Category: White Papers

Unprecedented In-Tunnel Diameter Conversion of the Largest Hard Rock TBM in the U.S.

The largest hard rock TBM ever to bore in the USA, an 11.6 m diameter Robbins Main Beam TBM, recently underwent a planned in-tunnel diameter change to a more compact 9.9 meters. The first-of-its-kind conversion process for the Main Beam TBM was undertaken 2.8 km into the bore and was not done inside a shaft or pre-excavated portal. This paper will detail the unique dual-diameter machine designed for the Mill Creek Drainage Relief Tunnel in Dallas, Texas, USA, machine performance, and successful size conversion process that took place in early 2021—a process that utilized the four C’s of construction to enormous benefit: Communication, Cooperation, Collaboration and Coordination.


Hard Rock Tunnel Boring at the Jefferson Barracks Tunnel

The Metropolitan St. Louis Water District’s Project Clear is a 28-year program targeting wastewater capacity throughout St. Louis, MO. The extensive program includes the Jefferson Barracks Tunnel, running parallel to the Mississippi River at 2 m ID and 5,400 m long.  A rebuilt Robbins Main Beam TBM began boring but hit challenging conditions about 2,400 m in, including water inflows. A larger 4.1 m Robbins Main Beam machine, launched in 2022, is now completing the remaining 3,050 m in limestone, dolomite, and shale. The TBM is utilizing a high-powered, high breakout torque cutterhead along with enhanced 360-degree probing & grouting capabilities to detect any karst formations.


The Next Generation of Mixed Ground Tunnel Boring Machines

What is the most economical way of tunneling in mixed ground that may experience high pressures? Non-continuously pressurized, mixed ground Tunnel Boring Machines (TBMs) are being utilized to deal with a wide range of geology. Continuous improvements in these mixed ground machines allow for ever-increasing efficiency and reduction of project risk due to unexpected conditions. Read this paper for a look at how new improvements to Crossover machines will enable excavation of an expanded range of ground conditions. These conditions include mixed ground with low fines, mixed face rock, and fracture / fault zones with high pressures where in the past a Slurry TBM may have been utilized.


Rock Tunnels at High Water Pressure: Non-Continuous Pressurized TBMs vs. Slurry

The choice of TBM type is never easy, but it becomes especially challenging when faced with a hard rock tunnel with expected high water flows and pressure.  Slurry Shield tunneling has a long history of being used in these conditions to minimize the risk, though this method has brought with it other risks along with cost considerations. At recent projects around the world, another method has been proven to effectively manage these project risks without utilizing Slurry Shield tunneling: Shielded, Non-Continuous Pressurized (NCP)-TBM tunneling in rock with a comprehensive grouting program. In this paper, the authors will analyze the use of Shielded NCP TBMs at projects around the world as compared with slurry shield tunneling in rock under water pressure. Recommendations will be given in order to establish a clear picture of the optimal tunneling method.


Hybrid TBM Excavation in Challenging Mixed Ground Conditions at the Mumbai Metro

Excavation in mixed ground conditions is always a challenge, but under a densely urban environment the stakes become even higher. At India’s Mumbai Metro, two 6.65 m hybrid-type rock/soft ground Single Shield TBMs are successfully boring parallel 2.8 km tunnels in basalt rock with transition zones of shale, tuff, and breccia below the city. They have made intermediate breakthroughs at the 1.2 km mark and overcome rock strengths up to 125 MPa UCS with significant water ingress, all just one year after factory acceptance, shipping, site assembly, and launch. The hybrid machines are optimized for abrasive rock geology using a robust cutterhead mounted with disc cutters and a reinforced screw conveyor at the centerline. The machines can also operate in closed or semi-closed mode using features designed to advance in soft ground with water inflows: dual ratio gearboxes to adjust cutterhead speed and torque to the geology, screw conveyors with bulkhead gates and discharge gates, ground conditioning with foam and polymers, and probe drills for pre-excavation grouting.


TBM Excavation in Himalayan Geology: Over 1,200 Meters per Month at the Bheri Babai Diversion Multipurpose Project

A Double Shield TBM achieved in 17 months what was projected to have taken 12 years with Drill & Blast: The 12.2 km long Bheri Babai Diversion Multipurpose Project (BBDMP).  Bored in Himalayan geology including sandstone, mudstone, and conglomerate, the excavation was able to achieve over 1,200 m advance per month on multiple occasions.   Crews achieved this while traversing a fault zone and getting through one section that required a bypass tunnel constructed in just five days. The success of this tunnel is not only in breaking through a historically difficult mountain range, but also in changing the notion, to the people of Nepal, that drill and blast is the way to excavate mountainous rock tunnels.


Tunneling through 48 Fault Zones and High Water Pressures on Turkey’s Gerede Water Transmission Tunnel

The December 2018 breakthrough of a 5.5 m diameter hybrid-type Single Shield/EPB TBM at the Gerede Water Transmission Tunnel in Central Turkey was a feat of modern construction. The 9 km leg was the final section of the 31.6 km long water supply line bored through what is widely considered to be Turkey’s most challenging geology. The project was originally started with the contractor selecting three Double Shield machines, which were procured and supplied without Robbins involvement. When two of the machines became stuck and were unable to continue, the solution of the hybrid-type TBM was developed to complete the rest of the tunnel. The TBM was assembled and launched more than 7 km from the tunnel portal and successfully navigated 48 fault zones as well as hydrostatic pressures up to 26 bar.


Overcoming Multiple Caverns: Successful TBM Tunneling in Karst Geology at Galerie des Janots

In April 2019, a 3.5 m diameter open-type, Main Beam TBM and its crew broke through at the Galerie des Janots Tunnel in La Ciotat, France after encountering two large, uncharted caverns.  The 2.8 km long tunnel, excavated in limestone known to have groundwater, karstic features, and voids, took two years to complete due to the challenges encountered.    Limestone and powdery clays made for slow going early on in tunneling, until a cavern measuring 8,000 cubic meters in size was encountered on the TBMs left side at the 1,035 m mark. The crew had to erect a 4 m high wall of concrete so the TBM would have something to grip against—a process that took about two weeks. The first cavern, while the largest, was not the most difficult void encountered. At the 2,157 m mark, crews encountered a 4,500 cubic meter cavity extending directly below the bore path. This cavern required stabilization, filling, six bypass galleries, and four months of work to get through.


TBMs For Norwegian Small Hydropower Projects

Small hydroelectric projects, with installed capacity up to 10 megawatts (MW), are a relatively untapped but potentially game-changing source of renewable energy in North America. In Norway, hydro projects are pioneering the use of small diameter TBMs in hard rock. Compared with drill and blast, TBMs offer increased production rates and reduction in cross section, among other benefits. The uniquely designed machines are engineered to take on steep gradients, up to a 45-degree angle in some cases.


Completing Mexico City’s Mixed Ground Mega Tunnel: Emisor Oriente

On May 23, 2019, the last of six 8.93 m diameter EPBs completed excavation at Mexico City’s Túnel Emisor Oriente (TEO), a feat marking the completion of ten years and 62.1 km of tunneling. The TEO is a critically-designated plan to stem severe flooding while boosting wastewater capacity, and is the country’s largest infrastructure project. The six EPB TBMs excavated some of the most complex geology on earth, ranging from abrasive volcanic rock to watery clays.