Dynamic compaction of saturated sands and silty sands: design

Current practice for design, suitability assessment, and determination of the optimum field operation parameters for dynamic compaction rely mainly on field pilot tests, past experience, and empirical equations. At present there are no detailed analytical procedures available to determine the densification achievable, or to analyse the effects of various operational parameters on the degree of improvement achievable during dynamic compaction of sands and non-plastic silty soil deposits. This paper presents a set of simplified charts to determine the post-improvement penetration resistance of saturated sands and non-plastic silty sands, supplemented with pre-installed wick drains, due to improvement by dynamic compaction. The theoretical basis and the numerical schemes for simulation of dynamic compaction leading to these charts are presented elsewhere. The charts facilitate design choice of parameters such as grid spacing, number of impacts per grid point, energy per impact, time cycle between impacts, and drain spacing required to achieve a minimum specified post-improvement penetration resistance for a range of initial soil conditions. Simplified procedures for the use of these charts for liquefaction mitigation design are presented and illustrated using design examples.