Arizona Home on the Edge Part 2 – Technical Design Solutions
Retaining Wall and Home Stabilization
Cost of the project: $121,500
Project Start Date: August 2008
Project Finish Date: January 2009
Structural Engineer: Gervasio & Associates
Geotechnical Engineer: Copper State Engineering
The Gogte Residence had several foundation and stabilization problems before their home was complete (part 1). A hillside homeowner needed expert help and called in Fred Nelson PE, of Gervasio and Associates (Structural Engineers) and J. David Deatherage PE, of Copper State Engineering (Geotechnical Engineers) to assess the situation.As outlined in Part 1, the house had construction errors causing foundation problems. Specifically the retaining wall was higher than planned and the house was build closer to the wall than originally planned.Their Technical Design Plan to reinforce the home and addressing the foundation and retaining wall problems included a combination of 4 techniques using:
- Helical Piles
- Carbon Fiber Reinforcement
- Hollow Bar Tiebacks
- Permeation Grouting
The solutions chosen were to first install the helical piles under the foundation of the house to re-level the house and relieve soil pressure from the loads caused by the bearing pressure of the load bearing walls of the house on the soil behind the wall. The second step was to reinforce the retaining wall face by installing carbon fiber reinforcement in a grid pattern on the outside face for the positive moment. Although no reinforcement could practically be installed on the inside face for the negative moment, the combination of methods including eventual permeation grouting behind the wall to reduce active soil pressure were enough to keep the wall safely intact to span between micro pile tiebacks. The 3rd step was to install the hollow bar tiebacks. Contech 30/16 mm hollow bars were to be drilled and grouted simultaneously. This allowed tiebacks to be installed to a 20 foot length through soil and rocks with out fear of collapse of the drill hole. The 20 foot length was beyond the slip plane of the soil behind the retaining wall to be effective and in many locations socketed into the rock. These were particularly effective because of the large interface capacity of the grout around the hollow bar with the sandy rocky soils. Finally, once the walls were stabilized and the lateral loads reduced, permeation grouting was installed behind the wall to increase the shear capacity of the soil particles and reduce the lateral loads.
Details and notes showing the various solutions chosen to remediate the property
Now the challenge was to find a foundation repair contractor that could tackle the complexities of working in a preserve on a hillside. Arizona Ram Jack was chosen and their first task was creating temporary access for the construction work that was to be performed. Read more in Part 3…
