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Statistics and Data Analysis in Geology

Discrete particle simulation of particulate systems: A review of major applications and findings


 The spectral ratio between horizontal and vertical components (H/V ratio) of microtremors measured at the ground surface has been used to estimate fundamental periods and amplification factors of a site, although this technique lacks theoretical background. The aim of this article is to formulate the H/V technique in terms of the characteristics of Rayleigh and Love waves, and to contribute to improve the technique. The improvement includes use of not only peaks but also troughs in the H/V ratio for reliable estimation of the period and use of a newly proposed smoothing function for better estimation of the amplification factor. The formulation leads to a simple formula for the amplification factor expressed with the H/V ratio. With microtremor data measured at 546 junior high schools in 23 wards of Tokyo, the improved technique is applied to mapping site periods and amplification factors in the area.

Ground Motion Characteristics Estimated from Spectral Ratio between Horizontal and Verticcl Components of Mietremors.

A review of the recent advances on the treatment of industrial wastewaters by Sulfate Radical-based Advanced Oxidation Processes (SR-AOPs)

This paper describes laboratory model tests to determine the bearing capacity of an embedded circular footing supported by multiple layers of geogrid-reinforced sand beds. The embedment depth ratio of the footing was varied from zero to 0·6. The tests were conducted with one variety of geogrid in sand compacted to 70% relative density. Besides load settlement data, deformations on fill surface, strain in geogrid layer and pressure distribution in soil subgrade (below the geogrid layers) were measured. The test results demonstrate that the ultimate bearing pressure increases with embedment depth ratio of the foundation. With the provision of multiple layers of geogrid reinforcement in the sand bed, high-performance improvement is obtained, in terms of both increase in bearing capacity and reduction in surface deformation. Also, the footing pressure is redistributed more uniformly over a wider area on the subgrade soil. Strain measurements in the geogrid layers indicate that the geogrid reinforcement is mor...

Model studies of embedded circular footing on geogrid-reinforced sand beds

In the present study, an attempt has been made to evaluate the seismic hazard considering local site effects by carrying out detailed geotechnical and geophysical site characterization in Bangalore, India to develop microzonation maps. An area of 220 km2, encompassing Bangalore Mahanagara Palike (BMP) has been chosen as the study area. Seismic hazard analysis and microzonation of Bangalore are addressed in three parts: in the first part, estimation of seismic hazard is done using seismotectonic and geological information. Second part deals with site characterization using geotechnical and shallow geophysical techniques. In the last part, local site effects are assessed by carrying out one-dimensional (1-D) ground response analysis (using the program SHAKE2000) using both standard penetration test (SPT) data and shear wave velocity data from multichannel analysis of surface wave (MASW) survey. Further, field experiments using microtremor studies have also been carried out for evaluation of predominant frequency of the soil columns. The same has been assessed using 1-D ground response analysis and compared with microtremor results. Further, the Seed and Idriss simplified approach has been adopted to evaluate the soil liquefaction susceptibility and liquefaction resistance assessment. Microzonation maps have been prepared with a scale of 1:20,000. The detailed methodology, along with experimental details, collated data, results and maps are presented in this paper.

Seismic microzonation of Bangalore, India

In this paper, numerical simulation results of isotropic compression and triaxial static shear tests under drained and undrained stress paths on polydisperse assembly of loose and dense spheres are presented. An examination of the micromechanical behaviour of loose and dense assemblies under drained and undrained conditions, considering the particulate nature of granular materials, has been carried out to explain micromechanically the granular material behaviour at the grain scale level. The numerical simulations have been carried out using a discrete element model (DEM) which considers a 1000 sphere particle polydisperse assembly with periodic space representing an infinite three-dimensional space. In this paper, we present how DEM simulations can contribute to developments in constitutive modelling of granular materials through micromechanical approach using information on microstructure evolution. A series of numerical tests are performed using DEM on 3-D assemblages of spheres to study the evolution of the internal variables such as average co-ordination number and induced anisotropy during deformation along with the macroscopic behaviour of the assemblage in drained and undrained shear tests. In a qualitative sense, the macroscopic stress-strain results and stress path evolution in these simulations using 3-D assemblies demonstrate that DEM simulations are capable of reproducing ealistic compression and shear behaviour of granular materials.

Micromechanical modelling of monotonic drained and undrained shear behaviour of granular media using three dimensional DEM

The complete microzonation and site response studies require the characterization of subsurface materials considering local subsurface profiles of the site or region. The general site characterization comprises of the evaluation of subsurface features, material types, material properties and buried/hollow structures, by which it is determined whether the site is safe against earthquake effects. In this study, an attempt has been made to characterize the Bangalore Mahanagar Palike (BMP) area of about 220km2 using the shallow geophysical method, Multichannel Analysis of Surface wave (MASW), which identifies each type of seismic wave on a multichannel record using the refraction survey and produces shear-wave velocity (Vs) profiles. The study area of BMP has been characterized as per NEHRP (National Earthquake Hazards Reduction Program) and IBC (International Building Code) site classification using an average shear wave velocity (Vs30) of 30m, obtained from MASW. In the study area, 58 one-dimensional (1-D) MASW survey has been carried out and respective velocity profiles are obtained. The major part of the BMP area can be classified as "site class D", and "site class C" and a smaller part in and around Lalbagh Park is classified as" site class B". Further site response has been carried out using measured shear wave velocity and synthetic ground motion developed by Sitharam and Anbazhagan [11]. Site response study shows that due to soil condition, large modification of wave amplitudes are observed resulting in higher peak ground acceleration when compared to rock level acceleration.

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Site Characterization and Site Response Studies Using Shear Wave Velocity

In this paper an attempt has been made to evaluate the spatial variability of the depth of weathered and engineering bedrock in Bangalore, south India using Multichannel Analysis of Surface Wave (MASW) survey. One-dimensional MASW survey has been carried out at 58 locations and shear-wave velocities are measured. Using velocity profiles, the depth of weathered rock and engineering rock surface levels has been determined. Based on the literature, shear-wave velocity of 330 ± 30 m/s for weathered rock or soft rock and 760 ± 60 m/s for engineering rock or hard rock has been considered. Depths corresponding to these velocity ranges are evaluated with respect to ground contour levels and top surface levels have been mapped with an interpolation technique using natural neighborhood. The depth of weathered rock varies from 1 m to about 21 m. In 58 testing locations, only 42 locations reached the depths which have a shear-wave velocity of more than 760 ± 60 m/s. The depth of engineering rock is evaluated from these data and it varies from 1 m to about 50 m. Further, these rock depths have been compared with a subsurface profile obtained from a two-dimensional (2-D) MASW survey at 20 locations and a few selected available bore logs from the deep geotechnical boreholes.

T. G. Sitharam

Papers

Model studies of embedded circular footing on geogrid-reinforced sand beds

Seismic microzonation of Bangalore, India

Micromechanical modelling of monotonic drained and undrained shear behaviour of granular media using three dimensional DEM

Site Characterization and Site Response Studies Using Shear Wave Velocity

Spatial Variability of the Depth of Weathered and Engineering Bedrock using Multichannel Analysis of Surface Wave Method