Graduate Thesis Or Dissertation
 

Predicting pore pressure response in in-situ liquefaction studies using controlled blasting

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/44558g279

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  • Originally used as a method to densify loose soils, controlled blasting has expanded its applicability to geotechnical engineering by becoming a research tool to physically generate liquefaction for full-scale in-situ tests, ranging from seismic performance of deep foundations to evaluating ground improvement techniques. Current methods used to design the blasting layout (i.e. charge weight, placement, etc.) rely upon empirical models that typically do not consider in-situ soil conditions in predicting pore pressure response. In addition, these empirical models were developed for single blasts whereas current blasting studies rely upon the use of multiple blasts in loading the soil. Through the investigation of several controlled blasting case histories, a statistical analysis was performed on the recorded blasting results and in-situ soil data to observe if in-situ soil conditions significantly influence the generation of residual pore pressures for both single and multiple blasts. Based upon the study, it was found that the development of residual pore pressure during multiple blasts is highly influenced by the initial in-situ soil conditions and should be accounted for in predicting pore pressure response. Several multiple regression analyses were performed to identify which in-situ soil properties should be considered in an empirical model that predicts the blast-induced residual pore pressure. It was found that the best model was as a function of the blasting layout and the initial soil conditions represented by the SPT (N₁)₆₀ blow counts and the effective overburden pressure, σ’[subscript v0], expressed in kPa. The model was evaluated on case history data and it was found to be valid for blasting layouts that are relatively simple (i.e. square grid or circular array with less than 30 charges), but became unreliable for complex blasting layouts consisting of many charges (more than 30) or erratic blasting patterns. In addition, it was found that the model was statistically acceptable to be used for single blasts as well. The new empirical model estimates the extent of liquefaction and residual pore pressure for both single and multiple blasts and can be used in design of future blasting studies. Although the empirical model has yet to be validated from experimental field tests, it is anticipated that this model could be a step in the development of energy-based design for assessing liquefaction potential and in performing ground improvement evaluations. As more blasting studies are being performed, the model is expected to be refined and improved with the increase in case history data.
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