Geotechnical Services Division

Retaining Walls

WSDOT uses many different types of retaining walls.  The Geotechnical Division is responsible for determining the best and most cost effective retaining wall to use on a project.  We assist the design offices in the State with selecting the most effective location for the retaining wall, and we provide critical design information regarding the stability, settlement, and earth pressures exerted on the different types of walls we use.  Some walls are designed entirely within our office, and others are designed by our Structures office or by a proprietary company with our involvement.

• WSDOT Designed Walls

• Preapproved Proprietary Walls

WSDOT Designed Walls

Chapter 1130 of the WSDOT Design Manual provides additional guidance about the use of retaining walls on DOT projects.  

WSDOT designs and uses many types of retaining walls on its projects.   The Geotechnical Division, Region Materials Offices, and the Bridge and Structures Office coordinate on the design of specialty walls.  Some of the specialty walls requiring the involvement of the Geotechnical Division and the Bridge and Structures Office include:

• Tie Back Walls

• Soldier Pile Walls

• Cylinder Pile Walls

• Soil Nail Walls

• Gabion Walls

• Geosynthetic Walls

• Temporary Walls

• Rock Walls

The Bridge and Structures Office will usually prepare the Plans Specifications and Estimates (PS&E) for most specialty walls with assistance from the Geotechnical Division.  On occasion, the Region Offices, with assistance from the Geotechnical Division, will prepare the PS&E for specialty walls such as when a Geosynthetic Wall is used on a project. 

Geosynthetic Walls require the use of a General Special Provision and the Qualified Products List. The General Special Provision for Geosynthetic walls can be found under CONSTRUCTION GEOTEXTILE in Divison 2 of the General Special Provisions.

Appendix D of the Qualified Products List contains a listing of the approved geosynthetic materials for use in geosynthetic walls on WSDOT projects. 

For all walls, our Region Design Offices are responsible for determining the wall geometry.  The Region Offices are also responsible to prepare the Plans Specifications and Estimates (PS&E) for the Reinforced Concrete Cantilever Walls found in Section D of our Standard Plans. 

Preapproved Proprietary Walls

• Concrete Panel Faced
• Modular Block Faced
• Wire Faced

Many private companies design, market, and sell retaining wall systems.  These proprietary companies have trademarks, licenses, or patents on the wall systems that they represent.  As a Public Agency, WSDOT cannot “design” these wall systems.  However, we can utilize them on our projects through the competitive bid process.  To streamline the bid process and ensure quality, WSDOT has reviewed the wall systems of several manufactures and preapproved their systems for use on DOT projects. 

Chapter 1130 of the WSDOT Design Manual provides additional guidance about the use of proprietary retaining walls on DOT projects.

What is Preapproval?

 The preapproval process enables WSDOT to perform a detailed review of:

• The design methods used by the Proprietary  Co. to design their walls
• The wall details
• Wall materials
• Wall construction methods

The Highway Innovative Technology Evaluation Center HITEC produces technical reports on the available wall types.  WSDOT will use the HITEC report and any additional information supplied by the wall manufacturer to complete the preapproval process.  If you are a wall supplier and would like more information regarding preapproving your wall system please contact the Bridge and Structures Office.

WSDOT has General Special Provisions that are to be included in our contracts for our commonly used Preapproved Proprietary Walls.  The Concrete Panel Faced and Modular Block Faced preapproved proprietary walls can be found in the General Special Provision (GSP) Structural Earth Wall and the Wire Wall can be found in the GSP Wire Wall.  They are available at WSDOT’s Project Development web site.

Concrete Panel Faced Preapproved Proprietary Walls

The concrete panel faced walls that have been preapproved are very similar in their appearance. The facing panels that make up the part of the wall you can see are about 5 feet wide by 5 feet tall and are made from concrete.  They look very similar to the wall at the right, which was recently constructed on the Sunset Interchange project in Issaquah.

The concrete panels you can see are about 4 to 6 inches in thickness.  Behind the concrete, there are reinforcing elements buried in the soil. These reinforcing elements hold the panels in place and strengthen the soil so that the soil, reinforcing, and the facing panels all work together to form the wall.  The various walls systems differ in the type of reinforcement that is used and in the connection of the reinforcement to the facing panel, but they are all very simple and similar.

 
Examples of two different types of soil reinforcing, wire ladder and steel strips.

The following table lists the current preapproved proprietary walls that have concrete panel faces.

Modular Block Faced Preapproved Proprietary Walls

The modular block faced walls that have been preapproved are very similar in their appearance. The concrete blocks that make up the part of the wall you can see are typically eight inches tall and 12 inches wide.  They look very similar to the wall at the right.

Behind the blocks, there are reinforcing elements buried in the soil. These reinforcing elements hold the blocks in place and strengthen the soil so that the soil, reinforcing, and the blocks all work together to form the wall.  The various walls systems differ in the type of reinforcement that is used, the shape of the block, and in the connection of the reinforcement to the block.

The following table lists the current preapproved proprietary walls that have modular block faces.  

 Wire Faced Preapproved Proprietary Walls

There is only one wire faced wall that is currently preapproved.  It is distributed by Hilfiker Retaining Walls.  The system is comprised of welded wire mats that interlock at the face.   The mats are spaced about 2 feet vertically and rock is placed at the face to keep the finer grained backfill from spilling through the large wire openings.

Wire walls are especially settlement tolerant and are often used where there are poor soils and settlement is expected to be severe.  Use of this wall may require sole source approval if there are no other suitable wall types that can be include in the Special Provisions.