Physical_Data_Geotech_Report__02-16_Lakeshore.pdf

Geotechnical Investigation Report

Lakeshore Drive Phase 2 Cascade, Idaho

02718

February 2, 2016

WFLH Geotechnical Report #02-16

Cascade, Idaho

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TABLE OF CONTENTS

PAGE

1.0 EXECUTIVE SUMMARY

2.0 INTRODUCTION

2.1 Purpose and Scope of Work

2.2 Project Description

2.3 Geology

2.4 Site Conditions

3.0 METHOD OF STUDY

3.1 General Reconnaissance

3.2 Field Explorations

3.3 Laboratory Evaluation

4.0 SUBSURFACE CONDITIONS

4.1 Generalized Subsurface Profile

4.2 Groundwater

4.3 Frost Susceptibility

4.4 Corrosion Soil and/or Rock and Water Conditions

5.0 DESIGN RECOMMENDATIONS

5.1 General

5.2 Earthwork

5.2.1 Roadbed Preparation and Pavement Surface Grading

5.2.2 Embankments and Permanent Fill Slopes

5.2.3 Backfilling Utilities Trenches

5.3 Pavement Sections

5.3.1 Design Criteria

5.3.2 Flexible Pavement Design

5.3.3 Tack Coat

5.3.4 Specifications for Cement-Treated Subbase

5.3.5 Mix Design

5.3.6 Recycled Asphalt Pavement Preparation

5.3.7 Connection to Existing Roadway Pavement and Urban Approaches

5.3.8 Seal Coat

5.3.9 Construction

5.3.10 Compaction

5.3.11 Alternative Mix Design Requirements

5.3.12 Mircrocracking

5.3.13 Trafficking

5.3.14 Base and Hot Mix Asphalt Placement

5.3.15 Notes to Designer:

5.3.16 pH of Subgrade Soil and Cement-Treated Subbase

5.4 Structural Backfill

5.5 Soft Spot Repair

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5.6 MSE Retaining Walls

5.6.1 Design Methodology

5.6.2 Reinforcement

5.6.3 MSE Wall Backfill

5.6.4 Reinforced Backfill

5.6.5 Retained Backfill

5.6.6 Subgrade Preparation for MSE Walls

5.6.7 Notes to the Project Designers

5.6.8 Geotechnical Hazards

5.7 Storm Water Drainage

5.8 Subsurface Infiltration of Storm Water

5.9 Review of Final Design Drawings and Specifications

6.0 CONSTRUCTION CONSIDERATIONS

6.1 Temporary Excavations and Construction Slopes

6.2 Erosion Potential

6.3 Retaining Walls Foundations

6.4 Temporary Shoring/Cut Excavations

6.5 Blasting for Granite Excavations

7.0 REFERENCES

8.0 LIMITATIONS

APPENDICES

A Vicinity Map Exploration Location Map Site Photographs

B Logs of Exploration Triggs Wildcat DCP Logs Laboratory Test Reports

C Traffic Information Pavement Calculations

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1.0 EXECUTIVE SUMMARY

American Geotechnics performed a site reconnaissance and literature review, field investigation, laboratory testing on select samples, engineering analyses, and prepared this report for the Lakeshore Dr. Reconstruction Phase 2 (Phase 2) project in Cascade Idaho in accordance with a preapproved scope of work. The project is approximately 2,123 feet of Lakeshore Dr. between Par Dr. and Duffers Ln.

Our field reconnaissance included advancing three boring through the existing roadway, advancing three Triggs Wildcat dynamic cone penetrometer (DCP) tests at the toe of existing embankments anticipated to be widened, and using adjacent field investigation results from the Lakeshore Dr. Reconstruction Phase 1 (Phase 1) project from Old State Highway to Par Dr. The existing Lakeshore Dr. roadway between Par Dr. and Duffers Ln. consists of asphalt concrete over a base varying in materials and consisting of asphalt-treated Poorly Graded Sand with Silt and Gravel (SP-SM), Silty Sand with gravel (SM), and Poorly Graded Gravel with Silt and Sand (GP-GM). The pavement base is underlain with Silty Sand (SM) and Clayey Sand (SC-SM) fill on top of native Silt (ML) and weathered granitic rock and sand (SP). Groundwater was not encountered during the field excavation, but is anticipated to be at depths of up to 10 feet below the existing ground in the roadway and shallower at the toe of the embankments in the adjacent golf course. The groundwater is anticipated to seasonally fluctuate due to precipitation and irrigation.

Traffic loads provided by Horrocks were adjusted using an approximate 2 percent growth rate to determine traffic loads and a traffic index for a 20-year flexible pavement analyses. Because the sampled soil conditions and traffic loads for the Phase 2 roadway are similar to those evaluated for the Phase 1 project, the recommendations for the Phase 1 project regarding pavement section, design requirements and construction considerations are expected to be appropriate for the Phase 2 project.

Recommendations include a reconstructed flexible pavement over an aggregate base, and a cement treated subbase. Additional recommendations are provided for reusing the existing asphalt, addressing and mitigating geotechnical hazards, and the design and construction of

American Geotechnics 2 improved drainage features, embankment construction, and MSE walls.

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2.0 INTRODUCTION

2.1 Purpose and Scope of Work

The general purposes of this investigation were to evaluate the subsurface conditions and provide geotechnical recommendations relating to the proposed general site preparation, pavements, and embankments design for the Lakeshore Drive Phase 2 (Phase 2) project. The investigation included a desktop review of available references, subsurface exploration, representative soil sampling, and field and laboratory testing. Our recommendations are based on engineering analyses consistent with the standard of care in Idaho. This report was prepared in general accordance with the Federal Highway Administration (FHWA) Draft Geotechnics Technical Guidance Manual Section 5.1.2 (2007).

This report presents the results of our geotechnical investigation performed for the proposed Lakeshore Drive Phase 2 project in Cascade, Idaho. The site is located as shown on the Vicinity Map, included as Figure 1 in Appendix A.

The work performed for this report was authorized by Horrocks Engineers with funding provided by Western Federal Lands (2015) and was conducted in general accordance with our original June 4, 2015, proposed scope of work and letter of understanding.

2.2 Project Description

The Lake Shore Drive Phase 2 project is in the western-central portion of Valley County. The project site is located in Township 14 North, Range 3 East, Section 35, Boise Meridian, in Cascade, Valley County, Idaho. Based on information provided to American Geotechnics by Horrocks Engineers (Horrocks, 2015), the proposed project consists of reconstructing approximately of 2,123 feet of Lakeshore Drive from approximately 77 feet south of Duffers Lane (Begin Project at Sta. 10+00) to 39 feet north east of Par Drive (End Project at Sta.

31+23.00) as shown in the attached Figure 1. The average elevation ranges from about 4855 feet to 4880 feet above mean sea level.

Anticipated project improvements include construction of:

· curb and gutter on both sides of the roadway,

· 5-foot wide bike lane on both sides of the roadway, American Geotechnics 4

· 12-foot wide flexible pavement lane in both the northbound and southbound directions, which is to include pulverizing the existing asphalt concrete and using the pulverized asphalt concrete and underlying aggregate base removed together (referred to as reclaimed asphalt pavement (RAP)) for use in the reconstructed pavement section and for backfill,

· where possible, roadways are to slope 2 percent or greater drain stormwater.

· roadway edge drains to shed storm water to the west to the golf course or to existing conveyance and drainage features,

· possible use of existing on-site subsurface retention and infiltration systems,

· cuts and embankments are anticipated to be up to 25 feet above the existing ground surface, and

· mechanically stabilized (MSE) retaining walls up to 10 feet (including foundation depth) may be required.

We understand the City of Cascade currently owns about 80 feet of existing right-of-way and does not intend to acquire additional right of way to accommodate the proposed storm water retention and infiltration system.

2.3 Geology

The project area is situated within Long Valley, which is bounded on the west by the West Mountains, a block of tilted Columbia River basalt, and on the east by the Salmon River Mountains of the Idaho Batholith. Valley alluvium and mountain-slope colluvium dominate the geology of this part of Long Valley. The Phase 2 project site primarily overlies colluvium consisting of granitic, angular, coarse-grained particles of sand and gravel, outcrops of weathered granite and gneiss and several silty sandy to pebbly coarse sand fans and aprons formed in the foot slopes. The gently sloping colluvial slopes were formed during Holocene and Pleistocene ages. (Breckenridge, 2006).

2.4 Site Conditions

In general, Lakeshore Drive is cut and filled on a native alluvial and colluvial shoreline of Cascade Lake sloping towards the lake and to the west. In general, Lakeshore Drive slopes to the southwest and downward from Par Drive approximately 1.3 percent to 3.4 percent towards

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Duffers Lane. Existing cut slopes are as steep as 1(h):1(v) on the uphill side and as tall as 21 feet.

Existing embankment slopes are as steep as 1.4(h):1(v) on the downhill side and as tall as 17 feet. The slopes are rocky with occasional decomposed granite outcrops (Horrocks, 2015).

The project limits include forested residential properties on the east and the Cascade Golf Course on the west. Utilities include buried gravity flow and pressurized sewer lines, buried water lines, telecommunication lines, and storm drainage culverts.

The existing pavements are in poor condition and in need of replacement.

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3.0 METHOD OF STUDY

3.1 General Reconnaissance

Data, including a site plan provided by Horrocks Engineering, was reviewed before starting the field investigation. The site was visited on June 11, 2015, to mark the field exploration locations, coordinate a utility clearance for subsurface explorations, and assess site access.

We reviewed the United States Department of Agriculture (USDA) Soil Survey report (Rasmussen, 2012) for the site area to obtain information related to the typical soil associations expected in the upper 6 feet of the surficial soils. The soils in the upper 6 feet at the project location typically consist of alternating areas of Shellrock Loamy Coarse Sand and Gestrin Loam, which are non-plastic sands with silts and low plasticity silts and clays, respectively. The Gestrin Loam occurs in the lower drainage areas. Parent material of the Shellrock Loamy Coarse Sand is colluvium over residuum weathered from granite and/or quartz-diorite and the parent material of the Gestrin Loam is mixed alluvium and/or outwash derived from granite.

The USDA Soil Survey also indicated the depth to groundwater for this area is typically greater than 6-feet deep below ground surface (BGS) in the Shellrock Loamy Coarse Sand and roughly 2.5-feet in the Gestrin Loam areas. We also reviewed available well driller reports recorded by the Idaho Department of Water Resources (IDWR, 2015) to further determine soil conditions and obtain approximate groundwater depth at the site. The available well driller reports indicated groundwater was first encountered as shallow as 19 feet BGS. Thus, ground water in the area ranges from 2.5 feet to 19 feet BGS. Most likely, groundwater is 2.5-foot to 6-foot BGS in the low natural drainage areas near existing drainage culvert locations and low-lying embankment foundations.

On June 11, 2015, our observations indicated sand and clay fill was used for existing embankments in the existing natural drainages and the existing cuts were primarily in decomposed granite hillsides. The fill areas appeared to be up to 20 feet above the existing drainage inverts. The weathered granite appeared rippable up to a few inches into the surface, but we anticipate blasting will be required beyond a few inches below the material’s weathered surface because the weathering decreases and the strength increases. From conversations with Mr. Steve Yamamoto, Superintendent of Cascade Public Works, blasting was required during recent sewer line installation within the project site roadway (American Geotechnics, 2015).

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The Phase 2 project soils investigation, topography, and available soils databases indicate the soils anticipated to be encountered within 5 feet of the roadway surface are primarily clay, clayey sands, silt, silty sands, sands, and possibly decomposed granite. The Phase 1 Triggs Wildcat DCP TR-2 tested at the foot of the existing embankment near the intersection of Lakeshore Drive and Par Drive, showed the upper six feet of soils are very loose to loose (American Geotechnics, 2013). Probing and hand digging in the granite outcrops indicate the granite is highly weathered and friable on the surface with a decrease in weathering and increase in strength with depth.

3.2 Field Explorations

American Geotechnics explored the subsurface soil conditions by advancing three borings within the existing roadway to depths of up to 7.0 feet below the existing grade. We also advanced three Triggs Wildcat DCP tests near existing embankment’ toes where the embankments are anticipated to be widened. The DCP soundings were advanced up to 14.7 feet BGS. The Phase 1 project’s DCP TR-2 and Phase 2 project’s DCP TR-3, TR-4, and TR-5 results were correlated to equivalent standard penetration N-values for the soils encountered at the existing culvert location. The DCP field test results are included in Appendix C. The approximate locations of the test borings and DCPs are shown on Figure 2 in Appendix A. American Geotechnics recorded the subsurface conditions encountered in the test borings on logs of exploration, and the N-values on the DCP logs presented in Appendix B.

Subsurface drilling was accomplished using American Geotechnics’ trailer-mounted drill rig equipped with hollow-stem augers for soil sampling. Soil samples were obtained using standard and oversized split-spoon samplers driven with a hydraulic hammer. Soil samples were identified, described, and classified in the field using ASTM D 2488. Representative samples were packaged and transported to our laboratory.

3.3 Laboratory Evaluation

Representative samples were selected for laboratory testing to evaluate the pertinent physical and engineering properties of the soils. The laboratory test results are presented in the body of this report and in Appendix B. The following test methods and procedures were used:

· ASTM C117 – Standard Test Method for Materials Finer than 75-mm (No. 200) Sieve in Mineral Aggregates by Washing.

· ASTM C136 – Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates.

· ASTM D2216 – Standard Test Method for laboratory Determination of Water (Moisture)

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Content of Soil and Rock by Mass

· ASTM D2419 – Standard Test Method for Sand Equivalent Value of Soils and Fine Aggregate

· ASTM D2487 – Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)

· ASTM D2488 – Standard Practice for Description and Identification of Soils (Visual- Manual Procedure)

· ASTM D4318 – Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils

· IDAHO T-8 – Idaho R-Value

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4.0 SUBSURFACE CONDITIONS

4.1 Generalized Subsurface Profile

A generalized subsurface profile was developed for this project to provide a basis for discussion of soil conditions for the proposed roadway. This subsurface profile is based on Boring B-01 from the Geotechnical Investigation performed for the Phase 1 project (American Geotechnics, 2013), Borings B-5, B-6, and B-7 from the Phase 2 project’s field test data and exploration logs, and the laboratory testing program conducted by American Geotechnics.

Generalized Subsurface Profile(1)

Stratum Generalized Soil Description

I Asphalt concrete was encountered from the ground surface to depths ranging from

0.28 feet to 0.55 feet below ground surface (BGS). The asphalt concrete averaged approximately 0.37-feet thick.

II Poorly Graded Sand with Silt and Gravel (SP-SM) (asphalt treated), Silty Sand with Gravel (SM) and Poorly Graded Gravel with Silt and Sand (GP-GM) base was encountered from the bottom of the asphalt concrete to depths ranging 0.75 feet to

1.55 feet BGS. The average base thickness was approximately 1.05-feet.

III Silty Sand (SM); Silty Clayey Sand (SC-SM) fill was encountered from the bottom of the asphalt-treated base to 0.75 feet to 9.5 feet BGS in borings B-01, B-05, and B-07. The Silty Sand fill averaged approximately 6-feet thick.

Native Clayey Sand (SC) was encountered from 1.35 feet to 5.0 feet BGS in Boring B-06. The Lean Clay with Sand in Boring B-06 was approximately 4-feet thick

IV Native Silt with Sand (ML) was encountered from 9.5 feet to 10 feet BGS in Boring B-01. Visible outcrops show highly weather granitic sand (SP) and rock, that has been excavated for the existing roadway profile.

Notes:

1. See the logs of exploration (Appendix B) for detailed subsurface information.

Soils near the toe of embankment slopes are anticipated to be Silty Sand (SM) and Clayey Sand (SC). The correlated Triggs Wildcat DCP tests N-values ranged from 1 to 25 blows per foot of penetration and an average of 13 blows per foot of penetration indicating the subsurface soils at the toe of the embankment slopes ranged from very loose to dense.

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4.2 Groundwater

Groundwater was not observed at the time of our field investigation at depths of up to 10 feet below the existing ground surface. Local residents indicate the groundwater may emerge from a cut slope near Sta. 15+50 and the adjacent golf course personnel indicated ground water seeped from the ground from the fill slope at Sta. 18+60 (Horrocks, 2015). Groundwater levels may fluctuate seasonally in response to precipitation, land use, irrigation and other factors.

Monitoring of groundwater levels was beyond the scope of this investigation.

4.3 Frost Susceptibility

The USDA Soil Survey (Rasmussen, 2012) indicates the surface soils in the Phase 2 project have a moderate frost heave potential. Frost depth is estimated to extend up to 30-inches deep BGS.

The Clayey Sand sample collected from Boring B-7 is the same soil as the Clayey Sand sample taken from the Phase 1 project’s Boring B-4. Hydrometer test results for B-4’s Clayey Sand sample classified the Clayey Sand into the “F3” Frost Group per the Unified Facilities Criteria (UFC, 2001). Thus, although designers typically require a pavement thickness to be at least 70 percent of the local frost depth, which is 21-inches thick, research and experience with cement-treated base pavement in cold climates indicates cement-treated subbase pavements are not frost susceptible (Syed, 2007; Halsted, 2007; and PCA, 2013).

4.4 Corrosion Soil and/or Rock and Water Conditions

The USDA Soil Survey (Rasmussen, 2012) indicates that the corrosion potential of the near surface project soils are moderate for both concrete and uncoated steel. The National Soil Survey Handbook (NRCS, 2015) defines a moderate class for corrosion potential for uncoated steel is a soil having a resistivity of 2,000 to 5,000 ohm/cm and a moderate corrosion potential for concrete as soils having a sulfate or magnesium sulfate content of 1,000 to 7,000 ppm and a sodium chloride content of 2,000 to 10,000 ppm.

The USDA Soil Survey (Rasmussen, 2012) indicates these moderate class soils have a pH of 5.7.

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5.0 DESIGN RECOMMENDATIONS

5.1 General

Based on our observations, the site appears to be suitable for the proposed construction so long as all of the recommendations of this report are implemented. Notify American Geotechnics to review and possibly modify our recommendations if any revisions in the nature, design, or location of the proposed roadway are made at a later date that significantly alter the present definition of the project.

Construction is to follow the Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects FP-14 (Federal Lands, 2014), except as noted herein.

5.2 Earthwork

5.2.1 Roadbed Preparation and Pavement Surface Grading

For this report, Roadbed for Lakeshore Drive is defined as the upper 12 inches of the subgrade soil, immediately below the pavement ballast. Roadbed may be undisturbed native or properly compacted fill obtained from required project excavations or imported. Imported Roadbed materials are to classify as sand (classifying as SP, SW, SM, and SC according to ASTM D2487). The geotechnical exploration encountered clay (CL) subgrade soils in Borings B-7 at

1.5 feet BGS. Native clay soils (classifying as CL or CH according to ASTM D2487) are allowed in the Roadbed as long as the Roadbed can be compacted, as discussed herein. If acceptable compaction is not obtainable, the Contractor is to excavate, remove and replace clay soils within the Roadbed. The Engineer is to direct the Contractor where to waste the clay soils.

The subbase and base layer thicknesses shown herein are designed solely for post-construction traffic and may not be suitable to support repeated loading from heavy construction equipment.

Subbase and/or base layers may be damaged (e.g., rutting, waving, or loss of density) from repeated loading of heavy construction equipment.

The Contractor is to notify the Engineer of any poor quality Roadbed and Subgrade materials, soft spots, clays, silts, frozen, and/or organic materials as soon as they are encountered.

5.2.2 Embankments and Permanent Fill Slopes

Fill slopes on this project are also relatively minor. The anticipated maximum embankment slope heights for the project are shown in the table below.

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Anticipated Embankment Slope Heights

Approximate Stationing

Max. Height (ft)

Max. Height (ft)

West Side of Lakeshore Dr. East Side of Lakeshore Dr.

10+00 to 13+54 10 (Fill) 10+00 to 12+21 6 (Cut) 13+54 to 16+14 8 (Cut) 16+14 to 19+36 17 (Fill) 19+36 to 21+71 5 (Cut) 21+71 to 25+18 17 (Fill) 25+18 to 28+14 16 (Cut) 28+14 to 31+23 20 (Fill)

Excavate embankments in accordance with Section 204.06 of FP-14. Prepare embankment foundations in accordance with Section 204.09 of FP-14. Construct the embankments as specified in Section 204.10 of FP-14 using Select Borrow in accordance with Section 704.07 and having a friction angle of at least 32 degrees. The Contractor may construct embankments using RAP having a friction angle of a least 32 degrees and maximum particle size of 3-inches.

Embankments are to be widened with the roadway, graded to a slope no steeper than 2.0(H):1(V), and compacted to a minimum of 95 percent of maximum dry density in accordance with AASHTO T 99 and as required in Section 204.11 of FP-14.

The Contractor is to key all new embankment fill to be constructed on preexisting slopes steeper than 5(H):1(V) using horizontal benches having a vertical face of approximately 1 foot in height and in accordance with Section 204.09 of PF-14. Each bench is to be sloped to drain. As approved by the Engineer, the Contractor is to incorporate material excavated from the benches into the embankments or wasted as directed.

5.2.3 Backfilling Utilities Trenches

Materials obtained from required project excavations may be used to backfill utilities trenches as long as the material consists of sand, sand-gravel, and sand and rock mixtures (SP, SW, SM, or SC according to ASTM D2487) and having and a sand equivalent greater than of 30. Place utility trench backfill in uniform horizontal layers not exceeding 6 inches in loose thickness and in accordance with Section 209.09 of FP-14.

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In pavement and non-paved areas, compact each layer to at least 95 percent of the maximum laboratory dry density in accordance with AASHTO T 99 and in Section 209.10 of FP-14. Do not permit jetting or flooding of any backfill material in utility trenches.

5.3 Pavement Sections

5.3.1 Design Criteria

Traffic loads were determined using the 20-year traffic forecast provided by Horrocks in 2012, adjusted to 2016 to 2036 using the same growth rate of 2.1 percent and 3 percent estimated trucks (Horrocks, 2012). The resulting 20-year traffic projection is 160,280 Equivalent Single Axle Loads (ESALs) for years 2016 to 2036. Using a resilient modulus of 2,600 psi based on an R-value of 7 and the AASHTO 1993 pavement design method results in the same flexible reconstruction ballast sections as reported for Phase 1 project.

5.3.2 Flexible Pavement Design

Five flexible pavement alternatives were evaluated for the Phase 1 project from about 39 feet northeast of Par Drive to Lake Cascade Parkway. (American Geotechnics, 2013). The calculations for these pavement designs are not included herein, but are provided in the Phase I Report.

Horrocks performed a cost evaluation to verify the Flexible Reconstruction using a Cement- Treated Subbase with Mixed Reclaimed Asphalt Pavement (RAP) and Subgrade Soils is the thinnest section, requires the least amount of borrow materials, and is the least expensive section providing a similar performance as the other pavement sections (Horrocks, 2015). Thus, for the Phase 2 project, we recommend Flexible Reconstruction using a Cement-Treated Subbase with Mixed Reclaimed Asphalt Pavement (RAP) and Subgrade Soils similar to the reconstructed pavement used for the Phase 1 project.

The recommended Flexible Reconstruction using a Cement-Treated Subbase Section with Mixed Reclaimed Asphalt Pavement (RAP) and Subgrade Soils consists of preparing the Roadbed, hauling and placing the stockpiled RAP on top of the Roadbed, mixing water and cement to the proper depth within the Roadbed to create the cement-treated subbase. After thoroughly mixing and creating the cement-treated subbase, the cement-treated subbase is to be compacted and graded, then allowed to cure and be microcracked. Once cured and microcracked, base material is placed over the cement-treated subbase and hot mix asphalt is placed over the base materials.

The Table below shows the estimated material application rate and material unit weights needed

American Geotechnics 14 to construct a compacted 10-inch thick cement-treated subbase, assuming a 13 percent expansion for loose RAP and Roadbed. The mix design should be recalculated if the material unit weights vary by more than 5 pcf or if the material expansion varies by more than 2 percent.

Estimated Material Application to Obtain a 10-inch thick Cement-Treated Subbase Assuming 13% Expansion

Material Unit Weight

(pcf) Application

Type II Portland Cement 94 53 lb/sy RAP 145 2.25-inch thick loose Roadbed 125 8-inch thick compacted Notes:

1. The depth of admixing is approximately 11 inches.

Therefore, assuming compacted RAP and Roadbed materials swell to 1.13 times their original volume and the estimated unit weights shown in the table above, the Contractor is to place a 2.25-inch thick loose layer RAP on top of the prepared and compacted Roadbed. The Contractor is to spread 94 lb/sy of Type II portland cement with sufficient water to mix and compact the material to 98 percent maximum dry density at optimum moisture content in accordance with ASTM D558. The required depth of mixing will be about 11 inches.

The AASHTO 1993 Pavement Design Guide method resulted in the flexible Cement-Treated Subbase pavement section presented in the following table.

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Flexible Pavement Using Cement Treated Subbase of 20% Mixed Reclaimed Asphalt Pavement (RAP) with 80% Roadbed Soils Section

Material Material Thickness

(inches)

Hot Mix Asphalt SP-2 HMA, ½-inch, PG 58-34(1)

3.0 Placed using 2 lifts

¾-inch (Grade E) Crushed Aggregate for Base 5.0 Cement Treated-Subbase 20% RAP and 80% sandy Roadbed Soil. Mix 5% cement by weight of the RAP and Roadbed Soil.(2)

10.0

TOTAL (3) 18.0

Note:

1. Pavement binder grades specified represent minimum binder grades recommended for construction using

LTTPBIND 3.1 Beta software (Pavement Systems, 2005).

2. Subbase must be course grained soil classifying as Clayey Sand (SC) or Silty Sand (SM) having less than 36% passing the #200 sieve. Soils classified as clay (CL) in accordance with ASTM D2487 are not acceptable for use.

3. The frost depth at the project location is approximately 30-inches. However, research and experience with cement-treated base pavement in cold climates indicates cement-treated subbase pavements are not prone to damage due to frost heave (Syed, 2007; Halsted, 2007; and PCA, 2013).

5.3.3 Tack Coat

Tack Coat for paving is to be applied to existing pavement prior to placement of a new HMA course and between asphalt cement lifts. Apply CSS-1 diluted asphalt for Tack Coat at 0.08 gal/sy (Estimated) and in accordance with Section 412 of FP-14.

5.3.4 Specifications for Cement-Treated Subbase

Cement-Treated Subbase for this project is a mixture of aggregate material, granular soils, and RAP, combined with measured amounts of portland cement and water that hardens after compaction and curing to form a durable paving material. The mix design requirements are presented below.

5.3.5 Mix Design

In general, the site investigation and laboratory testing verified the sampled Phase 2 project soils appear to be very similar to the Phase 1 project soils. Thus, the mix design used to construct the Phase 1 project pavement is suitable for the Phase 2 project and is reproduced below.

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The cement-treated subbase mix was evaluated using combined silty sand (SM) subgrade samples from the Phase 1 project Borings B-1 and B-2 to create a composite silty sand subgrade sample (Sample #1). Likewise, combined clayey sand (SC) subgrade samples from the Phase 1 project Borings B-3 and B-4 to create a composite clayey sand subgrade sample (Sample #2).

For the Phase 1 project effort, RAP having a maximum 1/2-inch diameter particles were collected then thoroughly mixed with the composite subgrade samples such that 20 percent of the sample was RAP and 80 percent of the sample was a composite silty sand or clayey sand subgrade. These samples were compacted to determine the target optimum dry densities and target optimum moisture contents using AASHTO T-99 as shown in the table below.

Lakeshore Dr. Phase 1 Project’s Subbase Composite Soil Samples (American Geotechnics, 2013)

Composite Sample

I.D.

Classification Sample I.D. Boring

With 20% RAP by Weight

Target Dry

Density (pcf)

Target Optimum Moisture Content

(pcf)

#1 Silty Sand (SM) with RAP

BK-15 and SS-16 B-1

124.3 9.5

BK-2 and SS-33 B-2

#2 Clayey Sand (SC) with RAP

BK-11 and SS-12 B-3

121.2 11.2

BK-6 and SS-7 B-4

Notes:

1. Reclaimed asphalt pavement (RAP) is the term given to removed and/or processed materials containing asphalt and aggregates.

Each composite silty sand or clayey sand subgrade soil type was mixed with 4, 6, and 8 percent Type II Portland cement, moisture conditioned, molded and cured for 7 days to determine the amount of portland cement required to construct a sandy Roadbed/RAP cement-treated subbase.

The Portland Cement Association (PCA) recommends the desired cement-treated subbase compressive strength ranges from 300 psi to 400 psi (Halsted, 2007). Cement-treated subbase samples were cured in accordance with ASTM D1632 and then tested for compressive strength

American Geotechnics 17 in accordance with ASTM D1633.

Plotting the compressive strength test results on the chart shown below indicates both the project sampled silty sand and clayey sand subgrade soils reached a 7-day compressive strength between 300-psi to 400-psi using 4 percent to 5 percent Portland cement. We recommend the Contractor use 5 percent Portland cement with the RAP/subgrade soil materials.

4% 6% 8%

C om pr es si ve

S tr en gt h (p si

Cement Added by Weight

Cement-Treated Subbase Strength

Composite #1 Composite #2

Figure 1. Compressive Strength Test Results (ASTM D1633)

5.3.6 Recycled Asphalt Pavement Preparation

The Contractor is to document the existing pavement thickness every 0.15 miles in each lane and provide documentation the pavement thickness to the Engineer upon request. Spot check the measurements once or more per day or as required by the Engineer to verify accurate measurements are being made and that the full thickness of pavement is being pulverized.

The Contractor is to keep the fracture of aggregates to a minimum during asphalt and the underlying base material pulverization and mixing. It is anticipated that the pulverized material will swell 15 to 30 percent prior to compaction.

5.3.7 Connection to Existing Roadway Pavement and Urban Approaches

Where Phase 2 project pavements are to connect to existing pavements, the Contractor is to saw cut existing pavements adjacent to the area to be excavated that are designated to remain. Make

Area of Interest

American Geotechnics 18 saw cuts perpendicular to the roadway surface and at right angles to each other. Remove the pavement, base and subgrade to the depth shown in the project plans.

5.3.8 Seal Coat

We recommended a seal coat be applied within one-year after construction to the surface of the flexible pavement. The seal coat inhibits water intrusion through the asphalt concrete into the base, subbase, and subgrade soils; thereby, promoting longevity of the flexible pavement section.

We also recommend sealing all cracks on a regularly scheduled basis to inhibit water infiltration.

5.3.9 Construction

After excavating, removing, and stockpiling the existing RAP, the Contractor is to excavate or backfill to the proposed top of Roadbed elevation, then haul and spread the recommended RAP to the recommended loose lift thickness over the prepared and compacted Roadbed. The contractor will spread Type II Portland cement over the RAP, then add water and thoroughly mix the RAP, Roadbed and portland cement.

The Contractor is to use a pulverizer capable of fully mixing the soils, cement, and water to the full depth of the cement-treated subbase and approved by the Engineer.

The cement spreader for in-place mixing is to uniformly distribute the cement at the specified rate. Cement may be added in a dry or slurry form. If applied in slurry form, the slurry mixer and spreading equipment are to completely disperse the cement and water and maintaining uniform, consistent slurry without separation throughout the slurry placement.

Apply water through the mixer or with water trucks equipped with pressure-spray bars.

The contractor may not commence processing cement-treated subbase when the soil/aggregate or Roadbed is frozen, or when the air temperature is below 40°F (4°C). When applying the cement, the Contractor may not exceed the quantity of moisture that prevents a uniform and intimate mixture of the cement, RAP, and Roadbed soils during mixing operations. At the start of compaction, the quantity of moisture is to be within 2 percent of the optimum moisture content for the processed materials. The Contractor may not leave any pavement section undisturbed for longer than 30 minutes during compaction operations and is to complete all compaction operations within 2 hours from the start of mixing.

After placement, the Contractor may moist cure the cement-treated subbase for 48 hours to prevent excessive drying using water spray that will not erode the surface of the cement-treated

American Geotechnics 19 subbase or other an approved sealing membrane. The Contractor may immediately open completed portions of the cement-treated subbase to low-speed local traffic and to construction equipment, provided the moist curing operations are not impaired, and provided the cement-treated subbase is sufficiently stable to withstand marring or permanent deformation. If continuous moist curing is employed in lieu of a curing compound or subsequent surfacing within 7 days, the Contractor may open the cement-treated subbase to all traffic after the 7-day moist curing period, provided it has hardened sufficiently to prevent marring or permanent deformation.

5.3.10 Compaction

Uniformly compact the processed cement-treated material to a minimum of 98% of maximum dry density using AASHTO T-99 based on a moving average of five consecutive tests with no individual test below 96%. Determine the optimum moisture and maximum dry density of the material in the field prior to start of construction and during construction by a moisture-density test using ASTM D558 or AASHTO T 134.

Compact the processed cement-treated material with one or a combination of the following:

tamping or grid roller, pneumatic-tire roller, steel-wheel roller, vibratory roller, or vibrating-plate compactor.

5.3.11 Alternative Mix Design Requirements

The cement-treated subbase mix design, as described herein, is recommended, but the Contractor may provide an alternative mix design. Submit alternative mix designs to the Engineer for approval prior to pavement construction. The Contractor is to include details on soil/RAP gradation, cementitious materials, compressive strengths, and required moisture and density to be achieved during compaction in his mix design.

5.3.12 Mircrocracking

After curing for 2-3 days in non-winter months (average daily temperature is above 59oF) and 4 days in winter months (average daily temperature is below 60oF), microcrack the cement-treated subbase. Microcracking consists of performing three full passes (one pass is down and back) over the entire section traveling 2 to 3 mph using a 12-ton vibratory roller on maximum amplitude (Sebesta, 2006).

5.3.13 Trafficking

Completed portions of cement-treated subbase can be opened immediately to low-speed, local

American Geotechnics 20 traffic and to construction equipment, provided the curing material or moist curing operations are not impaired, and provided the cement-treated subbase is sufficiently stable to withstand marring or permanent deformation.

The Contractor may open pavement section to all traffic after the cement-treated subbase has received a curing compound or subsequent surface and is sufficiently stable to withstand marring or permanent deformation.

If continuous moist curing is employed in lieu of a curing compound or subsequent surfacing within 7 days, the Contractor may open the cement-treated subbase to all traffic after the 7-day moist curing period, provided the cement-treated subbase has hardened sufficiently to prevent marring or permanent deformation.

5.3.14 Base and Hot Mix Asphalt Placement

The Contractor may place subsequent pavement layers (base, hot mix asphalt) at any time after microcracking, as long as the cement-treated subbase is sufficiently stable to support the required construction equipment without marring or permanent distortion of the surface.

5.3.15 Notes to Designer:

We recommend the City of Cascade and Department of Lands select a Contractor with documented experience of having constructed a minimum of 74,000 square feet of cement-treated subbase for roadway within the last 5 years. We further recommend the Contractor’s Construction Supervisor be on site and responsible for all cement-treated subbase construction including Roadbed acceptance and acceptance of stockpiled recycled asphalt, base, and Roadbed materials. The Construction Supervisor is to have supervised the construction of a minimum of 74,000 square feet of cement-treated base or cement-treated subbase.

Construction quality assurance is critical to the success of this pavement. Quality control and assurance is to include properly documentation and preparation of the Roadbed, amount of cement placed into the mixture, admixing depth, and uniformity of the cement-soil mixing.

Prior to mobilization, we recommend the Contractor be required to submit a Plan of operations for approval. The Plan of Operations is to include a method to loosen and pulverize the entire existing roadway material to the width(s) shown on the typical section.

The Contractor is to pulverize the existing RAP and stockpile the pulverized materials for future use as subbase materials. If the RAP is used for other materials such as ¾-inch Crushed

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Aggregate for Base (Grade D in accordance with Section 703.05 of FP-14) or Embankment Material (Select Borrow in accordance with Section 704.07), the RAP used for those materials must conform to the appropriate gradation and properties as specified by Section 704 of FP-14 and in this report. Do not allow more than 50 percent RAP to be mixed with ¾-inch Grade D Crushed Aggregate for Base.

The RAP is to be pulverized to conform to the following gradation.

Sieve Sizes Percent by Weight Passing Sieve

3” 100

2” 95

#4 55

5.3.16 pH of Subgrade Soil and Cement-Treated Subbase

Quality Control includes using pH meter or pH indicating dye to perform pH testing of the RAP and Roadbed mixture prior to the Contractor adding cement. Perform pH testing randomly at three depths at the same location and at a maximum of 500-foot intervals per lane. The individual results are to be averaged at each location to determine as the average pH of the mixture at that station. A large variation of pH with depth and from location to location indicates insufficient mixing of cement, RAP, and Roadbed materials.

To provide an indication of the soil pH for the Roadbed and cement-treated base mixture, soil pH tests were performed on the Phase 1 project’s composite cement treated base samples 1 and 2.

The untreated sandy subgrade soils had a pH ranging from 8.6 to 8.8 and the same soil samples with 5 percent cement by weight had a pH ranging from 11.3 to 12. Therefore, adding 5 percent cement increased the soils pH 2.7 to 3.2 pH units as shown in the table below. Therefore, prior to adding the Portland cement, a RAP/Roadbed material will have a pH of approximately 9 and a thoroughly mixed cement-treated subbase will have a pH ranging between 11 to 12.

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Subbase Composite Soil and Cement-Treated Soil pH

Composite Sample I.D.

Sandy Subgrade Classification

Additive pH

#1 Silty Sand (SM) 5% Cement(1) 12.0

None 8.8

#2 Clayey Sand (SC) 5% Cement(1) 11.3

None 8.6 Notes:

1. Five percent by weight of the RAP/sandy subgrade material.

5.4 Structural Backfill

Material placed as structural fill in pavement areas, or as subbase is to conform to the requirements meeting Grade A Uncrushed Aggregate having a maximum particle size of 2.5-inches as shown in Table 703-2 of Section 703.05 of FP-14. Compact the Grade A Uncrushed Aggregate to a minimum of 95 percent of maximum dry density in accordance with AASHTO T 99 and Section 209 of FP-14.

5.5 Soft Spot Repair

The Contractor is to aerate and dry soft spots due to over-saturation back to optimum moisture and recompact the material at no cost to the owner. In areas where the required subgrade compaction is unattainable due to localized unsuitable material, the Contractor is to excavate the subgrade to a depth of 24-inches and backfill with Grade A Uncrushed Aggregate. Place backfill with compacted layers not exceeding 6 inches in depth compacted to a minimum of 95 percent of maximum dry density in accordance with AASHTO T 99 and Section 209 of FP-14. The Engineer is to direct Soft Spot repair work.

5.6 MSE Retaining Walls

Rising of the existing Phase 2 roadway elevation will necessitate the inclusion of embankments or Mechanically Stabilized Earth (MSE) walls along Lakeshore Drive. Design recommendations and construction considerations regarding the MSE walls are as follows.

The Contractor is to design the MSE walls in accordance with Sections 255 and 257 of FP-14.

We recommend an MSE wall system for the Phase 2 project, such as a Hilfiker welded wire wall, having a compressible face that can accommodate ground settlement.

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5.6.1 Design Methodology

Design the MSE wall and reinforced embankment fill in accordance with the AASHTO LRFD Bridge Design Specifications (2014), including all current revisions. The Contractor’s wall designer is to consider the following:

· Temporary surcharge or other loadings proposed by the Contractor including trucks, cranes, and stockpiles.

· Neglect passive resistance at the base of the MSE walls due to wall embedment in the wall design.

· Design the MSE walls and reinforced embankment fill for a minimum service life of 75 years, including corrosion.

· Select materials and perform construction and workmanship in accordance with the latest edition of the ISPWC and project special provisions.

5.6.2 Reinforcement

In order to reduce potential soil deformations, it is preferred that steel (inextensible or semi-extensible) soil reinforcement be used for the MSE walls for the Phase 2 project. MSE Wall materials shall comply with Section 720 of FP-14.

The wall designer is to submit corrosion calculations in accordance with the AASHTO method for sacrificial steel.

Construct the minimum length for the MSE reinforcement to be 0.7 times the height of the MSE wall or 8 feet, whichever is greater.

Identify and consider in the reinforcement design, any cutouts or proposed penetrations through the reinforced soil zone, including for drainpipes, drop inlet boxes, utility lines or other project components.

5.6.3 MSE Wall Backfill

Reinforced MSE wall backfill is to conform to the wall system manufacturer’s requirements for MSE backfill. Inhibit any penetration of deicing salts into the reinforced soil backfill by using a properly drained and buried liner.

American Geotechnics 24

5.6.4 Reinforced Backfill

Reinforced Backfill (stabilized volume) shall consist of Select Granular Backfill as defined in Section 704.08 of FP-14, having a minimum sand equivalent of 30, and a friction angle of at least 32degrees. Compact Reinforced Backfill a minimum of 95 percent of maximum dry density as required in Section 209.10 of FP-14.

5.6.5 Retained Backfill

Retained Backfill shall consist of Unclassified Borrow with Section 704.06 of FP-14, having a maximum particle size of 3-inches, having a minimum sand equivalent of 30, having a friction angle of at least 32 degrees. Compact the Retained Backfill (behind the stabilized volume) to a minimum of 95 percent of maximum dry density in accordance with AASHTO T 99 and as required in Section 209.10 of FP-14.

5.6.6 Subgrade Preparation for MSE Walls

Prepare subgrade for MSE walls in accordance with Section 209.07 of FP-14. Excavate soils from beneath the prism of the reinforced MSE wall areas to the design MSE wall base elevation.

Embed the design base elevation of the reinforced MSE wall areas to a minimum depth of 2 feet.

After excavation, moisture condition and proof roll the exposed subgrade area of the reinforced MSE wall areas with a minimum of 12 full coverages using a vibratory roller having a minimum dynamic force of 30,000 lb. per impact and at least 1000 vibrations per minute. The Engineer is to observe and document the proof rolling.

Loose or soft soils where encountered at the exposed subgrade surfaces that cannot be effectively compacted by repeated passes of the vibratory compactor, are to be removed and replaced as directed by the Engineer. Replaced these materials with properly compacted 3-inch uncrushed Aggregate having a minimum sand equivalent of 30 and compacted to a minimum of 95 percent of maximum dry density in accordance with AASHTO T 99 and as required in Section 209 of

FP-14.

The designer should specify a qualified geotechnical engineer is to perform observations and document the proof rolling of the subgrade surface in the reinforced MSE wall areas and the replacement of any soft soils with compacted granular fill, as discussed above.

5.6.7 Notes to the Project Designers

We understand the Contractor’s wall designer will prepare the following documents.

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1. Situation and Layout Drawing

2. Design and General Notes Drawing

3. MSE Wall Design Drawing

Provide the following information on the drawings for the Contractor’s wall designer.

· Stations, offsets, and elevations of the wall layout line. Show the wall layout lines on a plan drawing and indicate a typical section.

· Maximum cross-sections showing the relationship of the existing ground to the wall, backfills, and assumed excavations.

· Locations of proposed penetrations through the reinforced zone, including drainpipes and guardrails. Except for gas lines, do not place utilities longitudinal to the wall within the reinforced zone. Gas lines less than 4 inches in diameter may be placed longitudinal to the wall in the reinforced zone provided the gas line is sleeved and does not interfere with the MSE wall reinforcement.

· The original ground line and the finish grade line at the toe of the wall.

· High groundwater elevation, if applicable.

· Foundations are buried 30 inches BGS.

· Minimum 4-foot-wide horizontal bench at the toe of the wall.

· Estimated seismic acceleration values as provided in the Geotechnical Hazards section of this report.

· The MSE wall supplier may apply design soil parameters, as shown on the following table, to both internal and external long-term stability analysis of the MSE walls.

American Geotechnics 26

MSE Wall Soil Properties for Long-Term Stability Analysis

Material Moist Unit

Weight (pcf)

Cohesion (psf)

Friction Angle

(degrees)

Allowable Bearing

(psf) Reinforced MSE Backfill 130 0 34 Not Applicable Retained Backfill 130 0 30 Not Applicable

Foundation Soil 100 0 20 1,500

Loose or soft soils were encountered within the project boundaries that could require over-excavation to meet the material properties above for the native soils. See the Section 5.6.5 above for subgrade preparation for MSE walls.

5.6.8 Geotechnical Hazards

This section presents a discussion of the geotechnical hazards and the potential impacts on the proposed project.

Settlement and Embankment Foundations

The existing Phase 2 project’s pavement surface does not exhibit evidence of subsidence associated with the consolidation of fine grained embankment materials. Clay and silt deposits were observed in the Phase 2 project explorations and were also described in the NRCS soils data base. Some settlement could occur in these subgrades soils when overlain with new embankments soils where the existing embankments are widened. Thus, embankment foundations and MSE wall shallow foundations may require over-excavation up to 7 feet BGS and backfilled with compacted crushed aggregates having a nominal maximum 3-inch diameter in accordance with the Structural Backfill as specified in Section 704.04 of

PF-14.

Seismic Risk

Based on the IDWR well driller’s reports (2015) and our understanding of the project geology, the…