Abstract
Seismic refraction survey is a non destructive method used in site investigation to identify the seismic velocity subsurface strata. Although it is widely known, the reliability of the result is still doubtable for some reason as well as due to an engineer’s ignorant, which insist on using conventional method rather than new advanced method causing the lack of usage in geophysical method for testing. This study aims to produce a correlation between P-wave velocity value and point load strength index value for shale. Both field and laboratory tests were carried out. In order to obtain the P-wave value, seismic refraction method was conducted as a field test at Precint 4, Putrajaya, Malaysia to achieve the Pwave velocity value of the shale bed. Ten samples of shale were collected from the field and laboratory tests were conducted. The tests are divided into three sections, namely non-destructive laboratory test, physical properties test and mechanical properties test. Ultrasonic Velocity Test via PUNDIT test was conducted as non-destructive laboratory test to acknowledge the P-wave velocity value in laboratory. Both field and laboratory P-wave velocity value were then compared and the result delivers are reliable due to it is within the range. For physical properties test, the rock density and porosity were acknowledged. Meanwhile, Point Load Test was conducted as mechanical properties. Correlation for both Pwave velocity value and point load strength value were achieved via producing an empirical relationship as the end result. Prediction of uniaxial compressive strength (UCS) value was made via converting the point load strength value to UCS value using a correlation. By acknowledging this empirical relationship, it shows that geophysical methods are able to produce a reliable result. Hence more and widely used of geophysical method will be profound in the future.
Highlights
Prior to site investigation purposed, most of the methods used are destructive, consumed more time and high cost
Geophysical methods are becoming popular in producing the subsurface profile especially in differentiating the soil and rock layers
Many studies have been conducted to prove the reliability of the geophysical test results as well as correlations between the geophysics and strength parameters to promote this advanced non-destructive method without the needs to use the conventional methods
Summary
Prior to site investigation purposed, most of the methods used are destructive, consumed more time and high cost. The results are discrete which is only single point of data could be obtained. Underground profile produced from this method is from combining a few numbers of results of the holes points. A continuous profile shows the soil and rock layer by assuming the layer is similar from one point to another. The reliability of the result is still doubtable due to misinterpret of the profile between the points. Geophysical methods are becoming popular in producing the subsurface profile especially in differentiating the soil and rock layers. Many studies have been conducted to prove the reliability of the geophysical test results as well as correlations between the geophysics and strength parameters to promote this advanced non-destructive method without the needs to use the conventional methods
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