B08_Attachment_20_Geotechnical_Report-2022.pdf

Report of Geotechnical Evaluation Perry’s Victory and International Peace Memorial

Put-in-Bay, Ohio

Registered in North Carolina Engineering and Land Surveying License No. F-1253 Geology License No. C-247

Wood’ is a trading name for John Wood Group PLC and its subsidiaries

January 26, 2022

National Park Service Denver Service Center 12795 W Alameda Pkwy Denver, CO 80228

Subject: Report of Geotechnical Evaluation

Perry’s Victory and international Peace Memorial Put-in-Bay, OH 43456 Wood Project No. 6227-21-0305

Wood Environment & Infrastructure Solutions, Inc. (Wood) is pleased to provide this Report of Geotechnical Evaluation for the proposed renovations at the existing memorial located in Put-in-Bay, Ohio. Our services were provided in accordance with our revised proposal dated November 1, 2021 and authorized by you.

The purpose of our evaluation was to assess the subsurface conditions at the site in order to provide geotechnical recommendations for the design and construction of the project. This report presents the results of our evaluation, seismic site classification, site preparation guidelines, and geotechnical design parameters for the planned improvements.

Thank you for the opportunity to provide our professional geotechnical services during the planning phase of your project. We would be pleased to discuss our recommendations with you and welcome the opportunity to continue to provide geotechnical consulting services as this project progresses.

Sincerely, Wood Environment & Infrastructure Solutions, Inc.

James P. Racine, PE (VA, MD, NC, SC, DC) Don Dotson, PE, PEng, DGE Associate Geotechnical Engineer Principal Engineer - GeoStructural Registered, Ohio 72544

Wood Environment & Infrastructure Solutions, Inc.

2801 Yorkmont Road, Suite 100 Charlotte, North Carolina 28208

United States T: +704 357 8600 www.woodplc.com don.dotson Image

Table of Contents

1. Project and Site Information

Introduction Site and Existing Structure Description Proposed Construction

2. Field Evaluation General Drilling Methods Boring Logs Test Pitting Infiltration Testing Results Concrete Cores and Break Results

3. Area Geology and Subsurface Conditions Geologic Setting Generalized Subsurface Stratigraphy Topsoil Existing Fill Soils Lacustrine Soils (Lake Deposits) Glacial Till Partially Weathered Rock/Rock Groundwater Observations Laboratory Testing Existing Geotechnical Information

4. Geotechnical Considerations

5. Recommendations

Foundations Option 1 – Ground Improvement Option 2 –Micropiles

Basement Slabs Below-grade Walls Underslab Drainage Kart Considerations/Sinkhole Development Potential Pavement Subgrade Recommendations Seismic Site Class Temporary and Permanent Slopes Stormwater Management Facilities

Temporary Construction Dewatering Earthwork

Site Preparation Re-use of Excavated Materials Fill Materials Fill Placement and Compaction Site Drainage

Pre-Construction Conference Construction Observation and Testing Construction Monitoring Final Report Preparation

6. Qualifications

Tables Table 1 – Boring Summary

Figures Figure 1 – Boring Location Plan Figure 2 – Subsurface Profile Figure 3 – Coring and Test Pit Location Diagram

Attachments Key to Symbols and Descriptions Soil Boring Logs Laboratory Testing Results Test Pit Photographs Concrete Break Results Infiltration Test Results

1. Project and Site Information Introduction In accordance with our revised proposal dated November 1, 2021 and authorized by you, we have performed a geotechnical evaluation for the proposed renovations at the existing memorial located in Put-in-Bay, Ohio. The purpose of our evaluation was to assess the subsurface conditions at the site in order to provide geotechnical recommendations for the design and construction of the project.

This report presents the results of our evaluation, seismic site classification, site preparation guidelines, and geotechnical design parameters for the proposed development.

Site and Existing Structure Description The existing memorial, constructed around 1915, is located at 93 Delaware Ave, Put-In-Bay, Ohio and consists of a 352 foot tall columnal-type monument surrounded by a one-story plaza structure. The plaza structure is surrounded (almost entirely) by a soil berm that extends from existing grades up to the first and only elevated floor level, which functions as both the upper plaza and roof of the plaza structure. The on-grade, ground floor portion of the structure functions as a walk-out basement and access to the below-grade area is made on the northeastern side of the structure. An on-grade lower plaza area is located on the northwestern side of the memorial with access between the upper and lower plazas accommodated by granite stairs. Detail 1 (after detail G3.1 on the Emergency Preservation of Monument Plan Set, dated June 11, 2009), which can be seen below details a generalized cross section of the memorial.

Detail 1: Showing a generalized cross section of the memorial

The site is located on a narrow (approximately 450 feet wide), but central portion of South Bass Island and is surrounded by Lake Erie.

The Lake has a reference water surface elevation of EL. +569 feet above mean sea level. Based on our review of the provided Survey Plan (dated June 22, 2020), the existing site is relatively flat with existing grades around the memorial ranging from EL. +575 to +576 feet. The overall site grades gradually rise towards the northeast up to EL. +580 feet. The finished floor slab elevation of the on-grade portion of the memorial is EL. +575 feet. The upper and lower plaza elevations are EL. +585 and +579 feet, respectively.

Based on our understanding of the project, the plaza structure is constructed of consists of concrete columns and beams with a concrete roof. The below-grade basement walls that retain the soil berm are constructed of concrete. The finished basement floor area is partially a concrete slab on grade with the remainder of the floor area consisting of a gravel floor. The basement area is primarily used for storage and mechanical equipment space, but is also used as office space. Neither foundation nor structural drawings were available during our exploration. It was assumed prior to our exploration that the plaza structure and monument were supported on shallow foundations bearing directly on rock. Further discussion regarding our on-site observations and exploration can be found in subsequent report sections.

Proposed Construction We understand that the current plaza structure has deteriorated significantly due to failed waterproofing and significant water intrusion. Despite previous repair efforts, the plaza will require extensive rehabilitation and replacement. The portions of the structure that will require full replacement are unknown at this time. However, from our discussions with the project structural engineer, we understand that most of the structural elements including columns, slabs, walls, and beams will be replaced or reinforced in-place with new structural elements supported on new foundations. It is not anticipated at this time that existing foundation elements will be re-utilized for support. We understand that there are no structural modifications planned for the tower structure, which is understood to be structurally independent from the plaza.

From the project structural engineer, we understand that typical column loads will be on the order of 50 kips per column. Wall loading has not been provided; however, we assume they will be relatively lightly loaded and on the order of 2 kips per linear foot or less. We understand that the proposed finished ground floor elevation will be lowered approximate 2 feet (to achieve more below-grade headroom) to EL. +573 feet; therefore, the bottom of foundation elevations are anticipated to be at approximate EL. +570 feet. Slab loads, while also not available, are anticipated to be relatively light and on the order of 150 psf or less (dead and live load).

It is important to note that the overall site area is below the 100 year flood plain, which is mapped by FEMA at EL. +577 feet. However, we understand that the flooding issue will be resolved by the construction of a proposed sea wall. The recommendations contained herein therefore assume that flooding will not occur on-site. We also assume that interior drainage issues caused by the construction of a seawall will also be accounted for by the seawall designer and will not impact the existing or proposed plaza structure.

Outside of the rehabilitation of the plaza structure, the remainder of the renovations include new asphalt parking areas along Bayview Avenue, site utilities, and a new underground stormwater management facility. Proposed details for the stormwater facility (including type, invert, and dimensions) were unknown at the time of our exploration. While a proposed grading plan was not provided, we anticipate very minor grading on the order of +/- 1 feet of cut and fill will be required to establish the final grades. Additional site improvements beyond those noted above are not anticipated at this time.

The description of this project is based on the information provided to us. If any of this information is inaccurate, we recommend that we be contacted in order to provided additional and/or alternate recommendations that may be warranted.

2. Field Evaluation General On December 6, 2021, Wood’s drilling subcontractor, TTL Associates, Inc., mobilized to the site to conduct a limited subsurface evaluation at the project site in order to assess the existing subsurface conditions and to collect soil samples for classification and testing. While on-site, the subcontractor also conducted a limited exploration of the existing plaza structure, which is described in more detail below. The overall exploration consisted of drilling, logging, and sampling 11 exploratory soil borings, conducting three interior test pits, and one exterior test pit, conducting two infiltration tests, and conducting 6 concrete cores.

Soil borings were conducted in general accordance with ASTM D1586 using a Geoprobe 7822DT track-mounted drill rig and standard auger drilling equipment (with the exception on TP-11 (HA) which was conducted with standard hand auger and dynamic cone penetrometer methods). Borings were drilled to depths of 10 to 25 feet unless they terminated shallow of the planned depth due to auger refusal. Table 1 below presents the depth of each boring and associated feature.

Table 1 – Boring Summary

Boring # Planned Depth (feet)

Approximate Termination Depth (feet)

Location/ Structure

B-1 10.0 10.0 Roadway Parking/Expansion B-2 10.0 10.0 Roadway Parking/Expansion B-3 10.0 7.7 Roadway Parking/Expansion B-4 10.0 9.3 Roadway Parking/Expansion B-5 25.0 10.8 Plaza Structure B-6 25.0 17.4 Plaza Structure B-7 25.0 14.2 Plaza Structure B-8 25.0 8.1 Plaza Structure IT-9 10.0 6.5 Potential SWM Structure IT-10 10.0 10.0 Potential SWM Structure

TP-11 (HA) 10.0 10.0 Berm

Prior to drilling, the boring locations were staked by pacing from known features. The locations shown on the attached Boring Location Plan (Figure 1) should therefore be considered approximate. Prior to excavation work, a subcontracted Surface Utility Engineering (SUE) crew employed electro-magnetic (EM) and ground penetrating radar (GPR) techniques to attempt to locate existing underground utilities in conflict with each staked boring location.

Drilling Methods Soil test borings were drilled by mechanically twisting 3¼-inch diameter hollow-stem augers into the soil. Soil sampling and penetration testing were performed in general accordance with ASTM D1586 using an automatic hammer system. At assigned intervals, soil samples were obtained with a standard 1.4-inch I.D., 2-inch O.D. split-spoon sampler. The sampler was first seated 6 inches to penetrate any loose cuttings, and then driven an additional 12 inches with blows from a 140-pound hammer falling 30 inches.

The number of hammer blows required to drive the sampler the 2nd and 3rd 6-inch increments were recorded and summed and is designated the "N-Value" or "penetration resistance". The N-Value is used as an index to soil strength and foundation support capability.

Selected portions of split spoon samples were sealed in glass jars and returned to our laboratory in Charlotte, North Carolina for further visual/manual classification as determined by a geotechnical engineer. Bulk samples from the auger cuttings were also obtained. The depth to water was measured in the boreholes at the time of drilling and upon completion, where practical. The boreholes were then backfilled with soil cuttings mixed with bentonite chips.

Boring Logs The attached Soil Boring Logs represent our interpretation of the field drilling logs based on engineering examination of the field samples. Each sample was visually classified on the basis of texture and plasticity in accordance with the Unified Soil Classifications System (UCSC) and ASTM D-2488 (Description and Identification of Soils Visual/Manual Procedures). After classification, the various soil types were grouped into the major zones noted on the logs. Therefore, these boring logs contain both factual and interpretive information. Lines delineating subsurface strata on the boring logs are intended to group soils having similar engineering properties and characteristics. They should be considered approximate as the actual transition between soil types (strata) may be gradual. A Key to the Soil Symbols and Descriptions used on the boring logs is also included.

Test Pitting As part of the geotechnical scope of work, test pits were planned at several wall and column locations to measure the geometry (width, depth from existing grades, and thickness) of the assumed spread footings supporting the plaza structure. Four test pits (three interior and one exterior) were excavated at locations established by the project team; hand tools (shovels and picks) were used to explore to a maximum depth of approximately 2 to 3 feet below existing grades. After exposing a portion of the edge and tops of the foundation elements, it was observed that the walls and columns were supported on pile caps and grade beams and not on spread footings as assumed; and he project team decided to terminate test pitting operations. Please see the attached test pit photos and report attached to this report.

At the exterior test pit location, TP-11 , a hand auger boring was conducted to explore the relative density of the berm materials to a depth of 10 feet below existing grades along with dynamic cone penetrometer testing conducted at regular intervals. In addition to the hand auger, the exterior basement wall was examined to see if drain board or water proofing was present. After extending the test pit about 14 inches below the bottom of the wall coping, it was observed that no water proofing or drain board was present at these depths; the test pit was then terminated. While on-site, Electro-magnetic (EM) testing indicated that a linear metal feature may be present about 3 to 5 feet off of the exterior southwestern building wall and it was surmised that an historic sheet pile may be present. The TP-11 test pit was extended above this scanned location to a depth of 21 inches, but no sheet pile was found. Please see the attached test pit photos and report attached to this report.

The test pits were backfilled with the test pit spoils and tamped into place with hand tools. Please note that depending on the final foundation type, the soil within the test pit backfill areas may not be suitable for foundation support and will need to be remediated by the contractor during the construction phase operations. For this reason, test pit locations should be shown on the foundation and sitework drawings.

Infiltration Testing Results Two infiltration tests were performed at Borings IT-9 and IT-10, which were located in potential underground stormwater management facility locations selected by the project team. Boring IT-9 encountered refusal on at 6.5 feet below existing grades while Boring IT-10 extended to the planned end of boring depth of 10 feet below existing grades. Groundwater was not observed at IT-9, but was observed at IT-10 at 4.5 feet during drilling and 5.5 feet below existing grade upon completion of drilling. Test depths were selected to be approximately 2 feet above bedrock or groundwater. Therefore, the test depths were set at 4.5 and 3.5 feet below existing grades for IT-9 and IT-10, respectively.

Offset infiltration test holes were drilled down to the design depths noted above using the rig augers. The bottom 12 inches was filled with pea gravel and the hole was filled with water to soak overnight. Upon returning the next day, the holes were observed to have caved. New holes were drilled that morning, filled with 12 inches of pea gravel bedding material, and then a 4 inch PVC pipe was placed within the hole. Water was filled to the top of pipe (stickup above grade of about 12 and 7 inches for IT-9 and I0-10, respectively) and allowed to soak until the early afternoon. Water infiltrating from the boring sidewalls was observed before starting the test and the annulus between the pipe and the soil was packed with bentonite chips to reduce seepage. The bentonite chips were allowed to hydrate before testing was started.

A falling head test was conducted and the depth of water within the pipe (in relation to the starting elevation) was recorded every 10 minutes for a total of 240 minutes. After 240 minutes, the test was extended another 40 to 50 minutes to attempt to obtain another one hour increment; however, the infiltration rate appeared to be approaching zero and the remaining increment of the test was cancelled. The one hour field infiltration rate increments were calculated and presented herein for design use by others. Please see the attached test results. The final design infiltration rate is up the future the designer, but is typically the average of the four increments or the last reading.

Concrete Cores and Break Results Six concrete cores were drilled by Duffey Concrete Cutting, Incorporated at wall and column locations selected and approved by the project team. The cores were drilled with water and generated approximately 3.75 inch diameter cores ranging in length from 8.5 to

13.5 inches. The cores were moisture conditioned, prepared, and broken in our lab in Charlotte, NC in general accordance with ASTM C42. Please see the attached core break results and the location diagram for more details.

3. Area Geology and Subsurface Conditions Geologic Setting The project site is located in the Huron-Erie Lake Plains Physiographic Providence and specifically within the Maumee Lake Plains. The Maumee Lake Plains are described by the Ohio Department of Natural Resources as a “flat-lying Ice-Age lake basin with beach ridges, bars, dunes, deltas, and clay flats” and include Pleistocene-age silty and clayey tills and lake deposits overlying Silurian and Devonian-age carbonate rocks and shales. According to published geologic literature, the site area is mapped (T)/D, which corresponds to Till over Dolomite bedrock (Pavey et. al 2005). The parentheses indicate that the till is discontinuous and may not be present in the full mapped area. The site’s location on the map noted above can be found below.

Map Excerpt 1: Surficial Geology of the Lorain and Put-in-Bay 30x60 minute quadrangles

Karst is a surface topography that is characterized by caves, sinkholes, voids, and surface depressions that form in rocks subject to dissolution. Dolomite, which is mapped on this parcel, is one such carbonate rock that is susceptible to dissolution when exposed to water. Long term dissolution can lead to the formation of sinkholes which can be detrimental to structures and hardscapes if not addressed or considered. The subsequent sections discuss the risk of sinkhole formation of this site and its impact to the proposed construction. Significantly, we note that sinkholes have been mapped on South Bass Island and in the general vicinity of this project.

Please see the publicly available mapping noted below.

Map Excerpt 2: Karst Mapping (reference Chapter 9 of the Ohio Coastal Atlas, 3rd Edition)

Finally, we note that the site has been graded and modified in the past. Historic photos of the site during construction of the plaza structure indicate that the area was previously a low-lying marshy area that appears to have been reclaimed and infilled. Therefore, undocumented fill and unsuitable material may be present on the site. The quality of anthropogenic fills can vary significantly, and it is often difficult to assess the engineering properties of existing fills.

Generalized Subsurface Stratigraphy General subsurface conditions observed during our geotechnical evaluation are described in this section. For more detailed soil descriptions and stratifications at a particular boring location, the respective Soil Boring Logs, attached to this report should be reviewed. In addition, generalized subsurface profiles are included as Figure 2, attached to this report.

Topsoil Each of the borings encountered between an approximately 3 to 5-inch surficial topsoil/grass mat layer.

Existing Fill Soils Existing fill soils were encountered below the surficial topsoil layer at each of the borings and extended approximately 3.5 to 10 feet below existing grades. The existing fill soils generally consist of very soft to firm CLAYS (CL and CH) and loose SILTY SANDS (SM) with varying amount of sand. Within these materials, the measured SPT N-values generally ranged from 3 to 8 blows per foot (bpf) of penetration. Compaction records associated with the fill materials are not available.

At Boring B-7, an approximately 3 feet thick layer of ORGANIC SILT (OL) with SAND, was observed within the fill at about 4.5 feet below grade. The moisture content and organic content within this OL material was 116.1% and 10.6%, respectively and is assumed to be buried topsoil/organics within the fill.

Lacustrine Soils (Lake Deposits) In most of the borings (excluding B-1, B-3, B-4, and IT-9) and below the fill, very soft to soft CLAYS (CH) and very loose to loose SILTY SAND (SM) lacustrine deposits were encountered to depths of about 8 to 12 below existing grades. Within these materials, the measured SPT N-values generally ranged from weight of hammer (WOH) to 7 blows per foot (bpf) of penetration.

Glacial Till Glacial till was encountered below the fill, and if present, the Lacustrine Deposits in borings B-3, B-4, and B-6 and consisted of stiff to hard Sandy CLAY (CL) and very dense CLAYEY SAND (SC). The till was encountered to depths of about 7 to 14.5 below existing grades.

Within these materials, the measured SPT N-values generally ranged from weight of hammer (WOH) to 12 bpf to 50 blows over 5 inches of penetration.

Partially Weathered Rock/Rock Underlying the above materials, except at B-1, B-2, and IT-10, very dense (SPT N-Value of 50 blows over 3 to 6 inches of penetration) partially weathered rock sampled as CLAYEY SAND (SC) and SANDY CLAY (CL) was observed at depth of about 7 to 17 feet below existing grades unless auger or spoon refusal occurred. Rock material is typically indicated by auger and spoon refusal depths. Rock coring was not conducted as it was beyond the scope of this report. From the geologic mapping, we understand that the parent rock on this site is primarily Dolomite.

Groundwater Observations Borings were drilled using dry-auger techniques in an attempt to observe groundwater seepage into the open boreholes. Free water within the open borehole was measured at Borings B-2, B-5, B-6 to B-8, and IT-10 while drilling at depths of approximately 3 to 6 feet below existing grades. Upon completion of drilling, groundwater was observed at Borings B-2, B-7, B-8, and IT-10 at depths of approximately 5.5 to 8 feet below existing grades. No long-term groundwater readings were obtained.

The groundwater level at the project site is anticipated to fluctuate seasonally depending on the amount of rainfall, prevailing weather conditions, lake conditions, and subsurface drainage characteristics and the highest groundwater observations are normally encountered in late winter and early spring. Long-term groundwater levels could also be influenced by climate change. If more detailed groundwater information is required, monitoring wells or piezometers can be installed.

Laboratory Testing Soil index testing including moisture content (ASTM D2216), Atterberg Limits (ASTM D4318), organic content (ASTM D2974), and sieve analysis (ASTM D1140 and ASTM D6913) were conducted by a Wood laboratory on selected soil samples to aid in the classification of soils in accordance with USCS and to quantify and correlate engineering properties. The results of the jar sample laboratory testing can be found in the appendix of this report.

In addition, due to their size, the bulk samples obtained were submitted by our subconsultant to an outside laboratory to conduct the following testing: Index testing (ASTM D4318, D6913, and D7928), California bearing ratio (ASTM D1883), lab box resistivity (ASTM G57), chloride and sulphate content (EPA 9056A), pH (ASTM D4972) and Standard Proctor (ASTM D698). These results are also attached to this report.

Existing Geotechnical Information Soil Test Borings and a Geotechnical Report (Prepared by CH2M Hill, LLC, dated January 22, 2021) from the adjacent seawall project were provided to us for our review after our exploration was completed. These borings generally indicate similar soil conditions as noted above. As part of the seawall project, rock coring was conducted which noted the predominate rock type to be Limestone with the degree of weathering decreasing with depth. Percent Recovery and Rock Quality Designation (RQD) in the rock cores was varied and ranged from 33 to 100 and 0 to 91%, respectively. The RQD was described qualitatively with an overall range of very poor to excellent, but generally most of the cores were described as poor to good (RQD ranging from 25 to 90). Voids with an approximate thickness of about 2 feet were noted in some of the rock cores.

4. Geotechnical Considerations Based on the results of our subsurface evaluation and analysis, the proposed construction is feasible from a geotechnical standpoint, provided the recommendations in this report are incorporated into the design and construction of the project, as appropriate.

Geotechnical considerations include the following:

The soils relative density / consistency below the proposed foundation elevations was generally low, particularly within the upper 4 to 10 feet of existing grades performed in the vicinity of planned plaza. Furthermore, these soils consist of undocumented fills that are not suitable for foundation support. In addition, as groundwater is anticipated to fluctuate with adjacent lake elevations, removal and replacement of these fills and soft soils could be challenging. Based on this consideration, we don’t not anticipate that shallow foundations would be an appropriate option.

Foundation alternatives have been provided herein which include ground improvement and deep foundations. Commentary for each option can be found in the sections below.

Based on depths at which groundwater was encountered and anticipated grading/excavations, temporary dewatering may be required during construction of foundation elements, utilities, and other below-grade structures. The Contractor is responsible for managing groundwater during construction.

Because this site is underlain by carbonate rock, there is a risk of sinkhole development within the subject property. We note that the present state-of-the-art of geotechnical engineering does not permit accurate prediction of where or when sinkholes will occur, therefore the Owner should realize that the possibility for post-construction sinkhole development cannot be eliminated and that construction on this property, or essentially any other site within this geologic setting, carries with it some risk that future sinkholes may occur. The associated risk can be reduced by careful attention to the details of site preparation/foundation installation presented later in this report. Site grading should be established to provide positive drainage, both during and after construction, to minimize the potential for future sinkhole development. During construction, the grading contractor should be alert to any indication of possible incipient sinkholes within the subsurface. Any such features encountered during the site grading, or during later stages of construction, should be repaired under the direction of the geotechnical engineer.

Earthwork contractors should be made aware of the moisture sensitivity of fine-grained near surface soils encountered in some areas and potential compaction difficulties associated with such soils.

Soil conditions that differ from those encountered in our borings may be encountered during construction.

5. Recommendations The following sections present our geotechnical recommendations and were developed based on our understanding of the proposed construction, the observed subsurface conditions, and our experience. If the proposed construction is changed from that discussed herein or subsurface conditions other than those shown on the boring logs are observed at the time of construction, Wood should be retained to conduct a review of the new information and to evaluate the need for additional recommendations.

Foundations Undocumented soft and loose fill soil were encountered within the upper 4 to 10 feet of existing grades. There soils are not suitable for shallow foundation support due to the inherent risk of unsuitable soils within the fill, the generally loose nature of the fill, and the present of organic materials observed within the fill unless these fills are removed and replaced. Furthermore, groundwater was observed about 5 to 6 feet below existing grades, which would make removal and replacement of these deeper fill soils challenging and therefore make this option likely to be uneconomical.

We should also note that the existing structure is currently not supported on shallow foundations, but on driven piles; though details associated with these piles were unavailable. We have therefore provided two additional foundation options for consideration. The final foundation type will be selected by the final design-build team.

Option 1 – Ground Improvement

Shallow foundations supported on the existing undocumented fills is not suitable for the reasons described above. However, to reduce the risk of unsuitable total or differential settlements, ground improvement (GI) methods could be considered for this project. Before ground improvement can be considered, the risk associated with vibrations and displacement/compaction operations adjacent to the historic tower should be considered by the final design team. At a minimum, and should a GI option be pursued, we recommend that a vibration monitoring plan and a three-dimensional displacement monitoring plan be prepared so that unsuitable movements or disturbance of the moment do not occur during construction. In addition, further structural and geotechnical exploration of the existing tower structure and its foundation may be needed to reduce this risk. These items are beyond the scope of this report.

Ground improvement typically consists of a grid of aggregate or cemented piers, sometimes in conjunction with a gravel or concrete transfer platform, underlying spread footings. An aggregate pier ground improvement system is composed of densely compacted aggregate piers that somewhat resemble piles or caissons when arranged in a group under a spread footing element (thus resembling a pile cap) or rows under a wall footing. Aggregate piers are designed so that the modulus of the bearing strata is improved and total and differential settlements are reduced.

Similar to aggregate piers, rigid inclusion ground improvement elements could also be considered. Rigid inclusions, unlike aggregate piers, utilize cemented materials such as concrete, grout and aggregate, or cement treated aggregate to backfill the pier annulus. Since the pier is typically much more rigid than the surrounding soils, the loads are transferred to the pier and then shed into denser soils or rock below via skin friction and end bearing. Rigid inclusions require a gravel load transfer pad to transfer the load out of the footing and into the rigid inclusion element.

For this project, we anticipate total settlements could be reduced once GI is installed to one inch or less with differential settlements to be about half that amount between columns. The final pier diameters, depths, and layout would be determined by the specialty design-build contractor based on the loads furnished by the structural engineer and the results of field and laboratory testing shown on the attached soil boring logs. We recommend that aggregate piers be extended to the bottom of the fill at a minimum and into the very loose and soft lacustrine soils as needed to control settlements. For rigid inclusions, the piers should be extended at a minimum into the dense till or weathered rock materials to obtain a suitable geotechnical capacity. However, the final lengths are designed by the specialty contractor and will depend on the loading and soil conditions anticipated.

Preliminarily, we recommend that a bearing capacity of 4,000 psf be used for the ground improvement areas; however, the final bearing capacity should be provided by the design-build contractor, and they should be consulted before the final foundation plan is prepared.

Installation of ground improvement piers should be continuously monitored and documented by an experienced engineering technician. It should be noted that the ground improvement piers can be installed in saturated conditions and can also be designed to provide increased lateral and uplift resistance. At least one static loading test (ASTM D 1143) should be required to verify design values for compression. We recommend that the test be run up to 150% of the design maximum top of pier stress.

Option 2 –Micropiles

To reduce the risk of excessive differential settlement, the use of a deep foundation system to transfer the foundation loads through the fill and soft native soils is recommended. Drilled deep foundations (compared to ground improvement or driven piles) are typically associated with lower displacement and vibrations which is beneficial considering the historic nature of the adjacent monument.

Because of uncertainty as to the amount of load that would actually be transferred to the tip of the pile, we recommend the capacity of each micropile be computed conservatively based on skin friction only with no contribution from end bearing. Furthermore, we recommend pile design be based on an allowable rock to grout ultimate bond strength of 145 psi assuming a gravity installation method. We recommend that skin friction within the soil layers be conservatively neglected in pile capacity design. Bedrock layers 12 inches or thicker can be utilized in computing the allowable rock to grout adhesion, provided the rock socket is terminated in at least 5 feet of continuous bedrock. In some locations, voids observed in the limestone will require longer pile embedment lengths. We recommend that rock socket lengths be confirmed in the field by the design-build team’s geotechnical engineer. Typical pile sizes and allowable compressive capacities are as follows:

75 kips: 5.5-inch-diameter pile with a 5 foot long rock socket

100 kips: 7-inch-diameter pile with a 5 foot long rock socket

130 kips: 9 5/8-inch-diameter pile with a 5 foot long rock socket

Preliminarily, we recommend that the compressive capacity of the piles be confirmed by performance of a load test (ASTM D 1143) on one pile prior to construction. A contingency for a second load test should be included. We recommend load testing to failure or 200 percent of design load. Production piles should not be used for testing. Once the final foundation design is known, the load demand per pile may be less than noted above depending on how many piles per column are required per code. Depending on the design-build team’s risk tolerance, the final allowable load per pile, and the design Factor of Safety, the design-build team could consider removing the need for a full-scale load test.

We recommend that pile design, installation, and load testing be performed by an experienced geotechnical specialty contractor having experience in this geologic setting. It is very important that the project design-build geotechnical engineer have an on-site representative to monitor pile installation and confirm that the interpretation of suitable bearing rock and depth of socket are consistent with this report. With design and construction as previously described, we estimate that total and differential settlement of the micropile foundations in excess of the structural elastic deformation of the pile itself will be approximately ½ inch or less.

The depth to rock is fairly variable; borings in the vicinity of the structure indicated auger refusal depths ranging from EL. +568 to +558 feet. Thus, variation in pile lengths should be anticipated. Based on the available boring information, we estimate the average depth of the micropiles into the bedrock to reach suitable bearing rock and to obtain the above noted geotechnical capacities will range between 15 to 25 feet below the existing ground surface elevation (EL. +575). The design socket length per pile, with some allowance for cavities in the bedrock, should be added to the estimated pile footage.

Basement Slabs The on-site fill soils at the basement level FFE are considered suitable for the support of concrete slabs on grade provided they are properly prepared in accordance with the subgrade preparation recommendations in this report. Alternately, the slab can be designed as a structural slab and supported on the deep foundation elements.

Should the slab be designed as a soil supported slab and as the compactive effort of these fill materials were not documented when placed, we recommend that great care be taken to identify any soft/yielding areas or unsuitable materials at slab subgrade.

We recommend that the floor slab be isolated from the foundation elements so that differential settlement of the structure will not induce shear stresses in the floor slab. Furthermore, to reduce the crack width of any shrinkage cracks that may develop near the surface of the slab, we recommend steel reinforcement be included in the design of the floor slab. Special attention should be given to the surface curing of the slab in order to reduce uneven drying of the slab and associated cracking.

We also recommend that the lower floor slab be underlain by a minimum of 8 inches of granular material having a maximum aggregate size of 1.5 inches and no more than 2% soil fines passing the No. 200 sieve. This granular layer will facilitate the fine grading of the subgrade and provide a drainage layer for the floor slab. Prior to placing the granular material, the floor subgrade soil should be properly compacted, proofrolled, and free of standing water, mud, and frozen soil. Before the placement of concrete, a vapor barrier may be placed on top of the granular material to reduce the amount of moisture intrusion unless required by the local building code.

A preliminary subgrade modulus value k, of 150 pci, may be used for design of slabs placed on compacted engineered fill or on successfully proof rolled soil. This recommended subgrade modulus is for a 12-inch by 12-inch test plate and should be reduced for design of a full-size slab. If needed, Wood can provide additional recommendations for the appropriate subgrade modulus value to be used for design.

Below-grade Walls We recommend below grade walls be designed to withstand lateral earth pressures (drained conditions) and surcharge loads from soil, adjacent building foundations, and streets. A lateral earth pressure of 60 psf should be utilized in the design of the below grade walls not free to rotate, for which drainage is provided (no hydrostatic pressures). The wall drainage system must effectively eliminate hydrostatic pressures behind the walls. Any surcharge loads imposed within a 45 degree slope of the base of the wall should be considered in the below grade wall design. The influence of these surcharge loads on the below grade walls should be based on an at-rest pressure coefficient, ko, of 0.5.

To reduce excessive pressures against the below grade walls, and to reduce the settlement of the wall backfill, it is recommended that the wall backfill be compacted to 95% of the maximum dry density determined in accordance with ASTM D698, the Standard Proctor Method. Where the fill will be supporting pavement or other structures, the fill should also be compacted to 98% of this standard.

Backfill materials which are placed behind below-grade walls should be free of organic materials and debris, free-draining, non-frost susceptible, and should not include any highly plastic clays or silts (CH or MH). It is imperative that no CH or MH soils be used as backfill, due to the shrink-swell potential of these materials. The backfill should also have a Liquid Limit less than 40 and Plasticity Index of less than 20. The fill placed adjacent to the below grade walls should not be over compacted. Heavy earthwork equipment should maintain a minimum horizontal distance away from the below grade walls of 1 foot per foot of vertical wall height. Lighter compaction equipment should be used close to the below grade walls.

Prefabricated drainage materials should be used in addition to the granular backfill, adjacent to the below grade walls. Examples of suitable materials include Inca Mat, Aquadrain, Mira-drain, or Geodic drains. These materials should be covered with a filter fabric having an apparent open size (AOS) consistent with the size of the soil to be retained. The material should be placed in accordance with the manufacturer’s recommendations and connected to either the perimeter drain system or the underslab drainage system, which in turn should be properly drained by sumps. We recommend that the entire below grade structure be waterproofed with suitable water stops between the walls and floor slab at the foundation level.

Underslab Drainage Groundwater was encountered during drilling as shallow as 3 to 8 feet below existing grades and may vary based on seasonal changes, construction, and installation of groundwater control measures. Groundwater should therefore be accounted for during construction and after construction. We recommend that the below-berm (i.e. basement) areas be provided with a perimeter and underslab subdrainage system.

The subdrainage system may consist of perforated, closed joint, drain tiles located around the interior perimeter of the below berm areas, as close as feasible to the exterior wall, below the finished floor elevation. Weep holes (which convey drainage from behind the walls to the underslab subdrainage system) should be placed at a spacing of no greater than 8 feet on center on all below grade walls.

The weep holes should be a minimum of four inches in diameter, and should freely drain from the exterior drainage medium to be collected by the interior perimeter drain line just inside the base of the wall. The drain lines should be surrounded by a minimum of 4 inches of gravel or clean sand material having a gradation compatible with the size of the opening utilized in the drain lines and the surrounding soils to be retained.

We recommend that the perimeter and underslab drain system for the proposed structures be designed to flow to a permanent sump and then to an appropriate discharge location determined by the Civil Engineer of Record. If a permanent sump configuration is utilized, it is possible to utilize one below-grade sump pit for the entire building. The sump should be designed to withstand the hydrostatic uplift forces applied to it.

We recommend that the permanent sump(s) be preliminarily designed with a full duplex capability (i.e. two pumps per pit), with each individual pump rated at no less than 75 gallons per minute (gpm). This preliminary flow rate is for groundwater needs only and would not include other sources of water such as flood or collected surface water. With this configuration, under emergency conditions, these individual sumps would have the capacity to pump 150 gpm (groundwater flow only). During construction, the contractor should monitor the pumping rate of the temporary construction pumps to verify that the permanent sump pumps has been adequately sized.

Smaller or conversely larger pumps may ultimately be needed and the final design and sizing of the pumping system will be by others.

Lateral drain lines under the floor slab should be placed at no more than 25 feet on center. Underslab drain lines should have a minimum diameter of 4 inches, and they should be slotted or appropriately perforated. Clean out access should be installed at all sharp bends and at approximately every 100 feet for straight runs. A grit collection chamber should be installed upstream of the sump to reduce the amount of granular materials reaching the pumps. A final under slab drainage design and submittal should be completed by an appropriate design professional prior to construction.

Kart Considerations/Sinkhole Development Potential The existing structure has been in place for about 100 years and we understand that no structure issues associated with sinkholes activity has been noted. However, as noted in the geology section of this report, carbonate rock which is associated with sinkhole formation is mapped on-site and existing sinkhole activity is mapped on South Bass Island. Sinkholes form when soil travels via infiltrating water or from falling into voids or fractures created from dissolution within the bedrock material. No sinkholes or closed depressions were observed on the provided project survey documents and evidence was not observed during the subsurface exploration; however, this site was historically a low-lying area which has been altered by human activity and evidence of historic sink sinkholes may have since been covered. Since sinkholes can develop at any time, we recommend that the project design-build team be alert for evidence of sinkhole activity during on-site activities.

While there is always the potential for sinkhole development in Karst geology, no construction method or engineering recommendation can prevent the formation of sinkholes. To reduce the long-term risk of sinkhole formation, geophysical surveys could be considered to attempt to observe evidence of sink hole formation. We therefore recommend that some contingencies be developed for the repair of any sinkholes found during construction; however, we would consider the risk of sinkholes on this site to be low considering the age of the existing structures on-site and lack of surface formation features noted. Finally, to reduce the risk of sinkhole formation, the following construction practices should be incorporated into the project.

1. Avoiding the routing of roof drains beneath the structure or if not practical, solid pipe these drain to a suitable outlet.

2. Verifying that under-slab piping beneath structures is carefully constructed and pressure tested prior to its placement in service.

3. The use of paved ditches or geomembrane-lined ditches, particularly in cut areas, to efficiently collect and transport surface water.

4. Maintaining site drainage during construction to avoid ponding of water and to promote the rapid removal of surface waters.

5. The scarification and recompaction of the upper nine inches of soil exposed in cut sections, thereby creating a blanket of less permeable material.

6. Backfilling utility trenches with flowable fill or compacted clayey fill instead of clean-graded stone. Stone backfill is more porous and can act as a sump thus collecting water that results in greater seepage pressure and an increased potential for subsurface erosion.

7. Further, it is important that excavated areas, as well as the rest of the construction site be maintained in a well-drained condition. Temporary and final grades should positively route waters from the site.

Pavement Subgrade Recommendations We understand that asphalt parking areas will be added along Bayview Avenue. While the final pavement design is beyond the scope of this report, the pavement subgrade recommendations presented below are based on our experience with similar projects, the subgrade conditions encountered during our geotechnical evaluation, and those anticipated after grading is complete.

Pavements and aggregate stone bases should be constructed in accordance with guidelines and specifications provided by the Ohio Department of Transportation Standard Specifications.

Subgrade soils should be evaluated using proofrolling methods discussed herein and repaired where needed prior to construction of pavement sections.

Laboratory testing of onsite soils indicated a CBR value of 3.6; we recommend a design CBR value of 3 be used for in-place compacted soils or properly placed and compacted fill. The CBR value should be confirmed with laboratory testing prior to construction if the soils differ than those tested as part of this scope of work.

Flexible pavement sections are appropriate for areas subjected to normal traffic patterns.

Curbs or curb and gutter systems should be installed along pavement perimeters to aid in the drainage of surface water runoff and minimize water infiltration into the pavement subgrade.

Seismic Site Class Seismic site class is calculated in accordance with the 2017 OH Building Code (IBC 2015 with amendments) based on the average Standard Penetration Testing (SPT) N60-values (i.e., the standard penetration resistance based on…