19Aug 2014

How URETEK Repairs Mechanically Stabilized Earth (MSE) Walls

By Robert Armstead

What is an MSE Wall?

For more than 40 years, mechanically stabilized earth (MSE) retaining walls have been used to reinforce earthen structures, such as those found in constructing highways and roads, dams, bridge abutments, seawalls, dikes, golf courses, and other grade separation applications.

MSE wall systems are popular because they allow engineers, architects, and landscape and road designers to effectively integrate designs, that are cost effective and structurally sound, into tight site conditions.  Today, there are many types of MSE wall options including  geocells, segmental block, wire mesh and Bin-Wall.

A retaining wall on private property
An MSE retaining wall on private property

Sustainability of MSE Retaining Walls

A major design concern for MSE structures has been their durability in the soil/water environments in which they are being used.  Problems begin when aging MSE walls begin to degrade and lose their structural integrity due to corrosion of the galvanized steel used in the concrete facings, or water infiltration degrading the support soils behind the MSE wall.

According to Steve Wendland, a professional engineer at Kleinfelder, the failure rate of MSE walls is “1 in every 1,000.”  In his article When Retaining Walls Fail, Mr. Wendland writes that MSE retaining walls fail because of poor communication between the project team and, of course, water.

Photo courtesy of Steve Wendland, PE, RG
Failure of an MSE Wall
Photo courtesy of Steve Wendland, PE, RG

Repairing MSE Walls

In beginning the process for repairing an MSE retaining wall, engineers implement different field evaluation schemes to monitor the corrosion and degradation mechanisms in the constructed MSE structure.

Ground Penetrating Radar (GPR), is often used to locate voids behind the walls.

Injecting geopolymer behind MSE retaining wall.
Injecting geopolymer behind MSE retaining wall.

If soil reinforcement is required, URETEK Holdings is called in to inject geotechnical polymer into the void.  In consultation with the engineers on each project, URETEK designs a custom injection plan for the polymer to stabilize the loose soil and fill voids to minimize further soil erosion.

During injection, the URETEK team uses lasers to monitor the slightest movement of the MSE wall.  Every movement is calculated to ensure the wall does not collapse from the pressure of the material.

Repairing an MSE wall for the Florida Department of Transportation.
Repairing an MSE wall for the Florida Department of Transportation.

Benefits of Using Polymers in Repairing MSE Walls

The polymer actually displaces trapped water and is not compromised by wet conditions during or after installation.  Once the curing process is complete, the cured polymer retards further water infiltration.

By using URETEK’s polymer and deep injection method, private citizens and municipalities will mitigate time and expenses by not having to completely replace an MSE retaining wall.