Holly Farm Geo 5-18-23.pdf

Foundation Engineering, Inc.

Professional Geotechnical Services

820 NW Cornell Avenue • Corvallis, Oregon 97330 • 541-757-7645

7857 SW Cirrus Drive, Bldg 24 • Beaverton, Oregon 97008 • 503-643-1541

Rich Belloni May 18, 2023

Lincoln County School District

295 NE Burgess

Toledo, Oregon 97391

LCSD Holly Farm Grading Project No.: 2231009

Geotechnical Investigation

Lincoln County, Oregon

Dear Mr. Belloni:

We have completed the requested geotechnical investigation for the above-referenced project. Our report includes a description of our work, a discussion of the site conditions, a summary of laboratory testing, and a discussion of site preparation and grading recommendations.

There are numerous values in geotechnical investigations that are approximate, including measured lengths and soil layer depths and elevations. For brevity, the symbol

“±” is used throughout this report to represent the words approximate or approximately when discussing approximate values.

BACKGROUND

The Lincoln County School District (LCSD) is in the planning stages of development of a currently vacant parcel of land for a future school facility. The site location is shown in Figure 1A (Appendix A). Previous geotechnical exploration at the site included 16 test pits excavated across the site by FEI Testing and Inspection in 2017.

A site plan showing the approximate locations of the test pits and the summary test pit logs are included in Appendix D.

We understand LCSD plans to complete initial site grading on the sloping site to provide a relatively level pad to accommodate future development. Details of the layout and proposed structures are currently unknown but are expected to include a one or two-story school building and associated pavements and fields.

Limited stripping of the topsoil and some fill placement has been completed. We understand LCSD would like to complete initial site grading that can support the future development. The parcel includes a significant drainage that flows from north to south, bisecting the eastern portion of the parcel. The drainage includes moderate to steep slopes. A landslide zone and instability are present below the existing access road adjacent to the drainage that will require stabilization. The current grading work is set-back from the existing instability, and we understand that stabilization of the area is also planned.

DRAFT

LCSD Holly Farm Grading May 18, 2023

Geotechnical Investigation 2 Project No.: 2231009

Lincoln City, Oregon Lincoln County School District

LCSD is the owner and Devco Engineering, Inc. is providing civil design services for the grading. LCSD retained Foundation Engineering, Inc. as the geotechnical consultant. Our scope of work was outlined in a proposal dated March 15, 2023, and authorized by Purchase Order No. 230051174.

FIELD EXPLORATION

We supplemented the existing subsurface data from the test pits with three deeper borings (BH-1 through BH-3). The borings were drilled on April 10, 2023, using a trailer-mounted drill rig. The approximate boring locations are shown in Figure 2A

(Appendix A).

The borings were advanced to depths of ±16.4 to 36.5 feet using solid-stem auger drilling techniques. Soil samples were typically obtained at 2½-foot intervals to a depth of ±20 feet and at 5-foot intervals thereafter. Sampling was conducted using a split-spoon sampler in conjunction with the Standard Penetration Test (SPT). The

SPT, which is performed when the split-spoon sampler is driven, provides an indication of the stiffness or density of the foundation soil. The sampler is driven three consecutive 6-inch increments and the blows required to drive the sampler through each increment are recorded. The number of blows required to drive the sampler the final 12 inches represents the standard penetration resistance or N-value in blows per foot (bpf).

The borings were continually logged during drilling by a Foundation Engineering representative. The final logs (Appendix B) were prepared based on a review of the field logs and the laboratory test results, and an examination of the samples in our office. Upon the completion of drilling, the boreholes were backfilled in general accordance with Oregon Water Resources Department (OWRD) guidelines.

LABORATORY TESTING

The laboratory testing included moisture content, percent fines, and Atterberg limits tests to help classify the soil according to the Unified Classification System (USCS) and estimate their overall engineering properties. The test results are summarized in

Table 1C (Appendix C). The moisture contents are also shown on the boring logs.

Non-tested samples were visually classified in general accordance with the procedures outlined in ASTM D2487 and ASTM D2488. The USCS symbols shown on the logs for untested samples should be considered approximations.

Natural moisture contents for the residual soils are relatively high, with typical values over 50%. Atterberg limits testing on sample SS-1-7 also suggests the materials have high moisture content (59%) at the plastic limit. Therefore, we anticipate that on-site soils will have high moisture sensitivity and poor workability. A bulk density test was completed on Shelby tube sample SH-1-3 to determine the typical dry and moist unit weight of the fill material. The results indicate a moist unit weight of 100.5 lb/ft3 (pcf) and a dry unit weight of 63.2 pcf.

Geotechnical Investigation 3 Project No.: 2231009

Lincoln City, Oregon Lincoln County School District

SURFACE AND SUBSURFACE CONDITIONS

Surface Conditions

The site is located on a vacant parcel in the hilly terrain northeast of NE Devils Lake

Blvd. The parcel was previously used as a holly farm and the bulk of the proposed development area has been cleared of trees. A few trees are still present near the center of the parcel at the east end of the proposed grading limits. A school bus depot presently occupies the northeast corner of the site, and a gravel access road provides access to the depot from NE Devils Lake Blvd.

We understand the proposed grading limits include some isolated areas of existing fill. The south-central portion of the development area includes a fill area that was identified in the 2017 exploration. This fill area typically includes silty clay with some scattered debris, including concrete and asphalt exposed at the surface. The other area of fill is adjacent to the drainage, immediately east of the proposed grading limits. It appears that much of this material consists of the organic topsoil that was stripped from other portions of the site.

Subsurface Conditions

A general discussion of the subsurface conditions encountered in the borings is presented in the following sections. More detailed descriptions of the subsurface conditions encountered in each boring are summarized on the boring logs.

Additional information regarding the boring logs and the definitions of symbols and descriptive terms used in the logs are provided on the Important Information and

Symbols, the Common Soil Descriptions Terms, and the Common Rock Descriptions

Terms sheets in Appendix B. The sheets also include a discussion of the interpretation of the subsurface profiles at the boring locations and the potential for inherent variations in the subsurface conditions across the site.

BH-1 was drilled southeast of the vehicle turnout on the east side of the site. Drilling at this location encountered topsoil/fill consisting of soft silt with scattered to some organics to ±5.8 feet followed by fill consisting of medium stiff to stiff sandy silt to

±12.5 feet. The fill is underlain by stiff clayey silt with some sand to ±20 feet and medium dense clayey rock fragments to ±25 feet. Possible colluvium consisting of very stiff to hard clayey silt to ±32 feet and stiff clayey silt with some sand to

±36.5 feet, the maximum depth of the boring.

BH-2 was drilled northeast of the vehicle turnout on the northwest side of the site.

Drilling encountered a thin topsoil layer consisting of soft silt with scattered organics to ±12 inches. The topsoil is underlain by residual soil consisting of stiff silt with some clay to ±5 feet and very stiff to hard silt to ±15 feet. The residual soil is underlain by extremely weak to very weak (R0 to R1) siltstone (Yamhill Formation) to ±16.5 feet, the maximum depth of the boring. The boring was terminated due to practical auger refusal in the weak rock.

Geotechnical Investigation 4 Project No.: 2231009

Lincoln City, Oregon Lincoln County School District

BH-3 was drilled east of the terminus of the southern gravel access road. The surface at this location was covered with ±12 inches of dense ±6-inch-minus crushed rock fill. The crushed rock is underlain by additional fill consisting of stiff silt to ±5 feet.

Residual soil consisting of very stiff to hard silt follows from ±5 to 25.5 feet and is underlain by extremely weak to very weak (R0 to R1) siltstone (Yamhill Formation) to ±30.4 feet, the maximum depth of the boring.

Groundwater Conditions

Groundwater was encountered in BH-1 at ±4 feet and in BH-3 at ±17.5 feet. BH-2 did not encounter groundwater to a depth of ±16.4 feet, the maximum depth of the boring. Some of the previous test pit excavations encountered water infiltration at depths of ±3 to 9 feet below existing grades.

Based on the subsurface conditions and previous observations of groundwater, we anticipate perched water may develop at relatively shallow depths during periods of sustained or heavy precipitation due to the low permeability of the soils across the site. In addition, zones of seepage may be encountered at variable depths within the residual soil or weathered rock across the site.

DISCUSSION

Site grading will require significant cuts and fills to create a ±17.2-acre level pad at

El. 214 to El. 215. The site grading plan prepared by Devco indicates cuts up to

±30 feet in the northwest corner and fills up to ±43 feet on the east side of the pad. The proposed grading has been balanced to allow the majority of the excavated materials to be placed as fill for the new pad.

Unsuitable Topsoil and Fill

Not all materials from the excavations will be suitable for re-use as fill for the new pad. All existing topsoil is unsuitable for re-use during site grading due to the presence of organic material. Soils containing abundant fine-organic material should be stockpiled on-site for placement over the completed pad to facilitate vegetation of the completed grading. We anticipate that the upper ±6 inches of the pad will consist of the topsoil.

Subgrade soils are expected to expose firm, residual soil. Where the grading exposes existing fill, the excavation depth will need to be extended to remove the fill and any underlying topsoil.

Fill materials that include high plasticity clay, debris, deleterious materials, or large organics will be unsuitable for reuse at the site and should be hauled from the site or disposed of in an approved area.

Geotechnical Investigation 5 Project No.: 2231009

Lincoln City, Oregon Lincoln County School District

Re-use of On-site Materials

The residual soil and underlying siltstone will be suitable for re-use during site grading. The on-site soils are expected to be highly moisture sensitive and include relatively high natural moisture contents. Most of the residual soils are expected to consist of high plasticity silt. The plasticity, sand content, and moisture conditions are expected to vary with location and excavation depth. Therefore, documentation of the suitability of the on-site materials will be required throughout the work. The suitability of using the existing site soils during site grading should be evaluated at the time of construction by a representative of Foundation Engineering.

Keying and Benching

The grading will include construction of large embankment fills at several areas across the site. Portions of the upper residual soil include zones of relatively soft soil conditions in the upper several feet of the soils profile. Therefore, it will be necessary to construct a key trench at the toe of most of the fill slope to integrate the fill into the underlying stiff residual soil. Compaction of the subgrade should be completed to provide a firm, stable surface for embankment fill placement and compaction.

Installation of a key trench drain may be required if seepage is encountered in the excavation.

In addition, the embankment fill will require benching into the existing sloping terrain for all fill areas constructed over existing slope that are greater than 10%. The benching should include a near vertical face that exposes firm, residual soil on the upslope side of the embankment. All keying and benching excavations should bypass all soft or organic soils.

Underdrain Construction

An underdrain should be installed along the existing drainage slope near the center of the planned level pad. The underdrain should consist of a 6-inch perforated or slotted PVC pipe. The pipe should be bedded in at least 12 inches of Drain Rock. The entire mass of Drain Rock should be wrapped in Subsurface Drainage Geotextile that laps at least 12 inches at the top. The approximate location is shown in Figure 2A

(Appendix A).

Moisture Conditioning and Compaction

Moisture conditioning of the soil will only be practical during dry weather conditions when moisture content can be more easily controlled. The on-site soil will likely require scarification throughout moisture conditioning to provide the uniform moisture content required for efficient compaction. The high plasticity silt will be susceptible to deflection and pumping under heavy construction traffic at higher moisture contents. Therefore, we recommend that the select on-site soils be moisture conditioned to within a range of -4% to +2% of the optimum moisture content for compaction.

Geotechnical Investigation 6 Project No.: 2231009

Lincoln City, Oregon Lincoln County School District

All embankment fill should be compacted in loose lifts not exceeding 12 inches, assuming a large tamping foot roller will be used to compact the fill. The fill should be spread in relatively level lifts and compacted with multiple passes of the roller. All embankment fill should be compacted to 95% relative compaction according to

ASTM D698. In addition, individual lifts should provide a firm, stable surface that is capable of supporting rubber-tired heavy construction equipment without pumping and only minor deflections. Documentation of embankment fill moisture conditioning and compaction will be required throughout the work.

RECOMMENDATIONS

Construction recommendations proved below assume the earthwork will occur during dry weather. Site work using on-site soils during wet weather is expected to be impractical without amendment. Depending on the actual time of year construction begins, modifications to the respective recommendations may be required. Therefore, we recommend a preconstruction conference with the earthwork contractor to review the recommendations and project requirements.

General Earthwork and Material Recommendations

1. Topsoil should consist of organic rich soils from required excavations. The topsoil should not include large roots or debris. Topsoil should be stockpiled for placement in approved areas over the completed pad in a 6-inch-thick lift.

2. Unsuitable soil should consist of soils containing large organics, debris or high plastic clay. The unsuitable soils should be hauled from the site or placed in approved areas away from moderately sloping terrain.

3. Select Site Fill should consist of fine-grained soil generated from site grading which is free of organics or other deleterious materials. A representative of

Foundation Engineering should be on-site during grading to approve the use of existing soils.

4. Drain Rock should consist of clean, ¾ to 1½-inch, open-graded crushed gravel, or rock. Other gradation sizes may be appropriate. A material gradation sheet should be provided to Foundation Engineering for approval prior to delivery to the site.

5. Subsurface Drainage Geotextile should be a non-woven geotextile with Mean

Average Roll Value (MARV) strength properties meeting the requirements of an AASHTO M 288-17 Class 2 geotextile (Subsurface Drainage Geotextile) with a maximum AOS of 0.3 mm (max average roll value) and a permittivity greater than 0.1 sec-1. We should be provided a specification sheet on the selected geotextile for approval prior to delivery to the site.

Geotechnical Investigation 7 Project No.: 2231009

Lincoln City, Oregon Lincoln County School District

6. Moisture condition the subgrade and fill to near optimum moisture and compact to a minimum of 95% relative compaction. The maximum dry density of ASTM D698 should be used as the standard for estimating relative compaction. Compaction of fine-grained material should be completed with a padfoot roller. Compact all fill in loose lifts not exceeding 12 inches.

7. Compaction verification should be completed frequently during site grading.

The verification should be performed by field density testing arrays and by observation of the compaction procedure as well as the compacted surface via proof-rolling using a loaded 10-yd3 dump truck or another approved vehicle. Adequate compaction based on proof-rolling should be confirmed by a Foundation Engineering representative. Areas of pumping or deflection observed beneath the truck wheels should be re-compacted or overexcavated and replaced with compacted Select Site Fill and proof-rolled again.

8. Construct the underdrain near the lower limit of the existing drainage swale as shown on the plans. The drain should consist of a 6-inch diameter drainpipe that is bedded and backfilled with drain rock. The drain excavation should be at least 18 inches wide and extend at least 18 inches below the original site grades. The entire mass of drain rock should be wrapped in a

Subsurface Drainage Geotextile. The drain should extend through the existing fill east of the new embankment fill limits to daylight adjacent to the drainage ravine.

Site Grading

9. Strip the ground surface as needed to remove the existing topsoil, site fill, and organics (i.e., existing vegetation and roots). Stockpile topsoil for reuse following site grading.

10. Embankment slopes should be keyed into the existing topography. The excavation for the key should extend a minimum of 3 feet below the existing grades and provide a minimum 10-foot bench at the base as shown in Figure

3A (Appendix A).

11. Place and spread the Select Site Fill in maximum 12-inch thick, loose lifts.

Moisture condition as needed by aerating and blending (or moistening) to allow efficient compaction. Moisture conditioning should target a moisture content within -4% to +2% of the optimum moisture.

Geotechnical Investigation 8 Project No.: 2231009

Lincoln City, Oregon Lincoln County School District

12. Compact the subgrade and Select Site Fill, using multiple passes of a large tamping foot roller as specified above. Adjust truck and construction traffic across the site to prevent disturbance or pumping of on-site soils.

Contractors have various means and methods to process and place fine-grained materials. Therefore, we recommend a pre-construction meeting to discuss the proposed approach for excavation, processing, and placement with the contractor at the time of construction.

13. Grade all permanent slopes to 2H:1V unless otherwise directed.

14. Grade the pad surface as specified to promote positive drainage to the perimeter slopes. Concentrated runoff should not be directed onto the completed fill slopes. Excavation of shallow drainage swales should be completed along the toe of all cut slopes to direct surface run off away from the pad.

DESIGN REVIEW/CONSTRUCTION OBSERVATION/TESTING

Foundation Engineering should be retained to assist in documenting all site grading.

Mitigation of any unsuitable fill, organics, debris, high plasticity clay, or soft soils will require engineering review and judgement. That judgement should be provided by one of our representatives. In addition, regular documentation of embankment fill materials, moisture conditioning and compaction will be required. We recommend that we be retained to provide the necessary construction observation during site grading.

VARIATION OF SUBSURFACE CONDITIONS, USE OF THIS REPORT, AND WARRANTY

The conclusions and recommendations contained herein assume the soil conditions encountered in the explorations are representative of the overall site conditions. This report is intended for site grading only and does not include recommendations for building foundations or pavements. The above recommendations assume we will have the opportunity to approve the re-use of Select Site Fill material and be present during grading to confirm subgrade conditions. No changes to the enclosed recommendations should be made without our approval. We will assume no responsibility or liability for any engineering judgement, inspection, or testing performed by others.

This report was prepared for the exclusive use of the Lincoln County School District, Devco Engineering, Inc., and their design consultants for the LCSD Holly Farm

Grading project in Lincoln City, Oregon. The information contained herein should not be used for other sites or for unanticipated construction without our written consent.

Contractors using this information to estimate construction quantities or costs do so at their own risk. Our services do not include any survey or assessment of potential surface contamination or contamination of the soil or ground water by hazardous or toxic materials. We assume those services, if needed, will be completed by others.

Geotechnical Investigation 9 Project No.: 2231009

Lincoln City, Oregon Lincoln County School District

Our work was done in accordance with generally accepted soil and foundation engineering practices. No other warranty, expressed or implied, is made.

It has been a pleasure assisting you with this phase of your project. Please do not hesitate to call if you have any questions or if we can be of further assistance.

Sincerely, FOUNDATION ENGINEERING, INC.

Mallory L. McAdams, P.E. Mel McCracken, P.E., G.E.

Project Engineer Senior Geotechnical Engineer

MLM/MJM/lh

Enclosure

Appendix A Figures

Foundation Engineering, Inc.

Professional Geotechnical Services

DRAFT

NVilleneuve Image

NOTE:

MAP OBTAINED FROM THE OREGON DEPARTMENT OF TRANSPORTATION

WEBSITE (WWW.ODOT.GOV)

SCALE IN FEET

0 1,000 2,000 4,000

SITE

PROJECT NO.

FIGURE NO.

DRAWN BY:DATE:

Foundation Engineering, Inc.

Professional Geotechnical Services

1A

VICINITY MAP

LCSD HOLLY FARM GRADING

LINCOLN CITY, OREGON2231009 MAY 2023 MLM

X

X

BH-2

BH-1

BH-3

Approximate underdrain location

Approximate area of existing fill

Approximate area of existing fill Foundation Engineering Boring

LEGEND

BH-1

NOTES:

1. BORING LOCATIONS ESTABLISHED REFERENCING EXISTING LANDMARKS AND ARE APPROXIMATE.

2. SEE REPORT FOR A DISCUSSION OF SITE CONDITIONS.

3. TOPOGRAPHIC SURVEY PROVIDED BY DEVCO ENGINEERING, INC.

SCALE IN FEET

0 50 100 200

Foundation Engineering, Inc.

Professional Geotechnical Services

PROJECT NO.

FIGURE NO.

DRAWN BY:DATE: 2A

EXISING TOPOGRAPHY & BORING LOCATIONS

LCSD HOLLY FARM GRADING

LINCOLN CITY, OREGON2231009 MAY 2023 MLM

DRAFT

AutoCAD SHX Text

SILT FENCING

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SILT FENCING

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SILT FENCING

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SILT FENCING

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SILT FENCING

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SILT FENCING

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SILT FENCING

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SILT FENCING

AutoCAD SHX Text

GRAVEL DRIVE

AutoCAD SHX Text

GRAVEL DRIVE

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GRAVEL DRIVE

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EX. BUILDING

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EX. BUILDING

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EX. SEPTIC TANK LID

AutoCAD SHX Text

RIM=201.9

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IRR

AutoCAD SHX Text P

AutoCAD SHX Text

EX. CULVERT

AutoCAD SHX Text

IE 15" CPP=145.0

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OLD GRAVEL ROAD

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OLD GRAVEL ROAD

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SILT FENCING

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SILT FENCING

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EX. CULVERT

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IE 12" CPVC=165.3

Original ground surface

10 ft. minimum

Excavate key a minimum of 3 feet below existing grades.

Place, moisture condition and compact select on-site fill in horizontal lifts. Document compaction of individual lifts.

Bench embankment fill into existing slope for slopes greater than 10%

Excavate key at toe of slope

Foundation Engineering, Inc.

Professional Geotechnical Services

PROJECT NO.

FIGURE NO.

DRAWN BY:DATE:

EMBANKMENT FILL SECTION

LCSD HOLLY FARM

LINCOLN CITY, OREGON

MJM2231009

3A

MAY 2023

Appendix B Boring Logs

Foundation Engineering, Inc.

Professional Geotechnical Services

DRAFT

Professional Geotechnical Services IMPORTANT INFORMATION AND SYMBOLS

EXPLORATION LOG KEY

DISTINCTION BETWEEN FIELD LOGS AND FINAL LOGS

A field log is prepared for each exploration by our field representative. The log contains information concerning sampling depths and the presence of various materials such as gravel, cobbles, and fill, and observations of groundwater. It also contains our interpretation of the soil conditions between samples.

The final logs presented in this report represent our interpretation of the contents of the field logs and the results of the sample examinations and laboratory test results. Our recommendations are based on the contents of the final logs and the information contained therein and not on the field logs.

VARIATION IN SOILS BETWEEN EXPLORATIONS

The final log and related information depict subsurface conditions only at the specific location and on the date indicated. Those using the information contained herein should be aware that soil conditions at other locations or on other dates may differ. Actual foundation or subgrade conditions should be confirmed by Foundation Engineering during construction.

TRANSITION BETWEEN SOIL OR ROCK TYPES

The lines designating the interface between soil, fill or rock on the final logs and on subsurface profiles presented in the report are determined by interpolation and are therefore approximate. The transition between the materials may be abrupt or gradual. Only at boring or test pit locations should profiles be considered as reasonably accurate and then only to the degree implied by the notes thereon.

SS - 3 - 4

Bottom of Sample Attempt

Unrecovered Portion

Exploration Number

Recovered Portion

Top of Sample Attempt

Sample Type

Sample Number

SAMPLE AND TEST SYMBOLS

C - Pavement Core Sample

CS - Rock Core Sample OS - Oversize Sample (3-inch O.D. split-spoon)

S - Grab Sample SH - Thin-walled Undisturbed Sample SS - SPT Sample (2-inch O.D. split-spoon)

FIELD SHEAR STRENGTH TEST

Shear strength measurements on test pit side walls, blocks of soil or undisturbed samples are typically made with Torvane or Field Vane shear devices.

Values reported as undrained shear strength (Su) in tsf.

TYPICAL SOIL/ROCK SYMBOLS

GROUNDWATER

Groundwater Location

Date of Measurement(1/31/21)

Concrete

Organics

Clay Gravel

Silt

Sand Sandstone

Basalt

Siltstone

Standard Penetration Test resistance equals the number of blows a 140 lb. weight falling 30 in. is required to drive a standard split-spoon sampler 1 ft. Practical refusal is equal to 50 or more blows per 6 in. of sampler penetration.

Water Content (%)

UNIFIED SOIL CLASSIFICATION SYMBOLS

G - Gravel S - Sand M - Silt C - Clay Pt - Peat

W - Well Graded P - Poorly Graded L - Low Plasticity H - High Plasticity O - Organic

SSSH

Professional Geotechnical Services COMMON SOIL DESCRIPTION TERMS

EXPLORATION LOG KEY

Explanation of Common Terms Used in Soil Descriptions

Field Identification Cohesive Soils Granular Soils

SPT* Su** (tsf) Term SPT* Term

Easily penetrated several inches by fist. 0 - 2 < 0.125 Very Soft 0 - 4 Very Loose

Easily penetrated several inches by thumb. 2 - 4 0.125 - 0.25 Soft 4 - 10 Loose

Can be penetrated several inches by thumb with moderate effort. 4 - 8 0.25 - 0.50 Medium Stiff 10 - 30 Medium Dense

Readily indented by thumb but penetrated only with great effort. 8 - 15 0.50 - 1.0 Stiff 30 - 50 Dense

Readily indented by thumbnail. 15 - 30 1.0 - 2.0 Very Stiff > 50 Very Dense

Indented with difficulty by thumbnail. > 30 > 2.0 Hard

Term Soil Moisture Field Description Dry Absence of moisture. Dusty. Dry to the touch.

Damp Soil has moisture. Cohesive soils are below plastic limit and usually moldable.

Moist Grains appear darkened, but no visible water. Silt/clay will clump. Sand will bulk. Soils are often at or near plastic limit.

Wet Visible water on larger grain surfaces. Sand and cohesionless silt exhibit dilatancy. Cohesive soil can be readily remolded. Soil leaves wetness on the hand when squeezed. Soil is wetter than the optimum moisture content and above the plastic limit.

Term PI Plasticity Field Test Non-plastic 0 - 3 Cannot be rolled into a thread at any moisture.

Low Plasticity 3 - 15 Can be rolled into a thread with some difficulty.

Medium Plasticity 15 - 30 Easily rolled into thread.

High Plasticity > 30 Easily rolled and re-rolled into thread.

Term Soil Structure Criteria Stratified Alternating layers at least ¼ inch thick.

Laminated Alternating layers less than ¼ inch thick.

Fissured Contains shears and partings along planes of weakness.

Slickensided Partings appear glossy or striated.

Blocky Breaks along surfaces into smaller lumps or blocks. Slickensides may be visible.

Lensed Contains pockets of different soils.

Term Soil Cementation Criteria

Weak Breaks under light finger pressure.

Moderate Breaks under hard finger pressure.

Strong Will not break with finger pressure.

* SPT N-value in blows per foot (bpf) ** Undrained shear strength

Professional Geotechnical Services COMMON ROCK DESCRIPTION TERMS

EXPLORATION LOG KEY

Rock Quality Designation (RQD) is the cumulative length of intact rock core pieces 4 inches or longer (excluding breaks caused by drilling and handling) divided by run length, expressed as a percentage.

Explanation of Common Terms Used in Rock Descriptions

Field Identification UCS (psi) Strength Hardness

(ODOT)

Indented by thumbnail. R0 < 100 Extremely Weak Extremely Soft

Crumbles under firm blows with geological hammer.

Can be peeled by a pocket knife. R1 100 - 1,000 Very Weak Very Soft

Can be peeled by a pocket knife with difficulty, shallow indentations made by firm blow with geological hammer. R2 1,000 - 4,000 Weak Soft

Cannot be scraped or peeled with a pocket knife, specimen can be fractured with a single blow of geological hammer. R3 4,000 - 8,000 Medium Strong Medium Hard

Specimen requires more than one blow of geological hammer to fracture it. R4 8,000 - 16,000 Strong Hard

Specimen requires many blows of geological hammer to fracture it. R5 > 16,000 Very Strong Very Hard

Term (ODOT) Weathering Field Identification

Fresh Crystals are bright. Discontinuities may show some minor surface staining. No discoloration in rock fabric.

Slightly Weathered Rock mass is generally fresh. Discontinuities are stained and may contain clay. Some discoloration in rock fabric.

Moderatedly Weathered

Significant portions of rock show discoloration and weathering effects. Crystals are dull and show visible chemical alteration. Discontinuities are stained and may contain secondary mineral deposits.

Highly Weathered (Predominately Decomposed)

Rock can be excavated with geologist's pick. All discontinuities exhibit secondary mineralization. Complete discoloration of rock fabric. Surface of core is friable and usually pitted due to washing out of highly altered minerals by drilling water.

Decomposed Rock mass is completely decomposed. Original rock "fabric" may be evident (relict texture). May be reduced to soil with hand pressure.

Spacing (metric) Spacing (imperial) Spacing Term Bedding/Foliation < 6 cm < 2 in Very Close Very Thin (Laminated)

6 cm - 30 cm 2 in - 1 ft Close Thin 30 cm - 90 cm 1 ft - 3 ft Moderately Close Medium 90 cm - 3.0 m 3 ft - 10 ft Wide Thick

> 3.0 m > 10 ft Very Wide Very Thick (Massive)

Vesicle Term Volume Some vesicles 5 - 25%

Highly vesicular 25 - 50% Scoriaceous > 50%

Stratification Term Description Lamination < 1 cm (0.4 in) thick beds

Fissile Preferred break along laminations

Parting Preferred break parallel to bedding

Foliation Metamorpic layering and segregation of minerals

RQD % Designation RQD % Designation 0 - 25 Very Poor 75 - 90 Good 25 - 50 Poor 90 - 100 Excellent 50 - 75 Fair

Backfilled with bentonite chips

Groundwater encountered during drilling

SS-1-1

SS-1-2

SH-1-3

SS-1-4

SS-1-5

SS-1-6

SS-1-7

SS-1-8

SS-1-9

SS-1-10

SS-1-11

Soft SILT, scattered to some organics (ML/OL); dark brown, damp to moist, low plasticity, organics consist of fine roots, (topsoil/fill).

Medium stiff to stiff sandy SILT (ML); light grey to orange-brown and iron-stained, moist, low plasticity, fine sand, (fill).

Stiff clayey SILT, some sand (MH); light grey to orange-brown and iron-stained, moist, high plasticity, fine sand, (colluvium).

Wet below ±17.5 feet.

Medium dense clayey ROCK FRAGMENTS (GP); light brown and iron-stained, dry to moist, medium plasticity, fine sand-sized to coarse gravel-sized subangular rock fragments, (colluvium).

Very stiff to hard clayey SILT (MH); light grey-brown and iron-stained, damp, low to medium plasticity, (colluvium).

Stiff clayey SILT, some sand (MH); light grey-brown to orange-brown and iron-stained, moist, medium plasticity, medium sand, (colluvium).

BOTTOM OF BORING

162.7 5.8

156.0 12.5

150.3 18.2

143.5 25.0

136.5 32.0

132.0 36.5

SPT

N-Value

Moisture (%) Groundwater Log

Depth

Depth and

Comments

Core Recovery (%)

RQD (%)

0 50 100

Elev. Backfill/ Installations/

(ft)

Sample Number and Location

Soil / Rock Description

2231009

BORING LOG: BH-1Project No.:

Surface Elevation:

Date of Boring: April 10, 2023

LCSD Holly Farm Grading

Lincoln City, Oregon

BH-1

168.5 feet (Approx.)

Professional Geotechnical Services Foundation Engineering, Inc.

chips

SS-2-1

SS-2-2

SS-2-3

SS-2-4

SS-2-5

SS-2-6

Soft SILT, scattered organics (ML); dark brown, moist, low plasticity, organics consist of fine roots, (topsoil).

Stiff SILT, some clay (ML); brown, moist, low to medium plasticity, (residual soil).

Very stiff to hard SILT (ML); light grey-brown and iron-and manganese-stained, damp, low plasticity, relict siltstone texture, (residual soil).

Extremely weak to very weak (R0 to R1) SILTSTONE;

dark grey, slightly weathered, (Yamhill Formation).

BOTTOM OF BORING

229.0 1.0

225.0 5.0

214.5 15.5

213.6 16.4

SPT

N-Value

Moisture (%) Groundwater Log

Depth

Depth and

Comments

Core Recovery (%)

RQD (%)

0 50 100

Elev. Backfill/ Installations/

(ft)

Sample Number and Location

Soil / Rock Description

2231009

BORING LOG: BH-2Project No.:

Surface Elevation:

Date of Boring: April 10, 2023

LCSD Holly Farm Grading

Lincoln City, Oregon

BH-2

230.0 feet (Approx.)

Professional Geotechnical Services Foundation Engineering, Inc.

90/11"

90/11" chips

Groundwater encountered during drilling

SS-3-1

SS-3-2

SS-3-3

SS-3-4

SS-3-5

SS-3-6

SS-3-7

SS-3-8

SS-3-9

Dense QUARRY ROCK (GW); dark grey, damp to moist, up to ±6-inch diameter rock, (fill).

Stiff SILT (ML); brown, damp to moist, low plasticity, (residual soil).

Very stiff to hard SILT (ML); light grey-brown and iron-and manganese-stained, damp, low plasticity, relict siltstone texture, (residual soil).

Extremely weak to very weak (R0 to R1) SILTSTONE;

dark grey, slightly weathered to fresh, (Yamhill Formation).

BOTTOM OF BORING

234.0 1.0

230.0 5.0

209.5 25.5

204.6 30.4

SPT

N-Value

Moisture (%) Groundwater Log

Depth

Depth and

Comments

Core Recovery (%)

RQD (%)

0 50 100

Elev. Backfill/ Installations/

(ft)

Sample Number and Location

Soil / Rock Description

2231009

BORING LOG: BH-3Project No.:

Surface Elevation:

Date of Boring: April 10, 2023

LCSD Holly Farm Grading

Lincoln City, Oregon

BH-3

235.0 feet (Approx.)

Professional Geotechnical Services Foundation Engineering, Inc.

50/1st 5"

50/1st 5"

Appendix C Laboratory Testing

Foundation Engineering, Inc.

Professional Geotechnical Services

DRAFT

LCSD Holly Farm Grading Project No.: 2231009

Table 1C. Moisture Contents (ASTM D2216), Percent Fines (ASTM D1140), and Atterberg Limits (ASTM D4318)

Sample Number

Sample Depth

(ft)

Moisture Content

Fines

Atterberg Limits USCS Classification LL PL PI

SS-1-1 2.5 - 4.0 48.4

SS-1-2 5.0 - 6.5 69.3 55.1

SH-1-3 7.5 - 9.5 59.2

SS-1-4 9.5 - 11.0 60.3

SS-1-5 12.5 - 14.0 55.9

SS-1-6 15.0 - 16.5 59.3

SS-1-7 17.5 - 19.0 60.6 92 59 33 MH

SS-2-1 2.5 - 4.0 51.1

SS-2-2 5.0 - 6.5 62.1

SS-2-3 7.5 - 9.0 55.2

SS-3-1 2.5 - 4.0 45.9

SS-3-2 5.0 - 6.5 65.1

SS-3-3 7.5 - 9.0 63.5

SS-3-4 10.0 - 11.5 58.9

SS-3-5 12.5 - 14.0 48.2

SS-3-6 15.0 - 16.5 63.6

SS-3-7 20.0 - 21.5 61.0

SS-3-8 25.0 - 26.5 56.8

Appendix D Previous Test Pits

Professional Geotechnical Services

Figure 1. Preliminary Site Plan LCSD Holly Farm Site NE Devils Lake Blvd.

Lincoln City, Oregon

Legend

Alternative Development Area

Test Pit Location

Fill

LCSD Parcel

Proposed Building Site

Slope Stability Hazard

900 ft

N

N © 2017 Google

© 2017 Google

© 2017 Google

December 6, 2017

LCSD – Holly Farm Site Geotechnical Investigation – Appendix B NE Devils Lake Road Project No. 2177183 Lincoln City, Oregon

Geotechnical Investigation LCSD – Holly Farm Site

NE Devils Lake Road Lincoln City, Oregon

APPENDIX B

NARRATIVE TEST PIT SUMMARIES

Logged on November 27, 2017

Test Pit: TP-1

Depth (feet) Material Description Notes/Sampling

0 to 1.9 Soft SILT with some organics and trace sand; dark brown, moist, loosely structured with abundant roots in upper foot, (Topsoil).

Grass with scattered trees and brush surrounding.

1.9 to 3.3 Medium stiff clayey SILT with some sand;

orange-brown, moist, medium plasticity.

S-1-2 @ 2’-3’

3.3 to 11.0 Stiff clayey SAND with some silt; grey, red-brown and black, slightly moist, deeper material includes some cementation with gravel sized fragments, (decomposed siltstone).

No ground water infiltration observed.

LCSD – Holly Farm Site Geotechnical Investigation – Appendix B NE Devils Lake Road Project No. 2177183

Test Pit: TP-2

0 to 1.0 Soft SILT with some organics; dark brown, moist, loosely structured, (Topsoil).

1.0 to 2.3 Medium stiff clayey SILT with some sand;

orange-brown, moist, medium plasticity.

2.3 to 5.5 Stiff sandy CLAY; grey, orange-brown and black, moist, some cementation with gravel sized fragments, (decomposed siltstone).

Slight to moderate ground water infiltration below 3.8’.

LCSD – Holly Farm Site Geotechnical Investigation – Appendix B NE Devils Lake Road Project No. 2177183

Test Pit: TP-3

0 to 1.0 Soft organic SILT; dark brown, moist, low plasticity, loosely structured, (Topsoil).

Test pit excavated near scarp.

1.0 to 4.0 Medium stiff silty CLAY with trace sand;

4.0 to 9.0 Stiff sandy CLAY; grey, red-brown, grey and black, moist, some cementation with gravel sized fragments, (decomposed siltstone).

Slight ground water infiltration noted below 8 feet.

LCSD – Holly Farm Site Geotechnical Investigation – Appendix B NE Devils Lake Road Project No. 2177183

Test Pit: TP-4

0 to 1.7 Soft organic SILT; dark brown, moist, moderate roots, loosely structured,

1.7 to 6.3 Soft to medium stiff clayey SILT with trace sand; light brown, moist, medium plasticity.

S-4-1 @ 3’-4’

6.3 to 7.0 Stiff clayey SAND; grey, orange-brown and some black staining, moist, (decomposed siltstone).

noted.

LCSD – Holly Farm Site Geotechnical Investigation – Appendix B NE Devils Lake Road Project No. 2177183

Test Pit: TP-5

0 to 1.9 Soft organic SILT; dark brown, moist,

1.9 to 3.8 Soft to medium stiff clayey SILT with trace sand; brown, moist, medium plasticity.

3.8 to 11.0 Stiff silty CLAY with some sand; grey, orange-brown with black staining, very moist to wet, moderate cementation with relict structure and jointing below ±7 feet, (decomposed siltstone).

Moderate to heavy ground water infiltration noted below 7.5 feet.

LCSD – Holly Farm Site Geotechnical Investigation – Appendix B NE Devils Lake Road Project No. 2177183

Test Pit: TP-6

0 to 2.9 Soft organic SILT; dark brown, moist,

2.9 to 5.6 Medium stiff sandy CLAY; light brown with some iron-staining, moist, medium plasticity, some cemented fragments.

5.6 to 14.0 Stiff clayey SILT with some sand; light brown with iron staining, moist to very moist, fragments with moderate cementation and relict structure, (decomposed siltstone).

S-6-1 @

LCSD – Holly Farm Site Geotechnical Investigation – Appendix B NE Devils Lake Road Project No. 2177183

Test Pit: TP-7

0 to 2.0 Soft organic SILT; black, moist, fine to

2.0 to 7.0 Soft to medium stiff silty CLAY with trace sand; brown to orange-brown, wet, medium plasticity.

7.0 to 9.0 Stiff sandy CLAY with some silt; grey, red-brown with black staining, very moist to wet, medium plasticity, (decomposed siltstone).

Moderate to slight ground water infiltration noted below 3 feet. Minor caving of test pit side walls.

LCSD – Holly Farm Site Geotechnical Investigation – Appendix B NE Devils Lake Road Project No. 2177183

Test Pit: TP-8

0 to 1.8 Soft organic SILT; black, moist, fine to

1.8 to 2.6 Medium stiff silty CLAY; brown, moist,

2.6 to 14.0 Medium stiff to stiff silty CLAY with some sand; brown to light brown with iron staining, moist, fragments with moderate cementation and relict structure and jointing, (decomposed siltstone).

S-8-1 @ 12’-14’

LCSD – Holly Farm Site Geotechnical Investigation – Appendix B NE Devils Lake Road Project No. 2177183

Test Pit: TP-9

0 to 1.8 Soft organic SILT with some clay; black, moist, fine roots, loosely structured,

1.8 to 3.5 Medium stiff silty CLAY with trace sand;

brown, moist, medium plasticity.

3.5 to 6.0 Stiff clayey SILT with some sand; grey and brown with heavy iron-staining, very moist to wet, cemented fragments with relict structure noted, (decomposed siltstone).

Moderate ground water infiltration noted below 4.5

LCSD – Holly Farm Site Geotechnical Investigation – Appendix B NE Devils Lake Road Project No. 2177183

Test Pit: TP-10

0 to 8.0 Soft silty CLAY with some sand and organics; brown to light grey and black, moist, variable (FILL).

Moderate caving of test pit side walls

8.0 to 11.0 Soft to medium stiff organic SILT with some clay; black, moist to wet, medium plasticity, (FILL/Topsoil).

Slight ground water infiltration noted below 9

LCSD – Holly Farm Site Geotechnical Investigation – Appendix B NE Devils Lake Road Project No. 2177183

Test Pit: TP-11

0 to 6.0 Soft silty CLAY with decomposed sandstone fragments; orange-brown, tan and grey, moist, variable, loosely structured, (FILL).

6.0 to 7.5 Soft organic SILT; black, moist, some coarse organics, (Topsoil).

7.5 to 11.0 Medium stiff sandy CLAY; red-brown with iron staining, moist, low plasticity, (decomposed siltstone).

LCSD – Holly Farm Site Geotechnical Investigation – Appendix B NE Devils Lake Road Project No. 2177183

Test Pit: TP-12

0 to 1.5 Soft organic SILT; black, moist, fine roots, loosely structured, (Topsoil).

1.5 to 7.0 Medium dense SAND; red-brown, moist, medium to fine grained.

7.0 to 9.0 Dense silty SAND with trace clay; grey and brown, moist, some cementation, (decomposed sandstone).

9.0 to 11.0 Stiff CLAY with some silt; grey, slightly moist, includes small cemented fragments, high plastic clay, (decomposed siltstone).

LCSD – Holly Farm Site Geotechnical Investigation – Appendix B NE Devils Lake Road Project No. 2177183

Test Pit: TP-13

0 to 1.0 Soft organic SILT; black, moist, fine to

1.0 to 2.0 Medium stiff silty CLAY; brown, moist,

2.0 to 10.0 Medium stiff to stiff clayey SILT with trace sand; grey and brown with some iron-staining, moist, includes some cementation and excavates in fragments, (decomposed siltstone).

LCSD – Holly Farm Site Geotechnical Investigation – Appendix B NE Devils Lake Road Project No. 2177183

Test Pit: TP-14

0 to 1.4 Soft organic SILT; black, moist, fine

1.4 to 4.3 Medium stiff clayey SILT with trace sand;

4.3 to 8.5 Stiff silty CLAY; grey and brown with iron-staining, moist, some cementation and relict structure and jointing, (decomposed siltstone).

LCSD – Holly Farm Site Geotechnical Investigation – Appendix B NE Devils Lake Road Project No. 2177183

Test Pit: TP-15

0 to 1.5 Soft organic SILT; black, moist, fine to

1.5 to 5.4 Medium stiff clayey SILT with some sand;

brown, moist, medium plasticity clay, fine to medium sand.

5.4 to 11.5 Medium stiff to stiff clayey SILT with some sand; red-brown, very moist to wet, medium plasticity clay, (decomposed siltstone).

LCSD – Holly Farm Site Geotechnical Investigation – Appendix B NE Devils Lake Road Project No. 2177183

Test Pit: TP-16

0 to 2.3 Soft organic SILT; black, moist, fine

2.3 to 5.5 Medium stiff CLAY with some silt and sand; grey with some brown, moist, high plasticity.

5.5 to 7.0 Medium stiff to stiff sandy CLAY; grey and light brown, moist to very moist, medium plasticity clay, (decomposed siltstone).

2231009 - gint logs bh-1 to bh-3 (5-18-23).pdf

LCSD Holly Farm Grading - Draft text(5-18-23).pdf