Micropiles in Action!
SSR’s structural team previously published a blog post on micropiles, where we explained what a micropile is, when they are ideal to use, and the benefits of a micropile foundation. This post will review recent, real-world applications of micropiles.
An existing client in Kentucky wanted to add a pedestrian bridge connecting two existing buildings that were separated by a large parking lot. An underground vault was located adjacent to one of the buildings near where the pedestrian bridge was going to tie into the building. This vault prohibited us from being able to dig deeper than it and was something that we would have to build the foundation around. Additionally, there was an existing water main that could not be re-routed or interrupted, and our team had to work around. Our team determined that micropiles would allow the foundation to have a smaller footing that did not disrupt the water main or underground vault. The geographic area is also favorable to the use of micropiles since they get strength from the surrounding earth and can still be effective if a sinkhole opens, which is common in this area.
A utility district in east Tennessee had an existing pump station in a flood basin with severe erosion underneath the pump house pad (see attached photo). The erosion created an elevated slab condition causing the slab to not only span when not intended to, but also is unsupported at slab ends as shown, which led to concrete delamination and overall structural issues. The utility district wanted a new pump house to be placed with greater supportive weight than previously required. The initial thought was to demolish and place a new slab on grade to support the new housing; however, with high drainage still present regardless of the new structure, utilizing micropiles was the structural support recommended and designed for. Micropiles are great for transferring high compressive forces into soil sublayers. While this is not the case as the new pump housing does not contain a great load, the efficiency in the micropiles creates a sub-grade column system to where, in the event similar flooding and erosion, the supportive slab for the pump housing would not be spanning when not intended, or freely cantilevering. Rather, the slab would be spanning between the micropiles, and the micropiles would be supported by the side friction of the embedment through the length of the micropiles.
A third example of micropiles in action is at another existing pump station designed for future expansion. The expansion would include adding an additional dry-well and connecting it to the existing wet well and main building. The sub-grade dry-well would dowel into the existing wet well and a doorway in the existing masonry walls would be installed to create an additional area for 1-story concrete masonry unit (CMU) wall structure on top of the sub-grade well. The CMU building would be constructed on wall footings with micropiles spaced evenly around the perimeter. The base slab of the drywell would be supported by micropiles as well. The micropiles’ purpose was two-fold: the dry-well would be asserting decently large loads on the lowest foundation level, and the existing portion was constructed on micropiles, so to avoid any differential settlement between the portions of the structure (new well and existing) micropiles were placed. Another advantage of micropiles is they can be installed easily, even in close proximity (within 5 feet) of an existing building since they are not destructive (see photo 2). The micropiles being installed for the new CMU wall grade beam supports approximately 3’-0” away from the existing building, which was easily achieved without concern for damage to the existing building foundation system.
These are just a few recent examples of how our team was able to utilize micropiles in the field, to the benefit of the project and client. Reach out to see if micropiles are a solution for your next project.