Retaining Wall Design Concepts For 3 Metre High Walls  

The retaining wall design concepts below are based on the Bosun Robust Block.

NOTE: These design concepts are merely just GUIDELINES ONLY. An engineer’s consultation is needed before building Retaining Walls.

For walls higher than 1.2m an engineer design and certificate is required.

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Normal Conditions

Normal conditions can be defined as:

  • The area must have good compactable soil (No sand or clay).
  • If the area does not have good compactable soil, fill material should be imported (G5 or G6 is acceptable).
  • No structural or vehicular loading.
  • No severe surface or ground water in the area.

Foundation:

  • Excavate to a depth of ±330mm.
  • Compact the soil 130mm below the intended concrete foundation to 93% MOD ASSHTO.
  • Construct a 400mm x 200mm, 20 Mpa concrete foundation – A concrete foundation will enable easier levelling.
  • The first block should preferably be placed below the ground level.

Construction:

  • It is recommended that the wall  be constructed at a 75° angle.
  • After each block layer the soil should be compacted to 93% MOD ASSHTO. Do not compact layers more than 150mm thick.
  • Use a vibrating roller or jumping jack tamper for compaction. Any mechanical compaction must not be closer than 300mm behind the block. 300mm and closer must be hand compacted in order to prevent blocks from tilting.
  • Install 40/40 composite reinforcing geogrid between every second row of blocks.  The geogrid should be ±800mm from the front edge of the blocks (It is recommended to use RockGrid® by Kaytech).
  • After the first three layers of geotextile, the width can be reduced to 1500mm.
  • The geotextile should be laid flat without creases.

Bosun Versoblock installations, use a geogrid after every third block.

  • The most important aspect of Retaining Block Walls is the compaction behind the blocks. The Blocks act merely as the system’s skin.

Subsoil drain:

  • The subsoil drain should preferably be installed ±1100mm behind the blocks in order for water to flow into the drain opposed to the compacted area.
  • Use a 110mm perforated pipe, enclosed in 19mm or 6mm stone and wrapped in 200mm x 200mm A2 nonwoven filament geotextile (Bosun recommends A2 Bidim® by Kaytech).
  • Fines will clog the system if a geotextile is not used.
  • Construct outlets every 6 meters dispose of water at the lowest end of the subsoil drain.
  • 3m Retaining Wall Design Concept under Normal Conditions

Click to enlarge

Areas with moderate surface or sub-surface water including a wick drain

Normal condition definition must be considered.

Foundation:

  • Excavate to a depth of ±330mm.
  • Compact the soil 130mm below the intended concrete foundation to 93% MOD ASSHTO.
  • Construct a 400mm x 200mm, 20 Mpa concrete foundation – A concrete foundation will enable easier levelling.
  • The first block should preferably be placed below the ground level.

Construction:

  • It is recommended that the wall  be constructed at a 75° angle.
  • After each block layer the soil should be compacted to 93% MOD ASSHTO. Do not compact layers more than 150mm thick.
  • Use a vibrating roller or jumping jack tamper for compaction. Any mechanical compaction must not be closer than 300mm behind the block. 300mm and closer must be hand compacted in order to prevent blocks from tilting.
  • Install 40/40 composite reinforcing geogrid between every second row of blocks.  The geogrid should be ±800mm from the front edge of the blocks (It is recommended to use RockGrid® by Kaytech).
  • After the first two layers of geotextile, the width can be reduced to 1500mm.
  • The geotextile should be laid evenly without creases.

Bosun Versoblock installations, use a geotextile between every third block.

  • The most important aspect of Retaining Block Walls is the compaction behind the blocks. The Blocks act merely as the system’s skin.

Subsoil drain with wick drain:

  • The subsoil drain should preferably be installed ±1100mm behind the blocks in order for water to flow into the drain opposed to the compacted area.
  • Use a 75mm perforated pipe, enclosed in 19mm or 6mm stone and wrapped in 150mm x 150mm A2 nonwoven filament geotextile (It is recommended to use RockGrid® by Kaytech).
  • Fines will clog the system if a geotextile is not used.
  • Construct outlets every 6 meters dispose of water at the lowest end of the subsoil drain.
  • Wick drains (Bosun recommends WickDrain® by Kaytech) are laid at 45° angle with 1.5m spacing, rearward.  Lengths vary according to design, e.g. 1.7m (1.7m x length of the wall / 1.5 = length needed).

V-drain or kerb:

  • The purpose of the V drain is to direct water away from the Retaining Block Wall.
  • The V drain or kerb should be ±2.5m behind the top edge of the wall, in order to divert water from the compacted area.
  • 3m Retaining Wall Wick Drain

Click to enlarge

Areas with moderate surface or sub-surface water including flo drain

Normal conditions definition must be considered.

Foundation:

  • Excavate to a depth of ±330mm.
  • Compact the soil 130mm below the intended concrete foundation to 93% MOD ASSHTO.
  • Construct a 400mm x 200mm, 20 Mpa concrete foundation – A concrete foundation will enable easier levelling.
  • The first block should preferably be placed below the ground level.

Construction:

  • It is recommended that the wall  be constructed at a 75° angle.
  • After each block layer the soil should be compacted to 93% MOD ASSHTO. Do not compact layers more than 150mm thick.
  • Use a vibrating roller or jumping jack tamper for compaction.
  • Install 40/40 composite reinforcing geotextile between every second row of blocks.  The geotextile should be±1800mm from the front edge of the blocks. (It is recommended to use RockGrid® by Kaytech).
  • After the first two layers of geotextile, the width can be reduced to 1500mm.
  • The geotextile should be laid evenly without creases.

Bosun Versoblock installations, use a geotextile between every third block.

  • The most important aspect of Retaining Block Walls is the compaction behind the blocks. The Blocks act merely as the system’s skin.

Subsoil drain with flo drain:

  • It is recommended that the wall  be constructed at a 75° angle.
  • After each block layer the soil should be compacted to 93% MOD ASSHTO. Do not compact layers more than 150mm thick.
  • Use a vibrating roller or jumping jack tamper for compaction.
  • Install 40/40 composite reinforcing geotextile between every second row of blocks.  The geotextile should be±1800mm from the front edge of the blocks. (It is recommended to use RockGrid® by Kaytech).
  • After the first two layers of geotextile, the width can be reduced to 1500mm.
  • The geotextile should be laid evenly without creases.

Bosun Versoblock installations, use a geotextile between every third block.

  • The most important aspect of Retaining Block Walls is the compaction behind the blocks. The Blocks act merely as the system’s skin.

V-drain or kerb:

  • The purpose of the V drain is to direct water away from the Retaining Block Wall.
  • The V drain or kerb should be ±2.5m behind the top edge of the wall, in order to divert water from the compacted area.
  • 3m Retaining Wall Flow Drain

Click to enlarge

Areas subject to structural or vehicular loads with sufficient space

Load is at least 3.3m from edge of wall.
Normal conditions definition must be considered.

Foundation:

  • Excavate to a depth of ±330mm.
  • Compact the soil 130mm below the intended concrete foundation to 93% MOD ASSHTO.
  • Construct a 400mm x 200mm, 20 Mpa concrete foundation – A concrete foundation will enable easier levelling.
  • The first block should preferably be placed below the ground level.

Construction:

  • It is recommended to use the wall be constructed at a 75° angle.
  • After each block layer the soil should be compacted to 93% MOD ASSHTO. Do not compact layers more than 150mm thick.
  • Use a vibrating roller or jumping jack tamper for compaction.
  • Install 40/40 composite reinforcing geotextile between every second row of blocks.  The geotextile should be±1800mm from the front edge of the blocks. (It is recommended to use RockGrid® by Kaytech).
  • After the first three layers of geotextile, the width can be reduced to 1500mm.
  • The geotextile should be laid evenly without creases.

Bosun Versoblock installations, use a geotextile between every third block.

  • The most important aspect of Retaining Block Walls is the compaction behind the blocks. The Blocks act merely as the system’s skin.

Subsoil drain:

  • The subsoil drain should preferably be installed ±1100mm behind the blocks in order for water to flow into the drain opposed to the compacted area.
  • Use a 110mm perforated pipe, enclosed in 19mm or 6mm stone and wrapped in 200mm x 200mm A2 nonwoven filament geotextile (It is recommended to use A2 Bidim® by Kaytech).
  • Fines will clog the system if a geotextile is not used.
  • Construct outlets every 6 meters dispose of water at the lowest end of the subsoil drain.

V-drain or kerb:

  • The purpose of the V drain is to direct water away from the Retaining Block Wall.
  • The V drain or kerb should be ±2.5m behind the top edge of the wall, in order to divert water from the compacted area.
  • 3m Retaining Wall Design Concept with Load Foundation Detail
  • 3m Retaining Wall Subsoil Drain Design
  • 3m Retaining Wall Design Concept for Structural Load with Space
  • 3m Retaining Wall Design Concept for Vehicular Load with Space

Click to enlarge

Areas with structural or vehicular loads with limited space

Loads should not be closer than 1.5m from the top edge of the retaining wall (consult a civil engineer if the load is closer than 1m).
Normal conditions definition must be considered.

Foundation:

  • Excavate to a depth of ±330mm.
  • Compact the soil 130mm below the intended concrete foundation to 93% MOD ASSHTO.
  • Construct a 400mm x 200mm, 20 Mpa concrete foundation – A concrete foundation will enable easier levelling.
  • The first block should preferably be placed below the ground level.
  • Ref 193 Mesh or Y10 reinforcing can be added to the foundation depending on the load.

Construction:

  • It is recommended to use the wall be constructed at a 75° angle.
  • After each block layer the soil should be compacted to 93% MOD ASSHTO. Do not compact layers more than 150mm thick.
  • Use a vibrating roller or jumping jack tamper for compaction.
  • Install 40/40 composite reinforcing geotextile between every second row of blocks.  The geotextile should be±1800mm from the front edge of the blocks. (It is recommended to use RockGrid® by Kaytech).
  • The last two geotextile layers must be laid under the load foundation ±2000mm from the top edge of the wall.
  • The geotextile should be laid evenly without creases.

Bosun Versoblock installations, use a geogrid between every third block.

  • The most important aspect of Retaining Block Walls is the compaction behind the blocks. The Blocks act merely as the system’s skin.

Subsoil drain:

  • The subsoil drain should preferably be installed ±1100mm behind the blocks in order for water to flow into the drain opposed to the compacted area.
  • Use a 110mm perforated pipe, enclosed in 19mm or 6mm stone and wrapped in 200mm x 200mm A2 nonwoven filament geotextile (Bosun recommends A2 Bidim® by Kaytech).
  • Fines will clog the system if a geotextile is not used.
  • Construct outlets every 6 meters dispose of water at the lowest end of the subsoil drain.

V-drain or kerb:

  • The purpose of the V drain is to direct water away from the Retaining Block Wall.
  • The V drain or kerb should be ±2.5m behind the top edge of the wall, in order to divert water from the compacted area.
  • 3m Retaining Wall Design Concept with Load Foundation Detail
  • 3m Retaining Wall Subsoil Drain Design
  • 3m Retaining Wall Design Concept for Structural Load with Limited Space
  • 3m Retaining Wall Design Concept for Vehicular Load with Limited Space

Click to enlarge