Concrete interlocking block retaining wall design

Concrete interlocking blocks make very good retaining walls. The benefits are:

• Durable and long lasting (>100 years)
• Fast to build
• Economical

The wall heights are in modules of either 600mm or 800mm depending of the size of wall and the block used.

They can be used from a height of 0.6m to 4m.

The concrete design mix is normally 35 to 50kN/mm2 in strength and there is no steel reinforcement in the blocks. Concrete strengths less than this will reduce the design life of the blocks.

There is no need for a heavy foundation. The blocks need to be laid on firm ground on 100mm of concrete to give the wall a level and flat foundation.

Drainage is required at the back of the wall to stop any hydrostatic pressure building up that may cause an issue. The drainage is normally a perforated pipe and the back of the wall back filled with clear stone to allow for water to flow down to the drain.

Height	1200	1600	1800	2400	3000	3200	4000
Block Type	600	800	600	800	600	800	800
Base Width	800	1000	1400	1800	2600	2600	2600
Base Depth	100	100	100	100	100	100	100
Surcharge	2.5kn/m²	2.5kn/m²	2.5kn/m²	2.5kn/m²	2.5kn/m²	2.5kn/m²	2.5kn/m²
Factor of Safety	M=1.5	M=1.5	M=1.5	M=1.5	M=1.5	M=1.5	M=1.5
Cost Index	30	41	42	73	77	89	125
Sketch

You can use the concrete interlocking block retaining wall design table above as a guide only to develop budgets for construction. The table gives you a number of wall heights and the number and size of blocks required for the height of the wall. You can use this information to prepare a cost plan for your project.

The design table above are for the gravity block retaining walls, and are Indicative designs based upon a base material with allowable bearing pressure of >200kPa.

The retained material is assumed to be well graded, granular backfill with back of wall drainage or weep holes to relieve hydrostatic pressure.

All indicative information presented in this table is based upon assumed loading and ground conditions and will be subject to change following detailed, site specific design.