Use of Dynamic Compaction in Constructing Subgrades Over Reclaimed Fills

Abstract

In recent times, rapid urbanization coupled with an acute shortage of suitable lands for construction of transportation infrastructures have opened up arenas for finding means of utilizing existing weak subgrades by adopting eco-friendly ground improvement technologies. In this context, dynamic compaction (DC) has evolved as a viable option in view of the simplicity, cost-effectiveness and low-carbon footprint associated with this technique. In the present paper, an attempt has been made to investigate the effectiveness of DC in facilitating construction of pavements and road subgrades over loose reclaimed fills and engineered MSW landfills post their design life. The primary objective is to assess and identify the various geotechnical parameters guiding the efficiency of the mechanism depending upon the road functionality and traffic expectations. Five influencing factors that need to be considered in the field are discussed in this respect, wherein the first factor involves consideration of the deformation modulus of the weak subgrade illustrated through construction of a moderately large road project over a reclaimed island of 198,000 m2 extent consisting of extremely loose silty sand deposits. Pressuremeter tests conducted post DC revealed substantial improvement in the upper 7 m of stratum with an increase of about 4 times the average deformation modulus of soil. The next factor is the liquefaction susceptibility of the fill material, which is demonstrated through a case study involving improvement of liquefiable flood-plain site by heavy tamping, resulting in significant reduction in liquefaction susceptibility of the remediated ground. The third criteria considered is the initial moisture content of the fill material related to placement of a road embankment foundation over a marshy land by DC associated with sand-drain installation, which resulted in significant improvement in the dry density and cohesion of the in situ soil. The fourth factor is the energy level involved in compaction process, the importance of which is demonstrated through a project involving extensive treatment of a hydraulic fill consisting of primarily compressible clays by DC for future infrastructural constructions. The fifth parameter discussed is the effect of DC on long-term settlements of infrastructures observed during reclamation of a MSW site by high-energy DC methodology for constructing highway embankments and road utilities. Based on these compilations, a relationship between tamper mass and height of fall adopted in the field is suggested in this paper, and the depth of improvement and surface settlements incurred during DC in case of reclaimed fill materials are evaluated for optimizing the process of foundation design in the field.