The Thistle landslide came down because excess groundwater "triggered the sleeping giant," two defense witnesses said in 4th District Court Thursday.
Both witnesses, James Slosson and Norbert Morgenstern, said slide movement initiated at the head and the driving force came from the upper portion of the slide. Following their testimony, defense attorney Michael Richman, representing the Denver & Rio Grande Western Railroad, rested his case.Fifteen Thistle property owners are asking for $1 million in damages caused when the slide blocked the Spanish Fork River and flooded their land and homes in April 1983. They claim D&RGW contributed to the slide and could have prevented it.
Slosson, a California geotechnical engineer, said tear fractures on the slide indicated that it was a "mass swelling of material" and not a result of progressive failure - meaning that it did not start at the bottom and progress upward.
"The dominant forces would be from up-slope, where compression is occurring," Slosson said.
Slosson said that the railroad cut did not contribute to the slide's release and that a separate, smaller slide occurred where the railroad and highway cut had been made. He said that the "humping" of the railroad tracks that occurred over the years was "subtle movement of the separate slide."
Slosson said that water buildup at the head of the slide initiated its release. Without the rainfall of 1980-83 "there would not have been sufficient moisture to mobilize the slide," he said.
Despite strong objection from the defense, plaintiffs' attorney Allen K. Young was allowed to introduce Slosson's deposition from the Utah Railway Co. vs. D&RGW case during cross-examination. In that case, which was settled out of court, Slosson was a witness for the Utah Railway Co., who also claimed D&RGW was negligent in not preventing the slide.
Young asked Slosson about several reports he had written about the prevention of the Thistle slide. In those reports, Slosson said the slide was preventable and early warning signs should have alerted a qualified civil engineer. He said if a proper drainage system had been installed in time, the slide could have been prevented.
"If the surface water had been eliminated and ground water been dropped, the giant slide would not have happened," Slosson said.
Morgenstern, a geotechnical engineer and professor at the University of Alberta, agreed with Slosson's analysis of the cracks on the slide and said they were inconsistent with progressive failure. He testified that a drainage system on the slide would not have been effective because of the non-permeability of the slide's clay material.
However, on cross-examination, Morgenstern said that had groundwater pressures been reduced, "we would not be here today." He said more testing should have been conducted at the slide site.
Jurors were to travel to Thistle Friday to visit the slide site and to see the town of Thistle. Judge Cullen Y. Christensen is scheduled to give jury instructions on Monday and closing arguments will likely be on Tuesday.