Palmer_Jct_Final_Geotechnical_Report__Recommedations_GR_05-15_(8_13_15).pdf

Memorandum

Western Federal Lands Highway Division 610 E. Fifth Street

Vancouver, WA 98661-3801

Project: OR PFH 146 (4) Date: March 8, 2016 Palmer Junction Road MP 0.0 to MP 15.1

From: Nathan Jenks WFL Supervisory Geotechnical Engineer

To: Project File

Subject: Geotechnical Report No. 05-15

The Palmer Junction Road MP 0.0 to MP 15.1 project is a roadway resurfacing project that includes two large aquatic organism passage structure replacements and areas of shoulder stabilization.

The Palmer Junction Road Final Geotechnical Report & Recommendations was completed in August 2015. The report was for a project much broader in scope than the current Palmer Junction Project.

The Geotechnical Report will be provided as physical data for prospective bidders; however bidders should reference the plan sheets for mitigation and repair locations.

(Intentionally left blank)

Geotechnical Report No. 05-15

August 2015

Palmer Junction Road Final Geotechnical Report & Recommendations

OR PFH 146(4)

Union County, Oregon

CONTENTS Page

1. INTRODUCTION AND SCOPE 1

2. CLIMATE, GEOLOGIC SETTING & SITE CHARACTERIZATION 3

2.1 Climate 3

2.2 Geologic Setting 4

2.3 Project Site Characterization 5

3. SUBSURFACE INVESTIGATIONS & LABORATORY TESTING PROGRAM 5

3.1 Subsurface Drilling Investigations & Procedures 5

4. FIELD RECCONNAISSANCE & OBSERVATIONS 9

5 MITIGATION CATEGORIES 10

5.1 Over-steepened Roadway Embankments – Category I Mitigation Locations 10

5.2 Over-steepened Roadway Embankments – Category II Mitigation Locations 13

5.3 Over-steepened Roadway Embankments & Slumping Pavement Areas – 14 Category II Mitigation Locations

5.4 Gravity Walls Section, Stations XX+XX to XX+XX – Category IV Mitigation Location 15

5.5 Fatigue Failure Areas – Category V Mitigation Locations 15

6 MITIGATION CATEGORY REPAIR RECOMMENDATIONS 16

6.1 Category I Repair Recommendations 16

6.2 Category II Repair Recommendations 17

6.3 Category III Repair Recommendations 18

6.3.a Deep Patch Repair, Type 1 18 6.3.b Shoulder Support with Slope Armor Repair 19

6.4 Category IV Repair Recommendation – Gravity Walls Section 21

6.5 Category V Repair Recommendations 22

6.6 Construction Advisory 23

7 GORDON CREEK AND SOUTH FORK CABIN CREEK CULVERT 25

REPLACEMENT LOCATIONS

8 PAVEMENT RECOMMENDATIONS 26

TABLES Page

TABLE 1 Temperature & Precipitation & Snowfall Data, 1981 - 2010 3

TABLE 2 Subgrade Boring Locations, Drilling Date, Hole Depth, Pavement 6 Structure Thicknesses, & Interpreted USCS Soil Identification

TABLE 3 Geotechnical Test Hole Locations, Date of Drilling, Hole Depths, 8 Soil Types, Depth to Bedrock, and Groundwater

TABLE 4 Category I Mitigation Locations 11

TABLE 5 Category II Mitigation Locations 13

TABLE 6 Category III Mitigation Locations 14

TABLE 7 Category V Mitigation Locations 15

TABLE 8 Reinforced Shoulder Stabilization Locations 18

TABLE 9 Deep Patch Repair, Type 1 Locations 19

TABLE 10 Shoulder Stabilization with Slope Armor Mitigation Locations 20

TABLE 11 Deep Patch, Type 2 Mitigation Limits 22

TABLE 12 Subexcavation Repair Locations 23

FIGURES Page

FIGURE 1 Project Location Map 1

FIGURE 2 Project Vicinity Map 2

FIGURE 3 Site Geology 4

FIGURE 4 Elevation Profile 5

FIGURE 5 Deep Shoulder Repair Detail (Conceptual) 16

FIGURE 6 Shoulder Stabilization Repair Detail (Conceptual) 17

FIGURE 7 Deep Patch Repair, Type 1 Detail (Conceptual) 29

FIGURE 8 Shoulder Support with Slope Armor Repair Detail (Conceptual) 20

FIGURE 9 Deep Patch Repair, Type 2 Detail (Conceptual) 21

FIGURE 10 Subexcavation Repair Detail (Conceptual) 22

APPENDICES

APPENDIX A Project Photos

APPENDIX B Borings and Project Features Locations, USCS & AASHTO Soils Classification Systems Details, Soil Descriptive Terminology, Rock Descriptive Terms, & Boring Logs

APPENDIX C Pavement Design Memorandum

Final Geotechnical Report and Recommendations Geotechnical Report No. 05-15

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1. INTRODUCTION AND SCOPE

Introduction

The Palmer Junction Road Project is located in northeast Oregon near the Washington and Idaho borders. The beginning of the project is located slightly to the west of Elgin, Oregon and runs generally to the north. Elgin is located roughly north of, and east of, Pendleton and La Grande, Oregon, respectively. (Approximately 63 miles driving distance from Pendleton and 20 miles driving distance from La Grande. The project location is shown in Figure 1.

Figure 1: Project Location Map

Palmer Junction Road (FH 146, FR 63 and FR 62) is located in Union County. The project begins at the intersection of Middle Road and OR 204 just west of Elgin and extends in a general northerly direction for about 15.6 miles. The road provides access to the Umatilla National Forest and is maintained by Union County. A project Vicinity Map is shown as Figure 2.

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Figure 2: Project Vicinity Map

Scope

The Umatilla National Forest and Union County are considering improvements that involve about 15.6 miles of the Palmer Junction Road. The scope of the project includes:

• Pavement resurfacing improvements, including repair of edge cracking and failing shoulders,

• Repair of a section of road where gravity walls are located and settlement is occurring in the roadway,

• Improvements to deficient drainage structures located at Gordon Creek and South Fork Cabin Creek and improved fish passage at other locations. Project scope also includes replacement-in-kind of 30 inch culverts located at Partridge Creek and at Station 415+60.

Western Federal Lands Highway Division (WFLHD) is designing the road and fish passage improvements. Drainage and fish passage improvements have been addressed by the WFLHD Hydraulics Section in a memorandum entitled Palmer Junction Road Fish Passage Improvements AOP Hydraulics Report, dated December 1, 2014. Union County will perform some of the shoulder stabilization work on the project.

This memorandum provides geotechnical information and final recommendations for the design

OR PFH 146(4) P a g e | 3 of 27 of shoulder stabilization and provides final recommendations for the gravity walls section located at approximate milepost (MP) 5.8 (Stations 308+90 to 310+30).

Preliminary geotechnical information and recommendations were provided directly to the project design team through email or one-on-one meetings. A preliminary report or memorandum was not part of the project scope.

This report also includes the results of subsurface investigations comprised of 30 subgrade borings located between the BOP and EOP. Also included are the results of eleven geotechnical borings that were drilled at the Gordon Creek culvert (2), the Pine Creek culvert (1), the South Fork Cabin Creek Culvert (4), the Moses Creek culvert (1), and the Gravity Walls Section (3).

2. CLIMATE, GEOLOGIC SETTING, & SITE CHARACTERIZATION

2.1 Climate

The Rocky Mountains partly shield the vicinity of the project from strong arctic winds, so winters generally are not too severe, though cold. In summer, winds from over the Pacific Ocean are partially blocked. Days are hot, but nights are fairly cool. Precipitation is scant in summer.

As seen in Table 1, the total amount of precipitation averages about 24 inches per year, of which roughly 34 percent usually falls in April through September. Average seasonal snowfall is approximately 46 inches, primarily falling in November through March.

Table 1: Temperature, Precipitation and Snowfall Data 1) 1981 – 2010

Month Temperature Precipitation Snowfall 2)

Monthly Maximum

(oF)

Monthly Minimum

(oF) Monthly Average

(oF) Monthly Average

(inches) Monthly Average

(inches) January 38.2 23.2 30.7 3.17 14.2 February 43.6 23.9 33.7 2.33 9.3

March 52.5 29.0 40.7 2.20 2.3 April 60.1 32.7 46.7 1.99 0.5 May 68.7 38.8 53.7 2.23 0.0 June 76.1 44.0 60.1 1.75 0.0 July 85.9 46.8 66.4 0.70 0.0

August 86.2 45.5 65.8 0.66 0.0 September 77.7 38.1 57.9 0.82 0.0

October 63.6 31.4 47.5 1.70 0.0 November 46.9 28.2 37.6 3.12 4.4 December 37.4 21.9 29.6 3.07 15.2 Average = 61.4 33.6 47.5 --- ---

Total = --- --- --- 23.7 45.9

1) Long term monthly averages obtained from the National Climatic Data Center (NCDC) station in Elgin, OR Station ID: GHCND:USC00352597.

2) Snowfall averages are included in the Monthly Average Precipitation quantities shown. They have been broken out and shown for convenience.

(E.g., in the month of January the 3.17 inches of precipitation shown includes the 14.2 inches of average precipitation that would be expected in the form of snow.)

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2.2 Geologic Setting

The project is situated within two mapped geological units. It begins west of Elgin where it is shown to extend over lacustrine and fluvial sedimentary rocks, Cg, (Pleistocene) to about the location of the Gordon Creek culvert, as can be seen in Figure 3. The Cg material is described as unconsolidated to semi-consolidated lacustrine clay, silt, sand, and gravel; and in places includes some fluvial and eolian deposits and discontinuous layers of peat. It includes older alluvium and related deposits of Piper (1942), Willamette Silt (Allison, 1953; Wells and Peck, 1961), alluvial silt, sand, and gravel that form terrace deposits of Wells and others (1983), and Gresham and Estacada Formations of Trimble (1963). In places contains mollusks or vertebrate fossils indicating Pleistocene age; mostly deposits of late Pleistocene age, but locally includes some deposits of early Holocene age. Additionally, it includes Touchet Beds of Flint (1938), deposits of valley terraces of Newcomb (1965), and glacial lake sediments of Hogenson (1964).

North of Gordon Creek the alignment traverses through mapped Saddle Mountains Basalt, Tcs (upper and middle Miocene), described as petrographically diverse flows of basalt that erupted between about 13.5 and 6 million years ago (McKee and others, 1977; Swanson and others, 1979). Outcrops of basalt were observed in the upper portion of the project. (See photos 1 through 3 in Appendix A for some examples.)

Figure 3: Site Geology

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2.3 Project Site Characterization

The project site is located in an area of gently rolling slopes and having paved widths averaging at about 26 feet with narrow shoulders that are constructed on top of over-steepened embankments. Private residences are generally widely spaced.

The project begins at MP 0.0 (Station 0 + 36) at an elevation of about 2910 feet and ends at about MP 15.6 (Station 821+63) at approximately 2880 feet. (Elevation information obtained from Google Earth Pro with the alignment shown in Figure 3.) The maximum elevation is about 3135 feet and the minimum about 2800 feet.

3. SUBSURFACE INVESTIGATIONS & LABORATORY TESTING PROGRAM

3.1 Subsurface Drilling Investigations and Procedures

Subsurface investigations were performed that consisted of 30 subgrade borings (PJSG12-01 through PJSG12-30) and 11 deep-hole geotechnical borings (PJ12-01 through PJ12-11), both drilled in June, 2012 by Haz-tech Drilling Inc., Meridian, Idaho. WFLHD personnel field-logged the holes and prepared the final boring logs. Boring locations and logs appear in Appendix B.

The subgrade borings were generally drilled at half mile spacing and alternated left and right of centerline. The geotechnical borings were drilled at the Gordon Creek culvert (2), the Pine Creek culvert (1), the South Fork Cabin Creek Culvert (4), the Moses Creek culvert (1), and at the gravity walls section (3).

A 14 inch outside diameter (OD) solid stem auger was used for all subgrade holes. In the holes where augur refusal was encountered, either tightly nested cobbles, boulders, or top of bedrock were thought to be encountered. The geotechnical test holes were advanced using a Longyear CME-75 truck-mounted drill rig using an 8.25 inch OD hollow stem auger. Standard Penetration Tests (SPTs) were conducting using an automatic hammer with an efficiency rating of 84 percent. HQ-3 diamond bit rock coring tools were used to advance borings beneath the depth of refusal.

SPTs were carried out in the geotechnical test holes. The exception to this usually occurred in the upper 5 feet of the upper stratum where initial auguring was required to seat the drill rods.

SPT samples were obtained at intervals of 2.5 feet or 5.0 feet with a 3.0 inch OD (Dames & Moore) oversized split spoon sampler. Corrections were applied to the field penetration numbers (N values) to account for hammer energy efficiency and for the over-sized split-spoon samplers, resulting in standard penetration numbers shown in the boring logs as N60 values. In addition, corrections for overburden pressure were applied where granular soils were encountered to determine the standard penetration test values (N1)60. “Undisturbed” samples were obtained at depths of interest using 3 inch ID diameter thin-walled Shelby tubes. Core samples were obtained in some holes utilizing HQ-3 coring tools when bedrock was encountered. (It should be

OR PFH 146(4) P a g e | 6 of 27 understood that the N-values shown in the “N” column in the boring logs can be influenced by the presence of coarse gravel, cobbles, or boulders, which would tend to overstate the penetration resistance of the subsurface materials.)

It is generally understood implicitly that the materials and conditions encountered in the borings should only be considered to be representative of the subsurface conditions and materials encountered at the location of the test hole and the depth of the test at the time of drilling.

Subsurface groundwater conditions and material or depth at which a given material or groundwater is encountered can vary seasonally and between, or closely beyond, test hole locations.

Table 2 shows the subgrade hole designations, locations, and offsets, date of drilling, thicknesses of pavement components, and interpreted soil types encountered. No laboratory testing was performed. All soil classification descriptions are field interpretations by the WFL drill inspector. As shown in the table the encountered soil material types consisted of both granular and cohesive according to the United Soil Classification System (USCS). Encountered base materials were generally interpreted to classify as sandy gravel (GW or GP), silty, sandy gravel or sandy, silty gravel (GP-GM or GM or GM-SM), or silty, clayey gravel (GC-GM). Subbase materials encountered were interpreted largely as silty gravel (GM), clayey gravel (GC), silty, clayey gravel, (GC-GM), sandy, silty gravel (GP, GP-GM or GM-SM), sandy, clayey silty gravel (GP-GC), silty, gravelly clay (CL) or gravelly silt (ML). Subgrade materials were interpreted to classify as sandy, silty, gravelly clay (CL-CH), clayey silt or gravelly, clayey or gravelly silt (ML), silty clay (CL or CL-ML), gravelly, silty clay (CL-ML or CL), Appendix B contains the subgrade boring logs and details of the USCS.

Table 2: Subgrade Boring Locations, Drilling Date, Hole Depth, Pavement Structure Thicknesses, and Interpreted UCSC Soil Identification

Boring Designation

Station 1.)

/ Offset (ft) 1.), 2.) Drilling Date

Hole Depth

(ft)

Thicknesses 1) of

Pavement / Base

/ Subbase

Interpreted USCS Soil

Identification 2) of / Base

/ Subbase / Subgrade

Notes

PJSG12-01 MP 0.007

/ 7.2 Rt 6/22/2012 5.0

/ 11 / 18

GWS

/ GC

/ CL-CH

PJSG12-02 0.500

/ 5.9 LT 6/28/2012 5.0

6.5 / 11

/ 10.5

GWS

/ GM

/ ML-CL

PJSG12-03 1.000

/ 6.6 RT 6/28/2012 5.0

6.5 / 7.5 /16?

GM

/ GP-GM

No field description provided for the subgrade soils encountered.

PJSG12-04 1.500

/ 7.9 LT 6/28/2012 5.0

/ 3.5

/ 32.5

GWS

/ GPS & GP-GM

/ ML-CL

PJSG12-05 2.030

/ 6.9 RT 6/28/2012 5.0

/ 4

/ 19

GWS

/ GP-GM

/ MLG or FILL

Material encountered below subgrade indeterminable.

PJSG12-06 2.525

/ 7.6 LT 6/19/2012 5.0

Second layer of asphalt encountered below existing pavement structure.

1) Thicknesses shown in inches.

2) No laboratory testing performed. All soil types are interpreted.

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Table 2: Subgrade Boring Locations, Drilling Date, Hole Depth, Pavement Structure Thicknesses, and Interpreted UCSC Soil Identification (Cont.)

Boring Designation

Station 1.)

/ Offset (ft) 1.), 2.) Drilling Date

Hole Depth

(ft)

Thicknesses 1) of

Pavement / Base

/ Subbase

Interpreted USCS Soil

Identification 2) of / Base

PJSG12-07 2.923

/ 5.9 RT 6/28/2012 5.0

/ 10 / 24

GC-GM

/ CL

/ CL

PJSG12-08 3.472

/ 8.4 LT 6/28/2012 5.0

7.5 / 8.5 / 31

GWS

/ GC-GM

/ CL-ML

PJSG12-09 3.969

/ 5.5 RT 6/28/2012 1.4

/ 4.5

/ 5.5?

GM-SM

/ GM

/ Not Encountered

Refusal on large cobble or boulder

PJSG12-10 4.468

/ 6.2 LT 6/27/2012 1.5

/ 9?

/ Not Encountered

Refusal (on large cobble or boulder?)

PJSG12-11 4.973

/ 6.4 RT 6/27/2012 5.0

/ 4

/ 48

GM-SM

/ Not Encountered

/ MLG

PJSG12-12 5.523

/ 7.0 LT 6/27/2012 1.2

/ 2 / 4

GM-SM

/ MLG

/ Not Encountered

Refusal on large cobble or boulder

PJSG12-13 5.977

/ 5.9 RT 6/27/2012 5.0

4.5 / 7

/ 7.5?

GM-SM

/ GM-SM

/ MLG

PJSG12-14 6.529

/ 6.9 LT 6/27/2012 1.5

4.5 / 3

/ 10.5?

GM-SM

/ GM-SM

/ Not Encountered Refusal on boulder

PJSG12-15 6.955

/ 5.7 RT 6/27/2012 5.0

2.5 / 6.5 / 21

GM-SM

/ GM-SM

/ MLG or FILL

Material encountered below subgrade indeterminable.

PJSG12-16 7.621

/ 6.7 LT 6/27/2012 2.4

/ 3

/ 21

GM-SM

/ GM

/ Not Encountered

Refusal on large cobble or boulder

PJSG12-17 8.114

/ 5.4 RT 6/27/2012 3.1

/ 5

/ 14

GM-SM

/ GM-SM

/ MLG

Assumed refusal on large cobble, boulder, or top of bedrock

PJSG12-18 8.665

/ 6.4 LT 6/27/20122.1 2.1

4.5 / 5

/ 11.5

GM-SM

/ GM-SM

/ BEDROCK?

Refusal on large cobble, boulder or top of bedrock

PJSG12-19 9.100

/ 6.2 RT 6/27/2012 1.5

8.5 / 4.5 / 5?

GM-SM

/ GM-SM

/ Not Encountered

Refusal on large cobble, boulder or top of bedrock

PJSG12-20 9.647

/ 6.2 LT 6/27/2012 5.0

/ 9

/ 18

GM-SM

/ GPS

/ MLG

PJSG12-21 10.275

/ 6.2 RT 6/27/2012 5.0

/ 19 / 13

GM-SM

/ MLG

/ ML-CL

PJSG12-22 10.912

/ 6.89 LT 6/27/2012 5.0

/ 6

/ 15

GWS

/ GM-SM

/ CL

PJSG12-23 11.545

/ 5.9 RT 6/25/2012 2.1

6.5 / 5

/ 13.5?

GWS

/ GM-SM

/ Not Encountered

Refusal on large cobbles or boulder

PJSG12-24 12.064

/ 7.1 LT 6/25/2012 5.0

/ 6

/ 30

GWS

/ GM-SM

/ MLG

PJSG12-25 12.542

/ 7.0 RT 6/25/2012 5.0

/ 6

/ 18

GWS

/ GM-SM

/ GM-SM

PJSG12-26 13.092

/ 7.9 LT 6/25/2012 5.0

5.5 / 6.5 / 6?

GWS

/ GM-SM

/ MLG

1) Thicknesses shown in inches.

2) No laboratory testing performed. All soil types are interpreted.

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Table 3: Subgrade Boring Locations, Drilling Date, Hole Depth, Pavement Structure Thicknesses, and Interpreted UCSC Soil Identification (Cont.)

Boring Designation

Station 1.)

/ Offset (ft) 1.), 2.) Drilling Date

Hole Depth

(ft)

Thicknesses 1) of

Pavement / Base

/ Subbase

Interpreted USCS Soil

Identification 2) of / Base

PJSG12-27 13.535

/ 6.0 RT 6/25/2012 2.3

/ 2

/ 17

GWS

/ GM-SM?

/ GM-SM?

Refusal on nested cobbles or boulders

PJSG12-28 14.034

/ 7.0 LT 6/19/2012 2.6

/ 5

/ 19

GPS

/ GM-SM

/ Not Encountered

Refusal on possible old culvert

PJSG12-29 14.632

/ 6.2 RT 6/24/2012 5.0

6.5 / 5.5 / 48?

GWS

/ GP-GC

/ GP-GC

PJSG12-30 15.125

/ 6.2 LT 6/24/2012 5.0

6.5 / 9.5 / 33

GM-SM

/ GM-SM

/ MLG

1) Thicknesses shown in inches.

2) No laboratory testing performed. All soil types are interpreted.

Table 3 shows the geotechnical test hole designations, location and offsets, drilling date, hole depth, interpreted USCS soil types encountered, depth to bedrock and depth of groundwater during drilling. As can be seen in the table the soil material types consisted of both granular and cohesive according to the USCS. Granular materials were interpreted to classify as fill (FILL), poorly-graded gravel with sand (GP), poorly graded gravel with clay (GC), well graded sand (SW), clayey sand (SC), and sand with silt (SM) as examples. Examples of the interpreted cohesive soils are silty clay (CL-ML) and clay and gravelly clay (CL). The granular materials ranged from dense to very dense. Cohesive materials ranged from soft to very stiff.

Bedrock was identified as vesicular basalt, as defined in the geologic unit mapping discussed under Section 2. The basalt is described as slightly to highly weathered, with close to moderate fracture spacing and strong to very strong. Appendix B contains the geotechnical test hole boring logs and soil and rock descriptive terminology.

Table 3: Geotechnical Test Hole Locations, Date of Drilling, Hole Depths, Soil Types, Depth to Bedrock and Groundwater

Boring Designation

Location / MP Location

/ Offset (ft)

Date of Drilling

Hole Depth

(ft) USCS Soil Types

Encountered 1) Depth to

Bedrock (ft)

Depth of Groundwater

During Drilling (ft)

PJ12-01

Gordon Creek Culvert

/ 2.534 / 8.53 Lt

6/19/2012 31.5 GP, SW, GC Not encountered 11.0

PJ12-02

Gordon Creek Culvert

/ 2.534

/ 6.1 RT

6/19/2012 31.5 GP, SM, CL, Not encountered 11.3

PJ12-03

Pine Creek Culvert

/ 2.725

/ 14.5 LT

6/28/2012 28.2 CL-ML, ML, GC Not encountered 12.8

1) Interpreted USCS designations provided for interpreted native soils below FILL. In most holes FILL materials were encountered above native soils.

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Table 3: Geotechnical Test Hole Locations, Date of Drilling, Hole Depths, Soil Types, Depth to Bedrock and Groundwater (Cont)

Boring Designation

Location / MP Location

/ Offset (ft)

Date of Drilling

Hole Depth

(ft) USCS Soil Types

Encountered 1) Depth to

Bedrock (ft)

Depth of Groundwater

During Drilling (ft)

PJ12-04

South Fork Cabin Creek Culvert

/ 11.111

/ 5.5 RT

6/25/2012 32.7 CL-ML, CL, GP 25.0 19.8

PJ12-05

South Fork Cabin Creek Culvert

/ 11.111

/ 6.7 LT

6/26/2012 30.2 GC 20.0 Not encountered

PJ12-06

South Fork Cabin Creek Culvert

/ 11.111

/ 7.9 RT

6/26/2012 29.5 GC, GP 20.5 Not encountered

PJ12-07

South Fork Cabin Creek Culvert

/ 11.111

/ 7.7 LT

6/26/2012 31.2 GM 22.3 Not encountered

PJ12-08

Moses Creek Culvert

/ 14.006

/ 7.7 RT

6/24/2012 36.5 GM, OL, CL Not encountered Not encountered

PJ12-09

Concrete Gravity Wall Location / 5.845

/ 12.0 RT

6/19/2012 30.1 CL-ML 29.3 17.5

PJ12-10

Concrete Gravity Wall Location / 5.845

/ 9.8 LT

6/20/2012 31.5 CL, GC Not encountered 15.6

PJ12-11

Concrete Gravity Wall Location / 5.857

6/20/2012 36.5 GC Not encountered Not encountered

1) Interpreted USCS designations provided for interpreted native soils below FILL. In most holes FILL materials were encountered above native soils.

4. FIELD RECONNAISSANCE & OBSERVATIONS

WFLHD geotechnical personnel performed geotechnical site reconnaissance in September 2010 and April/May of 2012 to inspect the condition of the roadway and record observations.

Additional reconnaissance was performed in June 2012 during location markings for the subsurface investigations discussed under Section 4. The project was shelved briefly and a final reconnaissance was performed in April 2015 to see the current condition of the road and supplement earlier observations.

The roadway appeared to be in relatively good condition during each reconnaissance; however, over-steeped embankment fills and narrow shoulders have resulted in a condition in which many areas experience ongoing pavement edge cracking and/or loss (edge raveling), with some areas showing signs of distress that reach into the travel lane. Evidence of erosion and disturbance caused by animal movements was also visible. Some areas exhibit thermal cracking transverse to roadway centerline and/or pavement distress due to fatigue failure (alligator cracking). Other areas show signs of settlement at the road grade. Areas of delamination and thermal cracking were also observed.

Based on surface observations there are two types of embankment fill soils containing gravel and

OR PFH 146(4) P a g e | 10 of 27 cobble-sized components that were either 1) subround to round or 2) subangular to angular. It is presumed that the subround to round material represent the fill used during original embankment construction. The subangular to angular material appeared to have been placed over the original material at some time subsequent to original construction to possibly widen the embankment, raise the grade, replace eroded material, or some combination thereof. The areas containing the angular material appear to be performing better than the areas containing the rounded material by appearing to be more stable with less edge raveling.

5. MITIGATION CATEGORIES

The areas exhibiting pavement distress are discussed in this section. The interpreted cause of the edge raveling and intermittent pavement distress is due primarily to over-steepened embankments, round to rounded particles in the embankment fill, and in some locations inadequate top width.

The distressed areas are assigned a Category based on the type of distress observed, embankment geometry, physical characteristics, and anticipated mitigation solution. (Conceptual mitigation recommendations are discussed under Section 6.)

Locations within Categories were assigned a Severity Level to designate perceived severity within each Category. The levels are based arbitrarily on the perceived degree of distress observed during the reconnaissance, so no quantitative method or means was used for determining or assigning levels. Severity Levels range from minor to severe. For example, a section of roadway may fall within Category I and have a perceived Severity Level of minor, moderate, moderate-to-severe, etc. Severity Levels can be used as a basis for prioritizing repairs with respect to funding availability.

5.1 Category I Mitigation Locations

Many areas were observed where moderately over-steepened embankments and surficial erosion have resulted in edge raveling and/or longitudinal pavement cracks at the edge of the pavement.

The areas appearing in Table 4 generally exhibit minor or minor-to-moderate severity, with few interpreted as moderate-to-severe. All locations shown in the table are approximate. The embankment slopes were estimated to be standing at inclinations of about 1:1.4 to 1:1.3 (V:H), and surficially comprised of embankment fills that include subround to round gravel and cobble size particles. See Photos 4, 5, and 6 in Appendix A for examples of minor severity, Photos 7, 8 and 9 for minor to moderate, and Photos 10 and 11, and 12 for moderate to severe. Category I mitigation recommendations are described under Section 6.1.

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Table 4: Category I Mitigation Locations

Station Range Length (ft) Relation to CL Severity Level

9+63 - 13+24 361 LT Minor

13+24 - 16+78 354 LT Minor to Moderate

26+31 - 26+67 36 RT Moderate

42+00 - 45+05 305 LT Minor

75+65 - 83+68 803 RT Minor to Moderate

85+28 - 94+29 901 RT Minor

93+21 - 100+28 707 LT Moderate

120+95 - 125+92 497 RT Minor

131+08 - 131+65 57 RT Moderate

141+92 - 142+41 49 RT Minor to Moderate

143+35 - 146+24 289 LT Minor to Moderate

147+96 - 149+85 189 LT Minor to Moderate

149+88 - 159+93 1005 RT Minor to Moderate

169+57 - 173+23 366 RT Moderate

234+89 - 235+98 109 RT Minor

240+77 - 241+65 88 RT Minor

240+81 - 242+53 172 LT Moderate

247+04 - 248+60 156 LT Minor to Moderate

250+41 - 252+09 168 RT Minor

250+41 - 251+86 145 LT Minor to Moderate

255+53 - 259+00 347 RT Minor to Moderate

262+96 - 263+64 68 RT Minor to Moderate

262+43 - 264+10 167 LT Minor to Moderate

300+09 - 300+59 50 LT Minor

321+37 - 324+17 280 LT Moderate

357+44 - 358+10 66 RT Minor

OR PFH 146(4) P a g e | 12 of 27

Table 4: Category I Mitigation Locations (Cont.)

Station Range Length (ft)

Relation to CL Severity Level

413+76 - 414+45 69 LT Minor to Moderate

428+45 – 430+60 215 LT Minor

510+75 - 516+39 564 LT Moderate

542+34 - 545+74 340 LT Moderate to Severe

569+03 - 569+72 69 LT Minor

594+29 - 599+85 556 LT Minor

642+15 - 644+42 227 RT Minor

647+66 - 649+88 222 RT Moderate

651+18 - 654+70 352 RT Moderate

656+29 - 657+51 122 LT Minor to Moderate

658+28 - 659+30 102 RT Minor to Moderate

658+50 - 661+09 259 LT Moderate

677+27 - 679+61 234 RT Moderate

679+04 - 682+47 343 LT Minor

687+07 - 689+17 210 RT Minor

709+64 - 714+49 485 RT Minor to Moderate

715+29 - 719+58 429 RT Moderate

722+13 - 723+29 116 RT Moderate

725+73 - 727+01 128 LT Minor

727+26 - 728+96 170 RT Moderate

727+00 - 728+04 104 LT Minor

729+76 - 730+92 116 LT Minor

731+13 - 733+13 200 RT Moderate

748+75 - 749+85 110 RT Minor to Moderate

794+07 - 794+74 67 RT Minor

749+59 - 750+52 93 LT Minor

OR PFH 146(4) P a g e | 13 of 27

Table 4: Category I Mitigation Locations (Cont.)

Station Range Length (ft)

Relation to CL Severity Level

762+64 - 763+32 68 LT Minor to Moderate

765+40 - 766+82 142 RT Minor to Moderate

767+83 - 769+37 154 RT Moderate to Severe

772+99 - 773+68 69 RT Minor

778+28 - 781+36 308 RT Minor

788+10 - 790+60 250 RT Minor

796+11 - 799+04 293 RT Minor

800+63 - 802+07 144 RT Minor

803+85 - 806+47 262 RT Minor

5.2 Category II Mitigation Locations

Many pavement shoulder areas exhibited distress in the form of pavement edge raveling that was more acute and required mitigation in excess of that required for Category I Mitigation locations.

This is primarily due to the steeper embankment slopes or slopes being closer to the paved edge.

(See Photos 13, 14, 15, 16, and 17 for some examples.) As can be seen in some of the photos the existing pavement is broken and detached from the main paved section.

Table 5 lists the locations of the areas requiring a higher degree of mitigation, length of the distressed zone, side of road, and Severity Level. All locations are approximate. Category II mitigation repair recommendations are described under Section 6.2.

Table 5: Category II Mitigation Locations

Station Range Length (ft) Relation to CL Severity Level

4+34 – 6+45 211 LT Moderate to Severe

223+86 – 227+85 399 RT Moderate

416+30 – 420+45 415 RT Moderate

OR PFH 146(4) P a g e | 14 of 27

Table 5: Category II Mitigation Locations (Cont.)

Station Range Length (ft) Relation to CL Severity Level

567+28 – 567+89 61 LT Severe

567+89 – 569+03 114 LT Severe

584+10 – 585+25 115 RT Moderate to Severe

593+90 – 595+51 161 RT Severe

645+53 – 647+81 228 RT Moderate to Severe

684+85 – 687+07 222 RT Moderate to Severe

694+71 – 698+65 394 RT Minor to Moderate

737+70 – 738+84 114 RT Moderate

744+22 – 745+05 83 LT Minor

754+42 – 757+38 296 LT Moderate to Severe

769+75 – 770+92 117 LT Moderate to Severe

776+71 – 777+58 87 LT Moderate to Severe

784+08 – 784+43 35 RT Minor to Moderate

5.3 Category III Mitigation Locations

Some areas exhibit distress in the form of pavement edge loss combined with embankment loss exacerbated by erosion, with pavement distress extending into the travel way, and in some cases, slumping at the pavement surface. (See photos 18 and 19 for examples.)

Table 6 lists Category III mitigation locations, repair length, side of road relative to centerline, and Severity Level. All locations are approximate. Category III mitigation repair recommendations are described under Section 6.3.

Table 6: Category III Mitigation Locations

Stationing Length (ft) Relation to Centerline Severity Level

144+49 – 146+46 197 RT Moderate to Severe

192+39 – 193+20 81 RT Minor to Moderate

224+89 – 226+42 153 LT Severe

OR PFH 146(4) P a g e | 15 of 27

Table 6: Category III Mitigation Locations (Cont.)

Stationing Length (ft) Relation to Centerline Severity Level

316+44 – 317+09 65 RT Moderate to Severe

337+52 – 338+09 57 RT Moderate

341+00 – 342+95 195 RT Moderate to Severe

581+29 – 583+64 235 RT Severe

5.4 Category IV Mitigation Location (Gravity Walls Section)

The Gravity Walls Section (Stations 308+90 to 310+30) is a through-fill section of road where concrete gravity blocks were installed to retain the roadway embankment on each side of the road prism. (See photos 20 through 25 in the appendix.) The walls are supporting the upper portion of the embankment fill. It is not known if the concrete blocks were placed during original road construction. Distortion at the pavement surface and sagging at the shoulder at some locations was observed. The gravity blocks show signs of rotation and lateral displacement on the right side (east side) of the road. The gravity blocks on the left side (west side) show little sign of rotation but were likely pushed to some degree laterally. It is inferred that the settlement occurring at this location is due to the loose embankment fill materials and possible consolidation of the underling cohesive soils that were encountered in the subsurface investigation. (See Section 4 and boring logs PJ12-09, PJ12-10 and PJ12-11.) Fill heights are estimated to be about 15 feet on the east side and 6 feet on the west side. Category IV mitigation repair recommendations are described under Section 6.4.

5.5 Category V Mitigation Locations

Several areas along the alignment showed evidence of fatigue failure in the form of random cracking (alligator cracking) in the pavement. Alligator cracking is typically an indicator of poor or weakened subgrade conditions. Table 7 contains the locations, lengths, and relationship to centerline of observed alligator cracking. Severity Levels are not assigned to these locations since all will be recommended for repair under Subsection 6.5.

Table 7: Category V Mitigation Locations

Stationing Length (ft) Relation to Centerline Proposed Mitigation

220+69 – 223+58 289 Full Subex 241+16 – 241+66 50 RT Subex 327+35 – 330+94 359 RT Subex 514+79 – 516+39 160 LT Subex

OR PFH 146(4) P a g e | 16 of 27

6. MITIGATION CATEGORY REPAIR RECOMMENDATIONS

This section presents mitigation repair recommendations for the five categories described in the previous section. Repair recommendations are based on the factors unique to each category as observed during the field reconnaissance and the subsurface investigations.

6.1 Category I Repair Recommendations:

Category I sites were described under Subsection 5.1 as being characterized as having steep to moderately-steep embankment slopes with most of the problems at these sites attributable to surficial erosion of the embankment fill slopes resulting in loss (or imminent loss) of the edge of pavement. Fill materials on the embankment surfaces were subrounded to rounded at many (if not most) of these locations.

Figure 5 illustrates the conceptual Deep Shoulder Repair design proposed for the Category I sites. The design requires only shallow excavation of the upper portion of the existing embankment and replacing it with a higher strength material. Refer to Table 4 for the locations where the Deep Shoulder Repair is recommended.

Figure 5: Deep Shoulder Repair Detail (Conceptual)

The proposed backfill material is class 1 riprap, which will have a higher internal strength than the existing fill in order to 1) stand slightly steeper than the existing embankment fill comprised of subround to round material and 2) provide increased resistance to erosion, animal migration, etc. Riprap must be angular and well-graded according to 705.02 and Table 705-1 of the FP and

OR PFH 146(4) P a g e | 17 of 27 the SCRs.

6.2 Category II Repair Recommendations

As discussed under Subsection 5.2 many pavement shoulder areas showed distress in the form of pavement edge loss that is considered to be acute, thus requiring mitigation beyond that required for the Category I sites. The steeper geometry and degree of damage, or perceived impending damage, at the pavement edge at the Category II sites requires a higher level of mitigation.

Figure 6 shows the Reinforced Shoulder Stabilization design recommended for Category II repair locations.

Figure 6: Reinforced Shoulder Stabilization Repair Detail (Conceptual)

The repair involves removal of pavement and base materials and excavating to 3.5 feet below the existing pavement surface. A 1 foot high wrapped reinforced course of reinforcement geogrid and select granular backfill will be constructed first, then a 1.5 feet high wrapped geogrid reinforced course that is stabilized at the face with a welded wire form. Hardware cloth will be placed behind the 4 x 4 - W4.0 x W4.0 welded wire form to contain the select granular backfill.

The repair will extend 7 feet from the pavement hinge point to about the center of the travel lane.

Table 8 shows the locations where Reinforced Shoulder Stabilization is planned, length of the repair, and relationship to centerline.

Geogrid, reinforcement

OR PFH 146(4) P a g e | 18 of 27

Table 8: Reinforced Shoulder Stabilization Repair Locations

Section Limits Length (ft) Relation to CL Severity Level

4+34 – 6+45 211 LT Moderate to Severe

223+86 – 227+85 399 RT Moderate

416+30 – 420+45 415 RT Moderate

567+28 – 567+89 61 LT Severe

567+89 – 569+03 114 LT Severe

584+10 – 585+25 115 RT Moderate to Severe

593+90 – 595+51 161 RT Severe

645+53 – 647+81 228 RT Moderate to Severe

684+85 – 687+07 222 RT Moderate to Severe

694+71 – 698+65 394 RT Minor to Moderate

737+70 – 738+84 114 RT Moderate

744+22 – 745+05 83 LT Minor

754+42 – 757+38 296 LT Moderate to Severe

769+75 – 770+92 117 LT Moderate to Severe

776+71 – 777+58 87 LT Moderate to Severe

784+08 – 784+43 35 RT Minor to Moderate

6.3 Category III Repair Recommendations

As discussed under Subsection 5.3 some areas exhibit distress in the form of pavement edge loss combined with embankment loss due to erosion in excess of the Category I locations and/or pavement distress extending into the travel way and/or slumping pavement. These areas require a level of mitigation that will address the unique issues observed at these sites. Refer to Subsection 5.3 for Category III locations, length, side of road relative to centerline, and severity level.

6.3.a Deep Patch Repair, Type 1

Figure 7 shows a deep patch design that has been prepared for four of the Category III repair locations. The design is similar to shoulder stabilization design developed for the Category II sites, with the main differences being that this design is wider (12 ft) to account for the pavement distress occurring in the travel way, welded wire forms and hardware cloth are not required, and

OR PFH 146(4) P a g e | 19 of 27 the repair depth is 6-inches less (24 inches). Welded wire forms are not required in the Deep Patch Type 1 owing to the fact that the embankment slopes are “flatter” and pavement edge loss is not as severe, thus not requiring the additional support at the paved edge that would be provided by the welded wire forms.

Figure 7: Deep Patch Repair, Type 1 (Conceptual)

Table 9 lists the locations, length, and location relative to centerline where the Deep Patch Type-1 is planned.

Table 9: Deep Patch Repair, Type 1 Locations

Section Limits Length (ft) Relation to Centerline

144+49 – 146+46 197 RT

192+39 – 193+20 81 RT

337+52 – 338+9 57 RT

341+00 – 342+95 195 RT

6.3.b Shoulder Support with Slope Armor Repair

Figure 8 shows a shoulder support with slope armor design that has been prepared for the remaining Category III repair locations. This design takes into account the edge loss and embankment loss caused by erosion that was observed at these sites.

OR PFH 146(4) P a g e | 20 of 27

Figure 8: Shoulder Support with Slope Armor Repair Detail (Conceptual)

The design calls for removal of the existing pavement, base, and subgrade materials to a depth of

2.5 feet below the existing top of pavement and removal of a sufficient amount of existing embankment material to place a 2 feet thick layer of Class 1 riprap on the embankment slope.

Geotextile filter fabric is recommended behind the riprap. An 18” course of select granular backfill that is wrapped in reinforcement geogrid is recommended on top of the subgrade plus crushed aggregate and topsoil placed on top of the riprap at the front of the reinforced select granular backfill course.

Table 10 lists the locations where the Shoulder Stabilization with Slope Armor Repair is anticipated.

Table 10: Shoulder Stabilization with Slope Armor Locations

Section Limits Length (ft) Relation to Centerline Height, ft

224+89 – 226+42 153 LT 6.0

316+44 – 317+09 65 RT 3.7

581+29 – 581+50 21 RT 11.5

581+50 – 581+75 25 RT 12.5

OR PFH 146(4) P a g e | 21 of 27

Table 10: Shoulder Stabilization with Slope Armor Locations (Cont.)

Section Limits Length (ft) Relation to Centerline Height, ft

581+75 – 582+50 75 RT 12.0

582+50 – 583+10 60 RT 11.5

583+10 – 583+64 54 RT 6.5

6.4 Category IV Repair Recommendation – Gravity Walls Section

As discussed under Subsection 5.4 the Category IV repair location (Gravity Walls Section) is a through-fill section of road where concrete gravity blocks were placed to retain the roadway embankment on each side of the road. Distortion at the pavement surface and shoulder slumping was observed and the gravity blocks show signs of rotation and lateral displacement. The settlement occurring at this location is likely due to loose embankment fill materials and possible consolidation of the underling cohesive soils. Figure 9 shows a deep patch design that has been prepared for the Gravity Walls Section.

Figure 9: Deep Patch Repair, Type 2 Detail (Conceptual—6 feet high structure shown)

(Half-width excavation shown for relationship with centerline)

The Deep Patch Type 2 design is similar to the Deep Patch Type 1 design developed under Section 6.3, with the main differences being that the Type 2 design varies in height from 3 feet to 6 feet, it is constructed full-width or half-width depending on location, and the excavation is lined on all sides with a geotextile filter fabric to provide separation between the backfill material and the clay foundation soils.

The Type 2 design calls for the reinforcement geogrid to be wrapped to encapsulate the backfill and control lateral deflection of the backfill, thus providing better long-term pavement support.

As shown in the figure the top lap extends full-width. A drainage system is incorporated in the design by placing an encapsulated perforated collector pipe behind the face. The collector is

OR PFH 146(4) P a g e | 22 of 27 connected to solid wall outlet pipes that will direct water from the collector pipe to daylight through the embankment slope.

Laboratory testing to analyze for further consolidation of the clay foundation soils was not performed since significant settlement, if any, is interpreted to be complete and no additional load will be introduced at the site.

Table 11 shows Deep Patch Type 2 section limits, repair length, width, and height.

Table 11: Deep Patch Repair, Type 2 Limits

Section Limits Length, ft Width Height, ft (H)

308+90 – 309+05 15 Full 3.0

309+05 – 309+15 10 Full 4.5

309+15 – 309+45 30 Full 6.0

309+45 – 309+60 15 Full 4.5

309+60 – 310+15 55 ½ (Right) 4.5

310+15 – 310+30 15 ½ (Right) 3.0

6.5 Category V Repair Recommendations

As discussed under Subsection 5.5 several discrete areas along the project alignment showed evidence of fatigue failure in the form of alligator cracking, indicating inadequate pavement support. Figure 10 shows a subexcavation design that has been prepared for the Category V repairs.

Figure 10: Full Subexcavation Repair Detail (Conceptual)

(Half Width RT shown for relationship with centerline)

OR PFH 146(4) P a g e | 23 of 27

Subexcavation repair requires excavating 24” of unsuitable soil. Line the excavation with a geotextile filter on all sides and place a stabilization geogrid at the bottom of the excavation before backfilling with select Granular backfill.

Table 12 shows Subexcavation section limits, repair length and width.

Table 12: Subexcavation Repair Locations

Section Limits Length (ft) Width, ft

220+69 – 223+58 289 26 (Full) 241+16 – 241+66 50 13 (Half, RT) 327+35 – 330+94 359 13 (Half, RT) 514+79 – 516+39 160 13 (Half, LT)

6.6 Construction Advisory

The figures appearing herein are provided as conceptual illustrations only. Refer to the contract documents for final repair location and design and construction requirements.

The Contractor will be responsible for providing construction materials from available sources.

At the time of memorandum release, it was anticipated the wasted materials will be disposed of offsite. Refer to the final contract documents for the requirements for wasting materials.

The bottom of the excavations should be compacted prior to placement of any geotextile and/or geogrid (geosynthetics) and backfilled in accordance with the requirements in the “Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects (FP-14)” and the project SCRs.

Where reinforcement geogrid is used a minimum nominal long-term strength (Tal) of at least 1,300 lb/ft is required. Tal is determined by the method described under 714.04 in the FP-14.

The reduction factor against installation damage (RFID) used in calculating Tal of the reinforcement is dependent on the angularity and maximum particle size of the backfill material.

In addition to the topics described above, discussions of construction issues pertinent to each mitigation repair recommendation are presented below.

Category I Repair Recommendation – Deep Shoulder Repair

At the time of report release it is anticipated that the Deep Shoulder Repairs (Subsection 6.1) will commence following completion of other construction on the project, including the pavement overlay. It will be important to carefully remove existing embankment materials at those locations in a manner that does not disturb, damage, or undermine the paved section, including the base course.

OR PFH 146(4) P a g e | 24 of 27

It is important that the riprap backfill material is “keyed” at the base as shown in the figure, which will assist in supporting the backfill and provide resistance to erosion.

Category II Repair Recommendations—Reinforced Shoulder Stabilization Repair

Place 4” of backfill material between successive courses of geogrid to avoid direct contact between the geogrid. Extend top course lap to the back of the temporary excavation.

Place support struts at 24” max spacing. Hardware cloth shown behind the welded wire forms can be cut to length prior to installation to facilitate placement of the struts first.

Construction should proceed so that the conserved backfill is placed and compacted coincident with construction of the wrapped reinforced courses so that the lifts of conserved backfill extend to the limits of the temporary excavation line and level with the top of each reinforced course.

For areas where an existing culvert is located or is to be replaced the Contractor should coordinate with the CO to verify culvert depths within the repair areas. During construction, if a portion of an exposed culvert pipe is above the bottom of the repair excavation and more than half of the pipe cross-section is exposed, the geogrid should be trimmed so that it butts up along the entire length of the pipe. If the exposed portion is less than half the pipe cross-section, the geogrid should be placed over the pipe as a continuous reinforcement layer. Only light weight compactors should be used over culvert pipes until sufficient cover has been provided.

Category III Repair Recommendations – Deep Patch Repair, Type I & Shoulder Support with Slope Armor

Place 4” of backfill material between successive courses of geogrid to avoid direct contact between the geogrid. Extend the top lap to the back of the temporary excavation. Place the Class 1 riprap in a manner that avoids segregation of the particle sizes. Place the crushed aggregate to achieve a “resistant” boundary that prevents the migration of the topsoil and select granular backfill into the riprap slope armor.

Category IV Repair Recommendation – Deep Patch, Type II (Gravity Walls Section)

The Contractor should be made aware that the excavation at the Gravity Walls Section will be into soft clayey soils with unknown sensitivity. Therefore, disturbance at the foundation through excessive exposure to construction equipment has the potential to create conditions conducive to further weakening and pumping of the soils and making compaction difficult within the first course. It is our recommendation that construction should proceed during the dryer months of July into September and to limit construction activities directly on the subgrade once the excavation is opened up. The gradation of the backfill is such that the compaction should be easily achieved. Construction should proceed so that the backfill materials that are placed outside of the wrapped reinforced courses at the same time as each course is constructed so that the “external” backfill (in this case conserved backfill and Class 1 riprap) extends to the limits of the temporary excavation line and level with each wrapped reinforcement course.

OR PFH 146(4) P a g e | 25 of 27

Excavated materials from this site are unsuitable to be used as conserved backfill on the project.

Suitable conserved backfill (granular soils) for this site can be obtained from other repair sites on the project where it is allowed.

At the time of report release it is our understanding that traffic delays will be limited to 20 minutes and that the ROW limits are 60 feet (30 feet each side of CL). To work around these restrictions it our understanding that the ditch on the west side of the repair zone may be filled in to allow for temporary traffic diversion. No subsurface investigations were performed outside of the roadway prism at the Gravity Walls section and subsurface conditions are unknown.

However, it should be conservatively assumed that the soft clayey soils extend into the ditch section. In this case a rocky fill material, such as Class 1 riprap, is advised.

Repair at this section involves removal of the existing concrete gravity blocks, which will be returned to the County following removal. It is our understanding that the Contractor will be responsible for delivering the concrete blocks to the County.

Category V Repair Recommendation – Subexcavation

Excavated material from the subexcavation repair locations is not suitable to be used as conserved backfill on the project.

7. CULVERT REPLACEMENT LOCATIONS (GORDON CREEK, SOUTH FORK CABIN CREEK,

PARTRIDGE CREEK & 415+60)

As discussed under Section 3, bedrock was encountered in the geotechnical test holes at the South Fork Cabin Creek culvert location. (See the PJ12-04 through PJ12-07 boring logs in Appendix B.) The bedrock was identified as vesicular basalt and described as slightly to highly weathered, with close to moderate fracture spacing and having hardness of strong to very strong.

Bedrock was not encountered at the Gordon Creek culvert location (PJ112-01 and PJ12-02 boring logs); however, dense to very dense granular materials were encountered. The Contractor is advised to be prepared to excavate into strong to very strong bedrock and very dense granular soils at the footing elevations of the South Fork Cabin Creek and Gordon Creek Culvert locations, respectively. See Photo 26 for the location of the South Fork Cabin Creek Culvert and Photo 27 for the Gordon Creek Culvert.

The Partridge Creek and 415+60 Culvert locations were not discovered until the April 2015 site reconnaissance and as a result no subsurface investigations were performed and no subsurface…