Situated in Kāpiti Coast, Wellington, New Zealand, the Peka Peka to Ōtaki Expressway is a 13 km, 4-lane upgraded route of State Highway 1. It joins the southern section reaching the MacKays to Peka Peka Expressway and extends north past Taylors Road intersection. The expressway construction involved ground improvement works as the alignment encountered very soft and compressible soils reaching depths of approximately 7 m. The underlying reasons for such soft soil conditions were unique topographical and geological factors, leading to poorly drained ground conditions. This paper presents the improvement techniques employed to manage these geotechnical challenges and treat the soft soils. Additionally, it provides insights into the monitoring program implemented during construction, as well as the subsequent evaluation of the effectiveness of the soft soil improvement work.