CHAPTER 1
INTRODUCTION
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1.1 |
RRR: Definition |
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1.2 |
Scope of Application |
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1.3 |
Terminologies |
1.1 RRR: DEFINITION
RRR is the abbreviation for geosynthetic-reinforced soil retaining wall (GRS-RW) system that was constructed with a facing having flexural rigidity.
RRR (Reinforced Railroad/Road with Rigid Facing) is the geosynthetic-reinforced soil retaining wall system developed by the Japan Railway Technical Research Institute.
RRR uses a rigid facing with the geosynthetic reinforcement to allow for near-vertical and steep slope construction (Figure 1.1). The advantages of this construction procedure include, but are not limited to the followings:
1. It requires very limited construction space compared to the conventional wall systems.
2. The completed structure occupies less space compared to the conventional wall systems.
3. By using a facing of high rigidity, the stability of the wall system is increased while the deformation is minimized.
4. The geosynthetic layers are closely spaced so that a wide range of backfill can be used without affecting performance.
The reinforced soil system using metallic strips was pioneered by Teree Armee (so called Reinforced Earthâ ). Steep reinforced slopes of geogrids are becoming very popular. A series of long-term research revealed that by installing a rigid facing, the stability of the reinforced soil system can be enhanced with very small deformation. The RRR method was developed based on this concept and has been used successfully to construct many railway structures, in particular widening of existing embankments. This construction procedure is highly accepted by the railway companies. It is highly relevant for replacing conventional retaining wall systems in the highway construction, such as widening of highway embankment and bridge abutments.
1.2 SCOPE OF APPLICATION
This Manual compiles technical information for RRR used in highway construction. It is not intended for some others specific applications, such as private housing and land development, where related specifications and guidelines should also be consulted.
RRR renders a high stability and minimizes deformation. It is applicable to retaining wall systems up to considerable height. This Manual is intended for design and construction of GRS-RW system up to a maximum height of 10 m. Beyond this height, the design specialists should be consulted. For applications other than highways, related specifications and guidelines should also be consulted.
A list of relevant Japanese specifications and guidelines are given below:
This Manual is written based on the results of application to railway-related structures, which are subject to stringent technical requirements. The references are as follows:
1.3 TERMINOLOGIES
RRR uses a rigid facing with the geosynthetic reinforcements to allow for near-vertical and steep slope construction.
RRR Method - The retaining wall system which uses a facing having flexural rigidity combined with the geosynthetic reinforcement to allow near-vertical and steep slopes to be constructed.
Geosynthetic - The geosynthetics used in RRR method should posses adequate tensile strength and have passed the specified tests.
Facing - The facing is constructed in front of the slope to increase stability while minimizing deformation. The facing used in RRR can be the unreinforced or reinforced concrete.
Subgrade - The soil foundation below the pavement that serves as the base to determine the thickness of pavement.
Road Structure - The portion of soil in reinforced soil, excluding subgrade.
Reinforced Zone - The portion of soil that is densely reinforced by geosynthetic layers.
Reinforced Soil Retaining Wall (GRS-RW) - The geosynthetic-reinforced soil retaining wall constructed by the RRR method.
Reinforcement - The tensile reinforcements which are embedded in the soil. In the RRR method, geosynthetic reinforcements are used.
The different components of GRS-RW are illustrated in Figure 1.2.
