14. Back-side construction method for reinforced soil retaining walls applicable to narrow areas

Reinforced soil retaining walls (RRR method) are generally constructed in two stages: the reinforced embankment is built (STEP 1 in Figure 1), and the wall is built after settlement has converged (STEP 2 in Figure 1).
In STEP 2, the construction of the wall requires scaffolding in front of the wall, making it difficult to construct the wall in narrow areas.
In particular, construction work in close proximity to the commercial lines was carried out at night during railway track closing, resulting in prolonged construction and high costs (Figure 1).

In response, we proposed a back-side construction method where formwork is installed simultaneously with the reinforced embankment from the back side of the wall (embankment side), allowing construction without interfering with the front of the wall. The formwork for the wall, which was conventionally installed after the reinforced embankment was constructed, is placed from the back side of the wall (embankment side) using lightweight buried formwork that does not require form removal (Figure 2(a)).
On the other hand, when reinforced embankment and buried formwork are installed simultaneously, the buried formwork is supported by L-shaped steel and anchor materials from the embankment side, which causes deformation as the reinforced embankment settles. In response, we developed a settlement-allowing member that can slide vertically along L-shaped steel. By attaching this settlement-allowing member to the anchor material, it can accommodate the settlement of the embankment (Figure 2(b)).
The proposed method can reduce construction time by 30% and construction cost by 15% for the construction of narrow areas close to commercial lines.

For these methods, we have prepared manuals for design and construction, cost estimation, and materials, which are applicable for actual construction projects.