🕑 Reading time: 1 minuteGeogrid segmental retaining wall is used where tall wall is required. Details and design of geogrid segmental retaining wall with calculations is described in this article. Segmental retaining wall height is restricted due to stability issues, but the height can be increased with the help of using woven synthetic sheet or in another term geogrids as successive layers at the back face of the wall. Layers are positioned and anchored into the facing blocks as shown in Figure-1 result in creating reinforced earth unit mass that acts against overturning and sliding actions. The geogrid segmental retaining walls can be constructed for height more than 12m. Different loads and reactions acted on the wall are shown in Figure-2.
Figure-1: Geogrid anchored into the facing blocks
Figure-2: Loads and Forces acting on Geogrid Segmental Retaining WallThere are various types of geogrids with different tensile strength that produced by manufacturers. Generally, Geogrids are 3.65 m wide and the length is depending on design requirements. Ultimate strength of geogrids is determined by test as per either ASTM or Geosynthetic Research Institute (GRI). Moreover, long term design strength is calculated from ultimate tensile strength by using a safety factor to take detrimental effects to considerations, such as long term degradation, damages during construction, material deficiency. Additionally, design safety factor 1.5 is used for Long Term Allowable Design Strength (LTADS) and it would be (LTADS/1.5). Geogrids are commonly anchored into the facing wall joints at one end and in-situ soil beyond the backfill to achieve effective utilization of geogrids. Resistance against pullout is consist of friction coefficient at block joint and any engagement technique that is employed for example pins through geogrid interstices, folding geogrids over a lip in the block as shown Figure-3 and Figure-4 in respectively.
Figure-3: Pin through geogrid interstice
Figure-4: Engagement of geogrid by a lip of blocksBlocks are tested to determine connection values for various types of geogrids. Ultimate connection value for blocks is computed as follow: Peak connection strength = 425 + 0.27N, with a maximum of 8.45 KN –> Equation-1 Where: 425: is the value of the proprietary geogrid engagement to the block 0.27: is the tangent of block-geogrid-block friction angle N: is the weight of overlaying blocks And safety factor of 1.5 is used for connections.
- Procedure for Design of Geogrid Segmental Retaining Wall
- Design Criteria for Geogrid Segmental Retaining Wall
- Masonry Units
- Calculation of Lateral Soil Pressure
- Coulomb Equation for Lateral Earth Pressure Calculation
- Selection of Geogrid for Segmental Retaining Wall
- Check Required Geogrid Length beyond Failure Plane:
- Determine Geogrid Embedment Length (Le)
- Retaining Wall Base Width Calculation
- Check for Overturning of Retaining Wall
- Sliding Check at Lowest Geogrid Layer
- Check for Soil Bearing Pressure
- Soil bearing capacity