Value Engineering through Systematic Site Investigation and Design Optimization

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This case study describes value engineering for a 24 m deep, 350 m long underground MRT station excavation in a dense Singapore urban setting, close to existing buildings, roads and a sensitive viaduct. Highly variable ground conditions and more than 1,200 bored piles created significant geotechnical and construction risks.<br /><br />The project team reviewed tender-stage information, divided the works into 18 design zones, and collaborated closely with the contractor. More than 120 additional boreholes, closely spaced SPTs and targeted rock permeability tests improved understanding of soil strength, rock levels and groundwater conditions. This enabled more reliable design decisions and reduced uncertainty.<br /><br />The investigation supported several cost- and time-saving changes. These included shortening retaining piles where shallow strong rock allowed excavation by rock cutting; optimizing soil stiffness and wall design parameters; reducing fissure grouting by confirming low rock permeability or extending wall toes; and using low-cost Liquefied Stabilised Soil piles for ground improvement. Low-strength concrete was adopted for non-load-bearing soft piles, while semi top-down construction and reinforced concrete struts replaced more costly temporary works in selected areas. At one entrance, a cantilever bored-pile wall with ground improvement avoided complex temporary support and pier underpinning.<br /><br />An extensive real-time monitoring program tracked wall movements, strut forces, groundwater and vibration. Observed wall deflections and strut forces were generally below design predictions, and recharge wells limited groundwater drawdown near sensitive structures.<br /><br />The project demonstrates that systematic, targeted site investigation and early contractor collaboration can enable safer, more constructible and economical designs. Instrumentation and monitoring are essential both to verify design assumptions and to manage residual risks during construction.

Keywords

value engineering

underground MRT station

Singapore construction

geotechnical investigation

construction risk

retaining piles

ground improvement

real-time monitoring

semi top-down construction

site collaboration