SAN ROQUE MULTIPURPOSE PROJECT PERFORMANCE

8/18/2019 SAN ROQUE MULTIPURPOSE PROJECT PERFORMANCE

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Hosted by

Black & Veatch Corporation

GEI Consultants, Inc.

Kleinfelder, Inc.

MWH Americas, Inc.

Parsons Water and Infrastructure Inc.

URS Corporation

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 region’s

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

Library of Congress Control Number: 2011924673ISBN 978-1-884575-52-5

U.S. Society on Dams

1616 Seventeenth Street, #483

Denver, CO 80202

Telephone: 303-628-5430

Fax: 303-628-5431

E-mail: [email protected]

Internet: www.ussdams.org

U.S. Society on Dams

Vision

To be the nation's leading organization of professionals dedicated to advancing the role of dams

for the benefit of society.

Mission — USSD is dedicated to:

• Advancing the knowledge of dam engineering, construction, planning, operation,

performance, rehabilitation, decommissioning, maintenance, security and safety;

• Fostering dam technology for socially, environmentally and financially sustainable water

resources systems;

• Providing public awareness of the role of dams in the management of the nation's water

resources;

• Enhancing practices to meet current and future challenges on dams; and

• Representing the United States as an active member of the International Commission onLarge Dams (ICOLD).


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Performance Monitoring Assessment 1479

SAN ROQUE MULTIPURPOSE PROJECT PERFORMANCE MONITORING

ASSESSMENT

Michael Pavone, P.E.1 Joseph Ehasz, P.E.

2

Stephen Benson, PE.

3

Bonnie Witek, L.G., L.E.G.4

ABSTRACT

The San Roque Multipurpose Project (SRMP) is a major hydroelectric and flood-control project in Asia. The 200-meter-high, central clay core, rock-fill dam is the 12th highestdam of its kind in the world. It is located on the Agno River in the Philippines andimpounds a reservoir with a surface area of about 12.8 square kilometers that providesflood attenuation benefits downstream of the dam. The SRMP has an installed ratedcapacity of 411 megawatts.

URS was awarded two contracts totaling $705 million for the engineer-procure-construct(EPC) work by San Roque Power Corporation. Performance monitoring of the project began prior to first filling of the reservoir and continues on a regular schedule.

Key design requirements included stringent leakage criteria and reliability in thisseismically active region. The performance monitoring program for San Roque Damincludes instrumentation monitoring and routine visual inspections. The program isintended to provide verification of design parameters, analyze adverse effects, verify performance, and identify any potential safety concerns. Instrumentation includes: 1) piezometers, 2) movement survey monuments, 3) seepage flow measurement stations, 4)rainfall gauge, and 5) turbidity meters.

This paper presents the evaluation of monitoring program data with regards to pore water pressures, seepage, and deformation considering the designer’s (URS’) prediction of performance. Performance prediction is generally tied to the appropriate factors of safetywhich, along with other design parameters such as calculated deformations, seepageflows and piezometric pressures, determine the desired threshold limits for the designconditions.

INTRODUCTION

Located in the mountains 200 kilometers north of the capital of Manila in the Philippines,the SRMP is a major hydroelectric and flood-control project in Asia. Its major feature is a

1 Manager of Engineering, URS Energy and Construction, Bellevue, Washington, [email protected] Vice President, URS Energy and Construction, Bellevue, Washington, [email protected] Manager of Geotechnical Engineering, URS Energy and Construction, Bellevue, Washington,[email protected] Senior Engineering Geologist, URS Energy and Construction, Bellevue, Washington, [email protected]


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21st Century Dam Design — Advances and Adaptations1480

200 meter high central core, rock-fill dam which is the 12th highest dam of its kind in theworld. Often called a national flagship project for the Philippines, in addition to providing flood control and irrigation, the SRMP supplies clean hydroelectric power forcommercial and industrial use to a region that desperately needs it. In 1998, URS wasawarded contracts totaling $705 million for the engineer-procure-construct (EPC) work

by San Roque Power Corporation, an international consortium led by United States-basedSithe Energies, and presently under the joint venture of Marubeni and Kansai Electric.San Roque Power worked under a build-operate-transfer contract with the state-run National Power Corporation.

The dam, spillway and powerhouse and appurtenant structures were constructed entirely by URS owned equipment and staff composed of 80 expatriate employees and as many as4,000 local Pilipino workers. The Project was designed by URS Office staffs in NewYork and Bellevue, Washington, as well as local site support staff at the Project Site.

Major project features include:

• An earth and rockfill dam, 200 meters high. The dam consists of 41 million cubicmeters of combined gravel fill and rockfill shell zones, filter, drain and transitionzones and an impermeable core.

• A concrete spillway with six 15-meter-wide by 18.6-meter-high radial gates, and

a 485-meter-long, 100-meter-wide concrete chute ending in a flip bucket. Thespillway is designed to pass 12,800 cms.

• A power tunnel, 8.5 meters in diameter and 1,300 meters long which includes a pair of wheel gates in a shaft near the intake to shut off flow, a surge shaft forcontrol of hydraulic gradients and a steel-lined high-pressure segment.

• A low-level outlet tunnel, 5.5 meters in diameter, 1,300 meters long with an

intake and flow control by a set of slide gates near the dam centerline.• Three diversion tunnels, two which are 10 meters wide by 15 meters high and one

which is 6 meters wide by 6 meters high.

• Below ground powerhouse with three 137 MW turbine generators.

• Electrical substation and nine kilometer long 230 kW transmission line.

In addition to the dam’s production of non-polluting hydroelectric power, its five-square-mile reservoir serves as a settling basin that entraps sediment above the dam, thusimproving water quality below the dam. These project features are shown on theaccompanying photograph.


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PROJECT DESCRIPTION

General Geology

The San Roque Multipurpose Project is located on the southern flank of the CentralCordillera, the mountain highlands that make up the northwestern part of the island ofLuzon. The project takes advantage of the major change in topography at the southernedge of the Cordillera where the Agno River flows from a steep, narrow-walled canyonin the mountains out into the relatively flat Central Valley basin of Pangasinan Province.

The basement rocks of the southern part the Central Cordillera include pre-Tertiary phyllite, schist, plutonic rocks, pillow basalt, chert, and a variety of clastic rocks. Thespecific lithologies and deformational history of this sequence varies widely throughoutthe region. Overlying the basement complex are probable Eocene to lower Miocenevolcanic rocks composed of andesite flows, basalt flows, and breccias and other pyroclastic rocks intercalated with chert, argillite, sandstone, and conglomerate, known asthe Pugo Formation. Both of these rock sequences have been intruded by Tertiary plutons, generally middle Oligocene to late Miocene. Deformation associated with theintrusives has locally deformed the Pugo Formation. A thick, early Miocene toPleistocene, sedimentary section with some volcanic components is draped over thesouthern and western flanks of the Central Cordillera and is present as the KlondykeFormation in limited areas at the project. A number of early Quaternary intrusive rocksare associated with the extensive mineralization that has been exploited in the Baguiodistrict in the upper reaches of the reservoir.


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Most of the major project structures (dam, spillway, and most of the tunnels) are foundedon or excavated in metamorphosed volcanic, sedimentary, and volcaniclastic rocks, probably equivalent to the Pugo Formation. Various diorite intrusions of the AgnoBatholith are also present, especially in the powerhouse area, on the left bank of the riverat its last major bend between the dam and the powerhouse, and in the spillway chute

area. The Klondyke Formation forms a sedimentary sequence of conglomerates,sandstones, and claystones that thickens down dip south and east of the dam.

Bedrock at the dam is primarily volcanic and volcaniclastic rock, which has been subjectto low grade metamorphism and intruded by diorite. The dominant foundation rock typeis metamorphosed volcanic breccia, with minor intercalations of fine-grainedmetavolcanic/metasedimentary rocks. Numerous joints are infilled with calcite, quartz,and other minerals.

Pleistocene to Recent alluvial channel deposits of the Agno River are found in the steepnarrow-walled canyon where the dam is located as well as in the broad valley

downstream. Alluvial terrace deposits of the Agno River and alluvial fan deposits fromtributary drainages are also present along the sides of the riverbed in some areas.Landslide deposits are also widespread upstream in reservoir and along the front of theCentral Cordillera, most notably east of the powerhouse.

Abutments

The abutments of the dam are primarily underlain by volcanic breccia with minoramounts of metavolcanic/metasedimentary rocks. The diorite intrusion crops out at thesurface in only a few places, but is present in the subsurface of the left abutment and has probably contributed to the alteration of the volcanic breccia by contact metamorphism orthe source of hydrothermal fluids. Both abutments had a significant thickness ofoverburden, consisting of soil and completely weathered rock. The overburden thicknessranged from more than 20 meters on the upper left abutment to zero where slightlyweathered rock crops out along the left bank of the Agno River. In general, theoverburden was thicker on the left abutment than the right abutment, where soil andcompletely weathered rock was generally 5 to 15 meters thick.

Below the overburden, the volcanic breccia of the dam abutments generally becomeshighly weathered. The rock has significant cohesion. Joints and other structures aremeasurable in the rock. They are generally tight but can be open with or without filling.Although weathering intensity generally decreases with depth, the weathering profile ishighly variable. Weathering appears to be controlled by permeable fractures and zones ofrelatively competent rock are underlain by moderately to highly weathered material.

The crystalline bedrock at the dam site exhibits varying degrees of fracturing as a resultof the stresses associated with tectonic history. In general, the meta-volcanic and meta-sedimentary rock and the volcanic breccia are more highly fractured than the diorite unit.In most locations, more than 3 joint sets can be observed. Joint spacing for each joint setvaries from about 2 to 20 cm. The most highly fractured areas are often at the margins of


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the contact with diorite intrusions.

A number of shear zones are present on the abutments as observed both in borings and inthe excavation. These zones are characterized by crushed rock and clay gouge that mayvary in thickness from less than a centimeter to several tens of meters. Almost every core

boring in the dam footprint encountered sheared zones. Most of the shear zones observedin the dam excavation are less than two meters wide. Some shear zones are associatedwith diorite intrusions. Slickensides were observed in many of the shear zones. The presence of calcite veins and other mineral infillings in many of the shear zones indicatesthat these are not geologically recent features. The combination of the above poor rockconditions made foundation treatment very difficult. The design-build nature of thecontract and project enabled the close coordination of design and construction to meet thefoundation treatment objectives.

River Channel

The riverbed area is generally covered by various alluvial deposits. Most of the alluviumat the dam site consists of Agno River channel deposits of sand, gravel, cobbles, and boulders. Older channel alluvium can be distinguished from younger more recentdeposits, generally on the basis of density. The deposits vary in thickness from 4 to 15meters, but average close to 15 meters in the main river channel under the dam.

Bedrock beneath the alluvium is similar to that found on the abutments, primarilyvolcanic breccia with lesser amounts of meta-volcanic/meta-sedimentary rock and diorite.Unlike the abutments, the weathering profile was much shallower, with residual soil andcompletely weathered rock being absent, and a rather quick transition into moderately toslightly weathered rock. Like the abutments, there are numerous joints and shear zones inthe bedrock mass, however several features are especially distinctive. A narrow deeplyincised old river channel, eroded into the bedrock, crosses the main dam axis. Two majorshear zones, one approximately 20 meters wide and the other about 30 meters also crossthe dam axis. These shear zones are characterized by alternating zones of clay gouge,crushed rock, and highly fractured rock. Where intercepted, these shear zones areassociated with significant water inflows.

Foundation Excavation Criteria

All areas of the core trench are founded on rock. The depth of excavation to the finalsurface were based on the assessment of rock quality and consisted of two requirements:(1) the rock must be treatable by grouting and be hard enough to allow setting of packersfor grouting and (2) where geologic features (joints, fissures, or shear zones), areencountered, the features must be tight and characterized by a general absence of internalerosion of erodible material (piping).

A method specification based on equipment performance was developed to achieve theabove design objectives. Based on the results of field trials, the limit of core zoneexcavation is specified as rock of hardness and structure such that the material can no


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longer be effectively removed by a three-tooth ripper of a Caterpillar D-9 tractor dozerequipped with a ripper of standard manufacturer’s design, working on a production basis,and operating in low gear.

The design of core zone foundation required shaping of the rock to provide a generally

uniform foundation surface that improves long-term performance of the dam by reducingthe potential for differential settlement, cracking, and seepage paths.

The design of the shell zone foundations required removal of any unsuitable materials toa level where the foundation materials have strength and elastic characteristics equal to orgreater than the overlying shell zone materials. The acceptance criterion for shell zonefoundation on rock was based on equipment performance and verification of rock qualityconditions. The limit of shell zone excavation in rock was specified as excavation to arock surface such that materials can no longer be effectively removed by the blade of aCaterpillar D-7 tractor dozer equipped with a blade of standard manufacturer’s design,working on a production basis, and operating in low gear.

Alluvium at the dam site consisted mostly of gravel and cobbles, with lesser amount ofsand and boulders. Older alluvium at depth was distinguished from younger alluviumnear the surface on the basis of density. Older alluvium is very dense and can beexcavated in near-vertical cuts. Correlation of shear wave velocity with the potential forsoil liquefaction and the results of large-scale density and gradation test were used as a basis for determining the thickness and extent of alluvium to be removed and replacedwith compacted fill for the foundations of the shell zones of the dam.

Grouting Program and Foundation Preparation

The dam foundation grouting program included a combination of single and double linegrout curtain, consolidation grouting, and stitch grouting. Grouting was accomplishedfrom both the surface and the grouting galleries (Figures 8 and 9) in the foundation rock.

Curtain grouting consisted of a row of grout holes near the main dam axis, designed todecrease seepage through the foundation rock and abutments. The grout curtain is a planeinclined 70 degrees upstream to improve its intersection with vertical joints and shearzones. In general, the grout curtain extends 80 meters below the core trench foundation.On the upper abutments, the depth is gradually reduced to 40 meters as the reservoir headis less in these areas. Because of water inflows into the gallery associated with the shearzones, a double curtain was installed between stations 7+95 and 8+95 from the lowergallery.

Consolidation grouting consists of a grid of relatively shallow grout holes in the maindam core trench foundation to decrease the permeability of surficial fractured zonesadjacent to the grout curtain and reduce the potential for embankment materials to becarried into the foundation rock mass (piping). Consolidation grouting in the groutinggalleries was done to repair rock that may have been opened by excavation and to reduceseepage flow into the galleries on the upstream (grout curtain) side.


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Stitch grouting was used for treatment of features such as a shear or fracture zone in a pattern of holes designed to intersect that feature at various depths at angles favorable togrout penetration. Stitch grouting was done from the surface and extends the full width ofthe core trench if the feature is a significant seepage pathway. Stitch grouting was

performed for the full core trench width in the 20 and 30 meter wide shear zones in theriverbed portion of the core trench.

Embankment Section — As Constructed

The general arrangement and dimensions of the zones within the embankment dam areshown on the typical section on Figure 1. The maximum height of the dam from the coretrench to the crest is 200 meters. Both the upstream and downstream slopes are 2H:1V.The crest width is 12 meters and the width of the core at the top is 6 meters. The centralimpervious core has an upstream and downstream slopes of 0.2H:1.0V.

Figure 1. Idealized Section on Alluvial Foundation

• Zone 1 Upper Core Material ( PI ≥15)

• Zone 1A Base of Core (PI > 20)

• Zone 1B Core - Material obtained from overburden excavation (% fines>

20)

• Zone 2 Transition

• Zone 3 Filter

•

Zone 4 Drain• Zone 5 Clean Shell (Processed from alluvial borrow or rock quarry areas –

0-30% passing No. 4 sieve)

• Zone 6 Shell (0-50% passing No. 4 sieve)

• Zone 7A Random Rockfill (obtained from rock excavation – 0-60% passing No. 4 sieve)

•

Zone 7B Select Rockfill (obtained from rock excavation – 0-30% passing No. 4 sieve)


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• Zone 8 Riprap

•

Zone 5/7B Shell (co-mingled with alluvium and rockfill)

• Zone 6/7B Shell (co-mingled with alluvium and rockfill)

• Zone 6/7A Shell (co-mingled with alluvium and rockfill)

The zone arrangement depicted on Figure 1, evolved as construction progressed in orderto make maximum utilization of the required excavation material from the damfoundation and spillway. A plan view of the embankment and project is shown on Figure2.

Figure 2. Plan view of the SRMP

INSTRUMENTATION

The instrumentation monitoring and periodic visual inspections taken collectively provided an overview of dam performance during construction, first reservoir filling, andlong-term operation. The main objectives of instrumentation monitoring and visualinspections are: verify project performance, identify any potential safety concern,analytical assessment and prediction of future performance. Within the analyticalassessment, instrumentation data can verify design assumptions and constructiontechniques as well as analyze adverse events that may occur during the construction ofthe dam. Prediction of future performance is associated with deviations of data trends andidentification of unusual data.

To perform these verifications and analyses, various instruments were placed at specificlocations of the structure during construction. These instruments measure:


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• pore-water pressures within the dam and its foundation

• seepage

• deformation

• precipitation

•

turbidity

Most of the embankment piezometers and settlement cells are located at five differentelevations along four lines perpendicular to the dam axis. The four lines are at damstation 5+00, 7+00, 9+25, and 11+00. Station 9+25 is near the maximum section of thedam. Foundation piezometers are located in the grouting galleries underneath the dam inholes oriented upstream and downstream of the grout curtain. Additional abutment piezometers are located in the gallery access adits (Figure 9). Flow measurement stationsare located in the galleries, adits, and at the downstream collector pipe near the toe of thedam. Movement survey monuments are located on the surface of the dam. A plan viewand cross-sections of the instrument locations are shown on Figures 3 through 7.


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Figure 3. Plan View of Instrumentation


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Figure 4. Instrumentation Section – Station 5+00




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Pore Water Pressure

Piezometers are used to monitor pore water pressure and free water surfaces within the

dam foundation and abutments and to monitor uplift pressure beneath the spillway ogeesection. Pore water pressure measurements are necessary to determine the phreaticsurface in the embankment and thus evaluate slope stability, evaluate design assumptions,and seepage or other changes which could indicate changing conditions within the core orfill. During early reservoir filling, piezometer readings were used to verify phreaticassumptions used in the analyses, evaluate pore pressure dissipation across a givensection of the dam and to assess the effectiveness of the impervious core and foundationgrouting.

Four types of piezometers were used for the project in order to increase reliability ofresults. These include:

• Vibrating Wire Piezometers

The vibrating wire (VW) piezometer is an accurate piezometer that is relatively easy toinstall and monitor. The VW piezometer converts water pressure into a frequency signalvia a diaphragm, a tensioned steel wire, and an electro-magnetic coil. The instrument isdesigned so that a change in pressure on the diaphragm causes a change in tension of thewire. When excited by the electro-magnetic coil, the wire vibrates at its naturalfrequency. The vibration of the wire in the proximity of the magnetic coil generates afrequency signal that is transmitted to the readout device. The readout device processesthe signal, applies calibration factors, and displays a reading in the required engineering

unit. A total of 27 VW piezometers were installed at various levels in the dam. Twenty-five additional VW piezometers were installed in the upstream holes drilled from thegalleries.

• Pneumatic Piezometers

Pneumatic piezometers were used as an alternative measuring method to the VW piezometers and, as a back-up in the event that a VW piezometer(s) were damaged. The


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advantage of the pneumatic piezometer is that it uses a simple diaphragm with noelectrical parts and therefore is not susceptible to lightening damage. In order to enhancelong-term performance, corrosion-resistant plastic construction, polyethylene tubing, andin-line filters were used at all connectors. A total of 7 pneumatic piezometers wereincluded in the dam.

• Open Standpipe Piezometers

Open standpipe piezometers were installed along the downstream toe of the dam tomeasure pore water pressure in the abutments. Four open standpipe piezometers wereinstalled at locations shown on Figure 3. The open standpipe piezometers included a drillhole approximately 15 meters deep, 75 mm diameter and having a PVC pipe extendingapproximately 0.5 meters above grade. The PVC pipe extends into and was grouted intothe hole.

• Pressure Gage Piezometers

Pressure gages piezometers were installed at three locations in the dam and spillwaydrainage galleries. These pressure gage piezometers were primarily oriented downstreamof the gallery.

A section view showing location of the gallery piezometers is shown on Figure 8.

Figure 8. Gallery Piezometers

Seepage

The amount of seepage migrating through, under, and around the embankment isnecessary information as it relates to the internal stability of the structure and theverification that the dam drainage zones are functioning properly. Monitoring seepage isessential during construction, first filling, and in establishing long-term trends. Seepage ismeasured by means of weirs, volume vaults or wet wells (calibrated containers).

A system of flow measuring weirs was established to collect and measure seepage andleakage that passes the dam. Leakage through the dam’s grout curtain and rockfoundation is collected by the foundation drainage system. The foundation drainage


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system consists of drain holes drilled from within the grouting galleries under the dam.The galleries run primarily along the centerline of the dam. Water collected in thegalleries and access adits flow by gravity to flow measuring stations. Several flowmeasurement stations are provided within the galleries to isolate and measure the quantityand locations of leakage at specific points along the gallery. The locations of the flow

measurement stations are shown on Figure 9.

Seepage through the dam is collected along the inclined drain zone adjacent to the coreand collected by the blanket drain beneath the downstream shell. This flow is conveyedto a buried collection pipe system just beyond the toe of the dam where it is measured bya weir.

The project’s drainage collection system was sized to accommodate a total of 320 liters /second (l/s), which includes an allowance for rainfall infiltration, natural groundwater,and backflow from tailwater. One hundred-fifty l/s was assumed to flow into thegalleries and adits and 170 l/s into the embankment drain zones.

Figure 9. Flow Measurement Stations in Galleries

Deformation

Surface deformation includes horizontal movement, settlement and heave of theembankment. To monitor these changes, Movement survey monuments (MSM) areinstalled on the dam crest, downstream slope, upstream slope, and on the spillway ogeesection.

The monuments are surveyed using conventional survey equipment to measure overallvertical and horizontal movements of the dam. A total of 67 MSM were installed. Ten

are located on the dam crest, 35 are located on the downstream slope, 3 on the spillwaystructure piers, and 19 are installed on the upstream slope. In addition, a settlementmonument was installed immediately in front of each monitoring station. Locations ofmovement survey monuments are show in Figure 10.


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Figure 10. Location of Survey Monuments

Vibrating wire (VW) settlement cells were installed in the core and downstream shellzones zone to monitor settlement during construction and first filing. A total of 14vibrating wire settlement cells were installed in the downstream half of the imperviouscore and downstream shell fill at the locations shown on Figures 3 through 7.


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Rainfall Measurement Devices

Rain gages were installed in order to measure rainfall in the immediate vicinity of the project structures in order to correlate rainfall infiltration with measured drainage gallery

flows and the flows measured at the blanket drain weir beyond the toe of the dam.Baseline data and correlations between precipitation and drain response were developed prior to the initiation of reservoir filling operations in order to estimate flows resultingfrom precipitation and infiltration versus those resulting from seepage and leakage pastthe dam.

Turbidity Measurement Devices

The purpose of measuring turbidity of the seepage water collected in the dam’s drainagesystem is to reveal if there is any piping or loss of material through the drain systemtaking place. A turbidity meter measures turbidity in nephelometric turbidity units (NTU)

that can be generally correlated to the dissolved and suspended sediment concentration ina water sample. Nephelometric refers to the way the instrument, a nephelometer, orturbidity meter, measures how much light is scattered by suspended particles in the water.Sampling is conducted at the various seepage and leakage measurement stations locatedin the galleries and adits, and at the collection and measurement structure for thehorizontal drain of the main dam. Similarly, the turbidity meter can be used in thesampling and measuring of turbidity at any location along the river. Low NTU valuesindicate high water clarity, while high NTU units indicate low water clarity.

Leakage flow is sampled and measured for turbidity at the various weirs located in theadits and galleries and at the blanket drain collection location

PREDICTED PERFORMANCE

Pore Water Pressure

Pore water pressures for design of the dam were computed from the location of thetheoretical piezometric surface, which varied for the various loading conditionsconsidered. The piezometric surface for the normal operation steady-state seepagecondition was conservatively assumed to be a horizontal line at elevation 280 m in theupstream rockfill shell and the core to a point 3 m beyond the core in the Zone 3 filter.From that point, the phreatic surface was assumed to be parallel to the downstream face

of the core extending to the Zone 4 blanket drain. Beyond the limits of the shell, the piezometric line was assumed at elevation 108 m at the maximum downstream section.The downstream phreatic line for the maximum upstream section was assumed at the base of the embankment on the excavation surface. The results of steady-state seepagefinite element analyses were used to verify the locations of the phreatic surfacesdescribed above. In general, the pore pressures indicated by the finite element analysesare lower than the values assumed for the design phreatic surface. Therefore, the stabilityanalyses results were based on conservative pore pressures. Piezometric head levels


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predicted by design computations for steady state conditions for piezometers located inthe maximum section of the dam at Station 9+25 are summarized in Table 1. Monitoringdata from these piezometers are discussed below in Evaluation and Performance.

Table 1. Maximum Section (Station 9+25) Piezometric Design Levels

Piezometer No. Location Distance fromAxis(m)

Tip Elevation(m) Design Head(m)

VWP - 11 Core 5 240.0 280

VWP - 12 Core 8 184.6 280

VWP - 13 Core 20 184.5 224

VWP - 14 Core 10 131.3 274

VWP - 15 Core 30 131.4 174

VWP - 16 Shell 80 130.4 108

VWP - 17 Shell 175 131.1 108

VWP - 18 Core 10 102.5 274

VWP - 19 Core 40 103.4 124

VWP - 20 Shell 125 106.7 108VWP - 21 Shell 225 106.5 108

VWP - 22 Shell 330 105.8 108

Seepage

Seepage analyses were performed using the two-dimensional finite element computer program SEEP/W (Geo-Slope International Ltd., 1998). Numerous analyses were performed as the design and construction was advanced.

Two-dimensional finite element analysis models were developed for several selected

transverse sections along the length of the dam. Total seepage through the dam andfoundation was obtained by using the end-area method to extrapolate two-dimensionalresults at each cross section and summing them along the axis of the dam.

For the initial analysis, four sections were selected to represent the dam, the arrangementof the drainage gallery, variations in foundation excavation geometry and foundationstratigraphy. Permeability values for various zones within the bedrock foundation wereinitially estimated based on field permeability testing of borings, performed as part of thefoundation core drilling exploration program at selected locations within the main damfootprint area. With the completion of the construction of the dam, but prior to reservoirfilling, the designers availed themselves to as-built excavation topography and extensive

water pressure test data obtained from Primary (P) and Verification (V) grout holes to better model pre- and post-grouted rock permeabilities, respectively. Therefore, as thedesign and construction advanced, the number of representative sections was increased,ultimately up to fifteen, to accommodate the actual foundation excavation geometry,expanded subsurface information obtained from foundation mapping, water pressure testresults from foundation grout holes, and changes to the embankment cross section anddrainage gallery arrangement. The seepage prediction analysis results described hereinare for the final post-construction, pre-filling “as-built” conditions.


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The permeability values, calculated from the field exploration permeability tests and Pand V grout hole pressure testing were plotted, by dam station, versus depth in order toevaluate the grouted and ungrouted rock permeability values representative of eachanalysis cross section. The permeability values, calculated from the field permeabilitytests performed within each section, were evaluated versus depth and representative

values for analysis were selected for ungrouted rock. The anisotrophy ratio was assumedto be 1.0 for all rock material. The results are summarized in the following Table 2.

Table 2. Representative Permeability Values for Ungrouted Foundation MaterialsStation Depths (m) Permeability (cm/sec)

2+50 to 6+00 0 - 20 1x10-3

20 – 60 3x10-4

60 – 110 1x10-4

>110 2x10-5

6+00 to 8+12.5 0 – 20 3x10-4

20 – 35 2x10-4

>35 8x10-5

8+12.5 to 9+00 0 - 30 6x10-4 30 – 50 1x10-4

>50 5x10-5

9+00 to 10+37.5 0 – 30 2x10-4

>30 5x10-5

10+37.5 to 13+80 0 – 30 3x10-4

30 – 75 2x10-4

>75 4x10-5

13+80 to 15+00 0 – 30 3x10-4

30 – 75 2x10-4

>75 4x10-5

Again, it should be reiterated that these are the values used in the final “as-built” analysis.Leading up to this analysis were numerous other analyses that also examined lower andupper bound ungrouted rock permeability ranges versus depth.

The original permeability (hydraulic conductivity) goals for the consolidation grout zoneand curtain grout zone were 20 Lugeons and 10 Lugeons, respectively and were based onearly grouting test section results. These values were used in the earlier seepageanalyses. The “as-built” analysis used grouted rock permeability coefficients that weredetermined from V grout hole pressure testing results. Final “as-built” grouted rock permeabilities of 2.64x10

-4 cm/sec. (20 Lugeons) and 6.6x10

-5 cm/sec. (5 Lugeons) were

used in the consolidation grout zone and curtain grout zone, respectively.

The two impervious core zone materials, Zone 1 and 1B, were modeled with permeabilitycoefficients of 2.0x10

-8 cm/sec. and 5.0x10

-7 cm/sec., respectively. These values were

based on laboratory determinations in accordance with ASTM D-5084. The anisotropyratio (the ratio of the hydraulic conductivity in the horizontal direction to the verticaldirection) was assumed as 2.0 for Zone 1 and 5.0 for Zone 1B and were based onspecified compaction methods.


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The total seepage was estimated based on fifteen selected analysis sections. The endarea method was used to compute the total seepage between sections. The first and lastsections with assumed seepage equal to zero were STA 2+50 on the left abutment andSTA 15+00 on the right abutment. Calculated seepage rates are summarized in Table 3 by station interval and by seepage collection feature (i.e. drainage gallery segment and

blanket drain). The predicted combined gallery flow was calculated to be 240 l/sec.Similarly, the predicted downstream blanket drain flow was calculated to be 67 l/sec. fora combined predicted seepage rate of 307 l/sec.

Table 3. “As Built” Seepage Analysis ResultsStation Interval Upper

LeftGallery(l/sec.)

Lower LeftGallery(l/sec.)

Upper RightGallery(l/sec.)

Lower RightGallery(l/sec.)

DownstreamBlanket Drain(l/sec.)

2+50 to 4+00 16.5 - - - 2.9

4+00 to 5+00 27.0 - - - 0.7

5+00 to 6+00 53.5 - - - 0.0

6+00 to 6+70 - 17.2 - - 8.16+70 to 7+00 - - - - 6.3

7+00 to 8+00 - - - - 19.2

8+00 to 8+12.5 - - - - 2.2

8+12.5 to 9+00 - - - - 9.0

9+00 10+00 - - - - 15.5

10+00 to 10+37.5 - - - 9.7 0.5

10+37.5 to 11+50 - - - 43.7 2.5

11+50 to 13+00 - - 42.8 - 0.1

13+00 to 13+80 - - 15.5 - -

13+80 to 14+50 - - 8.3 - -

14+50 to 15+00 - - 6.1 - -

Total Seepage byCollection Feature

(l/sec.)

97.0 17.2 72.7 53.4 67

Total GallerySeepage (l/sec.)

240 -

Total DownstreamBlanket Seepage(l/sec.)

- - - - 67

Combined TotalSeepage (l/sec.)

307

Deformation

Long term deformation of the dam was evaluated for final design by two methods: 1)review of data related to the long term deformation of large dams with features similar toSan Roque Dam, and 2) determine the rough magnitude of long term consolidationsettlement of the core zone using Terzaghi’s one-dimensional consolidation theory.


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The results of the first approach (case history study) were used to calibrate numericalstatic stress and deformation analyses of the dam. Because of the many limitingassumptions related to pore water pressure generation during construction, one-dimensional consolidation modeling, and the variability associated with large-scale placement and field compaction of cohesive soils, it is generally accepted that numerical

models tend to overestimate the magnitude of post-construction deformation of damcores. A more pragmatic and reliable approach to evaluating the effects of coredeformation (and the associated redistribution of stresses) was adopted that consideredcase histories of post-construction settlement of dams coupled with stress analysis using awell-validated generalized soil constitutive model.

Well-documented case histories of the long-term settlement behavior of rockfill damswith finer-grained cores (Dascal 1987, Clements 1984, Kollgaard and Chadwick 1988)among others) served as the basis of the case history study. Approximately 90 casehistories were initially considered, and of these, fifteen were judged to be similar enoughto San Roque Dam to be included in the deformation evaluation. The selected case

histories were generally similar to San Roque Dam in core, shell, and foundationmaterials; dam height; and the construction technique. The soil compaction effort for SanRoque was judged to be higher than those of the older dams. Therefore, settlementestimates based on case histories were somewhat conservative to use for this project.

The case history data indicated that dams with characteristics similar to the San Roquedam typically experience long term (about 40 years) maximum vertical strains(settlement per unit height) of about 0.4 percent. Based on this evaluation of performanceof existing dams similar to San Roque, long-term post-construction vertical strains of thedam core were predicted to be on the order of 0.5 percent at the maximum station 9+00(1m). These strains were expected to decrease to close to 0 percent near the abutments ofthe dam. Although it was believed that long-term vertical strains will be limited to about0.5 percent, to assess the sensitivity of the results and possible variation in totalsettlement, the stress analysis were performed considering 1.0 percent vertical strain(2m).

The results of the second approach (consolidation settlement analysis) are known tooverestimate long term consolidation settlement of central core embankment dams;however the analysis was performed to obtain an upper bound settlement value forcomparison to the results computed using more detailed long term deformation analysistechniques.

A one-dimensional long-term consolidation settlement analysis was performed on thelongitudinal profile of the dam. The analysis was performed using a spreadsheet todetermine the order of magnitude of long-term consolidation settlement using Terzaghi’sone-dimensional consolidation theory. Compression index values (CC) were determinedfrom laboratory testing and used as input for the spreadsheet. Consolidation settlement ofthe core was calculated at 14 stations. At each of the stations, the core was divided intosublayers with heights corresponding to the height of core elements along the central axisof finite element models. The results of the analysis using the range of Cc values


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predicted that total long term settlement of the core would vary from 1.4 to 3.1 meters, atstations 8+50 to 10+00 (closest to the maximum section). An average value of 2 meterswas chosen to account for the long term consolidation settlement of the dam.

Camber was incorporated into the embankment design geometry to account for potential

earthquake-induced deformations of the crest of the dam and long-term staticdeformation caused by consolidation of core material. In order to compute camber, theestimated long-term deformation was added to the maximum anticipated dynamicdeformation. Details regarding the earthquake-induced deformation computationanalyses are outside the scope of this paper. The results of the analyses indicate amaximum dynamic deformation of 0.5 m and approximately 2.0 m of long-term staticdeformation, for a cumulative total of 2.5 m. Therefore, in addition to 15 m of freeboardabove the normal operating reservoir elevation 280, the crest of the dam was constructedwith a maximum 2.5 m of camber in the center of the dam.

EVALUATION OF PERFORMANCE

Performance During First Filling

Impoundment of the reservoir began on August 8, 2002 with closure of diversion tunnels2 and 3. Diversion Tunnel No. 1 was permanently closed earlier in the year. As of November 15, 2002, the reservoir had filled to elevation 268.8, about 11.2 meters belowthe normal maximum operating pool of elevation 280.0. The reservoir did not meet thedesign maximum pool until the 2003 wet season.

Evaluation of monitoring program data at the end of 2002 indicated that the dam and itsfoundations performed as anticipated during the first impoundment of the reservoir, andthere were no concerns with respect to the performance and safety of the dam. Thefollowing observations were made based on the inspections and data obtained at thattime:

• A number of the piezometers in the core were then responding to reservoir filling. A

steady state condition had not yet been established but the trend was in that direction.

• The downstream shell piezometers indicated that drainage occurred with essentiallyno increase in piezometric head.

• The piezometers in the foundation indicated head loss generally in accordance with

the seepage analyses.

•

Total seepage from the galleries, as of November 15, 2002, is approximately 55 l/s;seepage at the downstream toe of the dam is about 127 l/s. These flow rates werereasonable and acceptable considering the geology of the site. There was someindication, based on the response of the core piezometers, that the recent increase inthe seepage flow rate at the toe of the dam was the result of the normal developmentof saturation and seepage through the core.

• The maximum vertical settlement measured to date (November 2002) at the crest ofthe dam is 309 mm. This settlement was considerably less than the 2.5 meters of


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camber and is well within the anticipated post-construction settlement after sixmonths of the dam being completed.

• No indication of longitudinal cracking at the upstream edge of the crest was observedas a result of saturation of the upstream shell.

In 2003, the reservoir reached full operating level several times, and was above normaloperating level of elevation 280, for short periods during extreme typhoon events.Evaluation of monitoring program data at the end of 2003 again indicated that the damand its foundations performed as anticipated during the first impoundment of thereservoir, and there were no concerns with respect to the performance and safety of thedam. The following observations were made based on the inspections and data obtainedat that time:

• The piezometers in the core have responded to reservoir filling. A steady state

condition has not yet been established in some lower piezometers, but the trend is inthat direction.

•

The downstream shell piezometers indicated that drainage occurs with no increase in piezometric head.

• The piezometers in the foundation indicated head loss generally in accordance withthe seepage analyses.

• Total seepage from the galleries, as of October 14, 2003, was approximately 80 l/s;

seepage at the downstream toe of the dam was about 88 l/s. These flow rates werereasonable and acceptable considering the geology of the site. There was someindication, based on the response of the total seepage, that the slight decrease in theseepage flow rate from the galleries was a result of calcification or natural sealing ofthe rock fractures. In addition, the recent reduction of the toe drain seepage recorded,was a result of the drier weather conditions being experienced over the past few

weeks.•

The maximum vertical settlement measured to date at the crest of the dam was 443mm. This settlement was considerably less than the 2.5 meters of camber and waswell within the anticipated post-construction settlement after 17 months of the dam being completed.

• No indication of longitudinal cracking at the upstream edge of the crest was observedas a result of saturation of the upstream shell.

Following first filling in November 2003, it was concluded that there were redundanciesin the instruments designed into the dam instrumentation system, in particular, the piezometers and the settlement devices. The purpose of these instruments was for use

during construction and first filling of the reservoir. Based on the piezometer redundancyand the fact that the vibrating wire piezometers were performing well, the non-working pneumatic piezometers were decommissioned based on recommendations from the Boardof Consultants. Since the pneumatic piezometers were the redundant instruments, it wasconcluded that if or when the remainder do not perform then they should also bedecommissioned. These instruments are no longer read. In addition, since the shell piezometers were indicating little or no water pressure, all of the reading frequency wasreduced read to bi-monthly.


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Evaluation of monitoring data also indicated that the internal settlement cells were not performing properly. It also appeared that the dam settlements, as measured by theexternal settlement monuments, were consistent and valid, and were approaching stablevalues. Since the internal settlement cells were intended to measure settlement of the damduring construction and first filling, it was concluded that the usefulness of the internal

settlement cells was in question, and the internal settlement cells were decommissionedupon recommendation of the Board of Consultants. Subsequently, the monitoring ofdeformation for long term conditions has relied on the external settlement monuments.

Long Term Performance

Pore Water Pressure: Vibrating wire piezometers are installed at various elevations in thedownstream portion of the embankment core and in the downstream shell (Figures 11through 13). Piezometers in the core quickly responded to the filling of the reservoir andmimic the rising and falling levels of the reservoir. Data from the piezometers in the coreshow head levels that are consistently less than the phreatic surface assumed for the

design analyses. For the vibrating wire piezometers in the shell, the piezometers indicatedconstant stable readings near the design assumption, indicating the internal drain isfunctioning as intended by the deign with no increase in piezometric head in thedownstream shell zone of the dam.

Table 4 lists the highest reading for the calendar year for vibrating wire piezometers inthe core and shell zones where data is continually available since the beginning ofreservoir filling operations. The core piezometers show an increase with reservoir fillingand then stabilization over time. Water levels in the shell are typically dry or respond to precipitation and rises in the tailwater level. The 2010 water levels in these piezometersare shown on Figure 11. Superimposed on this figure is the estimated phreatic surfacecalculated during design using the Casagrande method. This level can be compared tothe 2010 measured levels.


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Figure 11. 2010 Water Levels in Core and Shell, Station 9+25


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Table 4. Highest Piezometer Reading per Calendar Year CorePiezometers

Elevation(m)

2002 2003 2004 2005 2006 2007 2008 2009 2010

VWP-11 240 254 260 259 258 260 259 259 263 256

VWP-13 184.5 208 218 216 216 213 210 210 210 208

VWP-14 131.3 183 212 217 216 211 207 206 207 201

VWP-18 102.5 112 163 172 172 178 179 179 183 181

ShellPiezometers

VWP-16 130.35 130 130 130 130 130 130 130 131 131

VWP-21 106.53 109 108 107 106 105 105 105 105 105

VWP-22 105.76 108 108 113 108 107 107 107 109 107

Figure 12. Water Levels in Core Piezometers


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Figure 13. Water Levels in Shell Piezometers

Monitoring of the foundation gallery piezometers indicate head loss generally inaccordance with the design seepage analyses. The gallery piezometers respond tochanges in reservoir elevation. Their pattern tends to mirror that of the change inreservoir levels. There is no direct link to changes in rainfall patterns, other than in thatthe rainfall affects the reservoir elevation. Table 5 shows for a typical group of gallery piezometers at or near the maximum section, the piezometric head after the first fillingand at current high reservoir levels and compares it to the analysis piezometric head.This table illustrates that most of the piezometric heads are at or below the analysis piezometric head.


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Table 5. Lower Gallery Piezometers Number Location Piezometric Head

at Tip (m)October 29, 2002

Piezometric Headat Tip (m)October 29, 2010

Analysis PiezometricHead at Tip(m)

GP-12-50-D 8+85 157.46 138.16 130

GP-12-20-D 8+85 152.30 137.13 160

GP-12-60-U 8+85 120.54 102.11 130

GP-12-50-U 8+85 145.76 130.19 150

GP-12-20-U 8+85 185.02 173.71 190

GP-13-70-D 9+00 126.62 114.90 90

GP-13-50-D 9+00 141.10 127.31 130

GP-13-20-D 9+00 178.69 169.04 170

GP-13-60-U 9+00 165.13 168.31 160

GP-13-50-U 9+00 177.16 135.33 170

GP-13-20-U 9+00 198.77 189.14 190

Seepage: The long term, total seepage reflects the reservoir level with the total amount of

seepage decreasing over time and appears to be approaching steady-state conditions.Total seepage from first filling to February 2010 is shown on Figure 14. Total seepageconsists of flow measured from the galleries and the toe drain. The monitoring datashows that the total flow has gradually decreased over time with a maximum flow of 220l/s in 2002 to a low value of 100 l/s in 2008. The total flow in 2009 spiked to 190 l/s;however, this increase is due to infiltration from extremely high precipitation thatinfluenced the toe drain readings. The gallery seepage has also had a net decrease overtime. There is some indication that the decrease in the seepage flow rate from thegalleries is a result of calcification or natural sealing of the rock fractures. In the upperleft grouting gallery, a limited remedial grouting program was conducted in areas of veryhigh seepage which resulted in a reduction of the inflow. Table 6 shows the decrease in

seepage over time. Seepage quantities reflect highest measured amounts per calendar yearat high reservoir levels. The high value for the toe drain in 2004 reflects high precipitation.

Table 6. Measured Seepage Flows (l/s)at Highest Reservoir Level in Year Shown

Location Predicted Value 2004 2007 2010

Toe Drain 67 112 45 36

Galleries 240 71 55 41

Total 307 183 100 77


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Figure 14. Total Seepage

Deformation: As predicted by design analyses and evaluations, the maximum amount ofsettlement has occurred at the maximum section of the dam, and appears at this time to bereaching equilibrium, as shown on the crest settlement profile on Figures 15 and 16.Figure 15 shows the longitudinal settlement profile across the crest of the dam. Asanticipated, the greatest amount of settlement has occurred in the highest central sectionsof the dam and decreases towards the abutments. Settlement at the maximum section ofthe dam is 756 mm (29.8 inches) and reduces to 230 mm (9.1 inches) at the left abutmentand 265 mm (10.4 inches) on the right abutment. Figure 16 shows a transversesettlement profile of the maximum section. As expected, at the deepest sections,monuments SP5 and SP49, show the greatest amount of settlement, 756 mm (29.8 inches)and 802 mm (31.6 inches), respectively.

The monitoring data indicates that the long term settlement is much less than the twometers of settlement predicted by design analyses and evaluations. There has been noindication of longitudinal cracking at the upstream edge of the crest as a result of thesaturation of the upstream shell.


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Figure 15. Crest Settlement Profile


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Figure 16. Settlement Profile – Maximum Section

CONCLUSIONS

The San Roque rockfill-central core dam has performed very well for the last eight years;essentially since its first filling in 2002. The embankment dam was designed usingsophisticated methods and checked using empirical methods and performancecharacteristics from similar dams. The foundation conditions were the most difficult toascertain and as a result considerable on-site modifications were made to accommodatethe poor geologic conditions. These modifications were necessary to ensure thesafeguards against piping as well as meeting the seepage and leakage objectives. Thefact that the design-build nature of the contract and project facilitated the rapidrecognition of unforeseen and unknown features during construction and enabledefficient and effective treatments made the project a success. The result, as indicatedabove, is that this large rockfill dam meets and exceeds its performance criteria andreinforces the current engineering methods of design.

ACKNOWLEDGEMENTS

The authors would like to acknowledge the assistance of Mr. William Connell – SeniorVice President for Plant Operations and Site Administrator, Mr. Jeric Codinera – SRPC


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Instrumentation Engineer and Mr. Raymund Mariano – SRPC Engineering Manager, fortheir help in providing the monitoring data and reviewing this paper.

REFERENCES

San Roque Power Corporation, Weekly Reports of Instrumentation Results, from 2002 to2010.

San Roque Consulting Panel, San Roque Multipurpose Project, SRPC Consulting PanelMeeting No. 12, July 17, 2002.

San Roque Consulting Panel, San Roque Multipurpose Project, SRPC Consulting PanelMeeting No. 13, November 18, 2002.

San Roque Consulting Panel, San Roque Multipurpose Project, SRPC Consulting PanelMeeting No. 14, October 26, 2003.

United Engineers International, Inc., Addendum 1, Design Statement – Level 2, MainDam Embankment, for the San Roque Multipurpose Project for the San Roque PowerCorporation, July 2000.

United Engineers International, Inc., Instrumentation Monitoring and Inspection Manual,for the San Roque Multipurpose Project for the San Roque Power Corporation, August2002.


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SAN ROQUE MULTIPURPOSE PROJECT PERFORMANCE