2018_-_Pohono_Bridge_Underwater_Final_Report.pdf

UNDERWATER BRIDGE INSPECTION REPORT

POHONO BRIDGE

VALLEY LOOP ROAD OVER MERCED RIVER

YOSEMITE NATIONAL PARK

STRUCTURE NO. 8800-001P

INSPECTION TYPE: UNDERWATER

INSPECTION DATE: 8/18/2018

Report prepared for: Report prepared by:

Federal Highway Administration Collins Engineers, Inc.

Federal Lands Bridge Office 10201 Fairfax Blvd, Suite 530 Bridge Inspection and Management Program Fairfax, VA 22030 21400 Ridgetop Circle Sterling, Virginia 20166

Engineer of Record

11/16/18 kstevens New Stamp

STRUCTURE SUMMARY STRUCTURE NO. 8800-001P

POHONO BRIDGE U/W INSPECTION DATE: 8/18/2018

INSPECTION TEAM & METHOD

The Pohono Bridge carries Valley Loop Road (oriented south to north) over Merced River in Yosemite National Park. The bridge is a single-span structure consisting of a masonry-faced concrete arch superstructure supported by two concrete abutments.

At the time of inspection (9:00 AM on 8/18/2018), the North and South Abutments were submerged in the river, and the water level was 23 ft. below the top of the masonry bridge railing at midspan on the upstream fascia of the bridge. In accordance with the previous routine inspection report and the available design drawings, the abutments are labeled as the North Abutment and South Abutment. The Merced River flows east to west at the structure.

The underwater inspection was performed on August 18, 2018. The underwater inspection was conducted by a three-person team consisting of a professional engineer-diver and team leader (Daniel Stromberg, P.E.), one engineer-diver (John Strub, E.I.T.), and one technician-diver (Matthew Stromberg). The inspection was performed by using commercial scuba. During the inspection, the inspection team worked from the north and south shorelines where a note taker recorded the inspection notes.

The underwater inspection consisted of a Level I visual and tactile examination of the substructure units from the waterline to the channel bottom with particular attention given to any observed areas of excessive deterioration or apparent distress. Level II inspection, which consisted of a detailed inspection at the waterline, mid-depth, and at the channel bottom, was conducted on each abutment. At each location, a 12 in. by 12 in. area of aquatic growth was removed so that the substrate condition could be more closely examined. In areas of observed deficiencies, the substructure surface was sufficiently cleaned to determine the extents of the deficiency. The type of channel bottom material, the presence or extent of shore and/or shoreline protection, the presence or extent of drift and debris, and observed scour conditions were noted. Underwater photographs of the various defect/deficiencies were attempted with various forms of equipment.

SUMMARY OF FINDINGS

Overall, the submerged substructure units are in Fair Condition (NBI Condition Rating = 5).

Aquatic growth up to 1/4 in. thick was observed from the channel bottom to the waterline. This growth consisted of algae covering 100 percent of the substructure’s submerged surface area.

The following sections present the findings for each substructure unit inspected.

South Abutment

The South Abutment was observed to be in Fair Condition with three structural deficiencies observed, but no new deficiencies since the 2016 Inspection. The specific deficiencies observed at the South Abutment are detailed in the following table:

Deficiency Location Description

Heavy Scaling

Entirety of abutment face, from channel bottom to 2 ft above the waterline.

Typically 3/4 in. deep with up to a maximum of 1-1/4 in. deep and larger concentrated areas of section loss up to 1

in. deep.

Void Upstream and Downstream ends, just below the stone arch ring

Voids measured up to 2 ft wide by 1 ft high with up to 15 inches of penetration.

Debris Entirety of abutment face Scattered timber debris along the abutment consisting of branches that measured up to 4 in. in diameter

Refer to Page 5 of 15, in the Substructure Drawings Section, for detailed underwater inspection notes pertaining to the South Abutment.

North Abutment

The North Abutment was observed to be in Fair Condition with three structural deficiencies observed. Since the 2016 inspection, the areas of undermining have either remained comparable or increased slightly. The 2016 inspection reported that the North Abutment footing was exposed and significantly undermined with cavities measuring up to 1.2 ft. high having up to 5 ft. of horizontal penetration. After reviewing the design drawings, it has been determined that the previously reported North Abutment footing is actually scour protection for the footing, which was not exposed and not undermined at the time of inspection. The specific minor deficiencies of note observed in North Abutment are presented in the following table:

Deficiency Location Description

Heavy Scaling

Entirety of abutment face, from top of grouted riprap to 2 ft. above the waterline.

Typically 3/4 in. deep with up a maximum of 1-1/4 in. deep and larger concentrated areas of section loss up to 1 in. deep.

Heavy Scaling Entirety of the footing scour protection.

Typically 3 in. penetration with up to 12 in.

maximum.

Undermining Footing scour protection Concrete footing scour protection was undermined along 80% of its length consisting of two cavities, 16 ft long by 1.5

ft. high by 6 ft penetration and 6 ft long by

1.5 ft high by 6 ft penetration.

Refer to Page 6 of 15, in the Substructure Drawings Section, for detailed underwater inspection notes pertaining to North Abutment.

Channel Bottom

The channel and channel protection are rated in Satisfactory Condition (NBI Condition Rating = 6). The channel embankments are stable.

The channel bottom consisted of sand over cobbles and rocks allowing probe rod penetrations up to 2 in. A comparison of soundings and vertical foundation exposure measurements conducted during this inspection to those of the 2016 inspection indicate relatively no change. There was scattered light timber debris along the South Abutment consisting of sticks and branches measuring up to 4 in. in diameter. There is grouted riprap atop the footing scour protection at the North Abutment. The embankments are moderately sloped with riprap measuring up to 3 ft. in diameter. The upstream and downstream embankments did not have any significant erosion.

Evaluations and Recommendations

The substructure units of the Phono Bridge were observed to be in Fair Condition below the high water line with age-related deficiencies consisting of a heavy scaling on both abutment faces typically 3/4 in. deep with up a maximum of 1-1/4 in. deep and minor areas of section loss up to 1 in. deep. The deficiencies do not appear to have developed since the 2016 inspection, with the exception of the footing scour protection undermining. The previously reported undermining of the North Abutment footing is actually undermining/voids of the footing scour protection; the North Abutment footing is not exposed at this time; however, it is recommended that the undermining of the North Abutment footing scour protection be repaired.

Finally, in accordance with NBIS, it is recommended that an underwater inspection of the bridge be performed at intervals not to exceed 60 months.

Inspection Team Leader: QA/QC Review:

9/24/2018 9/24/2018 Daniel G. Stromberg, P.E. Date Charles H. Conrad, P.E. Date

SUBSTRUCTURE DRAWINGS

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UNDERWATER INSPECTION

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SOUTH ABUTMENT (NORTH ELEVATION)

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STRUCTURE NO. 8800-001P

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GENERAL CONDITION RATING: FAIR (5)

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OF

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INSPECTION DATE: 8/18/2018

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LEGEND: =INSPECTION NOTE

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AutoCAD SHX Text INSPECTION NOTES: 1. CONCRETE SURFACES WERE GENERALLY SOUND WITH AREAS OF MODERATE TO HEAVY SCALING CONCRETE SURFACES WERE GENERALLY SOUND WITH AREAS OF MODERATE TO HEAVY SCALING TYPICALLY INCHES DEEP, MAXIMUM 1-1/4 INCH DEEP, WITH LARGER CONCENTRATED AREAS OF 34 INCHES DEEP, MAXIMUM 1-1/4 INCH DEEP, WITH LARGER CONCENTRATED AREAS OF SECTION LOSS UP TO 1 IN. DEEP. 2. CONCRETE VOID AT THE WEST END, JUST BELOW THE STONE ARCH RING, MEASURING CONCRETE VOID AT THE WEST END, JUST BELOW THE STONE ARCH RING, MEASURING APPROXIMATELY 2 FEET WIDE BY 1 FOOT HIGH WITH UP TO 15 INCHES OF PENETRATION. 3. CONCRETE VOID AT THE EAST END, JUST BELOW THE STONE ARCH RING, MEASURING CONCRETE VOID AT THE EAST END, JUST BELOW THE STONE ARCH RING, MEASURING APPROXIMATELY 22 INCHES WIDE BY 7 INCHES HIGH WITH UP TO 12 INCHES OF PENETRATION. 4. LEFT IN PLACE TIMBER PLANKING ALONG THE WESTERN 9 FEET, AND EXTENDING FROM THE LEFT IN PLACE TIMBER PLANKING ALONG THE WESTERN 9 FEET, AND EXTENDING FROM THE CHANNEL BOTTOM UP 2 FEET. 5. SCATTERED TIMBER DEBRIS ALONG THE ABUTMENT CONSISTING OF BRANCHES UP TO 4 INCHES IN SCATTERED TIMBER DEBRIS ALONG THE ABUTMENT CONSISTING OF BRANCHES UP TO 4 INCHES IN DIAMETER. GENERAL NOTES: 1. AT THE TIME OF INSPECTION, THE WATERLINE WAS LOCATED 23.0 FEET BELOW THE TOP OF THE AT THE TIME OF INSPECTION, THE WATERLINE WAS LOCATED 23.0 FEET BELOW THE TOP OF THE MASONRY BRIDGE RAILING AT MIDSPAN ON THE UPSTREAM FASCIA. 2. SOUNDINGS INDICATE THE WATER DEPTHS AT THE TIME OF INSPECTION AND ARE MEASURED IN SOUNDINGS INDICATE THE WATER DEPTHS AT THE TIME OF INSPECTION AND ARE MEASURED IN FEET.

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ARCH INTRADOS

SOUTH ABUTMENT FACE

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UNDERWATER INSPECTION

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NORTH ABUTMENT (SOUTH ELEVATION)

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STRUCTURE NO. 8800-001P

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GENERAL CONDITION RATING: FAIR (5)

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OF

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INSPECTION DATE: 8/18/2018

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LEGEND: =INSPECTION NOTE

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AutoCAD SHX Text INSPECTION NOTES: 1. THE CONCRETE SCOUR PROTECTION SOUTH FACE WAS EXPOSED ALONG THE ENTIRETY OF THE THE CONCRETE SCOUR PROTECTION SOUTH FACE WAS EXPOSED ALONG THE ENTIRETY OF THE NORTH ABUTMENT. THE SCOUR PROTECTION EXTENDS APPROXIMATELY 8 FEET OFF THE FACE OF THE ABUTMENT AND THE TOP OF THE PROTECTION WAS 6 INCHES BELOW THE WATERLINE AT THE TIME OF INSPECTION. 2. THE WESTERN HALF OF THE SCOUR PROTECTION IS MOSTLY UNDERMINED MEASURING THE WESTERN HALF OF THE SCOUR PROTECTION IS MOSTLY UNDERMINED MEASURING APPROXIMATELY 16 FEET LONG BY 1.5 FEET HIGH WITH UP TO 6 FEET OF PENETRATION. 3. THERE IS AN AREA OF UNDERMINING BELOW THE SCOUR PROTECTION LOCATED APPROXIMATELY 10 THERE IS AN AREA OF UNDERMINING BELOW THE SCOUR PROTECTION LOCATED APPROXIMATELY 10 FEET FROM THE EAST END AND MEASURED 6 FEET LONG BY 1.5 FEET HIGH WITH UP TO 6 FEET OF PENETRATION. 4. THE SCOUR PROTECTION HAS AN AREA OF OVERPOUR AT THE EAST END NEAR THE CHANNEL THE SCOUR PROTECTION HAS AN AREA OF OVERPOUR AT THE EAST END NEAR THE CHANNEL BOTTOM. 5. VERTICAL TIMBER FORMWORK PLANKS ARE IN PLACE FROM 16 FEET TO 20 FEET EAST OF THE VERTICAL TIMBER FORMWORK PLANKS ARE IN PLACE FROM 16 FEET TO 20 FEET EAST OF THE WEST END. 6. THE CONCRETE FACE OF THE FOOTING SCOUR PROTECTION HAS WIDESPREAD SECTION LOSS FROM THE CONCRETE FACE OF THE FOOTING SCOUR PROTECTION HAS WIDESPREAD SECTION LOSS FROM HEAVY SCALING WITH TYPICAL PENETRATIONS OF 3 INCHES AND MAXIMUM PENETRATIONS OF 12 INCHES. GENERAL NOTES: 1. AT THE TIME OF INSPECTION, THE WATERLINE WAS LOCATED 23.0 FEET BELOW THE TOP OF THE AT THE TIME OF INSPECTION, THE WATERLINE WAS LOCATED 23.0 FEET BELOW THE TOP OF THE MASONRY BRIDGE RAILING AT MIDSPAN ON THE UPSTREAM FASCIA. 2. SOUNDINGS INDICATE THE WATER DEPTHS AT THE TIME OF INSPECTION AND ARE MEASURED IN SOUNDINGS INDICATE THE WATER DEPTHS AT THE TIME OF INSPECTION AND ARE MEASURED IN FEET.

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NORTH ABUTMENT FACE

SCOUR PROTECTION FACE

PHOTOGRAPHS

PHOTOGRAPHS STRUCTURE NO. 8800-001P

PHOTO #1 – EAST (UPSTREAM) ELEVATION, LOOKING NORTHWEST

PHOTO #2 – WEST (DOWNSTREAM) ELEVATION, LOOKING EAST

PHOTO #3 – UPSTREAM CHANNEL, LOOKING EAST

PHOTO #4 – DOWNSTREAM CHANNEL, LOOKING WEST

PHOTO #5 –SOUTH ABUTMENT, LOOKING SOUTH

PHOTO #6 –NORTH ABUTMENT, LOOKING NORTHWEST

PHOTO #7 – VOID IN THE WEST END OF THE SOUTH ABUTMENT, LOOKING

SOUTH

PHOTO #8 – TYPICAL SCALING AT THE SOUTH ABUTMENT, LOOKING

SOUTHWEST

PHOTO #9 – UNDERMINING OF THE NORTH ABUTMENT FOOTING SCOUR

PROTECTION EAST END

PHOTO #10 – UNDERMINING OF THE NORTH ABUTMENT FOOTING SCOUR

PROTECTION WEST END

PHOTO #11 – TYPICAL HEAVY SCALING OF THE NORTH ABUTMENT FOOTING

SCOUR PROTECTION

NBI CONDITION RATING TABLE

NBI CONDITION RATING TABLE STRUCTURE NO. 8800-001P

9 EXCELLENT CONDITION Preservation/Cyclic Maintenance

8 VERY GOOD CONDITION—No problems noted.

7 GOOD CONDITION—Some minor problems.

SATISFACTORY CONDITION—Structural elements show some minor deterioration.

Preservation/ Condition‐Based Maintenance

FAIR CONDITION—All primary structural elements are sound but may have some minor section loss, cracking, spalling, or scour.

POOR CONDITION—Advanced section loss, deterioration, spalling, or scour.

Rehabilitation or Replacement

3 SERIOUS CONDITION—Loss of section, deterioration, spalling or scour have seriously affected primary structural components. Local failures are possible.

Fatigue cracks in steel or shear cracks in concrete may be present.

CRITICAL CONDITION—Advanced deterioration of primary structural elements.

Fatigue cracks in steel or shear cracks in concrete may be present, or scour may have removed substructure support. Unless closely monitored, the bridge may have to be closed until corrective action is taken.

IMMINENT FAILURE CONDITION—Major deterioration or section loss present in critical structural components, or obvious vertical or horizontal movement affecting structure stability. Bridge is closed to traffic, but corrective action may put it back in light service.

FAILED CONDITION—Out of service. Bridge is beyond corrective action