Bearing Capacity Enhancement Of Foundations By Pile Post-Grouting & Geosynthetic Encased Columns On Zambian Soils

The rapid urbanisation in Lusaka province,and Zambia at large,in the last 15 years has seen the increase in construction of various functional structures.Despite this development,Zambia still uses typical traditional construction methods for foundations with the use of conventional strip footings,pad and piling foundations.Predominant clay soils in Zambian geology and the use of conventional foundations and earth works could render poor performance and differential settlements in foundations,leading to early deterioration of bridges and structures.This necessitates the need for efficient ground improvement methods.This study investigates the possible use and effects of two novel ground improvement techniques on Zambian soils: post-grouted piles and geosynthetic encased columns(stone piles).These two methods of ground improvement were investigated by use of two case studies.A hypothetical hospital building which is founded on predominantly clay soils and a bridge structure which is similarly founded on clay and sandy clay soils.Both case studies are analysed by applying the post-grouted piles,geosynthetic columns and conventional piles,and compared.The analysis of these methods was done by manual calculations according to the Chinese Technical Design Codes and by using FEA in PLAXIS 3D software.Different load cases were applied to the post-grouted piles to enable assessment of the load-settlement patterns,general soil deformation and to observe the axial capacity of the piles with these techniques applied.The analysis showed that post-grouted piling increased the bearing capacity as minimal deformations were recorded in the FEA,whilst the stone piles significantly reduced the settlements in the embankment.Soil deformations for both case studies reduced greatly with the application of post-grouted piles and stone piles.The modelled foundation with the post-grouted piling group recorded a maximum soil deformation of 13 mm,whilst the stone pile group with geogrid deformed up to 26 mm in the z-axis.The hospital case study noted that the stone pile load capacity was8,000 KN,whilst the post-grouted pile capacity reached a maximum of 11,000 KN.The Kalungu Bridge noted considerable reduced settlements in the embankments with stone piles under.The untreated soil at Kalungu Bridge with conventional piles was only able to sustain 400 KN load,whilst the post-grouted piles were able to carry loads up to 4,000 KN.The stone piles also reduced soil consolidation time.It was further noted that the FEA in PLAXIS 3D provided in depth information on the soil behaviour under loading compared to the hand calculations.It was found from the FEA that for both case studies,post-grouted piles provided a greater and acceptable design safe factor for the pile load capacities.An economic evaluation was carried out for both case studies in order to compare the stone pile foundation and post-grouted piling foundation against the conventional piles construction cost.This was done by calculating the Net Present Values of the life cycle costs for each foundation option.This revealed that the post-grouted piling foundation had a greater NPV in the two case studies.It is recommended that relevant governing bodies include the financial feasibility to the study of novel ground improvement techniques in Zambia before application.