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World Environmental and Water Resources Congress 2017 382

Hollywood [Mulholland] Dam; a value of 0.667, or the tangent of 33.7 degrees. The queries
then shift to how that figure was estimated, which Bayley stated came from Hollywood
[Mulholland] Dam, which was founded on sandstone, and the “proper friction was assumed to be
two-thirds” (0.667).
No effort was made to determine the coefficient of friction at the St. Francis Dam site
that Hurlbut “was aware of.” Nor, did BWWS attempt any sort of laboratory test to evaluate the
concrete-rock friction coefficient at St. Francis. The concrete-to-rock friction was assumed from
figures cited in published literature prior to 1924. This became a significant issue in the
reassessment of Mulholland Dam in 1928-33, because of its structural similarity.
The interface friction value was much too high for the slippery micaceous foliation of the
Pelona Schist (but was reasonable for the Hollywood [Mulholland] dam site in Weid Canyon,
comprised of sandstone). Bayley was asked about the coefficient of friction at the St Francis
Dam site. He admits that “it would be low, likely something between 0.25 and 0.30, as an
“offhand estimate.” A more realistic figure would have been between 0.36 (20 degrees) and, at
most, 0.58 (30 degrees). In his third examination, Bayley stated that the actual figure used in the
design was 0.60, which would equate to 31 degrees.
There was no accounting for diminution in the coefficient of friction when the rock
material was saturated. William Mulholland responded that he assumed the mass concrete was
more or less impenetrable to seepage. The jurors also inquired about whether the BWWS design
team performed a basal sliding analysis, using stand-alone sections (vertical strips) of the dam.
They were informed that they had not.

PAUCITY OF FOUNDATION EXPLORATION

The poor quality of the arkosic Vasquez conglomerate exposed in the dam’s right (western)
abutment was confirmed when specimens of the gypsiferous horizons were observed to
disintegrate rapidly upon submersion in a glass of water. Many hours were taken up with
inquiries about how the dam site was explored and characterized, especially in regards to the
quality of the rock exposed in its abutments.
Almost all of the BWWS engineers who testified at the inquest were asked questions
about the geologic characterization and appraisal of the dam site. The jurors had been given
copies of the basic design plans, but nothing with any details about the dam site, except for plane
table maps of the topography. The jurors asked about what sort of site exploration had been
carried out on the dam site, “for the purpose of determining whether they could put a dam up
there?” Witness after witness replied that “they didn’t know.” They were asked to produce “a
plan, a diagram, or a log, or by whatever name you may call it, of the formations taken from the
core of the dam site?”
The witnesses responded that there was “a record of those wells which were put in there
in connection with the drainage system under the dam. Those were drilled down away into
bedrock.” Another witness told the inquest that a “shot drill” was used at the St. Francis dam site
to drill the cores (shot drills employed steel ball bearings to grind through the rock, using a
hollow cylinder drill bit). They were informed that “those cores were taken and inspected on the

ground by Mr. Mulholland and others.”
The jurors then asked to “see the cores,” but were told that the cores had been stored in
one of the exploratory adits “30 or 40 feet long in the left abutment just downstream of the dam,”
and that these had all been lost in the landslide of the east abutment during the failure. No

World Environmental and Water Resources Congress 2017