The collapse of gravesite excavations at Esikhaleni Cemetery is a problem associated with the loose sandy soils that cover the site. The aim of the study was to investigate a means by which the stability of the sidewalls of grave excavations can be economically improved to a stable depth of at least 2.5m for at least two days, thereby improving the appearance and safety of the gravesides for mourners and also ensure the safety of workers in and around the gravesites.
High energy impact compaction (HEIC) was used to investigate the feasibility of densifying the soils using impact rolling. To verify the effectiveness of the HEIC method and to confirm whether the project specification can be met, an extensive in-situ testing program was instituted to characterize the site conditions prior to densification and to assess the efficiency of the HEIC after treatment. This involved pre-, post- and control testing on five, 100m long, 10m wide trial lines on which 10, 20, 30, 40 and 50 passes were carried out.
Additional tests were performed (in-situ testing, soil laboratory testing and excavation monitoring) one month after the completion of the compaction work to study the ‘set-up effect’ – that is the time-dependent increase in the strength and the stiffness in recently densified sands.
Numerical modelling was undertaken to determine the slope stability; a provisional Factor of Safety (FoS) of the grave excavations and a probability of sidewall failure (PoF) were also determined.
The field measurements indicated that the depth of soil improvement extended to 2.5m below natural surface level and that the in-situ moisture content should be within an acceptable range of the optimum moisture content to ensure the effective densification by the impact roller carrying out the recommended 40 passes. However, the top 0.5m of the soil profile requires to be: –