SALUDA DAM MIX DESIGN PROGRAM - Rizzo Assocrizzoassoc.com/.../saluda_dam_remediation_rcc_mix_design_progra… · The first two Phases ... the east of the southern side of the Dam

Final Presented @ USSD Annual Conf, Charleston, SC April14-16, 2003

SALUDA DAM REMEDIATION RCC MIX DESIGN PROGRAM

Paul C. Rizzo, P.E.1 Luis Ruiz Gaekel 2 John P. Osterle 3 S. Harold Moxley, P.E.4

ABSTRACT

The proposed remediation of Saluda Dam, located approximately ten miles to the west of Columbia South Carolina, consists of a 5,500-foot-long Rockfill Berm and a 2,200-foot-long Roller Compacted Concrete (RCC) Berm. This combination RCC and Rockfill Berm will be constructed along the downstream toe of the existing 200-foot-high earth embankment dam. Should the existing Dam fail during a seismic event, the combination RCC and Rockfill berm will serve a backup dam to prevent an uncontrolled release of Lake Murray. Due to the sensitive nature of RCC mixes and the unique properties of the on-site landfill fly ash proposed for use in the RCC, the selection of the optimum mix design for the Saluda Dam Remediation Project required a rigorous approach consisting of three phases over a period of two years. The first two Phases (I and II), consisted of a series of lab trial mixes. The results from these two phases produced a baseline mix, which was used as the starting point for Phase III. The Phase III Mix Design Program consisted of a full-scale, 4,500 cubic yard RCC trial testing and placement program. The objective of Phase III was to select an appropriate mix consistency, refine the mix design based on field performance, and to prepare RCC samples for direct shear strength testing. The trial testing program also provided the opportunity to test a variety of other construction methods and procedures related to landfill ash processing, aggregate production and stockpiling, and RCC placement. Utilizing the baseline mix, three cement contents (i.e., 125, 150 and 175 pounds per cubic yard) and two mix consistencies (i.e., Vebe times of 15 to 20 seconds and 30 to 40 seconds) were tested in the field. The test placements revealed the necessity to adjust the mix gradation to address segregation and bleed water problems and suggested that a Vebe time of 25-35 seconds was the most appropriate for the selected gradation, mix proportions, and available aggregate and fly ash. The data obtained during the Phase III suggests that all RCC mixes demonstrated acceptable field behavior. However, the final mix selection will be based primarily on one-year direct shear strength tests results from RCC test blocks and associated unit weight tests. The field performance of the selected RCC mix will be further assessed in another full-scale test program (Phase IV) scheduled about two months before the actual placement of the proposed RCC Berm begins. ____________________________________________

1 President - Paul C. Rizzo Associates, 105 Mall Blvd. Suite 270 E, Monroeville, PA 15146 USA 2 Proj. Coordinator – Paul C. Rizzo Associates, 105 Mall Blvd. Suite 270 E, Monroeville, PA 15146 USA 3 Proj. Supervisor - Paul C. Rizzo Associates, 105 Mall Blvd. Suite 270 E, Monroeville, PA 15146 USA 4Construction Eng. - South Carolina Electric and Gas, 111 Research Drive, Columbia, SC 29203, USA


INTRODUCTION Saluda Dam is owned and operated by South Carolina Electric & Gas Company (SCE&G) and is located on the Saluda River approximately ten miles upstream (west) of Columbia, South Carolina. The Dam impounds Lake Murray, which is one of the largest man-made lakes in North America. The Dam is a semi-hydraulic fill structure constructed in 1930 following typical “puddle dam” construction technology popular in the early 1900’s. The existing Dam and associated hydroelectric plant is shown on Picture 1. Table 1 presents a summary of the main parameters describing the existing Dam and the impounded Lake.

Hydroelectric Plant

Lake Murray

Existing Dam

Picture 1. View of Existing Dam

Table 1. Summary of the Main Parameters

Lake Area 78 Square miles Lake Capacity 2,096,000 acre feet Dam Length 7,800 feet Max Dam Height 211 feet Powerhouse Capacity 206 MW Original Construction Semi-Hydraulic Fill Original Completion 1930

The primary purpose of the Dam when originally constructed was for hydroelectric generation by the Saluda Hydroelectric Plant located at the toe of the Dam. As such, the Dam is under the jurisdiction of the Federal Energy Regulatory Commission (FERC). Today, the Lake is a source of cooling water for the coal-fired McMeekin Steam Electric Plant located along the downstream toe of the Dam, drinking water for Columbia and adjacent communities, and a major recreation and residential community with statewide economic benefits. Beginning in 1989, Paul C. Rizzo Associates (RIZZO) began a series of geotechnical investigations to assess the safety of the existing Dam, particularly under seismic loading. In this part of South Carolina, seismic design bases for critical facilities are, for all


practical purposes, governed by a postulated re-occurrence of the 1886 Charleston Earthquake. The Charleston Earthquake is estimated to have had a Magnitude in the range of 7.1 to 7.5 with a recurrence interval in the range of 650 to 1000 years. This event has been established as the Design Seismic Event (DSE) for assessing the integrity of Saluda Dam. A comprehensive liquefaction analysis and a post-earthquake stability analysis were conducted with the DSE yielding typical results as shown on Figure 1. This Figure shows that under certain assumptions, deemed by the authors to be very conservative, a major portion of the embankment will liquefy if the DSE occurs.

Figure 1. Existing Saluda Dam Factor of Safety Against Liquefaction Should Saluda Dam fail, approximately 120,000 people would be in jeopardy, water supplies for Columbia and surrounding communities would be lost, extreme environmental impacts would be realized and countless millions of dollars would be lost in the local economy. Consequently, a major remediation project has been developed for implementation in the 2002 to 2005 time period. The selected remediation consists of constructing a combination Roller Compacted Concrete (RCC) and Rock Fill Berms along the downstream toe of the existing Dam. This Project is the largest active Dam construction project in the United States today and the final Project will involve the placement of approximately 1.3 million cubic yards of RCC and a 3.5 million cubic yards of Rockfill. The rock required for the RCC and Rockfill Berm will obtained from an on-site borrow area located approximately ¼ mile to the east of the southern side of the Dam. The RCC Berm will be about 2,300-feet long and the Rockfill berm will be about 5,500-feet long. RIZZO has prepared the Bid Documents for the seismic upgrade of the Saluda Dam. The Bid Documents were issued to three bidders in early April and SCE&G awarded the contract to Barnard Construction Company in August of 2002. Construction commenced in September of 2002. As part of the remediation design effort for the RCC Berm, a four-phase RCC Mix Design Testing Program was initiated. This Paper presents the results from Phases I, II and III of the Testing Program.

RCC TEST PROGRAM OVERVIEW

-0.02 0.32 0.66 1.001.00 1.33 1.67 2.002.00 3.78 5.57 7.35


The RCC Mix Design Program was undertaken to evaluate RCC constituents and engineering parameters as they relate to the RCC Berm. The four Phases of this Program and their status are summarized below in Table 2.

Table 2. Summary of RCC Mix Design Program Phases

Phase No. Description Schedule

I Initial Lab Program (13 Mixes)

Started May 2000 Status: Complete; 365-Day

II Final Lab Program (7 Verification Mixes)

Started December 2000 Status: Complete; 365-Day

III On-Site, Full-Scale RCC Test Pads using on-site Borrow Area.

Started August 2001 Status: 90% Complete, 365-day

IV Pre-Construction Test Pad for Verification of Contractor Methodology Status: Scheduled for Summer 2003

Phase I and Phase II Mix Design Program (Lab Phases) The Phase I Mix Design Program was initiated in May 2000 to provide a preliminary evaluation of the properties of RCC manufactured with locally available materials. Aggregates were obtained from a local commercial quarry. A total of 13 mixes were prepared at a local lab facility in Columbia, SC. All mixes used sluiced and landfilled ash obtained from the on-site ash landfill. A wide range of cement and fly ash contents were tested which provided useful data to refine the goals of the second Phase of the Program. The Phase II Mix Design Program was undertaken to optimize the RCC Mix Design by building on the knowledge gained from the previous Phase. The Phase II Program was initiated in February 2001and the aggregates were quarried from the Saluda Spillway and taken off-site for crushing and processing. Based on information lgathered in Phase I, seven mix designs were developed for testing in Phase II. Two of these mix designs were based on the 125+250 (Cement+Pozzolan) mix and only moisture contents were varied. The intent was to evaluate the effect of water content on the strength of the mix. Mix 3 was the baseline mix determined from the Phase I Program and Mix 2 varied the moisture content of the baseline mix. Similarly, Mixes 5 and 6 were developed to compare moisture content with strength for mixes with a higher cementous content. A secondary objective of the Phase II Program was to determine the optimum fly ash content. Three additional mixes were designed with similar cement contents (125 pounds) but with fly ash contents ranging between 54 to 67 percent (Mix 1,1A 3 and 4). As with Phase I, McMeekin landfill Fly Ash was used in Phase II.


Full Scale Phase III RCC Mix Design The major goal of the Phase III Testing Program was to confirm that the RCC properties required for the structural design are ultimately realized in the completed structure. SCE&G awarded the Phase III Testing Program to Barnard Construction Company to define the appropriate RCC mix proportions to yield the required properties in the field, i.e., shear strength, “in situ” RCC density and acceptable lift joint quality (bond, no segregation). Additionally, this full-scale field test program was conducted to find site specific problems related to different stages of RCC technology, such as aggregate crushing, handling, proportioning and RCC mixing, transporting, placing, and compaction. The trial placements were utilized to simulate particular placement conditions, demonstrate various lifts joint treatments, and research a variety of other aspects related to RCC construction including facing systems and anchor bars. To achieve the outlined objectives, the Phase III Test Program included three sets of RCC Pads (A, B and C). Each set was placed with a different mix design. Pad A was placed with 175 pounds per cubic yard (pcy) of cement (Alternate I Mix), Pad B was placed with 125 pcy of cement (Primary Mix) and Pads C with 150 pcy of cement (Alternate II Mix). All mixes contained 150 pcy of McMeekin Fly Ash. Two different types of Pads (Type 1 and 2) were constructed with each of the three mix designs. While Type 1 Pads aimed to simulate general aspects of RCC construction (placeability, density, joint treatment, facing systems, etc); Type 2 Pads were specifically designed to determine the shear strength of horizontal lift joints at different joint maturities. The overall layout of the Phase III Project area is shown on Picture 2, and a typical Data Summary for Tests Pads Type 2 is depicted on Figure 2.

Picture 2. Phase III Project Test Area


PADS C2 DATA SUMMARYMIX 150+150

PAD C2-2Date of Placement:

12-Dec-01 Mix Data Start Batching: 7:52 PM Vebe Time (sec.): 33Start Spreading 8:10 PM RCC Placing Temperature: Unit Weight (pcf): 148.6

Stop spreading 8:15 PM Pad C2-2 Lift 2 Air temperature:Start Rolling: 8:15 PM Moisture (Plant) = 7.2%

Stop Batching: 8:10 PMStop Rolling: 8:20 PM Bedding mix = 3/4" MSA

Target Joint Maturity: 3000 deg-hr10-Dec-01 Actual Joint Maturity: 3033 deg-hr

Vebe Time (sec.): 25Continuos placement RCC Placing Temperature: 59.3 Unit Weight (pcf): 148.2

between Pad 1 and Pad 2 Pad C2-2 Lift 1 Air temperature: 48.9Moisture (Plant) = 7.2%

Figure 2. Test Pad Data Summary

Based on the test results of the Phase I and Phase II Programs, a mix containing 125 pcf of cement and 150 pcf of pozzolan was selected as the Primary Mix for Phase III. This mix design was selected to optimize density, strength, and modulus properties while meeting all minimum design strengths. Two additional alternate mixes were added to Phase III test program. The goal of these additional mixes was to assess the behavior of a different mix consistency and higher cement content, in order to address suggestions from the FERC and Board of Consultants. Initially, the alternate mixes were targeted for a Vebe time in the range of 15 to 20 seconds and selected cement content were 175 pcf and 150 pcf Both mixes contained 150 pcf of fly ash. As explained later on, a drier mix consistency (Vebe time 25-35 secs) was chosen for the alternate mixes and proportions adjusted accordingly. The final mix proportions are presented in Table 3.

Table 3. Final RCC Mix Design for Phase III Test Program

COMPONENT

Primary Mix (lbs./cy)

Vebe 25-35

Pad B

Alternate I (a) Mix

(lbs./cy) Vebe 15-20 s

Pad A

Alternate I (b) Mix

(lbs./cy) Vebe 25-30 s

Pad A

Alternate II Mix

(lbs./cy) Vebe 30 Pad C

Cement 125 175 175 150

Fly Ash 150 150 150 150

Aggregates 3467 3323 3364 3423

Water 252 289 270 259

Water Content (SSD) 6.3% 6.0% 7.0% 6.8%


PHASE III TEST PROGRAM EXECUTION

Materials for RCC Rock to produce aggregates was quarried from the gneiss formation located at the Test Borrow Area downstream Saluda Dam. The location of the Test Borrow Area in relation to the RCC Test Pad Area and the existing Dam is shown on Figure 3. The aggregate produced for the RCC, was divided into two piles. The coarser fraction size was from nominal 1-1/2-inch (MSA) to 3/16 inch. The fine fraction consisted of material minus 3/16 inch. All natural fines were included in this fraction, as no washing was performed during the crushing operations. Once blended, the aggregate had to comply with the specified gradation discussed later in this Paper.

Figure 3. Plan View of Saluda Dam Site

Meeting gradation specifications, with only two crushing stages, was somewhat problematic. Typically, the produced sand was coarse on the #4 to #16 sieves region and tended to stick to the lower limits of the specifications. On the other hand, the coarse fraction leaned toward the finer side of the specifications. As a combined effect, the overall aggregate gradation curve tended, to meander from the upper to lower limit of the envelope. To stay within specifications, a relatively low percentage of sand without ash was used (48 percent). Although this produced an aggregate that was within the aggregate band provided in the specifications, the general shape of the aggregate curve was not the most favorable. Therefore, the Project Specifications were modified to include a tertiary crusher.

Cement used at the Project was Holnam Portland cement Type I/II, produced by Holcim in the Columbia Region. Type II was desirable but wasn’t available in the area. Cement was transported to the Project in 25-Ton trucks and delivered to an intermediate storage tank deployed close to the mixing plant from which it was later transferred to the pugmill’s 60-ton silo.


Fly ash used for Phase III was taken from the onsite ash landfill. This ash is a by-product of the coal burning operation of McMeekin Station. The ash was excavated from the landfill, and blended and disked with an agricultural 36-inch disk and stockpiled in the landfill area. From there, it was hauled to a secondary surge stockpile to be later loaded into one of the five bin feeders. The bin feeder was utilized to proportionate and blend the fly ash with the aggregates. Finally, combined aggregate and fly ash was fed to the pugmill. Fly ash feeding was one of the main concerns during the Phase III Test Program. The potential for clumping and clogging was considered high, because of the sticky nature of moist fly ash. The Contractor took preventive measures such as installing breaking chains at the bin feeder, use of an auger inside the bin feeder, and close supervision on the bin hopper to assure continuos flow of fly ash. These measures managed to keep the fly ash feed within the initially specified limits of 15 percent. Nevertheless, uniformity tests performed during the program showed that this tolerance was too high to obtain an acceptable final product. As a consequence, fly ash feeding tolerance for future construction (as batched weight accuracy) was restricted to 5 percent maximum. Water for RCC mixing and curing was obtained from Lake Murray. The intent was to take advantage of the lower temperature water from the depths of the lake. Lab test results indicated that this water is acceptable for use in RCC. Time of setting (Vicat Needle) and compressive strength tests to compare Lake water versus tap water suggested that Lake water produces only a slight retardation in the setting time and a minor reduction of compressive strength.

RCC PRODUCTION AND PLACEMENT

RCC was produced in a GEARS Accumix 600B Plant, which is a modified ARAN 280B, a model required in the Project Specifications. ARAN 280B is a continuous pugmill mixer that meters material delivery by volume. The GEARS Accumix has been equipped with a scale backup system, which records material delivery by weight. Although, the maximum capacity of this plant is about 600-tons per hour it was typically, operated at 350-tons per hour during Phase III, due to the relatively small volume of the RCC placements. Plant calibration was performed before the start of RCC placement and was repeated at the end of the placements. The Accumix Plant at Saluda delivered material within the specified limits listed in Table 4.

Table 4. Accuracy Limits for RCC Materials Delivery as Delivered to the Mixer

Component Accuracy Limit (% by Weight) Cement +/- 2% Fly Ash +/- 15%*

Aggregates +/- 3% Water +/- 2%

Notes: (*) Fly ash proportioned at the bin feeder. Limit reduced to 5 percent for future construction based on results of Phase III.


A total volume of about 4,500-cubic yards of RCC was placed in Phase III Test Pads (Type 1, Type 2 and bases) between November 17 and December 14, 2001. Considering Contractor’s trial placements, ramps, and waste, the gross volume produced was above 6,000 cubic yards. Peak daily production was achieved on November 19, 2001 during the construction of the Pad Bases when 671 cubic yards of RCC was placed and compacted.

TRANSPORTING, DELIVERING, SPREADING AND COMPACTION

All RCC produced during Phase III Test Program was transported to the placement area by a ROTEC 18-inch conveyor belt system. A ROTEC Super Swinger 105-18 delivered the material to the point of deposition. It was equipped with an elephant trunk at the end of the belt to prevent segregation. The Super Swinger was controlled by joystick and was able to comfortably reach any point within the Pads limits. Once deposited on the Pad, RCC was spread by a D-5 Dozer in layers one-foot thick after compaction. The Dozer operator was assisted by a laser guided system to keep the lift surface leveled to grade. The main compaction equipment consisted of a Caterpillar CS563D, single drum, vibratory roller. Normally, eight single passes were applied to achieve the required density. In some cases, a different number of passes were applied in order to establish the correlation between number of passes and density. For restricted areas and compaction close to the forms, small compaction equipment was used: small Roller Compactor IR SD 175, Plate Type Compactors Wacker BS600 and BPU 3345A. Lift Joint Cleaning/Treatment Phase III mix design program aimed to evaluate the impact of joint maturity in the construction process and in the properties of the hardened RCC mass, as well. The first aspect was assessed by closely following construction operations in Type 1 - Pads and the later will be quantified when the 1-year shear strength of blocks are extracted from Type 2 - Pads become available. Table 5 shows the joint maturities studied during Phase III.

Table 5. Joint Maturities for Phase III Testing Program

Joint Type Maturity Normal Less than 200 degF-hr Cold 1 500 degF-hr Cold 2 1500 degF-hr Cold 3 3000 degF-hr

Cleaning of lift joints by air blowing was the standard treatment required to remove loose material and contamination. Washing of the surface was not required and was expected only for high maturity cold joints on lower Vebe time mixes. Nevertheless, some areas in Pad B (125+150) (which normally, doesn’t need washing because of its drier


consistency) required washing to remove laitance related to bleed water in the RCC. As this is a relatively rare occurrence, further assessments of this phenomenon are scheduled before placement in the RCC berm starts. As standard practice, cold joints were prepared for the next lift by removing laitance, loose debris, and contaminants with air jet. Pressure water washing was occasionally used when necessary. After preparation, the surface was maintained in a damp condition until placement of the subsequent lift. A vacuum truck was available at all times at the placement area to assist in the lift cleaning operations. Bedding Mix All lifts of Type 1 Pads received a bedding mix treatment on half of their exposed horizontal surface. On the other hand, Type 2 Pads were placed in pairs; while one of the pads was covered with bedding mix, its companion pad was left without treatment. This was done in order to compare shear strength of lift joints treated with bedding mix versus joints without treatment. Two different types of bedding mix were tried: Sand mortar and 3/4-inch MSA gravel mix. The initial design compressive strength of the bedding mix was 4,000 psi. However, this requirement was later modified to 2500 psi at one year based on the structural demands of the RCC. A local concrete producer located outside of the Project supplied bedding mix. Transport from the mixing plant to the test area was by mixer trucks.

TESTING DURING PHASE III Testing during Phase III covered three main aspects: Lab testing to determine RCC engineering properties; uniformity testing to evaluate pugmill performance and production uniformity; and miscellaneous field tests to assess constructability. A comprehensive Lab testing program was implemented to determine physical, thermal and expansive properties of the three different RCC Mixes tested during the Phase III Program. Part of this testing is standard practice in RCC construction and was in place to verify the quality of the RCC mix and its components during placement, others are specific, supplementary tests performed to gather information to achieve the goals of the Mix Design Program. The Phase III QC Subcontractor (S&ME) conducted most of the testing work with the assistance of the Contractor and under the supervision of RIZZO. The following tests were performed on fresh RCC during the Phase III Testing Program: Moisture content, unit weight (full mix and air free mortar), percent of coarse aggregate, and Vebe time. In addition, the following tests were performed on hardened cylinders of RCC: compressive strength, indirect tensile strength, and modulus of elasticity. Field tests consisted of nuclear gage density and moisture content.


Production Uniformity Testing A uniformity test was conducted to provide information on the suitability of the mixing plant, the properties of the mix by comparison to the mix design and the uniformity of the RCC after mixing, delivering, and spreading. Three samples were collected throughout a shift of placement and tested for moisture content, coarse aggregate content, unit weight of the full mix, unit weight of the air-free mortar, air content, and 7-day compressive strength. Cement content testing was optional during Phase III. The results were calculated and were compared to permissible limits to assess performance. These results are shown on Table 6. Uniformity test was required during Phase III Program at the start of placement only. However, an additional uniformity test was conducted due to the excessive variation on the 7-days compressive strength in the first test.

Table 6. Mixer Performance Test Results

TEST SERIES A

Variation (%) Nov. 20, 2002

SERIES B Variation (%) Nov.29,2002

MAX. ALLOWED DIFFERENCE

(%) Water content (%) 9.8 13.6 15 Air Content 40.0 21.5 100 Compacted Unit Weight 0.0 0.4 2 Unit Weight of Air Free Mortar 1.1 N/A 2 Coarse Aggregate content (+#4) 6.9 N/A 15 Vebe Time 2.9 3.2 ** Compressive Strength (7 days) 30.6 19.2 25

SUMMARY OF RESULTS

RCC Mix Design A key issue during Phase III testing was the definition of the optimum consistency of the RCC mix for Saluda RCC Berm. Three cement contents and two different consistencies were evaluated. The Primary Mix (125+150) was designed for a Vebe Time of 30 to 35 seconds and the alternate mixes with (175+150 and 150+150) a Vebe Time of 15 to 20 seconds. Aggregate gradation was kept constant for all mixes. After the first lifts of low Vebe Time mix were placed in Pad A, several problems were evident. These included, excessive paste migration to the lift surface, deep “steps” between roller lanes, and deep ruts of rubber tired equipment that produced mix “pumping” on the sides of the tire tracks. After evaluation, the alternate mixes were adjusted to a drier consistency (Vebe time 25 to 30seconds). Based on the results of the Phase III Program, the consensus between RIZZO and the Board of Consultants was that the optimum mix consistency should be around a Vebe time of 30 seconds.


RCC Mix Gradation In general, the combined gradation of RCC aggregate was within the specified envelope shown on Figure 4. Nevertheless, as mentioned above, some episodes where the gradation curve was close to the limits were experienced and in two cases, the aggregate gradation utilized in the RCC Test Pads plotted outside of the specified gradation band. As shown on Figure 5, this was especially evident during placement of Pad B (Mix 125+150), when coarse sand and aggregate variations caused segregation problems in the mix. The tendency for segregation and variability in the stockpiles was partially originated in the initial difficulties experienced to optimize stockpile-building techniques. Specifically, the specifications called for constructing the stockpiles in layers, with the material for each layer delivered in piles or windrows not to exceed about five-feet. Windrows initially exceeded five-feet and RIZZO directed the Contractor to separate non-conforming material. Although the Contractor was quality conscious and his corrective actions successfully resulted in an acceptable overall gradation, some variable spots remained in the piles. Problems in the mix developed when these materials were utilized. The problems experienced highlighted the critical importance of stockpile construction methodology in RCC and demonstrate the necessity of a close and strict supervision on this issue during the RCC Berm construction. Additionally, based on this experience, the gradation envelope for the RCC Berm has been adjusted, tightened and specified not only in the terms of percent passing, but also by percent retained on each individual sieve.

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Overall Average Combined Gradation(including Ash)

Fine Aggregate (-3/16) GradationS&ME Avg.(11-18-01)

Coarse Aggregate GradationAverage Samples by E.S.

11-28-01

Specs. Limits (including ash)

Figure 4. Phase III Test Program RCC Aggregate Gradation


PAD A

MIX 175+150 PAD B

MIX 125+150 PAD C

MIX 150+150

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Figure 5. RCC Aggregate Gradation

Unit Weight and Air Content

Unit Weight is a key design parameter, since the stability of a gravity structure relies on its magnitude. For Saluda RCC Berm, an average density of 146 pcf has been established as the design criteria. Table 7 presents densities of laboratory prepared cylinders. Except for the initial (175+150) Mix, laboratory unit weights for all other mixes exceeded the 146-pcf criteria. The average air content was in the range of 0.8 to 0.9 percent for all mixes.

Table 7. Lab Unit Weights and Air Content

Mix ID Vebe Time (seconds)

Average Unit Weight

(pcf) Air Content (%) Method of

Compaction

Alternate I (a) PadA (175+150) 15-20 145.7 0.9 Hilti Hammer Alternate I (b) Pad A(175+150) 25-35 146.5 0.8 Hilti Hammer Primary MixPad B (125+150) 30-40 147.4 0.8 Air Tamper Alternate IIPad C(150+150) 25-35 147.5 0.9 Hilti Hammer

As shown on Figure 6, unit weights of cores extracted from the pads, correlate reasonably well with lab and field density measurements. Cores extracted from the 175+150 Mix with low Vebe time (15 to 20 seconds) showed lower unit weights than other mixes. Overall, cores from Pad A (Mix 175+150) average 145.8 pcf, Pad B (Mix


125+150) reached 146.2 pcf and Pad C (Mix 150+150) showed the highest average at 146.7 pcf. A summary of results is presented in Table 8.

130

134

138

142

146

150

154

158

162

166

170

A1L1

A1L2

A1L3

A1L4

A1L5

A1L6

A1L7 U-4

U-5

U-6

B1L2

B1L3

B1L4

B1L5

B1L6

B1L7

B1L8

B1L9

C1L

1

C1L

1A

C1L

2

C1L

3

C1L

4

C1L

5

C1L

6

C1L

7

C1L

8

C1L

9

Sample ID

Uni

t Wei

ght (

pcf)

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

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e an

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ir C

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nt(%

)

Unit Weight(pcf) Field Density (Double Probe)

Plant Setting Air Content (%)

PAD A (175+150) PAD B (125+150) PAD C (150+150)

Air (%)

Unit Weight (pcf)

Plant Moisture Setting (%)

Field Density

Figure 6. Summary of Unit Weight and Air and Moisture Content

Table 8. Average Test Pad Unit Weights Based on Cores

Pad Pad Side/Area Average Unit Weight using Production Lift Cores Only (pcf)

Average Unit Weight of All Cores (Including initial lifts

used for mix adjustments) (pcf)

A Bedding Mix Area 145.4 145.1 A Non-Bedding Mix 146.1 145.2 A Entire Pad 145.8 145.2 B Bedding Mix Area 146 146.5 B Non-Bedding Mix 146.4 146.5 B Entire Pad 146.2 146.5 C Bedding Mix Area 146.3 146.3 C Non-Bedding Mix 146.9 147.0 C Entire Pad 146.6 146.7

As shown on Figure 7, both Mix 125+150 and Mix 150+150 reach the required 2,300 psi compressive strength. While Mix 125+150 needs about 250 days to attain this strength, Mix 150+150 reaches this level at 150 days. Compressive strengths at the design age (one year) estimated from 180-day strength data are 2,700 and 3,300 psi for Mix 125+150 and 150+150, respectively. Although compressive strength is not the mix selection criteria for Saluda Dam, it represents an overall indicator of material properties and since Mix 150+150 provides a comfortable margin to allow for production variability, data point towards using this mix for the Project. However, the final selection will be made on the basis of 1-year, post-cracked direct shear strength results from blocks extracted from the Type 2 Test Pads.


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si)

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Mix 125+150

Required 1-yearstrength

Required Average S trength = 2300 psi

Figure 7. RCC Comressive Strength Gain Preliminary Direct Shear Testing Program An important design consideration for the RCC Berm is the post-cracking peak and residual direct shear strength along the RCC Bedding joint. Based on dynamic finite element analyses of the proposed RCC Berm, conducted by RIZZO and the FERC, it is postulated that a tension crack may form along the entire width of the Berm during the DSE. Therefore, the sliding stability of the RCC Berm along this horizontal plane of the postulated crack must be confirmed by post-earthquake limit equilibrium analysis. The key parameter in this analysis is the one-year residual shear strength along an RCC lift joint. Picture 3. Extracting RCC Test Blocks


A preliminary Laboratory Testing Program was conducted at the United States Army Engineer Research and Development Center (ERDC) located in Vicksburg, Mississippi. The purpose of this preliminary testing program was to develop the appropriate testing and sample preparation procedures for the final testing program. RIZZO’s RCC Consultant, Dr, Ernie Schrader, Mr. Jim Hinds and Mr. Billy Neely from the U.S. Army Corps of Engineers (USACE) performed the testing and provided technical assistance in interpreting the results. This testing program consisted of performing Direct Shear Tests on cracked block samples of RCC (12 inches by 12 inches by 18 inches) approximately 275 days old, in general accordance with ASTM D 5607-95 and the International Society of Rock Mechanics document entitled “Suggested Methods for Laboratory Determination of Direct Shear Strength (ISRM, 1974). Special RCC test pads were constructed during the Phase III construction for the RCC test blocks. The blocks were cut using a circular diamond blade saw and extracted with a winch, as shown on Picture 3. The post-cracked shear strength of the RCC samples were tested at the following normal stresses: 25 psi, 150 psi, and 300 psi (i.e., 3.6 ksf, 21.6, and 43.2 ksf). We anticipate that sample displacements to provide representative residual strengths will be on the order of 0.1 to 0.2 inches. However, the block samples were loaded up to a maximum displacement of 0.5 inches to ensure that no further reduction in shear strength occurs. The sixteen RCC test blocks extracted from Test Pad A2-5 (175+150 Mix) were carefully wrapped in bubble plastic, strapped onto wooden pallets, and transported from the Saluda site to ERDC by truck. Once at ERDC, nine blocks were pre-cracked using three different methods: direct tension, indirect tension, and indirect tension with a notch. For each direct shear test, a block was then re-mated and placed in a special test frame constructed by the USACE personnel for use with other projects. The normal load prescribed for the test was applied by a hydraulic jack. This normal load was kept constant during the test by manually adjusting the hydraulic pressure. The test frame apparatus was loaded into a 440,000-pound capacity Universal Testing Machine using a forklift. The Universal Testing Machine was used to apply the shear load onto one half of the RCC test block. The RCC test block, test reaction frame, and a Universal Testing Machine are shown on Picture 4. Direct shear tests were also performed on several uncracked blocks to compare with results from other RCC dam projects.

Picture 4. RCC Direct Shear Test


The RCC test block was instrumented with four Linear Variable Differential Transformers (LVDT) wired to an automated computer data acquisition system. All four LVDT’s measured shear displacements of the RCC block as it was being sheared by the Universal Testing Machine. Two LVDT’s were positioned at both sides of the block along the lift joint, and the remaining two LVDT’s were positioned approximately eight inches from the lift joint to measure the rotation of the block during the test. The Data Acquisition System recorded displacements, shear load, and normal loads at a rate of two readings per second. The following loading rates were used to perform the test: 0.05 in/min (inches per minute) up to a shear displacement of 0.2 inches, 0.02 in/min to 0.45 inches, and 0.05 in/min to 0.6 inches. Therefore, most direct shear tests were completed in about 30 minutes. A typical plot of shear stress versus displacement is shown on Figure 8. The preliminary results from this testing program consist of failure envelopes for different shear displacements (i.e., 0.1, 0.2, 0.3, 0.4, and 0.5 inches). Failure envelopes for pre-cracked samples by direct and indirect tension are presented on Figures 9 and 10, respectively. Preliminary friction angles and apparent cohesion’s for Mix 175+150 as a function of shear displacement are provided in graphical form on Figures 11 and 12. As shown on the referenced figures, both the friction angle and apparent cohesion of the RCC decrease as the shear displacements increase. Block rotations were calculated to be less than one degree. A detailed work plan was developed for the final RCC Direct Shear Testing Program based on the preliminary results obtained from the Preliminary Testing Program. The results from the Final Direct Shear Testing Program will be used to help select the appropriate RCC mix for the Saluda Dam Remediation Project. The Final testing program will utilize a single method of pre-cracking the samples. Pre-cracking the block by direct tension was the most difficult and labor intensive method tried in the laboratory and was also believed to be the least representative of a crack occurring along an RCC lift line due to seismic tensile stresses. The indirect tension methods were the easiest to perform in the laboratory and were believed to be more representative of a crack induced by seismic stresses. Accordingly, the indirect tension pre-cracking method will be used in the Final Testing Program. This method consists of cutting a one-inch wedge along the lift line of each RCC test block with a circular saw. A 9/16-inch diameter steel bar surrounded by a steel wedge is then inserted into all four sides of the one-inch wedge. The block is then positioned in a specially fabricated reaction frame and loaded in compression on two sides by hydraulic jacks as shown on Picture 5. By saw cutting the wedge into the RCC block serves two purposes: 1) the crack can be accurately aligned on the RCC lift line, and 2) the block is actually loaded in direct tension as shown on Figure 13.


Nominal Normal Stress = 300 psi

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Shear Displacement, in.

Shea

r S

tres

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si

Corrected for actual shear plane areaConstant (original) shear plane area

Constant (orig inal) bearing area: Peak shear stress = 559.1 psi Displacement @ peak shear stress = 0.0319 in. Shear stress @ 0.1- in. displacement = 387.6 psi Shear stress @ 0.2- in. displacement = 341.4 psi Shear stress @ 0.3- in. displacement = 312.7 psi Shear stress @ 0.4- in. displacement = 305.6 psi

Actual bearing area: Peak shear stress = 560.9 psi Displacement @ peak shear stress = 0.0319 in. Shear stress @ 0.1-in. displacement = 391.6 psi Shear stress @ 0.2-in. displacement = 348.4 psi Shear stress @ 0.3-in. displacement = 322.5 psi Shear stress @ 0.4-in. displacement = 318.5 psi

Picture 5. RCC Block Testing

Figure 8. Direct Shear Stress Versus Shear Displacement Normal Stress=300psi


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ess,

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Peak

displacement = 0.1 in.

Displacement = 0.2 in.




Shear stress corrected for actual shear plane area

Avg. angle of friction = 52.26Avg. cohesion = 11.08psi

Figure 9. Preliminary Failure Envelopes for Samples Pre-Cracked by Direct Tension

Saluda Dam RCCPrecracked - Indirect w/Notch

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angle of friction = 60.0 deg; cohesion = 58.9 psiangle of friction = 51.2 deg; cohesion = 28.9 psiangle of friction = 48.4 deg; cohesion = 21.2 psiangle of friction = 46.1 deg; cohesion = 24.2 psiangle of friction = 46.1 deg; cohesion = 14.3 psiangle of friction = 45.7 deg; cohesion = 17.1 psi


Figure10. Preliminary Failure Envelopes for Samples Pre-Cracked by Indirect Tension


Saluda Dam RCCPrec ra cked - D irect

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ictio

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eg

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hesi

on, p

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Shear stress corrected for actual shear Angle of Frictionplane area

CohesionCohesionAngle of Friction

Figure 11. Preliminary Shear Strength Versus Displacement for Samples Pre-Cracked by Direct Tension

Saluda Dam RCCPrecracked - Indirect w/Notch

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eg

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30

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Co

hesi

on, p

si

Angle of FrictionCohesionCohesionAngle of Friction


Figure 12. Preliminary Shear Strength Versus Displacement for Samples Pre-Cracked by Indirect Tension


Figure 13. Direct Tension Diagram

Tensile Strength Tensile strength is not a primary design criteria for the RCC Berm, but it is a relevant parameter in both the thermal and structural analyses. Tensile strength was evaluated by the Splitting Test Method; also know as the Brazilian Method. As shown on Figure 14, split tensile results at 180-days from all mixes tried in Phase III fall in the range of 12-15 percent of the compressive strength. Using correlation equations developed by E. Schrader, split test results were converted to Direct Tensile Strength. Estimated long-term static direct tensile strength for the RCC mass is within 9 to 12 percent of the compressive strength at the age. Same parameter for untreated lift joints (no cold joints) has been estimated as 5-6 percent of the compressive strength.

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C o m p re s s iv e S tr e n g th (p s i)

Split

Ten

sile

Str

engt

h (p

si)

1 2 5 + 1 5 0 P re d c i te dM ix 1 2 5 + 1 5 0

M ix 1 5 0 + 1 5 0

M ix 1 7 5 + 1 5 0

Figure 14. Split Tensile Strength Versus Compressive Strength


Compaction and Field Densities

The Phase III Test Program specification required a minimum field density of 146 pcf or 97 percent of the theoretical air free density (TAFD) whichever was greater. The actual density reference values varied for each mix design. As a standard procedure, eight single drum passes were applied to the RCC to get the required compaction. Mixes with a wetter consistency appeared to reach full compaction at a lower number of passes as compared to the drier consistency mixes. Compaction beyond eight single passes was found to bring marginal benefits only. Nevertheless, it was found that pausing for some minutes after initial compaction; then applying additional passes before initial set, was effective in increasing density. Preliminary indications are that this effect has been related to bleed water in the RCC mix. Further lab testing to investigate this observation is scheduled. As depicted in Figure 15, the impact of this effect was particularly evident during placement of Pad C Mix (150+150), which was the last pad to be constructed. This technique was effectively utilized during the construction of Pad C to achieve the required RCC density. Field densities in Pad C were less variable than in other Pads and all nuclear gauge average readings were above 146 pcf.

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9Sample ID

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pcf)

PAD A (MIX 175-150) PAD B (125-150) PAD C (150-150)

Field Density

Lab Unit Weight Cores

Figure 15. Field Densities and LAB Unit Weights for All Pads

CONCLUSIONS

Lessons learned during the execution of Phase III highlighted the importance of undertaking a full-scale Mix Design Program. All the parties involved, Owner, Designer and Contractor concurred that benefits offset, by far, the costs incurred in the program and agreed that such an exercise shall be a must in large dam projects such as Saluda.


The following paragraphs outline some of the lessons learned in Phase III RCC Mix Design Program. Mix Consistency The consensus between RIZZO and the Board of Consultants in Phase III was that the optimum consistency, for a RCC mix with Saluda materials and gradation, should be a Vebe Time of about 30 seconds. Although wetter mixes (Vebe 15 to 20 seconds) showed less tendency to segregate during placement, they also showed excessive paste migration to the lift surface, presented deep roller marks and ruts from tired equipment, and required a higher cleaning effort. Gradation and Segregation Although the gradation of RCC aggregate during Phase III was, in general, within the specified envelope the aggregate crushing system must be improved for the RCC Berm construction. The available crushing scheme produced a combined aggregate curve that tended to be fine on the gravel and coarse on the sand. This contributed to mix segregation and bleed water during placement. The results of Phase III suggest that a third crushing stage might be necessary during the main job execution. Mix Segregation problems were also caused by aggregate variability in the stockpiles. Stockpile segregation was partially due to pile building techniques applied at the beginning of the Project. Although corrective actions were successfully applied and a final overall acceptable product was achieved; some variability remained in the piles. In order to have a gradation, which is less susceptible to segregation, the aggregate specified for the main job is slightly finer than the Phase III gradation in the 3/4-inch region. Also, to avoid aggregate gradation meandering, the specifications require that the amount of material retained on each individual sieve be within a specified range. RCC Production Fly ash feeding system required close supervision during the Phase III Program. The system used by the Contractor was able to deliver fly ash within the specified accuracy of 15 percent by weight; nevertheless, uniformity tests showed that ash variations had an important effect in water demand and density in the mix. In consequence, this tolerance was restricted to a maximum of five percent for the RCC Berm construction. Density and Unit Weight An average density of 146 pcf can be achieved in the field. Average nuclear gauge (double probe) readings were equal to or higher than 146 pcf in all Pads. Pad A and Pad B both had the same average density of 146.1 pcf. Pad C showed not only the highest average field density (146.9 pcf), but also showed less scattered results. Except for the Alternate I (a) Mix (175+150), which averaged 145.7 pcf, unit weights from laboratory


cylinders were above 146 pcf. The Primary Mix (125+150) and Alternate II Mix (150+150) showed a mean unit weight around 147.5 pcf while the modified Alternate I (b) Mix (175+150) reached 146.5 pcf. Density measurements from core samples taken from the test pads indicate that the required density is also achievable in the field. Average air content measured at the lab was in the range of 0.8 to 0.9 percent for all mixes. Bedding Mix Sand mortar bedding mix was compared to 3/4-inch MSA gravel bedding mix. Both mixes showed good performance in the field. Sand mortar was easier to place and distribute over the RCC lift surface, but the trench cut evaluations, showed that the gravel bedding mix interlocks better with RCC, resulting in a more homogeneous concrete mass. When bedding was used as a facing system, both types of mixes appeared to be suited for this application. However, it was evident that when using sand mortar, more skilled manpower and guidance were necessary to obtain acceptable results. Properties of Hardened RCC Hardened RCC Properties during Phase III are consistent with predictions made on the basis of experienced gained from the Phase I and II laboratory Programs. Compressive strength test results indicate that required one-year design strength of 2300 psi icon be achieved during construction. Elastic modulus values obtained in Phase III are also consistent with the previous Mix Design Program Phases.

SUMMARY This Paper presents a detailed description and documentation of the RCC Testing Program and laboratory for the Remediation of the Saluda Dam. The focus of the Paper was to describe various field and laboratory activities. The Phase III Test Program included a full-scale test program and construction project undertaken to confirm design parameters and material properties for the Roller Compacted Concrete (RCC) and Rockfill Berms of the Saluda Dam Remediation Project.