Behind the house was a beautifully finished backyard, with multiple terraces down to a deck overlooking a ravine. This fall, mudslides carried quite a bit of soil away from the deck supports. What soil that remained was saturated with water; the contractor had already installed a supplemental drainage system to carry water away from the slope. Above, the terraces were visibly sagging downhill. With the slope in this condition, it was likely that a good portion of the backyard would slide into the ravine. The owner was worried about loosing her backyard, and had a contractor rearing to go, so we needed to get the design ready fast.
Working in cooperation with a soils engineer, we designed a 10′ retaining wall to hold back the soil at the base of the backyard. The retaining wall was comprised of steel pipe piles driven vertically into the ground, with 2 rows of anchors driven back into the soil at an angle to support the wall from falling outwards. Wood lagging was placed behind the driven piles to keep the soil from falling through, while allowing water to seep through the cracks. We used relatively small piles and anchors, as everything had to be hand-constructed, due to the difficulty in getting heavy machinery onto the site. This was a very specialized design, as the site conditions were very difficult.
I will be making several visits to the site in the coming weeks, as the work progresses, to ensure that the piles and anchors are installed correctly.