The Multi-Purpose Bottom Plug (MPBP): An Innovative Solution for the Galataport Project in Istanbul, Turkey-Paper

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The paper presents the Multi-Purpose Bottom Plug (MPBP), a geotechnical solution used for deep excavation at the Karaköy site of Istanbul’s Galataport project. The site’s thick, loose man-made fill and underlying liquefiable marine sand, combined with high groundwater levels and nearby historic buildings, made excavation and seismic protection particularly challenging.<br /><br />The MPBP combines three functions. Overlapping, 2 m diameter double-fluid jet-grouted columns form a hydraulic plug to control seepage and provide excavation stability. Above the plug, pseudo-elliptical jet-grouted columns create a lattice intended to limit soil deformation and liquefaction, while also supporting the future building. Permanent, double-corrosion-protected steel-bar micropiles installed within the treated columns resist uplift during temporary construction conditions.<br /><br />A nonlinear three-dimensional seismic analysis assessed the lattice’s liquefaction-mitigation performance. Results supported a 7 m by 7 m grid: pore-pressure buildup was substantially reduced compared with untreated soil. Advanced drilling-position and jet-control systems helped ensure column overlap, produce the elliptical geometry, and place micropiles within the treated ground.<br /><br />Quality checks confirmed that the improved soil met specified strength and stiffness targets, and cross-hole tomography indicated column widths exceeding 4 m. A preliminary micropile tension test reached 2,000 kN, corresponding to approximately 400 kPa of micropile-to-grout skin friction. The test also measured uplift and strain distribution within the micropile and surrounding grouted column.<br /><br />The authors conclude that the MPBP’s performance depended on combining geotechnical analysis, specialized construction technology, electronic positioning and monitoring, and engineering expertise. The project demonstrates the potential of elliptical jet grouting for both seismic ground improvement and structural support.

Keywords

Multi-Purpose Bottom Plug

MPBP

jet grouting

deep excavation

Karaköy

Galataport project

liquefaction mitigation

seismic analysis

micropiles

groundwater control