August 2003
Producing aggregate in underground mines can be the key to gaining the ability to access reserves in markets.
By Mary McCaig
In 2002, when Bluff City Materials, a sand and gravel company with operations in Bartlett and Elgin, Ill., decided to look at mining limestone underground in Bartlett, the company did so for several reasons. “For one thing, limestone exists underneath the sand and gravel operation in Bartlett, and also underneath a nearby fen — or rare wetland area — in the community,” says Rob Vogel, president of Vulcan Materials Co.’s Midwest Division. Vulcan will be working with Bluff City Materials as the mining company responsible for the underground part of the operation, with plans to tunnel approximately 300 to 600 ft. beneath the surface to mine the limestone located there.
“The upper level of limestone is critical to supporting the fen, but by going underground, we will not impact the environment. A local treasure will remain intact,” says Vogel. “In addition, going underground to mine the limestone will lessen the impact on the community. We get the raw aggregate material we need, while the operation is largely invisible to the community members.”
Gaining community approval
A small, but growing number of crushed stone producers, who are facing increasing criticism from neighbors with concerns about environmental impact, noise, and dust, are choosing to go underground to mine stone.
According to Valentin V. Tepordei, minerals information commodity specialist for the U.S. Geological Survey (USGS), there were 92 underground crushed stone operations in the United States, producing 29.8 million short tons of material in 1980. In 1991, 88 underground quarries produced 51 million short tons of material in the United States. In 2001, 78 underground mines in the United States produced 55.1 million short tons. Out of a total of 3,386 active quarries, and 1.76 billion short tons of crushed stone produced in the United States in 2001, aggregate from underground mines came to about 2.3 percent of the nation’s total. “It actually looks as if the numbers are declining, but I would tend to rely more on the recent figures and tons produced as far as defining true numbers of underground mines in the U.S., versus those of 20 years ago,” Tepordei says.
True underground mining, where a producer tunnels beneath the surface to mine stone, seems to be a small, but gradually growing trend, he continues. “It’s not a large portion of the crushed stone market in the United States,” Tepordei says,“and it’s not growing at any great rate, but to some extent, (mining aggregate underground) is a growing trend.”
The USGS noted this trend more than five years ago in its Crushed Stone Statistical Compendium, dated Nov. 4, 1997, which states, “Underground operations are becoming more common, especially for limestone mining in the central and eastern parts of the United States, as the advantages of such operations are increasingly recognized by the producers. By operating underground, a variety of problems usually connected with surface mining, such as environmental impacts and community acceptance, are significantly reduced.”
“In spite of apparent advantages to underground mining, surface mining is much easier, and more economical than going underground,” says Tepordei. “When you go underground, it becomes a true mining operation. There can be differences in permitting, your workforce must be more specialized — it can become a much more costly operation.”
Economic aspects
So concern for the environment and good public relations notwithstanding, why would a producer choose to go underground?
Often, when a company tunnels beneath the surface for stone, the decision is driven by economics, according to Stan Bass, Vulcan’s vice president, East Tennessee and Kentucky, Mid South Division. Vulcan operates three underground mines in its Mid South division, one in Tennessee and two in Kentucky, in and near Lexington. “If the overburden is greater than 1:1, the distance is prohibitive in regards to reaching the rock,” Bass says. “If you have to remove one unit of overburden to recover one unit of reserve, it’s no longer economical to produce the material as a surface operation.”
Bass says in Tennessee and Kentucky, where Vulcan’s underground mines are located, the permitting process is not much different for an underground mine than it is for a surface operation. “Permits seem to be more state-specific, and it wasn’t a big issue in this area. There are a few more regulations for safety and mine planning. And we have a few more people who are specially trained in our underground operations — mostly relative to the actual drilling and blasting and roofbolting and scaling of the pillars and roof,” he says.
Additionally, advantages to underground aggregate mining can include year-round mining options for operations in colder climates because temperatures underground remain constant. And problems with noise, vibrations, and fugitive dust can also be reduced when the stone is produced underground.
From Vulcan’s standpoint, because it is easier to access rock and it is less costly, an open-pit surface mine is the preferred method of aggregate mining, says Bass. “But underground mining can allow a company to gain access to reserves in areas where open-pit mining is economically prohibitive, or areas that are highly populated — such as the Bartlett operation.”
Bass is familiar with the Bartlett, Ill., endeavor because Vulcan and Bluff City Materials have made a concerted effort to gain community approval of the project — going so far as to fly town officials to Lexington to view operations at the two Vulcan underground mines located there. “The two operations are located near the thoroughbred horse farms, in areas highly sensitive for environmental habitat. The mining operations sit very nicely in those areas. We do our best to minimize our impact on neighbors,” Bass says. This is especially important because in an underground operation, blasting occurs daily.
“We drill and blast every day in our underground mines,” Bass explains. “We make smaller holes, using smaller shots, blasting more often. Above ground, you can’t hear it, and you can barely feel the vibrations.”
According to Vogel, under the agreement with Bluff City Materials, Bluff City owns the land (approximately 300 acres) and will continue to mine sand and gravel on the surface. The company is working to annex the area into the village of Bartlett. Bluff City is also the developer of the site, which will have a recycle operation, an asphalt plant, and a tenant concrete plant on the surface, and the company will reclaim the site later for residential and commercial use. Vulcan is responsible for the underground aggregate mining, which will continue as long as reserves are viable. Vogel and Bluff City Materials Vice President Dean Kelley agree that negotiations are positive. “It looks like it’s going to happen,” Vogel says.
Reclamation considerations
How the land is used after mining has ceased is something all producers must consider. What can be done with an old underground limestone mine? In the Kansas City, Mo., area, approximately 20 million sq. ft. of old underground limestone mine space is being used for business, industrial, and warehousing purposes — totaling more than 10 percent of the business and industrial space in the area.
And only a half hour west of Lexington, Ky., where Vulcan is currently mining limestone, another company’s former underground limestone mine is now home to a pair of businesses: Highbridge Spring Water, a bottled water company, and Kentucky Underground Storage, Inc., which stores documents and computer tapes for area businesses. The 32-acre “cave” has 30-ft. ceilings, supported by 110 columns, and 5.3 miles of corridors wide enough to accommodate trucks. Temperatures are steady at about 60 degrees.
According to National Public Radio’s Science Friday, costs for converting the underground “rooms” left behind by these limestone quarries are relatively low, involving painting, pouring a concrete floor, wiring, and putting up some walls. Leasing costs are also low for businesses — in some cases, costs are half those of leasing similar space above ground. A constant temperature of about 60 to 65 degrees makes the space ideal for long-term archival storage. And costs for such things as insurance, taxes, and security are also lower underground.
So while it is not a “no brainer,” the idea of going underground for aggregate material certainly is intriguing in terms of economics — when surface mining is not viable — and community acceptance. Low-cost reclamation options also are an advantage for underground aggregate mines. “It definitely is an option to consider,” says Tepordei.
Vulcan and Bluff City Materials hope to develop a new underground mine in Bartlett, Ill. At left is one of Vulcan’s existing underground operations located in Richard City, Tenn.
Sources:
Mary McCaig is a freelance writer specializing in the construction materials industry.
Electronics Enhance Hydraulic Muscle
Computer-controlled power management and system diagnostics boost excavator productivity and reliability.
By Bob Drake
Crawler excavators are possibly the most common pieces of mobile equipment at mining and construction sites — with the possible exception of wheel loaders. More than a dozen companies market lines of excavators in either backhoe, mass excavator, front shovel, or all three configurations.
Sifting through stacks of specification sheets and brochures from all the companies can be a confusing exercise. It’s made worse by numerous marketing agreements that result in multiple rebrandings of substantially similar machines. In North America, for example, several companies market the same Japanese-designed excavators under different names and model numbers.
The latest example of the complexity of the excavator market is an agreement between Caterpillar and Terex Mining. Under the agreement, Cat will acquire Terex’s eight-model line of Unit Rig DC and AC electric-drive mining trucks and the mechanical, all-wheel-drive Payhauler 350C. Terex will purchase the patents and designs for Cat’s 5110B, 5130B, and 5230B excavators to enhance its seven-model line of O&K excavators. However, Cat will retain its line of excavators for the construction and aggregates industries, including the 5080 and 5090B shovels. In addition, Cat dealers will distribute and service all of the O&K-branded machines.
Through a subsequent agreement with Daewoo Heavy Industries, Terex will distribute 26,000- to 94,000-lb. Daewoo crawler excavators and 2.0- to 5.3-cu. yd. Daewoo wheel loaders in North America. These machines will carry the Terex brand.
Common sourcing for several brands of excavators may make trends in technology seem more pronounced than they might be in reality. Nevertheless, most manufacturers emphasize the following developments:
- Computer control for engine and hydraulic power management to provide the most efficient and economical operation for the application;
- Engine emissions that conform to Environmental Protection Agency Tier II requirements;
- Self diagnostics that alert operators and mechanics to maintenance needs before they develop into serious problems and unscheduled downtime; and
- Improved operator visibility, comfort, and productivity as a result of larger cabs with greater glass area; adjustable armrests, controls, and suspension seats; and viscous cab mounts.
For high-volume truck-loading in stripping or production applications, many backhoes are available in mass excavator configurations. They have shorter, stronger booms and arms to handle larger buckets and exert greater digging forces.
Following are brief descriptions of excavators between 90,000 lb. and, at the extreme, 400,000 lb. operating weight that include the range of machines most commonly used at aggregate operations. Maximum bucket capacities, where noted, may not be appropriate for higher unit weight materials, such as stone, sand, and gravel, or for diffi-cult digging conditions. Additional information from each manufacturer is available using the appropriate InfoDirect number and the link on Aggregates Manager’s web site (www.aggman.com).
1. Broyt
Broyt, part of Sandvik Tamrock Corp., offers three series of hydraulic front shovels with the option of a traditional tracked undercarriage or steel wheels without a drive system. Two steel wheels on the front and two rubber wheels on the rear allow a haul truck to tow the shovel for rapid relocation and reduce undercarriage maintenance costs, Broyt says. Because of the boom geometry and hydraulic cylinder configuration, bucket loading forces press the shovel hard against the ground, which keeps the machine from pushing back from the pile and allows use of lighter counterweights, according to the company. The 600-, 800-, and 1000-series shovels have maximum bucket capacities of 5.2, 6.5, and 7.8 cu. yds., respectively. They can be powered by Volvo diesel engines or an electro-diesel hybrid system.
InfoDirect 701
2. Case Construction Equip.
Case Construction Equipment’s CX-Series offers two models in the weight range covered here: CX460 (316 hp; 4.05 cu. yd. bucket; 101,257 lb. operating weight) and CX800 (486 hp; 5.91 cu. yd.; 174,606 lbs.). Case CX excavators feature a Pro Control System (PCS) with an Auto Mode that senses load demands and automatically balances machine power and speed, Case says. Swing priority boosts flow to the swing motor or the arm cylinder when needed. Auto Power Boost increases power by 10 percent in 8-second intervals when needed. Electronically controlled diesel engines feature high-pressure fuel injection. Operator visibility is improved with 24 percent more glass than previous models, a skylight, roof hatch, and sliding windows, according to Case. Six silicon-filled viscous mounts help isolate the cab from vibration.
InfoDirect 702
3. Caterpillar
Caterpillar offers three excavator backhoes and one front shovel in the plus-90,000-lb. weight class. The 345B L Series II, 365B L Series II, and 385B are available with a variety of booms and sticks, including mass excavator configurations that allow use of larger buckets — up to 6.0 cu. yd. on the 365B L Series II and 7.25 cu. yd. on the 385B. The 5090B shovel has six bucket options, ranging from 6.0 to 7.5 cu. yd. All of Cat’s excavators feature Electronic Unit Injection fuel systems and Advanced Diesel Engine Modules (ADEM II) that electronically control timing and fuel metering. Cat excavators also have three electronically controlled hydraulic pumps, including a separate swing circuit, and Proportional Priority Pressure Compensating valves that the company says prioritize flow based on the operator’s joystick inputs. This eliminates the need to set work modes or swing priority, Cat says. The electronic joysticks eliminate pilot lines.
InfoDirect 703
4. Daewoo
Daewoo Heavy Industries America Corp. offers four large excavators (90,830 to 110,000 lb. operating weight) in its Solar V series — 420LC-V, 450LC-V, 470LC-V, and 500LC-V Giant. Maximum bucket capacities range from 2.85 cu. yd. (420LC-V) to 4.71 cu. yd. (500LC-V). Daewoo says operator visibility has been increased by a slight increase in cab size and the addition of glass area to the front and side windows and sunroof. A graphic display monitor shows up to nine operating conditions and can reveal 21 fault codes. A new Electronic Power Optimizing System (e-POS-V) includes a cross-sensing and fuel-saving pump system, auto idle system, computer-aided engine-pump control, and a working/power mode selection
InfoDirect 704
5. Hitachi
Hitachi recently introduced its Zaxis series of excavators and upgraded several of its mining shovels. The Zaxis 450, 600, and 800 have maximum backhoe bucket capacities of 2.71, 4.58, and 5.62 cu. yd., respectively. The 450 and 800 also are available in front shovel configuration. An on-board Machine Information Center logs performance data, such as engine speeds, hydraulic and coolant temperatures, pump pressures, alarms and faults, hours of operation, and swing/travel/front operation time. Data can be downloaded with a Palm Pilot and transferred to a PC for analysis. Hitachi’s EX1200-5 replaces the EX1100-3. Available in backhoe (maximum 9.3 cu. yd. bucket) and front shovel (maximum 8.5 cu. yd. bucket) configurations, the EX1200-5 has greater horsepower for increased crowding and breakout forces and 10 percent greater lifting capacity, the company says. Redesigned hydraulics result in faster boom-down operation, which decreases truck-loading cycle times, according to Hitachi.
InfoDirect 705
6. Hyundai
Hyundai Construction Equipment’s new Robex 7 series of excavators tops out with the 99,000-lb. 450LC-7. The maximum 3.96-cu. yd. backhoe features a Computer Aided Power Optimization (CAPO) system that maintains optimum engine and pump power levels, the company says. The system monitors engine speed and coolant and hydraulic fluid temperature and has self-diagnostic capabilities to detect electric and hydraulic malfunctions. CAPO can identify and display 48 types of errors. An instrument panel cluster mounted on the right side of the cab allows operators to set power mode (high or standard), work mode (heavy duty, general, or breaker) and user mode. The user mode is programmed to an operator’s preferred power setting.
InfoDirect 706
7. JCB
JCB offers one backhoe excavator in the 90,000-lb.-plus weight class. Its 305-hp., JS460L can handle up to a 3.99-cu. yd. bucket. The excavator has two, 89-gpm variable-displacement, axial piston-type hydraulic pumps. When required, pump flow is combined for faster and more efficient operation of the boom, arm, and bucket, JCB says. An Advanced Management System (AMS) matches engine power and pump output to optimize machine performance in each of four selectable work modes and monitors critical machine functions. A diagnostic function provides information on machine faults. JCB’s Easy Maintenance System extends excavator-end lubrication intervals to 1,000 hours, according to the company. The JS460L is available with a choice of four arm lengths to suit application requirements for reach, digging depth, loading height, and breakout.
InfoDirect 707
8. John Deere
Through a partnership, John Deere excavators are manufactured by Deere-Hitachi Construction Machinery. Deere’s C-Series excavators include three models in the weight class considered here: 450C LC, 600C LC, and 800C. The machines have two, variable-displacement axial-piston hydraulic pumps, each with maximum flow rates of 100 gpm, 117 gpm, and 133 gpm for the three models, respectively. Deere’s Powerwize II engine and hydraulics management system balances hydraulic pressure and flow to optimize performance and fuel economy, the company says. Changes in the pilot control system have increased smoothness, metering, and response, resulting in a 10-percent decrease in lever efforts, according to Deere. Optional mass excavation packages on the 600C LC and 800C use shorter booms and arms and larger buckets.
InfoDirect 708
9. Kobelco
The largest excavator in Kobelco Construction Machinery America’s Dynamic Acera series is the 108,000-lb. SK480LC. The machine is available in standard or mass excavator configurations with maximum bucket capacities of 4.0 and 6.0 cu. yd., respectively. In its latest upgrade, Kobelco says it enlarged the cab by 18 percent to make it the largest in the industry and increased cab glass area by 36 percent. Pilot control levers are adjustable to three heights to suit the operator. A selector switch provides three operating modes: Assist for light duty, Manual for heavy duty, and Breaker to pre-set the maximum pump flow for a hammer. A self-diagnostic function in the SK480LC’s computer collects and displays data on up to 68 service items as well as up to 100 fault codes.
InfoDirect 709
10. Komatsu America
Komatsu America offers three excavator models in its Avance series that are greater than 90,000 lb. operating weight — PC450LC-6, PC600LC-6, and PC750-6. These are available only as backhoes. The company also has three excavators less than 400,000 lb. operating weight that are available as backhoes or front shovels — PC1250-7, PC1400, and PC1800-6. All of Komatsu’s excavators feature two or three working modes to match engine speed, pump speed, and hydraulic system pressure to the application. In addition, two settings for the boom allow the operator to select a smooth mode for fine work or a power mode for aggressive digging. Komatsu’s larger excavators — PC600LC-6 and larger — use an open-center, load- and engine-sensing hydraulic system that enhances the machines’ speed and flexibility, the company says. Each main pump has
a high-pressure, in-line filter. Komatsu’s Vehicle Health Monitoring System (VHMS) provides diagnostics, a preventive maintenance scheduler, gauge panels with operator warning override, and downloadable machine performance history.
InfoDirect 710
11. LBX Company
LBX Company’s Link-Belt LX series includes the 101,000-lb. 460LX and 174,600-lb. 800LX excavator backhoes. The 800LX is available in standard and mass excavation versions. LBX’s Inte-LX computer control system monitors hydraulic output and pressures and regulates engine performance to balance speed, power, and fuel efficiency, the company says. An Auto Power-Up function automatically supplies a power increase without operator interaction and regardless of the work mode. When hydraulic pressure sensors detect resistance, pressure is increased by 9 percent for 8 seconds. Operators can choose one of four work modes or Auto-Mode, which uses working pressure readings to automatically change modes for the best combination of speed and power, LBX says. Inte-LX’s diagnostic system allows analysis of up to 148 items in four categories — machine status, troubleshooting, history, and systems configuration. LBX’s LX-series excavators use a Nephron hydraulic fluid filtration system that the company says eliminates contaminates of 1 micron or more in size, lengthening hydraulic fluid change intervals to 5,000 hours.
InfoDirect 711
12. Liebherr
Liebherr offers five models of medium-sized Litronic excavators available in backhoe, shovel, or clamshell/grapple configurations — R 954B, R 964B, R 974B, R 984B, and R 992. Operating weights for these models range from 107,590 lbs. to 315,250 lbs. The company says its Litronic system controls, regulates, and coordinates all key systems of the excavator. Using electronic engine speed-sensing pump regulation, the variable-displacement axial piston pumps can react in a fraction of a second to changing requirements for power or speed, according to Liebherr. Joystick levers provide independent, electric-over-hydraulic proportional control of each excavator function. The swing pump and motors are linked in an independent closed-loop circuit. Most models offer four mode selections to adjust machine performance to the application: Lift, Fine, Eco, and Power.
InfoDirect 712
13. Terex Mining
Terex Mining currently offers four O&K excavators between 90,000 and 400,000 lb. operating weight, the RH 30-F, RH 40-E, RH 90-C, and RH 120-E. During the fourth quarter of 2003, however, the company expects to begin North American distribution of Daewoo crawler excavators up to about 94,000 lbs. under the Terex brand (see Daewoo above). O&K excavators feature Cummins engines with Celect electronic engine management coupled with O&K’s Pump Managing System (PMS) to balance hydraulic power demand and power output of the engine(s) as well as for monitoring and diagnostics. Hydraulic oil cooling is independent from all the main circuits. On O&K shovels, boom and bucket cylinders connect to a triangular component on the boom that the company calls its TriPower geometry. According to Terex, TriPower increases crowd force along the entire crowd distance; maintains constant bucket angle at each boom position; provides automatic parallel bucket guidance when crowding at any level; increases effective lift forces; maintains constant boom momentum; and provides pressure-free retraction of the boom and stick cylinders. A Board Control System, standard on the RH120-E and an option on the RH40-E and RH90-C, monitors and displays operating information and alarms.
InfoDirect 713
14. Volvo
Volvo developed the 321-hp D12C EAE2 engine used in its EC460B backhoe especially for excavators. The engine provides low emissions, good fuel economy, low noise levels, and long service life, Volvo says. The 105,580-lb., 3.27-cu. yd. EC460B is the company’s largest excavator. Volvo’s Contronics electronic control system monitors machine function and provides diagnostic information. In addition, the hydraulic system, named Automatic Sensing Work Mode, includes a summation system to combine the flow of both hydraulic pumps when needed; boom priority; arm priority; swing priority; regeneration system; power boost; and holding valves.
InfoDirect 714
Bob Drake is editor for Aggregates Manager.
Sand Demand Poses Pond Problem
Installation of a fines processing system clarifies plant wash water and eliminates settling pond dredging.
Overflow from two 54-in. sand screws is pumped to a deaeration tank (background) to reduce velocity, turbulance, and foaming before introduction into the 40-ft.-diameter high-rate thickener (foreground). Clear water overflows the thickener.
For crushed stone producers, increased demand for manufactured sand can be a boon to balancing plant production. But increased specification sand production also can result in a greater volume of process water and fines (minus 200 mesh).
Sellersburg Stone Company operates a 186-ft.-deep limestone and dolomite quarry on an 800-acre site in Sellersburg, Ind., about 10 miles north of Louisville, Ky. With a crushing capacity of 1,000 tons per hour, the facility can simultaneously produce 12 products. Sellersburg says it is the only quarry in Indiana approved to provide limestone for polish-resistant aggregates for Indiana Department of Transportation road surfacing projects.
Sellersburg experienced a significant increase in demand for manufactured sand from a 550-tons per hour, on-site asphalt plant. At the time, the company had two, 5-acre settling ponds in a worked out area of the quarry that received overflow from a 36-in. sand screw. Addition of an Eagle Iron Works 54-in. sand screw to increase sand production also increased the amount of material sent to the ponds. As one pond filled with sediment, Sellersburg had to start dredging.
In 1997 the company added a second EIW 54-in. sand screw, which is fed by the discharge from the first screw. Sand fed to the first screw contains about 17 percent minus-200 mesh material. Discharge from the screw has 5 to 6 percent minus 200, according to Sellersburg. After passing through the second screw, the manufactured sand contains only 0.8 to 1.1 percent minus-200 mesh material.
While the reduction in fines benefits the manufactured sand, it increased problems in the settling ponds. By the spring of 1998, the second pond was filling significantly with sediment. In addition to increasing dredging costs, Sellersburg’s supply of clean, recycled water for its wash plant was diminishing.
Sellersburg chose to install a fines processing system manufactured by Phoenix Process Equipment Co. to help manage its settling ponds and wash water supply. The relatively compact system — thickener, polymer mixing system, and belt filter presses — is enclosed in a 50- x 80-ft. metal building near the ponds, a 4,000-sq. ft. building versus a 5-acre pond.
Overflow from the sand screws, containing about 8 to 10 percent solids, is pumped to a small deaeration tank. This tank reduces slurry velocity from the feed pipe and decreases turbulence and foaming as it enters the thickener.
The Phoenix HF-40 HiFlo thickener is 14 ft. high and 40 ft. in diameter. It has a capacity to handle about 4,000 gallons per minute (gpm); however, Sellersburg’s current operation feeds only 2,400 to 2,800 gpm slurry to the thickener, comprising 50 to 60 tons per hour of dry solids, which is matched by the capacity of its belt filter presses.
Clarified overflow from the thickener gravity flows to a fresh water storage pond. Underflow is dosed with polymer and split between two Phoenix WX-3.0 belt filter presses. Dewatered fines discharged from the belt filter presses contain about 25 percent moisture. They are dry enough, however, to convey to a small loading bin outside the building. As needed, the fines are emptied from the bin into a haul truck and stockpiled.
Underflow from a high-rate thickener is pumped to two belt filter presses. Water drains through a moving belt in the gravity zone and then is squeezed out of the slurry between two tensioned belts that wrap around a series of pressure rollers.
Dewatered fines from two belt filter presses are conveyed to a bin, then loaded into haul trucks for stockpiling.
The Bottom Line
When increased production of manufactured sand began rapidly filling settling ponds and diminishing the supply of clean water for its wash plant, Sellersburg Stone installed a fines processing system. The system — high-rate thickener and belt filter presses — recovers 50 to 60 tph of conveyable, haulable solids cake from 2,400 to 2,800 gpm slurry and produces clarified water with a suspended solids level of less than 200 parts per million..
To submit a suggestion for a Success in the Field or for more information about any of these stories, contact Aggregates Manager at 330-966-2454, Fax: 330-966-2454 or email at bob@aggman.com