Author: Lok Home

To Grout or Not to Grout? In Rock Tunnels encountering High Water Pressure, Grouting can offer Great Benefits over Slurry

An NCP-TBM with grouting (left) can be just as effective (and more efficient) than Slurry tunneling in rock with water (right).

When you’re faced with a hard rock tunnel where there are expected significant sections under high water pressure, which tunneling method do you choose?

While Slurry Shield tunneling has a long history of addressing this problem, this method has not always been problem free. I would argue Slurry tunneling in rock is not, in most cases, the lowest risk or the most cost-effective method.

At recent projects around the world, we have seen that two non-slurry methods can be highly effective: use of a shielded, Non-Continuous Pressurized (NCP)-TBM in rock with a comprehensive grouting program, or sequential advance in EPB mode.  Both types of tunneling operations have proven themselves safe, and have saved a significant amount of money for both contractors and owners.

Grout vs. Slurry

There are certain inherent traits to a Slurry tunneling operation that appear to give a lower level of risk: the entire operation is sealed; the slurry itself is conveyed to the surface through a system of pipes. But is this low risk truly the case?

Interventions

Hyperbaric interventions are high-risk operations, particularly as water pressures go up. In water pressures over 6.5 bar, divers are often not permitted to enter the cutterhead, so grout must be used or there must be an alternate plan to bring down the high pressure. Higher pressure hyperbaric interventions up to approximately 12 bars have been successfully performed, but at what risk? Pressures in some tunnels have far exceeded 12 bars and would make hyperbaric interventions even more costly, risky and time consuming or impossible.

Slurry Separation

In ground with fines, slurry separation can be costly and difficult. Slurry tunneling is also not immune to problems such as blowouts/loss of face pressure when a fault zone or low cover zone is encountered, as is well-known in our industry from projects such as Hallandsås in Sweden and the SMART Tunnel in Malaysia.

Probing and Grouting

In an NCP-TBM operation, crew members may be more exposed to the tunneling environment but risks are not increased. With a good geotechnical baseline report and ground investigation tools, contractors can determine the zones requiring grouting ahead of the machine. It is now common to drill probe holes accurately of plus 100 meters with Down-the-hole (DTH) drills.

While grouting does take time and cost money, this cost has to be balanced against the cost and time to do hyperbaric intervention during slurry tunneling. Even 100% grouting in a rock tunnel could require less time than high-pressure hyperbaric interventions. The practice of pre-grouting has been done for years in drill & blast rock tunnels in Scandinavia and worldwide.


This video shows the basic process of probe drilling and grouting in a shielded rock TBM.

Grouting can also be done from a Slurry TBM of course, and is normally done to set up safe zones. However, it is worth noting that based on having a pressurized face filled with slurry, drilling through the head is very difficult. Sealed pipes/ports need to be installed in advance, eating up space and compromising the working conditions during hyperbaric interventions.

Cutter Changes

There has been recent development to enact cutter changes by accessing the cutters through the cutterhead under atmospheric pressure.  However, this system requires a large diameter machine as well as a deep cutterhead structure. The deep structure severely affects muck flow and substantially increases the need for more frequent inspection and cutterhead repairs. These atmospherically accessed cutterheads do not address the problems of cutterhead repair, changing center cutters, or replacing scrapers, all of which are high wear items in rock tunneling at large diameters.

Geology Rules

Are there times when a Slurry TBM has an advantage over an NCP-TBM in rock? Yes. Rock properties can drive the decision: Some rock formations are very difficult or nearly impossible to grout, and therefore the success of pre-excavation grouting will not be a given.  If significant water inflows are predicted and the rock will not readily take common grouting material, or chemical grouting is not an approved option, a slurry TBM is the logical TBM selection.

Lining requirements are another potential reason not to go with Slurry: The operation of a slurry TBM goes hand-in-hand with the use of an (often expensive) segmental lining. Pre-excavation grouting using an NCP-TBM offers tremendous cost savings when done in a non-lined tunnel or when the liner can be installed independently after excavation.

In cases where a final liner has to be installed with tunnel boring, and often in cases where excessive water inflows are predicted, a slurry TBM may make more sense.  Under excessive water inflows a grouting operation may still experience leakage after the initial tunnel construction, making installation of a final liner afterwards potentially costly and time consuming.

In Depth: Slurry Tunneling vs. NCP-TBM Shielded Tunneling in Rock

Cutterhead Inspections

Cutterhead inspections in rock must be viewed with a different mindset than in soft ground tunneling. When tunneling in abrasive rock with any type of machine, inspections should be performed regularly; once per shift can be a requirement. This is in contrast to tunneling in soft ground, where cutterhead inspections are often planned and based on a set number of meters, for example every 100 m.

The Contractor Experience

Contractors who are used to tunneling in soft ground may not realize that when using a Slurry TBM in rock, inspections must be frequent due to increased cutter consumption. We have seen this borne out on recent projects such as the Hiroshima Expressway Line 5 in Japan. On that project, a 13.7 m diameter Robbins Slurry TBM is boring in granitic rock. The contractor opted for a Slurry machine because that was their historic experience, and they were expecting up to 13 bar water pressure. This high pressure water zone was only in a small section of the overall tunnel length, about 5 percent.

Hiroshima Slurry TBM

A full view of the 13.67 m (44.8 ft) Robbins Slurry TBM for the Hiroshima Expressway Line 5. Photo Credit: Mario Recena Areces

The contractor in Hiroshima had grouted off from the surface a planned safe zone in which to inspect the cutterhead without requiring a hyperbaric intervention, but this strategy did not go according to plan. The abrasive rock damaged the cutters and cutterhead before they could reach the safe zone, resulting in unplanned delays.

By far the biggest benefit of using a shielded NCP-TBM in rock, rather than Slurry, is the ease of cutter and cutterhead inspections. In areas with no pressure and with frequent or continuous grouting, the cutterhead can be inspected regularly and without the requirement of expensive, time consuming, and often risky pressurized interventions or complicated procedures to remove slurry from the cutterhead. Frequent inspections mean that cutter and cutterhead damage can be caught early before they cause significant downtime.

Robbins Single Shield TBM "Nora"

The Delaware Aqueduct Repair TBM, used in hard rock and designed to statically hold high water pressure, is a good example of an NCP-TBM.

Abrasive Wear

To go along with the above point, abrasive wear in any type of TBM is obviously always higher in rock than in soft ground, particularly when the rock has a high quartz or other abrasive mineral content. However, in Slurry machines, which crush the rock and send the rock chips through a system of pipes, abrasive wear is of even greater concern. Even with using durable slurry piping, transfer points and pipe elbows will require higher rates of replacement, causing more delays associated with muck removal than a typical NCP-TBM operation using a conveyor belt.

Dealing with Water Inrushes

If sudden water inrushes at high water pressure are a known risk, NCP-TBMs can effectively be designed to statically hold the pressure using sealable muck chutes in the bulkhead.  This type of design can be used as a pressure-relieving gate in semi-EPB mode, opening by pressure and allowing muck to be metered out onto the belt. Or in extreme cases, the sealed gates can be activated and probe/grout drills can be used to forward drill and grout for ground consolidation and to seal off the water. Extra seals around the main bearing can be filled with pressurized grease and other vulnerable points can be sealed off in the same manner.

A Crossover TBM can also be designed to keep boring under pressure by implementing a center-mounted screw conveyor.  A long screw conveyor can be used to draw down high water pressures and abrasion resistant hard facing can be added to the screw conveyor flights for abrasive wear. Under such conditions, a machine could operate continuously with, say, 3 bar pressure and sequentially in high pressure of 15-20 bar.  An example of this is our ongoing project Mumbai Metro, where two Robbins Crossover TBMs are excavating in mixed ground. In these machines, the center screw conveyor is able to seal itself off/hold pressure so the TBM can continuously bore or operate using the screw conveyor in a sequential fashion. Boring is done when there are not enough fines to form a plug. Take a look at the below figures for a summary of sequential boring operation.

Sequential Operation Step 1. Muck chute gate is open with high pressure water and cuttings flowing onto the screw conveyor as machine advances forward.

 

Sequential Operation Step 2. Muck chute gate is closed and water pressure is lowered, then muck is removed from the screw conveyor onto the back-up conveyor.

Dealing with Gasses and Contaminated Ground

In Slurry tunneling, dealing with gasses in the tunnel is relatively easy because the gasses are contained in the slurry pipes. Gasses can also effectively be contained and safely dispersed on non-pressurized TBMs using scrubbers and high volumes of air. On a recent Robbins TBM in Australia a machine was capable of operating in open mode with gasses using a bulkhead fitted with suction ports to draw any gas from the top of the cutterhead chamber and directly into a sealed ventilation system.

Contaminants such as asbestos may be better contained in slurry pipes, but many other types of contaminants may not be easily separated from the slurry and therefore easier to deal with using NCP- TBMs.  In Slurry operation the quality of Bentonite itself can vary widely, with some lower cost material containing heavy metals, which has the potential to be detrimental to the environment. The slurry solution itself also tends to bind well with heavy metals, contaminating the slurry and making separation difficult.

In Conclusion

The conclusions to draw from this discussion are straightforward. Is Slurry tunneling still a valid option in rock with potential of high water pressure?  The simple answer is yes. Is it the most cost-effective option? Is it safer than any other option? In many circumstances the answer is no.

Slurry TBMs need a level of expertise in operation that NCP-TBMs simply don’t require. The operation of most NCP-TBMs is both simple and straightforward, which in turn saves on personnel costs.

My hope is that consultants and owners realize that Slurry TBMs are not the only option when high water pressure is expected.  Slurry TBMs are not in most cases the lowest cost, and other methods can be just as safe while being simpler to operate. While grouting takes time, so does slurry tunneling with its typically lower advance rates and possible need for expensive, high risk hyperbaric interventions. When Slurry machines operate in rock, the need for frequent cutterhead inspections ultimately makes their use questionable. In most cases NCP-TBMs are the better option.

For Further Reading: Recent Industry Examples
The Mumbai Metro Project
Delaware Aqueduct Repair


Let’s Be Clear: Transparency is a Boon, not a Bust, for the Tunneling Industry

The idea of transparency is one that we most often hear touted in politics and policies.  But transparency is a concept that applies to our underground industry as well.  Widespread knowledge sharing can and should be the policy in our industry, but all too often jobsite politics, confidentiality agreements, and fear of poor public opinion limit what is ultimately divulged.  I argue that transparency in tunneling is a help, not a hindrance, and we can make steps today towards clearer communication.

Transparency

Transparency, achieved through better communication among all stakeholders, is the key to continued success in our industry.

Why It’s Needed

  • Learn from Experiences in the Field: Tunneling professionals deserve full access to the successes and the problems that have been encountered in the field. If we were to employ universal knowledge sharing, tunneling operations themselves could become safer and more efficient and overall project costs could be reduced.
  • Improve Tunneling Technology: Knowledge of advance rates, performance in specific ground conditions, wear rates for cutters and other surfaces in contact with the cutting face, performance of ground conditioners and foams, and many other types of info are imperative to improving technology. Tunnel boring could be made faster, safer, and more cost effective with such knowledge.  It could also improve willingness to try new and emerging technologies in the industry, which benefits all stakeholders.  With a good knowledge of TBM performances in specific ground conditions, TBM specifications could also be written to greater accuracy and result in using the most cost effective solutions.
  • Improve Risk Sharing: Risk is often apportioned unfairly on today’s tunneling projects. In many cases the TBM supplier is required to shoulder a larger part of that burden than their potential returns. With a better understanding of the risks through knowledge of past projects, as well as knowledge of past risk sharing strategies, this problem can be resolved.
  • Ensure Fair Financial Practices: With transparency in terms of contractual pricing and project spending, payments for work performed, etc. and other unsavory practices can be lessened.
  • Reduce Litigiousness: Claims in tunneling projects are on the rise worldwide. Recent projects have resulted in separate and duplicate claims against different parties, such as the equipment manufacturer and the owner, for the same issues and without their mutual knowledge. Such claims are unfair, and through transparency and equal access by all parties to a Dispute Review Board, the frequency and extent of lawsuits in our industry could be reduced.

From the Equipment Supplier Perspective

As equipment suppliers, we strive to share the information that is available to us.  We’ve opened up about stuck TBMs, challenging drives, and how we’ve overcome those issues.  We’ve also tried to share whenever possible why we think fast advance rates and good efficiency were achieved on various projects.

A bypass tunnel at Turkey’s ultimately successful Kargi project, where we shared information on seven such tunnels built in the first 2 km of tunneling.

Unfortunately knowledge is sometimes not shared even within parties on the same project, such as the contractor, project owner, owner’s representative, and equipment supplier.  Time and again we see that communication between all parties is key to overcoming challenging conditions. The road to transparency starts here: with clear communication between all coordinating parties on a given project.

Not Without Precedent

Transparency is not an untested idea in our industry.  A great recent example is that of the U.K.’s Crossrail project.  The project follows governmental codes of practice for data transparency and the country’s Freedom of Information Act.  Details such as project and equipment costs, spending budgets and records, safety records, and more are available for download on their website, and special requests can be made for additional data. Multiple reports have also been up front about TBM performance, advance rates, and other experiences on the project. The Crossrail project was highly successful and, arguably, transparency played a large part in that. Crossrail is also just one example of transparency at work in the U.K.—governmental programs such as Transport for London’s Transparency Strategy aim to give clear and consistent information to the public about all road and public transit spending.

A Call for Clarity

Transparency is possible in the tunneling industry, but it may require things like international regulations, or at the very least certifications that could be provided by an international organization like the ITA.  Such a certificate would be highly beneficial to all stakeholders: It could certify corruption-free practices, and guarantee knowledge sharing.  Transparency is not an easy thing to achieve, and there are certainly barriers to the process in various areas of the world. But we can start with transparency requirements within projects, and then move outward.  To be clear: knowledge sharing is something that can only benefit our industry. It is our recommendation we start today.


Are You in Tough Ground? Learn from our Trials and Tribulations in some of the Tunneling World’s Most Difficult Projects

Squeezing Ground, Fault Zones, Water Inflows, and More

True story: In a mountain range, crews worked on a shielded TBM more than 500 m below the surface. The TBM had excavated several kilometers in worsening conditions.  The crew encountered karstic aquifers filled with mud and water.  Personnel were pumping polyurethane through the cutting face to staunch the water inflows.

Suddenly, water inrushes climbed to a rate of 1,500 liters/second, creating a knee-deep underground river and causing the machine to become stuck. Thankfully, the crew was able to exit the tunnel, unharmed. The massive inrush created a damming effect with enough pressure to crush the TBM shields and send cylinders catapulting into the back-up.

As quickly as it had started, the machine ground to a halt, deep underground.

What happens when you encounter an unforeseen condition? A severe water inflow, fault zone, or squeezing ground? A geological feature that seems like it might stall your tunneling operation altogether? Some of our most difficult challenges—spanning from New York to Peru to the Republic of Georgia—are detailed below.  These case studies are meant to pass on our knowledge and experiences to help you overcome obstacles, unforeseen or otherwise.

How to Overcome an Epic Flood: New York’s Harbor Siphons project

Sometimes an unforeseen condition requires a rescue effort to overcome. In October 2012, a storm was coming to New York City’s Harbor Siphons Project on the shores of Staten Island. The undersea tunnel and its 3.6 m CAT EPB ground to a halt when hit by Superstorm Sandy.  The monstrous hurricane battered the eastern seaboard of the U.S. with winds of 145 kph.

The launch shaft was inundated with seawater despite contractor Tully/OHL’s best efforts.  Flood water entered the tunnel and stopped the TBM just 460 m into its 2.9 km long drive. A 2013 post-storm survey of the tunnel showed a damaged machine extensively corroded by saltwater. All electrical components needed to be replaced.

Contractor OHL turned to Robbins for help. During the downtime, the original TBM manufacturer had exited the tunneling industry. Robbins worked with the contractor to come up with a multi-pronged approach to bring the TBM back to life.

Flooded TBM

Flooded TBM: A view of the initial inspection after the flood, looking at the machine’s drive motors submerged in seawater.

Hiring a Dedicated Team

Per the scope of work, defined jointly by OHL and Robbins, crews temporarily excluded the cutterhead and main bearing of the TBM for refurbishment, as they were under earth pressure and not accessible. The Robbins team would need to complete the refurbishment taking into account unknowns, such as the condition of the cutterhead. The segmented concrete tunnel lining would not permit the removal of many of the larger TBM components, so these would have to be refurbished onsite.

The Robbins crew was contracted to guide onsite personnel in replacing corroded hydraulic components and installing all new electrical components. Variable Frequency Drives, PLCs, and wiring were replaced inside the small tunnel under atmospheric pressure of 3 bar. Crews constantly monitored earth pressure during the refurbishment. The machine had been stopped with its thrust cylinders in, and thus the crew could not replace or evaluate certain components before the machine started up.

Reverse-Engineering Electrical Components

By mid-December 2013, Robbins PLC technicians were reverse engineering the TBM’s control system. The team understood early on that the previous control programming would be unusable given the PLC change. The technicians had only limited assembly drawings from the CAT manual, so much of the refurbishment, including the PLC system, had to be built from the ground up. The team at site understood how the machine should work and therefore were able to build the correct PLC system.

Harbor Siphons Operator Cab

Reworked Electronics: The Harbor Siphons TBM required all new electronic systems.

Coordinating Success

Despite all of the challenges, the refurbishment project was a success. Crews had gone from a shipwrecked TBM—rusted, corroded, and abandoned in the tunnel—to a successful tunneling operation. It was a monumental task, scheduled to be completed in four months, and finished on schedule.

Harbor Siphons project crew

A Good Result: The happy crew during TBM boring, after the full refurbishment.

In the final phase of the refurbishment, a Robbins PLC technician was able to complete the commissioning of the TBM and on April 14, 2014 the machine officially returned to mining. The machine successfully completed its tunnel in February 2015.

Read more in the white paper here.

Make Rock Bursting Conditions Safe for Your Crew: The Olmos Trans-Andean Tunnel

If 16,000 recorded rock bursting events in the world’s second deepest tunnel weren’t enough, the crew at Peru’s Olmos Trans-Andean Tunnel had another problem. As the machine progressed and the cover grew higher—up to 2,000 m at the highest point—the rock bursts became more violent. Crews experienced large over-breaks and cathedralling in fractured and unstable ground. Teams of personnel had to inject concrete into large cavities that had formed during stress-relieving activities and stabilize these cavities with spiling.  Then, several kilometers into the tunnel, a major rock bursting event occurred that twisted ring beams and caused damage in 45 m of lined tunnel. Damage was extensive to the TBM gripper, which was ballooned and blown off its mountings. Damage also occurred to other hydraulic cylinders.  Thankfully crew members were not harmed, but downtime for repairs would be substantial.

A Century-Long Effort

The Olmos tunnel is a 12.5 km long water transfer tunnel that was bored through the Andes Mountains to bring irrigation to drought-ridden areas on the pacific coast. The project was more than 100 years in the making, with several attempts being made and thwarted by incredibly difficult geology as recently as the 1950s.

In 2007, with Odebrecht as the main contractor, the tunnel was finally completed using a 5.3 m diameter Robbins Main Beam TBM after other attempts with conventional methods failed. The route is the world’s second deepest civil works tunnel with overburden of up to 2,000 m.  The tunnel alignment traverses complex geology consisting of quartz porphyry, andesite, and tuff with rock strengths ranging from 60 to 225 MPa UCS. The machine crossed over 400 fault lines including two major faults of approximately 50 m wide.

A Rocky Start

The machine was launched in March 2007, in ground conditions that immediately became more complex than anticipated. As the height of the overburden increased, long stretches of extremely loose, blocky ground were encountered. TBM utilization was as low as 18.7% of working time because rock support installation was requiring a very high 43.5% of the working time.

A rocky start: Rock bursting conditions at Olmos prompted a major overhaul of the TBM in the tunnel.

One of the main problems faced was ground deterioration and the resulting falls of blocky ground. The majority of these events occurred during the time taken for the newly excavated bore to pass behind the rear fingers of the roof shield, where ring beams and mesh were installed.

Modifying the Machine in the Tunnel

During consultations between Robbins and Odebrecht, a decision was made to modify the machine in the tunnel. The TBM would be reworked to use the McNally roof support system, which allows support to be installed directly behind the main roof shield. Crews removed the roof shield fingers and installed a series of rectangular pockets in their place. The pockets ran from the rear side of the cutterhead to the trailing edge of the roof support. These pockets were designed to be used with rebar, which is part of the McNally Roof Support System. At a later stage when the ground conditions worsened these pockets were extended to cover the sides of the TBM as well.

TBM Modifications: The crew add McNally pockets to the TBM roof shield in the tunnel.

The McNally Support System

One big advantage of the McNally support system is that it is possible to install ground support closer to the face than other ground support methods used on TBMs. It holds loose rock in place, which in turn helps to activate the strength of the rock mass and maintain the inherent strength of the tunnel arch. When used correctly the system can significantly reduce the time taken to provide adequate support. It can also offer reductions in the level of support required, and contain rock bursts and collapsing ground.  The greatest benefit of the system, by far, is its ability to provide a much safer work area.

Crown Control: McNally slat installation at the Olmos Trans-Andean Tunnel.

Incorporation of the McNally support system and various other modifications to the TBM resulted in a steady increase in production rates in spite of continuous rock bursting events. The machine broke though in December 2011 having achieved production rates in excess of 670 m a month.

Read more about the McNally Support System here.

Make short work of an unforeseen cavern: The MKTVARI project

The Republic of Georgia’s Mktvari Hydropower Plant Construction project, along the river of the same name, was a challenge from the outset. The initial contractor used drill and blast for the 9.5 km long headrace tunnel through hard rock, but after 1.5 years they had only advanced about 200 m. The new contractor took over a previously-ordered non-Robbins hard rock machine but enlisted Robbins to help with the TBM assembly. They also wanted Robbins to be available if problems occurred.  The machine did well at the outset, boring up to 900 m per month.  But then, the machine hit bad ground.

Cavernous Conditions

Crews hit an unforeseen cavern above the TBM and were unsure of how to proceed through mixed layers of breccia, andesite, and bands of clay with light water inflows.   A Robbins Field Service Manager was sent to the site, where he determined that the cavern was part of a fault zone consisting of unstable material that fell onto the cutterhead. At the time of his arrival, the TBM had passed through most of the fault zone but huge voids were left behind the segments.

Using pea gravel pumped through holes drilled in the segments, combined with cementitious grout, the crew was able to stabilize the existing segments and safely advance through the cavern in about 10 additional segments.  There was also a probe drill onsite that had not been used; the Robbins manager persuaded the crew to install the probe drill and conduct systematic probing ahead of the machine, in case a larger section of clay was encountered.

Crossing the Void: Robbins worked with the contractor to backfill the cavern, enabling the crew to advance out of the void in 10 additional segment rings.

Key Takeaways

As can be seen in these examples, planning is key. But, even the best-laid plans can go awry. When conditions go from bad to worse, having an expert team of personnel on your side is by far the most valuable tool and the most positive predictor of a project’s ultimate success.  That true story I started off with certainly wasn’t the first such incident in the tunneling world, and it won’t be the last.  Be prepared by arming yourself with knowledge, and with a knowledgeable team.

Information at your Fingertips

Learn more about our vast experience in difficult ground conditions.  Our selection of white papers covers some of the world’s most challenging projects, while our Project Solutions section offers many examples of past successes.

 

 


From Risk Aversion to Risk Reduction: How Elon Musk could usher in a New Era of Tunnel Boring

 

The factory acceptance of the Robbins TBM for the Rondout West Bypass on February 17, 2017.

Tunnel boring machines like the one here, for New York’s Delaware Aqueduct Repair, are turning risk aversion on its head.

It has been some time since I have written on the Robbins blog page, but I am inspired to do so by the announcement that Elon Musk is entering our business—the tunnel boring business.  It is great to see people with a vision of an improved world enter our industry.  I agree with Musk that the advance rate of tunnels can be significantly improved if development money comes into the industry.  Development money in tunneling, however, is at best minimal and is more often essentially nonexistent.  Nearly all tunnels are heavily specified to avoid risk taking by owners (therefore discouraging new development).  Nearly all tunnels go to the low bidder and low bidders try to buy the TBMs at the lowest price; a further discouragement of development. The industry has therefore been slow to improve advance rates, but with Musk bringing the issue into the spotlight, perhaps things will change.


Risk Aversion and How to Reverse it

There are some exceptions to this practice of risk aversion for new technology, and one is the Delaware Aqueduct Repair. This tunnel corrects heavy water leakage occurring from the 1940’s-built aqueduct tunnel for New York City.  We are just completing Factory Acceptance in our plant in Solon, Ohio of this unique Single Shield TBM.  The tunnel is at significant depth (approximately 300 m / 900 ft) with the distinct possibility of encountering very high water pressure (up to 30 bars).  The contractor JV of Kiewit/Shea have shown their willingness to move forward with several new developments for this project.  The concept of grouting off high water pressure as the primary means to allow advance in such conditions, rather than use an EPB or Slurry TBM, is in my view a significant step forward for our industry.  Granted there have been halfway attempts with a combination of grouting and pressurized tunneling at recent projects like the Arrowhead Tunnels and Lake Mead Intake No. 3, but these have come at high cost and sometimes long delays.  The Delaware Aqueduct TBM, by contrast, is designed to hold up to 30 bars of pressure while grouting occurs.   Boring and cutter changes are done in atmospheric pressure.

Chemical grouting and grouting technology in general have advanced multifold in recent years, and it is commendable to see it used extensively on several aspects of the Delaware Aqueduct Project. It’s a great example of what can be done when a contractor is willing to use new technology to address potential risks—it appears it can actually reduce risk in the long run.  It is a great honor to be working with the capable Kiewit/Shea JV team to be a part of advancing technology.

The enhanced probe drilling and grouting capabilities as seen in trajectories (orange and red) on the Rondout TBM 3D model.

The enhanced probe drilling and grouting capabilities as seen in trajectories (orange and red) on the Delaware Aqueduct TBM 3D model.

Areas Ripe for Change

The Delaware Aqueduct Repair project is a flagship project for what I hope will become more common in the industry: instead of low bidding with the cheapest possible machine, offering a reasonable bid with a specialized TBM that has a higher initial investment, but ultimately a lower cost overall. The project’s use of technology is wide-reaching, particularly atmospheric cutter changes and chemical grouting, which have the potential to reduce downtime and increase safety. I do not see the future of rock tunneling under high water pressure being left to divers to change cutters and repair the cutterhead.  We all know it is not cost effective to send divers to work in confined spaces over 10 bars.  It should be noted that the long-duration Hallandsås Tunnel, for example, finished the majority of its TBM advance by relying on effectively this technique of grouting and advance after failing with a Slurry System.  There are lots of tunnels to be built with above 10 bars pressure that will use this technology.  The industry needs to automate cutter and bit changes as much as possible, and increase the integration of chemical grouting in tunneling.

Project officials examine the cutterhead and cutters of the Rondout TBM. The machine can bore and cutters can be changed at atmospheric pressure.

Niels Kofoed and Danny Smith of contractor Kiewit examine the cutterhead and cutters of the Delaware Aqueduct TBM. The machine can bore and cutters can be changed at atmospheric pressure.

Certainly there are many areas for advancement in our industry, and major public figures like Musk drawing attention to it is ultimately a good thing.  After all, getting the general public to think about solving traffic by going underground is no easy feat. Even more so, getting the tunneling industry to think about its own risk-averse practices has a big potential benefit. Hopefully all of this attention will result in more tunnels, more business, and better infrastructure. Musk’s willingness to take a risk aimed at making the underground construction industry potentially faster and more stable is a good bet to take.


The Light at the End of the Tunnel: The Positive Side of Seattle’s SR99 Project

Robbins Bertha Blog

Bertha ship docks at the Port of Seattle. Photo cred: WSDOT.

Seattle is the founding city of The Robbins Company, and a place where I lived for nearly 15 years and commuted on SR99 while working at Robbins early in my career. As such, the new SR99 Viaduct Replacement Tunnel Project is of great interest to me.

The industry is all too familiar with Seattle’s SR99 Tunnel and its TBM, known as “Big Bertha”. More specifically, much has been written with regards to the TBM needing repairs after about 300 m of boring. The TBM is the world’s current largest at 17.5 m in diameter, and is excavating a 2.7 km long drive.

Robbins Bertha Blog

Bertha’s parts parked on Alaskan Way. Photo cred: WSDOT.

Robbins Bertha Blog

Last day above ground for Bertha’s cutterhead. Photo cred: WSDOT.

TBM Tendering

Robbins was a relatively new entry into the EPB/soft ground tunneling business when tenders were called for the latest SR99 project in 2011, and we made a concerted effort to get the order for this particular TBM. We teamed up with Japanese TBM manufacturer Mitsubishi Heavy Industries (MHI) to get the order. Robbins has had an association with MHI for more than 20 years, with jointly-designed machines operating around the world on projects in India, China, the U.S., and more. MHI has built over 1,000 EPB machines and in my opinion, the Japanese TBM manufacturers are further advanced in EPB technology than their European and American counterparts.

Through the process of trying to receive this order, we learned a lot about the geology, as well as the contractors’ and TBM’s specification requirements. The contractor Dragados, one of the JV partners and very well-experienced in soft ground tunneling technology, developed a high-level specification for the TBM suppliers. All of the prospective TBM suppliers were required to quote and if successful, supply to this standard. We eventually stepped out of the tendering process to supply this TBM, as the lower prices and greater assumption of contract risk offered by our competitors made the TBM supply an impractical business option for us.

Robbins Bertha Blog

Bertha’s parking spot. Photo cred: WSDOT.

Tough Tunneling

The current situation at the SR99 project is more positive than media tend to paint it. The project design consultant did a commendable job on laying out the tunnel route and building in a contingency plan. Boring through glacial till, even with modern TBMs, is never an easy task as previous projects like the Brightwater Conveyance Tunnels have taught the city of Seattle. This is doubly so along the Seattle waterfront, which includes manmade fill, utilities, and buried refuse. In such ground, TBMs can encounter rapidly changing geology; pockets of groundwater; abrasive soil; and manmade objects such as unmapped disused pipes; foundation piles; etc.

Robbins Bertha Blog

Survey says, “This is one big tunnel.” Photo cred: WSDOT.

Aware of the problems that can develop while using an EPB TBM in glacial till under a city with a lot of backfill, the SR99 designer wisely developed a contingency plan. The strategy, in addition to pre-planned safe havens, involved a “shake down” stretch of tunnel, which ran under no buildings. If problems did occur repairs to the TBM could be made by sinking a surface access shaft at this location. Unfortunately the need for that repair event occurred shortly after the machine commenced excavation.

Why there were failures of the cutterhead seals, and potentially the cutterhead main bearing, is yet to be determined. I doubt there will be any signs of failure of the main bearing when the crews get to inspect it. However, all parties involved are wisely taking precautions and installing a new main bearing in addition to the seals.

Bertha’s Lessons

The Seattle Tunnel Partners and WSDOT have in place a panel of experts to advise them on the highly technical details of the TBM design. I personally know several of these experts and they are well qualified to recommend and supervise the necessary repairs and procedures to get the TBM into a condition where it is able to finish this tunnel.

Robbins Bertha Blog

The experts behind the world’s largest TBM. Photo cred: WSDOT.

Having been in the TBM supply business for quite a few years, I unfortunately have to admit having been in a similar (fortunately not as well published) situation as the TBM supplier on more than one occasion. This situation–significant TBM problems at the beginning of boring—can result from many different factors and is not unique to the SR99 project. In fact, Robbins recently had a similar situation (admittedly on a smaller scale in terms of both public and financial impact) on a project in Turkey known as the Kargi HEPP. Despite extensive pre-planning, unexpected ground was encountered, which resulted in several in-tunnel stops and machine modifications in the first few hundred meters of the tunnel. What happens in these situations is you pull in the best minds with the most experience and immediately analyze the problem. The ultimate fix often ends up as a multi-level solution. You must ensure you have the problem under control, plus take additional measures to monitor the vulnerable components and operating procedures. At Kargi, this process resulted in the remainder of the project being finished without significant TBM problems. Without a doubt a similar process is going on at SR99 with Hitachi Zosen engineers, the contractor’s specialists, and the city’s board of experts.

Being one who is keenly interested in this project, I believe that this TBM will soon be back to boring with a new completion date, which will be fulfilled. I am optimistic that this project will one day be seen as a positive in the tunneling industry, where many lessons were learned and advancements were made. Such advancements will be put to use in Seattle and in other cities that greatly benefit from the excavation of more underground infrastructure.


Research and Development: A Sneak Peek at the Next Generation of Disc Cutters

Cutter Changing in Malaysia

Cutter Changing at Malaysia’s Pahang Selangor Raw Water Tunnel

R & D is important in any industry, and it is no less true for the tunneling industry.  Evolution, even if it is incremental, is where most research and development successes are made.  Such improvement forms part of the competitiveness among manufacturers and thus begets further improvements.  I also believe it is our obligation, as equipment manufacturers, to assist the market in driving down the costs of tunneling in general by improved product performance and product life.

Take, for example the research and development going on with our disc cutters: Robbins disc cutters have improved dramatically since the 1950s when they achieved their first success at 11 inches in diameter in crystalline limestone of 190 MPa (28,000 psi) UCS.  Today’s disc cutters do reach 20 inches in diameter and cost-effectively excavate rock strengths of 400 MPa (60,000 psi) UCS, all while lasting much longer than their predecessors.

Single Disc Cutter in a workshop.

Today’s disc cutters are capable of excavating 400 MPa (60,000 psi) UCS rock.

That being said, we believe there is always room for improvement.  We are working hard right now to develop customized cutters for EPB tunneling in soft and mixed ground, and to optimize those designs so they can excavate under high pressure.  In hard rock, we are researching and testing new steels, and developing monitoring systems to allow contractors to plan cutter changes.

Here’s a snapshot of what research and development is going on in the cutter department, both in the lab and in the field:

Improved Metallurgy

Working with the University of Trondheim and the Norwegian government, we are commencing a program of laboratory and field testing to improve the materials making up the disc ring itself.  We are always testing new materials in order to find the most durable materials based on the ground conditions. An example of past cutter research in the lab can be seen below:


Pressure Compensated Disc Cutters

We are currently developing improved disc cutters specifically for use on EPB and Slurry TBMs at high pressures of plus 10 bars, using a testing module in our Kent, Washington facility.  The module duplicates a pressurized operational environment so that we can analyze how the cutter seals perform under pressure—the design is in its 3rd or 4th generation with continuous improvements being made.

Testing module for pressure compensated disc cutters.

Pressure vessel testing module for pressure compensated disc cutters.


Remote Cutter Monitoring

Our remote cutter monitoring system is a breakthrough that we have been field testing for four years.  The system is now undergoing full scale testing on three Main Beam TBMs at Malaysia’s Pahang Selangor Raw Water Tunnel.  The setup allows crews to more closely monitor the actual working conditions and cutter wear.  We project, through this system, to increase the TBM utilization of each machine by 3 to 4% and to reduce cutter cost by 10%.

We’re also working on expanding this wireless system to EPB and Slurry machines, so that monitoring of cutter wear and rotation can be used while those machines are in closed mode.  This would be a highly beneficial development, because under pressure the detection of tool wear is difficult.  Our goal here is to reduce or better plan interventions because of tool wear.

Robbins remote cutter monitoring system.

Sample screenshot of the Robbins remote cutter monitoring systems. Failed cutters are highlighted by a color on the screen.


Robbins Atmospheric Cutter Change System (RACCS)

Finally, we are developing a system to allow cutter changes at atmospheric pressure on large diameter EPBs.  This atmospheric cutter change system is superior to other systems on the market because it allows muck to flow through.  Other systems on the market are very prone to clogging. Each spoke of an EPB cutterhead will contain a chamber at atmospheric pressure.   Cutters can be rotated from the pressure zone into the chamber to allow for efficient and relatively fast cutter changes.

The development is also significant because a huge cost of operating large diameter EPBs is associated with intervention for cutter inspection and change.  We are currently building a large test fixture for this system, which will analyze how RACCS reacts in sand, gravel, boulders, clay, and mud conditions under pressure.

 

Conclusions

These research and development projects are all aimed at solving a particular problem or shortfall—with the objective to bore more meters per month.  It is not the only area where we have research and development underway, as we have similar programs to investigate improvements of the probe drilling and lube systems on our TBMs.  The process is usually rigorous, as designs need to be tested and re-tested in both the lab and the field.

I am not a big believer in “Big Step” research and development as was tried in earlier days at Robbins with the Mobile Miner and the Bore Pack.  Such “Big Step” research and development usually leads to disappointment and heavy cost for the client and the company.

However, improvements like the 19” cutters and the cutter monitoring systems are and will be big wins for the contractors and for Robbins.

Cutter Changing in Malaysia

Cutter Changing at Malaysia’s Pahang Selangor Raw Water Tunnel

 

 

 

 

 

 

 

 

 

 

 

 

 

 

R & D is important in any industry, and it is no less true for the tunneling industry.  Evolution, even if it is incremental, is where most research and development successes are made.  Such improvement forms part of the competitiveness among manufacturers and thus begets further improvements.  I also believe it is our obligation, as equipment manufacturers, to assist the market in driving down the costs of tunneling in general by improved product performance and product life.

Take, for example the research and development going on with our disc cutters: Robbins disc cutters have improved dramatically since the 1950s when they achieved their first success at 11 inches in diameter in crystalline limestone of 190 MPa (28,000 psi) UCS.  Today’s disc cutters do reach 20 inches in diameter and cost-effectively excavate rock strengths of 400 MPa (60,000 psi) UCS, all while lasting much longer than their predecessors.

[Photo of a disc cutter]

That being said, we believe there is always room for improvement.  We are working hard right now to develop customized cutters for EPB tunneling in soft and mixed ground, and to optimize those designs so they can excavate under high pressure.  In hard rock, we are researching and testing new steels, and developing monitoring systems to allow contractors to plan cutter changes.

Here’s a snapshot of what research and development is going on in the cutter department, both in the lab and in the field:

Improved Metallurgy

Working with the University of Trondheim and the Norwegian government, we are commencing a program of laboratory and field testing to improve the materials making up the disc ring itself.  We are always testing new materials in order to find the most durable materials based on the ground conditions. An example of past cutter research in the lab can be seen below:

Pressure Compensated Disc Cutters

We are currently developing improved disc cutters specifically for use on EPB and Slurry TBMs at high pressures of plus 10 bars, using a testing module in our Kent, Washington facility.  The module duplicates a pressurized operational environment so that we can analyze how the cutter seals perform under pressure—the design is in its 3rd or 4th generation with continuous improvements being made.  [Photo of testing facility?]

 

Remote Cutter Monitoring

Our remote cutter monitoring system is a breakthrough that we have been field testing for four years.  The system is now undergoing full scale testing on three Main Beam TBMs at Malaysia’s Pahang Selangor Raw Water Tunnel.  The setup allows crews to more closely monitor the actual working conditions and cutter wear.  We project, through this system, to increase the TBM utilization of each machine by 3 to 4% and to reduce cutter cost by 10%.

We’re also working on expanding this wireless system to EPB and Slurry machines, so that monitoring of cutter wear and rotation can be used while those machines are in closed mode.  This would be a highly beneficial development, because under pressure the detection of tool wear is difficult.  Our goal here is to reduce or better plan interventions because of tool wear.

[Show screen shot of monitoring system]


Robbins Atmospheric Cutter Change System (RACCS)

Finally, we are developing a system to allow cutter changes at atmospheric pressure on large diameter EPBs.  This atmospheric cutter change system is superior to other systems on the market because it allows muck to flow through.  Other systems on the market are very prone to clogging. Each spoke of an EPB cutterhead will contain a chamber at atmospheric pressure.   Cutters can be rotated from the pressure zone into the chamber to allow for efficient and relatively fast cutter changes.

The development is also significant because a huge cost of operating large diameter EPBs is associated with intervention for cutter inspection and change.  We are currently building a large test fixture for this system, which will analyze how RACCS reacts in sand, gravel, boulders, clay, and mud conditions under pressure.

 

Conclusions

These research and development projects are all aimed at solving a particular problem or shortfall—with the objective to bore more meters per month.  It is not the only area where we have research and development underway, as we have similar programs to investigate improvements of the probe drilling and lube systems on our TBMs.  The process is usually rigorous, as designs need to be tested and re-tested in both the lab and the field.

I am not a big believer in “Big Step” research and development as was tried in earlier days at Robbins with the Mobile Miner and the Bore Pack.  Such “Big Step” research and development usually leads to disappointment and heavy cost for the client and the company.

However, improvements like the 19” cutters and the cutter monitoring systems are and will be big wins for the contractors and for Robbins.