Innovations in Microtunneling and Ground Improvement

Sealing off groundwater from the TBM was the key to successfully completing the Arrowhead tunnels.

Sealing off groundwater from the TBM was the key to successfully completing the Arrowhead tunnels.

In our sister publication Trenchless Technology, publisher Bernie Krzys highlighted what he viewed as the greatest innovations in the industry in the last 20 years. He highlighted these innovations throughout 2014 in his “Publisher’s Message” columns. Two of those innovations, curved microtunneling and ground improvement, have a direct link to TBM: Tunnel Business Magazine – curved microtunneling and ground improvement.

Both of these areas have evolved over the years with new technologies and improved techniques. To delve further into the developments in these areas, we asked leading experts to share their thoughts on how the processes have advanced.

Curved Microtunneling

In August 2014, Krzys tackled curved microtunneling and for this section we received responses from Rory Ball, senior project manager at Hatch Mott MacDonald, and Richard Palmer, tunneling manager for Northeast Remsco Construction Inc. Of note, Northeast Remsco was the contractor that completed the first curved microtunnel project in the United States.

In his column Krzys wrote, “Curved microtunneling is truly an amazing technological innovation that has recently been introduced in North America. Added to this innovation in microtunneling are the fascinating interjacks, as well as automated bentonite systems that now help microtunnelers to achieve much longer drives. While I highlight these microtunneling technological advances as they relate to North America, curved microtunneling has been used in other countries such as Japan for quite some time.”

What significant developments have occurred in this area?

Ball: Outside of North America, the world has been completing curved drives for a long time. Although we are still playing catch up, we are way ahead of where we were even five years ago. What has happened recently has been a drastic leap forward for us in terms of the kind of projects contractors and owners are willing to do. However, this is just the beginning of where we will go.

Recently, contractors have been more willing to bring forward value engineering proposals on their own that incorporate curves and offer savings in terms of the impact to the public or in terms of saving time and money. This has been the huge step for the industry because most owners have not been willing to go out to bid with curves in the design drawings. Soon we will get to a point where owners are willing to have curved drives on their actual bid sets.

Palmer: The most significant development to me is the growing acceptance within the engineering community that curved microtunneling is a viable option in the North American marketplace. This has been reinforced by the inclusion of a curved microtunneling section in the 2015 edition of the ASCE Microtunneling Standards (ASCE 36-15), which fairly discusses the benefits of curved microtunneling, as well as the associated design and construction challenges.

What were some of the limitations or challenges with the technology previously?

Ball: Historically, owners have not wanted to step forward and take on the risk of bidding curved alignments. It took one contractor stepping forward with a value engineering proposal and taking on all of the risk himself on that drive. Since then, the majority of curves have come from the contractors who have had to present proposals in a way to the owners that made sense in terms of the benefits and management of each of the risks.

Northeast Remsco successgfully completed the first curved microtunnel drive in the United States in 2010.

Northeast Remsco successgfully completed the first curved microtunnel drive in the United States in 2010.

In terms of engineers and planners, many do not have the experience and understanding in design and construction to address risks in terms of curved microtunneling. The contractors have taken the lead in pushing the industry for not only the owners, but in challenging the engineers to step up their expertise.

A major challenge is that pipes available to North American contractors need to be able to go through the curves properly, and maintain both their structural and joint integrity.

Palmer: The principal challenge was to overcome the liability concerns associated with curved microtunneling. U.S. engineering firms were reluctant to design a project that required the use of a “never been done in the U.S.” microtunneling technique. In order to help break down that barrier, in 2010 Northeast Remsco proposed a curved microtunneling alternative on a project in Hartford, Connecticut, in lieu of a straight microtunnel reach and an open-cut reach. Fortunately, the designer engineer and the owner were receptive to the idea and collaborated on the final version of that curved microtunnel. It is interesting to note that the change order authorizing the curved microtunnel included language that shifted all of the risk to the contractor; shedding the risk was paramount to breaking down the barrier.

What has been the impact of these developments in the market?

Ball: The major impact has been that more owners are willing to talk about curved microtunneling. Now that they are seeing projects completed successfully in North America, they are engaged in the discussion and eager to learn more. They are more receptive to comparing the advantages and risks and see if it makes sense to do a curve.

As the infrastructure inevitably becomes denser, being able to reduce the number of shafts, reduce shaft depths, provide flexibility along the right of way or the alignment, and avoid obstacles, sensitive zones or utility crossings will lead to more significant direct and indirect cost savings.

In terms of pipe quality, we have seen a partnering approach between contractors and manufacturers to step up the pipe quality, tighten up tolerances and provide more joint configuration options.

Palmer: Curved microtunnels are now being designed into projects from the beginning rather than being proposals after the fact made by the microtunneling contractors. Even with the additional challenges associated with curved microtunneling, when used appropriately it can solve alignment problems, reduce the impact on neighborhoods and lower project costs.

How is the technology continuing to evolve?

Ball: Advances in machinery and the ancillary support systems that work with the machines are improving. In terms of machines themselves, we have advances like the Direct Pipe system; it’s an advancement that is relatively new almost worldwide that offers a great option for the engineering and construction community. It is getting more and more use with contractors having bought the machines for their own use in North America.

Some MTBMs now have circumferential lubrication so the rear of the machine can actually inject lubrication on its entire circumference as you mine. This is a great improvement for both long distance and curved drives to maintain the integrity of the annulus.

Other advances include better metallurgy of wearable components that support curved and longer drives, better real-time data recording capabilities and higher efficiency separation plants. In terms of data recording, contractors and engineers must learn to use the available metrics on a daily basis to proactively address risk on all microtunnel drives.

 Palmer: Several supporting technologies have already been on the market for a number of years outside the United States. These include: gyroscopic and laser theodolite guidance systems, enhanced auto-lubrication systems, and innovative packing systems for load transfer across deflected pipe joints. I believe the near term evolution of curved microtunneling in the United States will be our effort to “catch-up” by embracing these technologies.

What are some notable projects or products that use the new technology?

Ball: Much of the most advanced usage of curved tunnelling is happening in Canada under Ward & Burke. They are successfully completing longer drives and more complex curves like the Keswick WPCP Effluent Outfall Project, which had both a horizontal and vertical curve.

The Santa Ana River Interceptor (SARI) Project utilized Jackcontrol’s hydraulic joint and joint monitoring system for the first time in North America. Fowler, the microtunnel subcontractor, utilized this system to provide real-time feedback on the joint loading and rotation. This option provided comfort to the owner and engineer as a risk mitigation, thereby helping the value engineering proposal to be approved.

Palmer: The Homestead Avenue Interceptor Extension in Hartford, Connecticut, included the installation of 3,350 lf of 72-in. PVC-lined RCP via microtunneling through mixed ground and varied clays in five drives. The contractor proposed extending the final 310 lf microtunnel an additional 290 lf and incorporating a curve to accommodate a planned 4 degree horizontal deflection. The resultant drive was 600 lf comprised of a 200-ft tangent followed by a 200-ft curve on a 1,359-ft radius followed by a 200-ft tangent. The contractor used 10-ft pipe lengths and limited the joint deflection to 0.25 degrees in order to use standard 3/4-in. plywood joint packers. A VMT laser theodolite system was used for the curved guidance, and an auto-lubrication system to reduce jacking loads.

Ground Improvement

In his October 2014 column, Krzys discussed ground improvement. For this section, we spoke to Hayward Baker senior vice president of engineering George K. Burke and Dr. Raymond Henn, chief consultant for Brierley Associates.
Krzys wrote, “Over the years, it has really amazed me how trenchless projects can be completed in what would otherwise be presented as impossible ground conditions, such as water, loose soil, etc. Today, projects these days are being successfully completed in part due to the advances made in the area of ground improvement — i.e. jet grouting, freezing and groundwater cut off. Sometimes you look at a microtunneling project, for example, and ask “How could they have possibly gone through that kind of geology?” Yet, they do. For our part, we annually team with the Colorado School of Mines to present a Ground Improvement Short Course. This course presents a greater review of all the latest advances in ground improvement technology.”

What significant developments have occurred in this area?

Burke: Ground improvement technologies have matured…applications are many and experience grows. Product perception is also better, and constructability and logistics are better understood. This is certainly the case with jet grouting, soil mixing and chemical grouting.

Henn: The increased use of ultrafine/microfine cement for grouting of soil and rock.

What were some of the limitations or challenges with the technology previously?

Burke: The product perception and the verification requirements have often been unrealistic, causing extreme conservatism, very high construction risk and qualifications. Understanding the differences would make for a lower cost, completed faster, with a product that could meet the design intent.

Henn: Ultrafine/microfine cement costs between three to five times more than the cost of Portland cement.

What has been the impact of these developments in the market?

Burke: By using ground improvement techniques, we are able to use more applications and reduce risk and costs.

Henn: Being able to use common grouting equipment for ultrafine/microfine grouting, the type used to mix and pump Portland cement base grout, has allowed contractors to self-perform water cutoff grouting with their own on-site forces.

How is the technology continuing to evolve?

Burke: All of these technologies continue to adopt processes and equipment that improve efficiency while maintaining the minimum requirements of the product.
Henn: Suppliers are coming up with smaller and smaller sized cement particles for their ultrafine/microfine products. Also, pumice-based ultrafine (manufactured in the United States) is getting a bigger and bigger market share.

What are some notable projects or products that use the new technology?

Henn: The Arrowhead project – these two tunnels, which are located in California, each measure 12 ft in diameter and have a combined length of 9.6 miles. These tunnels were excavated using two hybrid tunnel boring machines (TBMs) with the West tunnel being the most difficult, taking over four years to bore through the mountain. The use of grouting to seal off groundwater was a critical element in completing this tunnel due to tight environmental requirements.

Mike Kezdi is a contributing editor to TBM.

Comments are closed here.