II.H.08.01_-_Optional_Bid_Item_0003_-_Geophysical_Survey.pdf

Optional Bid Item 0003-Spillway Geophysical Survey and Non-Destructive Testing

A) Geophysical Surveys and Non-Destructive Testing - General:

1. Intent: The purpose of geophysical surveys and non-destructive testing (NDT) is to define the location and geometry of potential voids beneath, and within, the concrete slabs of the spillway channel. In addition, the surveys and testing will assist in making a determination whether or not voids are filled or open. Geophysical survey methods are appropriate for imaging and evaluating the subsurface, while NDT methods are designed to evaluate man-made structures.

2. Work Extents: The work shall be performed throughout the full extent of the spillway slabs downstream of the two tainter gates (T1 & T2) from the base of the weir to the flip bucket. The work shall also be performed in the warm water chute from the outlet QC gate to the flip bucket.

3. Work Timing Restriction: Performance of work within this bid item shall not be performed until after the new Warm Water Intake Gates have been fabricated, installed and accepted by the government. The Contractor shall also coordinate scheduling of the work to periods that will ensure results are not adversely affected by other construction activities (due to vibrations, etc).

4. Work Staging/Phasing: A staged approach consisting of geophysical methods and

NDT methods shall be implemented. Additionally, prior to the geophysical methods, a video inspection of slab weepholes shall be performed. After inspecting the weepholes, the first stage shall consist of geophysical methods including ground penetrating radar (GPR) and spectral analysis of surface waves (SASW). The second stage shall consist of NDT methods including Slab Impulse Response (SIR) and Impact Echo (IE).

Geophysical surveys and NDT methods are complementary. Following completion of the geophysical surveys, NDT methods will then be implemented based on the results of the GPR and SASW surveys.

5. Field Validation of Methods: Initial field validation shall consist of testing each geophysical and NDT method at a designated location on the spillway channel floor.

Testing of each method is to be conducted before using a particular method. The results will be used to determine details regarding implementation of each method at the project location and how best to proceed. The testing shall be performed in the presence of the COR’s geophysics representative.

6. Coordination Scheduling: The spillway where the work is to be performed is used for releases of flow from the reservoir. The contractor shall coordinate with the COR on dates of planned work well in advance to ensure that necessary spillway discharges are not adversely impacted. The Contractor shall also be aware that in high water events, the government may require demobilization from the spillway area to allow for discharge from the reservoir.

Optional Bid Item 0003 - Spillway Geophysical Survey and Non-Destructive Testing

7. Pre-Construction Meeting: After submission of the Contractor’s work plan, a meeting shall be held to discuss the intent and implementation details of the work. The meeting shall include the Contractor’s geophysical consultant that will perform the work, the COR and the COR’s geophysics representative.

8. Software: The contractor shall use the latest versions of data acquisition, processing, and presentation software used to execute this scope of work in order to maximize software interoperability. This includes, but is not limited to, Adobe Professional, Microsoft Office, map preparation software such as Google Earth, and/or any supporting data collection, processing, and interpretation software.

B) Qualifications:

The company performing the work shall be specialized in subsurface geophysical investigations and shall have performed a minimum of 3 projects using the geophysical and NDT methods identified herein. Fieldwork and office technical work shall be performed by a Professional Engineer (PE) or Professional Geologist (PG) with 5 years or greater experience.

Resumes of staff shall be submitted.

C) Video Inspection of Weepholes:

There are approximately 275 weepholes in the spillway slab. The holes are 3 inch diameter, approximately 15 feet in length and extend through the slab into the underlying bedrock.

Video inspection of the full depth of each weephole with a lighted camera shall be performed.

The intent of the video is to determine whether the slab is in intimate contact with the underlying bedrock and to check for any gaps or voids below the level of the slab. A report shall be prepared documenting the findings and the video files shall also be submitted. A numbering system shall be assigned to the weepholes and shown on a plan view drawing and the video files named accordingly. The report and files shall be submitted for review prior to the initiation of geophysical surveys.

D) Positional Surveys:

Locations of geophysical transects and NDT measurements shall be recorded with real-time kinematic (RTK) differential global positioning system (dGPS) methods. Field locations shall also be recorded as measured from permanent structures depicted on as-built plans. Locations of anomalies shall be recorded with RTK dGPS and field measurements and anomaly locations shall be marked in the field with permanent paint and/or survey nails.

E) Geophysical Methods:

Geophysical Methods are intended for subsurface imaging, including detection of subgrade voids beneath concrete spillway slabs and imaging of rebar reinforcement in concrete.

GPR was selected as the first method to use because of its cost and time effectiveness, and the method is expected to provide a general location of voids.

GPR results will provide valuable information upon which additional geophysical (SASW) and NDT surveys will be based.

1. Ground Penetrating Radar (GPR):

Ground Penetrating Radar (GPR) is a method whereby high frequency radio waves are transmitted downward into the subsurface from a transmitter/receiver antenna mounted on an apparatus that is pulled over the ground surface.

Electromagnetic (EM) waves are reflected by changes in subsurface conditions (e.g.

dielectric constant) and are recorded by receiver antennae. A cross-section of the subsurface is depicted after the information is evaluated. This method requires a 4-foot wide path cleared along the survey transects for multiple passes of the GPR equipment.

Mobile GPR equipment with a survey wheel for distance and RTK dGPS shall be used to scan the area to detect anomalies that are indicative of subsurface voids.

The gated spillway channel consists of two approximately 45 ft. wide channels and an intervening approximately 8 ft. wide warm water channel. All three channels are approximately 439-ft long.

The minimum thickness of the concrete slab is 2 ft. 6 inches. Concrete slabs are anchored with #11 steel bar (1.4 in diameter) hooked over rebar reinforcement. Anchor bars have 15 ft. embedment into underlying rock. The anchors are spaced 5 ft. 8 inches apart

Drains are perpendicular to the concrete slabs and are 2 3/8 inch diameter with 15 ft. of embedment into underlying rock.

The GPR grid will be composed of traverses parallel to, and perpendicular to, the spillway channel. GPR data are recommended to be collected along a 2 ft. by 2 ft. grid.

The gated spillway channels have a total width of approximately 100 ft. and a length of approximately 439 ft.

Therefore, there will be approximately 50 GPR lines parallel to the length of the spillway and approximately 219 GPR cross lines perpendicular to the spillway.

The expectation is that the anomalies identified in the GPR surveys will be used to plot the locations of potential voids which will then be used to focus the NDT surveys.

For this application it is anticipated that an antennae in the frequency range of 400 to 1500 MHz will be used. A 400 MHz antenna is appropriate for void detection beneath the concrete channel spillway slab, while a higher frequency antenna would be appropriate for imaging the depth and condition of reinforcement within the concrete slab.

The GPR data shall be reduced using RADAN software by Geophysical Survey Systems, Inc., or equivalent.

GPR work shall be conducted in general accordance with the following standards:

• ASTM D6432-11 Standard Guide for Using the Surface Ground Penetrating Radar Method for Subsurface Investigation

• ASTM D6429-99 (2011) Standard Guide for Selecting Surface Geophysical Methods

• AASHTO TP-36, Standard Test Method for Evaluating Asphalt-Covered Concrete Bridge Decks Using Pulsed Radar

• ASTM D6087, Standard Test Method for Evaluating Asphalt-Covered Concrete Bridge Decks Using GROUND Penetrating Radar

• ACI 228.2R Nondestructive Test Methods for Evaluation of Concrete in Structures, ACI Manual of Concrete Practice, Part 2, Construction Practices and Inspection, Pavements, ACI International

• AASHTO PP 40, Application of Ground Penetrating Radar (GPR) to Highways

• ASTM D4748, Standard Test Method for Determining the Thickness of Bound

Pavement Layers Using Short-Pulse Radar

• FHWA-HIF-00-015, Ground Penetrating Radar for Measuring Pavement Layer

Thickness

• NCHRP Synthesis No. 255, Ground Penetrating Radar for Evaluating

Subsurface Conditions for Transportation Facilities

• SHRP C-101, Condition Evaluation of Concrete Bridges Relative to

Reinforcement Corrosion

• SHRP Catalogue No. 4008, Pavement Thickness Software using Radar

2. Spectral Analysis of Surface Waves (SASW)

SASW requires a source (e.g. hammer) and receiver or multiple geophone receivers.

SASW is conducted to determine material stiffness and layer thickness via shear wave velocity and the development of a shear wave velocity profile. Changes in material stiffness can be attributable to interior degradation due to freeze/thaw cycles and the depth of freeze-thaw damage, cracking due to alkali-silica or alkali-aggregate reactions.

Potential voids behind a concrete slab can also be detected. SASW can also be used to evaluate joint integrity and depth of visible cracks. Collect two profiles (forward and reverse) along each transect with source at opposite ends.

SASW work shall be conducted in general accordance with the following standards:

• ASTM D6429-99 (2011) Standard Guide for Selecting Surface Geophysical Methods

• ASTM D6758-18 Standard Test Method for Measuring Stiffness and Apparent Modulus of Soil and Soil Aggregate In-Place by Electro-Mechanical Method

• ACI 228.2R Nondestructive Test Methods for Evaluation of Concrete in Structures, ACI Manual of Concrete Practice, Part 2, Construction Practices and Inspection, Pavements, ACI International

F) NDT Methods:

Non-Destructive Testing methods are intended for characterizing the man-made concrete structures.

1. Slab Impulse Response (SIR):

Slab Impulse Response (SIR) utilizes an impulse hammer and geophone receiver and is recorded on a field PC. SIR is conducted for delamination and void detection beneath concrete slabs and can be used to compare pre and post repair slab support conditions.

SIR is a point test with an effective radius of .5 to 1.0 feet.

SIR is a dynamic stiffness test for evaluation of slab subgrade support conditions.

Good subgrade support is characterized by low flexibility/mobility, while poor subgrade support is characterized by high flexibility/mobility.

Slab Impulse Response (SIR) measurements shall be collected at each node of the 2 ft.

by 2 ft. GPR grid.

SIR work shall be conducted in general accordance with the following standards:

• ASTM C1740-16 Standard Practice for Evaluating the Condition of Concrete Plates Using the Impulse-Response Method

• ACI 228.2R Nondestructive Test Methods for Evaluation of Concrete in Structures, ACI Manual of Concrete Practice, Part 2, Construction Practices and Inspection, Pavements, ACI International)

• FLH 521.830 – Standard Method for Determining Pulse Velocity Through Concrete in Drilled Shafts.

2. Impact Echo (IE):

Impact Echo (IE) or Ultrasonic Pulse Echo (UPE) is conducted for delamination, void, honeycomb, and crack detection. The thickness of concrete can also be determined and the depth and lateral location and extent of defects can be mapped. IE shall be collected at each node of the 2 ft. by 2 ft. GPR grid.

IE work shall be conducted in general accordance with the following standard:

• ASTM C1383-15 Standard Test Method for Measuring the P-Wave Speed and the Thickness of Concrete Plates Using the Impact-Echo Method

G) Data Collection:

Representative GPR and seismic velocities for concrete and native sandstone shall be measured from the concrete spillway channel and a minimum of one bedrock outcrop.

GPR antenna frequency and length of data collection profile shall be appropriate for the length of the outcrop, visible fractures, and site constraints.

H) Calibration/Standardization and Function Checks:

GPS systems used to locate site features and profile data shall be field checked, and recalibrated if necessary at a surveyed benchmark. The COR can provide available information on a benchmark at the dam upon request. Data collection on site shall include at least three measurements at a measuring point to assess instrument drift and provide a quantitative basis for implementing corrections (beginning/middle/end of day).

Seismic and GPR surface geophysics and NDT instruments shall undergo a noise test to verify sensors and recording systems function properly.

Calibration procedures are performed at the vendor, manufacturer, or laboratory before the instrument is taken to the field. Physical properties or environmental values of interest are measured in an infinite or semi-infinite model under a controlled environment.

Calibration does not guarantee that measurements have a quantitative value in terms of geologic properties, but it does ensure that the measurements are consistent and repeatable.

I) Safety:

Work shall be performed in accordance with Section 01 35 26 Governmental Safety Requirements. The Contractor shall note that the spillway and warm water channels are steep and slippery due to wet surfaces. Work cannot be performed safety in freezing weather due to icy conditions.

J) Submittals:

1. General:

• Submittals shall meet the requirements of Section 01 33 00 Submittal Procedures.

• Report Submittals shall be reviewed by a geoscience technical writer prior to submission. This is in addition to the Contractor’s standard management review. Review shall ensure that all text, figures, and tables are internally consistent, and the document was prepared in accordance with the scope of work.

• Level of completeness for each discipline shall be commensurate with the level of effort required for that submission (geology, geophysics). Documents shall be reviewed for conflicts, errors, and omissions, and corrected before submittal to USACE.

2. Required Submittals:

• Division 1 submittals (AHA, APP, QC reports, etc) shall be performed in accordance with the specifications and are not specifically identified herein.

• Qualifications – Resumes of key staff performing the work.

• Work Plan – Specific requirements are provided in subsequent paragraphs.

The work plan shall be submitted a minimum of 30 days prior to the planned work.

• Preliminary Weephole Video Inspection Report - A report shall be provided after completion of the Weephole Video Inspection, documenting the work performed and the findings. The Governments representative shall be provided 14 days for review of the report.

• Preliminary GPR report – A report shall be provided after completion of the GPR survey documenting the work performed and the findings. The Governments Geophysical representative shall be provided 14 days for review of the report. Discussions between the Contractor’s geophysical consultant and the Government’s Geophysical reviewer shall occur to determine the impacts of the GPR findings on the subsequent SASW and NDT work.

• Final Report documenting all inspection, surveys and findings – Specific requirements are provided in subsequent paragraphs. The final report shall be submitted within 30 days of the completion of the field work.

K) Work Plan Submittal:

The Work Plan shall include Standard Operating Procedures (SOPs) for geophysical and NDT methods. The plan shall fully detail the work to be performed and shall include:

A schedule of the work and notifications to be approved by USACE.

Figures with proposed locations of geophysical and NDT survey grid lines and point measurements overlaid on as-built spillway plans.

The number, length, and spacing of geophysical and NDT transects perpendicular and parallel to the spillway channels.

Make and Model of Geophysical and NDT Instrumentation and equipment to be used on the project.

Name and version of software programs that are proposed to analyze geophysical and NDT data.

L) Final Report:

1. General:

The executive summary shall address goals and objectives. Findings unique to each profile and the Site shall be summarized, using a table where feasible. A summary figure shall also be included for illustrating site-wide trends. Results of the weephole video inspection shall also be included.

The main body shall discuss meeting project goals, data quality objectives, planning, execution/work flow, limitations, effectiveness of the new software (name and version) compared to the original data models, limitations influencing modeling, and interpretations. Geophone and GPR radar antenna performance and function check results shall be presented and assessed for probe drift and impacts on data quality and usability. Recommendations shall include a tabulated list of coring/drilling target locations on each GPR and seismic line, and be presented on a map, recommended positional, seismic and GPR EDD format and content for future projects. References used to help process and interpret the data shall be cited in the text and included in the reference list. Additional software used to conduct data collection and processing shall be described (name, version, vendor, workflow and assumptions used).

The report and its supporting EDDs shall be transmitted electronically via DVD, external hard drive, or AMRDEC SAFE Safe Access File Exchange.

2. Figures:

All maps and drawings shall be submitted in their native file format and a common, high-resolution export (e.g., JPG) on the EDD DVD/external hard drive. Data files shall be categorized using clearly labeled sub-folders by profile or general site data. All raw data (*.dwg, ASCII, GIS shape files with metadata) shall be provided electronically. When used, ARCGIS map documents (MXDs) shall be packaged using ESRI’s Map Package.

Include the start and stop coordinates for each profile, ground surface elevation, and bottom elevation referenced to the project datums in an Excel-compatible table.

All figures, maps, and drawings shall be completed in accordance with USACE (2002a, 2001a) or similar standards. All figures used in the report shall be exported to a high-resolution graphics file suitable for incorporation into Microsoft Office programs. All figures turned into Adobe PDF files shall use the Press Quality settings for maximum resolution.

3. Electronic Data Deliverables (EDD):

Data files and final deliverables shall be categorized using clearly labeled sub-folders on the submitted DVD/external hard drive. A README file shall accompany the data, explaining positional data collection method, results, and datums used. A location map in native file and PDF formats shall accompany the data set, showing locations of all investigation activity generating data contained on the DVD/external hard drive. Show scale, datums, north arrow, labeled locations, etc.

Interpreted surfaces, such as top of weathered rock, top of unweathered rock, and resolvable overburden units shall be exported as XYZ Excel-compatible files for each profile, with location and elevation referenced to the project datums (X=northing, Y=easting, Z=elevation). Excel-compatible seismic and GPR data model results shall be exported as XYZG Excel-compatible files for each profile with location and elevation referenced to the project datums (X=northing, Y=easting, Z=elevation, G=velocity).

Files accompanying the final report shall contain raw data files for SASW and GPR data, travel-time arrival picks and shot-receiver geometry information. A similar standard shall be used and documented for all NDT data sets. EDDs shall be reviewed for completeness and data structure compliance with the scope of work prior to submittal to USACE.

Spillway Channel Figures (Blue are tainter gate chutes and yellow is warm water gate chute)

Spillway Channel Photos: