TOP DOWN ROAD RECONSTRUCTION
The work was completed late 2011 and the site has per- formed exceptionally well ever since. The MoTI Road Area Managers comment when the work was completed “It is inter- esting, driving across it now “feels” solid.”. The last inspection in March 2014 found no reflective cracking or settlement.
Highway 4, Kennedy Hill East Slide Kennedy Hill East Slide was only 40m east of the West Slide (Figure 5), but the morphology of the slide was com- pletely different.
Figure 7. East Slide with shor- ing and
micro piles construct- ed.
Highway 4, Kennedy Lake Pinch Point The “Pinch Point” was a trafficablity challenge for decades
that became more of an issue with 2008 road improvements just to the west that widened the road and effectively increased the hourglass effect that pushed vehicles toward the inside cliff.
Figure 5. Typical West Coast Terrain and the site of the Kennedy Hill East and West Slides.
The site crossed a rock cut and fill section that was also widened using similar techniques of concrete block and geogrid in 2008. Unfortunately the additional width was unknow- ingly placed over the edge of a subsurface rock cliff and over the next 3 years the work progressively slid down the slope approximately 7m and reduced the road width back to pre construction widths (Figure 6).
Eastbound, the highway closely followed the shores of Kennedy Lake and then steeply climbed to an upper bench across a steep cliff face. The “pinch” was created at the base of this hill with the construction of cast in place gravity wall from the 1950’s.
Additional width was needed but infilling into the lake was not an option and deconstruction of the wall would render the highway impassable during construction (Figure 8).
Figure 8. Kennedy Hill Pinch Point overview.
Figure 6. Kennedy Hill East Slide pre 2011 construction.
This site was also investigated and the mitigation cost was prohibitive and the gaining the desired road width was not guaranteed. Using tie back anchors, micro piles and GRS fill, an additional 3m of width was constructed at a quarter of the traditional cost estimate.
The site was excavated to competent material, the road was shored up and the micro piles constructed to gain global stability for the GRS fill (Figure 7).
www.aipg.org
Due to numerous factors, the engineering and delivery was undertaken by the author, Peter Bullock, P.Eng., M.Eng. The design involved tie back support for the marginally stable grav- ity wall into bedrock, GRS fill supported by micropiles and a tie back anchor system to gain the additional width (Figure 9).
Figure 9. Typical Cross Section.
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