Seismic Coefficient Research Articles

Limit Equilibrium Method of Slope Stability Analysis: A Case Study of Outlet Tunnel Portal of Bagong Dam East Java Indonesia

Abstract Bagong Dam, located in Trenggalek Regency, has a diversion tunnel. The diversion tunnel is designed as a horseshoe-type tunnel with a diameter of 4 m and a length of 416 m. Although a general engineering geological investigation has been conducted at the dam site, slope stability has yet to be analyzed. This research seeks to categorize rock masses based on the Geological Strength Index (GSI) and evaluate the stability of the slope at the tunnel outlet using the Bishop Simplified and Morgenstern-Price Limit Equilibrium Methods (LEM), considering scenarios with and without seismic load. The results will determine the appropriate slope for the tunnel outlet portal. The data for the LEM analysis were gathered through surface geological mapping, subsurface core sampling, and laboratory testing of the rock samples. The geological engineering of the Bagong Dam tunnel outlet consists of andesite breccia (fair to good), interbedded sandstone clay (poor to good), and poor-quality limestone. The horizontal seismic load coefficient (kh) at this location is 0.175. LEM analysis shows that the portal slope is stable after excavation according to the design, static load shows a safety factor (Fs) = 2.16 > 1.5 using the Bishop Simplified and also shows a safety factor (Fs) = 2.15 > 1.5 using Morgenstren-Price. Post-seismic load analysis also shows a safety factor (Fs) = 1.94 > 1.1 using the Bishop Simplified and also shows a safety factor (Fs) = 1.89 > 1.1 using Morgenstren-Price. Slope failure does not occur because the safety factor values can be achieved using the original slope design, both with and without seismic load.

Stability analysis of a seabed under combined action of waves and seismic loading

The stability analysis of a seabed under wave and seismic loading is conducted within the framework of yield design theory using the pseudo-static method. The strength properties of the constitutive material are modeled by means of a purely cohesive condition. The loading associated with water waves is modeled through the linear wave theory, whereas the inertial forces induced by the passage of seismic waves is addressed in the framework of pseudo-static method. The material cohesion that increases linearly with dept is adopted in the analysis. A sufficient stability condition is obtained through the static approach of limit analysis, while a necessary condition is determined from the kinematic approach. The effects of seafloor surface inclination, as well as seismic intensity, are analyzed through pseudo-static coefficients. The determination of the limit load obtained through the pseudo-static approach is based on existing literature, particularly when seismic coefficients are not considered.

Seismic design coefficients verification of regular and vertically irregular high-rise shear wall buildings using bidirectional horizontal ground motions and 3D modeling

Seismic design coefficients verification of regular and vertically irregular high-rise shear wall buildings using bidirectional horizontal ground motions and 3D modeling

Amplitude variation with azimuth direct inversion for effective pressure-sensitivity parameters in horizontal transversely isotropic media

Effective pressure prediction is of great significance for fracturability evaluation in unconventional reservoirs. Quantitative characterization of effective pressure remains a great challenge in the inversion prediction of subsurface media. Our goal is to develop a novel Bayesian amplitude varying with azimuth (AVAZ) inversion method to estimate fracture weaknesses and effective pressure for a horizontal transversely isotropic (HTI) medium. Using Schoenberg’s linear slip model and pore space compressibility theory, an anisotropic saturated stiffness matrix directly characterized by effective pressure is derived based on a weak-contrast interface separating two weakly anisotropic half-spaces of HTI medium. Based on the perturbation stiffness matrix and scattering theory, we derive a PP-wave reflection coefficient approximation directly characterized by fracture weaknesses and effective pressure-sensitive parameters, which establishes a quantitative relationship between seismic reflection coefficient and effective pressure. The analysis of accuracy and sensitivity is performed to verify the reliability and applicability of the constructed reflection coefficient. And then, the azimuth-amplitude-difference forward solver is constructed based on seismic reflection coefficients to eliminate the influence of isotropic background perturbations on seismic reflection coefficients and reduce the condition number of the forward solver. Finally, we present a novel Bayesian azimuth-amplitude-difference AVAZ inversion method for transversely isotropic media constrained by Cauchy and Gaussian regularization to directly estimate the fracture weaknesses and effective pressure-sensitive parameters. The application of synthetic data and field data verifies that the inversion results are in good agreement with the actual data, indicating that the method can effectively realize the stable prediction of anisotropic parameters and effective pressure-sensitive parameters of complex media.

Seismic scattering inversion for multiple parameters of overburden-stressed isotropic media

Subsurface reservoirs are compressed by overburden stress resulting from the gravity of overlying masses, and the resulting stress changes significantly affect the seismic reflection responses generated at the reservoir interfaces. Several exact reflection coefficient equations have been well established to delineate the role that in situ stress plays in altering the energy transition and amplitude of seismic reflection responses. These exact equations, however, cannot be effectively used in practice due to their intricate formulations and the difficult geophysical estimation for the third-order elastic constants (3oECs) embedded in reflection coefficients. Based on the theories of nonlinear elasticity and elastic wave inverse scattering, we derive an approximate seismic reflection coefficient equation for overburden-stressed isotropic media in terms of the P-wave modulus, shear modulus, density, and a defined stress-related parameter (SRP). The SRP is a combined quantity of elastic moduli, 3oECs, and overburden stress, which can be naturally treated as a dimensionless stress-induced anisotropy parameter. Its inclusion effectively eliminates the need for 3oECs information when using our equation to estimate the desired reservoir properties from seismic observations. By comparing our equation to the exact one, we confirm its validity within the moderate-stress range. Then, we introduce a Bayesian inversion approach incorporating the new reflection coefficient equation to estimate four model parameters. In our approach, the Cauchy and Gaussian distribution functions are used for the a priori probability and the likelihood distributions, respectively. The synthetic tests from two well-log data sets and a field example demonstrate that four parameters can be reasonably inverted using our approach with rather smooth initial models, which illustrates the feasibility of our inversion approach.

Seismic performance of pentagonal type aluminum alloy suspen-dome structure with large opening

Seismic performance of pentagonal type aluminum alloy suspen-dome structure with large opening

The application of matching pursuit spectral blueing in post-stack seismic frequency enhancement

The calculation of the spectral blueing operator in the traditional spectral blueing method has singularity, which leads to poor performance in post-stack seimic frequency expansion. To this end, a frequency spreading technique based on matching pursuit (MP) and spectral blueing is proposed. Through time–frequency analysis processing, it is shown that the seismic signal extracted by matching tracking method has good stability and higher resolution. The specific process of the method in this paper firstly uses the matching tracking method to accurately divide the post-stack seismic data into multiple frequency-division seismic bodies; then, in the process of calculating the spectral blueing ization operators for each frequency band, the weighting idea is used to calculate the weights of the optimized spectral blueing ization operators for each frequency band based on the differences in energy in different frequency bands; finally, the optimized spectral blueing operator is convolved with seismic reflection coefficients to obtain high-resolution seismic data. The actual test results of poststack seismic data have proven that the frequency raising method proposed in this paper is superior to the traditional spectral blueing ization algorithm, greatly improving the high-frequency component information of poststack seismic data. After frequency extension, there are more seismic events and higher resolution. Finally, the practicability and rationality of the seismic data after frequency extraction are verified by a series of operations such as attribute extraction, well seismic calibration and inversion.

Seismic correlation coefficient evaluation for the application of separation of variables approach in fragility assessment

Seismic correlation coefficient evaluation for the application of separation of variables approach in fragility assessment

Seismic Safety Evaluation of Mechanically Stabilized Earth (MSE) Wall for Highway Construction

The usage of Mechanically Stabilized Earth (MSE) Walls has grown in popularity over the last few decades and has been widely used in many countries for highway construction, including Indonesia. As a country with a high risk against seismic hazards, a considerable stability analysis against earthquakes for construction must be conducted. This paper is directed to evaluate the static and seismic stability of MSE wall by adopting design criteria from SNI 8460:2017 using the pseudo-static approach with Limit Equilibrium Method (LEM) which modelling earthquake as a seismic coefficient, a one-way constant load and dynamic response approach with Finite Element Method (FEM) which modelling earthquake as ground motion, a fluctuating load which varies in time. The stability analysis is performed by considering three failure mechanisms that mostly occurred in MSE Walls; base sliding, tensile overstress, and slope failure. The earthquake load is modelled based 1000-year return period earthquake. Based on the analysis result, the most potential failure mechanism that may occur in the MSE wall is tensile overstress, while the least potential failure is base sliding. The analysis result also shows that the finite element method obtained higher safety factors compared to limit equilibrium, while on the other hand, the remaining two failure mechanisms shows the different result, with the finite element method obtaining lower safety factors than limit equilibrium. Modelling seismic load as an accelerogram indicates that earthquakes have higher impacts on structure stability compared to seismic coefficient, based on seismic safety factor reduction of each method. Although show differences in the value of the safety factor, the minimum safety factor required still complies with both methods.

Constraints on fracture connectivity from amplitude variations with incidence angle and azimuth analysis

The analysis of seismic reflection amplitude variations with incidence angle and azimuth (AVAz) is a powerful tool for studying and characterizing fractured formations. There is evidence to suggest that wave-induced fluid pressure diffusion (FPD) within connected fractures can significantly affect the AVAz response. This, in turn, indicates that this seismic attribute may contain information on the connectivity degree of the fracture network, which represents a key hydraulic property of fractured formations. The assessment of the sensitivity of seismic reflectivity with respect to fracture connectivity accounting for FPD effects to date is limited to 2D models, which is mainly due to the complexity and the associated computational cost of modeling the effective properties of the corresponding generically anisotropic 3D media. To overcome these issues, we use a numerical upscaling procedure based on Biot’s theory of poroelasticity that allows us to obtain effective anisotropic representations of 3D fractured formations accounting for the FPD effects. Using these effective properties, we then perform a plane-wave analysis to compute the reflection coefficients at the top of the corresponding fractured formation. The results of our numerical analyses extend the previous 2D studies and demonstrate that seismic reflection coefficients are highly sensitive to the degree of connectivity of the fracture networks. The reflectivity responses of formations comprising connected and unconnected fractures indicate pronounced differences not only with respect to incidence angle but also with respect to azimuth. Quite importantly, our results also demonstrate that crossplots of commonly used AVAz coefficients permit us to identify regions with higher or lower fracture connectivity.

Calculation method for static and seismic active earth pressure on counterweight retaining walls under translation based on two critical slip surfaces

Calculation method for static and seismic active earth pressure on counterweight retaining walls under translation based on two critical slip surfaces

Analytical solutions for the stability of stone column-supported and geosynthetic-reinforced embankment

This study presents a novel prediction model based on the three-wedge method, utilizing a force-based equilibrium model to evaluate the stability of embankments reinforced by stone columns and geosynthetics. The proposed model utilizes six slip surfaces, enabling it to accommodate diverse geometric configurations, shear strength parameters, reinforcement arrangements (i.e., stone columns and geosynthetic), surcharge, water level, and quasistatic seismic coefficients. A constant factor of safety is initially assumed for each slip surface and reinforcement element, although this assumption can be relaxed by varying the strength parameters. The factor of safety is determined analytically through the solution of a polynomial equation. The proposed analytical solutions, which offer a compact form, provide new insights for the three-wedge method and effectively customize the conditions for geosynthetic-reinforced column-supported embankment applications, characterized by wedge interaction between the embankment, clay, geosynthetics, and columns. Validations of the proposed method are performed using the results obtained from the centrifuge test and numerical modelling, demonstrating the reliability of the analytical solution.

Evaluasi Desain Struktur Gedung Pondok Pesantren At-Tibyan Deli Serdang

The structural design of this three-story Islamic boarding school building, the results obtained after analysis include; risk category II so that the earthquake priority factor is 1. The soil site class is soft soil. In the structural system, it is designed using a special moment resisting frame system (SRPMK). The seismic design category obtained is category D. Seismic inspection starting from checking irregularities, diaphragm design, checking the number of structural vibration variations, determining the fundamental period of the structure, seismic response coefficient values, seismic base shear, checking the deviation between floors is carried out based on SNI 1726-2019. for column elements, beams and also plates in existing conditions after analysis have met the requirements based on SNI 2847-2019. The conclusion in this final project research is based on the results of the analysis that the design of the Attybian Islamic boarding school building still meets the requirements based on SNI 1726-2019 concerning procedures for earthquake resistance planning for buildings and non-buildings and also for beam, column and plate elements have met the requirements based on SNI 2847-2019 concerning reinforced concrete structures. However, for the beam elements for the reinforcement requirements, it is still too wasteful so that in this analysis, the amount of reinforcement is reduced because in the planning principle it must be safe and economical.

Simplified Analysis Method of Seismic and Static Stability for Embankments Supported with Concrete Piles in Soft Ground

A simplified analytical method is provided for the overall seismic and static stability of embankments supported with concrete piles in soft soil according to the pseudo-static approach. Mobilized shear forces on the piles intersected by the slip surface are involved in the proposed method. This method was originally established on four aspects: the circular slip surface assumption, pile bending–tension failure mechanism, simplified Bishop’s assumption, and elastic-beam-on-foundation model. The proposed method innovatively obtained the overall safety factor and critical slip surface of the piled-embankment system as well as the bending moment and shear force profiles of the piles. Moreover, it reproduced the progressive failure process of the system with the piles fracturing gradually. This method was verified by centrifugal tests and numerical simulations, and their safety factor relative errors were within 5%. Examples showed the safety factor decreased nonlinearly by 33% as the horizontal seismic coefficient increased from 0 to 0.2. The piles fractured progressively toward the interior of the system after the first one failed at the embankment toe. As the pile spacing in the two directions respectively increased from 3 to 5 times the pile diameter, the shear force of the critical pile at the slip surface increased slightly. Reinforcements in the embankment cushion may deepen the pile failure positions. This work provides a significant design reference for piled embankments under seismic conditions, including aspects such as overall stability, internal forces, and the progressive fracture of piles.

Seismic analysis of geosynthetic-reinforced soil walls in tiered configuration

Seismic analysis of geosynthetic-reinforced soil walls in tiered configuration

Seismic Stability Study of Bedding Slope Based on a Pseudo-Dynamic Method and Its Numerical Validation

Earthquakes are one of the main causes of bedding slope instability, and scientifically and quantitively evaluating seismic stability is of great significance for preventing landslide disasters. This study aims to assess the bedding slope stability under seismic loading and the influences of various parameters on stability using a pseudo-dynamic method. Based on the limit equilibrium theory, a general solution for the dynamic safety factor of bedding slope is proposed. The effects of parameters such as slope height, slope angle, cohesion, internal friction angle, vibration time, shear wave velocity, seismic acceleration coefficient, and amplification factor on stability are discussed in detail. To evaluate the validity of the pseudo-dynamic solution, the safety factors are compared with those given by early cases, and the results show that the safety factors calculated by the present formulation coincide better with those of previous methods. Moreover, a two-dimensional numerical solution of bedding slope based on Mohr–Coulomb’s elastic–plastic failure criterion is also performed by using the finite element procedure, and the minimum safety factor is essentially consistent with the result of the pseudo-dynamic method. It is proved that the pseudo-dynamic method is effective for bedding slope stability analyses during earthquakes, and it can overcome the limitations of the pseudo-static method.

Theoretical Research and Shaking Table Test on Nominal Aspect Ratio of the Isolated Step-Terrace Structure

With the installation of rubber isolation bearings in the upper and lower ground layers, an isolated step-terrace structure was created. Considering the ultimate bearing capacity of the rubber bearing under tension as the critical condition, a comprehensive framework was established to evaluate the overturning failure mechanisms present in isolated step-terrace structures. The bound of nominal aspect ratio was identified as the principal control index within this framework, which incorporates critical parameters such as height ratio (α), width ratio (β), vertical tensile stiffness to compressive stiffness ratio (γ), seismic coefficient (k), and nominal vertical compressive stress (σ0) to provide a thorough analysis of the structural responses and potential failure scenarios. In order to further investigate this matter, a scaled model of an isolated step-terrace concrete frame structure featuring two dropped layers and a single span within an 8° seismic fortification zone was meticulously crafted at a 1:10 similarity ratio. Subsequently, a series of shaking table tests were conducted to analyze the structural response under seismic excitation. The findings indicate that: utilizing the bound of nominal aspect ratio as a metric to gauge the anti-overturning capacity of isolated step-terrace structures is a justified approach. In instances where the height ratio remains constant, the bound of nominal aspect ratio for both positive and negative overturning trended upward with an increase in the width ratio. Notably, the bound of nominal aspect ratio for positive overturning consistently registered lower values compared to that of the negative overturning, underscoring the heightened susceptibility of step-terrace structures to positive overturning. Moreover, in scenarios characterized by higher height and width ratios, the structural integrity remained unscathed by any overturning effects arising from insufficient tensile strength in rubber bearings. Furthermore, the bound of nominal aspect ratio exhibited an ascending trend as the seismic coefficient, nominal vertical compressive stress, and vertical tensile stiffness to compressive stiffness ratio decreased. The outcomes derived from the shaking table test not only confirm the impressive seismic performance of the structure, but also, by closely examining the instantaneous stress variations within the upper and lower isolation layers of the model, substantiate the existence of a positive overturning hazard in scenarios marked by higher seismic coefficients (k). This observation aligns seamlessly with the theoretical projections, thereby substantiating the efficacy of the structural overturning failure theory through direct empirical verification.

Seismic stability and failure mechanisms of gentle and steep slopes considering soil rotated anisotropy and spatial variability

Seismic stability and failure mechanisms of gentle and steep slopes considering soil rotated anisotropy and spatial variability

Impact of Vertical Irregularities on Seismic Response Modification Coefficients of Dual Concrete Shear Wall-Frame Systems

Impact of Vertical Irregularities on Seismic Response Modification Coefficients of Dual Concrete Shear Wall-Frame Systems

A Review on Seismic Response Analysis Methods for Underground Structures

Seismic safety of underground structures is of paramount importance. This paper reviews the current research status of seismic response analysis methods for underground structures, focuses on the basic principles, advantages and disadvantages, and applicability of the proposed static method and dynamic time course analysis method. It also analyses their applications in engineering. It is shown that the seismic coefficient method, although simple, may have relatively large calculation errors due to oversimplification. The free-field deformation method is simple in form and easy to implement, but ignores soil-structure interaction. The flexibility coefficient method is simple in form and considers soil-structure interaction, but ignores many factors. The reaction displacement method directly reflects the soil-structure interaction, but the foundation spring parameters are difficult to value. The reaction acceleration method has the same advantages as the reaction displacement method, but there is a certain error. The dynamic time-course analysis method is accurate but computationally intensive.