Investigation of explosive compaction (EC) for liquefaction mitigation using CPT records

Abstract

Explosive compaction (EC) or Blast densification (BD) has been realized as an efficient technique for soil improvement and mitigation of the liquefaction potential in loose saturated sands. Due to providing continuous and precise records, Piezocone (CPTu) is the most applicable in situ test in geotechnical practice for evaluation of liquefaction potential. In this research a data bank including eight case histories in different locations has been compiled for investigation of EC effects on mitigation of loose sands instability. The sites geomaterials are in the category of fine to medium sand, silty sand and mixture of sand and gravel with relative density between 30 and 60 % and thickness of 5–40 m. Four CPT-based criteria have been used including cyclic stress ratio approach, cone tip resistance (qc) variations before and after modification, Qtn and qc1N, and soil behavior classification charts. Analyses have shown that due to EC the state of soil changes from loose to dense, the contractive behavior of sands changes to dilative, and the liquefaction potential diminishes. Also, by using soil behavior classification charts pre and post explosion, it can be observed that improved soils are not in the liquefiable zone, anymore. This improvement has a significant effect on layers where located in deeper zones, whereas in surface layers in some cases, liquefaction phenomenon has been observed. Moreover, by blasting in two stages between first and phases for boreholes, liquefaction potential decreases significantly.