The job of a retaining wall is to keep tons of soil from escaping, year after year, without complaining. If it operates properly, it is unnoticed. Failure to do so is typically not due to a selection of the wrong wall type; it is typically due to the selection of the wrong supplier. This guide outlines the exact methods of selecting the right precast concrete retaining wall supplier to ensure that your project doesn’t fall into the second category, but into the first.
In This Article, the Author Examines the Question of Why the Supplier Choice Matters More Than the Wall Type
There are lots of guides available which just discuss wall types, gravity, cantilever, counterfort, and skip supplier choice. That’s backwards. The best wall design in the world will be a failure if the manufacturer does not implement quality control or and the reinforcement is incorrect.
Particularly, it is well known that the biggest reason for failing retaining walls is poor drainage, which depends on the skill of a supplier to engineer and construct the product, not only on the shape being sold to you. A supplier who is aware of this makes drainage facilities an integral part of the wall from the outset. One that does not will provide you with a handsome wall that will become useless in a couple of rainy seasons.
When You Are Buying a New Car, You Should Understand What You Are Purchasing Before You Do It
Prior to assessing suppliers, it is beneficial to have an idea about the type of wall you’re trying to build as this will influence which suppliers are deserving of a conversation.
Gravity Walls
Gravity walls are unsupported by any other means and only hold up against soil pressure by virtue of their own weight. They are simple, require no complex reinforcement and are economical until about 3 meters, and are more suitable for smaller projects.
A Cantilever or an L-Shaped Wall
A cantilever or an L-shaped wall is supported with a reinforced L- or T-shaped foundation with soil placed on the base slab providing counterweight against overturning. These require less concrete than gravity walls, but are more complex to design, and can be used to a much higher height than a gravity design can be used.
Counterfort Walls Precast Concrete Retaining Wall Supplier
As the height of the wall increases beyond about 7 to 8 m, counterfort walls become more economical than plain cantilever walls because they require less bending stress by adding vertical concrete webs behind the main wall.
Mechanically Stabilized Earth (MSE) Walls
Mechanically Stabilized Earth (MSE) walls use precast facing panels in conjunction with reinforcement layers (geogrid or steel strips) embedded in the backfill to act as a gravity wall system, not just a precast concrete facing wall.
Once you find out what type of wall is the appropriate choice, the amount of suppliers you need to contact for your project will be reduced significantly because not all precast manufacturers can make all wall types.
Inquire About Their Design Standards and Codes
The serious precast wall supplier designs to a set of codes, not some flaky rules that they have devised. Good manufacturers of L-shaped walls typically design to established Eurocode specific standards for geotechnical design and concrete structures, including some safety factors, typically to a minimum of about 2 for overturning and 1.5 for sliding.
It also involves the concrete grade and reinforcement cover. Typical industry specifications for precast L-shaped wall units include concrete strengths and specified cover depths for the reinforcement, depending on the exposure conditions—whether the site is in standard ground exposure or more severe exposure conditions such as chlorides or sulfates.
Seek clarification from your supplier about codes they are designing to and actual grades and cover provided. A supplier that responds with details is talking your language. A no-bullshit, “industry standard” type guy needs a second look.
Check Out How They Handle Drainage
Most retaining wall failures are due to poor drainage, hence this needs its own discussion with any possible supplier. Be sure to ask them specifically how the wall design is going to deal with water; whether it will have weep holes, a free draining granular backfill layer, filter fabric to prevent fines from blocking the drainage, or any built-in drainage channels within the units themselves.
Other precast systems incorporate a hollow block configuration that allows for drainage to be an integral part of the wall structure and also enhances the wall’s overall strength. There are others that depend on external drainage layers added when backfilling. Both methods can be used, but the supplier must give a definite answer, rather than a nebulous or ambiguous “drainage is included.
Examine Their Manufacturing Quality Control
The quality of precast concrete can be quite different among manufacturers, even if the shape of a wall is the same on paper. Inquire how they make their product – whether it’s wet-cast or dry-cast, what types of finishes they provide, and what quality control is performed prior to a unit shipping out of the factory.
Surface finish is also more than just an aesthetic element. A smooth, well-shaped precast finish will not allow dirt or algae to build up as quickly as a rough finish and properly chamfered edges will minimize the risk of chipping while transporting and installing the precast. Little details give you much insight as to the care put into a supplier’s production line.
Request Engineered Shop Drawings
A good supplier will offer engineered shop drawings in a system of retaining walls—not just an off-the-shelf spec sheet. The drawings should portray existing conditions, the height of your walls, type of soil, and any adjacent surcharge loads due to structures or traffic.
Sellers who provide drawings and also construction consulting services can spot site specific problems sooner before the installation creates a discrepancy between the design and ground conditions. If you are unable to get engineering assistance from the supplier you are purchasing from, then you are probably purchasing a standard product that was not built for your project.
Compare Installation Requirements Precast Concrete Retaining Wall Supplier
The installation requirements vary greatly from one precast wall system to another. Some gravity block systems use interlocking joints and careful leveling without mechanical fixings, and cantilever and L-wall systems frequently require a well engineered foundation into which the units bolt or are cast.
Inquire with your supplier what kind of foundation preparation their system needs, and if they provide instructions for installing or if they have contractors that are familiar with their product. You’re ordering a system that requires the foundation to be reinforced and your site team thought they were getting a system that would be installed with gravity only, which means you will be stuck with the added cost of having to reinforce the foundation when construction time comes.
Check Out Their Track Record and References Precast Concrete Retaining Wall Supplier
Certifications and design standards indicate the things a supplier can do. Projects that are done have delivered what they did. Request some examples of retaining walls they have provided with similar parameters as in your project such as height, soil type, surcharge loading, etc. and preferably with photos taken well after installation, not just on the day of delivery.
Take note of the performance of these walls throughout the years. When a wall is still level and well-drained after a few rainy seasons, it speaks more about the quality of the supplier than any brochure ever will.
Recognize Red Flags to Watch For Precast Concrete Retaining Wall Supplier
There are a number of warning indicators that have been regularly found to distinguish potential suppliers from reliable suppliers. Beware of general answers or a specific design code, hesitations to offer engineered shop drawings specific to your site, no clear explanation for how their system manages drainage and pricing that appears to be sharply under the pricing of competitors for no apparent reason.
Don’t let any of these turn a supplier away, but a combination of two or three can make the decision to go that bit harder, and make you ask a few more questions before you make the leap.
Integrate All the Elements Into a Cohesive Unit.Make It All Work
The best way to select the best precast concrete retaining wall supplier is to identify the type of wall you need and ensure that the supplier designs to a code of practice, manages drainage correctly and supports their product with real engineering and proven experience. Skip that verification, and you’re risking a structure that is supposed to stand for many years and pull up tons of soil. If you get it right, your wall is what a retaining wall should be – silent, permanent and invisible.
