Archival
research
and site survey were conducted by
the ACL on 4-7 November 2016. Stump assessment
has been significantly
informed by Young et. al. (2008), where
temperature and humidity data
were recorded over a winter and microporosity
between tracheids was
first noted. A glossary of conditions, specimen
survey, and a
conditions matrix were compiled. Archival
research was performed after
site familiarisation to inform the survey. The
results of this survey,
site research, and material characterisation led
to the design of the
mechanical pinning treatment testing program to
follow. |
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FLFO
archives
revealed critical information about the internal
composition
and physical integrity of the stumps. In her
Drilling Report, Kate
Gregory describes the process of obtaining two
cores from P46 as being
very difficult because of the lamellar nature of
stump fabric. Gregory
accompanied her report with a separate letter,
again highlighting the
fractured nature of the stumps as:
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"The first
few
inches of drilling water pumped into the
core hole to cool the drill
flowed back out the core hole. However,
the drill soon encountered
fractured zones filled with soil, or zones
of wood fibre which had
negligible hardness. Once these fracture
zones were encountered, all
water disappeared into the stump,
indicating the zones were pervasive.
In fact, fracture zones were so numerous
that the core came out in 1-2
inch pieces instead of one continuous
sequence. Thus, the stump is a
ring of petrified wood that surrounds a
fractured and intensely decayed
center."
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Planes of secondary
mineral infill on P47. Note on left that
material has preferentially exfoliated at
this interface.
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Park
personnel quickly named these rediscovered
documents the “Dead Tree
Scrolls.” Gregory’s discovery brought about many
questions about the
integrity of the stump core, and mused that coring
effluent might be
“mudflow,” meaning lahar. It is very common for
mature Sequoia trunks
to have hollow centres near their base.
Nevertheless, more research is
needed to determine if a stump core is hollow and
what it might be
filled with. Differential hygroscopic coefficients
of expansion and
discontinuities in thermal conductivity could
cause pathologies of
differential movement and result in further
fracturing.
The most significant intrinsic reason for material
decay is as a direct
result of silicification processes and blasting.
Stump jointing, a
geological term for planes of weakness or
preferential cleavage, is a
significant reason for deterioration. Site survey
and analysis
demonstrated that the interface of secondary or
tertiary
mineralisations of cracks determine areas of
tabular detachment. Field
microscopy with a hand held digital microscope
following visual
identification of botryoidal deposition determined
that these lines of
later mineralisation become the boundaries of
material detachment. |
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Geoengineers
have
developed the term Rock Quality Designation
(RQD) through core
analysis as a method of in situ evaluation of
the quality of a rock
mass determined by fractures and jointing. RQD
appraisals can be
complicated, being tailored to the geotechnical
requirements of the
mining industry. In her letters, Gregory
mentions that the drill
operators found it very difficult to core into
stump P46. How sensitive
the operators were is significant, because any
fractures caused by
either handling, or the drilling process must be
discounted. The RQD of
P46 directly relates to a combination of factors
including the
material's fossilized origins, its
silicification, the likely
excavation by dynamite, and subsequent
weathering. While geotechnical
assessment may be of use, its conventional use
for situations such as
faceplate pinning, webbing, and shotcrete are
not compatible with
preservation intent, site value, or touristic
display of the stumps.
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Large
excavated FLFO stumps such as P16, P20, P31, P46,
& P47 have
deterioration patterning that can be grouped in
three zones:
1)
Zone of Fragmentation-
The upper-most area of the stump exhibits
splintering, fibrous
disintegration, vegetative growth, fractures,
animal burrowing, and is
subjected to the most water from direct
precipitation: snow, ice, and
rain, more constant loading from thermal
radiation, and mechanical
interventions such as metal strapping bound to
halt fragmentation and
sectional loss. This area has the worst material
integrity.
2)
Zone of Exfoliation-
The middle area of a stump suffers from
dimensional loss due to
secondary mineralisations, fractures, lamellar
exfoliation, and can
have discolorations due to corrosive metals or
biocolonisation. This
area has the best material integrity.
3)
Zone of Rising Damp-
Stump base absorbs water through capillary flow
and snow piling. The
resultant undercutting, buttress root
fracturing, or basal
deterioration is the result. There is no
evidence of salt efflorescence.
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This project examines the
feasibility of stabilizing the
large petrified stumps at FLFO. These
petrified stumps constitute one
of the major natural resources of the park. Of
the nine stumps
currently exhibited on the Petrified Forest
Loop several of these are
visibly deteriorating due to cracking,
spalling and the loss of large
fragments of petrified wood. This project
addresses an urgent need for
conservation. While the research focuses on
remedial methods of
stabilization, the overall goal is to create a
stable environment for
the long-term preservation of the stumps in
situ. This thesis develops
site-based methods for the conservation of
petrified trees in order to
benefit the park’s mission to conserve its
fossil forest. The monument
is interactive with other petrified forest
sites internationally, thus
enabling broad sharing of methodologies for
the conservation of
petrified trees. |
The purpose of these
measurements was to understand the material
properties of FLFO
silicified wood behaviour in order to influence
the decision-making
process of mechanical pinning treatment design.
Samples available for
destructive analysis were procured from FLFO
during a site visit in
November 2016. Samples were sourced from material
found during
excavations for a new visitors centre in 2011, or
came from FLFO stump
P-47.
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Material
characterisation tests performed
included:
1) Gross Physical Characteristics:
Bulk Density,
Specific Gravity, and Colour
2) Water Absorption
3) Reflected and Stereoscope,
Polarised Light
Microscopy, and Scanning Electron
Microscopy
4) Thermal Linear Coefficient of
Expansion
5) Mechanical Properties
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Transverse view of
detail
of microcrack
occurring at late to early wood, the
annual ring. Anomalous
birefringence of quartz or quartz
polymorphs, such as chalcedony can be
accounted for thickness of section
preparation. Paleontologists who
view petrified wood often use thicker
sections for anatomy details,
around 50 microns. Sample P55a, George
Mustoe collection. Viewed at
100x in Plane Polarized Light top and
Cross Polarized Light bottom.
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Wood
cellular
density changes radically at the latewood to
spring wood
boundary. There is a concentration of what might
be relict organics or
iron oxides at the interface of this crack.
Textural density and
mineralogy may help explain why exfoliation or
tabular detachment often
occurs along annual rings. Radial section anatomy
can be seen to
correspond to annual rings. The same cracks
exhibited in transverse
grain can be confirmed as planar fissures when
viewed along the radial
grain.
Sub-micro porosity was visible with Scanning
Electron Microscopy (SEM)
at the boundaries between tracheids, probably as a
result of silicate
inaccessibility.
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A
three dimensional model of stump p-47. To
rotate the model place the
mouse over the image and, while left
clicking, move the mouse. Click on
each of the numbers to read more
information about that location. To
view the model in full frame mode, place
the mouse cursor over the view
and then click on the small double-ended
arrow icon which appears in
the bottom right corner of the view.
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