WYARALONG RCC DAM SUMMARY
Transcript of WYARALONG RCC DAM SUMMARY
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21st Century Dam Design
Advances and Adaptations
31st Annual USSD Conference
San Diego, California, April 11-15, 2011
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On the CoverArtist's rendition of San Vicente Dam after completion of the dam raise project to increase local storage and provide
a more flexible conveyance system for use during emergencies such as earthquakes that could curtail the regions
imported water supplies.The existing 220-foot-high dam, owned by the City of San Diego, will be raised by 117
feet to increase reservoir storage capacity by 152,000 acre-feet. The project will be the tallest dam raise in the
United States and tallest roller compacted concrete dam raise in the world.
The information contained in this publication regarding commercial projects or firms may not be used for
advertising or promotional purposes and may not be construed as an endorsement of any product or
from by the United States Society on Dams. USSD accepts no responsibility for the statements made
or the opinions expressed in this publication.
Copyright 2011 U.S. Society on Dams
Printed in the United States of America
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Wyaralong RCC Dam 245
WYARALONG RCC DAM SUMMARY & THE IMPACT OF LOW QUALITY
AGGREGATE ON DESIGN
Colleen Stratford1
Emily Schwartz2
Robert Montalvo
3
Ernest Schrader4
Richard Herweynen5
ABSTRACT
Wyaralong dam in Southeast Queensland, Australia is a 47 m high RCC dam containing160,000 m
3of RCC. Influenced by foundation concerns, the design used a reasonably
wide base. In combination with low seismic loading, this resulted in low stresses on the
order of only 1 MPa compression with no significant tension. The design team opted toachieve water tightness by using a wetter consistency RCC having a cement plus fly
ash content of 85 + 85 kg/m
3
, which is much more than needed for strength. Thisnormally would have required considerable cost to control thermal stresses due to
seasonal temperature changes, heat from hydration, and stiffness of the RCC. Typically,the modulus for a mix like this would be about 27 GPa. Tests with imported basalt,
initially considered by traditional thinking to be necessary because of the poor quality
of on-site sandstone, had these values. However, because strength was not an issue,sandstone was also included in studies of potential aggregate. The low specific gravity of
2,460 to 2,510 kg/m3and high absorption of 4.8% to 5.2% normally indicate unsuitable
material. However, adequate strengths were achieved, and tests showed durability wouldnot be an issue. In addition to cost savings and avoiding issues related to hauling
aggregate from a remote source, the most valuable advantage of the on-site sandstonewas its low RCC modulus at 10 GPa. In combination with high creep, thermal stresses
were reduced enough to allow placing with no forced cooling.
INTRODUCTION
As part of the Queensland Governments response to the water shortages, a number of
measures were proposed to improve the storage and use of water in the Logan Rivercatchment in south-east Queensland. As part of this plan, Wyaralong Dam was
constructed. Wyaralong Dam is located on the Teviot Brook approximately 65 km south
west of Brisbane, Australia, and has a storage capacity of 102,884 ML. The dam is a
1
Designer, SMEC, Level 5, 71 Queens Road, Melbourne, Victoria 3004, Australia, Australia,[email protected] & Field Engineer, Paul C. Rizzo Associates, Suite 100, Building 5, 500 Penn Center Blvd.,Pittsburgh, PA, 15235, USA, [email protected] & RCC/Materials Manager, Macmahon, Level 3, 104 Melbourne St, South Brisbane 4101,
Queensland, Australia, [email protected], Schrader Consulting, 1474 Blue Creek Road, Walla Walla, WA 99362, USA,[email protected] Dam Designer, Entura, GPO Box 355, Hobart 7001, Tasmania, Australia,
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roller-compacted concrete (RCC) gravity dam with a maximum height of approximately
48m and crest length of around 500m. The spillway is incorporated in the dam andcomprises a centrally located, uncontrolled 135 m wide primary spillway, with a 150 m
wide secondary spillway located on the left abutment. Also incorporated into the dam are
an outlet works and a bi-directional fishlift.
During the concept phase of the project, a review was undertaken of the construction
materials at which point it was determined that roller-compacted concrete (RCC) was the
most suitable and cheapest solution for the site, as opposed to earthfill or rockfillstructures. The decision was made to adopt a slightly wetter consistency RCC, with a
conventional concrete skin on the upstream and downstream faces. The design provided
water-tightness across lift joints without the use of bedding mix; however, as a riskreduction measure, it was decided to place bedding mix in the upstream section of each
lift joint for added protection against seepage.
PROJECT BACKGROUND
Design Build Alliance
The Wyaralong Dam was designed and constructed using the Alliance contracting
approach. Although this is fairly popular and successful in Australia, it is not yet
common in the USA and many other countries. In the alliance model the owner,contractor, and designers work together to deliver the project, in a risk and profit sharing
arrangement. The owner selects the Non-owner participants through a competitive
process.
Originally the project was much larger in scope, also encompassing a larger dam atTraveston. Four teams, or consortiums, were chosen that comprised of the biggest and
best design and construction companies in Australia, most strengthened with international
organizations plus international consultants. These teams competed at their own cost fora spot in the final two for this highly sought after project.
A different owner representative was embedded within each of the two selected teams,
who remained until selection of the winning proposal. The teams were each provided afixed amount of funding by the owner to cover the cost associated with preparation of the
final proposals, but the client then owned the work of both teams. The final proposals
included basic design and planning for essentially all construction issues, includingschedule.
A rough cost estimate was also prepared, but the basis of payment for doing the futurework was not agreed to until a Target Cost Estimate was negotiated after the winning
team was selected. The winning team was then assured payment according to this
estimate. Once the Target Cost Estimate was agreed upon, any cost overruns orsavings were shared equally between the Owner and the Non-owner participants, within
the Alliance Cost. Governance for the project was the Project Alliance Board, which
had representation from both the Owner and the Non-owner participants.
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The winning team for the Alliance was comprised of the design firms SMEC (Aus), Paul
C. Rizzo Associates (US), and Entura (Aus); and construction firms ASI Constructors(US), Macmahon (Aus), and Wagners (US). These companies along with the client,
Queensland Water Infrastructure, formed the Wyaralong Dam Alliance (WDA).
Dam Foundation
The foundation for Wyaralong dam is comprised of Gatton formation sandstone interlaid
predominantly with mudstone, conglomerates and coal. Investigations of the foundationwere undertaken during 2008 and 2009, and were used to develop a geological model of
the foundation. The rock was classified based on the degree of weathering, using the
classifications 'distinctly weathered with seams', 'distinctly weathered without seams', and'slightly weathered to fresh' rock. The design foundation level was generally based on the
degree of weathering; rock that was classified as distinctly weathered with seams was
removed from the dam foundation leaving only competent rock in place for the damfoundation.
The predominant defect sets consisted of sub-horizontal bedding planes dipping 14
degrees downstream and slightly towards the right abutment. Other significant defectsconsisted of near vertical joint sets located approximately parallel, and perpendicular to
the strike of the bedding. The geological model was also used to identify specific weak
layers, including sheared/crushed zones, clay infills and seams of shales and mudrock. Atotal of eight potential weak surfaces beneath the dam were identified during the
investigation stage, all of which were orientated generally along bedding planes. One of
these weak layers required excavation due to its close proximity to the dam-foundationcontact zone.
The stability of the dam was governed by sliding along the bedding and potential weak
planes immediately below the dam-foundation contact. Shear tests were used to
determine peak and residual shear strengths for these layers, taking into consideration thejoint roughness. The advice of rock mechanics expert Dr. Ted Brown was also sought
during the development of shear strength parameters, due to the considerable influence of
the parameters on the dam section. The bedding planes were found to have a peak
friction angle of around 36 degrees with no cohesion. The clay infill zones, which hadthe lowest shear strength of all weak planes, were found to have a peak friction angle of
only 20 degrees with no cohesion, and a residual friction angle of just 15 degrees.
Aggregate Options
Aggregate choice was limited by geography and cost to two options: imported basalt orsite-available sandstone. Initial investigation of the sandstone indicated that it might not
adequately meet strength and durability requirements for construction. The results of
core sample testing and analysis suggested high water absorption, a dramatic reduction inwet strength versus dry, and the possible presence of an expansive clay matrix. Initial
testing of the sandstone did not meet the requirements for conventional concrete
aggregate set by Australian Standard No. 2758.1.
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Table 1. On-Site Aggregate Test Results
Test Result
CVC
Acceptance
Criteria*
Effect on
Wyaralong
Dam RCC
Reason
LA Abrasion 46 61% 50kN
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temperature cycles (80oC to 3
oC), extreme wet and dry cycles (saturated to oven
dry), 72 hours of abrasion testing using iron bearing balls.
Trial Section testing all of the likely parameters that are likely to be experiencedduring the construction of the dam.
Based on this testing, a preliminary RCC mix design was developed and tested todemonstrate tolerable strength values, an initial design cross-section was proposed, and a
suitable quarry location was chosen on the site. The proposed design called for a
conventional concrete facing mix using the basalt aggregate to mitigate durabilityconcerns. This successful plan won the project.
MATERIALS TESTING & DEVELOPMENT OF RCC MIX DESIGN
Aggregate
As the onsite sandstone was originally reported to be unsuitable for use as RCC
aggregate, a comprehensive test program addressing perceived issues was conducted.Concerns surrounding the sandstones durability included the assumed presence of
swelling clays in the aggregate matrix, breakdown of aggregate at all stages of production(crushing, stockpiling, mixing, compaction), and the presence of excessive waste during
crushing.
Swelling: It is typical for rocks with textural accessibility to swelling clays to reactwithin days to ethylene glycol. However, the tests of onsite sandstone showed no
perceived reaction over even an extended period of several months. Additionally, rock
cores were subjected to extreme conditions of exposure, including wet and dry cycles,and hot (90 C) and cold (3C) cycles with no noticeable affects. Similar tests were later
carried out on RCC samples with analogous results.
Crushing: Continuous efforts to increase the efficiency of crushing during aggregate
production included allowance of more fines into the aggregate blend only after full
laboratory trials for each increase had been done. This approach ensured the affects ofthe change would not overly affect the mix properties. By the end of crushing, the fines
wastage had been reduced to 4%.
The adoption of an all-in aggregate stockpile and a continuous mixer helped minimize
concerns about breakdown.7The use of an all-in aggregate also had other related benefits,
including more efficient use of space and more consistency in the final product; the latter
relies on consistency during crushing and stockpiling (tight production controls) and can
be enhanced with appropriate blending of layers during extraction.
Once regular aggregate production commenced, quality control testing included: gradings
and moisture on a daily basis; and Atterberg limits, specific gravity and absorption on aweekly basis. The same tests and frequencies were applied to the feeding face of the
stockpile prior to RCC production.
7Refer to Herweynen et al, 2010.
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RCC
The trial mix program included a significant number of variables. A broad range of data
was obtained in order to ensure the specification parameters could be met with a
workable mix and also to look at opportunities for improvement (including the possibility
of allowing more fines into the aggregate).
Another perceived opportunity was the use of sandstone fines as pozzolan given that
preliminary chemical tests indicated pozzolanic potential. This, however, was discountedby the unsatisfactory test results.
Due to thermal and wetness concerns, the RCC mix design was planned based on arestriction of placement to night shift only. In order to ensure that the lift surface
remained live during the day shift so that subsequent layers would achieve full bond,
the RCC setting time was delayed for 24 hours with admixture. Retarding admixturesfrom two suppliers were trialed. The results were encouraging for one of the admixtures,
whereas the other one did not provide the desired results.
During construction, samples were taken from the field on the following shift afterplacement at different elevations. These samples were taken to the lab and re-compacted
into cylinders to be tested as regular production cylinders.
CVC
Facing. The abrasion resistance provided some concern for using the sandstone aggregatefor the spillway facing concrete. From a construction logistics point of view there was
reluctance to having two different concrete mixes for the facing concrete and a decisionwas made to use a basalt aggregate concrete for the facing mix. As such the final design
used the sandstone RCC, which was encased in a thin facing using a basalt conventional
concrete.
Figure 1 summarizes the abrasion test results carried out using sandstone and basalt
conventional concrete samples in a variation of ASTM C1138. A machine built in-house
was used to provide the rotating motion required to move the submerged iron bearingballs on the concrete.
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Figure 1. Abrasion Results: Sandstone (left) vs. Basalt (right)
Given the obvious property differences between RCC and facing, it was also important to
investigate the structural bonding of these two products due to likely shear and tensilestresses that the dam may experience along this interface. This investigation included thestresses resulting from thermal differentials and large variance in modulus.
Dental. Even though it was not used in the facing mix, sandstone was nevertheless usedin the project as dental and leveling concrete with properties more closely resembling
those of RCC than what a basalt concrete would have provided.
THERMAL ANALYSIS
Risks associated with hydration-induced heat generation in the RCC were a particularly
important component of the strain analysis conducted for Wyaralong Dam.
Thermal Risks
The exothermic reaction between water and cement, termed adiabatic temperature rise,
begins immediately after the material is mixed and continues through the placement and
curing processes. This results in a pattern of thermal expansion, followed by contraction
as the overall structure cools to ambient temperature. Volume changes during the initialexpansion occur across the entire structure at the same rate and generally only cause
compressive stresses, which are of minimal concern in the young and relatively elastic
material. As curing continues however, cooling-induced contraction occurs rapidly across
the exposed surfaces of the structure, with internal contraction occurring more slowly asheat dissipates outward over a period of months or years. This results in a variation of
tensile stresses in the cured material, which becomes brittle as it matures. Where thesetensile stresses exceed material capacities, internal, mass gradient cracking and/or
external, surface gradient cracking occur.
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Modeling and Analysis
Various levels of thermal analysis were undertaken during the preliminary and final
design phases to characterize the thermal risk. These included an initial, limited Level 1
analysis during the project proposal, followed by increasingly detailed Level 2 analyses
as the dam geometry and RCC mix designs were finalized. The more detailed Level 2analyses were conducted to ensure that the structures internal temperature gradients,
which are inherent to mass structures with long construction schedules, were structurally
insignificant. These analyses also confirmed, from a thermal standpoint, that specifieddesign limits were adequate. All analyses were conducted in accordance with USACE
guidelines as outlined in ETL 1110-2-542.
In the Level 2 analyses, two-dimensional cross-sections of both the primary spillway and
left abutment were developed for processing by the software THERM. These models
required input of the following variables:
A detailed finite element model of structure geometry and materials which
included structural foundation, surface detail, and design characteristics such asthe drainage gallery,
Thermal characteristics for all materials used, including conductivity, specific
heat, density, and age-dependent adiabatic temperature rise,
Semi-monthly estimation of the hourly air temperature cycle, termed an
environment,
Placement time, estimated to within a tenth of a day, of each vertical lift ofmaterial placed during construction,
Placement temperature of each vertical lift of material, and
Wind-dependent surface heat transfer coefficient, to be applied to all externally-
exposed surfaces through construction and during the observed curing period.
The detailed temperature histories resulting from THERM analysis were then examinedacross horizontal and vertical sections to determine detailed mass and surface
temperature gradient profiles. An example of a temperature history for estimated actual
placement temperatures at a single point in the spillway (RL 42.3m, offset 19 m fromupstream face) is illustrated in Figure 2. This time history was later compared to actual
data collected by thermocouples placed during construction. Discrepancies can beaccounted for by the two week delay in construction and a higher than modeled
placement temperature. It should be noted that the 5 difference in placement temperature
between modeled and actual results is carried through the entire time history.
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Figure 2. Temperature Comparison of Modeled vs. Actual for Primary Spillway
Modeling was also done using maximum allowable temperature to ensure no negative
structural impacts of unexpectedly warm placement. Based on multiple iterations of
analysis to determine sensitivity of placement temperature, the risk of thermal crackingwas found to be minimal. Worst case scenario cracking extended only though the facing
CVC with no penetration to RCC, and no risk for internal cracking. Such conditions were
produced only when modeling with maximum allowed placement temperatures (28C to
33C) combined with a day shift placement scenario. Such temperatures and shiftscheduling did not occur during actual construction, and no unexpected thermal cracking
was observed.
Impact of Aggregate
Use of previously termed poor quality aggregate proved helpful from a thermalstandpoint. As a way to mitigate low compressive strengths in the aggregate, the
Wyaralong mix design included higher cementitious and accompanying water content
than is typical in RCC construction. Such a mix would not have been possible hadaggregate demonstrated an elastic modulus more typical of RCC.
FINAL DESIGN
Final RCC Mix Design
Below are the design criteria for the RCC outlined in the Specification:
Provide adequate strength to meet structural design and durability criteria with
normal or above normal factors of safety;
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Minimize internal heat rise from hydration and subsequent stresses which may
develop, potentially leading to cracking;
Maximize stress relaxation through creep and elastic properties;
Provide a constructible mix;
Provide economy; and
Provide watertight lift joints.
The adopted mix design was selected based on the trial mix program data alreadydiscussed. The selected mix design (on the basis of compliance with expected
parameters, workability, ease of compaction and compatibility with a facing mix) was an
85+85+6.2(5)4X HC-M18mix with specific material properties summarized in Table 2.
Table 2 Summary of RCC propertiesProperty Age Value
3 days 0.36 MPaTensile Strength
28 days 1.16 MPa
28 days 4.4 MPaCompressive Strength Acc* 10.0 MPa
25% Modulus Acc 7.1 GPa
Mix Design Density - 2,239 kg/m3
Air Pot Density - 2,267 kg/m3
Air Content - 1.8%
*Acc = Accelerated cure at 90C, test at 14 days. Result is equivalent to 365-day strength
Based on all of the investigations undertaken on both the sandstone aggregate and the
RCC made from the sandstone aggregate, it was concluded that an RCC mix could bedeveloped to meet the design and construction requirements. This included sufficient
strength, workability and internal durability of the product.
Final Dam Wall Design
The potential for very low shear strength through weak planes, combined with
unfavorable defect orientation, resulted in a relatively large dam cross-section to resistsliding through the foundation. As a result, the dam section is much larger than would
ordinarily be required to meet acceptance levels for stresses within the dam body. The
final section comprises a 0.8H:1V downstream slope with a crest width of 6m. A typicalcross-section of the primary spillway section is provided in Figure 3.
8Denomination: 85+85+6.2(5)4X HC-M1 denotes 85 kg of cement + 85 kg of added pozzolan + 6.2%
water at 5 % passing 0.075 mm in the aggregate gradation at 4X the normal admix dose. M1 is Millmerran
commercial fly ash.
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Figure 3. Primary Spillway Cross Section
The stresses within the dam body were also reduced significantly by the very lowmodulus of elasticity of the sandstone RCC. The effect of the large cross-section
combined with the low modulus has ensured that even under the probable maximum
flood (PMF) and maximum design earthquake (MDE) events, only very minor tensilestresses will occur, and peak compressive stresses are only around 1MPa. Under normal
operation conditions, the compressive stresses are typically only 200kPa.
Despite the superior quality of the basalt, sandstone aggregate was still to be the preferredaggregate for the following reasons:
Exceptional performance in terms of thermal loading;
Reduced restrictions to placement schedule and cooling requirements;
Less expensive (including better efficiency through double shifting, and not
having a margin built into the price);
Assured supply;
No community impact;
Reduced environmental impact; and
No safety impact on public roads.
CONSTRUCTION
Construction on Wyaralong dam commenced in earnest in January 2010 with theexcavation of the foundation, and the dam started storing water in December 2010. Key
dates in the construction of Wyaralong dam are provided in Table 3. Figure 4 shows the
dam during construction.
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Table 3. Key Construction DatesArea Start Finish
Trial Section 26 March 2010 7 April 2010
Left Abutment 26 April 2010 6 May 2010
Right Abutment 10 May 2010 3 June 2010
Remainder of the Dam 7 June 2010 10 November 2010
Impoundment 17 December 2010
Figure 4. Wyaralong dam during construction
During the construction phase, minor changes were made to the design of the dam,
predominantly to optimize the construction program, improve quality and minimize risks.
The key changes included increasing the fines content of the RCC aggregate to minimizewastage as well as altering the retarder admixture to suit the climatic conditions and
placement rates.
These changes had a minor impact on the behavior of the RCC. As expected, strengths ofthe RCC dropped in response to the increase in fines, although the average strength was
still substantially higher than the allowable limit in the Specification. In addition, theModulus of Elasticity of the RCC was slightly higher than predicted, but this had an
insignificant impact on the stresses.
PROJECT COMPLETION AND OVERTOPPING PERFORMANCE
By early December 2010, construction of Wyaralong dam was completed to a stage
where water could be impounded. On December 17th
, the diversion pipe was pluggedduring a 12 hour operation.
An analysis undertaken using records of the last 40 years of flows on the Teviot Brooksuggested that the storage would take anywhere between 26 days to more than 1 year to
fill (assuming no outflows).
On December 27th
, a large flood event occurred in the Wyaralong catchment area,directing around 41,000 ML into the storage over a 27 hour period. The water in the
reservoir rose around 7.8m during this period. In the second week of January, extensive
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flooding rains hit south-east Queensland. Many parts of Queensland, including the state
capital city of Brisbane, were flooded. During this event, a further 60,000ML fell in theWyaralong catchment, of which 20,000 ML was stored in the reservoir. On January11
th,
just 24 days after impounding water, the Wyaralong reservoir reached full supply level
and the primary spillway initiated for the first time, passing around 40,000 ML and
peaking at an outflow of around 350 m
3
/s, as shown in Figure 5.
Figure 5. Wyaralong Dam first overtopping in January 2011(approx 1 of 15 AEP events)
Not only did Wyaralong dam prevent a substantial quantity of water from entering thealready swollen downstream river system, but it also delayed the peak of the flood and
has been reported to have prevented flooding of townships downstream of the dam. Thissuccess story is attributed to the fast construction program, which was only achievable
due to the use of RCC.
The unusually fast filling of Wyaralong dam has been the first major test in the design
and construction of the dam. Numerous dam safety instruments are installed in the damincluding 38 piezometers, 22 joint pins, 3 tiltmeters, seepage weirs and survey targets. In
general, the performance of the dam has been remarkably good, with piezometers
indicating low to normal uplift pressures, joint meters showing as expected movements,and seepage being particularly low.
CONCLUSION
In the earliest stages of the Wyaralong project, the onsite quarried sandstone aggregate
had many critics. In fact, many interested parties believed it was impossible to use as
RCC aggregate, predominantly due to its high absorption, its low specific gravity and theinitial fears that it was cemented with expansive clays.
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Extensive testing undertaken by the Wyaralong Dam Alliance indicated not only could it
be used as the aggregate, but it also offered some favorable characteristics, most notablythe extremely low modulus of elasticity. In summary, the key advantages of the use of
this aggregate were:
The low modulus of elasticity which minimized thermal stresses and avoided the
need to force cool the RCC. The low modulus of elasticity also meant that the properties of the dam closely
matched the foundation, thus minimizing the stresses in the dam under normaloperating, flood and earthquake load cases.
The relatively low cost of the aggregate as opposed to importing basalt aggregate.
Avoiding the heavy traffic on local roads (and impact on the local community) by
not importing aggregate.
Within 24 days after impounding water, Wyaralong dam spilled with a peak outflow of
around 350 m3/s. The dam passed its first test remarkably well, and is testament to the
idea that a low quality aggregate can produce a high quality result.
REFERENCES
Australian Standards, Aggregates and rock for engineering purposes, AS2758.1,
Standards Association of Australia, Homebush, New South Wales, Australia, 1998.
Herweynen, R., Montalvo, R. and Ager, J., Using a clay cemented sandstone as RCCaggregate a major breakthrough at Wyaralong Dam, ANCOLD / NZSOLD
Conference, Dam Decisions: Past Experiences, Future Challenges, 3-5 November 2010,
Hobart, Tasmania, Australia, 2010.
USACE, Thermal Studies of Mass Concrete Structures, ETL 1110-2-542, Washington,DC. 30 May 1997.