Methods for measurement, analysis and assessment of ground structure

Abstract

For determination of the laminar structure and other characteristics of a ground, oscillation sensors for detecting the vertical component or vertical and horizontal components of oscillations are disposed at three or more points within a comparatively small area at ground level to simultaneously measure microseisms at the respective points, if necessary with locations of said points being varied and measurements be performed at the respective locations and the vertical oscillation data or vertical and horizontal oscillation data thus generated are analyzed. This method not only permits an expedient, positive and accurate assessment of the laminar structure and other characteristics of the ground but also permits the measurement of ground structure even when the area available for measurement is small.

What is claimed is:  
     
         1 . A method for estimating the laminar structure and other characteristics of a ground which comprises disposing an oscillation sensor adapted to detect the vertical component or the vertical and horizontal components of oscillations at each of at least 3 points within a comparatively small area at ground level to simultaneously measure microseisms at such plural points, if necessary changing the locations of said points of measurement and repeating the measurements, and analyzing the vertical oscillation data or vertical and horizontal oscillation data.  
     
     
         2 . A method for estimating the laminar structure and other characteristics of a ground according to  claim 1  wherein said microseisms to be measured are short-period microseisms observed at ground level.  
     
     
         3 . A method according to  claim 1  wherein two oscillation sensors are disposed on each of 2 or more straight lines passing through the ground to be measured and dividing the azimuth of 360 degrees into an even-number of equal sections or straight lines paralled thereto in such a manner that sensor-to-sensor distances are equal on said straight lines.  
     
     
         4 . A method according to  claim 1  wherein said oscillation sensors are disposed at 3 or more points at qual spacings on the circumference of a circle and at one point in the center of the circle, or at a total of at least 4 points.  
     
     
         5 . A method according to  claim 1  wherein said oscillation sensors are disposed at apices of a regular triangle and the center of gravity thereof or a total of 4 points.  
     
     
         6 . A method for estimating the laminar structure and characteristics of a ground according to any of  claims 1  to  6  which comprises analyzing vertical oscillation data or vertical and horizontal oscillation data as measured simultaneously with said oscillation sensors, judging whether the oscillation waves detected by said oscillation sensors are surface waves or not, and extracting and analyzing the surface waves.  
     
     
         7 . A method for estimating the laminar structure and characteristics of a ground according to any of  claims 1  to  6 , which comprises analyzing the correlation coefficient and phase difference of oscillation data measured by equi-spaced oscillation sensors for each frequency, performing the analysis repeatedly with sensor-to-sensor distances varied, analyzing and computing the fundamental mode of surface waves based on results of the respective analyses and, if necessary, analyzing and computing the higher-mode wavelengths.  
     
     
         8 . A method for estimating the laminar structure and characteristics of a ground according to any of  claims 1  to  7  which comprises performing the measurement and analysis of microseisms repeatedly until it can be concluded that a relation between phase velocity and wavelength such as to give a sufficiently accurate assessment of ground structure is achieved.