Skaggs Island VORTAC Geotechnical Report 9-6-22.pdf

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Northern California Office Central California Office Southern California Office 330 Village Lane 6417 Dogtown Road 699 Hampshire Road, Suite 102 Los Gatos, CA 95030-7218 San Andreas, CA 95249-9640 Thousand Oaks, CA 91361-2352

(408) 354-5542 (209) 736-4252 (805) 370-8710 www.cottonshires.com

COTTON, SHIRES AND ASSOCIATES, INC.

CONSULTING ENGINEERS AND GEOLOGISTS

September 6, 2022

E6082 By email (David.De.Langis@faa.gov)

Mr. David De Langis Civil Engineer WSA Engineering Services

AJW-2W15U

United States Federal Aviation Administration Los Angeles, California

SUBJECT: Geotechnical Investigation

RE: FAA Skaggs Island (SGD) VORTAC Settlement, Creep and Seismic Hazards Skaggs Island, Sonoma County, California

Dear Mr. De Langis:

Cotton, Shires and Associates, Inc. (CSA) is pleased to provide the United States Federal Aviation Administration (FAA) with the following geotechnical report in which we describe the findings, conclusions and recommendations of our geotechnical investigation of the FAA VORTAC facility on Skaggs Island in Sonoma County, California. This investigation was performed in accordance with our Confirming Agreement with you dated November 19, 2021.

In this report, we summarize our characterization of the geotechnical conditions surrounding and underlying the site and provide our findings, conclusions and recommendations regarding mitigation of distress that has occurred to the structure since its installation presumably in the late 1950s.

Mr. David D. De Langis September 6, 2022 E6082

We appreciate the opportunity to have been of service to you on this project. If you have any questions regarding this report or need additional information, please feel free to contact us.

Sincerely, Patrick O. Shires Senior Principal Geotechnical Engineer

GE 770

Samuel W. Nolan Supervising Geotechnical Engineer

GE 3191

SWN:POS:st i

GEOTECHNICAL INVESTIGATION

FAA SKAGGS ISLAND (SGD) VORTAC

Sonoma County, California

Table of Contents

Page

1.0 INTRODUCTION

1.1 Project Description

1.2 Purpose and Scope of Work

2.0 PHYSICAL AND GEOLOGIC SETTING

2.1 Terrain

2.2 Geologic Setting

2.3 Site Geology

2.4 Seismic Setting

2.4.1 Site Class Determination

2.4.2 Site-Specific MCEG Peak Ground Acceleration

3.0 SITE CONDITIONS

3.1 Surface Conditions

3.2 Subsurface Conditions

3.2.1 Small-Diameter Borings

3.2.2 Cone Penetrometer Test (CPT) Probes

3.2.3 Laboratory Testing

3.2.4 Instrumentation

3.3 Groundwater Conditions

4.0 POTENTIAL GEOTECHNICAL HAZARDS

4.1 Seismic Hazards

4.2 Expansive Soils and Soil Creep Hazards

4.3 Settlement Hazard

4.3.1 Relative Elevation Surveys

4.4 Corrosivity and Sulfate Attack on Concrete Hazards

5.0 RECOMMENDATIONS

5.1 Site Considerations

5.2 Site Grading

5.3 Seismic Design

5.4 Bearing Capacity and Settlement Analyses

5.5 Technical Review

ii

5.6 Construction Observation and Testing

6.0 INVESTIGATION LIMITATIONS

7.0 REFERENCES

FIGURES

1 Site Location Map 2 Regional Geologic Map 3 San Francisco Bay Area Fault Map 4 Site Exploration Map 5 Relative Elevation Survey of Interior Slab-on-Grade 6 Relative Elevation Survey of Roof 7 Plot of Inclinometer Results

APPENDIX A - Field Investigation and Logs of Exploratory Borings Field Investigation .............................................................................................. A-1 Field Investigation Summary ............................................................................ A-2 Logs of Exploratory Borings .............................................................................. Follows ............................................................................. A-2 CPT Graphs ............................................................................. Follows ............................................................................. Above

APPENDIX B – Laboratory Testing ............................................................................. B-1 Summary of Laboratory Testing ....................................................................... B-2 Summary of Atterberg Limits Testing .............................................................. Follows .................................................................................. B-2 Summary of Triaxial Compression Shear Strength Testing .......................... Follows .................................................................................. Above Summary of Consolidation Testing .................................................................. Follows .................................................................................. Above

APPENDIX C – Original Design Drawings Provided ............................................. C-1

GEOTECHNICAL INVESTIGATION

FAA SKAGGS ISLAND (SGD) VORTAC

Sonoma County, California

1.0 INTRODUCTION

1.1 Project Description

In this report, Cotton, Shires and Associates, Inc. (CSA) presents the results of our geotechnical investigation of the FAA VORTAC facility (SGD) located on Skaggs Island in Sonoma County, California (see attached Site Location Map, Figure 1). It is our understanding that the structure was constructed in the late 1950s by creating a fill pad over former bay-lands. Since that time the structure has experienced some differential settlement and associated distress with ground cracks developing primarily on the west side of the building. CSA was retained to investigate the site to determine the likely cause of the settlement and to evaluate its anticipated performance in a design earthquake.

1.2 Purpose and Scope of Work

The purpose of our geotechnical investigation was to: 1) characterize the surface and subsurface earth materials present at the subject site; 2) monitor the ground movement impacting the site; 3) identify and evaluate the site geotechnical hazards;

4) develop a geologic model of the site; 5) characterize the geotechnical properties of the earth materials present at the site; 6) perform settlement and seismic analyses;

and 7) develop geotechnical design criteria and recommendations for mitigation of site hazards. The specific scope of work performed included the following tasks:

• Review of published geologic maps;

• Review of historical stereo-pair aerial photograph and Google Earth Pro images;

• Review of geotechnical investigation data and reports;

• Downloading and processing available LiDAR topographic information;

• Geologic hazard mapping of the site;

• Performance of three cone penetrometer probes;

• Drilling, sampling and logging of three exploratory borings;

• Installation and monitoring of inclinometer casing in one of the borings;

• Relative elevation surveys of the interior slab-on-grade floor and the roof of the building as well as the levelness of the antenna pole pad to the southeast of the building pad;

• Laboratory testing of representative samples from the borings;

• Review and compilation of subsurface exploration and laboratory testing data;

• Settlement and seismic analyses;

• Geotechnical engineering evaluation to prepare geotechnical design criteria and recommendations; and

• Preparation of this report.

2.0 PHYSICAL AND GEOLOGIC SETTING

2.1 Terrain

The Skaggs Island VORTAC site is located on relative flat land that was former bay-lands. The regional topography is shown on LiDAR Topography on NearMap Photo Base on Page 8 of this report.

2.2 Geologic Setting

The Skaggs Island VORTAC site is located in an area of Holocene estuarine deposits locally referred to as Young Bay Mud. The regional geology is presented on attached Figure 2 – Regional Geologic Map.

2.3 Site Geology

The site geology is characterized by a roughly 80-foot by 80-foot plan view 3- to 4-foot thick layer of artificial fill placed on Young Bay Mud (YBM) deposits to provide a building pad for the VORTAC structure. The YBM deposits are relatively thick and are underlain by older alluvium. The depth to bedrock was not determined as part of this investigation, but is assumed to be very deep. Because the depth of fill and depth to alluvium is relatively uniform, engineering geologic cross sections were not deemed necessary to prepare.

2.4 Seismic Setting

The FAA Skaggs Island (SGD) VORTAC building is situated in an area of high seismicity. The nearest controlling active fault, with respect to seismicity, is the Hayward Fault Rodgers Creek segment, located 5.9 km southwest of the site.

Other active faults close to this site include the West Napa (8.7 km northeast), Green Valley (20.7 km northeast), and the San Andreas Fault (38.9 km southwest).

Regional Faults are shown on attached Figure 3, San Francisco Bay Area Fault Map.

The site location is located between Cuttings Warf and Sears Point Quads, both of which have not been evaluated for liquefaction or landslide hazards by the California Geological Survey (CGS, 2003).

2.4.1 Site Class Determination – Site Classification was determined based on ASCE7-22 Chapter 20. The shear wave velocity of the site is estimated to be

176.1 m/s (578 f/s) based on California Geological Survey Map Sheet 48 (CGS, 2017).

Our subsurface investigation encountered up to 8 feet of organic soils), which would denote Site Class DE, unless any of the site class definitions for Site Class F (Section 20.2.1) or Site Class E (Section 20.2.2) are met. Site Class F is classified by four conditions: 1) liquefiable soils, quick and highly sensitive clays, or collapsible weakly cemented soils; 2) Soil profiles with more than 10 feet of organic clays; 3) Soil profiles with very high plasticity clays (H>25 ft with PI>75 ft); or 4) Soil profiles with very thick soft/medium stiff clays (H>120 ft with su<1000 psf). Our subsurface investigation did not encounter liquefiable soils. Our subsurface investigation encountered up to 8 feet of organic soils. Approximately 72 to 74 feet of clays, silt mixtures, and organic soils with a shear strength less than 1,000 psf, and approximately 48 to 50 feet with shear strengths less than 500 psf. Atterberg Limits resulted in Plasticity Indices between 20 and 30 percent, and Liquid Limits between 38 and 58 percent. Water contents in the Young Bay Mud varied between 36.8 and

95.2 percent. Based on these parameters, the site does not meet the conditions to be classified as Site Class F. The soft clay (Su < 500 psf) encountered is between 48 and 50 feet thick, therefore this site corresponds to Site Class E.

2.4.2 Site-Specific MCEG Peak Ground Acceleration – Based on 2022 ASCE 7, the factored site-specific MCEG PGAM is 0.56 g and should be used for design.

3.0 SITE CONDITIONS

3.1 Surface Conditions

The site is relatively flat with the exception of the elevated fill pad of approximately 3 to 4 feet high described above. In general, the live vegetation at the site is characterized by low vegetation, brush and grasses.

3.2 Subsurface Conditions

The subsurface conditions at the site and surrounding area have been explored with a total of three small-diameter borings and three CPT probes.

The locations of the exploratory borings and CPTs are shown on Figure 4, Site Exploration Map.

3.2.1 Small-Diameter Borings – CSA observed and logged three small-diameter borings. The depth of the borings observed varied from 23.5 feet to 81.5 feet below the existing ground surface. In Boring CSA/SD-1, located northwest of the structure, we observed loose sandy clayey gravel (fill) from the ground surface to a depth of 1.25 feet. Below the loose gravel, we observed stiff sandy gravelly clay (fill) to a depth of 3.75 feet. Underlying the fill, we observed soft (except stiff where desiccated directly below the fill) fat clay, Young Bay Mud (YBM), to a depth of 78.0 feet where silty clay alluvium was encountered. In Boring CSA/SD-2, located northeast of the VORTAC structure, we encountered the same fill sequence as at Boring CSA/SD-1, again overlying YBM to the bottom of the boring at 43.5 feet. In Boring CSA/SD-3, located southeast of the structure pad, we encountered soft (except stiff where desiccated at and just below the ground surface) fat clay YBM to the bottom of the boring at 23.5 feet. Detailed descriptions of the materials encountered in the small-diameter borings are shown on our boring logs in Appendix A.

3.2.2 Cone Penetrometer Test (CPT) Probes – In addition to the small-diameter borings CSA observed three CPT probes. In CPT-01, located northwest of the structure and south of CSA/SD-1, we encountered stiffer deposits down to about 7 feet (into the YBM) and then soft deposits which gradually increased in stiffness to a depth of about 78 feet where they markedly became stiffer to the bottom of the probe at 97 feet depth. In CPT-02, located north of the structure and east of CSA/SD-1, we encountered stiffer deposits down to about 6 feet (into the YBM) and then soft deposits which gradually increased in stiffness to a depth of about 79 feet where they markedly became stiffer to the bottom of the probe at 87 feet depth. In CPT-03, located northeast of the structure and north of CSA/SD-2, we encountered stiffer deposits down to about 6 feet (into the YBM) and then soft deposits which gradually increased in stiffness to a depth of about 78 feet where they markedly became stiffer to the bottom of the probe at 84 feet depth. Detailed graphs of the materials encountered in the CPTs are presented in Appendix A.

3.2.3 Laboratory Testing – Laboratory tests of representative samples collected at the subject site are presented on the boring logs in Appendix A and in Laboratory Testing Appendix B. Laboratory tests performed included moisture content (ASTM D2216); dry unit weight (ASTM D7263b); Atterberg Limits (ASTM D4318); unconsolidated-undrained triaxial compression shear strength (ASTM D2850); and one-dimensional incremental consolidation (ASTM D2435). The results of the laboratory testing were evaluated and utilized in forming the geotechnical design criteria and recommendations presented in this report.

3.2.4 Instrumentation – An inclinometer was installed in Boring CSA/SD-

1. The inclinometer recorded soil creep toward the west to a depth of about 16 feet below ground surface, with the majority of creep occurring in the upper 6 feet below ground surface. A plot of the inclinometer data is presented on Figure 7 – Plot of Inclinometer Results.

3.3 Groundwater Conditions

Shallow groundwater was encountered in all three of the small-diameter borings.

Groundwater was encountered at a depth of 3.5 feet below ground surface in CSA/ SD-1 and CSA/SD-2, drilled on the structural fill pad and at a depth of 2.5 feet below ground surface in CSA/ SD-3, south of the structural fill pad. The CPTu Pore Pressure Dissipation Tests indicated phreatic surfaces between 3.4 and 3.5 feet below ground surface.

Groundwater levels are subject to fluctuation and it should be understood that groundwater levels will vary at other locations, due to tidal fluctuations, other times of year and during other climatic conditions.

4.0 POTENTIAL GEOTECHNICAL HAZARDS

In the following sections, we list identified potential geotechnical hazards at the site, along with the corresponding degrees of estimated potential risk, and we provide recommendations for possible mitigation measures, where warranted.

4.1 Seismic Hazards

Seismic ground shaking associated with a large earthquake on the San Andreas, Napa West or Hayward Rogers Creek fault is considered to be a high potential hazard in the project area. Peak ground accelerations of up to 0.56g should be anticipated at the site (see report Section 2.4).

The subject property is not mapped within an Alquist Priolo fault zone, and no active faults have been recognized on, or mapped through, the subject property.

Consequently, the potential for surface faulting and ground rupture from faulting on the property is considered to be low.

Other seismically-induced ground failure mechanisms include: landsliding, liquefaction, lateral spreading, lurching, and differential compaction. As mentioned in Section 2.4, the site has not been evaluated for liquefaction or landslide potential. The potential for strong ground shaking to trigger a landslide on the subject property is considered to be low due to the flat topography with gentle slopes.

Soil liquefaction is a phenomenon in which a saturated, cohesionless or non-plastic, near-surface soil layer loses strength during cyclic loading (such as that typically generated by earthquakes). During the loss of strength, the soil develops mobility sufficient to permit both horizontal and vertical movements. Soils that are most susceptible to liquefaction are loose, saturated, fine-grained sands and non-plastic silts and clays that are generally located within 50 feet of the ground surface. Bray and Sancio (2006) determined that loose soils with PI<12 and wc/LL>0.85 were susceptible to liquefaction, loose soils with 12 < PI < 18 and wc/LL>0.8 were moderately susceptible, and soils with PI > 18 tested at low confining stresses were not susceptible to liquefaction. Boulanger and Idriss (2006) determined that fine-grained soils with PI > 7 are not susceptible to liquefaction.

The site is not located within a State-mapped liquefaction hazard zone. Groundwater was encountered during subsurface exploration at a depth approximately 3.5 feet below ground surface (elevation 1.5 M.S.L.); however, wetter years could raise the groundwater levels throughout the site. Based on Atterberg Limit tests, the PI of the materials encountered ranges between 20 to 30. For materials with a PI > 18, we judge the potential for liquefaction to be low.

4.2 Expansive Soils and Soil Creep Hazards

Based on the results of laboratory testing by others and our experience, it appears the artificial fill (PI = 20 to 22) and young bay mud (PI = 30) are potentially moderately to highly expansive. Expansive soils are subjected to volume changes due to seasonal fluctuations in moisture content. When expansive soils are present on a slope, soil creep is likely to occur. Soil creep is a type of slope movement typically characterized by the slow, downward progression of soil as it expands and contracts with changes in moisture.

We installed an inclinometer at SD/SI-2 to a depth of 78 feet. The inclinometer results show creeping soil to a depth of 16 feet, with a gradual increase in creep up to the ground surface. The current creep displacement measured is approximately 0.1 inch over a 2-month period, with the majority of the creep occurring in the upper 6 feet.

The direction of creep is toward the west, away from the structure, which correlates to observed ground cracking and loss of soil beneath and adjacent to the north and west sides of the building foundation.

It is interesting to note that on aerial images of the site and expressed in regional LiDAR topography, there appears to have been grading of a swale to the northwest of the building pad that may have some relationship to the direction of soil creep (see following annotated LiDAR topography on NearMap photo base).

LiDAR Topography on NearMap Photo Base

4.3 Settlement Hazard

Young Bay Mud (YBM) is subject to significant settlement when loads from fill and/or buildings are placed on it. Based on our laboratory testing, the YBM is highly compressible and the fill pad and building likely settled considerably after construction. Fortunately, the thickness of the building pad and the YBM beneath it are relatively uniform so the settlement experienced was likely relatively uniform without significant differential settlement.

4.3.1 Relative Elevation Surveys - CSA conducted relative elevation surveys of the roof of the structure and the interior slab-on-grade. The floor level survey of the interior slab-on-grade indicates relatively uniform floor levels with a differential of 1.2 inches, tilting down toward the east/northeast.

The roof level survey shows relatively uniform levels around the perimeter of the overhanging circular roof that are higher to the south and southeast and lower by up to 1.2 inches to the north/northwest where the inclinometer shows creep to the west and loss of foundation soils has exposed the perimeter footing. The levels of the interior of the roof surrounding the broadcasting antenna are significantly higher than the perimeter edge by up to 4.8 inches higher. The higher roof near the center was probably built into the structure to promote roof drainage and reduce the potential for ponding.

Because the interior slab-on-grade survey does not show a corresponding high point in the middle of the slab, the interpretation that the roof structure was built to promote drainage is supported. It is interesting to note that there do not appear to be support columns in the interior of the building supporting the broadcasting antenna central portion of the roof (as are shown on the 1957 plans provided to us), but since there is no sagging of the roof, the framing appears adequate to support the loads despite the lack of central support for the framing.

We also conducted measurements on the auxiliary antenna slab located to the southeast of the building pad. These measurements indicate that the auxiliary antenna slab is tilted approximately 4 inches down to the southwest across the 6-foot wide by 7.5’ long slab.

It is interesting to note that on aerial images of the site and expressed in regional LiDAR topography, there appears to have also been grading of a swale to the south of the VORTAC building pad that may have some relationship to the direction of slab tilt (see annotated LiDAR topography on NearMap photo base on Page 8).

4.4 Corrosivity and Sulfate Attack on Concrete Hazards

Corrosivity testing of site soils was beyond the scope of our services. Due to the YBM and marine environment, we recommend that the design team assume that the soils are corrosive with the potential for sulfate attack on concrete and use corrosion resistant design or consider testing site soils for corrosivity.

5.0 RECOMMENDATIONS

5.1 Site Considerations

The existing structure is currently being impacted by soil creep where foundation support material is being removed from beneath the exterior footings on the north and west sides of the building. To improve the future performance of the structure, we recommend that the structure be underpinned with push piles on all four sides of the structure. Push piles should be spaced at approximately 5 to 6 feet on centers.

Push piles will need to extend through the YBM to gain support in the alluvium below the YBM and should be hydraulically jacked until the foundation is lifted ¼ inch, or refusal. Additional releveling and/or filling of voids may be accomplished by using polyurethane grout injection through the interior slab-on-grade.

The existing auxiliary antenna pad to the southeast of the building pad is also tilted.

Field measurements of the tilt of the slab indicate that it is tilted to the southwest with approximately 4 inches of tilt across the 6-foot by 7.5-foot slab. We recommend supporting and releveling this pad with push piles around its perimeter. Additional releveling and/or filling of voids may be accomplished by using polyurethane grout injection.

The potentially corrosive marine environment should be considered with respect to the ability of the push pile underpinning to withstand corrosion over time. CSA does not have design expertise in corrosion protection. If push piles are susceptible to corrosion over the long term, then protective measures should be considered as recommended by a corrosion design specialist or the push piles should be replaced at the conclusion of their anticipated design life.

5.2 Site Grading

Based on the field investigation, we do not recommend additional grading at the site because of the potential to create additional settlement if additional fill is brought in and placed. Local minor backfill around the exterior footings should be acceptable to reduce the potential for burrowing rodents to enter beneath the slab-on-grade, particularly once the building has been underpinned.

5.3 Seismic Design

A peak ground acceleration of 0.56g should be anticipated for design purposes.

Based on our geotechnical investigation, the site location, our interpretation of the Hazards Report for ASCE/SEI 7-22 related to Earthquake Loads and using the online tool, we are providing the following parameter recommendations.

Two Period Design Parameters:

Parameter Value

Site Classification E Mapped Spectral Acc. 0.2 Sec. (g) Ss = 2.12 Mapped Spectral Acc. 1 Sec. (g) S1 = 0.86 SMS = FaSs 1.63 SM1 = FvS1 3.07

SDS=2/3 SMS 1.09

SD1=2/3 SM1 2.04

Multi-period Spectrum:

Period

(s)

MCER

Psa (g)

Design

Psa (g)

0 0.67 0.44

0.01 0.68 0.45

0.02 0.65 0.44

0.03 0.63 0.42

0.05 0.71 0.47

0.075 0.97 0.64

0.1 1.15 0.76

0.15 1.35 0.9

0.2 1.38 0.92

0.25 1.34 0.9

0.3 1.4 0.94

0.4 1.51 1.01

0.5 1.66 1.11

0.75 1.76 1.17 1 1.81 1.21

1.5 1.69 1.13 2 1.61 1.07 3 1.14 0.76 4 0.81 0.54 5 0.61 0.41

7.5 0.31 0.21 10 0.19 0.13

5.4 Bearing Capacity and Settlement Analyses

Bearing Capacity Analysis:

Based on the field investigation borings and CPTs, supplemented by laboratory testing, we analyzed the existing footings bearing capacity. The fill material is mostly friction-based material with CPTs indicating a friction angle between 28 to over 40 degrees. Taking 28 degrees, and the average unit weight of the fill material, the allowable bearing capacity is 1,300 psf for a 2-foot wide and 2-foot deep footing. For wider or deeper foundations, the bearing capacity typically increases as the critical bearing slip surface also deepens. However, the underlying material beneath the fill is very weak (Su < 500 psf). Consequently, increasing the depth or width will reduce the allowable bearing capacity to 900 psf.

Since our inclinometer results to date do not show evidence of a bearing capacity failure (such as a discrete kick in the inclinometer plot at a depth commensurate with a bearing capacity failure), we believe the existing structure is currently performing satisfactorily from a bearing capacity standpoint.

Settlement Analysis:

We analyzed future anticipated settlements of the young bay mud for different loading conditions using the results of our consolidation laboratory testing. A summary of the laboratory testing is provided below:

Material

Elevation (ft)

USCS

Dry Unit Weight (pcf)

Moisture Content

Wet Unit Weight (pcf)

Consolidation

Top Bottom Pp OCR CC CR

Fill 5 1 GW/CL 81.0 18.2 95.5 N/A N/A N/A N/A Upper

YBM

1 -27 CH 54.9 68.9 91.8 1338 1.47 0.05 0.51

Middle

YBM

-27 -47 CH 56.4 71.7 96.8 2139 1.37 0.04 0.46

Lower

YBM

-47 -75 CH 72.3 50.8 107.4 3200 1.44 0.03 0.52

Settlements were calculated for broad stress increases (uniform layer), for building stress increases (using the 2:1 method for a building pad of 36 [actual dimension] and 80 ft [building pad]), for strip footing loads (Bousinesq and Newmark), and for isolated square footings (Newmark). The loads required to reach settlements of 0.5, 1, 2, 3, 4, 5, and 6 inches were back-calculated and presented in the following table.

Load Type Settlement (inches)

0.5 1 2 3 4 5 6

Widespread psf 29 60 100 124 145 164 182 Building, B=80, 2:1 method psf 47 89 129 159 187 212 237 Building, B=36, 2:1 method psf 68 113 160 198 234 266 299 Strip Footing, Bousinesq plf 543 770 1115 1449 1734 2030 2341 Strip Footing, Newmark, B=1 psf 547 775 1122 1458 1743 2041 2351 Strip Footing, Newmark, B=2 psf 279 394 570 740 883 1034 1190 Square Footing, 2x2ft, Newark psf 1047 1504 2275 2991 3806 4567 5327 Square Footing, 3x3 ft, Newmark psf 505 720 1082 1421 1807 2149 2505

*Red indicates bearing capacity failure; For B>2, Qal=900; For B<2, Qal = 1300

Our recommended mitigation using push piles will not significantly increase the current loads at the site, and will transfer loads to the Alluvium underlying the compressible YBM. The settlement calculations presented above should be considered by a structural engineer if additional loads are contemplated for the site in the future. We also recommend additional readings of the inclinometer over time to further assess the creep movement expressed to date and to confirm bearing capacity failure is not a concern.

5.5 Technical Review

Supplemental geotechnical design recommendations should be provided by our firm based on specific design needs developed by the other project design professionals. This report, and any supplemental recommendations, should be reviewed by the contractor as part of the bid process. It is strongly recommended that no construction be started nor grading undertaken until the final drawings, specifications, and calculations have been reviewed and approved in writing by a representative of Cotton, Shires and Associates, Inc.

5.6 Construction Observation and Testing

All installation of push piles should be observed by a representative of Cotton, Shires and Associates, Inc. Our office should be contacted with a minimum of 48 hours advance notice of construction activities requiring inspection and/or testing services.

6.0 INVESTIGATION LIMITATIONS

Our services consist of professional opinions and recommendations made in accordance with generally accepted engineering geology and geotechnical engineering principles and practices. No warranty, expressed or implied, or merchantability of fitness, is made or intended in connection with our work, by the proposal for consulting or other services, or by the furnishing of oral or written reports or findings. It was not within our scope to investigate the site for environmental concerns such as contaminated soils and therefore we accept no liability associated with such materials being present.

Any recommendations and/or design criteria presented in this report are contingent upon our firm being retained to review the final drawings and specifications, to be consulted when any questions arise with regard to the recommendations contained herein, and to provide testing and inspection services for earthwork and construction operations. Unanticipated soil and geologic conditions are commonly encountered during construction which cannot be fully determined from existing exposures or by limited subsurface investigation. Such conditions may require additional expenditures during construction to obtain a properly constructed project. Some contingency fund is recommended to accommodate these possible extra costs.

This report is issued with the understanding that it is the responsibility of the owner, or of his representative, to ensure that the information and recommendations contained herein are called to the attention of the project engineer and incorporated into the plans. Furthermore, it is also the responsibility of the owner, or of his representative, to ensure that the contractor and subcontractors carry out such recommendations in the field.

7.0 REFERENCES

ASCE 7 Hazard Tool, Online Application, ASCE/SEI 7-16.

Bray, J.D., and Sancio, R.B., Assessment of the Liquefaction Susceptibility of Fine- Grained Soils, J. of Geotechnical and Geoenvironmental Engineering, ASCE, 2006, 132(9).

Boulanger, R.W., and Idriss I.M., Liquefaction Susceptibility Criteria for Silts and Clays, J. of Geotechnical and Geoenvironmental Engineering, ASCE, 2006, 132(11).

Bowles, J.E., Foundation Analysis and Design, Third Edition, 1982, McGraw-Hill Book Company, Page 184, and Tables 2-6 and 2-7.

California Geological Survey, Map Sheet 48 (Revised 2016) Earthquake Shaking Potential for California, 2016.

California Geological Survey, Guidelines for Evaluating and Mitigating Seismic Hazards in California: Special Publication 117A, 2008.

Duncan J.M., Horz R.C., and Yang T.L., August 1989, Shear Strength Correlations for Geotechnical Engineering, Virginia Tech, Department of Civil Engineering, Geotechnical Engineering, 1989.

Idriss I.M., Boulanger R.W., Soil Liquefaction During Earthquakes monograph, Earthquake Engineering Research Institute, 2008

U. S. Department of the Navy, 1982, Design Manual Soil Mechanics, Foundations, and Earth Structures, NAVFAC DM-7.2.

Woodward Clyde Sherard and Associates, Slope Investigation, 49 Vista Del Mar Court, dated July 27, 1960.

A - 1

APPENDIX A

Field Investigation

Logs of Exploratory Borings

CPT Graphs

A-

APPENDIX A

FIELD INVESTIGATION

We explored subsurface conditions at the FAA VORTAC site on Skaggs Island in Sonoma County, California on May 11 and 12, 2022 by means of three small-diameter borings extending to depths of approximately 23.5 to 81.5 feet, at the locations shown on Figure 4, Site Exploration Map. The geologist who logged the borings visually classified the soils in accordance with ASTM D-2487. Relatively undisturbed samples of the materials encountered at selected depths were obtained. These samples were obtained in 3-inch diameter 30-inch-long stainless-steel Shelby tubes or by using brass or stainless-steel liners that were 2.5 inches in outside diameter by 6 inches long and placed inside a 3-inch diameter modified split-barrel California Sampler for sampling. The California Sampler was driven with a rope and cathead 140-pound hammer that was allowed to freely fall about 30 inches. Standard Penetration Tests (SPT) were also performed at selected depths.

The depths of the sampling are shown on the boring logs. The number in the circle at the conclusion of the sampling interval represents the Standard Penetration Test blow count derived by multiplying the Modified California Sampler blow count by a factor of 0.68.

Descriptive logs of the borings are presented in this appendix. These logs depict our interpretation of the subsurface conditions at the dates and locations indicated, based on representative samples collected at roughly five-foot sampling intervals. It is not warranted that they are representative of subsurface conditions at other times and locations. The contacts on the logs represent the approximate boundaries between earth materials, and the transitions between these materials may be gradual.

B -

APPENDIX B

Laboratory Testing

Summary of Laboratory Testing

Atterberg Limits Test Results

Unconsolidated Undrained Shear Strength Test Results

Consolidation Test Results

B -

APPENDIX B

SUMMARY OF LABORATORY TESTING

The laboratory analysis performed for the site consisted of limited testing of the representative soil types sampled during the field investigation to evaluate index, strength and consolidation properties of subsurface materials. The soil descriptions and the field and laboratory test results were used to assign parameters to the various materials at the site. The results of the laboratory testing program are presented in this appendix and on the boring logs.

The following laboratory tests were performed as part of this investigation:

1. Detailed soil description, ASTM D2487;

2. Natural moisture content of the soil, ASTM D2216;

3. In-situ unit weight of the soil (wet and dry) ASTM D7263b;

4. Atterberg limits, ASTM D4318;

5. Unconsolidated undrained triaxial strength test, ASTM D2850; and

6. One-Dimensional Incremental Consolidation, ASTM D2435.

C - 1

APPENDIX C

Original Design Drawings Provided

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Site Exploration Map

Text

FAA Skaggs Island (SGD) VORTAC

SONOMA COUNTY, CALIFORNIA

N

GEO/ENG BY

CRS

APPROVED BY

POS

SCALE:

1” = 10’

DATE

September 2022

PROJECT NO.

E6082

FIGURE NO.

Low Point

High Points

NOTE: ALL NUMBERS

ARE INCHES HIGHER

THAN THE LOW POINT

Relative Elevation Survey of Interior Slab-on-Grade FAA Skaggs Island (SGD) VORTAC

SONOMA COUNTY, CALIFORNIA

GEO/ENG BY

CRS

APPROVED BY

POS

SCALE:

1” = 5’

DATE

September 2022

PROJECT NO.

E6082

FIGURE NO.

N

Relative Elevation Survey of Roof FAA Skaggs Island (SGD) VORTAC

SONOMA COUNTY, CALIFORNIA

GEO/ENG BY

CRS

APPROVED BY

POS

SCALE:

1” = 5’

DATE

September 2022

PROJECT NO.

E6082

FIGURE NO.

Low Points

High Point

NOTE: ALL NUMBERS

ARE INCHES HIGHER

THAN THE LOW POINT

N

Skaggs SI1 A

5/23/2022 6/23/2022 7/21/2022

D ep th in

F ee t

Profile Change in Inches -0.25 0 0.25

Skaggs SI1 B

5/23/2022 6/23/2022 7/21/2022

D ep th in

F ee t

Profile Change in Inches -0.25 0 0.25

PATRICK SHIRES

COTTON, SHIRES AND ASSOCIATES, INC.

PATRICK SHIRES

CONSULTING ENGINEERS AND GEOLOGISTS

PATRICK SHIRES

PLOT OF INCLINOMETER RESULTS

PATRICK SHIRES

FAA Skaggs Island (SGD) VORTAC

PATRICK SHIRES

FIGURE NO. 7

PATRICK SHIRES

West

PATRICK SHIRES

East

PATRICK SHIRES

North

PATRICK SHIRES

South

A - 1

APPENDIX A

Field Investigation Logs of Exploratory Borings

CPT Graphs

A-

APPENDIX A

FIELD INVESTIGATION

We explored subsurface conditions at the FAA VORTAC site on Skaggs Island in Sonoma County, California on May 11 and 12, 2022 by means of three small-diameter borings extending to depths of approximately 23.5 to 81.5 feet, at the locations shown on Figure 4, Site Exploration Map. The geologist who logged the borings visually classified the soils in accordance with ASTM D-2487. Relatively undisturbed samples of the materials encountered at selected depths were obtained. These samples were obtained in 3-inch diameter 30-inch-long stainless-steel Shelby tubes or by using brass or stainless-steel liners that were 2.5 inches in outside diameter by 6 inches long and placed inside a 3-inch diameter modified split-barrel California Sampler for sampling. The California Sampler was driven with a rope and cathead 140-pound hammer that was allowed to freely fall about 30 inches. Standard Penetration Tests (SPT) were also performed at selected depths.

The depths of the sampling are shown on the boring logs. The number in the circle at the conclusion of the sampling interval represents the Standard Penetration Test blow count derived by multiplying the Modified California Sampler blow count by a factor of 0.68.

Descriptive logs of the borings are presented in this appendix. These logs depict our interpretation of the subsurface conditions at the dates and locations indicated, based on representative samples collected at roughly five-foot sampling intervals. It is not warranted that they are representative of subsurface conditions at other times and locations. The contacts on the logs represent the approximate boundaries between earth materials, and the transitions between these materials may be gradual.

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PRESENTATION OF SITE

INVESTIGATION RESULTS

Prepared for:

ConeTec Job No:

Project Start Date:

Project End Date:

Report Date:

Prepared by:

ConeTec Inc.

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Tel: (�������������

ConeTec&$@conetec.com www.conetec.com www.conetecdataservices.com

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FAA Skaggs Island SGD Vortac

Cotton Shires & Associates

22-56-24133

2022-May-09 2022-May-09 2022-May-10

ABOUT THIS REPORT

The enclosed report presents the results of the site investigation program conducted by ConeTec, Inc. The program consisted of Piezocone Penetration Testing and Pore Pressure Dissipation Testing. Please note that this report, which also includes all accompanying data, are subject to the 3rd Party Disclaimer and Client Disclaimer that follow in the ‘Limitations’ section of this report.

Project Information

Client

Project

ConeTec Project Number

Rig Description

Coordinates

Collection Method

EPSG Number

Cone Penetration Test (CPTu)

Depth Reference Existing ground surface at the time of the investigation

6leeve data offset 0.1 Meters

Calculated Geotechnical Parameters Tables

Additional Information The Normalized Soil Behaviour Type Chart based on Qtn (SBT Qtn) (Robertson, 2009) was used to classify the soil for this project. A detailed set of calculated CPTu parameters have been generated and are provided in Excel format files in the release folder. The CPTu parameter calculations are based on values of corrected tip resistance (qt) sleeve friction (fs) and pore pressure (u2).

Effective stresses are calculated based on unit weights that have been assigned to the individual soil behaviour type zones and the assumed equilibrium pore pressure profile.

Soils were classified as either drained or undrained based on the Qtn Normalized Soil Behaviour Type Chart (Robertson, 2009). Calculations for both drained and undrained parameters were included for materials that classified as silt mixtures (zone 4).

Please refer to the list of attached documents following the text of this report. A test summary, location map, and plots are included. Thank you for the opportunity to work on this project.

Cotton Shires & Associates

FAA Skaggs Island SGD Vortac

22-56-24133

20-ton Track CPT Rig (GPT2)

Consumer Grade GPS

32610 (WGS 84 / UTM 10S)

LIMITATIONS

3rd Party Disclaimer

• The “Report” refers to this report titled

• The Report was prepared by ConeTec for

The Report is confidential and may not be distributed to or relied upon by any third parties without the express written consent of ConeTec. Any third parties gaining access to the Report do not acquire any rights as a result of such access.

Any use which a third party makes of the Report, or any reliance on or decisions made based on it, are the responsibility of such third parties. ConeTec accepts no responsibility for loss, damage and/or expense, if any, suffered by any third parties as a result of decisions made, or actions taken or not taken, which are in any way based on, or related to, the Report or any portion(s) thereof.

Client Disclaimer

• ConeTec was retained by

• The “Report” refers to this report titled

• ConeTec was retained to collect and provide the raw data (“Data”) which is included in the Report.

ConeTec has collected and reported the Data in accordance with current industry standards. No other warranty, express or implied, with respect to the Data is made by ConeTec. In order to properly understand the Data included in the Report, reference must be made to the documents accompanying and other sources referenced in the Report in their entirety. Other than the Data, the contents of the Report (including any Interpretations) should not be relied upon in any fashion without independent verification and ConeTec is in no way responsible for any loss, damage or expense resulting from the use of, and/or reliance on, such material by any party.

CONTENTS

The following listed below are included in the report:

- Site Map

- 3LH]RFRQH�3HQHWUDWLRQ�7HVW��&37X��Sounding Summary

- CPTu�6WDQGDUG�Plots��$GYDQFHG�3ORWV��DQG�1RUPDOL]HG�3ORWV

- SBT Zone Scatter Plots

- Pore Pressure Dissipation (PPD) Test Summary

- PPD Test Plots

- Methodology Statements

- Data File Formats

- 'HVFULSWLRQ�RI�0HWKRGV�IRU�&DOFXODWHG�&37�*HRWHFKQLFDO�3DUDPHWHUV

FAA Skaggs Island SGD Vortac

Cotton Shires & Associates

Cotton Shires & Associates

FAA Skaggs Island SGD Vortac

SITE MAP

ConeTec Job Number:

Client:

Sounding Location

All sounding locations are approximate

Project:

Report Date:

22-56-24133

Cotton Shires & Associates FAA Skaggs Island SGD Vortac

2022-May-10

Cone Penetration Test Summary and Standard Cone Penetration Test Plots

Job No: 22-56-24133 Client: Cotton Shires & Associates Project: FAA Skaggs Island SGD Vortac Start Date: 09-May-2022 End Date: 09-May-2022

CONE PENETRATION TEST SUMMARY

Sounding ID File Name Date Cone Cone Area

(cm2)

Assumed Phreatic Surface1

(ft)

Final Depth

(ft) Northing2 Easting2� Elevation3

(ft)

Refer to Notation Number

CPT-01 22-56-24133_CP01 09-May-2022 EC817:T1500F15U35 15 3.5 97.85 4225910 554898 7

CPT-02 22-56-24133_CP02 09-May-2022 EC817:T1500F15U35 15 3.3 87.84 4225913 554897 5

CPT-03 22-56-24133_CP03 09-May-2022 EC817:T1500F15U35 15 3.4 84.73 4225908 554909 5

1. The assumed phreatic surface was based off the shallowest pore pressure dissipation tests performed within or nearest the sounding. Hydrostatic conditions were assumed for the calculated parameters.

2. The coordinates were collected using consumer grade GPS equipment. EPSG number: 32610 (WGS84 / UTM Zone 10S).

3. Elevations are…