NV-AZ_FTBR_Old_US_93(2)_Hoover_Dam_Access_Road_V1_P&M_memo_11-20-17_FINAL.pdf

Subject: NV/AZ FTBR OLD US93(2) Hoover Dam Access Road Pavement Investigation & Recommendations

From: Mike Voth Pavement & Materials Team Leader, CFLHD

To: Brent Nagen, PM/COE, CFLHD Jeff Felling, Lead Designer, CFLHD

INTRODUCTION

The primary purpose of the project is to provide pavement preservation treatments to the 3.51 mile Hoover Dam Access Road and adjacent parking lots. This memorandum provides recommendations for pavement preservation treatments and pavement repairs for the Hoover Dam Access Road and 15 parking lots. This memorandum also serves as documentation of the exploration conducted and data gathered.

The road and parking lots provide access to the visitor center, overlooks and trails, and BOR administrative facilities of the Hoover Dam complex. The road supports a high volume of tourist related traffic including motor coach buses. The complex receives over 4 million visitors per year. The project location is shown in Figure 1.

Figure 1. Project Site

FIELD INVESTIGATION and EXISTING PAVEMENT CONDITIONS:

To develop, support, and validate the treatment and repair recommendations a pavement investigation was completed on July 6 & 7, 2017. Due to the high volume of traffic and pedestrians during daytime open hours, the BOR requested that the investigation take place at night after closure of the complex.

Resilient Drilling was contracted to complete the coring / pot-holing investigative work. Work began at

Technical Memorandum

Date: November 20, 2017

8:30 pm on July 6 and concluded at 5:00 am on July 7. Information gathered during the scoping trip May 30 – June 1, 2017 was also used to develop and support recommendations.

Resilient Drilling used an AMS PowerProbe (9120-RAP-D) attached to a small utility task vehicle (UTV). See photos at end of memorandum. A hydraulic hammer was used to push drive a 3” diameter hollow probe through the asphalt pavement. Pavement layer depths on top of the three bridge decks and the dam were determined without damaging the concrete surface. Pavement layer depths were determined in numerous roadway areas between stations 86+50 to 117+50. A total of 31 push-drive core samples were completed. See Table 1 for pavement depths, visual base identification, and other information.

Table 1. Asphalt Pavement Depths

Number Location – Station (approximations)

Asphalt Pavement

Depth (inches)

Visual Base Conditions Comments

C-1 Parking lot #14, east side 4.25 Brown sandy gravel 4” to 5” cobbles noted below pavement

C-2 Parking lot #14, west side 4.25 Red-brown sandy gravel 3” cobbles noted below pavement C-3 117+50 (gore area) 7 Gray-brown gravel base C-4 116+40, 20” offset LT 8 - AZ Spillway Bridge C-5 115+25, 12’ offset RT 9 - AZ Spillway Bridge C-6 115+20, 15’ offset LT 8.5 - AZ Spillway Bridge C-7 115+00, 5.5’ offset RT 7.5 Red-brown sandy gravel C-8 114+00, 7’ offset LT 8 Red-brown sandy gravel

C-9 112+80, 6.5’ offset RT 7 Red clayey-sandy gravel Moist conditions beneath pavement

C-10 111+50, 8’ offset LT 9 Red sandy gravel

C-11 110+50, 8.5’ offset RT 1.75 On concrete At entrance to employee parking lot

C-12 110+65, 7.5’ offset RT 4.75 On concrete or bedrock Searching for end of concrete C-13 111+15, 7’ offset RT 8 Red-brown sandy gravel Searching for end of concrete C-14 110+95, 7’ offset RT 4.25 On concrete or bedrock Searching for end of concrete C-15 109+80, 6.5’ offset LT 1.5 - Dam C-16 108+40, 7’ offset RT 2.5 - Dam C-17 107+40, 6.5’ offset LT 2 - Dam C-18 105+90, 6.5’ offset RT 2 - Dam C-19 103+00, 6.5’ offset LT 2.5 - Dam C-20 101+40, 7’ offset RT 2.25 - Dam C-21 99+90, 6.5’ offset LT 2.5 - Dam

C-22 98+50, 6.5 offset RT 2.25 - Dam, average thickness 2.2”

C-23 98+05, 6’ offset LT 12 Difficult to see conditions

Pavement was moist 4” to 8” below surface, stripping

C-24 97+80, 5.5’ offset RT 3 Waterproof membrane NV V.C. Roadway Bridge C-25 96+90, 5.5’ offset LT 3.75 Waterproof membrane NV V.C. Roadway Bridge C-26 96+40, 6.5’ offset RT 3 - NV Post-tensioned Bridge C-27 94+00, 7’ offset LT 3.5 - NV Post-tensioned Bridge C-28 91+70, 8’ offset RT 2.25 - NV Post-tensioned Bridge C-29 89+90, 4’ offset LT 11 Red sandy gravel C-30 88+20, 7’ offset RT 10 Red sandy gravel C-31 86+80, 6.5’ offset LT 10 Red sandy gravel

During the scoping trip and field investigation, pavement distress conditions were evaluated and recorded. Areas to receive patching were quantified. Refer to the photos at the end of this memorandum and Table 2 below for the typical pavement distress and severity.

Table 2. Pavement Distress Route / Parking

Lot Typical Distress Comments

Access Road, STA 21+66 to 86+59, 118+85 to 160+57

Low and moderate severity block cracking throughout the route. Low and moderate thermal cracking is also present.

Generally, rutting is not a concern, less than ½” typical.

There are spot areas of fatigue/alligator cracking that will need to be patched prior to treatment. Low severity longitudinal paving joint cracks were noted in some locations. Gouging of the pavement due to track vehicles (or similar) was noted from about station 72+00 to 76+00.

Candidate for pavement preservation treatment with pre-treatment cracking sealing and patching.

Recommend cracking sealing and spot patching (type 2) followed by ultra-thin bonded wearing course

Access Road – STA 86+59 to 91+16, 97+82 to ~98+25, 110+50 to 115+35

These segments are located adjacent and in between the numerous structures as follows: STA 86+59 to NV Post- Tensioned Bridge (STA 91+16), east abutment of NV Pedestrian Bridge to ~STA 98+25 (start of dam concrete), ~STA 110+50 (end of dam concrete) to west abutment of AZ Spillway Bridge (STA 115+35). Pavement conditions are similar to above access road conditions.

Mill 2” of asphalt, patch (type 2) as needed, crack seal, broom, tack and place 2” asphalt overlay.

Access Road, STA 117+02 to 118+85

This segment is from the east abutment of AZ Spillway Bridge to STA 118+85. This area has high severity block cracking and raveling of surface fines, especially in gore area.

Remove and replace asphalt pavement (large patch)

Access Road, STA 160+57 to 207+12 (closed to public)

Did not review. Oxidation and cracking similar to the access road segments open to the public was noted around

STA 160+60.

Heavy fog seal (rejuvenator)

NV Post- Tensioned Bridge

Rutting/shoving of pavement, ½” to 1” or more in deformations (bridge deck is on a relatively steep grade with cross-walks in the vicinity). Moderate severity longitudinal paving joint crack. Low severity block cracking.

Mill entire depth of asphalt, broom, tack and place 3.5” asphalt overlay.

NV Visitor Center Roadway Bridge

Pavement shoving, ½” to 1”. Slippage cracks noted throughout the deck. The bridge deck has a waterproof membrane that is to remain undisturbed (beyond scope to replace).

Mill 2” of asphalt, patch, broom, tack and place 2” asphalt overlay.

Across Dam Low and moderate reflection cracking at each joint in the dam. Some of the reflection cracking has expanded into fatigue cracking. Predominantly low severity block cracking. Rutting of ½” to 1” was noted on about the first 200’ on the Nevada side of the dam.

Mill entire depth of asphalt, broom, tack and place 2” asphalt overlay.

AZ Spillway Bridge

Moderate and high severity transverse cracks. Moderate and high severity block cracking. Relatively thick section of asphalt pavement exists on deck (~8”)

Mill 2” of asphalt, broom, tack and place 2” asphalt overlay.

NV Security Checkpoint Parking Area

Low and moderate block cracking throughout the parking / checkpoint area. Spot locations of fatigue cracking also present

No work. BOR plans to reconstruct this area in a few years

Route / Parking

Lot Typical Distress Comments

Memorial Bridge Parking Plaza

Good condition. No significant distress noted Micro surfacing only

Welcome to Nevada Parking lot

Good condition. No significant distress noted Micro surfacing only

Historic RR Trail Pick-up lot -Entrance Road -Police station lot -Cell Tower Rd

Low and moderate severity block cracking in police station employee lot (part of lot has gravel surfacing). Other areas more recently paved with less distress.

Cell Tower Access Road: on a very steep grade, highly fatigue cracked and block/transverse cracking throughout.

Not a candidate for preservation. Not open to public. BOR requests fog seal as band aid.

Crack seal and micro surfacing.

Cell Tower Road:

Fog seal only

Hoist House Parking lot

Moderate severity block cracking in lot. Access road has minimal distress.

Crack seal and micro surfacing (lot). Fog seal (access road)

Lot #7 (employee lot on NV spillway side)

Good condition. Low severity longitudinal paving joint cracks.

Crack seal and micro surfacing

Lot #8 (employee lot on AZ side)

Good condition. Repaved within the last 5 years. Low severity longitudinal cracking, typical.

Crack seal and micro surfacing

Lot #9 (pay lot) Very good condition. Repaved within the last 5 years. Low severity longitudinal cracking (< ¼ inch width or less, typical)

Crack seal and micro surfacing

Lot #10 Moderate severity block cracking, typical. Fatigue cracking along mainline access road shoulder will be addressed/patched as part of mainline access road

Crack seal and micro surfacing

Lot #11 Moderate severity block cracking, typical. Pedestrian area at overlook requires patching.

Crack seal and micro surfacing, one patch area

Lot #12 Moderate severity block cracking, typical. Some roughness/deformation of pavement.

Crack seal and micro surfacing

Lot #13 Moderate severity block cracking, typical. Some spot fatigue cracking. Minimal to no bus use.

Crack seal and micro surfacing

Lot #14 (and adjacent police pull-out)

Good candidate for FDR and overlay if funding available;

otherwise just place micro surfacing. Fatigue cracking throughout lot. High and moderate severity block cracking also present. Too much cracking in lot to cost effectively crack seal. High bus use parking lot.

Adjacent pull-out for police vehicles can be fog sealed.

Micro surfacing only (lot #14).

Fog seal (adjacent police pull-out)

Lot #15 (AZ overlook)

Good condition. Repaved within the last 5 years. Low severity block/longitudinal cracking, typical.

Crack seal and micro surfacing

Lot #16 (Heli-Pad parking lot)

Good condition. Newest lot in complex. Low severity block / longitudinal cracking, typical.

Asphalt perimeter around concrete heli-pad can be fog sealed.

Crack seal and micro surfacing (lot).

Fog seal (perimeter strip around heli-pad)

RECOMMNDATIONS:

CFLHD standards and guidelines were used to complete the pavement and materials recommendations.

Access Road- The access road will have an ultra-thin bonded wearing course (UTBWC) placed over most of the public access portion of the route (STA 21+66 to 86+59 and 118+85 to 160+57). An UTBWC is a 5/8-inch to 1-inch hot mix asphalt overlay placed over a polymer modified emulsion membrane. The emulsion membrane seals the surface and small cracks, and helps bond the two surfaces together. The roadway can be opened to traffic quickly. The construction process uses the following: a single machine (spray paver) to place the membrane and hot mix, a material transfer vehicle (MTV), and rollers to seat the UTBWC.

The UTBWC nominal depth for this project will be ¾-inch. UTBWC is a treatment commonly used in the Las Vegas area. An SCR for Section 429 has been developed for this project using components of the local specification. It includes requirements for the mix design, test strip, polymer modified emulsion membrane application rate, equipment, and other construction parameters.

The access road adjacent and in between the various structures (STA 86+59 to 118+85) will have a mill and overlay treatment. Refer to Table 1 & 2 above for specific depths and other details. The treatment for these access road segments matches the treatments that will be placed on the bridges and dam, and provides for continuity and ease of construction in this highly-congested area of the project. The moist/wet subgrade and moist pavement noted in a couple locations also supports a thin mill and overlay approach, given the scope and budget of this project.

Prior to placing the UTBWC and asphalt overlay, the roadway will be crack sealed and patched.

Quantities of patching (type 2) were estimated during the scoping trip held May 30-31, 2017. While a few specific sites may be noted on the plans, most of the locations will be determined in the field by the project engineer. The scoping plan set mark-up is available to use as a reference for the project engineer.

At the request of the BOR, the segment of the access road that is not open to the public (STA 160+57 to 207+12) will receive a fog seal to retard oxidation, seal the surface, and seal small cracks.

Material recommendations for the Access Road:

• UTBWC: nominal thickness ¾ inch. Allowable thickness range is 5/8-inch to 1-inch.

• UTBWC mix: gradation requirements developed from local standards and included in subsection

703.18 SCR.

• Asphalt binder (for both UTBWC and asphalt pavement): PG 76-22NV.

• Polymer modified emulsion membrane: SCR for 702.02(d) developed from local standards.

Application rate will be determined during test strip. A range of 0.15 to 0.20 gal/yd2 is typical.

Access Road over Structures- NV Post Tensioned Bridge: The existing asphalt pavement will be milled (by micro milling) and replaced. The bridge is on a relatively steep grade and achieving a good bond between the bridge deck and new overlay will be critical for long term performance. The deck should be well cleaned and properly tack coated prior to the overlay.

NV Visitor Center Roadway Bridge: This bridge has a waterproof membrane that is to remain undisturbed. It is beyond the scope (and budget) of this project to remove and replace the membrane.

The existing asphalt overlay will be milled 2 inches (by micro milling) and replaced with a 2-inch asphalt overlay. The intent is to leave 1 to 1½ inches of the existing asphalt in place after milling is complete.

Patch, as needed, if delamination or severe fatigue cracking exists on remaining pavement. The surface should be well cleaned and properly tack coated prior to the overlay.

Roadway across Hoover Dam: The existing asphalt pavement is relatively thin, see Table 1. The existing pavement will be milled (by micro milling) and replaced. The concrete surface should be well cleaned and properly tack coated prior to the overlay. Care should be taken to assure drainage patterns are not disturbed and drainage inlets are not impeded.

AZ Spillway Bridge: This bridge has a thick layer of asphalt over the deck (~8.5 inches). Although there are large, full-depth cracks in the asphalt pavement, it is beyond the scope of the project to remove and replace the entire thickness. A 2-inch mill and overlay will be completed. Care should be taken to assure drainage patterns are not disturbed.

Special equipment recommendations for milling operations:

• It is recommended to use micro milling cutting heads for asphalt milling operations on the NV

Post Tensioned Bridge, NV Visitor Center Roadway Bridge, and Hoover Dam. Micro milling allows for more optimal pavement removal and reduces the chance of damaging the concrete surface.

Parking Lots- Table 2 provides a summary of the recommended treatments. Micro surfacing (type 2) is the predominant treatment for the parking lots. Crack sealing, fog sealing, and small amounts of patching will be required on select parking lots. Micro surfacing will seal the surface, retard raveling, retard oxidation, and level minor ruts/deformations. Micro surfacing takes time to cure prior to opening to traffic. The micro surfacing should be fully cured prior to opening, which may take 24 hours or more depending upon weather conditions.

Table 3. Recommended Pay Items Item Number Item Description Unit 30202-2000 Roadway Aggregate, Method 2 TON 40301-0100 Asphalt concrete pavement, Type 1 TON 40601-0000 Fog Seal TON 40901-2000 Micro Surfacing, Type 2 SQYD 41201-0000 Tack Coat TON 41301-0000 Asphalt Pavement Milling SQYD 41402-2000 Cracks, cleaning and sealing MILE 41801-2000 Asphalt Concrete Pavement Patch, Type 2 SQYD 42901-0000 Ultra-thin Bonded Wearing Course TON 42905-0000 Polymer Modified Emulsion Membrane TON

CONSTRUCTION CONSIDERATIONS & SPECIAL CONTRACT PROVISIONS

Project specific SCRs have been developed and submitted for the following material sections: 302, 403, 413, 414, 418, 429, 702, and 703. For other sections, it is expected that standard SCRs from the library of specifications (LOS) will be used.

Due to day time restrictions for some construction operations and the expected season in which construction will occur, temperature requirements may be more challenging to meet. It will be important to pay monitor weather forecasts when scheduling/planning construction operations such as paving and the UTBWC. Weather data in Table 4 is from a Boulder City, NV weather station.

During the UTBWC placement, the polymer modified emulsion membrane will migrate down into the existing asphalt and upward into the mix filling voids and creating an interlayer of high cohesion that will not slip or delaminate when applied correctly. One of the keys to success is to have an adequate application rate of the emulsion membrane. One of the purposes of the test strip is to evaluate and approve this application rate.

Because all surface will receive either a UTBWC, asphalt overlay, or micro surfacing treatment, it is very important that crack sealing operations are completed flush with the existing pavement surface. No over banding is allowed. Allowing one month of cure time for the sealant prior to overlay is good practice.

TABLE 4: Weather Data*

Month Average

LOW

Average

HIGH

Record

LOW

Record

HIGH

Average

PRECIP.

January 38° 53° 11° 75° 0.73

February 42° 59° 12° 86° 0.77

March 46° 65° 25° 91° 0.93

April 53° 73° 31° 97° 0.25

May 61° 83° 37° 111° 0.22

June 71° 94° 41° 114° 0.11

July 77° 99° 56° 117° 0.55

August 75° 97° 59° 112° 0.89

September 69° 90° 43° 110° 0.62

October 58° 78° 30° 100° 0.29

November 46° 62° 4° 90° 0.49

December 38° 53° 9° 78° 0.47 *Temperatures are in °F and precipitations are in inches.

Attachment:

Scoping and Investigation Photos

11/03/2017

Scoping Trip Photos May 30 & 31, 2017

~STA 23+50: block cracking, some fatigue cracking

Security Checkpoint: fatigue cracking, patching, raveling

Security Checkpoint: fatigue cracking, patching, raveling

Police Station Parking Area: block cracking

~STA 74: longitudinal cracking, some surface scars

~STA 84: transverse and longitudinal cracking

Parking Lot 7: block cracking, longitudinal joint

Parking Lot 8

~STA 117+50: high severity block cracking

Parking Lot 9

Parking Lot 9

Parking Lot 10: block cracking

Fatigue cracking on shoulder of Access Road, adjacent to Parking Lot 10

Parking Lot 11

Parking Lot 11: block cracking

Parking Lot 12: deformation, raveling, block cracking

Parking Lot 12: block cracking

Parking Lot 13: block cracking, some deformation

~STA 135: block cracking, some fatigue cracking

Parking Lot 14: fatigue and block cracking, deformation

Parking Lot 14: fatigue cracking throughout lot

Parking Lot 15: low severity block cracking

Parking Lot 16 (Heli‐Pad): low severity block cracking

Field Investigation Photos July 6 & 7, 2017

AMS PowerProbe

(9120‐RAP‐D),

mounted on 4‐ wheeler

C‐1 Location, Parking lot 14

C‐2 Location, Parking lot 14

C‐5 Location, Arizona Spillway Bridge

C‐6 Location, Arizona Spillway Bridge

C‐10 location: fill/wall area

C‐11 Location, near entrance to parking lot 8

C‐23 Location, near visitor center

~STA 86+50: near C‐31 and gate

Gate at Arizona Spillway Bridge

Arizona Spillway Bridge deck

Joint on west side of Arizona Spillway

Bridge

Note the asphalt taper along curb – west of AZ Spillway Bridge

~STA 111‐114: rutting and shoving noted

Typical reflective crack on Hoover Dam at concrete expansion joint

Typical drain inlet on Hoover Dam

East abutment joint: Nevada Visitor Center Bridge

Abutment joint between Nevada Visitor Center Bridge and Nevada Post

Tensioned Bridge

General view: Nevada Visitor Center Bridge

Southwest abutment at parking garage:

Nevada Post

Tensioned Bridge

Nevada Post Tensioned Bridge:

joint for parking garage access road

General view:

Nevada Post

Tensioned Bridge