Drill-and-Blast for Tunnel Construction – A Historical Perspective

[EDITOR’S NOTE: This is the third in a series of articles from Dr. Gary S. Brierley reflecting on the history of tunneling. This first article appeared in the August 2014 issue of TBM: Tunnel Business Magazine and examined tunneling from its ancient roots to the present day. Subsequent articles examine specific elements within the tunneling market, with particular attention paid to the U.S. market. This installment discusses drill-and-blast tunneling.]

No one knows who invented gunpowder, but its use dates back to at least the 1200s. It was not until the 1600s, however, that black powder was used for mining projects, (including colonial America) and not until approximately 1800 that black powder became common for civil engineering projects such as canals and, later, for railroads.

In 1831, William Bickford invented the safety fuse, which greatly increased both the reliability and the applicability of blasting operations. As I have written and lectured many times, however, it was not until the famous Hoosac Tunnel project in western Massachusetts that the procedures for using drilling and blasting for tunneling projects were firmly established.

Prior to the Hoosac Tunnel, if you visited a tunneling project in rock you would have observed a hodgepodge of activities at the face with some workers drilling, some removing broken rock, and some preparing for the next blast. When the foreman felt that it was time for a blast, all of the workers were withdrawn, the blast ignited, and the process begun all over again.

That all changed around 1865 when Walter and Francis Shanley from Montreal were awarded the contract to finish the Hoosac Tunnel. It was the Shanleys who introduced the drill-load-blast-muck cycle to tunneling. It was also the Shanleys who began using liquid nitroglycerine to advance the heading and who facilitated the invention and use of compressed air drilling machines. By the time the Hoosac Tunnel holed through in 1873, the Shanleys had established all of the basic procedures that would be used to excavate the vast majority of rock tunnels for the next 100 years!

Drill-and-blast excavation for tunneling projects depends on the precise drilling of a collection of holes into the face and the precise detonation of the blasting agent, which allows the rock to be extracted from a highly confined space. For a long time it was only possible to use the classic “V cut” procedure to open the face and provide relief for all of the subsequent blasts. Without delays, each blast had to be planned and executed individually, meaning that the process was slow even though it was many times faster than the ancient methods.

With the introduction of delayed blasting caps and stronger explosives, it became possible to use a horizontal “burn cut” and to move much larger volumes of rock with better fracturing, better perimeter control, and less disturbance to nearby, existing structures. Over time, every aspect of drilling and blasting has seen innumerable improvements and advancements that have increased both drilling accuracy and blasting efficiency, and made the process safer and less costly.

With respect to drilling, all holes in rock were drilled by hand until the mid-1800s. Until then, no power source was available for work deep inside a tunnel except for human beings and mules. In the 1850s, however, experiments began with compressed air. Initially, many “experts” believed that compressed air would lose its “elastic force” if transmitted for long distances in small pipes but that was shown not to be the case. In order to utilize compressed air, however, inventions were also needed for air compressors and for drilling machines that could withstand the abuse associated with drilling hard rock. After many failed attempts, Charles Burleigh finally developed a workable drilling machine for use at the Hoosac Tunnel.

In order to utilize the full potential of Burleigh’s drill, however, the Shanleys also needed to develop drill carriages that could be used to transport and to support several drills at the tunnel heading. Interestingly, the miners also appreciated compressed air as a source of ventilation inside the extremely confined conditions of a tunnel heading.

Numerous other experiments were also taking place around the world during this same time period. The Italians, for instance, were experimenting with a compressed air rock drill invented by Germain Sommeiller for use at the Mont Cenis Tunnel in 1861. Numerous compressed air drilling machines were also being used for coal mining in Great Britain. As early as 1878, Alfred Brandt even started experimenting with hydraulic drills, which were used with great success for both mining and tunneling projects. Simon Ingersoll introduced an improved version of the Burleigh drill in New York in 1872, and Albert Rand, while manufacturing and selling black powder, realized that a more efficient drilling apparatus would increase the demand for his powder. In 1905, the firm of Ingersoll Rand was formed, followed in 1927 by the Gardner Denver. Both companies became instrumental in the development of drilling machines for mines and tunnels for decades.

Finally, during the1960s, the drilling industry began to concentrate on hydraulic drilling machines. In general, hydraulic drills have many advantages as compared to compressed air drills such as less power consumption, no need for expensive compressors and piping, less noise, and the ability to regulate the power of the drill to many different types of rock. It was also around 1960 when “button bits” were introduced, which greatly facilitated hole flushing and thus avoided regrinding.

Most recently, drilling jumbos now have computer controls that allow an entire tunnel round to be drilled without an operator. The drill rigs also contain a great deal of feedback information that allows for the continuous monitoring of drill rig performance. Finally, hole placement accuracy is vastly improved, allowing for precise perimeter control and a significant reduction in overbreak. Recent data suggest that the time to drill the tunnel face has been reduced from 50% of the round length in 1960 to around 20% today!

During this same time frame, the blasting industry was not standing still. Around 1960, a significant transition began from dynamite to water-based gels and emulsion explosives that are less costly and safer. Another huge improvement has been with respect to the delay accuracy of detonations. Modern detonators can be controlled to within a few milliseconds for any length of delay. This greatly improves blasting efficiency especially for the longer delay perimeter holes, which is exactly where you need the greatest precision. One recent article even discussed the possibility of “double-deck” blasting where one drill hole can be double stemmed and used to pull two round lengths of rock for one blast cycle.

Combining all of the above results in better drilling speed and increased drilling accuracy, more powerful and stable explosions, and extremely accurate detonations, which in turn resulted in vastly improved excavations and greatly reduced impacts to adjacent properties. TBMs are great for a lot of tunneling applications, but the drill-and-blast industry has been more than able to keep pace with no end in sight for possible future improvements. The tunneling industry is indeed fortunate to have access to both great TBMs and great drilling and blasting procedures.

Footnote: The author would like to thank Bill Warfield of Atlas Copco and Andy McKown of Brierley Associates for helping with the research for this paper. In addition, the author would like to refer the reader to an excellent article titled “Drilling Dilemmas” about the pros and cons of TBM vs. drill-and-blast tunneling that was published in the October 2014 edition of Tunnels and Tunnelling International and authored by S. Paul Singh and Derek Zoldy.

Gary S. Brierley is president of Dr. Mole Inc. He began his career in 1968 with the Bachelor’s Degree in Civil Engineering from Tufts University and the Masters and Doctoral Degrees from the University of Illinois in 1970 and 1975, respectively. During that time Dr. Brierley was fortunate to work on the instrumentation program for DuPont Circle Subway Station in Washington, D.C., a project that formed the basis for his doctoral dissertation. Since that time, Dr. Brierley has devoted his entire professional career to the design and construction management of underground openings.