• 한국지반환경공학회 논문집
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• 제24권2호
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• pp.13-24
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• 2023

Tunnels may undergo a larger or a smaller response compared with the free-field soil. In the pseudo-static procedure, the response of the tunnel is most often characterized by a curve that relates the racking ratio (R) with the flexibility ratio (F), where R represents the ratio of the tunnel response with respect to the free-field vibration and F is the relative stiffness of the tunnel and the surrounding soil. A set of analytical and empirical curves that do not account for the depth and the aspect ratio of the tunnel are typically used in practice. In this study, a series of dynamic analyses are conducted to develop a set of F-R_m relations for use in a frame analysis method. R_m is defined as an adjusted R where the rocking mode of deformation is removed and only the racking deformation is extracted. The numerical model is validated against centrifuge test recordings. The influence of aspect ratio, buried depth of tunnel on results is investigated. The results show that R_m increases with the increase of the buried depth and the aspect ratio. The widely used F-R relations are highlighted to be different compared with the obtained results in this study. Therefore, the updated F-R_m relations with proposed equations are recommended to be used in practice design. The rocking response decreases with either the decrease of the difference of stiffness between surrounding soil and tunnel or the larger aspect ratio of the tunnel section.

• 한국지반공학회논문집
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• 제40권4호
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• pp.19-32
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• 2024

동적 토압 해석은 지하 구조물의 내진 설계에서 핵심적인 파라미터이다. 그러나 기존 토압식들은 지반과 구조물의 상호작용, 상대적 유연성 비율(F) 및 구조물의 래킹 비율(R), 종횡비(L/H) 등 중요한 변수들을 종합적으로 고려하지 않은 것들이 대다수이다. 본 연구의 목적은 이러한 매개변수들이 동적 토압에 미치는 영향을 확인하여 기존의 옹벽 토압식의 신뢰도를 평가하는 것이며, 이를 위해 베이스먼트에 대해 동적 수치해석을 통한 매개변수 연구를 수행하였다. 그 결과, 종횡비가 높고 유연성이 낮은 구조물이 종횡비가 낮고 유연성이 높은 구조물보다 지진 토압에 더 취약하다는 사실을 확인하였다. 따라서 베이스먼트의 지진 토압 또는 동적 토압 추정에 있어 종횡비 및 유연비를 고려하는 것이 필요하고, 기존 옹벽의 토압식 적용 시 주의가 필요하다고 판단된다.

• Geomechanics and Engineering
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• 제22권1호
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• pp.49-63
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• 2020

Studying the critical response characteristics of box culverts with diverse geometrical configurations under seismic excitations is a necessary step to develop a reasonable design method. In this work, a numerical parametric study is conducted on various soil-culvert systems, aiming to highlight the critical difference in the seismic performances between three- and four-sided culverts. Two-dimensional numerical models consider a variety of burial depths, flexibility ratios and foundation widths, assuming a visco-elastic soil condition, which permits to compare with the analytical solutions and previous studies. The results show that flexible three-sided culverts at a shallow depth considerably amplify the spectral acceleration and Arias intensity. Larger racking deformation and rocking rotation are also predicted for the three-sided culverts, but the bottom slab influence decreases with increasing burial depth and foundation width. The bottom slab combined with the burial depth and structural stiffness also significantly influences the magnitude and distribution of the dynamic earth pressure. The findings of this work shed light on the critical role of the bottom slab in the seismic responses of box culverts and may have a certain reference value for the preliminary seismic design using R-F relation.