How deep should retaining wall posts be for concrete?

Author: Prof. Pattie Graham  |  Last update: Saturday, July 19, 2025

Post holes will be dug with a 450mm diameter, at a depth equal to your retaining wall's height. Your holes should be equally spaced, as this will keep your sleeper retaining wall level and structurally sound.

How deep to concrete retaining wall post?

The post holes into which the retaining wall posts will be placed shall be 450mm diameter with minimum 100mm concrete cover below the post. Footing depth is typically equal to the height of the retaining wall. For this example, therefore, the post hole is 1200mm.

How deep should a post be set in concrete?

How Deep Should I Set a Post in Concrete? In general, the depth of the concrete post hole should be 1/3 to 1/2 the height of the post. So, if your post is 6 feet high, then you should position it in a 2-foot to 3-foot hole. Check your local codes for specific project guidance.

What are the 7 common mistakes made when installing retaining wall blocks?

7 Common Mistakes To Avoid When Installing a Retaining Wall
  • Choosing the Wrong Material. ...
  • Not Providing Adequate Drainage. ...
  • Forgetting the Frost Line. ...
  • Too Much Weight Behind the Wall. ...
  • Inadequate Footing. ...
  • DIYing a Complicated Wall. ...
  • Not Maintaining Your Wall.

How deep should posts be for a retaining wall?

Depth of post holes: With wood retaining walls, the rule of thumb is that the height of the soil you hold back should roughly equal the depth of the post holes. Add preservatives: While the faces and factory-cut ends of pressure-treated wood are protected, the ends of site-cut wood are not protected.

Concrete Sleeper Retaining walls

Does a 2 foot retaining wall need drainage?

Absolutely! Even a 2-foot retaining wall needs an effective drainage system. Without it, water can build up behind the wall, leading to pressure that might cause the wall to lean or even collapse. All walls need systems to manage water effectively, preventing damage over time.

Can you use 4x4 posts for a retaining wall?

Building a solid retaining wall using 4x4 treated posts is a straightforward project you can complete yourself with just some basic tools and supplies.

How deep to bury retaining wall blocks?

Excavation

Preparing the base where the first layer of block will be placed is critical to building a well-placed, stable retaining wall. Dig a trench for the bottom row of blocks. They should be buried about 1 inch deep for every 8 inches of wall height.

What is the most common retaining wall failure?

Soil saturation is the most common external factor that causes retaining wall failure, but there are many ways to prevent it.

What is the thumb rule of retaining wall construction?

Rules of thumb commonly used by designers to establish the geometry of the wall include (refer to diagram): Base width = 1/2 to 1/3 of the height of the wall. Base thickness = 1/8 of the height of the wall but not less than 12 inches. Stem thickness = 6 inches + ¼ inch for each foot of wall height.

How deep should I put my post?

Also, before you start to dig, be sure to call your local utilities to come mark any underground wires or pipes. The general rule of thumb when setting a post is that the depth of the post's hole needs to be one-third to one-half of the actual above-ground height of the post.

How many bags of Quikrete do I need for a 4x4 post?

Mix two 50lb bags of concrete with water in a mixing tub or 5-gallon bucket. Add concrete into the hole and around the 4” x 4”. Depending on your climate, let concrete set up for 24 - 48 hours.

How deep to put a 4x4 post in the ground?

The depth of the hole should be 1/3-1/2 the post height above ground (i.e., a 6-foot tall fence would require a hole depth of at least 2 feet). Add about 6 inches of QUIKRETE All-Purpose Gravel into the bottom of the hole.

How deep do retaining posts need to be?

The rule of thumb – the post should be 2/3 of the height of wall in the ground. So if your wall is 1.2m high – your post hole should be 800mm deep. The hole diameter should be large enough to allow for slight movement of the auger when drilling and enough concrete around the post to hold it.

How deep should a concrete post be?

While there's no generic answer when it comes to concrete fence post depth, a general rule of thumb serves as a good starting point – at least one-third of the total post height should be buried underground. This ensures a good balance between stability and practicality.

How deep do retaining wall footings need to be?

The footing should be 150mm deep and 450mm wide if the wall being built is a retaining wall. For larger retaining walls an engineer may need to be approached for advice.

How long to leave a retaining wall before backfilling?

Sometimes retaining walls are designed as cantilevers. These typically include reinforcement and rely on the combined strength of the concrete and reinforcement to resist bending at the base of the wall. In that case, plan on waiting seven days before placing the full depth of backfill.

What makes the strongest retaining wall?

Poured concrete is the strongest and most durable choice for retaining walls. It may also be carved and formed to look like mortared stone depending on your taste.

What is the lifespan of a retaining wall?

Discover how the right retaining wall can reduce soil erosion, improve water drainage, and transform your property. Depending on the material, soil, and groundwater, a permanent retaining wall can last anywhere from 25 to 100 years.

How deep should a retaining wall post be?

Each hole is to be dug to the recommended depth (dependant on the wall height – rule of thumb half in the ground half out ie. 600mm high wall will require 600mm of post to be cemented into the ground) * Add 100mm to the depth of each hole for 20mm drainage gravel.

How deep should a 4 foot retaining wall be?

Base Installation

The depth of the trench should be one inch for every one foot of wall height.

Why put gravel behind a retaining wall?

This is why the drainage system and gravel backfill are crucial; they prevent water from becoming trapped and help maintain the wall's stability. Regardless of the style or material you choose, these components are the foundation of a long-lasting retaining wall system.

Can you use quick set concrete for retaining wall posts?

Below 20MPa: Regular quick-set products for filling or anchoring jobs that don't require structural strength. Such as letterboxes, fence posts, non-structural retaining wall posts and clotheslines.

Can I use pressure treated lumber for a retaining wall?

Your best choice is a pressure-treated wood that has a rating of . 40 or higher.

Does a concrete retaining wall need a footer?

A retaining wall without a footing may experience settlement, leaning, or failure over time. Footings help distribute the weight of the wall and its load, preventing excessive pressure on the soil and ensuring long-term stability.

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