For more than 30 years, providing access to the natural environment through the Open Spaces program has been a commitment in Jefferson County, Colorado. During that time, a comprehensive Trails 2000 plan was developed to connect thousands of acres of Open Spaces land. But, the plan to complete the Clear Creek Trail was delayed in the mid-1990s because the cost of using traditional cast-in-place concrete retaining walls was too high. Another challenge was the length of the project. While the trail is run by Jefferson County, the project crossed state highways, crossed railroad tracks and ran through an area owned by a local foundation. Each entity needed to approve the project design, materials and costs.
After the trail project sat on the shelf for years, it was revived, and segmental retaining walls were proposed as an alternative to cast-in-place walls. A Segmental Retaining Wall (SRW) system was chosen, in part, because the cost was less than half that of the cast-in-place wall estimate. One of the design hurdles was the need to build a third of the retaining walls near highways where there was no room for cuts to install geosynthetic reinforcement. A structural anchorage system made it possible to install the product, eliminating the need for extensive excavation. In fact, the contractor said the structural anchorage system was more economical to use in almost all of the cut applications. The contractor explained that this system also made it possible to install walls without closing adjacent roadways—another important consideration.
Preserving the natural environment is one of the reasons Open Spaces exists. Building segmental retaining walls without disturbing trees and vegetation was a key consideration as the project was designed. Controlling graffiti was another consideration. The rough texture and irregular stagger of the Landmark retaining wall system is not an ideal surface for graffiti and has deterred that nuisance. To date, the trail has remained graffiti-free. As for the four entities signing off on the project, the county led the way, working with the railroad to secure their approval. The county also received a quick approval for the Landmark system from the Colorado Department of Transportation. And, the foundation approved the project based on the look of the product. The buff color and rough texture blend with the surrounding landscape. After the initial period of learning how to install a new system, the contractor said the Landmark system worked well and that they were satisfied with this cost-effective product.
Jefferson County has an attractive, affordable addition to the 179-mile (288-kilometer) trail program they supervise, providing increased access to the Open Spaces where the mountains and plains meet. Using the SRW system, the trail was built across a wide range of sites without disturbing trees and vegetation or closing adjacent roadways. CMD
EngineerSoil Reinforcement Design, Inc., Woodstock, GA
Site ContractorConcrete Express, Denver, CO
SRW ProducerPavestone Company, Denver, CO
• 72,000 square feet (6,690 square meters) of wall
• Height varied, up to 25 feet (7.6-meter)
• Various walls along a nearly five-mile (8 kilometer) long trail
Photos courtesy of Anchor Wall.
|| Direct Anchorage Design
In many retaining wall applications, sufficient space does not exist behind the face units to allow excavation and subsequent placement of geosynthetic reinforcement. In these applications, a direct-anchorage retaining wall system is a more aesthetically pleasing and less costly alternative to the conventional cast-in-place concrete that would often be used in such situations.
Direct anchorage consists of an anchor (e.g., soil nail) installed into the ground and connected to galvanized steel beams (walers) placed within the horizontal cavity in the SRW units, which were specifically designed to accommodate them.
Each steel beam spans two adjacent anchors, transferring the load from the segmental retaining wall units to the anchors. The space between the excavated face and the SRW units is filled with free-draining aggregate.
In addition to transferring stresses from the retained soil to the block, the fill is selected to provide drainage between the excavated surface and the wall face. Since the SRW units are not mortared, but interlocked, hydrostatic pressure is released through the joints in the blocks as well as the drain outlets typically placed along the bottom of the wall.