Effects of hammer energy on borehole termination and SBC calculation through site-specific hammer energy measurement using SPT HEMA
By: Anbazhagan, P
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Contributor(s): Yadhunandan, M. E.
Publisher: New York Springer 2022Edition: Vol.52(2), April.Description: 381-399p.Subject(s): Civil EngineeringOnline resources: Click here
In:
Indian geotechnical journalSummary: Geotechnical investigation often engages several standard penetration tests (SPT) using different types of SPT equipment in a single project without energy measurement. It is a common practice in most Asian countries because there are no codal provisions for energy measurements during SPT. This study measured SPT hammer energy using two types of instrumented rods in a single project with multiple boreholes. Two different types of SPT equipment were used. This study was carried out with the aim of understanding the effects of hammer energy on the rebound or termination criteria and safe bearing capacity (SBC) estimation. SPT hammer energy measuring apparatus (SPT HEMA) is used for measuring energy below Anvil and above the Split spoon sampler. To validate the readings, SPT Analyzer is used below Anvil along with SPT HEMA at selected depths. SPT HEMA energy values recorded below Anvil closely match with those obtained from SPT Analyzer. Hammer energy at each SPT blow is used to estimate the average energy of SPT N-values at every depth, average borehole energy, average equipment energy, and average site energy from both SPT setups. A considerable difference was observed between these different energy ratio values. So adopting few energy measurements to assign energy ratio for correction factor estimation similar to developed countries should not be practiced as SPT equipment has different configuration and operation practices in developing countries. These differences in energy results have considerable variations in site-specific energy corrected N-values. In this study, the current method of correcting N-values as per IS 2131 resulted in N-values larger than actual, up to a depth of 6 m, thus giving in more SBC than actual. SBC for the site is estimated using codal procedure considering non-energy corrected N-values; energy corrected N-values for reference energy of 70% and measured shear wave velocity (Vs) in the same location. Net SBC estimated without applying energy correction is larger than SBC from energy corrected N-values and Vs values. So, there is a need to revisit SPT investigation practice, N correction, and SBC estimation in the places where no hammer energy is measured.
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School of Engineering & Technology (PG) Archieval Section | Not for loan | 2022-1351 |
Geotechnical investigation often engages several standard penetration tests (SPT) using different types of SPT equipment in a single project without energy measurement. It is a common practice in most Asian countries because there are no codal provisions for energy measurements during SPT. This study measured SPT hammer energy using two types of instrumented rods in a single project with multiple boreholes. Two different types of SPT equipment were used. This study was carried out with the aim of understanding the effects of hammer energy on the rebound or termination criteria and safe bearing capacity (SBC) estimation. SPT hammer energy measuring apparatus (SPT HEMA) is used for measuring energy below Anvil and above the Split spoon sampler. To validate the readings, SPT Analyzer is used below Anvil along with SPT HEMA at selected depths. SPT HEMA energy values recorded below Anvil closely match with those obtained from SPT Analyzer. Hammer energy at each SPT blow is used to estimate the average energy of SPT N-values at every depth, average borehole energy, average equipment energy, and average site energy from both SPT setups. A considerable difference was observed between these different energy ratio values. So adopting few energy measurements to assign energy ratio for correction factor estimation similar to developed countries should not be practiced as SPT equipment has different configuration and operation practices in developing countries. These differences in energy results have considerable variations in site-specific energy corrected N-values. In this study, the current method of correcting N-values as per IS 2131 resulted in N-values larger than actual, up to a depth of 6 m, thus giving in more SBC than actual. SBC for the site is estimated using codal procedure considering non-energy corrected N-values; energy corrected N-values for reference energy of 70% and measured shear wave velocity (Vs) in the same location. Net SBC estimated without applying energy correction is larger than SBC from energy corrected N-values and Vs values. So, there is a need to revisit SPT investigation practice, N correction, and SBC estimation in the places where no hammer energy is measured.
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