effects of increased mechanization on drill and blast & natm tunneling production rates and safety

SME Annual Meeting Feb. 28-Mar. 03, 2010, Phoenix, AZ

1 Copyright 2010 by SME

Preprint 10-108

EFFECTS OF INCREASED MECHANIZATION ON DRILL AND BLAST & NATM TUNNELING PRODUCTION RATES AND SAFETY (1994 2009)

B. Briggs, Atkinson Construction, Golden, CO.

ABSTRACT

Over the past 15 years, the tunneling industry has pushed towards a higher degree of mechanization in nearly every phase of construction. The overall objective of the mechanization was to increase production and the level of safety in tunnel operations. However, the overall complexity of some systems have been a hindrance to a seamless transition to the newer technologies as increased maintenance requirements and re-training of skilled workers has altered the benefit curve for some innovations.

Atkinson Construction has been tracking production and safety data for numerous drill and blast and NATM projects completed during this time frame. The purpose of this paper will be to analyze the relationship over the referenced time period between the increase in mechanization with overall production rates and job safety.

The analytical data will be coupled with narrative accounts of the projects to highlight the changes in technology along with the successes and challenges in implementing the new developments into a production tunneling environment.

OVERVIEW

The production information contained in this paper will revolve around 5 primary projects, The Allegheny Tunnel Project, The P- 1 Pressure Tunnel, The Mission Valley NATM tunnel, Dulles East and West APM NATM Tunnels, and a drill and blast tunnel in Utah for a private customer. This paper will summarize each projects production rates for the various tunneling methods. Secondarily, it will reduce the data to similar unit operations to provide comparable data points between projects.

The safety benefits realized by the increase in mechanization will be analyzed on qualitative basis with a heavy emphasis placed upon first hand narrative accounts of the individual projects.

ALLEGHENY TUNNEL PROJECT (1994-1995) Project Overview

The Allegheny Tunnel is located near Altoona, Pa and owned by The Consolidated Rail Corporation (CONRAIL).

The project consisted of the fast-track enlargement of two single track rail tunnels totaling 4,300 feet in length to double-track structures, including shotcrete and concrete lining. Utilization of both drill and blast and mechanical methods were utilized to enlarge tunnels from 22 feet in diameter to 36 feet.

The tunnel was driven utilizing sequential mining techniques through shales, sandstones, limestones, silt stones, and coal beds. Extensive consolidation grouting was performed to backfill unforeseen caverns and voids from coal mining activities adjacent to the tunnel.

The primary excavation method was drill and blast mining of the existing liner and intact ground. Mechanical excavation by hydraulic hammer was used as a secondary means of excavation for short segments of the tunnel run.

The ground supports consisted of steel sets, fiber reinforced shotcrete, resin grouted rock bolts, wire mesh and consolidation grouting.

Equipment Selection As the project called for substantial amounts of shotcrete, the

selection of shotcrete application and on-site batching equipment was critical to the success of the project. Atkinson Construction employed the use of two robotic shotcrete arms manufactured by Shotcrete Technologies for the project. The arms were mounted on flatbed truck carriers with on-board shotcrete and accelerator pumps. The shotcrete was produced on-site with a fully winterized plant capable of producing 40 CY/Hour. Delivery from the plant to the working faces was provided by modified 8CY transit mixers.

The excavation suite of equipment included Tamrock H207B Maximatic drill jumbos, various 5 and 3 CY LHDs, working in conjunction with 26 Ton mine trucks.

Figure 1. Typical tunnel heading, Allegheny Tunnel Project, Altoona, PA.

Production Summary As stated above, shotcrete productivity was a critical component

to the success of the project. The Allegheny Tunnel was supported with over 15,000 CY of fiber reinforced shotcrete; this equated to approximately 4.3 cubic yards (CY) / Linear Feet (LF) of tunnel. The average production rate achieved on the project was 0.86 Manhour(MHR)/ CY with peak performance reaching upwards of 0.5 MHR/CY. This equated to a typical placement rate of nearly 7 CY/HR with peak placement rates nearing an average of 12CY/HR.

The excavation of the existing brick liner and the intact rock was primarily performed using drill and blast techniques. The enlarged profile required approximately 15 bank cubic yards (BCY)/LF of excavation to reach the neat line excavation limit. Atkinson Construction realized an excavation rate of 0.495 MHR/BCY for the 61,000 BCY of excavation performed. This rate was inclusive of drilling, blasting, smoke time and inspection, scaling and mucking.

Resin grouted rock bolts and steel sets were also used as additional ground support measures on the project. The bolts were installed at a rate of 0.096 MHR/LF of bolt with the steel sets installed at a rate of 0.012 MHR/LB of steel.



Safety Narrative The safety program on the project was tailored to maximize the

benefits of the mechanized gear. This project represented one the earliest forays into the use of robotic shotcrete arms for Atkinson Construction. The robotic placing system allowed for the nozzleman to be a safe distance away from the placement area as well as limiting operator fatigue. The use of exclusively wet shotcrete was also a vast improvement over the dry shotcrete systems as it minimized the dust hazard in the tunnel.

The excavation suite of equipment was also selected to minimize exposure to unsupported ground. This proved to be extremely beneficial in the poor ground condition areas and allowed the work to be completed with limited exposure to the hazards.

P-1 PRESSURE TUNNEL (1996 -1998) Project Overview

The P-1 Pressure tunnel was comprised of 2,500ft. of drill and blast tunnel supported primarily by steel sets and lagging. A 16ft. diameter concrete encased steel pipe was placed as the final configuration inside of the 20ft x 20 ft. tunnel. This tunnel connects the P-1 Pumping Plant with the Inlet / Outlet works for the reservoir now called Diamond Valley Lake near Winchester CA. This tunnel is the primary structure used for moving water into or out of the water storage reservoir and is designed to handle flows of 2,100 cubic feet per second. The geology consisted of primarily granite diorite.

Figure 2. P-1 Pressure Tunnel, Winchester CA.

As work was being performed on the east side of the tunnel, the P-1 tunnel was driven primarily from the West Portal. The entire length of the tunnel was excavated using drill and blast techniques and support by timber lagged steel sets on 2ft, 4ft, or 6ft centers depending on the ground conditions.

Equipment Selection The primary focus on equipment selection for this project was

based from a cost benefit study performed prior to the start of the project. The study concluded that the most cost effective excavation scenario was to construct passing bays for multiple LHDs instead of a using a muck bay system with 40 ft bays installed on 500 ft centers.

Consequently, selection of the proper LHDs was quite important. Atkinson procured a Wagner ST8B 8CY LHD as the primary mucker with a ST5B 5 CY LHD and two 4CY JCI 400m LHDs to perform the work. The additional units were added to the fleet to insure that equipment downtime would not be a major issue on the project especially with the longer than normal tramming to be performed. Removable man safe work platforms were fabricated to allow the LHDs to be used as a work platform for utility installation and other work activities at heights in the tunnel.

The drilling and loading operations were performed primarily by a Tamrock Minimatic HS205D drill jumbo with two drill booms and center manbasket boom.

Production Summary The production at the P-1 tunnel was extremely consistent and

overall very good. On a 24 hr/ day 3 shift schedule the tunnel averaged 18ft/day of tunnel advance from a single heading. This equated to an excavation production rate of 6.15 MHR / LF or 0.465 MHR /BCY. This rate includes the drill, load, blast and mucking cycles.

The steel sets were installed at a production rate of 0.011 MHR /LB of steel and the timbering was installed at a rate of 5.8 MHR/Set.

Safety Narrative Overall the safety performance on this project was excellent.

However, this was much more a function of the repetitive nature of most of the tasks and a strong field supervision staff versus the benefits of mechanized equipment. The steel sets were erected manually with minor assistance from powered equipment to help carry the load. The lagging and blocking were also set manually.

MISSION VALLEY EAST LIGHT RAIL TRANSIT EXTENSION NATM TUNNEL (2001-2003)

Project Overview A portion of the Mission Valley Light Rail Transit Extension

contract contained 1,085ft. of underground tunneling via the New Austrian Tunneling Method (NATM) at the San Diego State University campus. The excavated 37ft. wide x 29ft. high single-tube double track NATM design replaced an original longer tunnel alignment based on twin tube, segmentally lined running tunnels. Excavation was via a Liebherr mechanical excavator through a conglomerate geology comprised of hard round cobbles and occasional boulders held in a sandy clay matrix. Sixteen meter long grouted canopy tubes, lattice girders and shotcrete were used as primary tunnel support. Dust and noise control was also a major requirement as the University was within close proximity.

Figure 3. Mission Valley East Light Rail Transit Extension NATM Tunnel, San Diego, CA.

Equipment Selection As the cobbles and boulders were hard materials, a Liebherr 902

tunnel excavator with digging bucket and quick connect hydraulic hammer was the primary means of excavation for the project. The spoils were removed from the face and trammed to the dump area by 3.5 CY LHDs. The top heading excavation averaged over 8CY of shotcrete per LF of tunnel. As a result, shotcrete equipment selection was again critical on this project.

Atkinson placed an RPM shotcrete plant on the job site capable of producing over 30CY per hour. Delivery of the shotcrete to the excavation was made by modified 8CY Diesel Transit Mixers. The



shotcrete was placed using a Shotcrete Technology robotic boom and nozzle carried on a flat bad truck with an onboard accelerator pump and accelerator storage and a shotcrete pump attached to the rear of the carrier.

Production Summary In general terms the top heading excavation proceeded at

approximately 1 lattice girder placed per 8 hour shift. This equated to heading excavation production rate of 0.316 MHR/BCY and a shotcrete placement rate of 1.5 Mhr/CY or approximately 5.5 CY / hr.

Safety Narrative The selection of highly mechanized equipment had an extremely

positive impact on this project. The combination of tunnel excavators and robotic shotcrete arms allowed for excavation and initial support to be installed without exposing any miners to open ground. The installation of the lattice girders was aided by telescopic boom forklifts with manbasket attachments. This allowed for the girders to be lifted, placed and aligned mechanically with only minor adjustments and hardware installation performed manually.

EAST & WEST APM TUNNEL (NATM TUNNELS) DULLES AIRPORT (2004-2005)

Project Overview The West Domestic Automated Mover (APM) Tunnel was

constructed on the west side Dulles Airport (near Washington DC) for the purpose of providing rapid passenger transportation from the Main Terminal building to the West APM station located on the west side of Concourse B. A portion of the total work package included the construction of approximately 1,861 linear feet of approximately 25 ft. diameter tunnel by NATM methods.

The East Domestic Automated People Mover (APM) Tunnel was constructed on the east side of the Washington Dulles International Airport for the purpose of providing rapid passenger transportation from the Main Terminal building to the proposed APM stations located on the east of the existing Concourse B, and the future Tiers 2 and 3. A portion of the total work package included the construction of 825 linerar feet of approximately 25ft. diameter tunnel by NATM methods.

The method of excavation for the NATM tunnels was via an AM-75 Roadheader manufactured by Voest-Alpine. Geology was a mixture of siltstone, mudstone and sandstone. The support of excavation included lattice girders, shotcrete, spiling and canopy tubes. Dust control was also critical as to not impede Traffic Controllers view of the airfield. All water had to be treated to potable standards before its release into local waterways.

Figure 4. Dulles NATM Tunnel, Roadheader Excavation.

Equipment Selection As stated above, an AM-75 Roadheader was employed as the

primary means of excavation with an AM-50 as the back-up / trimming

machine. The roadheaders transferred the muck using the onboard chain conveyors to LHD buckets positioned to receive the loads. The geology at the Dulles airport was ideal for roadheader excavation, as the picks easily excavated the material and the stand up time of the ground was more than sufficient to allow for initial flash coat of shotcrete prior to spalling.

As a NATM project, shotcrete delivery needs dictated an on-site batch plant be utilized. The project used a Terex mobile plant as the plant to service both projects. The shotcrete was delivered from the plants to shotcrete pumps located on the surface. The pumps were connected to slicklines that descended the open cut shafts and brought the material to the shotcrete robots. The robots for the project were a mixed assortment of Shotcrete Technology and Meyco Arms on various carriers. All the robots also used peristaltic accelerator pumps with digital controls to provide maximum control of the accelerator use to ensure a high quality final product.

Production Summary The layout of the project split the footage between five separate

access shafts and six individual NATM tunnel drives. Furthermore, the top heading and benches were excavated as separate operations as well. As a result, the roadheaders were routinely trammed between headings to maximize overall job production at the cost of lower individual heading productions.

The typical top heading advance rate on the project was 3.2 LF/ 8 hr shift. This rate breaks down to a 4CY/ HR shotcrete production rate, and an average excavation rate (roadhead and muck) of 2.8 LF/HR. The resultant manhour based production rate for the project were 1.75 MHR/CY for shotcreting and 0.17 MHR/BCY for excavating.

Figure 5. Dulles NATM Tunnel, hole through.

Safety Narrative The safety program at the Dulles NATM tunnels benefited from

the past experiences gained at the Mission Valley Tunnels. The ability to mechanize much of the traditional heavy labor required in the tunnel greatly lessened the miners exposures to hazards and falling ground. As a result, the combination of experience and mechanization helped create a safe work environment and minimized the contractors exposure to job hazards.

DRILL AND BLAST TUNNEL IN UTAH ( PRIVATE OWNER 2006 TO 2008)

Project Overview This project consisted of 15 ft. x15 ft. modified horseshoe tunnel

at a length of 7992 LF. The project also included the construction of multiple drill stations, sump stations, muck bays, and facilities.

The project was constructed entirely in hard rock using drill and blast techniques. The geology consisted primarily of monzonites and quartz monzonite porphyry with intrusive dikes of varying composition.



Figure 6. Utah Drill and Blast Tunnel.

EQUIPMENT SELECTION This project utilized a highly mechanized fleet for all aspects of

the tunneling operation. For drilling Cannon DPI-2-HE Jumbos were purchased new and fabricated for the project along with Cannon DPI-HD-RB3-8 bolting machines.

Atkinson employed a 7 CY MTI LT-950 along with JCI 700ms as the LHDs for the project. Muck Bays were placed on 500 LF centers for temporary muck storage then loaded out of the critical path into 16 ton MTI DT-1604 underground rear dump trucks.

For shotcreting , Atkinson employed a self contained Putzmiester shotcrete Robot as well as a Shotcrete Technologies robotic arm placed on a Kubota Tractor carrier. The shotcrete was batched on-site using a Mixer Systems Inc. Model 54 Praschak Paddle Mixer batch plant.

Figure 7. Cannon DPI-2-HE Drill Jumbo.

Production Summary Shotcrete application was a major component of the production

cycle on the project. The typical ground support installed was approximately 1.2 CY/ LF of tunnel. This represented approximately double the anticipated quantity for the project. Consequently, the batching and delivery systems for the project were somewhat undersized. The result was a lower than anticipated shotcrete application rate of approximately 3 CY/HR which equated to 1.67 MHR/CY.

The use of the Cannon Bolters for the installation of 8 ft long #7 resin grouted rock bolts resulted in an average production rate of 4.45 bolts/ hr which equates to 0.17 MHR/LF.

The excavation rate for the project, (Drill, Load, Blast, Scale, & Muck) averaged 1.72 hr/LF of tunnel or 0.467 MHR/ BCY. Safety Narrative

The use of highly mechanized equipment fleet was designed to eliminate the potential hazards associated with having miners working under unsupported ground. This goal was achieved on the project and consequently greatly reduced Atkinsons exposure to catastrophic injuries. The increased risk of injury occurring to miners working in close proximity to automated heavy equipment was greatly mitigated through the proactive use of a comprehensive Job Hazard Analysis and Equipment Risk Assessment program. Overall, this project represented a significant success in regards to safety practices as well as safety performance.

COMBINED PERFORMANCE ANALYSIS

Production Analysis Overview The original objective of this document was to explore the

Grumpy Old Man principle, or as we call it at Atkinson, the Pete Hancock principle. This principle basically suggests that mining production has significantly slowed as more technological advances have been introduced into the production cycle.

The case studies above provide a strong basis to suggest that the principle has actual merit and should be analyzed on a unit operation basis.

Shotcrete Production As the table shows, shotcrete production has slowed considerably

over the past 15 years. Examining the equipment used for each project helps to justify the pattern shown. The robots used for the Allegheny Tunnel were extremely basic units with limited moving parts and mounted on very robust domestic carriers. The accelerator was delivered to the nozzle using simple stainless steel barrel pumps. The overall result was a highly productive system with very little downtime.

Table 1. Shotcrete Production Rates Project MHR /CY CY / HR Year

Allegheny 0.86 7 1995 Mission V 1.5 5.5 2002

Dulles 1.75 4 2005 Utah 1.67 3 2007

The later projects all employed more sophisticated robots, peristaltic accelerator pumps with digital controls, and in some cases integrated pumps attached to the carriers. The added controls in the shotcrete mitigate overall costs by placing adequate controls on the metering of accelerator and consequently reducing rebound. The downside is realized in increased stoppages of production due to minor problems in any of the integrated systems.

The other factor to be considered is the individual characteristics of each project. The Allegheny Tunnel represented a nearly ideal shotcrete application. The tunnels were easily accessible by 8 CY transit mixers and large quantities were applied on each setup resulting in high production rates. The later projects all required less efficient shotcrete delivery systems due to project logistics. Secondly, the project designs impacted the production as well. Mission Valley, Dulles and Utah all had requirements for sealing shotcrete layers, this negatively impacted the production rates as more set ups and teardowns were required to achieve the same quantities.

Therefore, it can be concluded that the production rates for shotcrete have indeed been negatively impacted over time with several mitigating circumstances.



Figure 8. Robotic Shotcrete Placement, Dulles NATM Tunnels.

Rock Bolting Production Production rock bolting was a critical path activity on only two of

the case studies analyzed. Both projects employed similar diameter bars of similar length with resin grout. The vast difference in rates can be attributed almost entirely to the equipment used for installation.

Table 2. Rock Bolting Production Rates. Project MHR/LF Year

Allegheny 0.096 1995 Utah 0.17 2007

At the Allegheny Tunnel, the bolting was performed by the Tamrock Drill Jumbo working in conjunction with a JLG type manbasket for the bolts at height. The changes between the drill steel and bolt adapter were done manually as well as manual insertion of the resin in the hole.

At the Utah project, the bolting was performed using a Canon bolter. The entire operation was automated. From a single set-up the machine was designed to drill the hole, insert the resin with a pneumatic shooter, take a bolt off the carousel , attach it to the bolt adapter, insert the bolt through the resin and spin the bolt to mix the resin.

Figure 9. Bolt Installation, Utah Project. As with the shotcrete, the simpler set-up achieved an apparent

higher production rate. However it should be stated that the Canon bolter was used in a less than ideal situation. The geological structures on the project resulted in quite blocky ground leaving an irregular surface on the modified horeshoe arch. Consequently, the

geometry of the situation did not allow for the stinger on the bolter to typically be flush with the excavation profile. This resulted in manual resin placement in many situations followed by a realignment of the boom to install the bolt.

Nevertheless, it can also be concluded that that the production rates for the installation of resin bolts has also been negatively impacted over time.

EXCAVATION PRODUCTION ANALYSIS

As the table indicates, the excavation production rate as defined by this paper is dependent primarily on excavation type, not by date of the project. Table 3. Combined Excavation Production Rates

Project MHR/BCY Year Type Allegheny 0.495 1995 Drill/Blast

P-1 0.465 1998 Drill/Blast Mission V 0.316 2002 Mech.

Dulles 0.170 2005 Roadheader Utah 0.467 2007 Drill/Blast

The three drill and blast excavations analyzed all achieved very similar production rates for the drill, blast and muck cycles when leveled by manhours and excavation quantity. The conclusion can be made that the increased mechanization in the drill jumbos, (anti-jam technology, computer assisted drilling, auto return, etc.) have not resulted in a significant production gain over the past 15 years.

The two mechanical excavations at Mission Valley and Dulles provide an interesting contrast to the drill and blast rates and highlight the production gains that can be achieved in suitable materials.

COMBINED SAFETY ANALYSIS

Although the analysis over time bears out the Hancock principle that production has slowed, the increase in miner safety is more than an ample trade off. The development of the modern gear is pulling the miners away from the unsupported excavation face and successfully limiting the more dangerous hazards encountered during the typical excavation cycle.

Supplementing the technological advances in the equipment, systematic cultural changes in the Atkinson safety program have also increased the overall job safety on all projects. The implementation of proactive hazard communication programs, increases in safety training, and active participation of both labor and management in the program, coupled with equipment safety advances have enabled Atkinson to successfully limit many hazards on the job sites.

CONCLUSION

The simple conclusion is that mechanization has had a negative impact on production rates and positive impact on safety. However, not only would that be admitting that Pete was correct, but it ignores many of the mitigating factors in regards to the production rates. The increasing complexity in project designs, increased scopes of quality control testing, increased instrumentation, and variations in the quality of regional workforces all should be considered when comparing rates. As a result perhaps a better conclusion is that the mechanization has had substantial impact on all facets of the tunneling industry and will continue to do so in coming years.

ABSTRACTOVERVIEWALLEGHENY TUNNEL PROJECT (1994-1995)Project OverviewEquipment SelectionProduction SummarySafety Narrative

P-1 PRESSURE TUNNEL (1996 -1998)Project OverviewEquipment SelectionProduction SummarySafety Narrative

MISSION VALLEY EAST LIGHT RAIL TRANSIT EXTENSION NATM TUNNEL (2001-2003)Project OverviewEquipment SelectionProduction SummarySafety Narrative

EAST & WEST APM TUNNEL (NATM TUNNELS) DULLES AIRPORT (2004-2005)Project OverviewEquipment SelectionProduction SummarySafety Narrative

DRILL AND BLAST TUNNEL IN UTAH ( PRIVATE OWNER 2006 TO 2008)Project Overview

EQUIPMENT SELECTIONProduction SummarySafety Narrative

COMBINED PERFORMANCE ANALYSISProduction Analysis OverviewShotcrete ProductionRock Bolting Production

EXCAVATION PRODUCTION ANALYSIS COMBINED SAFETY ANALYSISCONCLUSION

effects of increased mechanization on drill and blast & natm tunneling production rates and safety

Documents