CONSTRUCTION ACCIDENT - OVERTURN TRACTOR-TRAILER
Review of the Event
A Tractor Trailer Dump Truck overturned to the passenger side while unloading topsoil at a landfill. A portion of the topsoil was stuck in the nose of the trailer and was not able to slide out. The driver (plaintiff), was sitting in the driver's seat
and controlled the raising of the trailer. He was injured when the overturn occurred. The driver was not wearing his seatbelt and was thrown against the passenger door when the tractor and trailer overturned.
Plaintiff's Statement
A. The plaintiff driver stated that the rear tandem wheels of the trailer were uneven. That the trailer passenger side wheels were lower than the trailer driver side wheels. He attributed this to the fact that the owners of the landfill had not smoothed and compacted the topsoil that was previously dumped.
B. The plaintiff stated that, " ... the passenger side tandem wheels of the trailer were 6" to 8" or maybe a foot sunken into the surface when the trailer was lying on its side."
C. The plaintiff also stated that the trailer pushes the tractor and trailer forward as the topsoil slides out of the rear of the trailer. The trailer was raised to the maximum dumping height when the trailer started to overturn.
D. The plaintiff stated that approximately 10 cubic yards of topsoil was stuck in the nose (front) of the trailer.
Engineering/Analysis/Calculations
Calculations in Mathcad in pdf format.
Photographs
A typical tractor-trailer dump truck dumping a load. Each section of the hydraulic lifter is approximately 5 feet. The height of the hydraulic lifter extends approximately 25 feet. The height of the bottom nose of the trailer is approximately 28 feet above the ground.
The photograph below shows the tire tracks that the loaded rear tandem trailer wheels make in the partially compacted surface of the landfill.
The photograph below shows a dumped load. Notice the tire track marks in front of the pile of earth. The depth of the tire tracks vary from the right side to the left side. This would cause the extended trailer to oscillate side to side when the load slides out of the rear of the trailer and pushes the trailer forward.
Results of the Calculations
The results of the calculations show that the forward acceleration of the tractor-trailer, in banging the tailgate to the trailer, caused harmonic motion (inverted pendulum effect) to the raised trailer. This inverted pendulum effect exceeded the static overturning torque and resulted in the tractor-trailer overturning.
Calculations in Mathcad in pdf format.
The case was settled.