DEPARTMENT OF LABOR
MINE SAFETY AND HEALTH ADMINISTRATION
Metal and Nonmetal Mine Safety and Health
REPORT OF INVESTIGATION
Surface Nonmetal Mine
(Sand and Gravel)
Fatal Powered Haulage Accident
October 21, 2002
R-D Mac, Inc.
R-D Mac, Inc.
La Grande, Union County, Oregon
Mine I.D. No. 35-00507
Larry L. Orton
Mine Safety and Health Inspector
John S. Miller
Mine Safety and Health Specialist
Robert V. Montoya
Mine Safety and Health Specialist
James C. Ernlinger
Darren J. Blank
Mine Safety and Health Administration
2060 Peabody Road Suite 610
Vacaville, California 95687
Lee D. Ratliff, District Manager
On October 21, 2002, Judith D. Beeson, truck driver, age 51, was injured when a portion of a dumpsite collapsed causing the truck she was driving to overturn and fall into the water at the #1 pit. The victim died of the injuries sustained on October 25, 2002.
The accident occurred as the base of the dumpsite became liquefied and collapsed under the weight of the truck and its load.
Beeson had 24 years of mining experience. She had received training in accordance with 30 CFR Part 46.
R-D Mac, Inc., a sand and gravel operation, owned and operated by R-D Mac, Inc., was located in LaGrande, Union County, Oregon. The principal operating official was Jerome J. Collman, owner. The mine was normally operated one 10-hour shift a day, 5 days a week. Total employment was three persons.
Sand and gravel was extracted from a single bench in the #2 pit with an excavator, loaded into haul trucks, transported to the plant, crushed, screened, and stockpiled. The reject topsoil was then transported to the # 1 pit for backfill. The finished product was used by the company in its concrete batch plant.
The last regular inspection at this operation was completed October 31, 2001.
On the day of the accident, Judith D. Beeson (victim) reported to work at 6:30 a.m., her normal starting time. Beeson inspected the haul truck she was going to operate and was assigned to haul material from the #2 pit area to the crusher for processing.
At about 2:30 p.m., Charles Hanson, crusher foreman, discovered problems with the screen unit and shut the crusher down. Hanson instructed Beeson to haul topsoil for the remainder of the shift. Beeson drove to the #2 pit and informed Connie R. Goff, excavator operator, of the change. Goff loaded the truck and Beeson drove to the dumpsite at the south side of the #1 pit. As Beeson backed the truck toward the berm of the dump area, the ground underneath the truck collapsed. The truck slid down the embankment and overturned, coming to rest in the water. Beeson was removed from the truck cab and transported by ambulance to the hospital where she passed away on October 25, 2002.
MSHA was notified of the accident at 3:30 p.m., on October 21, 2002, by a telephone call from Stacy Bowman, office manager, to Ronald Goldade, assistant district manager. An investigation was started on October 22, 2002. An order was issued under the provisions of Section 103(k) of the Act to ensure the safety of the miners. MSHA's accident investigation team traveled to the mine, made a physical inspection of the accident scene, interviewed employees, and reviewed training records and work procedures relevant to the accident. MSHA conducted the investigation with the assistance of mine management and employees.
Mining operations began at the site in the year 2000. The site was located in an old river base consisting of sand and gravel. The mine consisted of #1 Pit and #2 Pit. Before mining operations began, the top of #2 Pit was incised in order to collect the wastewater and tailings generated from washing material generated from #1 Pit. Fresh water for washing the sand and gravel was obtained from springs. The tailings appeared to be concentrated in the northern end of #2 Pit. Excess water was pumped into fields adjacent to the mine.
The accident occurred at # 1 Pit, which was triangular in shape. The east wall, approximately 500 feet long, consisted of an intact sand and gravel bank that was left unmined. At the northern limits of the pit, a bank of unmined material extended east and west for nearly 500 feet. The third section of the pit consisted of natural ground and overburden material sloped to 3H:1V. This wall was approximately 700 feet in length and longitudinally ran N450 W. The mined material appeared to be horizontally stratified, and rounded to sub-angular in shape. Waste materials had been dumped in the northeast and south corners to an elevation near the top of the pit. The ground water table in the area was approximately 8 feet below the top of the pit.
Approximately 6 hours of each workday would consist of mining sand and gravel, and 2 hours would be dedicated to stripping and dumping activities. On average each day, 20 loads of overburden and tailings would be hauled by truck and dumped into the north and south ends of #1 Pit. The dumped materials formed a slope at the angle of repose at the northern end of the pit. This angle was observed to be between 30 to 35 degrees. Due to recovery operations at the accident scene, the slope of the dump area at the southern end of the pit was flattened and disturbed.
The week prior to the accident, the crushing plant was down for repairs and stripping work was performed daily for the entire week. The number of loads dumped during this week averaged about 100 per day. During this period, a total of about 20,000 cubic yards of waste material was dumped in the southern end of #1 Pit. The weather during the week prior to the accident was reported to be sunny and mild with the highs in the mid 50's and lows in the upper 20's to lower 30's. The last load of material dumped prior to the accident was Friday afternoon, October 18, 2002.
The vehicle involved in the accident was a 1970 Caterpillar model 769B dump truck. The truck was 11 feet 11-1/2 inches wide, 25 feet 9 inches long and 12 feet 9 inches high. The truck weighed 61,800 pounds. The rated load capacity was 70,000 pounds. The center-to-center spacing between the front and rear axles was 11 feet 3 inches. The truck had two tires on the front axle and four tires on the rear axle. Each tire measured 18 inches wide with the contact area of each calculated to be 2 square feet. It was estimated that the truck bed contained 19 cubic yards of material, with an approximate weight of about 56,000 pounds. According to the Caterpillar representative, with the truck bed down, 60 percent of the vehicle's total weight was distributed to the rear tires while 40 percent was distributed to the front. Using this ratio, the four rear tires applied a force of approximately 9,000 pounds per square foot (psf) onto the bank. If the truck bed were raised at the time of the accident, the force from the rear wheel would have been greater.
The southern end of the waste dumpsite was 50 feet wide and extended 100 feet into the mined out #1 Pit for a distance of 50 feet. An approximately 4-foot-high berm was constructed at the edge of the spoil pile. Material was dumped short and pushed into the pit with either a small dozer or a loader. The dump area appeared to be sloped slightly away from the pool.
At the time of the accident, the rear tires were located about 5 feet from the inside toe of the berm, or nearly 13 feet from the upstream edge of the slope, and about 40 feet horizontally from natural ground. A large failure of the slope occurred, and the truck slid into the pit, rear end first. The slide measured 36 feet across the main scarp, approximately 40 feet high, and penetrated into the crest a maximum distance of about 15 feet. Based on these dimensions, it is estimated that 1,700 cubic yards of material were involved in the slide.
Soil samples were collected from the southern dump accident site for laboratory index testing. The results of the tests were used in the estimation of strength parameters used in slope stability analyses. Based on the results of grain size distribution, the soil was classified as a sand-clay mixture, with some gravel and organic material. The water content of the material was likely to be near its liquid limit. The flow curve obtained from Atterberg limit testing was relatively flat, indicating that the strength of the material is sensitive to the water content. With water content near the liquid limit, the strength of the fine soil would be significantly reduced.
Slope stability analyses were performed for estimated conditions prior to the truck backing out onto the fill and with the loaded truck at its final position at the time of slope failure. It was assumed that the pore water pressure within the fill did not change due to the weight of the loaded truck, although this value would be expected to rise resulting in a reduction in soil strength. Prior to the truck backing onto the fill, the factor of safety against slope failure for the surface that failed was found to be slightly greater than one, indicative of a marginally stable slope. For the same surface, but including the force from the rear tires, the factor of safety was reduced below one, indicating a slope failure. Raising of the truck bed at the time of the accident would increase the force from the rear tires, resulting in an even lower factor of safety.
The overburden and tailings dumped into #1 Pit formed a sand-clay matrix with some gravel and organic material. Due to the high percentage of fine material within the matrix, it is likely that the fine material controlled the strength, permeability, and compressibility properties of the fill. When material was initially dumped into the pit, a pool of water approximately 10 feet in depth existed. The dumped material quickly became saturated. Over a period of approximately 1 week, about 9,200 cubic yards of material were dumped on top of this saturated base. This rapid construction did not permit the relatively impermeable material to drain. This resulted in excess pore water pressures in the saturated foundation material and, possibly, within the bank itself.
When the victim backed the loaded truck onto the fill, the shear stresses tending to cause failure were increased in the marginally stable slope. The weight of the truck may have induced additional excess pore water pressures within the foundation and fill. This was the first load at this dumpsite since the previous Friday afternoon, 3 days prior to the accident. Additional shear stresses induced in the fill due to the surcharge load of the truck, coupled with the reduction in strength of the foundation material due to the generation of excess pore pressures, resulted in the failure of the slope.
The company had an approved training plan, and training had been given to the victim.
A root cause analysis was conducted. The following causal factors were identified that may have prevented the accident.
Causal Factor: The fine sand and clay material failed to adequately drain and support the weight of the truck.
Corrective Action: A plan should be established for the construction of the dumpsite areas. Material should be used capable of supporting the loads which it will be subjected to.
Causal Factor: The inability to recognize the effect that standing water in a pit has on the stability of the dumpsite area.
Corrective Action: A policy should be established that requires a competent person to examine each dumpsite area prior to work being performed and to identify the slope stability and strength of the material.
The accident occurred because the base of the dumpsite became liquefied and collapsed under the weight of the truck and its load. The large amounts of material dumped the prior week created instability.
The root causes identified during the investigation included the following: Failure of the fine sand and clay material to adequately drain, and the inability to recognize the effect that 10 to 15 feet of water already in the bottom of the dump area had on the stability of the fine sand and clay tailings that comprised the base.
Order No. 3914481 was issued on October 21, 2002, under the provisions of Section 103 (k) of the Mine Act:
A fatal accident occurred at this operation on October 21, 2002, when the ground of the waste dump collapsed causing a Caterpillar haul truck to overturn and fall in the water at the pit. This order is issued to assure the safety of all persons at this operation. It prohibits all activity at the accident dumpsite until MSHA has determined that it is safe to resume normal mining operations in the pit area. The mine operator shall obtain prior approval from an authorized representative for all actions to recover and/or restore operations to the affected areas.
This order was terminated on December 19, 2002, after it was determined that conditions which led to the accident no longer existed and normal operations could resume.
Related Fatal Alert Bulletin:
Persons Participating in the Investigation
R-D Mac Inc.
Jerome J. Collman ............. ownerMine Safety and Health Administration
Charlie W. Hanson ............. crusher foreman
Michael D. Good ............. general foreman
Larry Orton ............. mine safety and health compliance specialist
John S. Miller ............. mine safety and health specialist
Robert V. Montoya ............. mine safety and health specialist
James C. Ernlinger ............. electrical engineer
Darren J. Blank ............. civil engineer
R-D Mac, Inc.
Charlie W. Hanson ............. crusher foreman
Jerome J. Collman ............. owner
Connie R. Goff ............. equipment operator