RRR-B

Geosynthetic-Reinforced Soil (GRS) retaining Wall

RRR GRS retaining walls (RWs) are constructed by reinforcing the backfill with geosynthetic reinforcement layers that are firmly connected to the full-height rigid (FHR) facing.
Many RRR GRS RWs performed very well during recent major earthquakes, including the 1995 Kobe E.Q., the 2011 Great East Japan E.Q. and the 2016 Kumamoto E.Q. Besides, RRR GRS RWs have a high resistance against river floods and ocean storm waves.

Place the first layer of a geosynthetic reinforcement and gravel-filled bags (or welded wire mesh boxes), then place and compact the first soil layer.

Construct the second layer in the same way as the first layer.

Complete the full-height geosynthetic-reinforced soil wall by repeating the procedure shown above.

Cast-in-place concrete layer directly on the wall face, ensuring a firm connection between the facing and the geosynthetic reinforcement layers.

For RRR GRS RWs, the backfill is first constructed reinforced with planar geosynthetic reinforcement layers (usually geogrid layers). After the deformation of the supporting ground and the backfill due to the construction of backfill has sufficiently taken place, a lightly steel-reinforced full-height rigid (FHR) facing is constructed by casting-in-place fresh concrete on the vertical geosynthetic-wrapped-around wall face in such a manner that the FHR facing is firmly connected to the geosynthetic reinforcement layers. Hence, the facing and the facing/reinforcement connection are not damaged by relative vertical settlement between the facing and the backfill. Besides, a pile foundation for the facing becomes basically unnecessary.
RRR GRS RWs are highly cost-effective because of no use of pile foundation; no use of heavy construction machines; use of relatively short reinforcement; no strong restriction to the backfill type; use of FHR facing as foundation for other structures; use of the backfill crest close to the wall face; and no need for a space in front of the wall for propping of concrete form for the FHR facing construction.

The full-height rigid (FHR) facing confines effectively the backfill by developing high earth pressure. Therefore, high connection force and high tensile force develop in the reinforcement layers. As a result, the backfill, in particular in the zone immediately behind the wall face, becomes very stable. Even if part of the wall is damaged locally, it does not develop into the failure of the whole wall.

Moreover, the FHR (full-height rigid) facing can be used as a foundation for other structures, such as crash barriers, noise/wind barriers, electric power supply poles etc. Unlike other types of reinforced soil RWs having a facing that is not FHR (e.g., discrete panels or modular blocks), roads and railways can be arranged very close to the wall face relying on high stability of the reinforced backfill immediately behind the FHR facing.

RRR GRS retaining wall with FHR facing for very busy urban railways near Shinjuku Station, Tokyo, constructed during 1995 - 2000

Omura train yard of Kyusyu Shinkansen under construction 2018

Recently, many railways (including high-speed railways) use continuous RC slab tracks because of a high lifetime cost-effectiveness resulting from very low maintenance cost despite relatively high construction cost. However, RC slab tracks cannot be constructed on ordinary embankment and the backfill retained by conventional RWs due to their potentially high residual deformation. On the other hand, RC slab tracks are constructed without any problem on RRR GRS RWs because of very small residual deformation of the backfill that is well-compacted and stabilized by taking advantage of closely arranged geosynthetic reinforcement layers (with a vertical spacing of 30 cm) that are firmly connected to the FHR facing.