Project Case Study: Saving a critical slope

September 2006 » Feature Articles
The world-renowned number 12 green at Muirfield Village Golf Club in Dublin, Ohio, benefits from modular gabion basket design in the stabilization and repair of an adjacent pond bank.
Paul B. Latshaw

DETAILS
Project:
Muirfield Village Golf Club, Dublin, Ohio
Civil engineer: Hull & Associates, Inc., Dublin, Ohio
Product application: Subsurface, modular gabion baskets stabilized the bank of a pond while retaining the aesthetics and challenge of a championship golf course.

Creative stabilization keeps Muirfield's 12th green a tough shot on tour

For years, the world-renowned number 12 green at Muirfield Village Golf Club in Dublin, Ohio, has provided one of the most challenging shots on the PGA Tour. Course designer and Memorial Tournament founder Jack Nicklaus created a hole where the tee shot must carry 166 yards over a picturesque pond onto a small green. A steep slope and sand trap defend both the back and front of the green, while an intimidating pond stands guard over the front and right side of the green. Shots that fall short or to the right of the green will roll down a steep slope and be swallowed up by the pond.

For the past few years, the slope along the front and right side of the green was showing signs of failing and slipping into the pond. Severe erosion at the waterline was obvious in some areas. To eliminate the visible signs, greens crews attempted to stabilize the slippage by placing railroad ties, stakes, and other materials at the toe of the slope just below the waterline. Despite these efforts, the ground continued to move and exhibited cracks near the top of the slope where it had separated from the flat surface of the green.

Number 12 Green

The number 12 green at Muirfield Village Golf Club, shown here after repair, is surrounded by sand traps and, on two sides, steep slopes leading to a pond

Jack Nicklaus identified three criteria for design of a cost-effective repair that would prevent continued slope failure of the number 12 green:

  • the repair must maintain the original shape of the green;
  • structural components of the repair could not be visible; and
  • the slope of the front and right sides of the green must be maintained so that any shot that fell short of the green would roll into the pond.

To kick off the project in early 2005, two geotechnical borings were installed. One was drilled 20 feet deep to determine the general subsurface characteristics in the area; the other boring helped to determine the subsurface characteristics of the green. The boring near the green was installed with hand-operated equipment and was drilled adjacent to the right side of the green at the top of the slope. This boring showed that the current green had been constructed over an original green surface approximately 4 feet below the existing ground level. This original green surface had not been structurally integrated into the base of the current green when it was raised, and presented a plane at which saturation from the original green drainage layer was present and contributing to a potential for slippage.

< The ground exhibited cracks near the top of the slope where it had separated from the flat surface of the green

Several slope-repair alternatives were evaluated to meet Muirfield Village Golf Club's criteria, including steel sheet piling, soil anchors, mechanically stabilized earth (MSE) slope reinforcement, and gabion baskets. Ultimately, the golf club chose to use gabion baskets because the modular flexibility provided by the basket design and the fact that the installation would not require heavy equipment. The modular structure of the gabion basket design allowed use of erosion prevention capabilities at the toe of the slope at the water's edge and offset of the remaining portion of the retaining wall within the slope, essentially to hide it from view.

Only six months during the winter and early spring months of 2005 were available to make the repairs—without disturbing the green—and have the hole ready in time for the Memorial Tournament in June. Soil anchors and MSE slope reinforcement were not possible because both techniques required excavation into the slope that would have disturbed the existing green surface. Steel sheet piling could have been used at the toe of the slope below the waterline; however, heavy equipment access to the green was limited, and the final cost was too high. Gabion baskets provided the best alternative because they could be installed with smaller equipment and personnel from the club's greens crew.

The club's greens crew installed the gabion baskets using small equipment, minimizing disturbance to the golf course

The final design used a stair-step gabion basket retaining wall. The top of the base block at the toe of the wall was designed to be located at the same elevation as the normal pool level of the pond. This block also serves as erosion protection at the toe of the slope. From that point, the retaining wall was offset back from the face of the slope in a stair-step fashion (see Figure 1).

Figure 1: The stair-step gabion basket retaining wall was covered with compacted soil, a turf reinforcement mat, and sod to maintain a steep, stable slope

Gabion baskets, manufactured by Modular Gabion Systems and distributed by CONTECH Earth Stabilization Solutions, were sized and designed to minimize the amount of soil while maintaining a minimum 2:1 slope. The gabion baskets within the soil slope were wrapped with a non-woven geotextile to prevent soil from working its way into the gabion baskets. A 3-foot-wide layer of gabion baskets was added to the toe of the retaining wall one foot below the normal pool level. This layer provides a stable surface for the greens crew to stand on while conducting maintenance on the front and right sides of the green slopes.

Once the gabion retaining wall was constructed, a layer of soil was compacted and shaped over the basket wall as closely as possible to the original shape of the green. A layer of topsoil was added and a turf reinforcement mat was installed from the top surface of the slope to the normal pool elevation. Finally, turf sod was placed on the slope and anchored. After two months of growth, the turf slope was ready for tournament play. The construction process was completed in seven weeks.

Following the success of the design and implementation of this project, Muirfield Village Golf Club expects to use the concept of modular gabion basket design for stabilization of other pond banks and streams throughout the course. It provides a flexible and economical solution to erosion and soil stability problems and will be instrumental in reducing maintenance of these areas on the course for years to come.

Paul B. Latshaw is the course superintendent with Muirfield Village Golf Club in Dublin, Ohio. Mark J. Bonifas, P.E., is the civil engineering practice leader and senior project manager with Hull & Associates, Inc., in Dublin, Ohio. He can be contacted at mbonifas@hullinc.com.


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