PHASE 100 REPORT

751/20092.ABG Straits State Harbor Triangle Phase 100 Study Mackinaw City, Michigan

Department of Technology, Management & Budget December 28, 2022 State Facilities Administration NTH Project #: 22000435 Design and Construction Division 3111 West St. Joseph Street Lansing, MI 48909 ATTN: Alan Goschka, AIA, Project Director

NTH Consultants, Ltd.

41780 Six Mile Rd Suite 200 Northville, MI 48168

NTH Consultants, Ltd. 2990 W. Grand Blvd. Suite M-10 Detroit, MI 48202 Infrastructure Engineering 313.237.3900 and Environmental Services 313.237.3909 Fax

Department of Technology, Management & Budget December 28, 2022 State Facilities Administration NTH Project No. 22000435 Design and Construction Division 3111 West St. Joseph Street Lansing, Michigan 48909 ATTN: Alan Goschka, AIA, Project Director

RE: 751/20092.ABG Straits State Harbor Triangle Phase 100 Study

Department of Natural Resources – Straits State Harbor Mackinaw City, Michigan

Dear Mr. Goschka:

NTH Consultants, Ltd. (NTH) is pleased to submit this Phase 100 Study report to the Department of Technology, Management & Budget (DTMB) and the Michigan Department of Natural Resources (MDNR) regarding the evaluation of the shoreline structures and pavement at the Straits State Harbor located in Mackinaw City, Michigan. We performed this work in accordance with the agreed-upon scope of work outlined in our Proposal No 22000435, dated July 28, 2022.

We appreciate the opportunity to have been of service to you. Should you have any questions, or require additional information, please call.

Sincerely, NTH Consultants, Ltd.

Lauren Granger, P.E. Jason R. Edberg, P.E.

Project Engineer Senior Vice President

Attachments

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TABLE OF CONTENTS

Page No.

1.0 EXECUTIVE SUMMARY 1

2.0 INTRODUCTION AND PROJECT BACKGROUND 2

2.1 INTRODUCTION 2

2.2 PROJECT DESCRIPTION 2

3.0 FIELD EXPLORATION ACTIVITIES 3

3.1 UNDERWATER ROV INSPECTION 3

3.2 SHORELINE VISUAL SURVEY AND CONDITION ASSESSMENT 3

3.3 PAVEMENT EVALUATION 3

3.4 GEOPHYSICAL INVESTIGATION 3

3.4.1 Ground Penetrating Radar 3

3.4.2 Multi-Channel Analysis of Surface Waves 4

4.0 EVALUATIONS 5

4.1 SHORELINE CONDITION ASSESSMENT 5

4.1.1 Docking Pier / Triangle 5

4.1.2 North Pier 13

4.1.3 Transfer Bridge Abutment 16

4.1.4 Fishing Pier 16

4.1.5 East Face Steel Sheet Pile Seawall 18

4.1.6 Dolphin 21

4.1.7 North and South Armored Shorelines 21

4.2 PAVEMENT EVALUATION 23

4.2.1 Visual Pavement Evaluation 23

4.2.2 Falling Weight Deflectometer (FWD) Testing 24

4.2.3 Pavement Evaluation Summary 24

4.3 GPR EVALUATION 26

4.4 MASW SURVEY EVALUATION 26

4.4.1 Shear Wave Velocity Evaluation 26

4.4.2 MASW Limitations 29

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4.5 RECOMMENDATIONS 30

4.6 RECOMMENDATIONS FROM SHORELINE CONDITION

ASSESSMENT 30

4.7 RECOMMENDATIONS FROM PAVEMENT EVALUATION 31

4.8 RECOMMENDATIONS FROM MASW SURVEY 32

4.9 BUDGET ANALYSIS 33

4.10 LIMITATIONS 33

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1.0 EXECUTIVE SUMMARY

The scope of this project involves a portion of the Straits State Harbor facility that has been constructed and updated in several phases over nearly 100 years. The docking pier was constructed by the Michigan Highway Department for the State Ferry Service in 1923 and expanded over several years. The initial construction was a 25-foot wide, 1400-foot-long dock that accommodated one auto ferry for loading and unloading. In the early 1930’s the docking “triangle” was constructed. The docking structure was expanded again in 1938 to approximately 300 feet in width. After completion of the Mackinaw Bridge in 1957 the site has been used periodically for overflow parking by the Star Line passenger cruise line. In the years of 2007- 2009 a new harbor facility was constructed by the MDNR. The primary structural elements for the site include steel sheet pile seawalls and cofferdams, timber cribbing cofferdams, concrete caissons, and steel and timber piles – all capped with reinforced concrete. A partial dive inspection was performed in 2006, primarily focused on the “triangle” portion of the facility and noted a number of minor deficiencies. Historical reports and drawings were provided by the State for our review prior to the investigations and analyses described herein. We understand that local and community interests in expanding the current use of the site has prompted the MDNR Parks and Recreation Division (MDNR PRD) to assess the current condition of the pier, docking triangle, dolphins, and fishing pier, including the seawalls and drainage structures.

An underwater inspection of the existing shoreline elements was performed with our remotely operated vehicle (ROV) under the control of NTH field staff on September 12 through September 16, 2022. The condition of the structures was documented with underwater photographs and videos. A shoreline visual survey was performed in conjunction with the underwater ROV inspection on September 12 through September 16, 2022, by an NTH engineer. During the survey, the above-ground condition of the shoreline structures was observed and documented.

The site pavement conditions were evaluated through a visual inspection as well as by falling weight deflectometer (FWD) testing. The visual inspection was performed by NTH staff on September 16, 2022. The FWD testing was performed by Applied Research Associates, Inc.

(ARA) under the direction of NTH field staff on September 16, 2022. Field services for the geophysical exploration were performed between September 14 through 16, 2022. Geophysical exploration services consisted of performing ground penetrating radar (GPR) scans (also referred to as “lines”) along the various segments of the main harbor peninsula adjacent to the lake as well as Multi-Channel Analyses of Surface Waves (MASW) covering the north and south alignments of the main harbor peninsula.

Overall the facilities are in good condition, especially considering their age. The condition assessments revealed only minor defects in the various shoreline protection system, primarily consisting of holes in the steel sheet pile elements and gaps in the timber cribbing structures that allow portions of the internal aggregate fill to “leak” out into the lake. Recommended repairs include patching of holes and gaps, replacement of bolts, and replacement of lost aggregate fill within the structures. Details of the condition assessment, specific defects identified, and recommendations for repair are presented herein. Once the repairs are completed, it is reasonable to expect the structures to continue to perform over a 50 year remaining service life.

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The pavement evaluation indicates that the site pavements are in fair to good condition. With proper crack sealing and maintenance, the pavements should perform well through their remaining service life which, according to the original design parameters, is approximately 6-7 more years.

The pavements and shoreline elements are able to support anticipated loading from recreational and light commercial use. The shoreline elements, once repaired, will be able to support heavy commercial loading; however, these heavy loads could have a detrimental effect on the site pavements. Recommendations to accommodate these heavy commercial loads are provided herein.

2.0 INTRODUCTION AND PROJECT BACKGROUND

2.1 INTRODUCTION

NTH Consultants, Ltd. (NTH) has been contracted by the Department of Technology, Management & Budget (DTMB) and the Michigan Department of Natural Resources (MDNR) to perform a condition assessment of the shoreline structures and adjacent pavements at the Straits State Harbor in Mackinaw City, Michigan. This report presents pertinent information regarding our investigation, detailed findings, evaluations, and recommendations for current and future use.

2.2 PROJECT DESCRIPTION

The scope of this project involves a portion of the Straits State Harbor facility that has been constructed and updated in several phases over nearly 100 years. The docking pier was constructed by the Michigan Highway Department for the State Ferry Service in 1923 and expanded over several years. The initial construction was a 25-foot wide, 1400-foot-long dock that accommodated one auto ferry for loading and unloading. In the early 1930’s the docking “triangle” was constructed. The docking structure was expanded again in 1938 to approximately 300 feet in width. After completion of the Mackinaw Bridge in 1957 the site has been used periodically for overflow parking by the Star Line passenger cruise line. In the years of 2007- 2009 a new harbor facility was constructed by the MDNR. The primary structural elements for the site include steel sheet pile seawalls and cofferdams, timber cribbing cofferdams, concrete caissons, and steel and timber piles – all capped with reinforced concrete. A partial dive inspection was performed in 2006, primarily focused on the “triangle” portion of the facility and noted a number of minor deficiencies. Historical reports and drawings were provided by the State for our review prior to the investigations and analyses described herein.

We understand that local and community interests in expanding the current use of the site has prompted the MDNR Parks and Recreation Division (MDNR PRD) to assess the current condition of the pier, docking triangle, dolphins, and fishing pier, including the seawalls and drainage structures.

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3.0 FIELD EXPLORATION ACTIVITIES

3.1 UNDERWATER ROV INSPECTION

An underwater inspection of the existing shoreline elements was performed with our remotely operated vehicle (ROV) under the control of NTH field staff on September 12 through September 16, 2022. The condition of the structures was documented with underwater photographs and videos. Findings from the study are discussed in subsequent sections. The Docking Pier / Triangle and the Fishing Pier were stationed for location reference prior to starting the inspection.

The Docking Pier / Triangle was stationed beginning at the southwest corner and progressing counterclockwise around the structure perimeter to the northwest extent, following the layout of the structure numbering on the available plans. The Fishing Pier was stationed beginning at the western extent of the structure (access bridge not included) and progressed eastward to the east structure face down the centerline. Stations for the Fishing Pier are referenced herein as North Station and South Station to indicate the side of the structure. An overall site plan, and orientation plans of the Docking Pier / Triangle and Fishing Pier are attached herein as Figure Nos. 1 through 3 of the Appendix. Observations and images from the study are provided in the Log of Photographs for each structure, attached herein as Figure Nos. 4 through 10 of the Appendix.

3.2 SHORELINE VISUAL SURVEY AND CONDITION ASSESSMENT

A shoreline visual survey was performed in conjunction with the underwater ROV inspection on September 12 through September 16, 2022, by an NTH engineer. During the survey, the above-ground condition of the shoreline structures was observed and documented. Findings and images from the study are attached herein on the Log of Photographs for each structure, Figure Nos. 4 through 10 of the Appendix.

3.3 PAVEMENT EVALUATION

The site pavement conditions were evaluated through a visual inspection as well as by falling weight deflectometer (FWD) testing. The visual inspection was performed by NTH staff on September 16, 2022. The FWD testing was performed by Applied Research Associates, Inc.

(ARA) under the direction of NTH field staff on September 16, 2022

3.4 GEOPHYSICAL INVESTIGATION

Field services for the geophysical exploration were performed between September 14 through 16, 2022. Geophysical exploration services consisted of performing ground penetrating radar (GPR) scans (also referred to as “lines”) along the various segments of the main harbor peninsula adjacent to the lake as well as Multi-Channel Analyses of Surface Waves (MASW) covering the north and south alignments of the main harbor peninsula. The results of the MASW surveys are presented as Figure Nos. 11 and 12.

3.4.1 Ground Penetrating Radar

GPR is a high-resolution electromagnetic technique that is designed primarily to investigate shallow subsurface features. A Noggin Smartcart GPR unit with a 250 MHz transmitting antenna was selected and used for this project. When performing an individual GPR scan, an

- 4 -electromagnetic wave is radiated from a transmitting antenna and travels through the subsurface at a velocity which is determined primarily by the permittivity (ability to transmit an electric field) of the material being investigated. Waves spread and travel outward from the source until hitting an object that has different dielectric properties from the surrounding medium and are scattered from the object. The scattered waves are then detected by a receiving antenna and recorded on a digital storage device. The data were interpreted by NTH staff in the field.

3.4.2 Multi-Channel Analysis of Surface Waves

MASW entails generating seismic energy, collecting field data using a series of geophones, and processing and analyzing the field data using specialized computer software. In a MASW survey, seismic energy travels along the ground surface as a Rayleigh wave. Based on the dispersion characteristics of a Rayleigh wave, the particle movement (signal) is detected by the array of geophones, which are set a known distance from the energy source and recorded for a predetermined interval. The recorded signals (or traces) are then used to infer the shear wave velocity profile of the various soil and rock formations versus depth.

MASW surveys can be performed using several different sensor configurations and with varied energy sources. NTH selected a linear-array configuration with an active energy source as described below. Active MASW primarily records the seismic energy from an intentionally generated energy source such as a hammer. Passive MASW could not be used due to the lack of a secondary energy source, such as car traffic.

The seismic energy for the active survey was generated by a 40-kilogram hammer propelled energy generator (PEG-40). The PEG-40 is a cylindrical hammer raised to a predetermined height and released, accelerated downward due to its own mass. At the ground surface, the hammer struck an aluminum plate above a compressible rubber mat, which generated the low-frequency energy required for the survey. During the acquisition of the field data, one shot gather (record) was recorded at each station for a total of three seconds with a one millisecond sample interval.

The seismic signal from the source was detected along a 115-foot-long array of geophones having a natural resonant frequency of 4.5 Hertz (Hz). The geophones were placed at five-foot intervals (stations) offset 30 feet from the PEG-40 and rested on heavy tempered steel plates to achieve seismic coupling with the ground.

To facilitate rapid data collection, the geophones were connected to a woven strap in an arrangement termed a landstreamer. The landstreamer was then connected and towed behind a field vehicle during data acquisition. Each of the geophones was connected to a multi-channel seismograph (geode). The seismograph was connected to and controlled by a laptop computer, which translated and compiled the geophone signals into a record for later processing and analysis. Following the collection of the record, all geophones were progressed five feet along the direction of survey to the next station where the process was repeated.

The data collected in the field was analyzed using SurfSeis 6.5.4.30 developed at the Kansas Geological Survey. The records collected in the field were used to develop one-dimension (1D) shear wave profiles. Sequential arrays were evaluated for each change in station with 1D profiles

- 5 -combined to develop a two-dimensional (2D) shear wave profile for the entire survey length. The 2D profile was reviewed for each survey to evaluate and isolate any anomalous changes in shear wave velocities.

Rapid changes in soil shear wave velocities such as a decrease in velocity, a decrease in velocity with an increased velocity in an overlying soil “arch”, or velocities below those anticipated for soils known to the survey location, could indicate the loss or displacement of material.

As previously indicated, surveys were performed along the northern and southern shorelines of the main harbor peninsula. Each shoreline was split into two surveys due to obstructions hindering continues towing of the landstreamer. The two surveys conducted along the northern shoreline (Surveys 1 and 2) and southern shoreline (Surveys 3 and 4) were conducted on the respective sidewalks adjacent to the shorelines. Locations of the MASW surveys are shown on the MASW Survey Location Plan, Figure No. 1, and on individual MASW Surveys, Figure Nos. 2 through 5. A summary of the MASW survey results and noted anomalies are presented in the Shear Wave Velocity Evaluation section of this report. It should be noted that the MASW survey results should not be the lone consideration for remediation design and should be reviewed with and compared to site specific geotechnical borings. Information from soil borings will better contextualize the MASW survey results, significantly improving the resolution and reliability of the interpretations.

4.0 EVALUATIONS

4.1 SHORELINE CONDITION ASSESSMENT

4.1.1 Docking Pier / Triangle

Structure Description

Timber Crib Structure The original State Ferry Pier was constructed circa 1924 and consisted of an approximately 1,400-foot-long drive leading from the shoreline eastward to the 220-foot-long State Ferry Pier. Based on the available plans for the pier extension, the original pier appears to have been constructed of an earth filled timber crib; however, specific details regarding the structure of the access drive and pier are not available.

A triangular-shaped extension was constructed at the eastern end of the original pier structure circa 1931. The existing Docking Pier / Triangle structure measured approximately 300-feet by 350 feet by 400 feet and was constructed of a series of thirteen (13) timber crib structures located around the perimeter of the extension, the interior of which was filled with a well-drained sand/sandy loam material (Filling Material No. 3). Historical plans indicate the cribs are labeled numerically, with numbers increasing counterclockwise around the structure perimeter from southwest to northwest, beginning with crib 1 at the southwest pier extent and ending with crib 13 at the northwest pier extent. Cribs 1 through 4 comprise the southern boundary of the pier, cribs 5 through 8 comprise the eastern boundary, and cribs 9 through 13 originally comprised the northern boundary of the pier, until an addition was constructed in 1951.

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The crib structures measure 24 feet wide by approximately 17 feet tall by lengths that range from

56.5 feet to 100 feet. The cribs are constructed from a series of vertically stacked, 12-inch by 12-inch, flat faced timbers, oriented parallel to the lakeside face (longitudinals, stringers, stretchers) and perpendicular to the lakeside face (cross wall, ties, headers). The longitudinals are closely stacked and connected by 1-inch diameter drift bolts, resulting in minimal spacing between layers vertically and at the butt joints in longitudinal timbers. The cross wall headers are dovetailed into the stringers at the lake and landside faces, and consecutive crib structures are connected by tongue and groove at the landside of each joint. In general, the lakeside and landside face of the crib structures are tied together with two rows of 1-1/2-inch diameter tie rods, located at the longitudinal extents of each crib structure and at an approximate spacing of 25 feet between, approximately 4-feet from the top and bottom of the structure. 3-inch by 12-inch timbers comprise the floor atop the bottom layer of timbers.

The cribs are filled with a well-graded mixture of rock not exceeding 18-inches in diameter and finer materials to fill voids (Filling Material No. 2) and capped with a layer of longitudinal timbers. The base of the timber cribs is founded atop a 1-foot-thick mattress, consisting of clean crushed rock (Filling Material No. 1), on the order of 2 feet to 4.5 feet below the original lake bottom, the base of which bears at or slightly above top of rock. An approximately 3-foot-tall, sloped rock buttress, consisting of Filling Material No. 2, is constructed at the lakeside toe of the structures, presumably for additional sliding resistance.

Several ramps for ferry access are located around the Triangle perimeter within cribs 3, 4, 6, 7, 9, and 10; however, the ramps within cribs 9 and 10 have been removed. The ramps are comprised of a steel ramp platform, the slope and height of which are controlled by telescoping steel lift cylinders that appear to sit atop the uppermost row of longitudinals (crib cap). An approximately 4-foot-wide by 7.5-ft tall concrete wall is present at the lakeside edge of the cribs and bears atop a 1-foot-wide by 3.5-foot-thick concrete footing. The area behind the wall is backfilled, presumably with Filling Material No. 3, capped with topsoil, and vegetated. The concrete cap contains insets for removable timber wales and fenders, neither of which were present during the investigation; however, the steel bolts used to fasten the wales and fenders to the face of the cap remain.

Rip rap with large armor stone is present beginning from approximately Station 0+60 and extending west to approximately Station 0-60 (60 feet west of Station 0+00). Rip rap is present at the surface from approximately Station 0-60 to 0+07, at which point armor stone is present sloping down to the lake bottom to Station 0+60.

Cellular Cofferdam Structure An addition was constructed on the north side of the Triangle in 1951, consisting of a series of cellular cofferdams, constructed lakeward of cribs 9 through 13. The addition ranged in width from approximately 50 feet at the eastern extent to 25 feet at the western extent. The expansion was constructed from fourteen (14) steel sheet pile cofferdam cells (cells 1 through 14), filled with aggregate, and capped with a concrete deck. The cells are constructed from 30-foot-long Carnegie MP101 steel sheet piles and adjacent cells are typically interlocked with riveted X or Y pile connectors. The steel sheets are embedded 6 inches into a 10’-1” wide by 3’-6” thick

- 7 -concrete cap/footing supporting a 6’-9” tall by 4’ wide concrete wall. The concrete cap/wall structure extends outward approximately 1 foot to 4 feet from the outside face of the steel sheet piles and reaches to approximately 1 foot above the water line. The overall northern addition is covered by 1-foot of concrete pavement, which slopes upward on the order of 2 feet to 2.5 feet from the ground surface of the original triangle structure. The annulus between the concrete pavement and the top of cofferdam structures is sealed at the top and bottom with concrete diaphragms and filled with sand and gravel fill. The entire northern face of the concrete appears to have been covered with an HP 12x53 pile-supported spring fender system at the western end and timber lagging over the remaining length of the structure; however, the fenders and the lagging are no longer extant.

Condition Assessment / Observations

Timber Crib Structure In general, the lakeside faces of the crib structures appear to be in good condition, with no significant signs of structural instability. Minor to moderate gapping was observed at the joints between the timber members (on the order of 2 inches to 3 inches in width), with isolated locations of larger gaps. The timber members appear to be fully intact and in good structural condition, with the exception of the upper two rows (2 feet) of timbers, particularly along the eastern crib structures. In general, splitting, deterioration, and occasional absence of the outermost upper 1 to 2 longitudinals were observed along the eastern crib structures (cribs 5 through 8); however, an adjacent interior longitudinal appeared to be intact. Damage to the longitudinals was noted at Stations 0+80, 1+80, 2+10, 3+36, 3+50, 4+00, 4+35, 5+00, and 6+20, some of which also occur at joint locations. The concrete cap appears to be in good condition, with minor to moderate spalling occurring at the joints and the lakeside face; however, no significant structural cracking was observed.

Based on observations with the ROV during the inspection, it appears previous repairs have been made to the crib structures, the specific details of which are unavailable. Steel plates appear to have been attached to the lakeside face of the crib joints, with the exception of the joint between cribs 1 and 2, using possible drift pins or bolts through slotted holes on the plates. In general, the top portion (approximately 6 feet to 9 feet in height) of the steel plates is damaged or sheared off, resulting in some plates measuring as little as 4 feet tall at the base of the joint. Material can be seen escaping the sides of the plates, where present, and on the order of 1 foot to 2 feet of material loss is observed at the top of the joints. In general, the material appears to slope downwards from the central portion of the cribs to its lowest point at the lakeside face. Additionally, small mounds of material (on the order of 1 foot in height) are generally present at the lake bottom at each joint.

The mounds appear to consist primarily of finer materials; however, the materials may be obscured by silt accumulation.

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Timber crib structure with longitudinal and cross wall configuration (typical).

Exposed joint between Crib #4 and Crib #5, approximately Sta. 3+36. Remnant of steel plate joint repair visible near base of crib.

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It also appears the rock buttress at the toe of the crib structures was replaced with a concrete-filled line of sheet piling, measuring approximately 4 feet to 6 feet in height by 1 foot to 3 feet in width.

The sheet piling was assumed to be installed as formwork for the concrete buttress and is not assumed to provide structural resistance. The concrete buttress begins at approximately Station 2+44 along the south side of the structure and continues around the eastern structure extent to approximately Station 6+30, at the approximate interface with the cellular cofferdam addition.

The material loss observed within the crib structures agrees with observations made at the ground surface of the triangle structures. Within the vegetated green space behind the concrete cap, sinkholes were typically observed approximately 9 feet from the back of the concrete cap, 13 feet behind the lakeside face of the structures, and approximately 2 feet behind the concrete cap footing. The sinkholes are visible along the perimeter of the structure, and additional sinkholes tend to be present adjacent to the lateral extents of the ramp structures; however, the sinkholes adjacent to the ramp structures presumably result from wave action beneath the concrete cap at the ramp sides and/or at the ramp lift control vaults. The sinkholes are generally linear in configuration and parallel with the lakeside face of the structures, several of which are on the order of 1.5 feet to 2 feet deep; however, exact measurements and/or photo documentation were obscured with overgrown vegetation. Additional material settlement was observed near the elevator structure on the eastern side of the Triangle, particularly at the northwestern structure corner and beneath the pavement at the ground surface of the southeast corner. A void on the order of 6 to 12 inches deep was observed below the pavement apron surrounding the northwestern elevator building corner. The pavement at the surface of the southeast corner, approximately 9 feet behind the concrete cap, was in poor condition, with large cracks and a void on the order of 6 inches to 12 inches deep was also observed in this location.

Material pile at base of joint between Crib #1 and Crib #2, approximately Sta. 0+80.

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Water measurements obtained during the investigation indicated top of water surface was at 9.5 feet below top of concrete cap, approximately 1.5 feet above the top row of longitudinal timbers.

Water surface elevations obtained from the National Oceanic and Atmospheric Administration (NOAA) monitoring station at the Straits State Harbor (Station 9075080) during the time of the investigation indicate the average lake elevation was 579.7 feet (IGLD 85) over the 5 day investigation. Based on these measurements, top of concrete cap is at approximately EL 589.2 feet (IGLD 85), compared to the top of cap elevation of 590.5 feet indicated on the plans (datum unknown). Current low water datum (LWD) of Lake Huron obtained from the U.S. Army Corps of Engineers (USACE) is EL 577.5 feet (IGLD 85). These measurements suggest the top of timber cribs (approximately EL 578.2 feet; IGLD 85) are present between the ordinary high water mark (OHWM; EL 581.5 feet IGLD 85) and LWD, and as such, are subject to cyclical wetting and drying with fluctuating water levels. Based on the current water elevations, the uppermost timber is not permanently submerged, and based on the design drawings and past lake datums, the uppermost 2.5 timbers are not permanently submerged. This corresponds to the observations of deterioration and damage of the top one to two rows of timbers, particularly along the eastern crib structures. Additionally, ice forces acting along the face of the crib structures may also contribute to the observed damage and deterioration of the upper timbers, as well as the damage to the steel plates at the crib joints.

The telescoping steel lift cylinders to control the ramps appear to be in poor condition. In general, many of the lifts are damaged, unstable, or have collapsed. The operational status of the lifts is unknown at this time; however, we recommend further investigation and evaluation, if the ramps are planned to be used in the future.

Cellular Cofferdam Structure

In general, the structure of the cellular cofferdam addition to the Triangle appears to be in good condition, with sheets that appear to be plumb and interlocks that appear tight. The sheets generally appear to be embedded well into the lake bottom, with the exception of a gap between the bottom of a connector sheet at the interlock between two consecutive cells near Station 11+00 and the lake bottom. The connector sheet appears to have been driven short of the lake bottom or it is possible the sheet once reached the lake bottom and materials have since been removed.

Aggregate fill is visible through and coming out of the gap between bottom of sheet and lake bottom. In general, the riveted and non-riveted interlocks between consecutive cells were intact, with no observed missing rivets or gaps in the connections. Additionally, the top of the concrete cap at the water’s edge appears to be in good condition, with minor spalling on the outside face.

Moderate spalling is present near the bottom surface of the concrete cap. As the base of the cap is on the order of 1 foot above the water surface, wave action due to high winds causes the water to crash into the bottom of the cap and likely has caused additional damage along this surface.

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Typical sheeting for cellular cofferdam structure, approximately Sta. 6+30.

Structural hardware is generally absent from the face of the sheets; however, steel brackets are welded to the face of the sheets on either side of cofferdam cell interfaces on the order of 2 feet below the water surface. Details regarding the design and purpose of the brackets are not available. Additionally, steel bolts are visible approximately 6 inches to 1 foot above the water surface, presumably extending from the inside face of the cofferdam sheets to the outside face of the sheets. No nuts, washers, nor bolt heads are visible; however, the bolts occasionally extend through steel plates possibly welded to the face of the sheets. The bolts are generally present through every second sheet; however, bolts are occasionally missing, which may facilitate loss of fine fill materials within the cofferdam system. Details regarding the design and purpose of the bolts are not available. Occasionally, small windows are cut into the sheets near or slightly below the water line. Apparent concrete is visible within the bottom half of the window, possibly the concrete diaphragm at EL 577.5 feet (datum unknown). If so, the sand and gravel fill placed above the concrete diaphragm and below the concrete pavement may be lost through the window.

Additional rectangular holes are present at the top of the cofferdam sheets near Station 9+75, through which the top of the concrete diaphragm is visible. The space above the diaphragm appears to be empty, which may indicate loss of fill material between the diaphragm and the concrete pavement.

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Closeup view of cutout square within steel sheet pile, approximately Sta. 7+00. Note possible concrete diaphragm or cofferdam fill material visible through hole.

In general, the concrete pavement at the ground surface atop the cellular structures is in poor condition, with significant cracking, subsidence, and uneven pavement surfaces observed. In general, a longitudinal crack parallel with the northern face of the Triangle extends through the approximate centerline of the cofferdam extension. Gaps measuring up to 1 to 2 inches are present between the joints in the pavement oriented perpendicular to the northern face of the structure. Voids ranging from 12 inches to 4 feet deep were measured beneath the concrete pavement at the joints and longitudinal cracks, indicating significant loss or settlement of fill materials (likely sand and gravel fill) atop the concrete diaphragms. In general, we expect the mechanism of fill material loss is consistent with that observed on the north pier structure, as described in the subsequent section.

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Surface of concrete cap/pavement atop cellular cofferdam structure, approximately Sta. 7+15, looking west-southwest. Note significant subsidence of pavement surface near mid-line, longitudinal cracking, and widened construction/expansion joints

4.1.2 North Pier

Structure Description

The North Pier structure is located on the order of 40 feet to 86 feet northwest of the Triangle and 22 feet east of the main harbor peninsula. The North Pier was constructed in 1951 and is composed of 5 steel sheet pile cellular cofferdams (cells 15 through 19) and capped with concrete pavement. The design and structure of the North Pier is similar to that of the Triangle addition, as both structures were constructed as part of the same project. The majority of the structure was able to be observed with the ROV; however, isolated locations along the northern side of the structure were unable to be observed due to the lateral extents of the large stone breakwall located adjacent to the structure.

The cells consist of 30-foot-long Carnegie MP101 sheet piles filled with aggregate. Bolts were observed in a similar pattern to those on the Triangle cofferdams, and small square windows were also observed to be cut into the sheets between the bolted sheets. Consecutive cells were typically connected with riveted Y connector sheets, with the exception of the connection between cells 18 and 19. The connectors appeared to be intact, with no missing rivets; however, mounds of fill and/or lakebed materials were typically encountered at the joint locations. Additionally, a singular H-pile strut was present between cells 16 and 17 at the western structure face, approximately 1 to 2 feet below the water surface. This type of strut was not observed elsewhere on either of the cellular cofferdam structures. The southern extent of the pier formerly contained

- 14 -an HP 12x53 pile-supported spring fender system, similar to that of the Triangle, which has since been removed.

Steel sheet pile cellular cofferdam. Note set of two bolts every other pan (typical).

Condition Assessment / Observations

The cellular cofferdam structures appear to be in good condition, with no observed significant structural deficiencies. Occasional bolts are missing from a sheet pile, which may facilitate loss of fine fill materials within the cofferdam system. The concrete cap appears to generally be in good condition around the majority of the northern, southern, and western faces; however, increased spalling is noted on the bottom of the cap near the water surface, presumably due to wave action. The eastern face exhibits moderate spalling and appears to have been repaired at some point. Additionally, the southern edge of cell 18 (along Arc #3) extends outward approximately 1 foot from the concrete cap surface. This is not a typical configuration. The concrete diaphragm is visible at the top of the cofferdam cell, which suggests the fill material is still sealed within the structure; however, wave action may degrade the diaphragm faster than the cap, and as such, the condition should be monitored.

The concrete pavement at the ground surface atop the cellular structures is in poor condition, with significant cracking, subsidence, and uneven pavement surfaces observed. A longitudinal crack extends through the approximate centerline of the structure and cells in the east to west direction.

In general, the lowest point of the concrete pavement appears to be along the centerline crack, as the pavement appears to slope downwards from the northern and southern structure extents towards the centerline. 1 inch to 3 inch gaps are present at the expansion and construction joints within the pavement. During the investigation, one of the gaps was large enough to obtain video

- 15 -footage of the area. A large void was found between the concrete superstructure support walls that sit atop the east-west lateral extents of each cell structure. The void appeared to have once been filled with sand and gravel fill; however, the majority of the fill was absent. Additionally, the construction joint at the southern face of the concrete cap structure was visible through the void and appeared to be 2 inches to 3 inches wide. These findings suggest that wave action may be able to reach through the joints in the concrete cap and pavement and wash the fill material out through the unsealed joints. The top surface of the support wall appeared to be wet and a flow path for water appeared to be cut into the remaining fill near the interior of the void. A heavy rain occurred prior to the investigation. The wet concrete and flow path within the fill suggest water on the surface of the structure is infiltrating into the pavement cracks and joints and washing out through the construction joints within the concrete cap. Fill material smaller than the width of the joint are able to be carried out with the water. This may also account for the piles of materials observed at the cell joint locations. The void also suggests the subsidence and cracking in the concrete pavement is due to the loss of support from the fill beneath the pavement. These findings are likely present throughout the entire structure.

Top of North Pier pavement/concrete cap, looking east. Note longitudinal (east-west) crack in pavement surface, large cracks at joints, and subsidence of pavement.

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4.1.3 Transfer Bridge Abutment

Structure Description

The abutment for an approximately 50-foot-wide transfer bridge is located at the southwestern extent of the north pier, between the Triangle and the eastern extent of the north riprap shoreline.

When operational, the transfer bridge was a large steel ramp that was seated atop the abutment at the west and was supported by a large overhead steel frame and crane that met the ships to the east for vehicle loading/unloading; however, the transfer bridge has since been removed/demolished. The large abutment remains and consists of an approximately 25-foot-tall by approximately 32-foot-wide by approximately 50-foot-long concrete crib-like structure. The concrete face wall and side walls are 3 feet-thick and the structure also contains two 3-foot-thick interior walls. The interior chambers are filled with “borrow excavation” materials; however, we assume the fill materials may be dredged material from within the lake. The structure bears atop a 4-foot-thick concrete footing, with approximately 3 feet of embedment into the lake bottom. The entire structure appears to operate as a large gravity retaining wall at the bridge abutment.

Condition Assessment / Observations

The condition of the concrete was observed to be in good condition, with minor to moderate spalling on the concrete face, particularly near the water surface, with the exception of the northeastern corner of the structure. The northeastern corner of the structure exhibited moderate spalling at the corner; however, no exposed reinforcing steel was observed. Based on depths measured with the ROV, it appears the entirety or almost the entirety of the abutment footing may be exposed and sitting atop the lake bottom, suggesting the lake bottom materials have been removed or have eroded away from the face of the footing. While the loss of these materials likely results in reduced lateral and overall bearing capacity of the structure, no signs of instability were observed. However, we recommend replacement of the toe materials if the ramp is planned to be used in the future.

4.1.4 Fishing Pier

Structure Description

The Fishing Pier structure is located approximately 205 feet southwest of the Triangle and 41 feet east of the main harbor peninsula. The approximately 515-foot-long pier is composed of steel sheet pile structure capped with an approximately 12-inch-thick concrete deck. A steel-framed bridge with a timber deck provides access from the east extent of the main harbor peninsula to the western extent of the pier. Details regarding the design of the structure were unavailable;

however, the pier may have been constructed circa 1937, with the dredging of the area near the Triangle, and the filling what is now the main harbor peninsula. The dredging plans from 1937 indicate the proposed pier location; however, details regarding the design of the pier do not appear to be included, as the pier construction is assumed to be a separate project. Based on review of the plans and information gathered during the investigation, the sheet piles appear to be similar in design to those of the east face wall of the main harbor peninsula. Measurements and observations obtained during the investigation suggest the structure is constructed from

- 17 -

Bethlehem Z32 (ZP32) sheets (pair of sheets is 42 inches in width), which corresponds to the sheeting size on the east face wall. The sheets appear to be installed in a manner in which the structure is slightly wider at the base than it is at the top, as the sheets are angled slightly inward toward the interior of the structure from the base at the lake bottom.

Each inside pair of sheets generally contains two bolts with plate washers (1 per sheet); however, one bolt, three bolt, and four bolt arrangements are also present. The bolt arrangement suggests the walls of the sheeting may be tied together or an internal support structure (wale, ties, etc.)

exists. Each corner within the structure is constructed from riveted connector sheets. Bolts were also present within the riveted connector sheets at elevations consistent with the typical bolt configurations. At the north and south extents of the eastern end of the pier, flat steel plates riveted to the north and south corners extend approximately 1 foot eastward from the east face.

These plates may deflect ice from hitting directly at the face of the pier; however, the northern plate is bent at or slightly above the water level, and the corner of the pier is dented approximately 2 feet below the concrete cap. This may be from a collision or due to ice forces.

A possible concrete buttress is intermittently present along the northern side of the structure at the lake bottom between approximately Station 3+00 to 4+00 and near Station 1+50. Additionally, remains of timber crib fish habitats constructed circa 2006 are visible adjacent to the southern side of the pier. Debris, consisting of apparent pipe sections, steel bars, steel grates, timber piles, etc., is also present in numerous locations along the lake bottom on the southern side of the pier.

Remnants of a former fender system (broken welded clips) are visible along the northern face of the pier.

Condition Assessment / Observations

The steel sheeted structure appears to be in good condition with no obvious signs of structural distress. The sheeting appears to be relatively vertical and plumb, with good contact at the interlocks, with the exception of two outside pairs of sheets near North Station 1+50. At this location, the pans bow slightly lakeward, resulting in a slight gap at the interlock. No material appears to be escaping through the interlocks, and as such, no structural issues are anticipated. In general, the riveted corner sheets are intact with no missing rivets, and the bolts appear to be intact and in good condition, with the exception of two isolated locations. One bolt appears to be missing from the inside pan near South Station 0+85 and one bolt appears to be missing from the riveted corner sheet on the west face of the corner at North Station 0+85. Water was observed to be flowing into and out of the resulting hole in the sheets at North Station 0+85 in conjunction with the rising and lowering water surface of the waves. These holes may facilitate loss of fine materials if used to fill the structure; however, the structure fill is expected to be coarser rock material and as such, is not expected to significantly affect the stability. The side faces of the concrete cap exhibit mild to moderate spalling, particularly at the construction joints. The top surface of the concrete cap appears to be in good condition, with only minor surficial scaling, most of which appears to have been patched, and minor thermal cracking.

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- 18 -

4.1.5 East Face Steel Sheet Pile Seawall

Structure Description

The East Face seawall is located along the eastern extent of the main harbor peninsula. The seawall begins approximately 30 feet south of the Triangle, measuring approximately 247 lineal feet to the south, and extending approximately 66 lineal feet west along the southern extent of the main harbor peninsula. The seawall is an anchored steel sheet pile wall, consisting of 35-foot-long MZ-32 sheet piles tied back to a pile-supported timber dead man by 2-1/4-inch diameter smooth steel tie rods spaced at 7 feet on-center. A wale beam consisting of two back-to-back C12x25 channels is connected to the land side of the face sheets by 1-1/2-inch diameter fixing bolts at each inside pan (1 per sheet). The face sheeting is capped with an I 14x16 beam, which is bolted to the face sheets with 3/4-inch diameter bolts on the lakeside and landside faces of the sheets. Approximately 6 inches to 12 inches of concrete was added to the top of the steel I-beam cap and supports an approximately 4-foot-tall chain-link fence.

An approximately 30-foot-wide steel ramp, presumably for ship loading between the Fishing Pier and Dolphin, was once present approximately 20 feet north of the Fishing Pier access bridge north abutment and has since been demolished. The top portion of the steel sheet piling within this 30-foot-long section appears to lack the paint covering the adjacent face wall sheeting and the paint on the Fishing Pier sheeting, suggesting it was added later. It appears sheets were welded to the top of the original sheets in this location, assumedly following removal of the steel ramp.

Additionally, two small steel sheet pile cellular cofferdams, assumed to be filled with concrete, have collapsed within the lake approximately 20 feet to 25 feet lakeward of the east face seawall.

The cells appear to be connected with a steel H-pile (I-beam) below the water surface. Specific details regarding the structure are unavailable; however, the structure is assumed to be the lakeward support and extent of the steel ramp. Mooring bollards are present at the top of the cell concrete, suggesting ships once moored against the structure for loading.