Certified_Final_Tech_Specs_Volume_2_-_GBR.pdf

W911WN-13-R-0002

East Branch Lake East Branch Clarion River Elk County, Pennsylvania Dam Safety Modifications/Cutoff Wall

Certified Final Document Volume 2 – Geotechnical Baseline Report April 2013

Pittsburgh District April 2013

Geotechnical Baseline Report

East Branch Dam

Clarion River Elk County, Pennsylvania

East Branch Dam – Geotechnical Baseline Report April 2013 i

TABLE OF CONTENTS

SECTION PAGE

1. Introduction and Background

1.1 Location and Population at Risk

1.2 Background

2. Geology

2.1 Basic Geology

2.1.1. Regional Geology

2.1.2. Site Geology

2.1.3. Structural Geology

2.2 Site Specific Geologic Features

2.3 Description of Stratigraphy

3. Relevant Aspects of Construction and Repair

3.1 Embankment Construction

3.1.1. Right Abutment Cutoff Trench and Grouting

3.2 1952-1953 Left Abutment Grouting

3.3 1957 Incident and Emergency Repair

3.4 Potential Obstructions

3.4.1. Dam Cutoff Trench (6+09 to 11+02)

3.4.2. Grouted Void Area at Right Abutment

3.4.3. 1955-1956 Left Abutment Grouting

3.4.4. Pre-Construction Oil Wells

4. Site Explorations

4.1 Preconstruction

4.2 1957 Incident

4.3 1972 Piezometer Installations

4.4 1977 Exploration, Piezometer Installations and Dye Tests

4.5 1979 Dye Tests

4.6 1981 Cavity Exploration

4.7 1990 Piezometer Installation

4.8 1998 Left Abutment Exploration and Piezometer Installations

4.9 1999 Exploration and Piezometer Installations

4.10 2008-2009 Geophysical and Geotechnical Exploration and Piezometer Installations ii

4.11 2010 Inclinometer and Piezometer Installations

4.12 2010-2011 Exploration (Phase II HTRW Geotechnical)

4.13 2011-2012 Exploration

5. Instrumentation

5.1 Weirs

5.1.1. Right Abutment

5.1.2. Emergency Grouting Area

5.1.3. Left Abutment

5.2 Piezometers

5.2.1. Right Abutment

5.2.2. Grouted Embankment Area (Sta. 7+50 to 9+50)

5.2.3. Valley Section

5.2.4. Left Abutment

5.2.5. Downstream Toe

5.3 Movement

5.4 Seismic

6. Soil Conditions

6.1 Basic Characterization of Soil Properties of Foundation and Embankment Soils . 71

6.1.1. Soil Stratigraphy

6.1.2. Index Testing

6.1.3. Unit Weight & Specific Gravity

6.1.4. Permeability

6.1.5. Shear Strength

6.1.6. Mineralogy

6.2 Cobbles and Boulders in Embankment and Foundation

6.3 Erodible embankment and foundation soils

6.4 Loose/Soft Embankment Zones

6.5 Rock drain and Filter material

6.6 Presence of permeable gravel in foundation soils

6.7 Properties of Grout in the 1957 Emergency Repair Area

7. Foundation Rock Characterization

7.1 Recent Investigations and Rock Sampling

7.2 Discussion of Rock Quality and Permeability

7.2.1. Station 5+90 to Station 10+00

7.2.1. Station 10+00 to Station 18+05

7.2.2. Station 18+05 to Station 22+90

7.2.3. Spillway Section Dogleg

iii

7.3 Extents, orientation and sizes of vertical fractures, bedding planes and angled fractures.

7.3.1. Station 5+90 to Station 10+00

7.3.2. Station 10+00 to Station 18+05

7.3.3. Station 18+05 to Station 22+90

7.3.4. Spillway Section Dogleg

7.4 Characterization of Strength/Abrasivity/Abradability of Rock

7.4.1. Station 5+90 to Station 10+00

7.4.2. Station 10+00 to Station 18+05

7.4.3. Station 18+05 to Station 22+90

7.4.4. Spillway Section Dogleg

8. Characteristics Of Borrow Area Material

LIST OF FIGURES

FIGURE PAGE

Figure 1-1. Population Centers Downstream of Dam Figure 1-2. Project Location Figure 2-1. Outlet Works – Stilling Basin Figure 2-2. Outlet Works – Control Tower Figure 2-3. Service Bridge Abutment Foundation Figure 2-4. Bedrock Stratigraphy of Right Abutment Figure 3-1. Photo of Right Abutment Haul Road Figure 3-2. View showing rocky nature of downstream random fill soil Figure 3-3. Photo of Embankment Construction, Right Abutment Area Figure 3-4. Schematic Cross-Section of Cutoff Trench Figure 3-5. View of Upper Portion of Cutoff Trench Figure 3-6. Cutoff Trench at Sta. 9+80 Figure 3-7. Cutoff Trench at Sta. 9+80 Figure 3-8. Cutoff Trench at Sta. 8+58 Figure 3-9. Downstream Toe of Embankment in 1957 Figure 3-10. Plan of Right Abutment Emergency Investigations Figure 3-11. Plan of Right Abutment Consolidation Grouting Figure 3-12. Cross Section View of Grouted Void @ Sta. 8+30 Figure 3-13. Grout Cap and Embedded Grout Tubes – Sta. 10+50 Figure 3-14. Extents of Potential Grouting Steel in Right Abutment Rock Figure 3-15. Profile and Plan View of Left Abutment Grouting Showing Bit Loss Figure 4-1. Plan of 1977 and 1979 Dye Tests Figure 5-1. Plan View showing Weir Locations Figure 5-2. Weir 6 Time History Plot (with Instances of Turbid Flow) Figure 5-3. Flow at Weir 6 Correlation Plot Figure 5-4. Weir 1 Flow Correlation Plot Figure 5-5. Plan View Showing Right Abutment Piezometers Figure 5-6. Right Abutment Piezometer Readings and Pool Levels iv

Figure 5-7. Instrumentation in the Grouted Embankment Area Figure 5-8. Generalized Piezometric Condition - Grouted Embankment Zone Figure 5-9. Station 8+30 Piezometer Locations Figure 5-10. Typical Piezometer Response – Grouted Embankment Zone Figure 5-11. Piezometer Data Plots – Sta. 8+30 Figure 5-12. Piezometer Locations – Valley Section Figure 5-13. Cross Section 11+05 Figure 5-14. Piezometer Location – Left Abutment Figure 5-15. Cross Section 22+00 Figure 5-16. Time Plots - Piezometer Levels Figure 5-17. Piezometer Locations – Downstream Toe Figure 6-1. Typical Embankment Zoning Figure 6-2. Gradation Test Data from Historic Investigations Figure 6-3. Failure Envelopes from Laboratory Shear Strength Testing Figure 6-4. Failure Envelopes from Laboratory Shear Strength Testing Figure 6-5. Original stream channel. Note large boulders / slabs Figure 6-6. Preconstruction Borings That Utilized Coring to Penetrate Boulders Figure 6-7. Preconstruction Boring Logs That Identified Substantial Boulders During Drilling 85 Figure 6-8. Profile view of dam depicting location of boulders and cobbles encountered in borings drilled along centerline between station 6+00 and 15+00 Figure 6-9. Profile view of dam depicting location of boulders and cobbles encountered in borings drilled along centerline between station 15+00 and 24+00 Figure 6-10. 08-EBR-69 Sonic Drill Sample Figure 6-11. Boring 08-EBR-74 core box Figure 6-12. Boring E-51 sonic drill sample Figure 6-13. Plasticity Chart for Embankment Fill Material Figure 6-14. Plasticity Chart for Foundation Overburden Material Figure 6-15. Dam Profile - Grouted Void Area - Drawing 038b-U1-10_114 (Appendix B) Figure 6-16 Rock Drain & Toe Details Figure 6-17. Photo of rock drain / gravel filter placement along left downstream groin Figure 6-18. Profile view dam showing location of artesian pressures and grout losses Figure 6-19. Cross Section of Grouted Void (see Appendix B) Figure 7-1. 2008 Lugeon Testing at Right Abutment – 08-EBD-72 Figure 7-2. Right Abutment Figure Reference Figure 7-3. Upper Right Abutment Rock Characteristics Sta. 5+90 to 10+00 Figure 7-4. Upper Right Abutment Rock Characteristics Sta. 5+90 to 10+00 Figure 7-5. Figure Reference - Sta. 10+00 to 15+00 Figure 7-6. Rock Characteristics Sta. 10+00 to 15+00 Figure 7-7. Figure Reference - Sta. 15+00 to 18+05 Figure 7-8. Rock Characteristics Sta. 15+00 to 18+05 Figure 7-9. Figure Reference - Sta. 18+05 to 22+90 Figure 7-10. Rock Characteristics Sta. 18+05 to 22+90 Figure 7-11. Rock Characteristics Sta. 18+05 to 22+90 Figure 7-12. Figure Reference – Spillway Section Dogleg Figure 7-13. Rock Characteristics – Spillway Section Dogleg Figure 7-14. Rock Characteristics – Spillway Section Dogleg v

Figure 7-15. Stereo net – Right Abutment - Sta. 5+90 to 10+00 Figure 7-16. Sternest – Valley Center - Sta. 10+00 to 18+05 Figure 7-17. Stereo net – Left Abutment - Sta. 18+05 to 22+90 Figure 7-18. Stereo net – Spillway Section Dogleg Figure 7-19. Rock Strength Characteristics - Sta. 5+90 to 10+00 Figure 7-20. Rock Abrasiveness and Abrasivity Characteristics - Sta. 5+90 to 10+00 Figure 7-21. Rock Strength Characteristics - Sta. 10+00 to 18+05 Figure 7-22. Rock Strength Characteristics - Sta. 10+00 to 18+05 Figure 7-23. Rock Abrasiveness and Abrasivity Characteristics - Sta. 10+00 to 18+05 Figure 7-24. Rock Strength Characteristics - Sta. 18+05 to 22+90 Figure 7-25. Rock Abrasiveness and Abrasivity Characteristics - Sta. 18+05 to 22+90 Figure 7-26. Rock Strength Characteristics – Spillway Section Dogleg Figure 7-27. Rock Abrasiveness and Abrasivity Characteristics – Spillway Section Dogleg ... 151 Figure 8-1 – Borrow Area Location Figure 8-2. Boring Plan View – Borrow Area Figure 8-3. Rock Strength Characteristics – Borrow Area

LIST OF TABLES

TABLE PAGE

Table 3-1 – List of Remnant Drilling and Grouting Steel Table 4-1. Summary of Basic Information from 1972 Boring Logs Table 4-2. Summary of Basic Information from 1977 Boring Logs Table 4-3. Summary of Basic Information from 1981 Boring Logs Table 4-4. Summary of Basic Information from 1990 Boring Logs Table 4-5. Summary of Basic Information from 1998 Boring Logs Table 4-6. Summary of Basic Information from 1999 Boring Logs Table 4-7. Summary of Basic Information from 2009 Boring Logs Table 4-8. Summary of Basic Information from 2010 Boring Logs Table 4-9 Summary of Basic Information from 2011 Boring Logs Table 4-10. Summary of Basic Information from 2012 Boring Logs Table 5-1. Maximum Weir Flows Table 5-2. Piezometer Information – Right Abutment Table 5-3. Piezometer Information – Grouted Void Area Table 5-4. Piezometer Information – Valley Section Table 5-5. Piezometer Information – Left Abutment Table 5-6. Piezometer Information – Downstream Toe Table 6-1. Summary of Soil Classification Results for Foundation & Embankment Soils from 2012 Geotechnical Exploration Table 6-2. Summary of Unit Weight and Specific Gravity of Embankment Materials Table 6-3. Permeability Test Results Table 6-4 Grout Compressive Strength Test Results Table 7-1. Correlation of Lugeon Value to Permeability Table 7-2 Right Abutment RQD Summary Table 7-3. 2011-2012 Pressure Test Results – Sta 5+90 to 10+00 vi

Table 7-4. 2011-2012 Slurry Testing Results at Right Abutment Table 7-5. 2011-2012 Borehole Backfill Grout Takes – Sta 5+90 to 10+00 Table 7-6. Valley RQD Summary Table 7-7. 2011-2012 Slurry Testing Results at Valley Center Table 7-8. 2011-2012 Pressure Test Results – Sta 10+00 to 18+05 Table 7-9. 2011-2012 Borehole Backfill Grout Takes – Sta 10+00 to 18+05 Table 7-10. 2011-2012 Borehole Backfill Grout Takes – Sta 18+05+22+90 Table 7-11. 2011-2012 Pressure Test Results – Sta 18+05 to 22+90 Table 7-12. Left Abutment RQD Summary Table 7-13. 2011-2012 Borehole Backfill Grout Takes – Spillway Section Dogleg Table 7-14. 2011-2012 Pressure Test Results – Spillway Section Dogleg Table 7-15. Dogleg RQD Summary Table 7-16. Defect Characteristics - Sta. 5+90 to 10+00 Table 7-17. Defect Characteristics - Sta. 10+00 to 18+05 Table 7-18. Defect Characteristics - Sta. 18+05 to 22+90 Table 7-19. Defect Characteristics – Spillway Section Dogleg Table 7-20. Criteria for the CERCHAR Abrasiveness Index (ASTM D7625) Table 8-1. General Rock Quality – Borrow Area Table 8-2 – Rock Conditions Associated With UCS Samples

Appendices

Appendix A - References Appendix B – Drawings Drawing Index Drawing Development Drawings Descriptions Unit Descriptions Appendix C – As-Built Drawings Appendix D – Boring Logs Boring Log Summary Table Boring Location Plans Appendix E – Geotechnical Tables Soils Data Rock Data Miscellaneous Data Appendix F – Discontinuity Data Fracture Logs Borehole Imaging Fracture Tables Stereonets Discontinuity Spacing Figures Appendix G – Pressure Test and Slurry Test Data Appendix H – Grouted Void Data 1957 Emergency Borings and Grouting Consolidation Grouting vii

Grouted Void Dimensions Grout Core Tests Appendix I – Instrumentation Data Instrumentation Evaluation Precipitation Graphs Inclinometer Plots Weir Plots Piezometer Plots Alignment and Settlement Survey 2012 Field Falling/Rising Head Tests

Historical Instrumentation Plots Appendix J – Photographs

1. INTRODUCTION AND BACKGROUND

1.1 Location and Population at Risk

East Branch Dam is located on the East Branch Clarion River, 7.3 miles upstream of its confluence with the West Branch Clarion River at Johnsonburg, Pennsylvania, to form the Clarion River. The Clarion River is a major tributary of the Allegheny River.

There are two major population centers downstream of the dam which includes Johnsonburg, Pennsylvania, and Ridgway, Pennsylvania. Additionally, the village of Glen Hazel is less than two miles downstream of the dam. The figures below show the project location.

Figure 1-1. Population Centers Downstream of Dam

Figure 1-2. Project Location

Project Location

1.2 Background

East Branch Dam is a rolled earth fill embankment with outlet works located at the right abutment and an emergency spillway located in the left abutment. The embankment is 1,725 feet long and has a height of 184 feet, with top of dam elevation 1707 (all elevations are NAVD88 unless otherwise noted). The width is 20 feet at the top of the dam with a maximum width of 1,115 feet at the base. The dam consists of a central core of select impervious material with random fill zones on the upstream and downstream sides. A right abutment seepage cutoff trench, located at the centerline, cuts through the foundation soils into bedrock. The cutoff trench extends from the right end of the dam to the valley bottom just left of the original stream channel. A concrete grout cap was placed in the bottom of the trench and drilling and grouting of the right abutment were performed through the grout cap. The remainder of the embankment is founded on foundation soils with a shallow inspection trench in lieu of a cutoff.

The dam was screened under the Screening for Portfolio Risk Analysis (SPRA) program in 2006 and was placed into Dam Safety Action Class (DSAC) II, Urgent. An Interim Risk Reduction Measures Plan (IRRMP) was prepared in 2007 and revised in 2008. A potential failure mode analysis (PFMA) was performed in January 2008 by an interagency team including members from the U.S. Bureau of Reclamation (Reclamation), Pittsburgh District, the CESWD risk cadre, and members of the USACE Engineering Risk and Reliability Directory of Expertise. The PFMA was performed in conjunction with an engineering risk analysis. The results of the PFMA and risk analysis were used to guide implementation of IRRMs. The most notable IRRM was to lower the operating range of the reservoir by 20 feet in the summer and 30 feet in the winter, with potentially severe economic and environmental impacts. Following implementation of the IRRMS a Phase I Issue Evaluation Study (IES) was completed in 2008.

The IES and in 2010 a Dam Safety Modification Report (DSMR) was completed. The results of the IES and DSMR, recommended the construction of a cutoff wall in order to lower the risk associated with seepage through the dam. This report is intended to serve as a comprehensive summary of the existing soil and rock conditions at the East Branch Dam in preparation for construction of the planned cutoff wall and grouting program.

2. GEOLOGY

2.1 Basic Geology

2.1.1. Regional Geology

The reservoir is located in the northern part of the Kanawha Section of the Appalachian Plateaus Province. Although the drainage basin tributary to the dam site has a relief of about 700 feet, the basin is essentially a poorly dissected plateau with areas which are broad and gently rolling. The valleys have steep slopes which merge with the narrow to moderately broad flood plains. There is not a readily apparent indication of terrace development within the valleys. The geologic structure of the Appalachian Plateaus province is characterized by broad, open folds, and relatively horizontal bedding of rock strata.

2.1.2. Site Geology

The valley of the East Branch Clarion River lies south of the glacial terminus and was probably eroded during glacial time to a depth of about 40 feet below streambed. The valley was refilled with soil deposits which are part colluvial and part alluvial. These deposits are poorly stratified and contain material ranging in size from silt with traces of clay to large blocky boulders of sandstone. The only strictly alluvial materials were found in the middle of the valley as deposits of fine to coarse sand with some gravel and a little silt. However, several drill logs indicate the presence of a relatively clean gravel deposit near the original stream channel at the maximum dam section (approximate Sta. 11+00 to 13+00 and likely near Sta. 17+50 and Sta. 19+00) this is discussed further in Section 6.6.

The surface of bedrock through the valley encompassing East Branch Dam reservoir lies within the Shenango formation of the Mississippian System and the overlying Pottsville formation of the Pennsylvanian System. The transition between the formations is at approximately elevation 1800 near the Dam, or about 100 feet above the dam crest. Consequently, the Shenango formation underlies the entire footprint of the dam.

The Shenango formation consists of thinly interbedded sandstone, siltstone, and shale and contains bands of marine fossils. The overlying Pottsville formation consists mostly of gray sandstone and conglomeratic sandstone with thin beds of shale, claystone, limestone and coal.

Bedrock in the dam foundation and abutments is predominantly composed of shales and sandstones with some siltstone and thin limestone beds. The texture of the sandstones is generally fine to medium grained while the shales tend to be silty. The region and site are non-karstic and although there are instances of limestone within the site stratigraphy, these are isolated and thin beds that are not readily susceptible to solutioning.

2.1.3. Structural Geology

The dam is positioned approximately 4 miles west of the Hebron anticline, which plunges in a northwesterly direction, and 2.5 miles east of the Johnson Run syncline. As a result, the rock formations have been deformed into a series of northeastward-trending gentle folds with beds dipping regionally to the northwest with a maximum dip of about three percent. Structurally, the formations are well jointed with no evidence of faulting in the area. All of the fractured surfaces are weathered to approximately 10 to 20 feet depth into rock.

2.2 Site Specific Geologic Features

The substantial fracturing encountered at East Branch Dam during the original dam construction and subsequent exploratory drilling is a result of valley stress relief. Fractures in the bedrock can be relatively large, some with soil infill while others are clean. Deep and open vertical fractures parallel to the valley were observed during construction in the excavation of the cutoff trench, in the upper left abutment, and also in the spillway excavation. While prevalent in the abutments, these stress relief features are not noted to be present in the valley section. Construction photographs illustrate a vertical joint that is wider than 12 inches, possibly after cleanout (see Figure 3.8). This may be an unusual instance – the photographic record does not indicate the presence of other fractures this large, although 18-inch wide joints were evident at the service bridge abutment (see Figure 2-3). Additional significant joints were indentified in foundation reports during construction. Foundation Reports No. 2 and 3 for the Embankment and Spillway identified 3-6 in wide clay filled joints and 5-8 inch wide rusty vertical joints. Foundation Report No. 14 for the Outlet Works identified 3-9 inch wide weathered vertical joints. An evaluation of recently drilled test borings showed high angle fractures up to 11 inches wide.

Representative examples of bedrock conditions are shown in photographs of the original dam and its appurtenant structures, below. Refer to Section 7 for more detailed evaluation of the bedrock conditions at the site.

Figure 2-1 shows excavation at the stilling basin area (downstream) in June 1948. Rock excavation generally consisted of thinly laminated shale(s) and sandstone(s) with numerous vertical fractures. Considerable seepage occurred through these fractures and through holes drilled later for anchor rods.

Figure 2-1. Outlet Works – Stilling Basin

Figure 2-2 shows conditions at the founding level of the control tower (upstream), where a bed of hard gray sandy fossiliferous limestone was exposed, loosely bedded, badly fractured, with numerous mud-filled seams. The limestone was over-excavated and the tower was then founded on hard gray sandy shale.

Figure 2-2. Outlet Works – Control Tower

Figure 2-3 shows the foundations for the service bridge abutment and pier on medium hard silty fine sandstone with weathered mud-filled vertical fractures as wide as 18 inches.

Figure 2-3. Service Bridge Abutment Foundation.

2.3 Description of Stratigraphy

Historic and recent borehole logs were used to identify stratigraphic units below the dam. The units were originally derived from a 3-D model developed using historical and recent (2008) boring data submitted to the Pittsburgh District in the 2009 Geotechnical Data Report – Subsurface Exploration and Model Development. The results of the 3-D model were adjusted with the understanding that locally, the bedding dips from upstream of the left abutment to the right abutment (dipping gently to the west). In the spring of 2012, the geology was re-evaluated using additional borings from the 2011 Geotechnical Exploration and Phase II Environmental Site Investigation Summary and the 2012 Geotechnical Data Report. Symbols were assigned to the units based on the predominant rock type. The majority of the units are described as a sandstone (SS1-SS9) or shale (SH1-SH8) unit. The sandstone units typically contain siltstone or shaley interbeds or laminae and the shale units typically contain interbedded sandstone. The minor thin limestone beds were labeled as limestone units (L1-L5) which can generally be used as marker beds.

Only two of the units (SS3 and SS4) are identified and described in this report. These units are acknowledged because of their properties and relationship to the seepage history at the site. SS3 and SS4 units are predominantly iron stained sandstones with interbedded sandy silt shale and siltstone. The units experienced multiple zones of water loss near the bottom of SS3 and top of SS4. Water was also heard or seen flowing into boreholes within these units on the right and left abutments. Due to the fracturing in the rock, both units within the abutments underwent grouting programs in the 1950’s. Also on the right abutment, the units are exposed to the dam materials just below the 1957 void (see Appendix B drawing 038b-U1-10/105), which possibly influenced the formation of the void. The full unit descriptions can be found in Appendix B. Figure 2-4 depicts the bedrock stratigraphy of the right abutment. See drawing 038b-U1-10/104 Dam Profile Centerline – Sta. 5+25-26+00 in Appendix B for the stratigraphy across the length of the dam.

Figure 2-4. Bedrock Stratigraphy of Right Abutment

3. RELEVANT ASPECTS OF CONSTRUCTION AND REPAIR

3.1 Embankment Construction

The dam and appurtenant features were constructed between 1948 and 1952 under two separate contracts, one for the outlet works and another for the spillway and embankment. Construction was substantially complete by June 1952. The following sub-paragraphs discuss observations made during construction of the dam and appurtenant features.

Work on the dam embankment and spillway began on 1 August 1949 with clearing on the embankment site, which included clearing, stripping unsuitable material, and excavating for the cutoff trench on the right abutment. To facilitate work at each end of the outlet works, an access road was cut into the right abutment hillside, heading upgrade from downstream to upstream (Figure 3-1). During clearing, a large number of boulders were removed as well as an abandoned railroad grade. Silted back channels in the stream bed were excavated to suitable foundation material and a layer of gravel in the old stream bed was removed. Such excavations were performed only in the cutoff trench. The remainder of the dam was founded on in-situ soils.

Removal of boulders and topsoil possibly took place. Foundation Report Number 8 notes that a 3 to 5 foot cover of well-graded, impervious sandy silt was encountered upstream of the embankment. The Foundation Report notes that this material remains intact except in the area of the streambed, it is unknown if this layer was excavated from under the embankment.

Figure 3-1. Photo of Right Abutment Haul Road

Placement of embankment fill started on 16 May 1950 in the upstream random zone between Sta. 10+00 and 12+00. The cutoff trench was closed and placement in the impervious zone started on 3 June 1950. Placement of embankment proceeded until 16 November 1950 when the fill had reached elevation 1605. The embankment was constructed over two seasons. The shutdown at the end of the first season occurred when the top of the embankment was at El 1605.

There is no documentation regarding whether the surface layer of fill was removed or otherwise treated at the start of the second season. Following the winter shutdown, fill placement resumed on 18 April 1951 and was completed to finished grade on 13 October 1951.

Accounts of construction state that crushed, nondurable rock from the spillway excavation and soil borrow area material were placed in alternating lifts in the random fill zones from 15 June 1950 until 3 July 1951, when random fill zones had reached approximate Elevation 1629.

Afterward, the nondurable spillway rock was disposed. The accounts state that this rock was crushed to a maximum size of six inches, placed on the embankment in alternating courses with soil, mixed in place, and rolled. The specifications required that the ratio of crushed rock to overburden was not to exceed one part rock to one and one-half parts overburden. Reports state that layers of crushed rock also were placed on random fill zones to permit early resumption of fill operations after rainfall. Based on final quantities estimated at the end of construction, nondurable rock from spillway excavation actually corresponds to approximately 20 percent of the random fill volume (Figure 3-2). Where abutment slopes were excessively steep and prevented a firm bond between foundation and embankment, the abutment was benched as successive lifts were placed.

Figure 3-2. View showing rocky nature of downstream random fill soil

Samples retrieved from an exploration of the site in 2008-2009 included durable rock fragments in excess of 6 inches in size within the impervious fill zone. These rock fragments are most likely associated with cobbles and boulders in the borrow areas that were incorporated into the fill. No filter or transition zone was placed between the impervious and random fill zones.

During most of the embankment construction, the contractor worked two shifts, with night operations illuminated by floodlights. Fog was common at night and often hampered the work.

Rainfall was above normal during the 1950 construction season, causing frequent delays due to wet fill. From May through September 1950 the contractor experienced problems with material classification, moisture control, and compaction. By late September 1950 the situation was corrected. Higher densities and reduced variability were achieved for the remainder of the operation; however, by the time this occurred placement had progressed to the range of elevation 1575 to 1580. Over the period June 1950 through May 1951 the embankment engineer documented in the daily soils report instances of a variety of problems, including poor compaction at the right abutment and in the cutoff trench; with the cause generally attributed to short radius turning by the rollers and excessive lift thickness (Figure 3-3).

Figure 3-3. Photo of Embankment Construction, Right Abutment Area

Among documented problems, there were occasional instances of the following: placement of excessively moist material, placement of over-sized lifts, placement of fill over uncompacted lifts, lack of compaction equipment, bridging between large rocks, smooth unbonded surfaces between lifts, and shortage of inspection personnel. There is no documentation indicating that any of the listed deficiencies were corrected. Embankment materials were generally described as extremely rocky. Roller wear was rapid and the contractor maintained a welding force working 24-hours a day on roller repairs during busy placement periods. Oversize stones were removed to the upstream face and a crew of laborers with sledges reportedly patrolled the fill to break down stone to meet size requirements.

During embankment construction, springs were encountered in the foundation upstream of the centerline in the area of the original streambed, and along the right abutment. The right abutment springs occurred both upstream and downstream of the dam axis near Sta. 9+00. The upstream springs, with a flow of approximately three gpm, occurred at approximate elevation 1570 from a point 270 feet upstream of the axis and extending another 90 feet upstream. The downstream spring, with a flow not exceeding ¼ gpm, was located 60 feet downstream of the axis. This spring was first noted at elevation 1550 but was forced upward by placement of fill until it discharged near elevation 1570. The upstream springs were drained to the upstream slope of the dam through a six-inch porous concrete pipe bedded in filter material (Figure 3-3). The downstream spring was drained to the bottom filter of the downstream blanket drain through a drain constructed of filter material. The source of the upstream spring was noted as bedrock.

Reports note that both the impervious core and random fill materials were similar to each other, with the main difference being that the random fill contained a higher percentage of gravel and a higher maximum particle size. The exploration conducted in 2008-2009 encountered some large rock particles in the impervious fill zone. Rock particles that were obviously larger than the 6-inch sampler (used in the resonate-sonic borings) were encountered in the impervious fill zone.

Although it is obvious that the random fill and impervious core zones are close enough in gradation to be filter-compatible, the fines content of the random fill suggest it would not have sufficient permeability to serve as an ideal filter, and may sustain a crack.

A horizontal rock drain with a three-foot thickness surrounded by 18-inch-thick filter layers underlies the downstream random fill zone. This horizontal drain is the only internal drainage feature; there is no chimney filter/drain within the embankment.

3.1.1. Right Abutment Cutoff Trench and Grouting

A fairly narrow cutoff trench into rock forms the foundation for the impervious core from the right end of the dam at station 6+39 to the valley bottom left of the original streambed at station 11+02. The trench extended through overburden into the underlying bedrock to varying depths of two to eight feet depending on field conditions. A concrete grout cap was placed in the bottom of the trench. The foundation rock was grouted on the right side through the grout cap placed in the bottom of the cutoff trench (Figure 3-4). See Drawings 038b-U1-10_100, 038b- U1-10_101 and 038b-U1-10_101 in Appendix B for limits of the cutoff trench and right abutment grouting in plan and profile views.

Photos illustrating the geometry and geology associated with the right abutment are shown below (note the very steep to vertical side slopes and the presence of rock overhangs that were apparently left in place). Fine-grained soil of the impervious core was placed directly against the highly fractured rock in the right abutment cutoff trench without surface treatment or a filter.

Also, the natural overburden was not stripped from the remainder of the right abutment foundation, as would be standard practice today. An especially large fracture (at Sta. 8+58 in the cutoff trench) is documented in the construction photographs (Figure 3-8).

Figure 3-4. Schematic Cross-Section of Cutoff Trench

Figure 3-5. View of Upper Portion of Cutoff Trench

Figure 3-6. Cutoff Trench at Sta. 9+80

Figure 3-7. Cutoff Trench at Sta. 9+80

Figure 3-8. Cutoff Trench at Sta. 8+58

The right abutment cutoff trench was opened in September 1949 and work on the cutoff continued through winter to the following spring. Until the river was diverted through the tunnel in April 1950, a diversion trench and dike in the valley bottom carried flow around the left end of the cutoff trench. Grouting of the right abutment was done from November 1949 until May 1950. The foundation was grouted in three zones of depth through a double row of holes 2 ½ feet upstream and downstream of the axis. Grout holes were inclined into the abutment at angles ranging from 36 degrees from vertical at the right end of the dam (Sta. 6+39) to 10 degrees from vertical at the left end of the cutoff near the valley bottom (Sta. 11+02). The upstream line was completely grouted before the downstream line was begun. Within a line, each zone of depth was grouted in all holes before the next deeper zone was begun. The grouting of each zone was done by drilling and grouting in successive stages. The number and depth of stages varied with conditions encountered. Holes were grouted in three phases with successively reduced spacing.

The first phase holes were 20 feet apart. The second phase holes split the spacing to 10 feet and the third phase to five feet. No additional holes were drilled at closer spacing even though the contract contained provisions for additional grout holes. The final grout quantity of 43,678 bags exceeded the original estimate of 28,700 bags due to open seams, leakage, and hole interconnections. Six NX core holes were drilled along the grout curtain after completion of grouting to verify satisfactory conditions. Neither logs nor accounts of the findings associated with these borings are available.

3.2 1952-1953 Left Abutment Grouting

On 29 July 1953 the reservoir manager reported several springs between the spillway and the left side of the valley, about 1000 feet downstream of the embankment and adjacent to a construction haul road which paralleled the spillway. The largest spring was at the site of a pre-construction spring which had dried up when the spillway was excavated. All of the observed seepage was clear. Monitoring of the springs began in September 1953 and included construction of a number of weirs on the ground surface as well as in the spillway drainage galleries. Weir measurements were closely correlated with reservoir level. Chemical analysis of spring water and reservoir water samples compared with spring water sampled pre-construction also indicated the source of the observed seepage was the reservoir. District letter to the Division Engineer, dated 7 February 1955, described the seepage and monitoring and proposed a grouting program.

Based on the location where major seepage entered the spillway drainage gallery and the pool elevation initiating flow, the District judged that the seepage path was either a continuous open joint in bedrock or a series of interconnecting joints through a sandstone layer (SS4) in the left abutment. Reference drawing 038b-U1-10_104 in Appendix B for a profile view of the left abutment grouting in relation to geologic unit SS4. The potential danger to the dam was described in the letter as possible soil erosion of the intake area and of the clay joint filling which could lead to development of a flow channel within the soil overburden.

Based on concerns regarding the substantial seepage observed in the left abutment area, the District recommended grouting through a line of vertical grout holes spaced on five-foot centers along the upstream side of the dam crest for a distance of 205 feet riverward from the spillway and drilled to a depth of 107 feet. The recommendation was approved 10 February 1955.

Grouting of the left abutment was conducted from October 1955 through January 1956. Instead of a line of vertical grout holes as originally recommended and approved, an array of 8 inclined EX holes (1-7/16 inch) was drilled and grouted through the right wall of the spillway into the jointed sandstone stratum (Figure 3-15 and drawing 038b-U1-10_104). Inclinations of holes ranged from 1V on 1.10H to 1V on 14.6H and holes were aligned parallel with the dam axis. The total quantity of grout used was 7610 cubic feet. Measured spillway gallery flow showed a slight reduction during grouting. With the rise to summer pool during 1956, seepage was only marginally less than prior to grouting. The grouted zone extended between El 1610 and 1635.

After grouting was completed, seepage as measured at the weirs was reduced only slightly for pool elevations above 1631 to 1638. When the pool is below this range, the weirs along the left valley wall are essentially dry. However, the grouting may have had the unintended effect of perching groundwater within the abutment, which may have counterbalanced the slight decrease in observed gallery seepage. No further action has been taken to reduce left abutment seepage.

High pressures were used during grouting (on the order of 100 psi) such that there is concern that the upper rock strata as well as the embankment and overburden soils could have sustained damage as a result of this grouting work

3.3 1957 Incident and Emergency Repair

Seepage at the right abutment predates completion of the dam construction. A memorandum dating from dam construction documents the presence of several springs in the right abutment area during embankment construction. As referenced in Section 3.1, drains were installed during construction to intercept flow coming from the springs. In the project records, there is no explicit mention of unexpected seepage, beyond that coming from the known springs, observed in the right abutment area during the earliest years of reservoir operations (i.e., prior to Spring 1957). On 8 May 1957 (at the onset of a serious seepage-related incident) the reservoir manager reported muddy water flowing from the rock drain at the downstream toe of the dam in the original stream channel at approximate Sta.10+50 (Figure 3-9). The reservoir manager reported that the discoloration had been observed a week earlier but the flow now appeared to be increasing – as of 9 May 1957, the flow was measured at 9.6 cfs was and increasing. This report implies that clear flow had been present prior to that time, but it was not documented.

Figure 3-9. Downstream Toe of Embankment in 1957

After inspection by District Office staff the next day, an effort was begun to monitor the flow quantity and determine the source of the seepage. On 9 May 1957 a temporary weir was constructed, to measure the flow, and an initial reading was taken. The flow rate was measured at 9.6 cfs. By the next morning, flow had increased significantly. At that time a partial drawdown of the reservoir level (by 20 feet) was ordered. During reservoir drawdown, the increased outflow raised the water level at the downstream toe and flooded the weir.

Consequently, the gates had to be closed each time a weir reading was taken. This was very time consuming and slowed the drawdown process. To correct the problem, an earth dike was built to isolate the weir from the dam outflow and pumps were installed to discharge flow from the weir over the dike and into the outflow channel. By 15 May 1957 reliable weir readings could be taken without closing the gates. Because weir readings showed no further increase of muddy seepage, reservoir drawdown was stopped on 17 May 1957. The pool was maintained approximately 30 feet below summer pool. Drilling to locate the source of the seepage proceeded during the next two weeks. Holes were augured in the embankment with no sign of seepage or voids. Holes were then core drilled along the downstream right abutment contact. Drill water was lost in all three abutment holes; however, dye added to the holes did not appear in the seepage at the downstream toe.

While drilling focused on the abutment, changes were developing within the embankment. On the morning of 28 May 1957, a large rock, which had been covering one of the initial auger holes, was found several feet from the hole with bits of mud scattered around. The hole was at Sta. 8+25, four feet downstream of centerline. It was apparently blown off the hole by a surge of air pressure from a collapsing void in the embankment. Stones dropped in originally dry-holes indicated they now contained water.

The water level in the holes was measured the next day, and it was found to be nearly at the pool elevation. On the next day, 30 May 1957, a sound of rushing water described as “quite a roar” could be heard in the hole. Dye placed in the hole appeared at the downstream toe an hour later.

At this point, further drawdown of the reservoir was ordered. The dike protecting the weir had been breached two days earlier to save pumping costs and so had to be rebuilt. The pool was lowered an additional 20 feet from 30 May 1957 to 4 June 1957. The drawdown was halted because the leakage decreased.

A grout mixing plant and additional drilling equipment were mobilized by the District. Prior to grouting, additional exploratory drilling continued. On 10 June 1957, over a month after the initial report of muddy flow, one of the drill holes in the embankment encountered a void in the impervious core just above the grout cap at Sta. 8+25. No remedial action was taken, and drilling continued without further incident until 18 June 1957, when two more holes encountered voids.

This finally led to a decision to lower the pool an additional 60 feet (to El. 1560) over a 10 day period from 18 June 1957 to 28 June 1957. It is interpreted that a single void was detected in three subject borings and that the cross-section and elevation views of the grouted void are based on conditions encountered after all grout holes were drilled.

On 21 June 1957 initial grouting of the void began. Exploratory drilling continued in the embankment until October with the purpose of locating additional voids or piping channels. An unsuccessful attempt was made to locate the outlet of the pipe placed during construction to drain springs on the upstream right abutment. In general, the exploratory holes were grouted on completion; however, a row of holes drilled along the upstream edge of the blanket drain were partially backfilled with sand and capped with grout. There are no detailed logs from these borings, although there are limited records indicating depths at which water was lost while advancing borings and associated grout volumes. No additional voids were encountered;

however drill water was lost in most of these holes at or within several feet above top of rock.

Two exploratory holes had exceptionally high grout takes located 180 feet upstream of centerline at approximately the same station as the void. Both holes were drilled to top of rock and both lost drill water within two feet of that point.

From June until November repairs consisted of filling the void with grout and consolidation grouting the surrounding area of the foundation and embankment. A pattern of holes was drilled and grouted on five-foot centers from Sta. 7+90 to 8+65 extending 25 feet upstream and downstream from the dam axis. Initial efforts to fill the void with sand-cement grout left zones of soft wet material beneath the grout. After unsuccessful attempts to bail the wet material, a gravel pack grouting procedure was successful. Large diameter holes were filled with gravel and grouted with a neat cement grout through a two-inch pipe which had been placed to the bottom.

The neat cement grout displaced water and mud upward through the gravel and forced water out of adjacent holes. Four gravel-pack holes (two 12-inch and two 10-inch diameter) were drilled and grouted. After gravel pack grouting, on 17 August 1957, seepage at the downstream toe became clear. Figure 3-10 shows a plan of the exploratory drilling and emergency grouting.

Figure 3-11 shows a plan view of the consolidation grouting and Figure 3-12 shows the cross section view of the grouted void. Larger versions of these drawings can be found in Appendix H. Note that the cross-section view of the grouted void is based on conditions encountered after all grout holes were drilled. The void volume within the impervious core was estimated to be approximately 100 yd3. Refer to drawings 038-U1-10_113, 038-U1-10_114 and 038-U1-10_115 in Appendix B for full size plan, profile and section views of the grouted void area.

Prior to this, the seepage continued to be muddy, even 50 days after the reservoir level was drawn down to El. 1560 (the level that was maintained in the reservoir after three separate draw downs, culminating on 28 June 1957). Based on information obtained during the 1957 explorations, the bottom of the void was situated around El. 1600 to El. 1610 at the dam centerline. Therefore, the source of water feeding the muddy flow at this time was likely not the reservoir. It is possible that the internal erosion event created or enlarged a hydraulic connection with the right abutment and that seepage from the right abutment foundation was sufficient to allow internal erosion to continue once the reservoir level dropped below the level at which it could influence this seepage path. Initial grouting of the void required 831 bags of cement and 1,654 cubic feet of sand. The total grouting program, including the void itself and pattern grouting required 17,751 bags of cement.

It is worth reiterating that the exploratory drilling did not identify the downstream portion of the seepage path. An attempt was made to install a discontinuous vertical drain/filter by drilling small diameter holes along the upstream edge of the rock drain between approximate Sta. 8+30 to Sta. 9+80 and backfilling the holes with sand. In addition, an attempt was made to fill the upstream portion of the internal erosion path with grout. This attempt was partially successful in that a well-defined path was identified nearly due-upstream of the grouted void location. This grouting was terminated approximately 180 feet upstream of centerline (presumably near the edge of the reservoir). Grout takes at the upstream end of this grouting suggest that a large open path was left untreated: takes of 1280 and 1360 bags were recorded in two of these holes.

Figure 3-10. Plan of Right Abutment Emergency Investigations (See Appendix H for full scale drawing)

Note high grout takes at upstream end of emergency grouting.

Numbers shown at each hole represent the number of cement bags used to backfill the hole.

Holes backfilled with sand in an attempt to affect a filter.

Figure 3-11. Plan of Right Abutment Consolidation Grouting

Figure 3-12. Cross Section View of Grouted Void @ Sta. 8+30

3.4 Potential Obstructions

3.4.1. Dam Cutoff Trench (6+09 to 11+02)

As discussed previously in Section 3.1.1, extensive rock grouting was conducted in the dam cutoff trench between Stations 6+09 and 11+02. To accomplish this, two lines of two inch diameter steel grout pipes were embedded into the concrete grout cap (Figure 3-13) with a final spacing of 5 feet and left in place following completion of the grouting program. Location of the two grout lines (A and B) are 2.5 feet upstream and 2.5 feet downstream of the dam axis and are inclined towards the right abutment at 10 to 36 degrees from vertical. See Figure 3-14 for a profile view of the limits of right abutment grouting. Construction records note that seepage inflow near the original river channel, approximate Sta. 11+00, interfered with placement of impervious fill in the cutoff trench. The seepage was controlled by placing gravel covered with burlap on both sides of the grout cap and pumping through pipes connected to a header system while fill was being placed. The drains were gravity grouted through the header pipes when the cutoff was backfilled. There are conflicting records of the grouting. It is not clear if grouting was done on both sides of the grout cap or only on the upstream side.

Refer to drawing 038-U1-10/116 in Appendix B for a full size version of this figure showing the extents of grouting and the approximate elevations of the concrete grout cap. Section and plan drawings of the cutoff trench can also be found in Appendix B as drawings 038-U1-10/101, 038- U1-10/109 and 038-U1-10/110.

Figure 3-13. Grout Cap and Embedded Grout Tubes – Sta. 10+50

Figure 3-14. Extents of Potential Grouting Steel in Right Abutment Rock

See Drawing 038b-U1-10_116 in Appendix B for full size drawing

Approximate extents of grouting.

3.4.2. Grouted Void Area at Right Abutment

As part of the 1957 void repair, a pattern of holes was drilled and grouted on five-foot centers from Sta. 7+90 to 8+65 extending 25 feet upstream and downstream from the dam axis (Figure 3-11). Large diameter holes were drilled to rock followed by insertion of a two inch diameter grout pipe. Records indicate that grouting occurred until grout refusal at which point the grout pipes were gradually withdrawn followed by additional grouting. There is indication that some separation of grout tubing occurred during withdrawal resulting in tubing left in place. It is not clear at which holes this occurred. Drill steel and/or drill bits were lost at several of the exploratory holes. A listing of remnant drilling and grouting steel left in place, as per available documentation, can be found in Table 3-1. Piezometers were installed following the exploration and repair program. There is record of casing which was too difficult to extract in several holes during pz installation and was left in place. Refer to drawings 038-U1-10_113, 038-U1-10_114 and 038-U1-10_115 in Appendix B for full size plan, profile and section views of the grouted void area and limits of past consolidation grouting.

3.4.3. 1955-1956 Left Abutment Grouting

Documentation exists indicating that drill bits were lost in proposed holes G-1 and G-5 (Figure 3-15) resulting in abandonment and relocation of…