Ø1.8m Double Shield TBM for Mixed Ground Sewer Tunnels in Cincinnati

Size: px

Start display at page:

Download "Ø1.8m Double Shield TBM for Mixed Ground Sewer Tunnels in Cincinnati"

Roger Perry
5 years ago
Views:

1 Ø1.8m Double Shield TBM for Mixed Ground Sewer Tunnels in Cincinnati Steve Lamb The Robbins Company, Solon, Ohio, USA Steve Abernathy Midwest Mole, Inc., Indianapolis, Indiana, USA ABSTRACT: A Robbins Rockhead Ø1.8m double shield TBM is being used to excavate soft shale and harder limestone in Cincinnati, Ohio. Seven tunnels will be excavated, with lengths ranging from 250 to 610 meters (816 to 2,014 LF), for a total of 2,875 meters (9,430 LF). These are relatively long tunnel drives for such a small-diameter excavation. Primary support will be 100mm (4 in WF) steel ring beams on 1.5 meter (5 ft) centers. This paper will describe the special TBM, muck haulage, and launch shaft features which were carefully implemented to support rapid mobilization and excavation on this small diameter project. INTRODUCTION The Shayler Run Segment C project aims to update degraded and exposed sewer systems, and to protect the area surrounding environmentally sensitive Shayler Creek near Cincinnati, Ohio, USA. This USD $15 million project is a priority for the project owner, the Clermont County, Ohio Water Resources Department, because of severe pipeline erosion in the creek bed. Erosion of the creek bed has exposed the existing sewer pipe, which was installed in 1978, to the environment and put certain sections at high risk of failure. In fact, the exposed pipe has already dumped raw sewage into the creek. To address this problem, a new pipeline will be installed well below the creek bed, crossing the creek a total of seven times. Cover ranges from 3 to 30 m, with the majority of the pipeline running some distance from the waterway. The final carrier pipe will consist of 1.07 m (42 in) diameter Hobas Reline, which is much larger than the current 0.6 m (24 in) sewer line. The larger pipe diameter was decided on mainly to allow trenchless construction, though it has the added benefit of providing a larger capacity for future needs in the area as well. PROJECT LAYOUT The new pipeline consists of seven tunnels crisscrossing the creek, each connected by a 9.8 m (32 ft) diameter launch and receiving shaft, with a total of eight shafts in all. The shafts will eventually become fiberglass manhole structures to access the new pipeline. The original plan called for eleven shafts, but the general contractor for the project, Midwest Mole, Inc. based in Indiana, USA, proposed to eliminate three of the shafts. This partial redesign of the project resulted in a shorter project schedule and in substantial cost savings to be shared by the owner and contractor. The new drive lengths range from approximately 250 m to 610 m (816 ft to 2,014 ft), for a total of 2,875 m (9,430 ft). Both the original and modified plans are shown in Figure 1. The new plan calls for the removal of shafts four, eight, and ten, which results in longer drives through those areas. Boring will begin at the lower end of the pipeline from shaft eleven, and the machine will mine upward to the southern end near state route 32.

The seven tunnels, with their varying grades, result in a vertical change of 54 m (177 ft) over the course of the project.

2 Shaft 11 Shaft 10 Shaft 9 Shaft 8 Shaft 7 Shaft 6 Shaft 5 Shaft 4 Shaft 3 Shaft 2 Shaft 1 Figure 1. Left: original pipeline route. Right: modified route with shafts 4, 8, and 10 removed Geology In addition to the long tunnel drives, the geology of the area poses a challenge as well. The seven tunnels, with their varying grades, result in a vertical change of 54 m (177 ft) over the course of the project. As a result of the elevation change, the tunnels travel through different strata consisting of softer shale and limestone for the first 900 m (2950 ft), changing to harder, drier shale and limestone in the later tunnels. The ground conditions range from wet and sticky to dry, with rock quality designations (RQDs) ranging from about 20% to 70%. Figure 2 shows average RQDs at each of the shaft locations. There is a clearly visible jump of approximately 45% between shafts six and seven, where the transition from mixed ground to hard rock is expected to occur. Figure 2. Rock quality designation at shaft locations

3 MACHINE SELECTION The nature of the extensive gravity sewer made the machine selection challenging. To effectively excavate in the conditions, Midwest Mole needed a solution to mine in mixed ground as well as hard rock up to 165 MPa (24,000 psi) UCS. The original contract allowed for either microtunneling or two-pass tunneling, which allows for installation of a primary liner before placing the carrier pipe. Despite the highly changeable conditions, the contractor chose a single machine solution for the pipeline, a 1.8 m (72 in) diameter Double Shield Rockhead manufactured by The Robbins Company. Midwest Mole had a wealth of experience with similar Robbins machines, and felt the tunnels could be completed in a timely manner with the two-pass option. There are several factors that make the two-pass method a more attractive option despite the apparently greater complexity. First, the rockhead machine allows for cutter changes to be made in mid bore should the need arise. In a microtunneling machine of this size, cutters would only be able to be changed in the receiving shafts. Additionally, muck disposal is far simpler with the two-pass method. Using this method, the muck can easily be used as backfill around the manholes in the shafts and as fill on private property in the area. The wet, treated slurry produced in a microtunneling operation would be considerably more difficult to dispose of, particularly from this remote site. There are also additional costs that would be incurred using the microtunneling approach. In order to run the high capacity slurry treatment plant year round, a winterized enclosure would need to be constructed. The jacking quality pipe required for the microtunneling operation is also more expensive than the flush reline used in the two-pass method. The remoteness of the job site is also a factor, since the additional power and water required by the microtunneling slurry plant would need to be supplied by a generator and brought in by truck, respectively. Furthermore, the large cost savings associated with removing three shafts was made possible by the Robbins machine s ability to mine such long distances. This savings would not have been easily achieved with the microtunneling approach due to limitations of jacking lengths. Figure 3. Double Shield Rockhead used to excavate seven gravity sewers MACHINE FEATURES The 1.8 m (72 in) Double Shield Rockhead is designed and operates much like The Robbins Company s large Tunnel Boring Machines (TBMs). The operation sequence of the machine is based on a Double Shield design using a machine belt conveyor for spoils transfer through the machine. The TBM advances with the machine cutterhead thrust transferred to the cutting face by hydraulic thrust cylinders mounted inside the TBM. Upon completion of this stroke, large forward shield stabilizers extend and hold the cutterhead as the telescopic shield is retracted. If necessary the auxiliary thrust cylinders can be used to thrust against the tunnel liner for advancement. A schematic of this system is shown in Figure 4.

Articulating front shield Drive assembly Cutterhead Operator station Auxiliary thrust Belt conveyor Stabilizer pad Thrust cylinder Bearing housing assembly Gripper assembly Figure 4.

4 Articulating front shield Drive assembly Cutterhead Operator station Auxiliary thrust Belt conveyor Stabilizer pad Thrust cylinder Bearing housing assembly Gripper assembly Figure 4. Schematic of rockhead machine The TBM has an articulation system that allows it to be steered to a simple pipeline laser or a more advanced laser pipe jacking system with data logging print out. This laser system is installed in the pit above the concrete thrust block or in the rock roof of the tunnel on longer runs. The tunnel alignment is surveyed regularly to verify proper line and grade. Torque reaction from the cutterhead is countered by the gripper shield, roll correction cylinders, and torque keys inside the telescopic shield. A tail shield protects workers and facilitates construction of the 1.8 m (72 in) OD steel ring sets on 1.5 m (5 ft) centers. An operator s area in the rear shield holds all the required controls, auxiliary power pack, and machine lighting. Auxiliary power was installed for both electricity and hydraulics. This auxiliary power is used for the hydraulic ring expander and the portable welder. A three-way communication system is used to link the TBM operator, muck car operator, and site foreman. Provisions for Long Drives To rotate the cutterhead, the machine uses a variable-speed electric drive motor, gearbox, and torque protection device assembly. Power cables for this drive train run from a machine mounted electrical connection box to a surface mounted electrical disconnect cabinet installed in a 20 ft shipping container. A sine wave filter is used to filter the output of the VFD, eliminating harmful wave effects to the motors which would normally be caused by the long cable lengths. This feature enables the machine to mine up to 640 m (2,100 ft) at optimum productivity, allowing for the longer tunnels of the redesigned project. The machine s muck haulage system is also instrumental in making the long drives of this project possible. As the hard rock is excavated from the face, it is gravity fed through a muck opening onto a machine belt conveyor. The conveyor, when fully extended, reaches 30.5 m (100 ft) in total length, allowing for three muck cars to be filled in one train cycle. The three car train has the capacity for two pushes of excavated material, or 1.5 m (5 ft) of advancement, which equates to one ring set. This allows workers to build a ring set while the muck cars are being emptied, making efficient use of the relatively long train cycle time in the longer tunnels. The muck cars are moved in and out of the tunnel with a 96 V/5 ton locomotive. Cutterhead Solutions Because of the changing conditions over the course of the project, two different cutterhead solutions have been provided. For sections of the tunnel with low RQD, Robbins supplied a mixed ground cutterhead with 165 mm (6.5 in) single disc steel cutters and carbide cutter bits. The mixed ground cutterhead has carbide bits which are mounted 13 mm (0.5 in) back from the leading edge of the disc cutters. This allows for the disc cutters to do the job when the rock is solid and competent, and as the rock becomes fractured or mixed with soil the carbide bits begin to dig. With the carbide bits clearing the soft soil, the soil is prevented from clogging the cutterhead and locking down the cutters. This style of cutterhead, shown in Figure 5, has been very effective in multiple mixed ground conditions.

with a second cutterhead more suited to the conditions. For this, Robbins supplied a standard hard rock cutterhead, similar to the one shown in Figure 6, with 292 mm (11.

5 Figure 5. Mixed ground cutterhead provided for the double shield rockhead machine For the later tunnels with more competent rock where more thrust pressure is required, the mixed ground cutterhead is replaced with a second cutterhead more suited to the conditions. For this, Robbins supplied a standard hard rock cutterhead, similar to the one shown in Figure 6, with 292 mm (11.5 in) single disc steel cutters. The hard rock cutterhead allows for operation at thrust forces as high as 400,000 lbs. The cutterhead is supported by a heavy duty bearing housing assembly and attached to a heavy walled steel front casing assembly. This front casing assembly includes four hydraulic stabilizer cylinders required to hold the cutterhead for a consistent cutting pattern, known as kerf cutting. Figure 6. Hard rock cutterhead with 292 mm (11.5 in) single disc cutters JOBSITE OPERATION Excavation of the first tunnel began on May 19, 2010 from an 11 m (36 ft) deep shaft, and progress has been generally good. Recorded production rates have been as high as 21 m (70 ft) in one 12 hour shift, and are consistently in the range of 12 to 18 m (40 to 60 ft) per shift. The swift advance comes despite some unforeseen difficulties, including a section directly below the creek bed with significant groundwater and gripper slippage in the soft, wet ground during machine pushes. The high production rate can be attributed in part to the very systematic way in which the rib sets are installed, which does not hinder machine progress. The Robbins rockhead completed its first 474 m (1,555 ft) long drive in three months, holing through on August 18th into the receiving shaft. Even after this distance, Midwest Mole crews found almost no perceptible wear on the cutterhead (see Figure 7).

Figure 7. Left: initial machine launch in May 2010.

modifications. Changes included modifying the hydraulic system for increased gripper and roll correction cylinder pressure.

Launching the machine is a fairly simple operation, which is important because of the number of times it must be done over the course of the project.

6 Figure 7. Left: initial machine launch in May Right: cutterhead after 474 m (1,555 ft) The machine was launched from its receiving shaft to bore a second 575 m (1,886 ft) long tunnel on August 30, 2010 following some maintenance and modifications. Changes included modifying the hydraulic system for increased gripper and roll correction cylinder pressure. The increases allow the machine to grip and roll correct in the extremely soft, often wet rock. Launching the machine is a fairly simple operation, which is important because of the number of times it must be done over the course of the project. With the hydraulics toward the front of the machine and electrical components on the surface, the gripper and auxiliary thrust portions can easily be removed with minimal disruption of the system. This allows the machine to be shortened to allow adequate space in the launch shaft. The conveyor is also shortened at startup. Once the rockhead has been sufficiently buried, the rear sections are reattached and the conveyor extended. Figure 8. Launch of the machine on its second tunnel, August 2010 Operation of the machine has been smooth and well coordinated. To aid in construction of the primary liner, Midwest Mole designed and built a materials cart which attaches to the last muck car. It is used to haul the ring sets like those shown in Figure 9 to the back of the TBM, and it has a hydraulic push plate for easy unloading of the stacks at the rear of the tail shield. Workers can then assemble the rings in the safety of the tail shield as the machine bores.

excavation. Some open cut operations are also connecting existing, peripheral lines to the new sewer line. Midwest Mole recently utilized a 0.

7 Figure 9. Left: ring and board sets ready to load. Right: ring beams and lagging installed in the tunnel Work on the launch/receiving shafts is ongoing; five shafts are now complete using a combination of drill and blast techniques and manual excavation. Some open cut operations are also connecting existing, peripheral lines to the new sewer line. Midwest Mole recently utilized a 0.8 m (30 in) diameter Robbins SBU-A for a 46 m (150 ft) long crossing of the creek, which will connect a 0.5 m (18 in) diameter PVC sewer to the main line. The project s success to date can be attributed largely to close cooperation between Midwest Mole, Robbins field service, and the project owner. All seven of the tunnels and the eight manhole shafts are expected to be complete by May 2012.

2008 Underground Construction Technology International Conference & Exhibition, Cobb County Galleria Center, Atlanta, GA - January

Program: Title: Author: 2008 Underground Construction Technology International Conference & Exhibition, Cobb County Galleria Center, Atlanta, GA - January 29-31. Successful Technology for Utility Installations