stress-strain relationship of soft clay and kinds of stiffness degradation models have been adopted, which may consume considerable computing resources and is not applicable for the long-term bearing performance analysis of monopile. In this study, a modified cyclic stiffness degradation model considering the effect of plastic strain and pore pressure change has been proposed and validated by comparing with the triaxial test results. Subsequently, the effects of cyclic load ratio, pile aspect ratio, number of load cycles, and length to embedded depth ratio on the accumulated rotation angle and pore pressure are presented. The results indicate the number of load cycles can significantly affect the accumulated rotation angle of monopile, whereas the accumulated pore pressure distribution along the pile merely changes with pile diameter, embedded length, and the number of load cycles, the stiffness of monopile can be significantly weakened by decreasing the embedded depth ratio L/H of monopile. The stiffness degradation of soil is more significant in the passive earth pressure zone, in which soil liquefaction is likely to occur. Furthermore, the suitability of the "accumulated rotation angle" and "accumulated pore pressure" design criteria for determining the required cyclic load ratio are discussed.

• 한국지반공학회논문집
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• 제18권4호
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• pp.167-177
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• 2002

표준관입시험 시 항타로 인해 시추봉 두부에서 발생하는 응력파가 시추봉 선단과 접해 있는 지반에서 반사되어 돌아오는 동적신호를 분석함으로써, 시추봉 선단부에 인접한 지반의 임피던스(강성)에 관해 보다 상세한 정보를 얻고자 하는 시험방법이 시도되고 있다. 이 시험법의 실규모 시험에 선행하여 본 논문에서는 시추봉-지반시스템에 대한 동적유한요소해석을 통해 동적신호를 얻고, 이들 신호를 분석하여 추정한 지반의 임피던스와 탄성계수의 신뢰도를 평가함으로써 시험법의 적용성을 검토하고자 하였다. 또한 반사파의 특성에 영향을 미칠 수 있는 인자들에 대한 평가를 통해서 실규모 시험을 위한 참고자료를 제공하고자 하였다. 이러한 연구 결과, 시추봉과 지반의 접촉면에서 입사, 반사되는 파동의 진폭비($F_반F_입$)에 가장 심각하게 영향을 미치는 인자는 시추봉 선단과 접촉한 지반강성의 변화임을 알았으며, 이들 파동의 진폭비의 변화는 시추봉과 지반 간의 임피던스 비($\alpha$)의 변화와 밀접한 관련이 있는 것으로 나타났다. 이러한 결과로부터 SPT 동적신호를 분석하여 시추봉 선단과 직접 닿아 있는 지반에 대한 임피던스와 변형 계수를 추정하는 시험법의 적용 가능성이 있다는 결론을 얻었다.

• Geomechanics and Engineering
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• 제24권1호
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• pp.15-28
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• 2021

Digging well foundation has been widely used in railway bridges due to its good economy and reliability. In other instances, bridges with digging well foundation still have damage risks during earthquakes. However, there is still a lack of knowledge of lateral behavior of digging well foundation considering the soil-foundation interaction. In this study, scaled models of bridge pier-digging well foundation system are constructed for quasi-static test to investigate their lateral behaviors. The failure mechanism and responses of the soil-foundation-pier interaction system are analyzed. The testing results indicate that the digging foundations tend to rotate as a rigid body under cyclic lateral load. Moreover, the depth-width ratio of digging well foundation has a significant influence on the failure mode of the interaction system, especially on the distribution of foundation displacement and the failure of pier. The energy dissipation capacity of the interaction system is discussed by using index of the equivalent viscous damping ratio. The damping varies with the depth-width ratio changing. The equivalent stiffness of soil-digging well foundation-pier interaction system decreases with the increase of loading displacement in a nonlinear manner. The absolute values of the interaction system stiffness are significantly influenced by the depth-width ratio of the foundation.