Site-Specific Ground Motion Studies for a Deep Soil Site Near Ahmedabad, Gujarat

Design ground motions are usually developed by one of two approaches: by performing site-specific analyses or from provisions of building codes. Although contemporary codes consider the site effects to an extent, they provide more conservative estimates. Hence, site-specific analysis, which involves both the seismic hazard analysis and ground response analysis, is a preferred approach to obtain design ground motions. This chapter presents a site-specific analysis for a site near Ahmedabad, Gujarat. The seismic hazard analysis was carried out by DSHA approach. The site is predominantly characterized by deep stiff sandy clay deposits. Extensive shear wave velocity measurement is used for site classification and ground response analysis. The ground response analysis was carried out by using two approaches: the equivalent linear approach using SHAKE2000 and the non-linear approach using FLAC2D. The deep-stiff-soil site is found to amplify the ground motion. The response from nonlinear analysis is found to be considerably higher than those obtained from the equivalent linear approach.

Mitigation of Liquefaction Hazard Using Granular Piles

Ground improvement techniques are employed to mitigate liquefaction hazards. Granular piles are the most widely preferred alternative all over the world, due to several advantages associated with them. Different mechanisms operate in the function of stone columns/granular piles in liquefaction mitigation like drainage, storage, dilation, densification, and reinforcement. This chapter presents an overview of the use of granular piles as a liquefaction remedial measure for sand deposits. A brief description on the phenomenon of liquefaction and the associated features has been presented. A short discussion on various ground improvement methods available for liquefaction mitigation is presented in light of importance of granular piles. Different installation methods and design concepts for granular piles are presented. Various mechanisms of granular piles in mitigating the liquefaction potential of loose sand deposits are discussed and quantified in detail proving their effectiveness in hazard mitigation.

A Novel Meta-Integrative Platform for Effective Disaster Management

Disaster management is recognized as a complex task. Despite current facilities and advancements, each disaster continues to frustrate the government and the community. Well-known issues include lack of awareness, direction, preparation and planning, response, recovery, and policy vacuum, besides many other factors. Other issues include emerging drivers of change such as globalization, climate change, technology, social construct, global finance, and education. Despite the recognition of such complex issues, the pace of disaster management strategies seems to be inadequate. This is mainly due to the lack of an approach that can integrate the myriad of issues with the roles and responsibilities of stakeholders such as governments, practitioners, and the community. This chapter identifies a spatially enabled platform as a tool to overcome the aforementioned issues. A preliminary roadmap with “stakeholder position” as the central point of integration is presented. It is anticipated that the roadmap will provide governments and decision makers with the direction needed for future planning.

Advances in Extraction of Signal From Ground Motion Time Histories Using Time-Frequency Analysis

Time-frequency representation and spectral features extraction from a digitally recorded ground motion time history of an earthquake is cornerstone in earthquake engineering signal processing and interpretation. Recently developed time-frequency analysis (TFA) techniques are one of the most suitable techniques for the spectral estimation of signals whose frequency content varies with time. The most often used TFA techniques are short-term Fourier transform, Gabor transform, wavelet transform, Wigner-Ville distribution, Choi-William distribution, and cone shape distribution. The spectrograms of TFA reveal better spectral estimation in time-frequency domain and hence recommended to estimate local frequencies, dominate frequency and their incident time. Moreover, the time of occurrence of frequency component corresponding to maximum energy burst as well as its variation with time can also be identified. Results obtained from TFA techniques shows better picture of the spectral content in the data than the other conventional techniques.

Numerical Simulation of Seismic Interaction of Pile Foundation and Structure

Modeling a semi-infinite soil domain has always been a challenge, especially in problems where the interaction between the soil domain and structure domain is a dynamically responsive one, as in the case of seismic wave loading. Under such conditions, researchers used various strategies to simulate, both physically and numerically, the behavior of pile foundations under seismic loading. While describing the challenges and hitherto applied strategies, two comprehensive numerical studies are described: one at behavioral state in terms of inelastic response spectrum and the other at the limiting state of collapse.

Effect of Repeated Blast Vibrations on Rock Mass Damage in Tunnels

Blasting is the most common method of rock excavation technique in mining and civil construction and infrastructure projects. General blast-induced damage was extensively studied globally, but the studies on repeated blast induced damage is not yet reported, quantitatively. This chapter deals with the research work carried on the effect of repeated dynamic loading imparted on the jointed rock mass from subsequent blasts in the vicinity, on the jointed rock mass at Lohari Nag Pala Hydroelectric Power Construction Project. The blast-induced damage was monitored by borehole extensometers, borehole camera inspection surveys and triaxial geophones installed at three test sites of different joint orientations at the Main Access Tunnel of power house. The study reveals that the repeated blast vibrations resulted in extra damage of 60%. The results of the study indicate that repeated vibrations, resulted in inducing damage even at 23-33% of the critical vibrations (Vc) levels.

DEM Studies on the Liquefaction Behavior of Particles With Different Aspect Ratios

Discrete element method (DEM) provides insight into the fundamental physical principles leading to a better understanding of the complex behavior of granular materials under different loading conditions. In the reported studies adopting DEM, real particle shape is ignored, and the particles are modeled as spheres. Spherical shapes are preferred as they provide the simplest case with least computational effort in calculations and efficient algorithms. Hence, in this study, a comprehensive and comparative study on the mechanical behavior of assemblies consisting of particles with different aspect ratios is reported. The results indicate that the assemblies with lower aspect ratio lose its strength completely at less number of cycles when subjected to lower confining pressures. At higher confining stresses, the particles are not quick enough to rearrange themselves resulting in the reduction of average coordination number. This causes a drop of shear strength leading to lower resistance to liquefaction for non-spherical assemblies at high confining stresses.

Seismic Behavior and Dynamic Site Response of Municipal Solid Waste Landfill in India

Seismic behavior of landfills need for a better understanding of the dynamic properties of municipal solid waste (MSW) and site response of MSW landfill during seismic events. This chapter presents unit weight, shear wave velocity, strain-dependent normalized shear modulus reduction, and material damping ratio relationships for Mavallipura landfill based on field testing, laboratory measurements, and validated using semi-empirical methods. In addition, one-dimensional seismic response analysis by an equivalent linear method for Mavallipura landfill, Bangalore is done using software like SHAKE2000 and DEEPSOIL. Results indicated that the MSW landfill has less shear stiffness and more amplification due to the loose filling and damping, which need to be accounted for by seismically safe MSW landfill design in India. Also, results of seismic response analyses performed by the authors and other researchers are examined to assess the impact of stiffness and height of the landfill refuse fill on the overall response.

Mitigation of Seismic Accelerations by Soft Materials Embedded in the Ground

Seismically induced accelerations are greatly affected by the transmission through soil layers. The stiffness and damping of the material beneath a structure can therefore influence the seismic loads experienced in the structure. Recently, there has been interest in the use of very low shear stiffness materials in subsoil beneath structures in order to act as a filter to seismic motions, but there is significant skepticism as to its practicability. In this chapter, some notable contributions are discussed, and some work showing the physical modelling and numerical modelling of a soft-material scheme that showed initial promise is presented. This is seen to be readily modelled as a simple mass-spring system, which could be applied to other similar cases. Future challenges include development of a suitable material for the purpose, and reliably proving static stability.