Along the Nyköping River (100 km south of Stockholm), the slope of the northern
riverbank indicated a potential sliding failure – especially around the area called “Åkroken” which is
planned to become a new residential area. The cross section of “Åkroken” shows a steep slope (~ 20%)
with heavy surcharge loads on top due to the building plans. The geology consists of approx. 1 m upper
filling material “rich” on archaeological findings from medieval times (12th century). Beneath the filling
there is approx. 7-9 m silty-clayey layer over the bedrock. This slope is supported with masonry gravity
walls founded into the river bed. However, these walls showed clear signs of instability since the wall
was tilting towards the river. As a prevention measure, the city council cordoned off the area. ÅF Consult
was committed to assess the stability of the slope and design safety measures to both be able to renovate
the masonry walls and increase the factor of safety for the entire fringe.
As a remediation measure a micropile-wall was recommended to prevent the effects of a landslide failure
in the Nyköping River. The micro-pile wall’s main functions was to avoid further displacements during
the renovation of the old masonry walls, and later on to work as a permanent structure. The micropilewall
was designed for 100 years life-span according to Swedish Standards. Bored micropiles, Ruukki
RD 170/12.5 mm, were installed c/c 1 m and filled with concrete. Tieback anchors, Ischebeck TITAN
73/53, were installed c/c 2.5 m with a 45 degrees inclination and embedded in rock. Numerical analysis
(PLAXIS and Geostudio) were utilized to assess the slope stability and estimate the range of
displacements during the construction of the micropile walls. Geotechnical investigations estimated the
material properties for the calculations.
Subjects: micropile wall, slope stabilization, landslide, bored micropiles, tieback anchors
Author: Vazquez, A., Aronsson, S. and Marxmeier, N.
Publisher: ISM, DFI, ADSC