Category: White Papers

High Cover TBM Tunneling in the Andes Mountains—A Comparative Study of Two Challenging Tunnel Projects in Chile

The Andes Mountain range is among the youngest and most complex in the world, geologically speaking. Tunneling projects, particularly for hydroelectric and water transfer schemes, are not new to the range but their past history has met with mixed success. Two new projects utilizing very different tunnel boring machines and excavation strategies are now providing a testing ground for modern underground construction equipment in the Chilean Andes.

This paper will analyze two projects: the Alto Maipo and Los Condores Hydroelectric Projects, located approximately 100 km apart in the Andes Mountains. The two strategies being employed will be analyzed in detail, as one project is using an open-type Main Beam TBM plus extensive ground support, while the other is utilizing a Double Shield TBM and segmental lining. The authors will look at TBM performance and ground conditions encountered in the two tunnels and what effects the TBM selection and ground support strategy may have had on each tunneling operation.

Successful Excavation of Mexico City’s Emisor Poniente II Wastewater Tunnel—Use of a Dual-Mode, Crossover TBM in Challenging Geology

The history of Mexico City is inextricably linked to the issue of its geographic location. In the last 100 years, Mexico City has sunk by nearly 12 m. As a result, the city’s buildings, main streets, sewage systems, etc. have been extensively damaged.

In July 2015, the launch of a dual mode, Crossover type TBM marked the start of Mexico City’s next challenging wastewater project: the Túnel Emisor Poniente (TEP II). The 5.5 km long tunnel travels below a mountain at depths of 170 m as well as a section just 8 m below residential buildings, and the geology is equally varied. Ground consists of andesite and dacite with bands of tuff and fault zones, as well as a section of soft ground at the tunnel terminus.

This paper will detail the unique 8.7 m diameter Crossover TBM designed for the challenging conditions, and the successful excavation of the machine through fault zones, soft ground, and more. Strategies for excavation and advance rates, and downtimes will be analyzed. As the machine can be converted from hard rock mode to EPB mode in the tunnel, the authors will also look at the conversion process and how both modes worked to excavate in widely varying geological conditions.

Design and Implementation of a Large-Diameter, Dual-Mode “Crossover” TBM for the Akron Ohio Canal Interceptor Tunnel

The Ohio Canal Interceptor Tunnel (OCIT) Project involves construction of a conveyance and storage tunnel system to control combined sewer overflows for several regulators in the downtown Akron area. A Robbins dual mode type “Crossover” (XRE) Rock/ EPB TBM, Ø9.26m bore in diameter, will be used to excavate the tunnel and install the precast segmental lining.

The XRE TBM will feature characteristics of both Single Shield Hard Rock machines and EPBs for efficient excavation in mixed soils with rock, such as a flexible cutterhead design for proficient boring in both rock and soil conditions, adjustable main drive speed with an over-speed mode for operation in hard rock, and special screw conveyor wear protection measures. This paper describes these design features, their manufacturing process, and implementation in the field.

Carving a Path Through Extreme Conditions: An Integrated Ground Investigation System Optimized For Turkey's Difficult Geology

Turkey’s geologic framework, seated on an active tectonic belt, is made up of older rocks mixed with younger igneous rock. More than 80% of the country’s surface is rough and mountainous, and the ground conditions can be highly variable and unpredictable. Today’s adaptable TBMs are capable of tackling these tough conditions using cutting-edge technology coupled with modern ground investigation methods.

This presentation will explore several recent and ongoing projects in the tunneling industry that highlight the latest in TBM technology for difficult ground excavation. Whether smart features include a Measurement While Drilling (MWD) system, cutterhead inspection cameras, or sensors to monitor converging ground, today’s TBMs equip contractors with knowledge. Specialized sealing systems can arm contractors with methods to successfully and safely treat water head pressure up to 30 bar.

Tunnel Boring below Montreal: A Case Study of Urban Tunneling through Hard Limestone

Montreal, Quebec, Canada’s Rosemont Reservoir tunnel travels for 4.0 km below city streets, faulted rock, a disused quarry, and active subway. The story of the 3.0 m diameter Double Shield TBM’s successful breakthrough involves a careful analysis of geology, TBM operating parameters, and ground consolidation measures. Over the years, geologists conducted two diamond-drilling programs totaling 65 borehole tests to depths ranging from 21 to 65 m below residential and commercial neighborhoods along the tunnel alignment. The core sampling program indicated the presence of medium to thinly bedded limestone, with some shale and intrusive rocks, mainly dykes and sills. While the limestone averaged 50 to 300 MPa UCS, rock in the intrusives ranged from 100 to 430 MPa. More than 80 dykes and sills as small as a few centimeters wide and as large as 8 to 10 m wide were mapped along the 4.0 km tunnel. Contractor Foraction, Inc. took measures including cement injection of vertical boreholes in two suspected fault zones from the surface to a depth of 50 m. Even with these measures, fractured rock and water inflows, which had to be temporarily deviated, slowed progress and required alteration of the boring parameters in some sections. The crew were ultimately successful and made their final breakthrough with the TBM in November 2015. This paper will analyze TBM boring methods and performance based on the changing geological conditions below Montreal. Special attention will be paid to sections in fracture zones and below sensitive structures including the inactive quarry site and active Montreal subway. The authors will analyze how preliminary studies, combined with operational techniques and on-going geological monitoring, resulted in an ultimately very efficient tunnel boring project in a dense urban area.

A Novel Continuous Conveyor System and its Role in Record-Setting Rates at the Indianapolis Deep Rock Tunnel Connector

The Indianapolis Deep Rock Tunnel Connector (DRTC)—first in a vast network of storm water storage tunnels below Indiana, USA—was a wildly successful endeavor. Crews for the Shea/Kiewit JV drove a 6.2 m Robbins Main Beam TBM to world record rates. The machine achieved 124.9 m/day, 515.1 m/week, and 1,754 m/month in limestone and dolomite rock. The advance rates can be attributed to many factors including ground conditions and knowledgeable crew, but continuous conveyors are also of key importance.

The novel conveyor system, manufactured by The Robbins Company, enabled continuous tunneling in a difficult layout that included two 90-degree curves and two S-curves. Spanning 11,777 m in its longest iteration, the system included nine booster drives plus a main drive. A vertical belt moved muck up the 76 m deep shaft to a radial stacker for temporary storage. The system, one of the most complex in North America and the first to operate in 90-degree curves, made swift tunneling possible.

This paper will examine the world-class tunneling done at the Indianapolis DRTC and the role of continuous conveyance in reaching high advance rates. The logistics of the system will also be examined as it could apply to future tunneling projects with similarly complex layouts.

Use of Two Novel Hybrid-Type “Crossover” TBMs for Hard Rock Conditions with Water Inflows

Mixed ground tunnels come in all kinds. In rock tunnels with possible faults and high pressure water, the challenges are many. With the advent of Crossover TBMs, contractors can minimize risk in such conditions while maximizing efficiency. The newest generation of Crossover is exemplified by two projects in Albania and Turkey.

A 5.56 m Crossover TBM destined for Turkey’s Gerede Water Transmission will be assembled using Onsite First Time Assembly (OFTA) from within an existing tunnel. The unique machine will bore through 30 fault zones requiring the TBM to be sealable to up to 20 bar so pre-consolidation grouting can be done. EPB mode will only be used in poor ground—in this mode, the TBM will bore sequentially using the screw conveyor fore and aft gates.

Skewing further towards hard rock, a unique 6.2 m diameter Double Shield TBM with Crossover features was designed for Albania’s Moglicë Headrace Tunnel. The machine features closure doors and a sealing system to contain inrushes of water until they can be grouted off.

This paper will discuss the unique aspects of the Crossover designs and their utilization at the two projects.

The Next Generation of TBMs for Mining Applications

TBMs have been used in mining in decades past, but their use has been limited and sporadic, due to both perceived and actual application difficulties. With new technology and mounting success stories, this is changing. For both coal and metallurgical mining, deep ore bodies require long access tunnels, and an efficient and economical method of reaching those deposits.

Today, mining engineers are considering TBMs as part of the overall mine development plan. Planned TBM mine drifts are not only longer, but have more complicated trajectories. Mine development TBMs will have to cope with varying geology, potential for high water inflows, steep gradients, and high temperatures. TBM systems are being planned to cope with such difficulties. TBM systems will be considered and increasingly deployed for mine development, even if commodity prices remain low. TBMs can satisfy the need for increased productivity, better life of mine infrastructure, and safety.

This paper will review the historical use of TBMs in mining, and will discuss the 2015 status of TBMs in mining, and the special requirements and adaptable features needed in order to make efficient TBMs a reality in mines worldwide.

Concurrent Segment Lining and TBM Design: A Coordinated Approach for Tunneling Success

The success of a tunnel project relies on many factors, but one of the most important is also the most overlooked: coordination by all parties involved during the design stages. This is particularly true of segment design and TBM design. Tunnel lining with segmental rings is usually designed according to the standards of reinforced concrete construction based on a given GBR. However, for TBM tunneling, the determination of loads during ring erection, advance of the TBM, earth pressure, and bedding of the articulated ring are all part of the tunnel lining design as well. TBM design can be heavily affected by the segment arrangement, dimension, and weight, but these are usually given as a fixed input to the TBM manufacturer—a process that can cause unnecessary complications.

The authors propose that the industry evaluate the process as it stands. In order to find the optimum balance between lining design and TBM cost and operational workflow, both designs should be finalized concurrently. This requires coordination between the TBM manufacturer and segment designer from the early stages. The aim of this paper is to evaluate the influence of the segment lining design on TBM cost and performance, and to provide commentary on existing design guidelines to optimize lining and TBM procurement.

To Build a Tunnel Boring Machine: Why Assembly on Location is the Next Big Advancement

Is there a better way to build a Tunnel Boring Machine (TBM) that can benefit all parties involved? For decades TBMs have traditionally been assembled in factories, where the components are assembled and tested, then disassembled and shipped to the jobsite. Delivery of a machine can often be the critical path affecting project schedule, cost, manpower, and other factors. Onsite First Time Assembly (OFTA) has been developed and used on dozens of projects around the world to pass on cost and time benefits to contractors working on fast-paced projects with tight schedules. The use of OFTA is increasing, allowing for TBMs to be initially assembled at the jobsite, and cutting out extra shipping and disassembly steps. This paper will analyze the reasons for shop assembly vs. onsite assembly, determining the ultimate benefits and drawbacks of each. The paper will also draw quantitative comparisons in terms of time and money, as well as differences in carbon emissions, energy, and manpower requirements. The paper will conclude with a discussion on trends in TBM assembly today and where the future is headed when building these complex tunneling machines.