Slope Stabilization Using the Shotcrete Grid Beam System in Japan

Continuous grid beam structures made of shotcrete have been used for over 30 years in Japan to stabilize natural and man-made cut slopes. This slope stabilization structure, generally called œGrid Beam, is widely applied in Japan. It was used in more than 4600 slope stabilization sites in Japan in the year 2002 alone. The Grid Beam system is often used independently to protect slope surfaces from erosion, or used as a supporting structure, combined with ground anchors or soil nails to stabilize the slope against failures. The area surrounded by the beams is often revegetated to improve aesthetics and harmonize the installation with the surrounding environment (see Fig. 1). Due to the geometric flexibility of this system, the concrete beams can easily follow the undulations of natural slopes and maintain good contact with the surface.

Quality Management of Shotcrete in North America

As for all construction materials, a proper program of quality management should be implemented in shotcrete construction to protect the owner™s investment. This article briefly examines typical shotcrete Quality Management (QM) practice in North America. QM can be considered to be comprised of Quality Assurance (QA) and Quality Control (QC) functions.

Advantages of Using Shotcrete for Arch Culverts

A rich structures have been used in various forms of construction for thousands of years. The earliest arch structures date back to ancient times when crude arch prototypes were constructed by building a corbelled arch in which projecting elements from a wall rose in steps to meet at the center. The Egyptians, Greeks, and Romans all used the arch for various types of structures, including sewers, aqueducts, bridges, and ornamental architectural buildings such as palaces and churches. The fact that many of these ancient structures are still standing today is a testament to the durability and structural integrity of this design. Fast-forward 2000 years to modern construction practices, and the benefits of the arch design are still as valuable, relevant, and practical as ever.
Various Uses for Arch Culverts
Among the many modern-day uses of arch culverts are culverts, storm drains, bridges, cut and cover tunnels, pedestrian and equestrian underpasses, golf cart crossings, underground vaults and reservoirs, and environmentally sensitive wash-crossing structures. These types of crossings can be constructed on spread footings and without concrete inverts, thereby maintaining the natural integrity of the wash bed. Detailed engineering studies have verified that arch culverts will have a similar life cycle to comparably reinforced concrete box culverts.
Benefits of Arch Culverts
The advantages of using shotcrete arch culverts over traditional formed and poured concrete box culverts, concrete pipe, and corrugated metal pipe are as follows.

History of Shotcrete in Seismic Retrofit in California

The widespread use of structural shotcrete actually began long before the first appli-cation was made. Its rise was politically motivated and its continued development dictated by the occurrence of earthquakes. Responding to a school fire in the 1920s, the Los Angeles School Board directed that all future school buildings be constructed of masonry. However, masonry of the day was not reinforced, and several hundreds of these buildings were destroyed or damaged in the great Long Beach earthquake of 1933. Fortunately, the quake occurred in the early morning hours when the schools were unoccupied; had it been during the day, hundreds of deaths and thousands of injuries would have likely resulted.

Washington State’s Capitol Seismic Repair

Washington State’s Capitol Seismic Upgrade will surely rank as one of the top restoration projects of this decade and shotcrete proved to be essential to its success. As with most complex rehabilitations, many of the hurdles faced arose after the project had begun. The ability of the contractors, engineers, and architects working together to overcome these issues proved once again to be the crucial factor in the success of the project.

Thick Section overhead Repair and Strengthening of a Concrete Pier: A Viable Shotcrete Solution

When considering placement options for thick section overhead concrete repair or strengthening, more often than not, the consideration of a shotcrete solution is overlooked. Historically, shotcrete has suffered from being mainly associated with vertical placements for above ground work. This may be due to the fact that until 1983, silica fume enhanced shotcrete was unheard of in North America; therefore, building up placement lifts overhead of more than a few inches thick using shotcrete was not deemed possible. Additionally, many shotcrete contractors customarily have avoided low production applications where placement volumes are measured in cubic yards per day rather than cubic yards per hour. As a result, most thick overhead concrete sections have been placed via the more common method of forming and pumping.
In general, forming and pumping concrete overhead works adequately. In deep sections the concrete or repair material is pumped through a port or valve on the bottom or lower side of the stout form. In effect, the air inside the form is pushed up and ultimately out of the concrete placement location. In deep section repair, there can be challenges devising a methodology that ensures no air is trapped in the upper sections of prepared areas. Repairs to pile caps may preclude the coring of vent holes down through the top of the deck due to congestion of reinforcing steel. In a form and pump application, the issue of adequate bond to the prepared concrete substrate is also a consideration. Most repair installations require a composite action of new material to existing concrete. Curing, shrinkage, and the presence of bleed water floating on top of the new concrete placement may adversely affect the ultimate bond strength of these installations. The aspect of building forms for repair and strengthening placements, especially around precast piling, can be difficult and extremely time consuming as well.
Careful consideration of the pros and cons of shotcrete placement over a more traditional approach of forming and pumping for thick overhead sections offers compelling technical evidence for pursuing a shotcrete option. The following case

Use of Fiber-Reinforced Shotcrete

As many of you Shotcrete readers know, there have been many articles published here on FRS, and many more where FRS is mentioned. Two articles in the premier issue of Shotcrete in February, 1999, mentioned FRS. I have been keeping a bibliography of Shotcrete articles on FRS and, through Summer 2004, I have over 20 listed. These, of course, are available on the American Shotcrete Association (ASA) website. For example, in an editorial in the May 2000 issue, Mike Ballou says, œSteel Fiber Reinforced Concrete”It is time to fi nd out about it, and in a Spring 2003 Technical Tip, Denis O™Donnell discusses where fi bers should or should not be used in ground support for hard rock mining.