Deepankar Choudhury

EFFECTS OF BODY WAVES AND SOIL AMPLIFICATION ON SEISMIC EARTH PRESSURES

To design a retaining wall, conventional Mononobe–Okabe method, which is based on the pseudo-static approach and gives the linear distribution of seismic earth pressures in an approximate way, is used to compute the seismic earth pressures. In this paper, pseudo-dynamic approach is used to compute the seismic earth pressures on a rigid retaining wall by considering the effects of time, phase difference in shear and primary waves and soil amplification along with the horizontal and vertical seismic accelerations and other soil properties. Design value of the seismic active earth pressure coefficient is found to increase with increase in the seismic accelerations, phase difference in body waves and soil amplification, whereas the reverse trend is observed for the passive case. Influence of various soil parameters on seismic passive earth pressure is more significant than that for the active case under harmonic seismic loading. Results are provided in the combined tabular and graphical non-dimensional form for both the seismic active and passive earth pressures. Present results are compared with the available results in literature to validate the proposed non-linearity of seismic earth pressure distribution.

Behavior of Single Pile in Liquefied Deposits during Earthquakes

AbstractAnalysis of pile foundations for earthquake loads requires the consideration of inertial loads that result from the soil-pile-superstructure interaction, as well as the evaluation of kinematic interactions that result from the movement of the surrounding soil and the pile. Such soil-pile interaction analyses must consider the stiffness degradation that results from earthquake loading. In the current study, the soil-pile interaction analysis considers stiffness degradation effects for a range of earthquakes with different amplitudes [maximum horizontal acceleration (MHA)], mean time periods, and different durations of earthquakes. Effects of both kinematic and inertial interactions are evaluated using a seismic-deformation method. A computer program was developed using MATLAB for the analysis. Results of a ground-response analysis obtained from a separate study were used for the soil-pile interaction analysis. Pile response for kinematic interactions were validated with the available theoretical so...

New Approach to Determine Seismic Passive Resistance on Retaining Walls Considering Seismic Waves

AbstractCalculation of seismic earth pressure is important for design of retaining walls in earthquake-prone areas. Existing analytical methods for computation of seismic passive earth pressure do not consider the effect of Rayleigh waves, although they constitute about 67% of the total seismic energy. In this paper, a new dynamic approach is proposed by considering primary, shear, and Rayleigh waves for estimation of seismic passive earth pressure by satisfying all the boundary conditions including a zero-stress condition at the ground surface. The limit equilibrium method is used to calculate seismic passive earth pressure for a rigid retaining wall supporting cohesionless backfill with critical combinations of seismic accelerations. The seismic influence zone obtained in this study is about 23 and 14% larger compared with available pseudostatic and pseudodynamic methods, respectively, which indicates the effect of Rayleigh waves. Also, there is a decrease of 22 and 3% in seismic passive earth pressure ...

Simplified method to characterize municipal solid waste properties under seismic conditions

The response of municipal solid waste landfills during earthquakes is gaining worldwide attention due to the devastating nature of earthquakes on landfills. Safety code provisions and regulations of various countries require the incorporation of safety measures against seismic hazards in the design of new landfills, as well as for extensions of existing landfills in seismic zones. Determination of dynamic properties is the first step for the analysis of municipal solid waste materials under seismic conditions. Landfill composition and properties, like unit weight, shear wave velocity, shear strength, normalized shear modulus, and material damping, are the most important dynamic properties that have direct impact on the seismic behaviour of landfills, and need to be evaluated carefully. In the present study, based on the extensive data provided by various researchers, the dynamic properties of landfill materials are analyzed using curve-fitting techniques, and simple mathematical equations are proposed. The resulting profiles are compared with laboratory and field data wherever possible. These properties are difficult to generalize and may vary from landfill to landfill. Hence, the proposed simple mathematical models for these landfill properties can be used to design municipal solid waste landfills in the absence of landfill-specific field data under seismic conditions.

STABILITY OF WATERFRONT RETAINING WALL SUBJECTED TO PSEUDO-DYNAMIC EARTHQUAKE FORCES AND TSUNAMI

The paper pertains to a study in which the waterfront retaining wall has been analyzed for its stability when it is exposed to the forces jointly coming from an earthquake and tsunami. Closed form solutions following the simple limit equilibrium principles have been proposed. For the calculation of the seismic passive earth pressure and the wall inertia force, pseudo-dynamic approach has been considered, while the hydrodynamic and the tsunami wave pressures have been calculated using different approximating solutions available in literature. The results presented in the sliding and overturning modes of failure of the wall show that the stability of the wall gets seriously challenged when it gets jointly exposed to the effects of the tsunami and earthquake. About 92% decrease is observed in the value of the factor of safety in sliding mode of failure of the wall as the ratio of tsunami wave height to the upstream still water height increases from 0 to 1.5. Also, the critical mode of failure of the wall has been found to be that of the overturning. Effect of different parameters involved in the analysis has also been studied and it has been observed that quite a few of them like kh, kv, ϕ, δ, ru have a significant effect on the stability of the wall. Comparison with a previously existing methodology using pseudo-static approach suggests that the present pseudo-dynamic approach is more realistic and comparatively less conservative and hence can be used as a handy simple economic method for the design of the waterfront retaining walls exposed to the combined effects of earthquake and tsunami.

Seismic Uplift Capacity of Horizontal Strip Anchors Using a Modified Pseudodynamic Approach

AbstractThe uplift capacity of shallow horizontal strip anchors embedded in cohesionless soil has been obtained under seismic conditions. The limit equilibrium approach with log spiral failure surface together with modified pseudodynamic seismic forces has been adopted. In this modified pseudo dynamic approach, the soil is assumed to behave as a viscoelastic material overlying a rigid stratum and subjected to harmonic horizontal acceleration. This modified methodology satisfies the zero-stress boundary condition at the free ground surface. In the present methodology, the amplification of seismic acceleration depends on the soil properties and can be evaluated; hence, there is no need for assumption of any amplification value as is usually done in the literature. It is observed that the seismic acceleration distribution along the depth is highly nonlinear. The net seismic vertical uplift capacity factor for a unit weight component of soil (Fγd) is estimated. The results under static and seismic conditions ...

Prediction of Blast-Induced Vibration Parameters for Soil Sites

AbstractIn the recent past, the topic of blast loads on structures has received considerable attention from researchers. Site-specific empirical models for blast-induced vibration parameters like peak particle velocity (PPV), peak pressure (PP), peak particle displacement (PPD), and pore pressure ratio (PPR) are commonly used for blast-resistant designs. However, these empirical models do not consider the variation in soil properties, e.g., the degree of saturation and uncertain in situ conditions. Hence, in this paper, a total of 120 pieces of blast data from various soil sites have been collected and used to propose a generalized empirical model for estimating blast-induced vibration parameters by considering three basic soil properties, namely, unit weight, degree of saturation, and Young’s modulus. Standard errors and coefficients of correlation for the prediction of blast-induced vibration parameters by various empirical models are obtained with respect to the observed soil field data. The present em...

Seismic stability analysis of expanded MSW landfills using pseudo-static limit equilibrium method

Capacity expansion of existing landfills is the most economical alternative to constructing new landfills where cost of land is prohibitive. From the safety point of view, the stability analyses of existing landfills expanded either vertically and/or laterally are required for different stages of construction, operation and during closure of a landfill. In the present study, a pseudo-static limit equilibrium seismic stability analysis was performed for a typical side-hill type municipal solid waste (MSW) landfill expanded using an engineered berm. Seismic stability analyses were performed for the two critical cases, namely when the failure surface passes below the berm (under berm) and when the failure surface passes over the back slope of the berm (over berm). Close-form solutions were developed for the upper bound and lower bound factor of safety and the yield acceleration of such slopes under both failure conditions. From parametric analyses it was observed that as the height of the berm increased, the factor of safety for both the over-berm failure and the under-berm failure conditions also increased. The average factor of safety and yield acceleration coefficient were found and the under-berm failure condition became critical for a back slope steeper than 1.7H : 1V. The average factor of safety decreased as both horizontal and vertical seismic accelerations increased. Comparisons between the present results and those in the literature for the static case showed good agreement and the present results of the pseudo-static seismic case were found to be of particular importance.

Effect of cohesion and fill amplification on seismic stability of municipal solid waste landfills using limit equilibrium method

Municipal solid waste (MSW) landfills in seismic zones are subjected to the seismic forces both in the horizontal and vertical directions. The stability of landfills against these seismic forces was evaluated by computing the factor of safety of landfills with different modes of failure among which failures of landfills due to translation are very common. Conventionally, the seismic stability of landfill is evaluated by using pseudo-static limit equilibrium method. In the present study, seismic stability of landfills is evaluated by both the conventional pseudo-static and modern pseudo-dynamic method. The pseudo-dynamic method is superior as it takes into account the effect of duration and frequency of earthquake motion and corresponding body waves in addition to the variation of earthquake accelerations along depth and time. In the present study, the effects of cohesion and fill amplification on seismic stability of landfill are also taken into account. It was noticed that, neglecting cohesion of fill material as well as liner material, results in a lower factor of safety and, hence, a very conservative/uneconomic design. Also, fill amplification is found to reduce the factor of safety values computed only by using the pseudo-dynamic method, showing its advantage. Generalized expressions are developed for factor of safety and yield acceleration against translational failure, which can be used for evaluating the seismic stability of MSW landfills. Comparisons of results under static condition with existing, similar methodology show a very good agreement. However, the present study seems to provide unique results for the seismic case.

Translational Seismic Failure Analysis of MSW Landfills Using Pseudodynamic Approach

AbstractMost of the municipal solid waste (MSW) landfills can fail in different modes such as sliding, rotational, or translational mode under both static and seismic loading conditions. These landfills constructed in the seismic zones experience additional seismic inertial forces in both horizontal and vertical directions during earthquakes. The conventional pseudostatic method of analysis suffers from major limitations by not considering the dynamic nature of forces such as variation of seismic inertial forces with time, frequency and the effects of shear and primary waves in the analysis. The scope of this paper is to present the application of the modern pseudodynamic method for evaluating seismic stability of MSW landfills by using a translational failure mode. In the present analysis, closed-form solutions are developed for upper and lower ranges of the factor of safety against translational failure and the yield acceleration by using the limit equilibrium method for pseudodynamic forces. A parametr...