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Book ChapterDOI

Spatial Variability of Depth to Weathered Rock for Chennai Using Geostatistical Kriging

01 Jan 2020-pp 95-105
TL;DR: In this article, the authors evaluated the spatial variability of depth to weathered rock in Chennai city using field test data, which consists of nearly 400 borehole data covering the entire city with stratigraphic information.
Abstract: The objective of this study is to evaluate the spatial variability of depth to weathered rock in Chennai city using field test data. The database consists of nearly 400 borehole data covering the entire city with stratigraphic information and the same is used in the study. Ordinary kriging technique, which uses the spatial correlation of the data, is applied to estimate the depth at locations where the field measurements are not available. In addition, the variance of the estimated data is also computed. The developed map indicates that the depth to weathered rock in the study area varies from 3 to 30 m from the ground level. The estimated depths to weathered rock are compared and validated with a few selected borehole data and Multichannel Analysis of Surface Wave (MASW) test results. These maps can be used in the ground response analysis, foundation analysis, and design studies.
Citations
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Journal ArticleDOI
TL;DR: In this article, a shallow induced polarization (IP) was used to map details of bedrock and soil sediments, and the soil-bedrock interface was determined through a trial and error approach using a sharp boundary feature in the inversion model.

17 citations

References
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Journal ArticleDOI
TL;DR: In this article, a multichannel shot gather is decomposed into a swept-frequency record, allowing the fast generation of an accurate dispersion curve, which can then be examined and its effects appraised in both frequency and offset space.
Abstract: The frequency-dependent properties of Rayleigh-type surface waves can be utilized for imaging and characterizing the shallow subsurface. Most surface-wave analysis relies on the accurate calculation of phase velocities for the horizontally traveling fundamental-mode Rayleigh wave acquired by stepping out a pair of receivers at intervals based on calculated ground roll wavelengths. Interference by coherent source-generated noise inhibits the reliability of shear-wave velocities determined through inversion of the whole wave field. Among these nonplanar, nonfundamental-mode Rayleigh waves (noise) are body waves, scattered and nonsource-generated surface waves, and higher-mode surface waves. The degree to which each of these types of noise contaminates the dispersion curve and, ultimately, the inverted shear-wave velocity profile is dependent on frequency as well as distance from the source. Multichannel recording permits effective identification and isolation of noise according to distinctive traceto-trace coherency in arrival time and amplitude. An added advantage is the speed and redundancy of the measurement process. Decomposition of a multichannel record into a time variable-frequency format, similar to an uncorrelated Vibroseis record, permits analysis and display of each frequency component in a unique and continuous format. Coherent noise contamination can then be examined and its effects appraised in both frequency and offset space. Separation of frequency components permits real-time maximization of the S/N ratio during acquisition and subsequent processing steps. Linear separation of each ground roll frequency component allows calculation of phase velocities by simply measuring the linear slope of each frequency component. Breaks in coherent surface-wave arrivals, observable on the decomposed record, can be compensated for during acquisition and processing. Multichannel recording permits single-measurement surveying of a broad depth range, high levels of redundancy with a single field configuration, and the ability to adjust the offset, effectively reducing random or nonlinear noise introduced during recording. A multichannel shot gather decomposed into a sweptfrequency record allows the fast generation of an accurate dispersion curve. The accuracy of dispersion curves determined using this method is proven through field comparisons of the inverted shear-wave velocity (vs) profile with a downholevs profile.

2,131 citations

Journal ArticleDOI
TL;DR: In this article, 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.
Abstract: 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.

61 citations

Journal ArticleDOI
TL;DR: In this article, two geophysical methods based on seismic waves were employed to evaluate the geotechnical properties of the soil deposits at a site for a planned wind farm, where the acquired shot gathers were processed, from which primary wave and shear wave velocities were derived.

50 citations

Journal ArticleDOI
TL;DR: In this paper, the authors measured the shear wave velocity of soil layers at 30 locations in Chennai City by Multichannel Analysis of Surface Waves (MASW) test and nearly 300 borehole data were used to estimate V s based on the correlations between V s and SPT-N values.

34 citations

Journal ArticleDOI
TL;DR: In this paper, an integrated geographic information system (GIS)-based system for geotechnical data, called the Geotechnically Information System (GTIS), was developed to establish a regional counterplan against earthquake ground motions in the Seoul metropolitan area.

20 citations