The Chernigovskiy mine in Sibera operated a PR 776 (above) for 21 hours per day for two years with an average fuel consumption of 42 liters (11 gallons) per hour. (Photo: Liebherr)

Expert testimony and several case studies show that the low fuel-burn rate of the Liebherr PR 776 is fueling its growing popularity globally

By Jesse Morton, Technical Writer

Field results show that miners are adopting the Liebherr PR 776 dozer for its superior fuel efficiency. According to the supplier, in head-to-head trials, it repeatedly proves it can move more while burning less fuel. Operators like it because of features that make it easier and safer to operate.

For mines that are considering removing the operator from the cab, guidance was given in a new report funded by the National Institute for Occupational Safety and Health on the benefits and risks of remote-controlled and autonomous equipment. It states that dozer operators are safer and more comfortable working from an on-site control station. After looking at a collision at a Peabody mine between a semi-autonomous dozer and an excavator, it listed several steps that should be taken to prevent such collisions.

Liebherr Dozer Leads in Fuel Efficiency

A dozer expert at Liebherr said the PR 776 dozer is the most fuel-efficient dozer in its class.

“The combination of the hydrostatic transmission with the Liebherr D9512 engine, operating at constant rpm, means that our dozers have reduced fuel burn rates,” said Markus Wittwer, head of sales, PR 776, mining.

“In fact, the PR 776 dozer has the lowest fuel burn rate in the 70-metric ton (mt) (77-ton) class at equal production, with an average hourly fuel burn of less than 40 liters/hour (l/hr) (11 gallons/hr [g/hr]) across our entire global fleet,” he said. “Liebherr’s entire dozer portfolio uses intelligent engine technology to grant customers the lowest possible fuel-burn rates.”

The hydrostatic drive has fewer components than does the drive system of competitor models, and it gives operators greatly improved speed control. Compared to “other machines in the 70-mt class (77-ton), the main advantage of a hydrostatic transmission is the absence of gears, clutches, and brakes for maneuvering,” Wittwer said.

“This results in seamless operation, uninterrupted power flow, and infinitely variable speed control,” he said. “This transmission always delivers stepless track speed at full torque on each track side of the dozer.”

The dozer can be configured with remote control capabilities. “The PR 776 is designed to the highest safety standards, and we are investigating how the next iterations of our dozers could be implemented into an autonomous mine site environment,” Wittwer said. “We already offer remote operation capabilities for our PR 776 dozers in the form of our LiReCon system.” The system “allows operators to work from the safety of a cabin on site rather than in hazardous or hard-to-reach locations.”

The cab “offers a wide range of safety features, such as all-round visibility with integrated ROPS/FOPS protection, rear-view camera, working platforms, lighting for the access steps, optional powered access ladder and automatic parking brake,” he said.

Further, the dozer offers uncompromising safety for service personnel, Liebherr reported. The unit features a tilting cab, “which provides easy access to the hydrostatic transmission; a working platform for both operators and maintenance staff; and ground-level services.”

The cab design and platform means “maintenance and service points are readily accessible, and this enables maintenance and service work to be carried out rapidly and safely,” Wittwer said.

For simplified inventory management, the dozer is built entirely of Liebherr components. “We leverage the expertise and practical experience of the entire Liebherr Group and its 13 product segments by using Liebherr-made componentry in our dozers,” he said. “Our components undergo field tests under rigorous conditions to ensure maximum machine availability.”

The dozer can be configured to run on hydrotreated vegetable oil, “which can reduce GHG emissions by up to 90%,” Liebherr said.

The PR 776 launched in 2016 and has been deployed to roughly 115 countries, including Sweden, Iceland, Spain, Chile, China, Mongolia, and Uzbekistan. The dozer is at mine sites on every continent.

“The global PR 776 population has contributed to more than 3 million operating hours with the dozers delivered back in 2016 already reaching 45,000 operating hours,” Wittwer said.

Several Liebherr case studies show how, since then, the dozers deliver remarkable availability and fuel efficiency metrics.

For example, in 2016, Siberia’s SDS-Coal Holding Co., the third largest coal producer in Russia, bought a PR 776 for managing the dump area, road construction and site cleanup at the Chernigovskiy coal open pit. The unit had an 18.5-m3 (24-yd3) semi-U-blade and a single-shank ripper.

“After 24 months of operation, the dozer had more than 15,080 operating hours on the hour meter or an average operation of 20.7 operation hours every day since the dozer has commenced operation,” Liebherr reported. “The average fuel consumption over this period has been recorded with 42 l/hr (11 g/hr),” the supplier said. “Dozer performance, low fuel consumption, increased traction, comfortable handling and smooth travelling, efficient lighting quality for continuous operation of the machinery during nighttime, as well as lowest noise and vibration levels in the cabin were highly appreciated by operators.”

In 2017, Peabody’s Wilpinjong mine pitted a new PR 776 with a 22-m3 (29-yd3) U-blade against a competitor unit for three months. “Results showed that the PR 776 is a strong contender with superior operator visibility, excellent maneuverability, and better fuel consumption rate, providing the user with a comprehensive product to meet production targets efficiently,” Liebherr said.

South Africa’s Vanggatfontein Colliery, mined by the Liviero Group, deployed a PR 776 with a 22-m3 (29-yd3) U-blade. “The Liebherr V12 diesel engine delivers 440 kW (590 hp) in forward travel mode, and 565 kW (758 hp) in reverse travel mode to keep cycle times as short as possible,” Liebherr said. “The average fuel consumption of the PR 776 lies roughly at 41 l/hr (11 g/hr), which is considered very efficient by Liviero compared to competitor machines on site.”

Rix’s Creek in New South Wales, Australia, pitted a PR 776 against a competitor machine at typical mine site duties. “Local measurements confirm fuel consumption across the entire field trial was only 47 l/hr (12 g/hr), over 20% less than its competitor, with comparable performance,” Liebherr reported. “The lower fuel consumption indicated that a reduced cost per metric ton was achievable.”

Griffin Coal Mining Co.’s Ewington mine in Western Australia trialed a PR 776 from August 2019 to July 2020 at “all standard dozer applications,” Liebherr reported. “The machine availability KPI of 93% was exceeded in 11 of the 12 months, with 96.1% average availability over the trial period,” the supplier said. It had a fuel burn efficiency of 49.7 l/h (13 g/hr) compared to the expectation of 56 l/h (15 g/hr). “This 12-month trial with conditional purchase resulted in the customer purchasing the dozer after achieving, and exceeding, the agreed KPIs.”

Results like that have driven the widespread market acceptance of the dozer, Wittwer said. “It’s our winning combination of a dedicated factory team and the state-of-the-art tools and technology within our facility that makes it possible for us to achieve a 330% increase in the number of our dozers sold around the world since 2010,” he said. “Growing customer follow-up orders and higher interest in fleets show not only a trust in the Liebherr brand and its great and motivated employees, but also to the features and competitiveness of all the PR 776’s features.”

For example, “our dozer fleet in Indonesia has increased over the past 18 months, and we now have eight operating in the region with two more on the way,” Liebherr said last year. At that point, six more were calendared for delivery “to a large copper and gold mine.”

Separately, the PR 776 has been deployed to an underground mine in South America. “The machine is being used to quickly move material brought to the surface by the mine’s conveyor belt,” Liebherr said. “This niche application of the dozer highlights the adaptability of our machines.”

Liebherr reported that in 2023 a manganese mine in South Africa deployed four PR 776s in part because of the cost- and fuel-savings offered. “There was also a significant need for the 70-mt (77-ton) dozers and the PR 776 was able to meet the customer’s requirements,” Liebherr said. “This was due to the dozer’s hydrostatic transmission,” it said. “The fuel-saving nature of Liebherr machines is so important in reducing overall operating costs.”

Since then, the dozers have achieved “all of their key performance indicators and the customer has been extremely happy with the machine’s performance,” Liebherr said.

Customer feedback is a key driver of the research and development programs at Liebherr. “We are continually implementing operator feedback into the designs of our products so that they are constantly improving,” Wittwer said. “Therefore, we can rest assured knowing that our customers are receiving high-quality products that will not let them down on site.”

NIOSH Reports Benefits, Risks of Remote Control

A 2023 report* funded by NIOSH said the benefits of remotely operating semi-autonomous dozers are significant while the risks are real.

“Removing operators from surface drill rigs and dozers has both safety and health benefits,” said the report, authored by professors at the University of Pittsburgh and the University of Queensland. “At the same time, automation provides increased productivity through increased consistency of equipment operation and increased equipment utilization rates.”

The report covered remote control of multiple types of mining machines, including drills, trucks and longwalls. The benefits specific to remote control of semi-autonomous dozers include “eliminating exposure to whole body vibration and other musculoskeletal risk factors, access and egress, and site transport risks,” NIOSH reported. “Utilization has been increased 25% and productivity is enhanced by software that automates decision-making.” No case study illustrating those benefits was covered.

PR 776

The PR 776 (above) has intelligent engine technology for a lower fuel-burn rate and a hydrostatic drive that gives operators greatly improved speed control. (Photo: Liebherr)

Across the types of machines covered in the report, the drawbacks to implementing remote control semi-autonomous mining machines include a temporary reduction in output during commissioning, and the need for new procedures to preempt new failure modes. Those failure modes, which NIOSH said require further examination, include software shortcomings, communication technology disruption, cyber security breach, input errors, unpredictable complexity, sensor limitations and situational awareness shortfalls, over-trust, and unauthorized or anomalous access to autonomous zones.

In itemizing the benefits of remote control, the report focused primarily on machines other than dozers. However, when giving examples of failures, the report described primarily incidents involving trucks, drills and dozers.

The coverage of a dozer incident detailed a collision between a semi-automated dozer and an excavator at Peabody Energy’s Wilpinjong coal mine on May 27, 2019. The crash was detailed afterwards by a government oversight body and illustrated by a simulation.

At the mine, dozers were used for bulk push operations. An excavator first cleaned the rear bench, then the dozer pushed material that is used to “create a windrow across the back of the dozer push area,” the NIOSH report said.

A procedural control was in place to keep manually operated machines out of the dozer area. “At the time of the incident, no collision avoidance systems were operational,” the NIOSH report said.

The semi-autonomous dozers were remotely controlled by a supervised trainee in an operator station within view of the work area.

“In semi-autonomous mode, the operator allocates a dozer to a slot and conducts the first push of the mission via teleoperation mode,” NIOSH reported. When the operator allocates the dozer, video footage from four cameras on the dozer is fed to and displayed by four screens in the station.

After the operator controls the first push, the “dozer then continues to operate in the same slot autonomously until either the mission is completed or until 12 passes have been conducted and the operator must reconnect with the dozer.” The screens switch to the next dozer the operator allocates.

According to the oversight body, at 1:30 p.m., a manned excavator entered the dozer zone from the north, headed south. “As the edge bund [berm] was constructed using material from the highwall face, some loose material was hanging up across the face,” NIOSH reported. “The operator used the excavator to scale the loose material from the face, as he travelled towards the southern section of the” dozer zone.

The area had previously been scaled and cleaned and a windrow built. The excavator was between the highwall face and the windrow. “As loose material was scaled down, it was added to the windrow,” NIOSH reported. “The task progressed towards the south until the excavator travelled to the end of the windrow and was positioned adjacent to the rear of slot 16” at roughly 1:40 p.m.

A dozer was already semi-autonomously working that slot. The operator had allocated and was managing a dozer in an adjacent slot. The dozer in slot 16 hit the rear of the excavator.

“When initial contact was made, the excavator was pushed about 1.5 meters sideways, into the base of the highwall,” NIOSH reported. “The excavator then stopped sliding and dozer DZ2003 continued to tram in reverse, colliding with the excavator multiple times trying to reach its programmed GPS coordinates.”

The dozer lost traction, and after a few seconds idled. “From the initial contact to dozer DZ2003 stopping was about 14 seconds,” NIOSH reported. “The excavator had some damage; however, the operator was uninjured.”

To attempt to avoid such incidents, thorough risk analyses must be executed during system design. “The analyses undertaken should include task-based risk assessments involving a range of operators and others effected by the system, and systems-based techniques; in addition to conventional hazard based risk analysis techniques,” NIOSH reported. “As far as possible, the risks should be reduced during system design,” the report said. “Residual risks need to be understood by mine management to allow effective controls to be devised, implemented, and monitored.”

*Haight, Joel; Burgess-Limerick, Robin: Automation Experience with a Global Perspective – An Assessment of the Automation Impact on Worker Safety and Health (2023) NIOSH.