Showing papers by "T. G. Sitharam published in 2021"

Seismic Hazard Assessment and Land Use Analysis of Mangalore City, Karnataka, India

Abstract: This article presents a combined seismic risk assessment of Mangalore city, considering seismic hazard and Land Use (LU) patterns. Probabilistic seismic hazard analysis was carried out considering different source models and attenuation relations to predict Peak Ground Acceleration at every square kilometer. LU of the area was assessed using GIS tools with the built-in supervised Gaussian maximum likelihood algorithm on processed remote sensing data from temporal Landsat images. The risk map showed the concentration of built-up area South-West, toward the sea and the seismic hazard following an increasing trend from the coast to further inland.

Model Tests and Analytical Studies on Performance of Areca Leaf Cells as Cellular Confinement in Soil

Abstract: In this paper, the possibility of using naturally available low-cost areca leaf sheaths as an alternative to the commercially available HDPE geocell has been explored by conducting the laboratory m...

Appraisal of Thanneermukkom bund as a coastal reservoir in Kuttanad, Kerala

Abstract: This paper presents an overview of Thanneermukkom bund with its implications on water security in the region as a freshwater reservoir in the southwest coast of India. The bund was constructed in 1...

Probabilistic seismic hazard analysis of North and Central Himalayas using regional ground motion prediction equations

Abstract: Recently developed region-specific GMPEs are used for a comprehensive seismic hazard analysis (SHA) of the North and Central Himalayas (NCH) using a probabilistic approach considering two source models. Vulnerable seismic sources in the areas are identified based on the Seismotectonic Atlas (Dasgupta et al. 2000), published by the Geological Survey of India. An up to date, homogenized and declustered earthquake catalogue is compiled from various sources, with earthquake data since 250 BC, to create a new digitized seismotectonic representation of the region. Regional seismic zones having similar seismicity are recognized based on the Gutenberg-Richter (GR) parameters and the region is delineated into 5 seismic zones. The study area is divided into grids of size 0.05° × 0.05° and the hazard in terms of Peak Ground Acceleration (PGA) at the centre of each grid point is estimated and presented as hazard maps for individual seismic sources, maximum of all sources, and average of both sources. From the current study, it could be concluded that the PGA estimated in the regions is comparatively higher than what is reported in the codal provisions for seismic zonation and estimation of design horizontal acceleration for the region.

The Quintessence of 25 Years of Our Contributions to Geotechnical Earthquake Engineering

Abstract: An exponential rise in population along with uncontrolled and unplanned urbanization exposed to earthquakes reeks a plenitude of hazard in terms of life and property. Effects, mechanics, and impact of an earthquake in terms of ground shaking, site effects, liquefaction, and landslides had been broadly covered in the past, and the recent developments have catered profound understanding of earthquakes. Our recent studies on ground motion attenuation characteristics, comprehensive seismic hazard analyses, site effects, liquefaction behaviour, seismic microzonation, ground motion analyses, joint time–frequency analysis-based ground motion synthesis, etc., have largely contributed to geotechnical earthquake engineering. Our detailed experimental and numerical works on liquefaction have improved the understanding of liquefaction of sands. Installation of ground motion sensors and monitoring of earthquakes have further supplemented geotechnical earthquake engineering research in the country. Recent surveys on earthquake preparedness and readiness indices have pointed out the urgent need for general awareness, and an action plan towards mitigating and managing the hazard due to earthquakes. This paper discusses the Quintessence of 25 years of the author’s contribution to the field of Geotechnical Earthquake Engineering.

Liquefaction Resistance and Cyclic Response of Air Injected-Desaturated Sandy Soil

Abstract: Desaturation of in-situ saturated sandy soils is emerging as a new cost effective and environment friendly liquefaction mitigation technique. In the present study, stress controlled undrained cyclic triaxial tests have been conducted on air injected-desaturated sandy soil and various important issues such as number of cycles required for initial liquefaction, cyclic strength of desaturated sand, modes of failure, evolution of pore pressure, have been explored in detail. Number of cycles required for initial liquefaction increased exponentially with decrease in degree of saturation. Cyclic strength of desaturated sand with degree of saturation of 80% is found to be twice that of saturated sand, for relative density of 40%. Assessment of performance of desaturated sand under various earthquake records revealed that desaturated sand with degree of saturation of 70% can prevent liquefaction during moderate to strong earthquakes having peak ground acceleration as high as 0.30 g. Further, sample with high degree of saturation underwent cyclic mobility failure. In samples with low degree of saturation, two types of cyclic softening failures demarcated by two distinct phase transformation trends were observed. A pore pressure model proposed by Konstadinoun and Georgiannou (2014) has been modified to predict the pore pressure evolution in desaturated sand.

A systematic approach for the analyses and design of jointed rock mass slopes against wedge and toppling failures: a case study of the stability of the abutments of the bridge across the Chenab River

Abstract: The stability of jointed rock mass slopes in highly seismic areas is governed by the orientation of the joints with respect to the slope and the joint characteristics and the seismic accelerations....

Failure Modes of Air Desaturated Sand in Undrained Cyclic Loading: A Systematic Experimental Investigation

Abstract: This paper presents a systematic experimental investigation to understand different failure modes of air desaturated clean sand in undrained cyclic loading for a degree of saturation in the range of 70% to full saturation. Five distinct failure modes have been observed depending on the degree of saturation, relative density, effective confining pressure and cyclic shear stress ratio. Nearly saturated samples of loose sand at low confining pressure underwent hybrid cyclic liquefaction failure wherein it reached dense of critical state during compression stage of loading only. However, nearly saturated samples of medium dense sand at low confining pressure accumulated large plastic strain on the compression side owing to gradual strain softening. Both loose and medium dense samples, with a high degree of saturation, underwent cyclic mobility failure at high effective confining pressure, wherein the sample reached dense of critical state during both compression and extension stage of loading. Moreover, two types of cyclic softening failures, demarcated by two distinct phase transformation trends, were observed in samples with a low degree of saturation. Investigation from the critical state soil mechanics framework revealed that all test samples lay on the dense-of-critical side, and nearly saturated samples closest to critical state underwent cyclic mobility failure, whereas those at farthest from critical state failed by gradual strain softening.

Geophysical techniques for characterisation of municipal solid waste landfills

Abstract: This paper presents the seismic site characterisation of Mavallipura landfill in Bengaluru, India using multichannel analysis of surface waves (MASW). The survey was performed at top level up to a ...

Ground Response Analysis of a Nuclear Power Plant Site in Southern India: A Nonlinear Approach

Abstract: One-dimensional nonlinear ground response analysis is performed for a nuclear power plant site situated in east coast of south India. Since the strong motion records available for the study area are scarce, a synthetic ground motion time history developed for the same site by (James et al., Nat Hazards 71:419–462, 2014) and its scaled-up scaled-down versions are used as the input motion at bedrock level. A few more synthetic ground motion histories are also developed and applied as input motion in order to analyse the deviation in ground response with variation in frequency content and duration of bedrock motion. Martin–Finn–Seed pore pressure model is used to compute development of excess pore pressure during loading. The peak horizontal acceleration (PHA) profile, amplification spectra and response spectra at surface level for 5% damping are plotted for each location.

Site Characterization Using Satellite Data and Estimation of Seismic Hazard at Ground Surface

Abstract: This paper presents the seismic site characterization carried out for Karnataka (state level) as well as for India (country level) using topographic slope map derived from Digital Elevation Model (DEM) data. Two DEM data, SRTM, and ASTER were used to derive the slope maps. For Karnataka (state level), the slope map was generated from ASTER DEM considering a grid size of 5 × 5 km and for India (country level), the slope map was generated from SRTM DEM considering the grid size of 10 × 10 km. Based on the slope value, every grid point was characterized into various NEHRP site classes, and spatial variation of average shear wave velocity for top 30 m (Vs30) value throughout the study areas is presented in this paper. Peak horizontal acceleration (PHA) at bedrock level was evaluated for the same grid points using deterministic as well as probabilistic methodologies. The amplification factor for every grid point was obtained from the site coefficients corresponding to NEHRP site class. The surface level peak horizontal acceleration (PHA) was then evaluated for every grid point by multiplying bedrock level PHA with the corresponding amplification factor. Spatial variation of seismic hazard at the surface for the state of Karnataka as well as for entire India is presented in this paper.

Liquefaction Behavior of Low to Medium Plasticity Sand-Fines Mixtures

Abstract: During earthquake, soil deposits are subjected to cyclic loading. Under undrained conditions, cyclic shear stress causes transient disturbance and gives rise to an increase in excess pore water pressure leading to loss of shear strength in saturated soil deposits, there will be excessive strains with continued loss of shear strength resulting in liquefaction. Researchers have identified a significant number of cases where ground failure took place during earthquake in soil deposits containing fines leading to considerable damage to buildings. Some studies show a decrease in liquefaction resistance and others show an increase in liquefaction resistance with an increase in fines content in soil deposit. There is no clarity regarding the effect of fines. In view of this, an experimental investigation has been carried out to evaluate the liquefaction potential of sand-clay mixtures. A series of undrained stress-controlled cyclic triaxial shear tests were performed on reconstituted samples obtained from Cauvery River sand and sand mixtures containing different percentages of plastic fines up to 30%. This paper reports the results of stress-controlled cyclic triaxial shear tests under undrained conditions at 100 kPa confining pressure at a frequency of 0.1 Hz. The results show that the cyclic strength decrease with an increase in fines content upto 20% beyond which it increases. In the present investigation, the limiting fines content is 20%. The results of CRR were analyzed in terms of relative density, fines content, and plasticity characteristics. The results indicate that flow liquefaction depends on the acceleration (CSR) and initial state (void ratio).

Liquefaction Resistance of Desaturated and Partly Saturated Clean Sand

Abstract: Induced desaturation has been emerging as a new liquefaction mitigation technique Laboratory study carried out, so far, on induced desaturation has mainly focused on shaking table and centrifuge studies In the present study, triaxial specimens of saturated clean sand have been desaturated by injecting air/CO2 into it and stress-controlled undrained cyclic triaxial tests have been conducted on such samples Few tests have been conducted on partly saturated samples as well It is observed that the presence of air in the sample increases the liquefaction resistance of the sand Further, desaturation affected not only liquefaction resistance but also dilative and contractive tendency of the soil Slope of the phase transformation line on compression side initially increased and then decreased with reduction in degree of saturation whereas slope of phase transformation line on extension side initially decreased and then increased with reduction in the degree of saturation In most of the cases, slope of the phase transformation line on extension side is found to be smaller than that on compression side

Seismic Hazard Assessment of Nuclear Power Plant Site in Jaitapur: Deterministic and Probabilistic Approaches

Abstract: This paper presents the seismic hazard analysis of Jaitapur region on the west coast of India, where a nuclear power plant is being planned to locate. A homogenized earthquake catalog in unified moment magnitude scale for the region has been prepared compiling updated data from different agencies. The seismicity parameters were estimated for Jaitapur region, and the hazard evaluation has been performed using different methodologies with different source models and attenuation relations. The deterministic and probabilistic seismic hazard analyses were performed with currently available data and their best possible scientific interpretation by considering alternative models (source models, maximum magnitude, and attenuation relationships). The hazard maps have been produced for horizontal ground motion on the bedrock level using both deterministic and probabilistic methods. The value of Peak Horizontal Acceleration (PHA) for the study region estimated probabilistically for 475 year return period varies from 0.05 to 0.2 g, whereas with deterministic approach, PHA reaches value as high as 0.3 g.