Geotech Eng Exploration.pdf

GEOLABS, INC.

Geotechnical Engineering and Drilling Services

FINAL SUBMISSION

GEOTECHNICAL ENGINEERING EXPLORATION

WAIALE, POHAKUOKALA, AND ALAE BRIDGES

SEISMIC RETROFIT

KULA, MAUI, HAWAII

W.O. 8412-00(B) MARCH 25, 2026

Prepared for

WSP

94-429 Koaki Street, Suite 200 • Waipahu, HI 96797

Hawaii • California

GEOTECHNICAL ENGINEERING EXPLORATION

WAIALE, POHAKUOKALA, AND ALAE BRIDGES

SEISMIC RETROFIT

Prepared for

LICENSED

PROFESSIONAL

ENGINEER

No. 5635-C

THIS WORK WAS PREPARED BY

ME OR UNDER MY SUPERVISION.

4-30-26

SIGNATURE EXPIRATION DATE

OF THE LICENSE

94-429 Koaki Street, Suite 200 • Waipahu, Hawaii 96797

Telephone: (808) 841-5064 • E-mail: hawaii@geolabs.net

March 25, 2026 W.O. 8412-00(B)

Mr. Randall Urasaki

1001 Bishop Street, Suite 2400 American Savings Bank Tower Honolulu, HI 96813

Dear Mr. Urasaki:

Geolabs, Inc. is pleased to submit our report entitled “Geotechnical Engineering Exploration, Waiale, Pohakuokala, and Alae Bridges Seismic Retrofit, Kula, Maui, Hawaii.”

Our work for the project was performed in general accordance with the scope of services outlined in our revised fee proposal dated January 26, 2023.

Please note that the soil and rock samples recovered during our field exploration (remaining after testing) will be stored for a period of two months from the date of this report.

The samples will be discarded after that date unless special arrangements are made for a longer sample storage period. Please contact our office for alternative sample storage requirements, if appropriate.

Detailed discussion and specific design recommendations are contained in the body of this report. If there is any point that is not clear, please contact our office.

Very truly yours, Gerald Y. Seki, P.E.

Vice President

GS:JS:lf mailto:hawaii@geolabs.net

W.O. 8412-00(B) GEOLABS, INC. Page i

GEOTECHNICAL ENGINEERING EXPLORATION

WAIALE, POHAKUOKALA, AND ALAE BRIDGES

SEISMIC RETROFIT

TABLE OF CONTENTS

Page

SUMMARY OF FINDINGS AND RECOMMENDATIONS .............................................. iii

1. GENERAL

1.1 Introduction

1.2 Project Considerations

1.3 Scope of Work

2. SITE CHARACTERIZATION

2.1 Regional Geology

2.2 Existing Site Conditions

2.3 Subsurface Conditions

Waiale Bridge Pohakuokala Bridge Alae Bridge

2.4 Seismic Design Parameters

Earthquakes and Seismicity Liquefaction Potential Soil Profile Type for Seismic Design

3. DISCUSSION AND RECOMMENDATIONS

3.1 Stiffness Modeling Analysis

Bearing Capacities of Shallow Foundations Lateral Load Resistance of Shallow Foundations Lateral Load Resistance of Abutment Fills Active Lateral Earth Pressure Dynamic Lateral Earth Pressure

3.2 Soil-Nailed Anchor Beams

Excavation Preparation Soil Nailed Anchor Beams Soil Nail Installation Soil Nail Testing

3.3 Pavement

Design Traffic Loading Conditions/Traffic Index Design Subgrade Conditions Design Pavement Section Subgrade Preparation Below Pavement Sections Fill Materials

TABLE OF CONTENTS

Page

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Compaction Requirements Pavement Drainage

3.4 Design Review

3.5 Post-Design Services/Services During Construction

4. LIMITATIONS

CLOSURE

PLATES

Project Location Map ................................................................................... Plate 1 Site Plans .................................................................................. Plates 2.1 thru 2.3 Summary of Foundation Conditions .......................................... Plates 3.1 thru 3.3

Field Exploration ....................................................................... Pages A-1 and A-2 Soil Log Legend ..................................................................................... Plate A-0.1 Soil Classification Log Key .................................................................... Plate A-0.2 Rock Log Legend .................................................................................. Plate A-0.3 Logs of Borings ................................................................... Plates A-1.1 thru A-6.2

Laboratory Tests ...................................................................................... Page B-1 Laboratory Test Data .............................................................. Plates B-1 thru B-23

Photographs of Core Samples .................................................. Plates C-1 thru C-7

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GEOTECHNICAL ENGINEERING EXPLORATION

WAIALE, POHAKUOKALA, AND ALAE BRIDGES

SEISMIC RETROFIT

SUMMARY OF FINDINGS AND RECOMMENDATIONS

The subsurface conditions at the three bridge project sites were explored by drilling and sampling six borings (1 per bridge abutment), extending to depths from approximately 45 to 51.5 feet below the existing ground surface. The field exploration generally encountered a pavement structure consisting of 4 to 5 inches of asphaltic concrete at Waiale and Alae Bridges and 5.5 to 9 inches of asphaltic concrete at Pohakuokala Bridge, overlying silty gravel base material. This pavement structure was underlain by fill material and residual soils, extending to varying depths below the existing pavement surface. The fill and residual soils were generally underlain by weathered basalt rock formation and basalt rock formation with interbedded layers of clinker materials, extending to the maximum depth explored.

The fill materials generally consisted of loose silty sand and stiff sandy silt, medium dense silty gravel, and stiff to very stiff sandy silts. The residual soils generally consisted of medium dense silty sand and silty gravel, and very dense gravelly cobbles. The basalt rock formations encountered were generally hard to very hard and ranged from slightly to moderately weathered.

We did not encounter groundwater in the borings at the time of our field exploration.

However, it should be noted that groundwater levels are subject to change due to rainfall, time of year, seasonal precipitation, surface water runoff, and other factors.

Based on the information provided, the current retrofit design concept consists of utilizing a tie beam connected from the existing abutments to an anchor beam and soil nails to resist seismically induced loading. To reduce earth pressures on the abutment walls, lightweight cellular concrete backfill will be used as backfill within the tie beam and anchor beam excavations.

The soil-nailed anchor beam system for the bridge projects involves individual reinforcing bars grouted into drilled holes, connecting to an anchor beam and tie beams to resist seismically induced loading. Four 8-inch diameter soil nails with allowable tensile load capacities of 40 kips per anchor will be utilized for each bridge abutment. The installation of soil nails involves drilling a minimum 8-inch diameter hole at an inclination of approximately 20 degrees from horizontal, using ASTM A615 Grade 75 solid threaded bar with a minimum bar diameter of 1.5 inches and a double corrosion protection system for the nails.

SUMMARY OF FINDINGS AND RECOMMENDATIONS

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The text of this report should be referred to for detailed discussion and specific design recommendations.

END OF SUMMARY OF FINDINGS AND RECOMMENDATIONS

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SECTION 1. GENERAL

1.1 Introduction

This report presents the results of our geotechnical engineering exploration performed for the Waiale, Pohakuokala, and Alae Bridges project in Kula, on the Island of Maui, Hawaii. The project location and general vicinity of each bridge are shown on the

Project Location Map, Plate 1.

This report summarizes the findings and presents our geotechnical engineering recommendations derived from our field exploration, laboratory testing, and engineering analyses. These recommendations are intended for the design of the bridges’ seismic retrofit only. The findings and recommendations presented herein are subject to the limitations noted at the end of this report.

1.2 Project Considerations

The proposed project sites are located along Haleakala Highway and Kekaulike

Avenue in Kula on the Island of Maui, Hawaii. We understand that it is desired to perform a seismic retrofit for the following bridges:

1. Waiale Bridge, Bridge No. 009003770500540: Three-span reinforced concrete girder bridge about 150 feet in length and 27 feet in width.

2. Pohakuokala Bridge, Bridge No. 009003780500349: Three-span reinforced concrete girder bridge about 110 feet in length and 25 feet in width.

3. Alae Bridge, Bridge No. 009003770500058: Three-span reinforced concrete girder bridge about 150 feet in length and 25 feet in width.

Based on the information provided, the current retrofit design concept consists of utilizing a tie beam connected from the existing abutments to an anchor beam and soil nails to resist seismically induced loading. To reduce earth pressures on the abutment walls, lightweight cellular concrete backfill will be used as backfill within the tie beam and anchor beam excavations.

1.3 Scope of Work

The purpose of our geotechnical exploration was to obtain an overview of the surface and subsurface conditions to develop a soil and/or rock data set to formulate geotechnical

SECTION 1. GENERAL

W.O. 8412-00(B) GEOLABS, INC. Page 2 recommendations for the seismic retrofit design of the proposed project. Our work was performed in general accordance with our revised fee proposal dated January 26, 2023. Our scope of work generally consisted of the following tasks and work efforts:

1. Research and review of available subsurface information in the project vicinity and existing as-built drawings.

2. Perform a site reconnaissance to observe the existing bridge conditions.

3. Application for the Hawaii Department of Transportation (HDOT) roadway permit.

4. Application and coordination of underground utility toning.

5. Mobilization and demobilization of a truck-mounted drill rig and operators to the project site and back.

6. Drilling and sampling of six borings at selected locations (two per bridge location) extending to depths of 45 to 51.5 feet below the existing ground surface for a total of approximately 298 lineal feet of exploration.

7. Coordination of the field exploration and logging of the boreholes by our field geologist.

8. Geotechnical laboratory testing of selected soil samples obtained during the field exploration as an aid in classifying the materials and evaluating their engineering properties.

9. Analyses of the field and laboratory data to formulate geotechnical engineering recommendations for the seismic retrofit design of the proposed project.

10. Preparation of this formal report summarizing our work and presenting our findings and recommendations.

11. Coordination of our overall work on the project by our project engineer.

12. Quality assurance of our work and client/design team consultation by our principal engineer.

13. Miscellaneous work efforts, such as drafting, word processing, and clerical support.

SECTION 1. GENERAL

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Detailed descriptions of our field exploration methodology and the Logs of Borings are presented in Appendix A. Results of the laboratory tests performed on selected soil and rock samples retrieved from our field exploration are presented in Appendix B.

Photographs of core samples retrieved from the borings are presented in Appendix C.

END OF GENERAL

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SECTION 2. SITE CHARACTERIZATION

Of interest to our geotechnical engineering analysis are the subsurface materials encountered at the project site, the engineering properties of the materials encountered, and the variability of the subsurface conditions across the project site. Therefore, the following sections provide a description of the geologic setting of the project site, the surface and subsurface conditions encountered at the site, and a discussion of the items needed for seismic design, such as seismicity, soil liquefaction, and the soil profile characteristics for seismic analysis.

2.1 Regional Geology

The Island of Maui was built by two major volcanoes: the older West Maui (Tertiary

Epoch) and the more recent East Maui, also known as Haleakala (Pleistocene Epoch).

The Isthmus of Maui is a narrow, gently sloping plain between these two volcanoes.

The Isthmus of Maui was created by lava flows from Haleakala ponding on

West Maui. It is comprised of alluvium washed from the slopes of West Maui and

East Maui (Haleakala). The erosional processes are dominated by the detachment of soil and rock masses from the mountain walls, and the soil materials are transported downslope toward the isthmus primarily by gravity as colluvium. Once these materials reach the stream in the central portion of a valley, alluvial processes become dominant, and the sediments are transported and deposited as alluvium.

In general, stream flows in Hawaii are intermittent and flashy, such that the stream flows transmit large volumes of water for a very short duration. Because of this, the transport of sediments is intermittent, and the bulk of the stream's hydraulic load consists of a poorly sorted mixture of boulders, cobbles, gravel, sands, and fines. When the erosional base levels change, these sediment loads are left as deposits.

When deposits are left in place for long periods of time, chemical processes begin to alter the materials simultaneously causing a breakdown or weathering of the materials.

Chemical processes also cause induration, or cementation, of the coarse-grained portion of the sediment into a poorly consolidated sedimentary rock or conglomerate.

Simultaneously, erosion continues in the areas above the valley floors and upstream in

SECTION 2. SITE CHARACTERIZATION

W.O. 8412-00(B) GEOLABS, INC. Page 5 headwaters. This continued erosion generates material, which is transported downslope covering the older alluvial soil deposits. Depending on the local base level and rate of transport, these newer sediments are generally transient in terms of geologic time. In addition, their consistency and density are generally less than those of the older, partially consolidated deposits.

The project site generally is located on the western flank of Haleakala Volcano.

The bulk of the Haleakala Shield Volcano was built during the late Pliocene and early

Pleistocene Epoch by thinly bedded basaltic lava flows of the Honomanu Volcanic Series.

During the Pleistocene Epoch, the characteristics of the lava changed to very hard, thickly bedded flows of andesitic composition. These lavas have been grouped as the Kula

Volcanic Series. Typically, the basalt rock formation consists of thinly to thickly bedded a’a and pahoehoe type lava flows. Near the end of the eruptions of the Kula Volcanic

Series, the Haleakala Volcano rose to a summit possibly 3,500 feet higher than the present crater rim. At the end of the accumulation of the Kula Volcanic Series, volcanic activity became very infrequent, and stream erosion began to make progress in wearing away the mountain and carving master valleys. Finally, after this period of erosion, volcanic activity resumed. The principal rift zones reopened right across the depression at the top of the mountain and down the flanks, and the great erosional valleys were flooded with lava flows and filled with cinder cones.

2.2 Existing Site Conditions

The project sites are located along Haleakala Highway and Kekaulike Avenue in

Kula on the Island of Maui, Hawaii. The project locations are presented on the Site Plan, Plates 2.1 through 2.3. A site visit was conducted on December 29, 2022 to obtain an overview of the existing bridges and geologic features to assist in interpreting the anticipated subsurface conditions. A brief description of each bridge is provided in the subsections below.

Waiale Bridge (Bridge No. 009003770500540)

The Waiale Bridge is located on Haleakala Highway at Mile Post 3.74 and spans over the Waiale Gulch. The bridge was constructed in 1929 and is about 150 feet in length and 27 feet in width. The finish grade of the top of the deck is about +2,760 to +2,764 feet

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Mean Sea Level (MSL). The bridge is a three-span bridge supported by two end abutments and two piers. The two abutments and two piers are supported by spread footings. Based on the available as-built plans, the bottom elevation of the abutment spread footings is approximately +2,750 feet MSL at the north abutment, +2,757 feet MSL at the south abutment, +2,728 feet MSL at the north intermediate pier, and +2,726 feet

MSL at the south intermediate pier. Photographs of the existing bridge structure obtained during our site visit are provided below for reference.

Waiale Bridge North Abutment – Surface Fills and Weathered Basalt Observed

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Waiale Bridge South Abutment – Surface Fills and Weathered Basalt Observed

Waiale Bridge North Pier – Basalt Rock Formation Outcrop Observed

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Waiale Bridge South Pier – Basalt Rock Formation Outcrop Observed

Pohakuokala Bridge (Bridge No. 009003780500349)

The Pohakuokala Gulch Bridge is located on Haleakala Highway at Mile Post 5.66 and spans over the Pohakuokala Gulch. The bridge was constructed in 1929 and is about

110 feet in length and 25 feet in width. The finish grade of the top of the deck is about

+3,275 to +2,764 feet MSL. The bridge is a three-span bridge supported by two end abutments and two piers. The two abutments and two piers are supported by spread footings. Based on the available as-built plans, the bottom elevations of the abutment spread footings are approximately +3,260 feet MSL at the north abutment, +3,275 feet

MSL at the south abutment, and +3,244 feet MSL at the intermediate piers. Photographs of the existing bridge structure obtained during our site visit are provided below for reference.

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Pohakuokala Gulch Bridge North Abutment – Surface Fills and Weathered Basalt Observed

Pohakuokala Gulch Bridge South Abutment – Clinker and Weathered Basalt Observed

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Pohakuokala Gulch Bridge North Pier – Basalt Rock Formation Outcrop Observed

Pohakuokala Gulch Bridge South Pier – Weathered Basalt Rock Observed

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Alae Bridge (Bridge No. 009003770500058)

The Alae Bridge is located on Kekaulike Avenue at Mile Post 8.57 and spans over the Naalae Gulch. The bridge was constructed in 1932 and is about 150 feet in length and

25 feet in width. The finish grade of the top of the deck is about +3,275 to +2,764 feet MSL.

The bridge is a three-span bridge supported by two end abutments and two piers. The two abutments and two piers are supported by spread footings. Based on the available as-built plans, the bottom elevations of the abutment spread footings are approximately +3,244 feet

MSL at the north abutment, +3,248 feet MSL at the south abutment, +3,237 feet MSL at the north pier, and +3,219 feet MSL at the south pier. Photographs of the existing bridge structure obtained during our site visit are provided below for reference.

Alae Bridge North Abutment – Surface Fills and Weathered Basalt Observed

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South Abutment – Heavy Vegetation Obstructing View of Surface Conditions

Bridge Piers – Looking South

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Southeast Alae Channel Sidewalls – Weathered Basalt Outcrop Observed

2.3 Subsurface Conditions

We explored the subsurface conditions at each bridge project site by drilling and sampling six borings, designated as Boring Nos. W-1 and W-2 (Waiale Bridge), P-1 and

P-2 (Pohakuokala), and A-1 and A-2 (Alae Bridge), extending to depths ranging from approximately 45 to 51.5 feet below the existing ground surface. Bulk soil samples, designated as Bulk-1 through Bulk-6, were obtained near the ground surface at each boring location to evaluate the pavement support characteristics of the near-surface soils.

The approximate boring and bulk sample locations are shown on the Site Plan, Plates 2.1 through 2.3. The subsurface conditions encountered at each bridge are provided in the subsections below.

Waiale Bridge

We explored the subsurface conditions at Waiale Bridge by drilling and sampling two borings, designated as Boring Nos. W-1 and W-2. The borings were drilled generally behind the existing abutment structures. Our field exploration at the bridge generally encountered a pavement structure consisting of 4 to 5 inches of asphaltic concrete overlying 10 to 11 inches of silty gravel base material. The pavement structure was

W.O. 8412-00(B) GEOLABS, INC. Page 14 underlain by fill material generally consisting of loose silty sand and stiff sandy silt extending to depths of about 4.5 to 5.5 feet below the existing pavement surface.

The fill was generally underlain by residual soil consisting of soft to stiff clayey silts extending to depths of about 17 to 21 feet below the existing ground surface.

The residual soils were generally underlain by weathered basalt rock formation and basalt rock formation with interbedded layers of clinker materials, extending to the maximum depth explored of about 51 feet below the existing pavement surface. The weathered basalt and clinker generally consisted of dense silty gravel and sandy gravel with some cobbles. The basalt rock formations encountered were generally hard to very hard and moderately to slightly weathered.

We did not encounter groundwater in the borings at the time of our field exploration.

However, it should be noted that groundwater levels are subject to change due to rainfall, time of year, seasonal precipitation, surface water runoff, and other factors.

Pohakuokala Bridge

We explored the subsurface conditions at Waiale Bridge by drilling and sampling two borings, designated as Boring Nos. P-1 and P-2. The borings were drilled generally behind the existing abutment structures. Our field exploration at the bridge generally encountered a pavement structure consisting of 5.5 to 9 inches of asphaltic concrete overlying 6 to 9.5 inches of silty and sandy gravel base material. The pavement structure was underlain by fill material and residual soils generally consisting of medium dense to loose silty gravel and stiff to very stiff sandy silts extending to depths of about 8 to 10 feet below the existing pavement surface.

The fill and residual soils were generally underlain by weathered basalt rock formation and basalt rock formation with interbedded layers of clinker materials, extending to the maximum depth explored of about 50.5 feet below the existing pavement surface. The weathered basalt and clinker generally consisted of medium dense to very dense silty sands and sandy gravel. The basalt rock formations encountered were generally hard to very hard and moderately weathered to unweathered.

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We did not encounter groundwater in the borings at the time of our field exploration.

However, it should be noted that groundwater levels are subject to change due to rainfall, time of year, seasonal precipitation, surface water runoff, and other factors.

Alae Bridge

We explored the subsurface conditions at Alae Bridge by drilling and sampling two borings, designated as Boring Nos. A-1 and A-2. The borings were drilled generally behind the existing abutment structures. Our field exploration at the bridge generally encountered a pavement structure consisting of 4 to 5 inches of asphaltic concrete overlying 13 to 14 inches of silty gravel base material. The pavement structure was underlain by fill material generally consisting of medium dense to very dense silty sand/gravel and gravelly gobbles extending to depths of about 6 to 13 feet below the existing pavement surface. The fill was generally underlain by residual soil consisting of medium dense silty sand and silty gravel, and very dense gravelly cobbles extending to depths of about 6 to 13 feet below the existing ground surface.

The fills were generally underlain colluvium, volcanic ash deposits, residual soils, and saprolite. The colluvial deposits generally consisted of very dense clayey cobbles.

The volcanic ash generally consisted of loose to medium dense silty sands. The residual and saprolite generally consisted of stiff sandy silts and very dense sandy gravel. The colluvium, volcanic ash deposits, residual soils and saprolite were generally underlain by basalt rock formation with interbedded layers of clinker materials, extending to the maximum depth explored of about 51.5 feet below the existing pavement surface. The clinker generally consisted of sandy gravel and the basalt rock formations encountered were generally hard to very hard and slightly weathered.

We did not encounter groundwater in the borings at the time of our field exploration.

However, it should be noted that groundwater levels are subject to change due to rainfall, time of year, seasonal precipitation, surface water runoff, and other factors.

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Detailed descriptions of the field exploration methodology are presented in

Appendix A. Descriptions and graphic representations of the materials encountered in the borings are presented on the Logs of Borings in Appendix A. Laboratory tests were performed on selected soil and rock samples, and the test results are presented in

Appendix B. Photographs of core samples retrieved from the borings are presented in

Appendix C.

2.4 Seismic Design Parameters

Based on the AASHTO 2020 LRFD Bridge Design Specifications, 9th Edition, the project site may be subject to seismic activity, and seismic design considerations will need to be addressed for the project. The following sections provide discussions on seismicity, the potential for liquefaction at the project site, and the soil/rock profile (site class) for seismic design.

Earthquakes and Seismicity

In general, earthquakes throughout the world are caused by shifts in the tectonic plates. In contrast, earthquake activity in Hawaii is linked primarily to volcanic activity;

therefore, earthquake activity in Hawaii generally occurs before or during volcanic eruptions. In addition, earthquakes may result from the underground movement of magma that comes close to the surface but does not erupt. The Island of Hawaii experiences thousands of earthquakes each year, but most are so small that they can only be detected by sensitive instruments. However, some of the earthquakes are strong enough to be felt, and a few cause minor to moderate damage.

In general, earthquakes associated with volcanic activity are most common on the

Island of Hawaii. Earthquakes that are directly associated with the movement of magma are concentrated beneath the active Kilauea and Mauna Loa Volcanoes on the Island of Hawaii. Because the majority of earthquakes in Hawaii (over

90 percent) are related to volcanic activity, the risk of seismic activity and degree of ground shaking diminishes with increased distance from the Island of Hawaii. The

Island of Hawaii has experienced numerous earthquakes greater than Magnitude 5

(M5+); however, earthquakes are not confined only to the Island of Hawaii.

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To a lesser degree, the Island of Maui has experienced several earthquakes greater than Magnitude 5. Therefore, moderate to strong earthquakes have occurred in the

County of Maui. Due to the relatively short period of documented earthquake monitoring in the State of Hawaii, information pertaining to earthquakes on the Island of Maui may not be complete. However, the following are two examples of reported earthquakes within the County of Maui. A Magnitude 6.8 earthquake occurred on the

Island of Maui in 1938, and the Lanai Earthquake of 1871 was estimated at a

Magnitude 7 or greater. Based on these two reported earthquakes, the Island of Maui may be considered seismically active.

Liquefaction Potential

Based on the AASHTO 2020 LRFD Bridge Design Specifications, 9th Edition, the project site may be subject to seismic activity, and the potential for soil liquefaction at the project site will need to be evaluated.

Soil liquefaction is a condition where saturated cohesionless soils near the ground surface undergo a substantial loss of strength due to the build-up of excess pore water pressures resulting from cyclic stress applications induced by earthquakes. In this process, when the loose saturated sand deposit is subjected to vibration (such as during an earthquake), the soil tends to densify and decrease in volume, causing an increase in pore water pressure. If drainage is unable to occur rapidly enough to dissipate the build-up of pore water pressure, the effective stress (internal strength) of the soil is reduced. Under sustained vibrations, the pore water pressure build-up could equal the overburden pressure, essentially reducing the soil shear strength to zero and causing it to behave as a viscous fluid. During liquefaction, the soil acquires mobility sufficient to permit both horizontal and vertical movements, and if not confined, will result in significant deformations.

Soils most susceptible to liquefaction are loose, uniformly graded, fine-grained sands and loose silts with little cohesion. The major factors affecting the liquefaction characteristics of a soil deposit are as follows:

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FACTORS LIQUEFACTION SUSCEPTIBILITY

Grain Size Distribution Fine and uniform sands and silts are more susceptible to liquefaction than coarse or well-graded sands.

Initial Relative Density

Loose sands and silts are most susceptible to liquefaction. Liquefaction potential is inversely proportional to relative density.

Magnitude and Duration of Vibration

Liquefaction potential is directly proportional to the magnitude and duration of the earthquake.

In general, the subsurface information obtained from the drilled borings indicated that the project site is underlain by fills overlying colluvium, volcanic ash, residual soils, and saprolite overlying hard basalt rock formation with interbedded clinker layers.

Based on the subsurface conditions encountered in our field exploration, the geology in the area, and our engineering analyses, the potential for soil liquefaction at the project site is non-existent due to the presence of basalt rock formation and the absence of loose granular soils and groundwater table within the depths explored.

Therefore, the potential for liquefaction is not a design consideration at this project site.

Soil Profile Type for Seismic Design

Based on the subsurface materials encountered and available data, it is our opinion that the project sites may be classified from a seismic analysis standpoint as being a

“Very Dense Soil and Soft Rock” site corresponding to a Site Class C soil profile type based on AASHTO 2020 LRFD Bridge Design Specifications, 9th Edition.

Based on the AASHTO 2020 LRFD Bridge Design Specifications, the seismic retrofitted bridge structure will need to be designed based on an earthquake return period of 1,000 years. Based on a 1,000-year return period and the anticipated Site

Class, the following seismic design parameters were estimated and may be used for the seismic analysis of the bridge structure planned for the project.

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SEISMIC DESIGN PARAMETERS

WAIALE BRIDGE

AASHTO 2020 LRFD BRIDGE DESIGN SPECIFICATIONS

1,000-YEAR RETURN PERIOD

(~7% PROBABILITY OF EXCEEDANCE IN 75 YEARS)

Parameter Value

MCE Peak Bedrock Acceleration, PBA (Site Class B) 0.259g

Spectral Response Acceleration (Site Class B), SS 0.591g

Spectral Response Acceleration (Site Class B), S1 0.171g

Site Class “C”

Site Coefficient, Fpga 1.14

Site Coefficient, Fa 1.17

Site Coefficient, Fv 1.63

MCE Peak Ground Acceleration, PGA (Site Class C) or As 0.296g

Design Spectral Response Acceleration, SDS 0.687g

Design Spectral Response Acceleration, SD1 0.279g

SEISMIC DESIGN PARAMETERS

POHAKUOKALA BRIDGE

AASHTO 2020 LRFD BRIDGE DESIGN SPECIFICATIONS

1,000-YEAR RETURN PERIOD

(~7% PROBABILITY OF EXCEEDANCE IN 75 YEARS)

Parameter Value

MCE Peak Bedrock Acceleration, PBA (Site Class B) 0.259g

Spectral Response Acceleration (Site Class B), SS 0.589g

Spectral Response Acceleration (Site Class B), S1 0.172g

Site Class “C”

Site Coefficient, Fpga 1.14

Site Coefficient, Fa 1.16

Site Coefficient, Fv 1.63

MCE Peak Ground Acceleration, PGA (Site Class C) or As 0.296g

Design Spectral Response Acceleration, SDS 0.687g

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SEISMIC DESIGN PARAMETERS

ALAE BRIDGE

AASHTO 2020 LRFD BRIDGE DESIGN SPECIFICATIONS

1,000-YEAR RETURN PERIOD

(~7% PROBABILITY OF EXCEEDANCE IN 75 YEARS)

Parameter Value

MCE Peak Bedrock Acceleration, PBA (Site Class B) 0.258g

Spectral Response Acceleration (Site Class B), SS 0.585g

Spectral Response Acceleration (Site Class B), S1 0.171g

Site Class “C”

Site Coefficient, Fpga 1.14

Site Coefficient, Fa 1.17

Site Coefficient, Fv 1.63

MCE Peak Ground Acceleration, PGA (Site Class C) or As 0.294g

Design Spectral Response Acceleration, SDS 0.681g

END OF SITE CHARACTERIZATION

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SECTION 3. DISCUSSION AND RECOMMENDATIONS

Based on our field exploration and as-built drawings, the existing abutment and pier structures are bearing on the underlying colluvium, residual soils, and hard basalt rock formation. Bearing pressure coefficient of sliding friction and passive pressure resistance parameters were developed for the project.

Based on the information provided, the current retrofit design concept consists of utilizing a tie beam connected from the existing abutments to an anchor beam and soil nails to resist seismically induced loading. To reduce earth pressures on the abutment walls, lightweight cellular concrete backfill will be used as backfill within the tie beam and anchor beam excavations.

A detailed discussion of these items and our geotechnical recommendations for the seismic retrofit design of the existing bridge structures and other geotechnical aspects of the project are presented in the following sections.

3.1 Stiffness Modeling Analysis

In order to evaluate the lateral load resistance of the existing bridge structures, foundation capacities and stiffness modeling parameters were estimated based on the subsurface materials encountered in the borings. Based on the anticipated subsurface conditions, the following analyses were performed in support of the seismic evaluation of the existing bridges:

1. Bearing Capacities of Shallow Foundations

2. Lateral Load Resistance of Shallow Foundations

3. Lateral Load Resistance of Abutment Fills

4. Static Earth Pressure

5. Active Lateral Earth Pressure

Based on the anticipated subsurface conditions, the following subsections provide brief descriptions of the foundation parameters and our preliminary recommendations for use in evaluating the existing bridge structures.

SECTION 3. DISCUSSION AND RECOMMENDATIONS

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Bearing Capacities of Shallow Foundations

The ultimate and factored bearing capacities of the abutment and pier structures of the Waiale, Pohakuokala, and Alae Bridges supported on shallow foundations are provided in the Summary of Foundation Conditions, Plates 3.1 through 3.3.

Lateral Load Resistance of Shallow Foundations

For lateral load resistance of the shallow foundations, two components of lateral load resistance, as shown on Plates 3.1 through 3.3, may be used in combination. It should be noted that the lateral load resistance of shallow foundations is primarily from friction and adhesion (where provided) between the base of the footings and the supporting subgrade materials. The passive pressure resistance component should be secondary lateral load resistance mechanisms.

The component of passive pressure resistance should be reduced to account for strain compatibility due to the depth of the footings. Please note that the amount of deflection needed to mobilize the full passive pressure is indicated on Plates 3.1 through 3.3. For deflections less than the deflection needed to mobilize full passive pressure, a linearly interpolated reduced passive pressure may be used in evaluating the lateral load resistance of the footing.

Lateral Load Resistance of Abutment Fills

The abutment structures may be considered as a large footing bearing on the abutment fill soils for resistance of lateral loads during a seismic event in the longitudinal direction. For lateral loads imposed on the abutments, the stiffness of the abutment fill soils will generally be mobilized prior to the lateral resistance of its footings.

Provided that intimate contact exists between the backfill soil and the abutments, a soil stiffness spring equal to approximately 4 ksf per inch of deflection may be used in resisting lateral loads. To reduce the potential for shear failure in the abutment fill soils, the lateral deflection should be limited to 1.25 inches or less. Therefore, the maximum lateral load resistance of the abutment structure should be limited to 5 kips per square foot of the abutment wall face. The structural engineer should check the

W.O. 8412-00(B) GEOLABS, INC. Page 23 structure displacement required in order to engage the abutment fill soils for lateral load resistance.

Please note that the stiffness of the abutment fill soils only applies to forces that cause the abutment wall to move into the backfill soil (longitudinal direction normal to the abutment wall face). Therefore, only the lateral load resistance of the abutment foundation and wing walls may be utilized to resist the lateral loads in the transverse direction.

Active Lateral Earth Pressure

Based on the subsurface conditions encountered during our field exploration, we believe compacted fills are anticipated directly behind the abutment walls. For abutment walls with level backfill, the estimated static lateral earth pressures acting on the abutment and wing wall structures are presented in the following table:

STATIC LATERAL EARTH PRESSURES

Active (pcf)

At-Rest (pcf)

34 53

The lateral earth pressures shown above do not include hydrostatic pressures that might be caused by groundwater trapped behind the structures. The values provided above assume that existing on-site granular soils less than 3 inches in maximum dimension were used to backfill directly behind the retaining structures.

In general, an active condition may be used for structures that are free to deflect laterally by as much as 0.5 percent of the structure height. If the tops of the structures are not free to deflect beyond this degree or are restrained, the retaining structures should be evaluated for the at-rest condition.

Surcharge stresses due to areal surcharges, line loads, and point loads within a horizontal distance equal to the depth of the retaining structure should be considered in the design. For uniform surcharge stresses imposed on the loaded side of the structure, a rectangular distribution with a uniform pressure equal to 34 percent of the vertical surcharge pressure acting on the entire height of the structure, which is

W.O. 8412-00(B) GEOLABS, INC. Page 24 free to deflect (cantilever), may be used in the design. For retaining structures that are restrained, a rectangular distribution equal to 53 percent of the vertical surcharge pressure acting over the entire height of the structure may be used for the design.

Additional analyses during the design may be needed to evaluate the surcharge effects of point loads and line loads.

We understand that lightweight cellular concrete backfill will be used as backfill within the tie beam and anchor beam excavations. Lateral earth pressures acting on the existing abutment walls within the lightweight cellular concrete backfill zone will be negligible.

Dynamic Lateral Earth Pressure

Dynamic lateral earth forces due to seismic loading will need to be considered in the design of the retaining structures based on LRFD design methods. Seismic loading

(PGA or amax= 0.296g) is used to estimate the dynamic lateral earth pressures based on a peak bedrock acceleration (PBA) of 0.259g. The table below summarizes the dynamic lateral earth forces acting on the retaining structure in the event of an earthquake.

DYNAMIC LATERAL EARTH PRESSURES DUE TO

SEISMIC LOADING

Backfill Condition Active Condition (H2 pounds per linear foot)

At-Rest Condition (H2 pounds per linear foot)

Level 5.6 13.3

The active condition assumes that the walls will be allowed to move laterally by up to about 1 to 2 inches in the event of an earthquake. The at-rest condition should be used when walls are restrained (<0.5 inches of lateral movement). The resultant force of the dynamic lateral earth pressures should be assumed to act through the mid-height of the wall. It should be noted that the forces due to dynamic lateral earth pressures presented above are in addition to the static lateral earth pressures.

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3.2 Soil-Nailed Anchor Beams

Based on the information provided, the current retrofit design concept consists of utilizing a tie beam connected from the existing abutments to an anchor beam and soil nails to resist seismically induced loading.

Items pertaining to the soil-nailed anchor beams are addressed in the subsequent subsections and include the following:

1. Excavation Preparation

2. Soil Nailed Anchor Beams

3. Soil Nail Installation

4. Soil Nail Testing

Construction of the soil-nailed anchor beam system should be performed by a specialty contractor experienced in the construction of soil-nails. Due to the specialized nature of the construction, a Geolabs representative should be present to observe the geotechnical aspects of the soil-nailed anchor beam system and testing of the soil nails.

Excavation Preparation

At the on-set of construction, loose material and debris should be removed from the face of the excavation to receive soil nails. Care should be taken in removing material so that the stability of the excavation is not compromised.

Soil Nailed Anchor Beams

A soil-nailed anchor beam system consists of a series of individual reinforcing bars grouted into drilled holes. The soil nails connect to an anchor beam, which will subsequently connect to a series of tie beams. The tie beam will connect to the back of the existing abutments to resist seismically induced loading. Based on the information provided, four tie beams will be required per bridge abutment. The tie beams will induce a total load demand of 160 kips onto the proposed anchor beam.

Based on the current design concept, four soil nails with allowable tensile load capacities of 40 kips per anchor per soil nail will be utilized.

We understand that all bridge abutments will require the use of soil nails to anchor the tie beams. Based on the anticipated load demand, we recommended installing the soil nails by drilling a minimum 8-inch diameter hole with an inclination of

W.O. 8412-00(B) GEOLABS, INC. Page 26 approximately 20 degrees from horizontal. The soil nail bar should consist of ASTM

A615 Grade 75 solid threaded bar with a minimum bar diameter of 1.5 inches. We recommend using a double corrosion protection system for the nails. Epoxy coated bars surrounded by neat cement grout or sand-cement mixture with a minimum

28-day compressive strength of 4,000 pounds per square inch (psi) may be considered. A corrosion inhibitor, such as Coretec MCI 2005 NS Corrosion Inhibitor or equivalent, should also be included in the grout mix for the soil nail bar.

Based on our soil nail analysis, we recommend using design nail lengths of 30 to

45 feet, extending into the fill, residual soils, ash deposits, and basalt formations encountered in our field exploration. The following table provides a summary of soil nails for each bridge location.

SOIL NAIL SUMMARY

WAIALE BRIDGE

Location Abutment No. 1 (North)

Abutment No. 2 (South)

Soil Nail Inclination (degrees) 20 20

Soil Nail Length (feet) 45 45

Drill Hole Diameter (feet) 8 8

Soil Nail Bar Size No. 11 (Grade 75) No. 11 (Grade 75)

POHAKUOKALA BRIDGE

Location Abutment No. 1 (North)

Abutment No. 2 (South)

Soil Nail Inclination (degrees) 20 20

Soil Nail Length (feet) 35 35

Drill Hole Diameter (feet) 8 8

Soil Nail Bar Size No. 11 (Grade 75) No. 11 (Grade 75)

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SOIL NAIL SUMMARY

ALAE BRIDGE

Location Abutment No. 1 (North)

Abutment No. 2 (South)

Soil Nail Inclination (degrees) 20 20

Soil Nail Length (feet) 30 30

Drill Hole Diameter (feet) 8 8

Soil Nail Bar Size No. 11 (Grade 75) No. 11 (Grade 75)

Soil Nail Installation

Construction of the permanent soil nails should be performed by a specialty contractor experienced in the construction of soil nails. Due to the specialized nature of the soil nail construction, a Geolabs representative should be present to observe the geotechnical aspects of the soil nail construction. Potentially difficult drilling conditions may be encountered during the installation of the soil nails due to the potential of cobbles and boulders within the fill materials anticipated at the project site. Utilizing a temporary casing may be required to maintain an open hole for the soil nail installation. In addition, due to potential variations of basalt rock within the subsurface, hard drilling conditions may be anticipated. The contractor should fully investigate the project site and make his/her own interpretation as to the character of the materials to be encountered. It is the contractor’s responsibility to bid the project accordingly with sufficient contingency, taking into account potential caving-in, hard drilling, and difficult access conditions.

Soil Nail Testing

Based on the subsurface conditions anticipated behind the soil-nailed anchor beam, we recommend performing a minimum of one pre-production verification test on a sacrificial soil nail at each bridge site. In addition, proof tests should be performed on at least 10 percent of the production soil nails during construction to confirm the bond stresses used in the design.

The verification test should be loaded gradually to 150 percent of the design load for the creep test and subsequently to the maximum test load of about 200 percent of

W.O. 8412-00(B) GEOLABS, INC. Page 28 the design load. In addition, the load at every loading increment should be held for at least 10 minutes, and creep tests should be held for at least 60 minutes. The proof tests should consist of subjecting the soil nail to at least 150 percent of the design loads and the load should be held for at least 10 minutes (until stable). The proof test nails may be incorporated into the permanent soil nail retaining wall, provided they satisfy the test criteria. Pullout tests and creep tests on the soil nails are integral components of the design for the soil nail retaining wall system. Therefore, we recommend conducting pullout tests and creep tests in the presence of a Geolabs representative.

3.3 Pavement

We understand new pavement will be required at each abutment to replace the roadway pavement structure that will be removed during the seismic retrofit project. In general, asphaltic concrete pavement overlying reinforced concrete relief slabs will be utilized behind the existing abutments. However, pavements overlying existing in-situ soils will be required beyond the relief slabs. Asphaltic concrete pavement sections beyond the relief slabs are provided in subsequent sections. The flexible pavement sections presented herein were generally determined based on the methodology described in Chapter 3 of the revised Pavement Design Manual dated March 2002. The

Pavement Design Manual was prepared by the State of Hawaii - Department of

Transportation, Highways Division, Material Testing and Research Branch. The pavement design methodology is based on the Hveem Stabilometer method developed and used by the California Department of Transportation (Caltrans).

Design Traffic Loading Conditions/Traffic Index

Based on the design guidelines from the revised Pavement Design Manual dated

March 2002, the roadway at Waialae and Pohakuokala Bridges may be classified as a “Medium-Volume Rural” roadway, and the roadway at Alae Bridge may be classified as a “Low-Volume Paved” roadway. Therefore, new pavements for this project will need to be designed for a pavement life of 20 years. Design traffic parameters were obtained from the HDOT Planning Survey Engineer traffic data memorandum dated April 12, 2024. The following tables summarize the design traffic parameters used in our pavement analyses.

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DESIGN TRAFFIC PARAMETERS FOR

FLEXIBLE AND RIGID PAVEMENTS

Waialae and Pohakuokala Bridge

Design Period 20 Years

Average Daily Traffic

(ADT)

At Project Completion 50 Years After Project

Completion

Vehicles per day per direction

4,500 5,700

24-Hour Truck Traffic 6%

Type of Axle Truck Traffic Distribution 2-Axle 79.94% 3-Axle 17.76% 4-Axle 0.21% 5-Axle 0.14% 6-Axle 0.29% 7-Axle 1.66%

Alae Bridge

Design Period 20 Years

Average Daily Traffic

(ADT)

At Project Completion 50 Years After Project

Completion

Vehicles per day per direction

1,700 2,100

24-Hour Truck Traffic 6%

Type of Axle Truck Traffic Distribution 2-Axle 83.15% 3-Axle 14.15% 4-Axle 1.11% 5-Axle 0.00% 6-Axle 0.21% 7-Axle 1.39%

Based on a design period of 20 years, the traffic volume provided, and the assumed truck traffic distribution, a Traffic Index (TI) of 9 was determined for the Waialae and

Pohakuokala Bridges, and a Traffic Index (TI) of 8 was determined for the Alae Bridge project, respectively.

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Design Subgrade Conditions

Based on our field exploration and the current design concept, we anticipate that the pavement subgrade soils may consist of recompacted on-site soils. We anticipate that majority of the pavement subgrade soils generally will consist of silty sands and sandy silts.

Laboratory Resistance (R) value testing was performed on the near-surface soils at each bridge abutment to evaluate the use of the near-surface soils as roadway fill material. The R-values obtained for the existing subgrade soils ranged from 10 to

70. A summary of R-value test results is provided in the table below.

SUMMARY OF R-VALUE TEST RESULTS

Location Bulk Surface Sample R-Value

Waiale Bridge Bulk-1 26

Waiale Bridge Bulk-2 25

Pohakuokala Bridge Bulk-3 70

Pohakuokala Bridge Bulk-4 10

Alae Bridge Bulk-5 23

Alae Bridge Bulk-6 21

The results of the laboratory R-value tests are presented in Appendix B.