Equations to Correct SPT-N Values Obtained Using Non-standard Hammer Weight and Drop Height – Part III
The authors previously published two papers to study the influence of using non-standard hammer-weight (Wi) on the obtained blow counts, (Ni) during the SPT test. The current study is an extension to the past work; here the hammer drop height (Hi) has been changed to investigate its effect on the obtained blow counts, (Ni). Then, the multiple action of changing non-standard energy (Wi.Hi) is also investigated. The hammer weight, its drop height and the machine efficiency ( Open image in new window ) present the three main variables during the study.
The study methodology is experimental work and the method is physical model simulates the behavior of SPT-Rig. It has been designed and manufactured in house. The model is capable to change the hammer weight, its drop height and the overall machine efficiency. Five hammer weights, five drop heights and six different efficiencies have been changed all together; individually as well as in groups. The hammer weight ratios (Wi/Ws) and drop height ratios (Hi/Hs) each has been changed to cover the spans of 0.2, 0.4, 0.6, 0.8 and 1.0. Furthermore, six efficiencies ( Open image in new window ) have been changed with every change of the above ratios to cover the scope of, Open image in new window = 35%, 50%, 60%, 70%, 85% and 100%. Reconstituted well graded clean silicate dense sand (SW) is used for modeling the soil.
Novel procedure has been advised as well as empirical equations have been proposed to re-adjust the incorrect blow counts (Ni) obtained using non-standard SPT parameters or uses machines of a low efficiency. Also, a simplified method fast and costless has been suggested to sort out the problem of machines owing low efficiencies. Finally, some modifications to well-known formula are advised.
The authors present their deep gratitude to Prof Dr. A. Bazaraa for his kind personal communication, direct input and advices during discussions on topic.
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