Contract 2_Lewisville_GIR.pdf

FOR OFFICIAL USE ONLY

GEOTECHNICAL INTERPRETIVE REPORT

LEWISVILLE DAM SAFETY MODIFICATION

SPILLWAY AREA

DENTON COUNTY, TEXAS

US ARMY CORPS OF ENGINEERS

FORT WORTH DISTRICT &

SWD DAM SAFETY PRODUCTION CENTER

STATUS: 100% DESIGN

DATE: May 2021 Final Version

GEOTECHNICAL INTERPRETIVE REPORT STATUS: 100% DESIGN

LEWISVILLE DAM MODIFICATION – CONTRACT 2 DATE: May 2021

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DISCLAIMER AND LIMITATIONS

Disclaimer

This Geotechnical Interpretive Report (GIR) contains actual subsurface and other information that was collected at or adjacent to the Site by the Government, or for the Government, for use in preparing the Contract Documents.

This GIR contains interpretive information. This GIR is a summary, the full-text interpretive documents, are included in the interpretive appendices. A separate Geotechnical Data Report (GDR) and Non-Interpretive Appendices contains non-interpretive information. Offerors can review the information in the GIR, but they must draw their own interpretations of the information provided in this report and the interpretive appendices and must not solely rely on the provided interpretations in preparation of their proposals. The Contractor may not rely upon opinions and interpretations provided in the GIR. This report is provided to the bidders for informational purposes only.

Limitations

The Government does not represent that the boring and test pit/trench logs, field and laboratory test results and other available geologic information show the conditions that will be encountered in performing the work. The Government represents only that such information shows conditions at the locations of the borings, test pits/trenches, or other field data collection locations at the time that the data were collected. Each bidder must form their own opinion of the character of the work and of the materials to be excavated, make their own interpretations, and satisfy themselves by their own interpretations and research regarding all conditions affecting the work to be performed. The Contractor must assume all responsibility for deductions and conclusions as to the nature or condition of all earth, rock and other materials to be excavated and the difficulties of making and maintaining the required excavations, and of performing other work affected by the geology and subsurface conditions at the Site. The Contractor must assume that various rock and soil conditions may be encountered in excavations, including materials that are difficult to handle.

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52.236-4 Physical Data

As prescribed in 36.504, insert the following clause in solicitations and contracts when a fixed-price construction contract is contemplated and physical data (e.g., test borings, hydrographic, weather conditions data) will be furnished or made available to offerors.

All information to be furnished or made available to offerors before award that pertains to the performance of the work should be identified in the clause. When paragraphs are not applicable, they may be deleted.

PHYSICAL DATA (APR 1984)

Data and information furnished or referred to below is for the Contractor’s information.

The Government shall not be responsible for any interpretation of or conclusion drawn from the data or information by the Contractor.

The indications of physical conditions on the drawings by both USACE and Contractors working on the project from the 1940s to the present. The bidders are provided a Geotechnical Interpretive Report (GIR), that contains information that USACE considers interpretive. This GIR contains two parts, a summary narrative and a number of appendices. The appendices contain the original reports and/or drawings with the interpretive information.

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GIR REPORT FUNCTION

This report, the Geotechnical Interpretative Report (GIR), functions to provide a summary of interpretative reports, drawings, and figures for this project, created at different times. Some of the information within and attached was created by USACE, some by contractors working for USACE.

For more information, please see the full-text appendices that contain detailed reports for each specific subject.

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TABLE OF CONTENTS

DISCLAIMER AND LIMITATIONS ................................................................................................ ii GIR REPORT FUNCTION ........................................................................................................... iv

TABLE OF CONTENTS

INDEX OF FIGURES

INDEX OF TABLES

INDEX OF INTERPRETIVE APPENDICES

PART 1 - 1940-1950’s PRE-CONSTRUCTION INTERPRETIVE DOCUMENTS

1.1 Spillway Interpretive Sections and Profiles

PART 2 - 2015 SPILLWAY GEOLOGIC MAPPING (USACE)

2.1 Spillway Interpretive Bedrock Mapping (2015)

2.2 Rose Diagrams, USACE, 2016

PART 3 - 2017 INVESTIGATION SECTIONS & PROFILES (CDM-Smith)

3.1 CDM-Smith Interpretive Profiles

3.2 CDM Interpretive Cross-Section (2017)

3.3 CDM Smith Stereonet & Rose Diagram (2018)

3.4 Spillway Ground-Penetrating-Radar (GPR) Survey Interpretive Results (2017)

PART 4 - 2018 INVESTIGATION PROFILES & SECTIONS (STANTEC)

4.1 Stantec Interpretive Cross-Sections (2019)

PART 5 - 2019 ANCHOR STUDY (NICHOLSON/STANTEC)

5.1 Anchor Study Interpretive Report Conclusions

5.2 Anchor Study Report Lessons-learned

PART 6 - INTERPRETIVE ROCK STRENGTHS FROM LAB DATA

6.1 1947 Interpretive Rock Strengths

6.2 1951 Interpretive Rock Strengths

6.3 2015 Interpretive Eagle Ford Rock Strengths

DENTON COUNTY, TEXAS

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INDEX OF FIGURES

Figure 1-1 1947 USACE Interpreted Profile (USACE, 1947, Plate 4) Figure 1-2 Colorized Version of 1947 Whole-Dam Profile (Dam Safety Modification Report) ... 11 Figure 1-3 Index Map of Pre-Construction Cross-Sections (Plate IV-7, USACE) Figure 1-4 Legend (part 1 of 2) for Figure 1-6 through Figure 1-9 Figure 1-5 Legend (Part 2 of 2) for Figure 1-6 through Figure 1-9 Figure 1-6 Preconstruction Cross-Section A-A, across spillway, (Plate IV-7, USACE) Figure 1-7 Preconstruction Cross-Section B-B, D/S of Spillway (Plate IV-7, USACE) Figure 1-8 Preconstruction Cross-Section, C-C, D/S of Spillway (Plate IV-7, USACE) Figure 1-9 Preconstruction Cross-Section D-D, D/S of Spillway (Plate IV-7, USACE) Figure 1-10 Preconstruction Profile downstream of the future structure, showing [then] existing condition (Plate IV-6, USACE) Figure 1-11 Pre-Construction Profile, showing the [then] Future Condition (USACE) Figure 1-12 Pre-Construction Cross-Section of Spillway at Dam Centerline, (USACE) Figure 2-1 Overview Map of the 2015 Spillway Bedrock Mapping, also shows the locations of sheets 101, 102, and 103 Figure 2-2 Sheet 101 of Spillway Mapping Figure 2-3 Sheet 102 of Spillway Mapping Figure 2-4 Sheet 103 of Spillway Mapping Figure 2-5 USACE Interpretive Rose Diagram based on 2015 mapping (USACE, 2016) Figure 3-1 CDM Spillway Profile at Dam Station 279+00 (CDM Sheet 2-5) Figure 3-2 CDM Spillway Profile at Spillway Centerline (CDM Sheet 2-6) Figure 3-3 CDM Spillway Profile at Dam Station 285+50 (CDM Sheet 2-7) Figure 3-4 CDM Spillway Cross-Section, 30-ft D/S of Dam Centerline (CDM Sheet 2-4) Figure 3-5 Example of raw and interpreted downhole images of the optical televiewer logs (CDM-Smith, 2017) Figure 3-6 Example borehole Stereonet from interpreted downhole geophysics results (CDM- Smith, 2018) Figure 3-7 Example borehole Rose Diagram from interpreted downhole geophysical results (CDM-Smith, 2018) Figure 3-8 Interpretative Map of portions of the Lewisville Spillway (G&RK, 2018) Figure 3-9 Interpretation of features seen in a part of GPR survey, depth=2-feet (G&RK, 2018) Figure 3-10 Interpretation of Features seen in GPR map at 2-feet depth (G&RK, 2018) Figure 3-11 Interpretations of features seen in GPR survey at 4-feet depth (G&RK, 2018) Figure 4-1 Stantec Spillway Cross-Section, along Dam Centerline (Stantec Sheet I-1), 1 of 2 . 34 Figure 4-2 Stantec Spillway Cross-section, along Dam Centerline (Stantec Sheet I-1), 2 of 2 . 35 Figure 4-3 Stantec Spillway Cross-section, 30-ft D/S of Dam Centerline (Stantec Sheet I-1), 1 of 2 Figure 4-4 Stantec Spillway Cross-section, 30-ft D/S of Dam Centerline (Stantec Sheet I-1), 2 of 2 Figure 4-5 Stantec Spillway Cross-section 915-ft D/S of Dam Centerline (Stantec Sheet I-5) 1 of Figure 4-6 Stantec Spillway Cross-Section 915-ft D/S of Dam Centerline (Stantec Sheet I-5) 2 of 2 Figure 6-1 Interpretive Rock Strengths from 1951 Project Report

DENTON COUNTY, TEXAS

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INDEX OF TABLES

Table 6-1 Eagle Ford 1947 Direct Shear Test Results Table 6-2 Eagle Ford 2015 Consolidated-Undrained Triaxial Test Results Table 6-3 Eagle Ford Direct Shear Test Results

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INDEX OF INTERPRETIVE APPENDICES

USACE Preconstruction Drawings – 1950’s

USACE Pre-Construction Design Memorandum for Spillway (1951) USACE Pre-Construction Interpretive Sections and Profiles (1950’s)

USACE Spillway Mapping – 2010’s USACE Interpretive Spillway Mapping (2015) USACE Interpretive Fracture Rose Diagram (2016)

CDM Spillway Investigation – 2010’s

CDM Narrative Report (2017) CDM Interpretive Fractures from Optical Televiewer Logs (2018) CDM / G&RK Spillway Ground Penetrating Radar Report (2017)

Stantec Spillway Investigation – 2010’s

Stantec Narrative Report (2019) Stantec markups on USACE Interpretive Sections and Profiles (2019)

Nicholson / Stantec Anchor Study – 2010’s Anchor Study Narrative Report (2019)

GEOTECHNICAL INTERPRETATION REPORT STATUS: 100% DESIGN

LEWISVILLE DAM MODIFICATION DATE: May 2021

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PART 1 - 1940-1950’s PRE-CONSTRUCTION INTERPRETIVE

DOCUMENTS

1.1 Spillway Interpretive Sections and Profiles

Throughout this GIR, the words “cross-section” and “profile” refer to spillway stationing (unless otherwise noted), which is perpendicular to dam centerline stationing. To change to reference to dam centerline stationing, please reverse the terms in your mind.

The original preconstruction work included preparing plans and specifications. As part of that work, interpretive drawings were created.

The 1947 “Definitive Project Report contains a profile across the entire length of the dam (this is a case where dam stationing, not spillway stationing is used). This profile is shown as Figure 1-1, and a later colorized interpretive version is shown as Figure 1-2 (dam stationing, not spillway stationing, again). The profile shows weathered Eagle Ford Shale and intact Eagle Ford Shale underneath the spillway

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Figure 1-1 1947 USACE Interpreted Profile (USACE, 1947, Plate 4)

Sp illw ay

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Figure 1-2 Colorized Version of 1947 Whole-Dam Profile (Dam Safety Modification Report)

Sp illw ay

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The original spillway design included four (4) spillway geologic cross-sections. An index map is shown as Figure 1-3, and cross-sections A-A, B-B, C-C, and D-D are shown as Figure 1-6, Figure 1-7, Figure 1-8, and Figure 1-9, respectively. See the interpretive appendices for electronic versions of these drawings.

Figure 1-3 Index Map of Pre-Construction Cross-Sections (Plate IV-7, USACE)

A

C

D

N

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Figure 1-4 Legend (part 1 of 2) for Figure 1-6 through Figure 1-9.

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Figure 1-5 Legend (Part 2 of 2) for Figure 1-6 through Figure 1-9.

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Figure 1-6 Preconstruction Cross-Section A-A, across spillway, (Plate IV-7, USACE)

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Figure 1-7 Preconstruction Cross-Section B-B, D/S of Spillway (Plate IV-7, USACE)

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Figure 1-8 Preconstruction Cross-Section, C-C, D/S of Spillway (Plate IV-7, USACE)

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Figure 1-9 Preconstruction Cross-Section D-D, D/S of Spillway (Plate IV-7, USACE)

There are two wider profiles, the first profile, Figure 1-10, shows the pre-construction conditions of the area both upstream and downstream of the spillway, and the second profile, Figure 1-11 shows the [then future] post-construction condition of the area upstream and downstream of the spillway.

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Figure 1-10 Preconstruction Profile downstream of the future structure, showing [then] existing condition (Plate IV-6, USACE)

Figure 1-11 Pre-Construction Profile, showing the [then] Future Condition (USACE)

There is one preconstruction cross-section of the spillway, that shows the then proposed excavation limits, shown as Figure 1-12. This shows the existing ground line as well as the projected spillway configuration.

Flow

Flow

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Figure 1-12 Pre-Construction Cross-Section of Spillway at Dam Centerline, (USACE)

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PART 2 - 2015 SPILLWAY GEOLOGIC MAPPING (USACE)

2.1 Spillway Interpretive Bedrock Mapping (2015)

Foundation mapping was completed downstream of the spillway apron within a week of the 2015 spillway flow event by USACE personnel. The location of exposed rock, water, rubble, and fractures within the rock were mapped by professional geologists. Figure 2-1 is an overview map, and Figure 2-2, Figure 2-3, and Figure 2-4 are more detailed maps. See the interpretive appendices for electronic drawings.

Figure 2-1 Overview Map of the 2015 Spillway Bedrock Mapping, also shows the locations of sheets 101, 102, and 103.

FL

O

W

SHEET 102 SHEET 103

SHEET 101

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Figure 2-2 Sheet 101 of Spillway Mapping

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Figure 2-3 Sheet 102 of Spillway Mapping

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Figure 2-4 Sheet 103 of Spillway Mapping

2.2 Rose Diagrams, USACE, 2016

The New England District USACE used the surface fracture orientations from the 2015 spillway geologic mapping to create a rose diagram shown as Figure 2-5. See the interpretive appendices for the original electronic version.

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Figure 2-5 USACE Interpretive Rose Diagram based on 2015 mapping (USACE, 2016)

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PART 3 - 2017 INVESTIGATION SECTIONS & PROFILES

(CDM-Smith)

3.1 CDM-Smith Interpretive Profiles

Throughout this GIR, the words “cross-section” and “profile” refer to spillway stationing, which is perpendicular to dam centerline stationing. To change to reference to dam centerline stationing, please reverse the terms in your mind.

CDM-Smith created several spillway profiles, shown below as Figure 3-1, Figure 3-2, and Figure 3-3, for inclusion in their narrative report. The interpretive appendices contain electronic sheets.

Figure 3-1 CDM Spillway Profile at Dam Station 279+00 (CDM Sheet 2-5)

Figure 3-2 CDM Spillway Profile at Spillway Centerline (CDM Sheet 2-6)

Figure 3-3 CDM Spillway Profile at Dam Station 285+50 (CDM Sheet 2-7)

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3.2 CDM Interpretive Cross-Section (2017)

perpendicular to dam centerline stationing. To change to reference to dam centerline stationing, please reverse the terms in your mind.

CDM-Smith created a spillway cross-section, shown below as Figure 3-4, for inclusion in their narrative report. The interpretive appendices contain electronic sheets.

Figure 3-4 CDM Spillway Cross-Section, 30-ft D/S of Dam Centerline (CDM Sheet 2-4)

3.3 CDM Smith Stereonet & Rose Diagram (2018)

The CDM-Smith reports include interpretations of the locations of fractures and bedding planes in each boring based on the televiewer image. The interpretations were created in WellCAD. Figure 3-5 shows an example of a raw and interpreted downhole televiewer image. Based off these interpretations, the report includes stereonets and rose diagrams, for each boring. An example stereonet is shown on Figure 3-6, and an example rose diagram on Figure 3-7. To see the full electronic versions of the interpretive downhole geophysical data, stereonets, and the rose diagrams, see the interpretive appendices.

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Figure 3-5 Example of raw and interpreted downhole images of the optical televiewer logs

(CDM-Smith, 2017)

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Figure 3-6 Example borehole Stereonet from interpreted downhole geophysics results (CDM-

Smith, 2018)

Figure 3-7 Example borehole Rose Diagram from interpreted downhole geophysical results

(CDM-Smith, 2018)

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3.4 Spillway Ground-Penetrating-Radar (GPR) Survey Interpretive Results (2017)

G&RK Consulting Associates, LLC, perform a geophysical survey at the Lewisville Dam Spillway for CDM-Smith. In the report, the purpose was stated as; “CDM Smith contacted G&RK to perform a nondestructive subsurface investigation to locate possible voids under the Lake Lewisville Spillway prior to installation of heavy equipment.” The final report is provided in the interpretive appendices.

The scope of service, from the report was: “G&RK was contracted to perform a nondestructive subsurface investigation using Ground Penetrating Radar (GPR) to scan an area 566.5’ wide by 100’ long, encompassing the northern half of the spillway, for sub-slab voids. The entire 566.5’ width was to be scanned on a 2 foot grid.”

“On January 9, 10 and 11, 2017, Robert Hendricks PhD, Tori Carter and Linda McClellen P.E., performed the subsurface investigation on the above site. Equipment used on this project was a Geophysical Survey System Incorporated (GSSI) Ground Penetrating Radar (GPR) using a 400 MHz antenna set to a depth of 40 ns or about 6 feet.”

“The following are site-specific investigation details:

• 2’ grid lines were laid out in a north-south direction for the entire width of the spillway using a purpose-built device created by G&RK for this project. The spillway contains 27 sections of north/south trending panels.

• The ground penetrating radar initial scan line was evaluated to assess the need for filter and gain adjustments.

• Grid lines were scanned with GPR starting at the western side of the spillway and working eastward.

• The data gathered was reviewed in the field.

• The progress and information was noted in the field log and site photographed.

• Data was downloaded into an office computer and reviewed for accuracy and detail. A 3D model of the data was created from the individual scans.”

“Results:

• GPR successfully penetrated the subsurface of the spillway to a depth of about 6 feet.

• Rebar spacing was determined to be approximately 1 foot on center with the upper rebar at a depth of 6” below the concrete surface (see Figures AB-1 and AB-2 [note: available in the interpretive appendices]). A second mat of rebar is suspected but is difficult to detect with GPR due to interference from the upper mat. Concrete increases in thickness in the northern portion of the spillway to between 3 and 5 feet thick (see Figure AB-3 [note:

available in the interpretive appendices]).

• Moisture was detected under the slab in the western portion of the spillway and in an isolated area in the eastern portion of the spillway (see Drawing 2 and Figures AB-4 and AB-6 [note: available in the interpretive appendices]). This moisture could indicate the presence of possible sub-slab void space (i.e. signals could be void space filled with water).

The moisture regions are associated with the location of pressure relief wells (see Figure AB-1 [note: available in the interpretive appendices]) and construction joints (see Figure AB- 2 [note: available in the interpretive appendices]).

• Significant moisture and possible void space was detected by GPR in the northern portion of the spillway under the thickened concrete slabs. This moisture is located directly under the

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voids filled with water) (see Drawing 1 and Figure AB-5 [note: available in the interpretive appendices])”

“Limitations:

• Ground penetrating radar is limited by size of lines and depth ratio. Radar can detect anomalies at about 1” diameter per foot of depth.

• GPR signals from void space (air in the sub-surface) and moisture (water in the sub-surface) are similar. In wet conditions voids with pore space filled with water will produce GPR signals associated with moisture and not signals associated with air, possibly masking the presence of a void.

• Thickness of void space is difficult to determine due to the interaction of the electromagnetic wave across the concrete/air and soil/air interface. As such the GPR scans show the areal extent of the voids and are not used to calculate a volume of potential void space.

• The exact nature of the void space is undeterminable. Ground penetrating radar indicates a void if there is a high volume of air in the material, for example, loosely packed sand, large cobbles with significant pore space or a series of smaller voids spread throughout the area.

Anomalies noted as possible voids could be large rocks, branches or other debris mixed in the soil used for fill material.”

Figure 3-8, Figure 3-9, Figure 3-10, and Figure 3-11, below, show maps of the spillway GPR survey and contain interpretations of the anomalies seen thereon.

Figure 3-8 Interpretative Map of portions of the Lewisville Spillway (G&RK, 2018)

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Figure 3-9 Interpretation of features seen in a part of GPR survey, depth=2-feet (G&RK, 2018)

Figure 3-10 Interpretation of Features seen in GPR map at 2-feet depth (G&RK, 2018)

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Figure 3-11 Interpretations of features seen in GPR survey at 4-feet depth (G&RK, 2018)

The electronic drawings and documents are included in the full-text interpretive appendices.

GEOTECHNICAL BASELINE REPORT STATUS: 100% DESIGN

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PART 4 - 2018 INVESTIGATION PROFILES & SECTIONS

(STANTEC)

4.1 Stantec Interpretive Cross-Sections (2019)

perpendicular to dam centerline stationing. To change to reference dam centerline stationing, please reverse the terms in your mind.

Stantec updated three cross-sections as part of their investigation into the spillway. The first cross-section was along the spillway [dam] centerline (Figure 4-1 and Figure 4-2). Stantec created a second cross-section 30-feet downstream of the spillway [dam] centerline (Figure 4-3 and Figure 4-4). Stantec’s third cross-sections is 915-feet downstream of the dam centerline (Figure 4-5 and Figure 4-6). This is found on sheet ID 2-4 in their report.

Figure 4-1 Stantec Spillway Cross-Section, along Dam Centerline (Stantec Sheet I-1), 1 of 2

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Figure 4-2 Stantec Spillway Cross-section, along Dam Centerline (Stantec Sheet I-1), 2 of 2

Figure 4-3 Stantec Spillway Cross-section, 30-ft D/S of Dam Centerline (Stantec Sheet I-1), 1 of 2

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Figure 4-4 Stantec Spillway Cross-section, 30-ft D/S of Dam Centerline (Stantec Sheet I-1), 2 of 2

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Figure 4-5 Stantec Spillway Cross-section 915-ft D/S of Dam Centerline (Stantec Sheet I-5) 1 of 2

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Figure 4-6 Stantec Spillway Cross-Section 915-ft D/S of Dam Centerline (Stantec Sheet I-5) 2 of

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PART 5 - 2019 ANCHOR STUDY (NICHOLSON/STANTEC)

Please see the Anchor Study Narrative Report, in the full-text interpretive appendices, for more information on the anchor study.

5.1 Anchor Study Interpretive Report Conclusions

The anchor study contractor reached the following conclusions:

“Many changes were required from the original scope of work to find a solution to the weak bond strength in the Eagle Ford Shale. Analysis of Anchors 318, 320, and 427 shows that the underream method can provide the desired design capacity of 422 kips. The use of load cells under future anchor heads could be useful in monitoring total load loss, though load cells can have limitations in durability and longevity. Lift off testing can also be completed to check anchor load over the long term.”

“One inconclusive result is in the flushing of bond zones with water and air injection. Because post-grouting was successful in Anchors 425 and 426 it cannot be determined which variable increased bond strength from approximately 10 psi to 38 psi. It is believed that both had a positive influence on the performance of the grout to rock bond strength. Longer bond zone lengths may be able to achieve the capacity for 12-strand anchors, though post-grouting is not desired due to the required pressures, thus, additional testing would be needed for verification of the water and air injection flushing. For bar anchors with smaller load requirements, it would be advantageous to avoid the underreaming method because it would eliminate up to two trips of running drill rods in and out of the borehole. Duplex drilling with water and air injection may produce the required strength depending on the borehole diameter and length. The same protective measures would need to be in place for drilling the underream, but the time required could be reduced by eliminating the underream.”

“Another option to reduce cost is to make the underream hole smaller on the bar anchors. This would reduce the size of drill tooling, casing, concrete coring and bearing plates. There are manufacturers of underream tools which have options for a smaller body underreamer with differing opening diameters. In consideration of the design with smaller underream holes, future test holes should not be needed as long as the underream bearing area is proportionate to the 16-inch underream and the loading requirements of the small bar anchors.”

5.2 Anchor Study Report Lessons-learned

The anchor study report contains the following lessons-learned:

• “Installing anchors with a crane would be more efficient than using an uncoiler.”

• “Steel reference frames can be easily influenced by weather. Though production anchors would be stressed against concrete, stressing equipment could still be affected by major temperature changes and sunlight. Using tents to shade equipment could be beneficial in avoiding testing issues as well as providing cover for employees.”

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• “Anchor manufacturers have different anchor hardware designs/sizes (ex. Anchor heads, wedges, strand patterns) and often have stressing equipment that fits specifically for their anchor hardware. If using testing equipment not supplied by the anchor manufacturer, setup and alignment may be more difficult. Mock-up of the test setup can help in addressing this issue and allow modifications to be made prior to testing anchors.”

• “Alignment of the testing equipment is of the utmost importance prior to testing anchors both from a safety and performance standpoint. Checking for anchor head movement and/or shifting of testing equipment during the testing is also important.”

• “Single stage grouting restrains the strands at the top of the grout and can cause an angle in the strands from grout to anchor head if not centered at top of grout. On angled holes the strands should be centered at top of grout so that there is limited angle. Otherwise, the anchor head will be more susceptible to shifting during stressing. Larger centralizer in the free length would help in avoiding this.”

• “Single stage grouting can cause load loss over the free length of anchors. Additionally, the increased friction over the S-shape and change in diameter was not clearly understood from the strain gauge data which impacts how much load loss really occurred over the free length. Strain gauges could have been included above the bond zone within the free length before this transition. Feasibility to be discussed with strain gauge installer.”

• “Single stage grouting causes the strands to react slower to increases and decreases due to the friction in the free length.”

• “Future test anchors and select production anchors should have re-stressable heads for lift off tests. This would have allowed additional data to be gathered over time on the anchor load versus relying purely on strain gauge data.”

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PART 6 - INTERPRETIVE ROCK STRENGTHS FROM LAB DATA

Laboratory testing has lead to interpretive rock strengths.

6.1 1947 Interpretive Rock Strengths

A total of 58 direct shear tests are reported in the 1947 Lewisville Definitive Project Report (included in the non-interpretive appendices). Some of those are for soils, and some were weathered or unweathered rock.

The 1947 Lewisville Definitive Project Report contains direct shear testing that is summarized in Table 6-1. The Phi and Cohesion values are interpretive.

Table 6-1 Eagle Ford 1947 Direct Shear Test Results

Hole # Sample Depth (ft)

Direct Shear Remarks

Maximum Ultimate φ(˚) C

(tsf) φ(˚) C (tsf)

6C-11, 6C-12 & 6C-

Composite No. 2- 14.0-42.6

23.

1 0.5 15.1 0.52

Weathered Shale

6C-11, 6C-12 & 6C-

Composite No. 2- 14.0-42.6

22.

9 0.42 15.4 0.45

Weathered Shale

6C-11, 6C-12 & 6C-

Composite. No. 2- 14.0-42.6

21.

5 0.26 15.9 0.35

Weathered Shale

6C-12 & 6C-19 Composite. No. 3 - 42.6-61.4

30.

5 0.45 29.0 0.4

Shale

6C-12 & 6C-19 Composite. No. 3 - 42.6-61.4 26 0.3 24.5 0.3

Shale

6C-12 & 6C-19 Composite. No. 3 - 42.6-61.4 26 0.3 24 0.3

Shale

6.2 1951 Interpretive Rock Strengths

The 1951 Design Memorandum for Construction of Spillway Report contains a graph that could be considered interpretive. It is shown here as Figure 6-1. The 1951 report is found in the interpretive appendices.

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Figure 6-1 Interpretive Rock Strengths from 1951 Project Report

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6.3 2015 Interpretive Eagle Ford Rock Strengths

The phi and cohesion were interpreted from the laboratory curves from the 2015 Spillway exploration.

The results are shown as Table 6-2 and Table 6-3.

Table 6-2 Eagle Ford 2015 Consolidated-Undrained Triaxial Test Results B or in g N um be r

Sa m pl e

N um be r

Sa m pl e ep th

(f t)

Triaxial Difference (σ1'-σ3')max

Ratio (σ1'/σ3')max φ(˚) C (psi) φ(˚) C

(psi) 15-L309 Core 41-43 45.9 12.5 49.6 7.8

Table 6-3 Eagle Ford Direct Shear Test Results

H ol e

Sa m pl e

N um be r

Sa m pl e ep th

(f t)

Direct Shear

Maximum Residual Presplit Residual φ(˚) C (tsf) φ(˚) C

(tsf) φ(˚) C (tsf)

15-L300 Core 6.8-8.5 24.4 0.4 11.2 0.2 --- --- 15-L300 Core 26.9-27.8 52.9 0 17.1 0 --- --- 15-L301 Core 6.5-7 49.9 0.2 10.7 0.2 --- --- 15-L301 Core 18-20 --- --- --- --- 10 0.2 15-L301 Core 47.5-48.3 43.2 1.1 10.8 0.2 --- --- 15-L301 Core 78.5-79.5 37.8 1.3 16.2 0.2 --- --- 15-L302 Core 18.7-19.5 27.2 0.6 13.6 0.1 --- ---

15-L302 Core 23.5-25 --- --- --- --- 18.

2 0.09

15-L302 Core 48.8-49.6 24.2 0.4 10.5 0.2 --- ---

15-L308 Core 47.8-50 13.6 2 10.1 0.2 13.

1 0.06

15-L309 Core 72-73 28.1 1.6 12.9 0.2 --- ---

The 2015 Spillway laboratory test report can be found in the non-interpretive appendices.