Setting the Standard with Soil Nail Technologies

Nicholson Construction Company was awarded the con- tract to build a reinforced shotcrete soil nail retaining wall along State Route 9900 in Blair County, Penn-sylvania (U.S.). The 330-ft-(100-m)-long, 35-foot-(10.7-m)-high permanent retaining wall was cut into the hillside to provide an access route to the new Blair County Convention Center (see Figure 1). The general contractor for this project was HRI, Inc. and the owner was PennDOT.

Soil Nailing is Designed to Fit

Soil nailing has become a popular method to shore exca-vations and to build retaining walls due to its versatility and cost effectiveness. Generally broken into two cat-egories, temporary and permanent ground retention systems, soil nailing has evolved into many variations. A range of dif-ferent means and methods have emerged, giving the construc-tion industry an incredibly adaptable shoring system. The im-portance of a well-seasoned soil-nail team, however, cannot be understated for the success of any project.
Temporary soil nailing is the system that utilizes the nail for a limited time during construction process for ground support. Once the permanent structure is in place, the nails are essentially aban-doned. By contrast, permanent soil nails remain in service for the life of the wall. The shotcrete application required during the shor-ing process can also be temporary or permanent, but not necessar-ily the same as the nail. Hence, a temporary facing may be con-structed with permanent nails or vice versa.
Typically, in basement construction, soil nailing is used as a temporary shoring system and is installed concurrently with the excavation for the basement walls. After the basement has been excavated and the soil nail system is in place, either a mat slab or footings are poured and a permanent cast-in-place con-crete or shotcrete wall is installed. If a shotcrete wall is cho-sen, it can be installed with many different finishes to fit the use of the structure. Typically, shotcrete basement walls are fin-ished with wood or rubber floats to create a sand finish. In tem-porary soil nailed walls, the structural floors and walls are in-stalled; the soil nailing retention system is no longer needed to support the walls. In some cases, the wall is installed in a top down manner concurrent with the soil nail anchor installation, in both temporary and permanent shoring systems.
In the past, the highway departments often utilized the per-manent soil nail wall system with shotcrete lagging, covered with a cast-in-place or precast facing to give the completed wall a cast-in-place look. Now, however, permanent soil nailed walls are being used extensively along West Coast highways and freeways.
Although materials, equipment, and methods vary greatly, soil nail retaining wall construction involves variations of the following very basic steps:

Slope Reinforcement using Shotcrete in Arizona

With more than 7,000 cubic yards (5,350 m3) of shotcrete to be used for slope reinforcement in the Mesa­Payson Highway expansion in Arizona, it may be the biggest shotcrete application in the country. The project consists of shotcreting thirteen freshly-cut mountainsides in the Kitty Joe Canyon of the Matazel Mountain Range on Highway 87 between the cities of Mesa and Payson. The total cost of the 17-mile (27 km) road expansion is $55 million. “The entire project will take more than seven months to complete,” said Mickey Garner, president of Shotcrete Specialties, the sub-contractor. “And we’d be done if it hadn’t been for a freak snow last spring,” she continued. The area had about 3 feet (1 m) of snow just as the company was starting the project.

New Mixture Design and Guide Specifications and Inspector’s Manual

Shotcrete has not traditionally been a material of choice for repair of bridge structures by many state highway departments. One reason for this is that bridge engineers have not been aware of advances in the quality and durability possible with high-performance shotcrete over the last 10 to 15 years. In 1995, an effort was made to help facilitate and encourage the use of shotcrete in bridge repair, especially where it is particularly advantageous: in overhead and vertical surfaces and in thin layers, or a combination of thin and highly reinforced thick layers. The effort was organized by the AASHTO-AGC-ARTBA Joint Committee.

Application and Testing of Shotcrete

In 1989, the Austrian Concrete Society pub-lished a Guideline on Shotcrete that subse-quently served as a reference work and a contractual basis for shotcrete works in tunnel con-struction in Austria and abroad. Other standards,such as DIN 18551, focused more strongly on shotcrete for concrete repair works. At the end of 1998, after several revisions, a new edition of the Austrian Guideline was published that also con-siders recent developments in the field of shot-crete technology. Dealing with a
whole range of issues, from base ma-

Shotcrete Red Hot in Peru

An1amina copper mine is a Sl.2 btltion projcc1 in lhe Andes Mountailh of Peru. The projeci. owned by Canadian mining gi3111S Norandll. J’cck and Rio Afgom, i.s one of the. single largest mining inveso:nents in 1be Americ:iô€€£ at this moment and oomprises the cons1ruction of an open pi1, a co11veyor runnel, a tailings dam. a mill and pon facilities for ¢1’por1 of processed concenlrllle all over the globe.

The Use of Steel Fiber-Reinforced Shotcrete for the Support of Mine Openings

What separates the support of mining open­ings from the support of similar civil engineering structures is the fact that mine openings have to survive large defonnations as a result of changing stress conditions induced by progressive mining. Steel fibers impart to concrete and shotcrete a high degree of ductility which not only allows the shotcrete and concrete linings to absorb important rock movements, but also to increase their bearing capacity by a redistribution of the loads.
The use of shotcrete for the support of under­ground excavations was pioneered by the civil engineering industry. In recent years, the mining industry ha,;; become a major user of shotcrete for underground support. The simultaneous working

Steel Fiber Reinforced Shotcrete, It is time to find out about it.

In an age when the building, tunneling, and in some areas, min­ing industry, is thriving in North America, we in the shotcrete industry should be looking for ways to increase productivity and save on ever-increasing labor costs. This type of thinking often requires the use of products that we either are not familiar with or have never used at all. Since we are in an industry where our chief concerns are keeping a safe workplace, while at the same time, trying to increase production or speeding up project comple­tion time, we are often times unwilling to try new technology because we are afraid of the unknown. We fear a decrease in pro­duction, having to buy new equipment, and worst of all, lost­time accidents.For this reason-the unknown-many shotcrete contractors and mine managers have shied away from the use of steel fibers in their shotcrete. Their arguments against using steel fibers are often the same. “We use mesh or rebar for reinforcement because we know for sure that the reinforcement is in place before we apply shotcrete. That way, we don’t have to worry whether or not we have added the correct amount of steel fibers, or if the steel fibers are mixed uniformly, or if the fibers will do the job at all.” Or, we hear the all too familiar response, “If it is not broken, don’t fix it.”
In my opinion, this “if it is not broken, don’t fix it” attitude is keeping a lot of shotcrete contractors from increased production and greater financial successes. Sure, the economy in North America is strong now in the