Stabilization of the Nyköping’s riverbank with micropile-walls-Paper

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The northern bank of the Nyköping River in Åkroken, Sweden, showed signs of instability: existing masonry gravity walls were tilting toward the river, and slope analyses indicated a low factor of safety. The steep bank comprises about 1 m of archaeological fill over 7–9 m of silt and silty clay above bedrock. Planned development would add substantial loads, while archaeological constraints, nearby buildings, and the regulated river limited available remediation options.<br /><br />The design team recommended a micropile wall with tieback anchors to stabilize the slope, enable safe renovation of the masonry walls, and provide a permanent solution with a 100-year design life. The system uses concrete-filled Ruukki RD 170/12.5 mm bored micropiles at 1 m spacing, connected by steel plates, and Ischebeck TITAN 73/53 anchors at 2.5 m spacing. The anchors are inclined at 45 degrees and embedded in rock.<br /><br />Geotechnical investigations informed limit-equilibrium and numerical analyses using Slope/W, PLAXIS, and GeoStudio. The design assessed ultimate and serviceability limit states, including five construction stages, changing loads and groundwater conditions, and potential failure modes such as excavation-induced heave. Anchors were prestressed to 220 kN.<br /><br />The analyses predicted small horizontal movements during construction. The slope’s factor of safety improved to about 1.3 by the final stage, although the initial stage could temporarily have a factor below 1 under heavy pile-driving equipment loads. The team therefore recommended restricting nearby surcharge loads and using light machinery or maintaining a safe distance from the wall.<br /><br />The authors considered the staged analysis conservative, partly because it assumed a larger surcharge area than would occur in practice. They also noted that modeling unsaturated soil conditions might yield higher safety factors but would require further investigation. Overall, the micropile-wall system was judged well suited to the site because it stabilized the bank while minimizing disruption to the river and surrounding buildings.

Keywords

micropile wall

tieback anchors

slope stabilization

Nyköping River

Åkroken Sweden

masonry gravity walls

geotechnical analysis

factor of safety

PLAXIS

archaeological constraints