_2.6_CLASSIC_Carlson_Geotech.pdf

Office: 18270 SW Boones Ferry Road, Suite 6, Durham, Oregon 97224

Mailing: P.O. Box 230997, Tigard, Oregon 97281

Carlson Geotechnical A division of Carlson Testing, Inc.

Phone: (503) 601-8250 www.carlsontesting.com

Bend Office Eugene Office Salem Office Tigard Office

(541) 330-9155

(541) 345-0289

(503) 589-1252

(503) 684-3460

August 16, 2024

City of Manzanita

Dan Weitzel, Public Works Director

1090 Oak Street

Manzanita, Oregon 97130

Report of

Limited Geotechnical Investigation

Classic Street Improvements

Classic Street

Manzanita, Oregon

CGT Project Number G2406158

Dear Dan Weitzel:

Carlson Geotechnical (CGT), a division of Carlson Testing, Inc. (CTI), is pleased to submit this report summarizing the results of our limited geotechnical investigation for the proposed improvements to Classic

Street. The subject roadway is located between Dorcas Lane and Necarney City Road in Manzanita, Oregon. We performed our work in general accordance with CGT Proposal GP24-125, dated May 9, 2024.

Written authorization for our services was received on June 10, 2024.

We appreciate the opportunity to work with you on this project. Please contact us at (503) 601-8250 if you have any questions regarding this report.

Respectfully Submitted, CARLSON GEOTECHNICAL

M. David Irish, CESCL Brad M. Wilcox, P.E., G.E.

Geotechnical Project Manager Principal Geotechnical Engineer dirish@carlsontesting.com bwilcox@carlsontesting.com

Doc ID: \\geosrv\public\GEOTECH\PROJECTS\2024 Projects\G2406158 - Classic Street Improvements\G2406158 - GEO\008 -

Deliverables\Report\G2406158 Limited Geotechnical Investigation.docx http://www.carlsontesting.com/ mailto:dirish@carlsontesting.com mailto:bwilcox@carlsontesting.com

Classic Street Improvements

Carlson Geotechnical Page 3 of 25

TABLE OF CONTENTS

1.0 INTRODUCTION

1.1 Project Information

1.2 Scope of Services

2.0 SITE DESCRIPTION

2.1 Site Geology

2.2 Site Surface Conditions

2.3 Subsurface Conditions

3.0 PAVEMENT STRUCTURAL CAPACITY EVALUATION

4.0 CONCLUSIONS

4.1 Overview

4.2 Pavement Areas Exhibiting Subsidence

5.0 RECOMMENDATIONS: SITE WORK

5.1 Site Preparation

5.2 Temporary Excavations

5.3 Wet Weather Considerations

5.4 Structural Fill

5.5 Permanent Slopes

5.6 Additional Considerations

6.0 RECOMMENDATIONS: NEW PAVEMENTS

6.1 Option 1 – Pavement Overlay

6.2 Option 2 – Full Removal & Replacement

6.3 Option 3 – Full Depth Reclamation

7.0 RECOMMENDATIONS: NEW RETAINING WALLS

7.1 Option 1 – Conventional Cantilevered CIP Retaining Walls

7.2 Option 2 - Pile-Supported Retaining Walls

8.0 RECOMMENDED ADDITIONAL SERVICES

8.1 Design Review

8.2 Observation of Construction

9.0 LIMITATIONS

ATTACHMENTS

Site Location ........................................................................................................................................... Figure 1

Site Plan ................................................................................................................................................. Figure 2

Site Photographs .................................................................................................................................... Figure 3

Fill Slope Detail ....................................................................................................................................... Figure 4

Retaining Wall Static & Seismic Pressure Distribution ........................................................................... Figure 5

Retaining Wall Surcharge Pressure Distribution .................................................................................... Figure 6

Subsurface Investigation and Laboratory Testing ............................................................................. Appendix A

Results of DCP Tests ........................................................................................................................ Appendix B

Pavement Structural Capacity Evaluation ......................................................................................... Appendix C

Carlson Geotechnical Page 4 of 25

1.0 INTRODUCTION

Carlson Geotechnical (CGT), a division of Carlson Testing, Inc. (CTI), is pleased to submit this report summarizing the results of our limited geotechnical investigation for the proposed improvements to Classic

Street. The subject roadway is located between Dorcas Lane and Necarney City Road in Manzanita, Oregon, as shown on the attached Site Location, Figure 1.

1.1 Project Information

CGT developed an understanding of the proposed project based on our correspondence with the City of

Manzanita and project documents provided to us. The documents provided included an aerial image showing the proposed boring locations, and a site schematic plan, dated March 24, 2024. Based on our review, we understand the project will include improvements to the existing Classic Street. The improvements will take place over an approximate 2,220-foot long stretch of the roadway, effectively spanning between Dorcas Lane and Necarney City Road. The improvements are anticipated to include, but not limited, to widening of the roadway, installation of underground utilities, installation of sidewalks, installation of site retaining wall(s), and other features. Design of the roadway improvements will rest with others.

Although no grading plans have been provided, we anticipate permanent grade changes at the site will be minimal, with maximum cuts and fills on the order of 2 feet in depth.

Although no stormwater plans have been provided, we anticipate stormwater collected from new impervious areas of the site will be collected and routed to the nearest storm drain or other suitable discharge point(s) approved by Tillamook County.

1.2 Scope of Services

Our scope of work included the following:

Contact the Oregon Utilities Notification Center to mark the locations of public utilities within a 20-foot radius of our explorations at the site.

Explore subsurface conditions within the roadway (Classic Street) by advancing six drilled borings and six dynamic cone penetrometer (DCP) tests to depths of up to about 11½ feet below pavement surface

(bps). Details of the subsurface investigation are presented in Appendix A. Results of the DCP tests are presented in Appendix B.

Classify the soils encountered in the explorations in general accordance with ASTM D2488 (Visual-

Manual Procedure).

Provide a technical narrative describing surface and subsurface deposits, and local geology of the site, based on the results of our explorations and published geologic mapping.

Provide geotechnical recommendations for site preparation and earthwork.

Perform a structural capacity evaluation of the existing pavement structure within the referenced roadway in general accordance with Sections 5.3 and 5.4 of the 1993 AASHTO Pavement Design

Manual.

Provide geotechnical engineering recommendations for use in design and construction of site retaining walls and pavements.

Provide this written limited geotechnical report summarizing the results of the field investigation and recommendations for the project.

Carlson Geotechnical Page 5 of 25

This report is considered “limited” as this assignment did not include an evaluation of seismic/geologic hazards at the site.

2.0 SITE DESCRIPTION

2.1 Site Geology

Based on available geologic mapping of the area , the site is underlain by Holocene age, beach and dune deposits (Qb). This unit consists primarily of unconsolidated, moderately well sorted, fine- to medium-grained beach sand. The area is also composed of cross-bedded, fine-grained sand deposited through active and inactive dune ridges. The beach and dune deposits are occasionally interbedded with fluvial and lacustrine mud and sand deposits found inland from the dune ridges, as well as locally found basalt gravel and boulder debris deposited from erosion of rocky headlands.

2.2 Site Surface Conditions

The subject portion of Classic Street is a two-lane, asphalt-paved roadway that generally runs north to south.

Classic Street spans approximately 2,220 feet and connects Dorcas Lane and Necarney City Road. The road is located within a relatively level to gently sloping area and provides vehicular access to both established residential properties and unestablished residential properties (i.e., portions of subdivisions yet to be fully built out). Residential streets that intersect with Classic Street include Ridge Drive, Highlands Drive, and Jackson Way.

In terms of topography adjacent to the street, the northern 950 feet (approximate) of the street was flanked by a descending vegetated slope exhibiting gradients of about 2H:1V (horizontal:vertical) to 1½H:1V. The central portion of the street (between the south end of Jackson Way and spanning about 450 feet) was flanked by a vegetated/forested ascending slope exhibiting gradients of up to about 1½H:1V. The remaining street areas were generally flanked by level to gentle side slopes.

Site layout and surface conditions at the time of our field investigation are shown on the attached Site Plan

(Figure 2) and Site Photographs (Figure 3).

2.3 Subsurface Conditions

2.3.1 Subsurface Investigation & Laboratory Testing

Our subsurface investigation consisted of six drilled borings (B-1 through B-6) completed on July 8, 2014.

The approximate exploration locations are shown on the Site Plan, attached as Figure 2. In summary, the borings were advanced to depths of about 11½ feet bps. Details regarding the subsurface investigation, logs of the explorations, and results of laboratory testing are presented in Appendix A. Subsurface conditions encountered during our investigation are summarized below.

2.3.2 Subsurface Materials

Logs of the explorations are presented in Appendix A. The following describes each of the subsurface materials encountered at the site.

Wells, R.E., Snavely, P.D., MacLeod, N.S., Kelly, M.M., and Parker, M.J., 1994, Geologic map of the Tillamook Highlands, northwest Oregon Coast Range

(Tillamook, Nehalem, Enright, Timber, Fairdale, and Blaine 15 minute quadrangles): U.S. Geological Survey, Open-File Report OF-94-21, scale 1:62,500.

https://ngmdb.usgs.gov/Prodesc/proddesc_12441.htm https://ngmdb.usgs.gov/Prodesc/proddesc_12441.htm

Carlson Geotechnical Page 6 of 25

Asphalt Concrete Pavement

Asphalt concrete (AC) pavement was encountered at the surface of each boring and was about 2 to 3 inches thick.

Undocumented Poorly Graded Gravel Fill (GP Fill)

Undocumented poorly graded gravel fill (aggregate base rock) was encountered below the AC pavement in each boring. Undocumented fill refers to materials placed without (available) records of subgrade conditions or evaluation of compaction. The poorly graded gravel fill was typically brown, dry, angular, up to about ¾-inch in diameter, and contained no to trace low plasticity fines. The gravel fill extended to depths of about 1⅓ to 3 feet bps.

Elastic Silt (MH)

Underlying the gravel fill in boring B-6 was native elastic silt. This soil was typically stiff, brown, moist, exhibited medium plasticity, and contained trace fine-grained sand. This soil extended to a depth of about

5½ feet bgs in that boring.

Silty Sand (SM)

Underlying the gravel fill in borings B-2, B-3, and B-5, was native, silty sand. This soil was typically loose to medium dense, tan, moist, fine- to medium-grained, and contained varying amounts of low to medium plasticity silt. This soil extended to depths of about 5 feet bps in those borings.

Poorly Graded Sand (SP)

Underlying the gravel fill in borings B-1 and B-4, the silty sand in borings B-2, B-3 and B-5, and the elastic silt in boring B-6, was native, poorly graded sand. This soil was typically loose to medium dense, tan, moist to wet, fine- to medium-grained, and contained no to trace low plasticity silt. This soil extended to the full depths explored in the borings, about 11½ feet bps.

2.3.3 Groundwater

Groundwater was encountered at a depth of about 10 feet bgs in boring B-1 advanced on July 8, 2024.

Groundwater was not encountered within the remaining borings, B-2 through B-6, advanced on that day. To determine approximate regional groundwater levels in the area, we researched well logs available on the

Oregon Water Resources Department (OWRD) website for wells located within Section 29, Township 03

North, Range 10 West, Willamette Meridian. Our review indicated that groundwater levels in the area generally ranged from about 50 to 59 feet bgs. It should be noted groundwater levels vary with local topography. In addition, the groundwater levels reported on the OWRD logs often reflect the purpose of the well, so water well logs may only report deeper, confined groundwater, while geotechnical or environmental borings will often report any groundwater encountered, including shallow, unconfined groundwater.

Therefore, the levels reported on the OWRD well logs referenced above are considered generally indicative of local water levels and may not reflect actual groundwater levels at the project site. We anticipate that groundwater levels will fluctuate due to seasonal and annual variations in precipitation, changes in site utilization, or other factors. Additionally, the native elastic silt (MH) is conducive to formation of perched groundwater.

Oregon Water Resources Department, 2024. Well Log Records, accessed June 2024, from OWRD web site:

http://apps.wrd.state.or.us/apps/gw/well_log/.

http://apps.wrd.state.or.us/apps/gw/well_log/

Carlson Geotechnical Page 7 of 25

3.0 PAVEMENT STRUCTURAL CAPACITY EVALUATION

CGT performed a pavement structural capacity evaluation within the subject portion of Classic Street to determine whether structural enhancement (e.g. an overlay) was appropriate to help meet design vehicular traffic loading over a design period of 20 years and maintain a minimum standard level of serviceability. The results of the evaluation are presented in the attached Appendix C.

4.0 CONCLUSIONS

4.1 Overview

As indicated in the attached Appendix C, our analyses indicate the existing pavement structure within the subject portion of Classic Street exhibited a modest structural deficiency for the modeled vehicular traffic over a 20-year design period. As evidenced during our visual condition survey, we observed localized areas exhibiting fatigue cracking, longitudinal cracking, transverse cracking, and other distress within the existing

AC pavement. Three pavement areas within the north portion of the street exhibited localized subsidence

(slumping); additional discussion of those areas is presented in Section 4.2 above.

We conclude the existing AC pavement is approaching the end of its intended service life and improvements are warranted to maintain desired minimum level of serviceability over the indicated design period (20 years).

Three options may be considered for improving Classic Street, as follows:

Option 1 – Repair Surface Deficiencies & Install Overlay: This option would include repairing/treating surface deficiencies (e.g. fatigue cracking, longitudinal cracks, etc.) within the existing pavement structure and installing an overlay. Based on our analyses and factoring in best practices for placing AC pavement, we recommend the overlay be a minimum of 1½ inches thick. If overlaying is considered, we recommend the project civil engineer be consulted to review impacts to stormwater management, as well as review grade changes with respect to existing nearby features (public streets, sidewalks, curbs, etc.).

Geotechnical recommendations for placement of a pavement overlay within the subject roadway, if considered, are presented in Section 6.1 of this report.

Option 2 – Full Removal & Replacement (R&R): This option would include removing the existing AC pavement and installation of a new AC pavement section. Recommendations for this approach are presented in Section 6.2 of this report.

Option 3 – Full Depth Reclamation (FDR): This option would include pulverizing the existing AC, blending it with the underlying aggregate base in-situ, compacting the materials to serve as aggregate base, and placing a new AC section. If this is considered, we recommend the project civil engineer be consulted to review impacts to stormwater management, as well as review inherent grade changes with respect to existing nearby features (public streets, sidewalks, curbs, etc.). Recommendations for this approach are presented in Section 6.3 of this report.

Other options typically pursued in pavement rehabilitation, including “grind and inlay” and surface treatments

(e.g. slurry seals, chip seals, etc.), are not recommended for Classic Street. The grind and inlay technique is not recommended due to the relatively thin (predominantly 2 inches thick) existing pavement section.

Surface treatments are not recommended due to the structural deficiency identified in our analyses.

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4.2 Pavement Areas Exhibiting Subsidence

As indicated above and shown on the attached Site Plan, Figure 2, we observed three areas exhibiting subsidence (slumping) within the north portion of the street alignment. Each area was located along the west margin of the road and relatively close to a relatively steep, descending slope. The cause(s) of the subsidence was not unequivocally determined, but may be due to one, or a combination of, the following factors: (1) long-term (gradual) downslope movement (creep) of the near surface slope materials and (2) long-term consolidation (settlement) from transient (vehicular) loads of the subgrade materials directly below the pavement materials. Mitigation of these areas is recommended to provide assurance of long-term performance of the pavement structure. The following options are presented for consideration:

Installation of Retaining Wall(s): This option would include installation of engineered retaining wall(s) at the top, or at some point within, the descending slope directly west of those slumping areas.

Recognizing the relatively steep slopes, we recommend consideration be made to utilize pile-supported walls (e.g., sheet pile walls, soldier pile walls, etc.). Once the retaining wall(s) have been installed, the affected pavements should be removed and soft/loose subgrade soils (if present) should be over-excavated and replaced with structural fill. Geotechnical (soil) parameters for use in design of pile-supported walls are presented in Section 7.2 of this report.

Buttressing Slopes: This option would include buttressing the descending slope (west of street) by adding new fill in a controlled (engineered) manner and achieve a maximum gradient of 2H:1V. This would invariably include removal of existing trees and vegetation on the slope and near its toe, and extending the slope outward (beyond its current footprint) to achieve that gradient. Keying and benching of the existing slope is recommended prior to placement of new structural fill. If considered, we recommend this approach be reviewed by the project civil engineer to review whether special considerations are applicable for this construction.

Realignment of Street Segment: This option would include realigning this segment of the street towards the east to achieve a greater setback from the descending slope. If considered, we recommend this approach be reviewed by the project civil engineer to review whether special considerations are applicable to allow for this construction.

5.0 RECOMMENDATIONS: SITE WORK

The recommendations presented in this report are based on the information provided to us, results of our field investigation and analyses, laboratory data, and professional judgment. CGT has observed only a small portion of the pertinent subsurface conditions. The recommendations are based on the assumptions that the subsurface conditions do not deviate appreciably from those found during the field investigation. CGT should be consulted for further recommendations if the design of the proposed development changes and/or variations or undesirable geotechnical conditions are encountered during site development.

5.1 Site Preparation

The following recommendations are presented in the event the existing pavement structure is removed in its entirety (R&R) and/or the project includes widening the existing roadway beyond its current footprint.

Review of the extent of the public right of way and impacts to neighboring properties (to the west) would need to be evaluated.

Review of the extent of the public right of way and impacts to neighboring properties (to the east) would need to be evaluated.

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5.1.1 Stripping

Stripping activities associated with site preparation should be minimal at this site. Where slated for removal, existing asphalt concrete (AC) pavement, surface vegetation, and rooted soils should be removed from within, and for a minimum 3-foot margin around (where feasible), planned new pavements and retaining walls. Stripped AC should be transported off site for disposal, or stockpiled for later use as structural fill on the project site as described in Section 5.4.1 of this report. Stripped rooted soils should be transported off site for disposal, or stockpiled for later use as landscaping fill on the site.

5.1.2 Existing Utilities & Below-Grade Structures

All existing utilities at the site should be identified prior to excavation. Abandoned utility lines beneath the new pavements, retaining walls, and hardscaping features should be completely removed or grouted full.

Soft, loose, or otherwise unsuitable soils encountered in utility trench excavations should be removed and replaced with structural fill in conformance with Section 5.4 this report. Buried structures (i.e. footings, foundation walls, retaining walls, slabs-on-grade, tanks, etc.), if encountered during site development, should be completely removed and replaced with structural fill in conformance with Section 5.4 of this report.

5.1.3 Roadway Subgrade Preparation

5.1.3.1 Dry Weather Construction

After site preparation as recommended above, but prior to placement of structural fill and/or aggregate base, the geotechnical engineer or his representative should observe a proof roll test of the exposed subgrade soils in order to identify areas of excessive yielding. Proof rolling of subgrade soils is typically conducted during dry weather conditions using a fully-loaded, 10- to 12-cubic-yard, tandem-axle, tire-mounted, dump truck or equivalent weighted water truck. Areas that appear too soft and wet to support proof rolling equipment should be prepared in general accordance with the recommendations for wet weather construction presented in Section 5.3 of this report. If areas of soft soil or excessive yielding are identified, the affected material should be over-excavated to firm, stable subgrade, and replaced with imported granular structural fill in conformance with Section 5.4.2 of this report.

5.1.3.2 Wet Weather Construction

Preparation of pavement subgrade soils during wet weather should be in conformance with Section 5.3 of this report. As indicated therein, a granular sub-base and geotextile separation fabric may be required in wet conditions in order to support construction traffic and protect the subgrade. Cement amendment may also be considered to help stabilize subgrade soils during wet weather.

5.1.4 Erosion Control

Erosion and sedimentation control measures should be employed in accordance with applicable City, County, and State regulations.

5.2 Temporary Excavations

5.2.1 Overview

Conventional earthmoving equipment in proper working condition should be capable of making necessary excavations for the anticipated site cuts as described earlier in this report. All excavations should be in accordance with applicable OSHA and state regulations. It is the contractor's responsibility to select the excavation methods, to monitor site excavations for safety, and to provide any shoring required to protect

Carlson Geotechnical Page 10 of 25 personnel and adjacent improvements. A “competent person,” as defined by OR-OSHA, should be on-site during construction in accordance with regulations presented by OR-OSHA. CGT’s current role on the project does not include review or oversight of excavation safety.

5.2.2 OSHA Soil Type

For use in the planning and construction of temporary excavations up to 10 feet in depth, an OSHA soil type

“C” should be used for the granular soils (GP Fill, SM, SP) encountered in the borings. Similarly, an OSHA soil type “A” may be used for the native elastic silt (MH) encountered in boring B-6.

5.2.3 Utility Trenches

Caving is anticipated in excavations extending more than a few feet below the ground surface, particularly in areas underlain by relatively clean loose sand (SP). If seepage undermines the stability of the trench, or if caving of the sidewalls is observed during excavation, the sidewalls should be flattened or shored.

Depending on the time of year trench excavations occur, trench dewatering may be required in order to maintain dry working conditions. If groundwater is encountered, we recommend placing trench stabilization material at the base of the excavations. Trench stabilization material should be in conformance with Section

5.4.3 of this report.

5.2.4 Excavations Near Foundations

Excavations near footings should not extend within a 1 horizontal to 1 vertical (1H:1V) plane projected out and down from the outside, bottom edge of the footings. In the event excavation needs to extend below the referenced plane, temporary shoring of the excavation and/or underpinning of the subject footing may be required. The geotechnical engineer should be consulted to review proposed excavation plans for this design case to provide specific recommendations.

5.3 Wet Weather Considerations

For planning purposes, the wet season should be considered to extend from late September to late June. It is our experience that dry weather working conditions should prevail between early July and mid-September.

Notwithstanding the above, soil conditions should be evaluated in the field by the geotechnical engineer or their representative at the initial stage of site preparation to determine whether the recommendations within this section should be incorporated into construction.

5.3.1 Overview

Due to their fines content, the on-site near-surface silty soils (SM, MH) are susceptible to disturbance during wet weather. Trafficability of these soils may be difficult, and significant damage to subgrade soils could occur, if earthwork is undertaken without proper precautions at times when the exposed soils are more than a few percentage points above optimum moisture content. For wet weather construction, site preparation activities may need to be accomplished using track-mounted equipment, loading removed material onto trucks supported on granular haul roads, or other methods to limit soil disturbance. The geotechnical engineer’s representative should evaluate the subgrade during excavation by probing rather than proof rolling. Soils that have been disturbed during site preparation activities, or soft or loose areas identified during probing, should be over-excavated to firm, unyielding subgrade, and replaced with imported granular structural fill in conformance with Section 5.4.2.

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5.3.2 Geotextile Separation Fabric

We recommend a geotextile separation fabric be placed to serve as a barrier between the prepared subgrade and granular fill/base rock in areas of repeated or heavy construction traffic. The geotextile fabric should meet the requirements presented in the current Oregon Department of Transportation (ODOT)

Standard Specification for Construction (ODOT SSC), Section 02320.

5.3.3 Granular Working Surfaces (Haul Roads & Staging Areas)

Haul roads subjected to repeated heavy, tire-mounted, construction traffic (e.g. dump trucks, concrete trucks, etc.) will require a minimum of 18 inches of imported granular material. For light staging areas, 12 inches of imported granular material is typically sufficient. Additional granular material, cement amendment, or geo-grid reinforcement may be recommended based on site conditions and/or loading at the time of construction.

The imported granular material should be in conformance with Section 5.4.2 and have less than 5 percent material passing the U.S. Standard No. 200 Sieve. The prepared subgrade should be covered with geotextile fabric (Section 5.3.2) prior to placement of the imported granular material. The imported granular material should be placed in a single lift (up to 24 inches deep) and compacted using a smooth-drum, non-vibratory roller until well-keyed.

5.3.4 Cement Amendment

It is sometimes less costly to amend near-surface, moisture-sensitive, fine-grained soils with Portland cement than to remove and replace those soils with imported granular material. Successful use of soil cement amendment depends on use of correct techniques and equipment, soil moisture content, and the amount of cement added to the subgrade (mix design). We anticipate the on-site native silty and sandy soils

(SM, SP, MH) are conducive for cement amendment due to their generally low plasticity and experience with similar soils.

The recommended percentage of cement is based on soil moisture contents at the time the work is performed. Based on our experience, 3 percent cement by weight of dry soil can generally be used when the soil moisture content does not exceed approximately 20 percent. If the soil moisture content is in the range of

25 to 35 percent, 4 to 6 percent by weight of dry soil is recommended. Similarly, if the soil moisture content is in the range of 35 to 45 percent, 7 to 8 percent by weight of dry soil is recommended. It is difficult to accurately predict field performance due to the variability in soil response to cement amendment. The amount of cement added to the soil may need to be adjusted based on field observations and performance.

If cement amendment is considered, we recommend additional sampling, laboratory testing, and a mix design be performed to determine the level of improvement in engineering properties (strength, stiffness) of the on-site soils when blended with Portland cement. We recommend project scheduling allow for a minimum of 4 weeks for this testing and design to be completed, prior to initiating cement amendment.

5.3.5 Footing Subgrade Protection

A minimum of 3 inches of imported granular material (crushed rock) is recommended to protect fine-grained

(silty) footing subgrades from foot traffic during inclement weather. The imported granular material should be in conformance with Section 5.4.2. The maximum particle size should be limited to 1 inch. The imported granular material should be placed in one lift over the prepared, undisturbed subgrade, and compacted using non-vibratory equipment until well keyed.

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Surface water should not be allowed to collect in footing excavations. The excavations should be draped and/or provided with sumps to preclude water accumulation during inclement weather.

5.4 Structural Fill

The geotechnical engineer should be provided the opportunity to review all materials considered for use as structural fill (prior to placement). Samples of the proposed fill materials should be submitted to the geotechnical engineer a minimum of 5 business days prior their use on site . The geotechnical engineer or their representative should be contacted to evaluate compaction of structural fill as the material is being placed. Evaluation of compaction may take the form of in-place density tests and/or proof roll tests with suitable equipment. Structural fill should be evaluated at intervals not exceeding every 2 vertical feet as the fill is being placed. The following table presents recommended guidelines for frequency of density testing

(where practical) of various fill designations.

Table 1 Guidelines for Frequency of Density Testing of Structural Fill Materials

Fill Designation Recommended Frequency of Density Tests1

Maximum Depth Interval Area-Wide

General Structural Fill (Mass Grading) Test every 1 vertical foot At least one density test per every 100 feet of roadway

Utility Trench Backfill Test every 2 vertical feet At least one density test per 100 feet of trench line

Pavement Base Rock Test at surface of section At least one density test per every 100 feet of roadway

1 Or as specified by the City of Manzanita, where applicable.

5.4.1 On-Site Soils – General Use

5.4.1.1 Asphalt Concrete Debris

Debris resulting from the demolition of existing pavements can be re-used as structural fill if processed/crushed into material that is fairly well graded between coarse and fine. The processed/crushed concrete should contain no organic matter, debris, or particles larger than 4 inches in diameter. Moisture conditioning (wetting) should be expected in order to achieve adequate compaction. When used as structural fill, this material should be placed and compacted in general accordance with Section 5.4.2.

5.4.1.2 Poorly Graded Gravel Fill (GP Fill), Poorly Graded Sand (SP)

Re-use of the on-site, relatively clean, poorly graded gravel fill and relatively clean sand as structural fill is feasible, provided these materials are kept clean of organics, debris, and particles larger than 4 inches in diameter. If reused as structural fill, these materials should be prepared in general accordance with

Section 5.4.2.

5.4.1.3 Elastic Silt (MH), Silty Sand (SM)

Re-use of these soils as structural fill may be difficult because they are sensitive to small changes in moisture content and are difficult, if not impossible, to adequately compact during wet weather. We anticipate the moisture content of these soils will be higher than the optimum moisture content for satisfactory compaction. Therefore, moisture conditioning (drying) should be expected in order to achieve adequate compaction. If used as structural fill, these soils should be free of organic matter, debris, and particles larger than 4 inches. When used as structural fill, these soils should be placed in lifts with a maximum pre-compaction thickness of about 8 inches at moisture contents within –1 and +3 percent of optimum, and

Laboratory testing for moisture density relationship (Proctor) is required. Tests for gradation may be required.

Carlson Geotechnical Page 13 of 25 compacted to not less than 92 percent of the material’s maximum dry density, as determined in general accordance with AASHTO T180 (Modified Proctor).

If the on-site materials cannot be properly moisture-conditioned and/or processed, we recommend using imported granular material for structural fill.

5.4.2 Imported Granular Structural Fill – General Use

Imported granular structural fill should consist of angular pit or quarry run rock, crushed rock, or crushed gravel that is fairly well graded between coarse and fine particle sizes. The granular fill should contain no organic matter, debris, or particles larger than 4 inches, and have less than 5 percent material passing the

U.S. Standard No. 200 Sieve. For fine-grading purposes, the maximum particle size should be limited to 1½ inches. The percentage of fines can be increased to 12 percent of the material passing the U.S. Standard

No. 200 Sieve if placed during dry weather, and provided the fill material is moisture-conditioned, as necessary, for proper compaction. Imported granular fill material should be placed in lifts with a maximum thickness of about 12 inches, and compacted to not less than 95 percent of the material’s maximum dry density as determined in general accordance with AASHTO T180 (Modified Proctor). Proper moisture conditioning and the use of vibratory equipment will facilitate compaction of these materials.

Granular fill materials with high percentages of particle sizes in excess of 1½ inches are considered non-moisture-density testable materials. As an alternative to conventional density testing, compaction of these materials should be evaluated by proof roll test observation (deflection tests), where accepted by the geotechnical engineer.

5.4.3 Trench Base Stabilization Material

If groundwater is present at the base of utility excavations, trench base stabilization material should be placed. Trench base stabilization material should consist of a minimum of 1 foot of well-graded granular material with a maximum particle size of 4 inches and less than 5 percent material passing the U.S. Standard

No. 4 Sieve. The material should be free of organic matter and other deleterious material, placed in one lift, and compacted until well-keyed.

5.4.4 Trench Backfill Material

Trench backfill for the utility pipe base and pipe zone should consist of granular material as recommended by the utility pipe manufacturer. Trench backfill above the pipe zone should consist of well-graded granular material containing no organic matter or debris, have a maximum particle size of ¾ inch, and have less than

8 percent material passing the U.S. Standard No. 200 Sieve. As a guideline, trench backfill should be placed in maximum 12-inch-thick lifts. The earthwork contractor may elect to use alternative lift thicknesses based on their experience with specific equipment and fill material conditions during construction in order to achieve the required compaction. The following table presents recommended relative compaction percentages for utility trench backfill.

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Table 2 Utility Trench Backfill Compaction Recommendations

Backfill Zone Recommended Minimum Relative Compaction

Structural Areas1,2 Landscaping Areas

Pipe Base and Within Pipe Zone 90% AASHTO T180 or pipe manufacturer’s recommendation

85% AASHTO T180 or pipe manufacturer’s recommendation

Above Pipe Zone 92% AASHTO T180 88% AASHTO T180

Within 3 Feet of Design Subgrade 95% AASHTO T180 90% AASHTO T180

1 Includes proposed pavements, structural fill areas, hardscaping, etc.

2 Or as specified by the local jurisdiction where located in the public right of way.

5.4.5 Controlled Low-Strength Material (CLSM)

CLSM is a self-compacting, cementitious material that is typically considered when backfilling localized areas. CLSM is sometimes referred to as “controlled density fill” or CDF. Due to its flowable characteristics, CLSM typically can be placed in restricted-access excavations where placing and compacting fill is difficult. If chosen for use at this site, we recommend the CLSM be in conformance with Section 00442 of the most recent, ODOT SSC. The geotechnical engineer’s representative should observe placement of the CLSM and obtain samples for compression testing in accordance with ASTM D4832. As a guideline, for each day’s placement, two compressive strength specimens from the same CLSM sample should be tested. The results of the two individual compressive strength tests should be averaged to obtain the reported 28-day compressive strength. If CLSM is considered for use on this site, please contact the geotechnical engineer for site-specific and application-specific recommendations.

5.5 Permanent Slopes

5.5.1 Overview

Permanent cut or fill slopes constructed at the site, if any, should be graded at 2H:1V or flatter. Constructed slopes should be overbuilt by a few feet depending on their size and gradient so that they can be properly compacted prior to being cut to final grade. The surface of all slopes should be protected from erosion by seeding, sodding, or other acceptable means. Adjacent on-site and off-site structures should be located at least 5 feet from the top of slopes.

5.5.2 Placement of Fill on Slopes

New fill should be placed and compacted against horizontal surfaces. Where slopes exceed 5H:1V, the slopes should be keyed and benched prior to structural fill placement in general accordance with the attached Fill Slope Detail, Figure 4. If subdrains are needed on benches, subject to the review of the geotechnical representative, they should be placed as shown on the attached Fill Slope Detail. In order to achieve well-compacted slope faces, slopes should be overbuilt by a few feet and then trimmed back to proposed final grades. The geotechnical engineer or their representative should observe the benches, keyways, and associated subdrains, if needed, prior to placement of structural fill.

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5.6 Additional Considerations

5.6.1 Drainage

Subsurface drains should be connected to the nearest storm drain or other suitable discharge point. Surface water from paved surfaces and open spaces should be collected and routed to a suitable discharge point.

Surface water should not be directed into retaining wall drains or onto site slopes.

5.6.2 Expansive Potential

The near surface native soils consist of moderate plasticity elastic silt (MH) and sandy soils (SM, SP). Based on our experience with similar soils in the vicinity of the site, these soils are not considered to be susceptible to appreciable movements from changes in moisture content. Accordingly, no special considerations are required to mitigate expansive potential of the near surface soils at the site.

6.0 RECOMMENDATIONS: NEW PAVEMENTS

6.1 Option 1 – Pavement Overlay

6.1.1 Treatment of Surface Deficiencies

6.1.1.1 Overview

The long-term performance of repairs to surface deficiencies in asphalt pavement is highly dependent on the quality of workmanship. Accordingly, we recommend an experienced, qualified asphalt contractor be retained to repair deficiencies. The contractor is encouraged to follow repair guidelines and procedures presented in the most recent, ODOT Standard Specifications for Construction (ODOT SSC) and the most recent, “Asphalt in Pavement Maintenance” manual developed by the Asphalt Institute (AI). Other resources may be utilized for review of repair procedures. Subject to review of the pavement engineer, the contractor retained for the repair work may present alternative methods than those indicated below.

6.1.1.2 Fatigue Cracking

We recommend areas exhibiting moderate to severe fatigue (alligator) cracking be repaired as a “deep patch”. Sawcutting and removal of existing pavement should extend at least 1-foot into good pavement outside the cracked area. We recommend this form of pavement repair be in conformance with Section

00748 of the most recent, ODOT SSC. If encountered, soft, loose, or otherwise unsuitable subgrade materials should be removed to expose suitably firm subgrade, and brought back to grade with imported granular structural fill in conformance with Section 5.4.2 of this report. For planning purposes, we recommend a minimum 6 inches of subgrade over-excavation be performed at each deep patch location.

We recommend geotextile separation fabric be placed between the prepared subgrade and granular backfill.

The fabric should be in conformance with Section 02320 of the most recent, ODOT SSC.

6.1.1.3 Linear Cracking

For areas exhibiting linear (longitudinal and transverse) cracking, we recommend that all cracks exceeding

¼-inch in width be cleaned and sealed with rubber or other elastomeric modified asphalt in conformance with

Section 00746 of the most recent, ODOT SSC.

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6.1.2 Overlay

The following is recommended for overlay surface preparation and construction:

The subject portion of Classic Street that exhibits surface deficiencies should be repaired in conformance with the recommendations presented in Section 6.1.1 above.

Once repair of surface deficiencies is complete, the surface that is to be overlaid should be thoroughly cleaned. Compressed air should be used for cleaning to remove all loose matter.

A tack coat should be applied to the cleaned pavement surface in conformance with Section 00730 of

ODOT SSC.

The recommended minimum 1½-inch thick overlay section should be placed on the tack coated surface in conformance with the project civil plans. The AC pavement should consist of Level 2, ½-inch, dense-graded AC in conformance with the most recent ODOT SSC, or as specified by the City of Manzanita

(City). Minimum lift thickness of AC pavement should be 1½ inches, or as specified by City. Maximum lift thickness of AC pavement should be in conformance with Section 00748 of the most recent ODOT SSC, or as specified by City. AC pavement should be compacted to at least 91 percent of the material’s theoretical maximum density as determined in general accordance with ASTM D2041 (Rice Specific

Gravity), or as specified by the City.

6.2 Option 2 – Full Removal & Replacement

6.2.1 Subgrade Preparation

Pavement subgrade preparation should be in conformance with Section 5.1.3 of this report. Pavement subgrade surfaces should be crowned (or sloped) for proper drainage in accordance with specifications provided by the project civil engineer.

6.2.2 Input Parameters

Design of the asphalt concrete (AC) pavement section presented below were based on the parameters presented in the following table, the American Association of State Highway and Transportation Officials

(AASHTO) 1993 “Design of Pavement Structures” manual, and pavement design manuals presented by

APAO and ODOT . If any of the items listed need revision, please contact us and we will reassess the provided design sections.

Oregon Department of Transportation (ODOT) Pavement Design Guide, January 2019.

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Table 3 Input Parameters Used in AC Pavement Design

Parameter Value Parameter Value

Pavement Design Life (years)1 20 Resilient

Modulus

Aggregate Base (ksi) 2 20

Growth Rate (%) 0 Subgrade (ksi)3 8.2

Initial Serviceability2 4.2 Structural

Coefficient

Asphalt2 0.42

Terminal Serviceability2 2.5 Aggregate Base2 0.10

Standard Deviation2 0.49

Vehicle Traffic4 APAO Level III (Moderate)

(high end of this traffic level) 100,000 ESAL Reliability2 (%) 85

Drainage Coefficient – Asphalt, Base, Subgrade2 1.0

1 Value based on AASHTO and APAO guidelines for most pavements of this type.

2 Value based on guidelines presented by the referenced ODOT design manual for asphalt concrete pavements.

3 Values based on DCP testing (summarized in Appendix B) and consideration for seasonal variations.

4 ESAL = Total 18-Kip equivalent single axle load. Refer to Appendix C for additional discussion of value used for design.

6.2.3 Recommended Minimum Sections

The following table presents the minimum AC pavement section for the ESAL value indicated in the preceding table, based on the referenced AASHTO procedures.

Table 4 Minimum AC Pavement Section – Full Removal & Replacement

Material APAO Traffic Loading Level III

Asphalt Pavement (inches) 4

Crushed Aggregate Base (inches)1 8

Subgrade Soils Prepared in conformance with Section 5.1.3 of this report.

1 Where present, the existing gravel fill may be suitable for use as crushed aggregate base below new pavements at the site, provided it is kept clean of fines and other deleterious materials during construction and exhibits proper gradation and other characteristics preferred for pavement aggregate base. Geotechnical observation, sampling, and laboratory testing of the gravel fill may be recommended following stripping of the existing AC pavement to confirm the existing material(s) exhibit those desirable characteristics.

6.2.4 AC Pavement Materials

We recommend pavement aggregate base consist of dense-graded aggregate in conformance with

Section 02630.10 of the most recent ODOT SSC, with the following additional considerations. We recommend the material consist of crushed rock or gravel, have a maximum particle size of 1½ inches, and have less than 10 percent material passing the U.S. Standard No. 200 Sieve . Aggregate base should be compacted to not less than 95 percent of the material’s maximum dry density as determined in general accordance with AASHTO T180 (Modified Proctor), or as specified by City of Manzanita.

We recommend asphalt pavement consist of Level 2, ½-inch, dense-graded AC in conformance with the most recent ODOT SSC. Asphalt pavement should be compacted to at least 91 percent of the material’s theoretical maximum density as determined in general accordance with ASTM D2041 (Rice Specific Gravity), or as specified by City of Manzanita.

The recommendation to limit fines (e.g. silt or clay) within the base rock is intended to assist with moisture-conditioning and facilitating compaction of the layer, particularly if site work takes place during the traditional wet season in this region.

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6.3 Option 3 – Full Depth Reclamation

6.3.1 Overview

Full depth reclamation (FDR) consists of reclaiming the pavement and aggregate base by mechanically breaking up the existing AC section and mixing that material with the underlying aggregate base. The reclaimed material is pulverized in-place to a specified gradation and compaction to serve as granular base for the new pavement. This new base course shall be mixed, proportioned, placed, and compacted in accordance with Section 6.3.4.1 of this report, or as specified by City of Manzanita

6.3.2 Input Parameters

Design of the AC pavement sections presented below were based on the parameters presented in the following table, the AASHTO 1993 “Design of Pavement Structures” manual, and pavement design manuals presented by APAO and ODOT. If any of the items listed need revision, please contact us and we will reassess the provided design sections.

Table 5 Input Parameters Used in AC Pavement Design

Parameter Value Parameter Value

Pavement Design Life (years)1 20 Resilient Modulus

Reclaimed Agg. Base (ksi) 4 15

Growth Rate (%) 0 Subgrade (ksi)3 8.2

Initial Serviceability2 4.2 Structural

Coefficient

Asphalt2 0.42

Terminal Serviceability2 2.5 Reclaimed Agg. Base (ksi)4 0.08

Standard Deviation2 0.49

Vehicle Traffic5 APAO Level III (Moderate)

(high end of this traffic level)

100,000

ESAL

Reliability2 (%) 85

Drainage Coefficient – Asphalt, Base, Subgrade2 1.0

1 Value based on AASHTO and APAO guidelines for most pavements of this type.

2 Value based on guidelines presented by the referenced ODOT design manual for asphalt concrete pavements.

3 Values based on DCP testing (summarized in Appendix B) and consideration for seasonal variations.

4 Value based on examination of the existing aggregate base at boring locations.

5 ESAL = Total 18-Kip equivalent single axle load. Refer to Appendix C for additional discussion of value used for design.

6.3.3 Recommended Minimum Section

T…