Much has happened since the last update on the activities of various shotcrete organi-zations and committees in the Summer 2004 issue of Shotcrete. Probably the most important, at least to this author, is that I have retired from full-time employment from SI Concrete Systems and will consult in the industry if anyone will put up with me. I plan to continue my work with the various organizations discussed below. Readers are requested to contact the editor and author if inaccuracies are found or if additional activities should be reported.
Specified Dilemmas
On shotcrete sites, it is not unusual to hear comments starting with œIn a perfect world, … Of course, in a perfect world,there wouldn™t be any shotcrete because there wouldn™t be anything to repair or strengthen. Fortunately, there are plenty of imperfections in the jurisdiction where most of my work comes from. We ï¬nd them on cracked and ï¬ssured rock slopes next to highways, in ground to be tunneled for infrastructure improvements, in old masonry walls, washed-out bridge foundations, and in marine piers where the chloride concentration at the rebar level in the concrete exceeds the reasonable limit set for the onset of corrosion.
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 beneï¬ts 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 veriï¬ed that arch culverts will have a similar life cycle to comparably reinforced concrete box culverts.
Beneï¬ts 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.
Shotcrete – The Repair Solution for the Memorial Tunnel
In 1953, the Memorial Tunnel in Standard, WV, was constructed as a two-lane, 2800 ft (853 m) tunnel with semi-transverse ventilation. The owner operated the tunnel until the mid-1980s when a four-lane bypass was constructed to upgrade the turnpike to current Interstate standards. The tunnel was abandoned until 1989 when the Federal Highway Administration (FHWA), in conjunction with the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE), embarked on the Tunnel Fire Ventilation Test Program using funding from the Central Artery Project.
The test program consisted of performing controlled test ï¬res up to 100 megawatts. These intense ï¬res then provided valuable information for the design of ceiling wall partitions and the protection of facilities for power, ventilation, and lighting. In addition, it provided the opportunity to develop and evaluate methods of proper ventilation control of a tunnel under various ï¬re scenarios.
Parsons Brinckerhoff was retained to perform the test program. As part of that test program, an evaluation of the structural condition of the tunnel was performed and structural repairs were designed. A critical part of the design was to insulate structural portions of the tunnel for temperatures in excess of 2000 °F (1143 °C).
The rehabilitation program for the reuse of the tunnel required the sealing of all cracks in the tunnel liner because the bedrock around the tunnel contained low-flashpoint cannel coal. In addition to sealing the cracks, extensive structural rehabil-itation of the liner was performed to repair damage caused by the excavation for the bypass on the adjacent highway. Numerous products were evaluated to determine which would provide suitable fire protection for the structural elements of the ceiling and for mechanical equipment anchorages. The test program included the use of traditional venti-lation with a tunnel ceiling and tests with the ceiling removed for the use of jet fans. The construction contract for the rehabilitation of the tunnel and the removal of the ceiling had a projected cost of $10 million.
During the test program of 98 ï¬res, routine inspection of the tunnel was performed to evaluate the performance of the ï¬reprooï¬ng. Based on the performance of certain structural elements, changes were made in the use of structural ï¬re-prooï¬ng and code requirements for the protection of equipment. After the test program in 1991, the
Safety Shooter : Working Safely in Cold Weather
Once again the frost is on the pumpkin by guest author and Old Man Winter is at the door. With Todd Bennett less daylight and colder temperatures, we need to adjust our safety programs from avoiding heat exhaustion, dehydration, overexposure, and sun-related illnesses to preparing our ï¬eld crews to deal with the other extreme.
Seismic Retrofit of Littlerock Dam
History of Shotcrete in Seismic Retrofit in California
The widespread use of structural shotcrete actually began long before the ï¬rst appli-cation was made. Its rise was politically motivated and its continued development dictated by the occurrence of earthquakes. Responding to a school ï¬re 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.
Surface Preparation for Shotcrete Repairs
Surface preparation is an important element of the repair process, both with shotcrete and cast-in-place concrete. It covers a large scope, including concrete removal, saturation of the substrate, the use of bonding agents (rare with shotcrete), and cleaning of the surface. These operations are influenced by the local conditions (surface position: vertical or overhead, the presence of reinforcement) and are very important for both the short- and long-term bond strength and, thus, the repair integrity. When all steps involved in surface preparation are considered, it is obvious that these operations represent a large part of the repair cost and may reach up to 50% of the total repair cost. For this reason, it is important not to neglect surface preparation.
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.
The Use of Macro-Synthetic Fiber-Reinforced Shotcrete in Australia
Macro-synthetic ber-reinforced shotcrete (SnFRS) has rapidly gained popularity in Australia over the past 5 years. This can be attributed mainly to the huge improvement in post-crack performance that has been demonstrated over recent years and the almost universal adoption of this material for ground support by the underground mining industry.