CA_FTBL_67110(1)_Gecko_Road_Pavement_Engineering_Report_Final.pdf

PAVEMENT ENGINEERING REPORT

CA FTBL 67110 (1)

GECKO ROAD NETWORK

IMPERIAL SAND DUNES RECREATION AREA

IMPERIAL COUNTY, CALIFORNIA

YEH PROJECT NO.: 215-013

JUNE 8, 2015

Prepared for:

Atkins North America, Inc.

4601 DTC Boulevard, Suite 700

Denver, Colorado 80237 Attn: Ms. Heather Thomas, P.E.

Prepared by:

Yeh and Associates, Inc.

391 Front Street, Suite D

Grover Beach, California 93433

PAVEMENT ENGINEERING REPORT

CA FTBL 67110 (1)

GECKO ROAD NETWORK

IMPERIAL SAND DUNES RECREATION AREA

IMPERIAL COUNTY, CALIFORNIA

YEH PROJECT NO.:

215-013 JUNE 8, 2015*

Prepared by:

Jonathan D. Blanchard, GE2312 Simon P. Boone Principal Geotechnical Engineer Staff Geologist

Independent Reviewer:

Robert F. Laforce, P.E.

Sr. Materials Engineer

*revised station references only on 9/9/18

Pavement Engineering Report Yeh Project No. 215-013 Gecko Road Network June 8, 2015 i

Table of Contents

1. PURPOSE AND SCOPE OF STUDY

2. PROJECT UNDERSTANDING

3. FIELD EXPLORATION AND TESTING

3.1 EXPLORATORY BORINGS

3.2 LABORATORY TESTING

4. GEOLOGIC SETTING

5. SITE CONDITIONS

5.1 TERRAIN AND VEGETATION

5.2 CLIMATE

5.3 EXISTING PAVEMENT SURFACE CONDITION

6. SUBSURFACE CONDITIONS

7. GEOTECHNICAL CONSIDERATIONS FOR DESIGN AND CONSTRUCTION

7.1 COMPACTION

7.2 DESERT CONDITIONS

7.3 LOOSE DUNE SAND

7.4 PULVERIZATION FOR FDR

8. PAVEMENT DESIGN RECOMMENDATIONS

8.1 DESIGN TRAFFIC VOLUME AND SUBGRADE

8.2 STRUCTURAL SECTION

8.3 BINDER AND MIX RECOMMENDATIONS

8.4 SUBGRADE STABILIZATION

8.5 PAVEMENT MAINTENANCE

8.6 EARTHWORK DESIGN

8.6.1 General Grading

8.6.2 Graded Slope Design

8.6.3 Earthwork Factors

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9. MATERIAL SOURCES

10. LIMITATIONS

11. REFERENCES

List of Figures

FIGURE 1: PROJECT LOCATION MAP (NO SCALE)

FIGURE 2: GEOLOGIC MAP (STRAND 1962, NO SCALE)

FIGURE 3: TYPICAL SURFACE PAVEMENT CONDITIONS ALONG GECKO ROAD

FIGURE 4: STRUCTURAL SECTION PLACED WITH FDR OR AB

FIGURE 5: TYPICAL EMBANKMENT WIDENING

List of Tables

TABLE 1: EXISTING PAVEMENT CONDITIONS ENCOUNTERED

TABLE 2: SUBGRADE SOIL PROPERTIES TEST SUMMARY

List of Appendices

Page

Appendix A – Boring Logs

Fence Diagram for Gecko Road Boreholes .............................................................................................. A-2

Legend for Symbols used on Borehole Logs ............................................................................................ A-3

Borehole Logs for 15P-101 to 115 ................................................................................................. A-4 to 18

Test pit logs for 15T-107 and 111 ................................................................................................ A-19 to 20

Appendix B – Results of Laboratory Testing

Moisture and Density Measurements ............................................................................................. B-1 to 4

Percent Passing No. 200 Sieve ................................................................................................................ B-5

Mechanical Sieve Analysis .............................................................................................................. B-6 to12

Proctor Compaction .................................................................................................................... B-13 to 14

California Bearing Ratio .............................................................................................................. B-15 to 18

Unconfined Compression ..................................................................................................................... B-19

Appendix C – Pavement Design Calculations

AASHTO (1993) Spreadsheet calculations ........................................................................................ C-1 to 2

Appendix D – Draft Pavement Structural Sections memorandum (2 pages) file://YEH-1/Seagate%20Wireless/Projects%20-%20Yeh/215-013%20Atkins%20-%20Gecko%20Road/1.%20Report/215-013%20Yeh%20Pavement%20Engineering%20Rpt%20-%20Gecko%20Rd%20.docx%23_Toc421526460 file://YEH-1/Seagate%20Wireless/Projects%20-%20Yeh/215-013%20Atkins%20-%20Gecko%20Road/1.%20Report/215-013%20Yeh%20Pavement%20Engineering%20Rpt%20-%20Gecko%20Rd%20.docx%23_Toc421526463 file://YEH-1/Seagate%20Wireless/Projects%20-%20Yeh/215-013%20Atkins%20-%20Gecko%20Road/1.%20Report/215-013%20Yeh%20Pavement%20Engineering%20Rpt%20-%20Gecko%20Rd%20.docx%23_Toc421526464

1. PURPOSE AND SCOPE OF STUDY

Yeh and Associates was retained by

Atkins to provide geotechnical recommendations for the design of a new pavement structural section as part of the

Federal Highway Administration, Central

Federal Lands Highway Division (FHWA-

CFLHD) project to improve the Gecko

Road network at the Imperial Sand Dunes

Recreation Area in Imperial County, California. The location of the site is shown on Figure 1.

The geotechnical evaluation consisted of a program of project coordination, reviewing data, field exploration, laboratory testing, and engineering analyses as a basis for providing the recommendations in this report. This report provides recommendations for rehabilitation of the road using full depth reclamation and pulverization of the existing pavement, structural section thicknesses for the estimated traffic loading conditions, earthwork factors, slope design, compaction and fill placement.

2. PROJECT UNDERSTANDING

The project generally consists of a design to rehabilitate the Gecko Road network pavement.

Our understanding of the project is based on the Atkins (2014) trip report and preliminary plans provided for our use (Atkins 2015). The roadway will remain on essentially the same horizontal and vertical geometric alignment as the existing facility. Alternatives to rehabilitate the pavements for the Gecko Road network were presented in a memorandum submitted to Atkins in February 2015 (Yeh 2015). Based on review of the alternatives, Yeh has recommended to pulverize and recompact the roadway using full depth reclamation (FDR) with an asphalt concrete overlay. CFLHD has directed the design team to remove the upper 4 inches of FDR material to replace that material with 4 inches of aggregate base course material over the FDR material where the existing structural section includes cement treated sand.

Figure 1: Project Location Map (no scale)

Gecko Road is located within the Imperial Dunes and intersects Highway 78 approximately 20 miles east of Brawley, California. The existing roadway is two lanes, paved with asphalt concrete and extends for approximately 5.7 miles south of Highway 78 and dead ends at the

Road Runner Campground within the dunes. The roadway loop for the Road Runner

Campground is approximately 0.6 miles long. Gecko Campground is located on the east side of

Gecko Road, approximately 3.3 miles south of Highway 78. The Gecko Campground road and loops are approximately 1.3 miles long. The network includes the paved campground access road and loops at Gecko Road. All of the roads that will be improved are paved with asphalt concrete and will have a design road width of approximately 26 feet on the main road, 24 feet on the access road, and 14 feet on the paved loops within the campgrounds. The roadway is mostly constructed on embankment or near adjacent grade. The embankment fill ranges in thickness up to about 20 feet with 4:1 (horizontal to vertical) side slopes.

3. FIELD EXPLORATION AND TESTING

3.1 Exploratory Borings

The drilling subcontractor for this project was Enviro-Drill Inc. of Phoenix, Arizona. Enviro-Drill used a CME75 truck-mounted drill rig equipped with 8-inch diameter hollow stem augers to advance the 15 borings in Gecko Road on February 18, 2015. Memoranda describing the field exploration and findings were submitted by Yeh (2015a, 2015b). The boring locations are shown on the logs and a map in Appendix A. Quail Construction of Yuma, Arizona provided traffic control and flagging for the drilling. Atkins provided a cultural resources monitor for the drilling

(Mike DeGiovine). The logs of the borings are presented in Appendix B. Photos of the road surface conditions at the boring locations are presented with the logs in Appendix B.

The hole was initially drilled through the existing pavement structural section. The sides of the borehole were then scraped by the Yeh field geologist, and the thickness of the existing asphalt pavement and base course materials were measured and recorded on the logs. The drilling then continued and the holes were sampled by collecting bulk samples of the pavement and subgrade materials from the auger flights, and by driving a 2.5-inch California split spoon sampler into the subgrade soils encountered, typically at depths of approximately 1.5 and 4 feet below the road surface. The California sampler contained 4-inch high brass liners and were driven into the ground at the bottom of the hole using a 140-pound automatic trip hammer in general accordance with ASTM 1586 (the Standard Penetration Test (SPT). Yeh measured the thickness of the pavement and base course material at each location, collected bulk and drive samples for subsequent laboratory testing, recorded blow counts (N-values) for the driven samples, and prepared a field log of subsurface conditions encountered. The blow count can be used as a relative measure of material stiffness or density. Upon completion, the borings were backfilled with auger cuttings and topped with hand-mixed rapid set concrete.

3.2 Laboratory Testing

Laboratory testing was performed on selected samples recovered from the field exploration program by the GEO-E lab at the Cal Poly Civil Engineering Department in San Luis Obispo, California. Tests for moisture content, unit weight, percent passing the 200 sieve, particle size distribution by sieve analysis, unit weight versus moisture content relation by the modified

Proctor test, California Bearing Ratio (CBR), and unconfined compression strength (of cement treated soils) were performed as part of this program. The results of the laboratory tests are presented in Appendix C. Testing was performed accordance with American Association of

State Highway and Transportation Officials (AASHTO) methods as noted on the lab reports.

After the completion of the laboratory testing, the field descriptions were confirmed or modified as necessary and boring logs were prepared.

4. GEOLOGIC SETTING

The surface geology in the site vicinity is mapped by (Strand 1962) as Holocene-aged unconsolidated eolian deposits (Qs-Dune Sand) that comprise the active Algodones Dunes. It is thought that the Algodones dune field is comprised of sand blown from the receding shorelines of ancient Lake Cahuilla. The Salton Sea now occupies the Salton Sink, a regional depression that is interpreted to be the former location of Lake Cahuilla. Lake Cahuilla formed and receded many times, as the Colorado River periodically changed its course flowing west in the Salton

Sink due to the flat topography of the region. When the river flowed into the Salton Sink, Lake

Cahuilla grew and occupied much of the present Imperial Valley. When the river shifted its course and flowed into the Gulf of California, the arid climate caused the lake to shrink, large areas of former lakebed were exposed, and the sandy nearshore sediments were blown southeast by the prevailing westerly and northwesterly winds. The Imperial Sand Dune

Recreation Area is part of the resulting Algodones dune field that stretches for 43 miles from east of Calipatria to south of the US-Mexico border.

Gecko Road runs generally north-south near the eastern margin of the Imperial Sand Dunes

Recreational Area. The dune field has a generally uniform width, ranging from 4 to 7 miles wide over its length. The San Andreas Fault is mapped trending along the western margin of the dunes and is attributed to the characteristic uniform width of the Algodones dune field. Gecko

Road lies wholly within the central part of the dune field, and extends roughly 6 miles into the dunes in a southeast direction from its intersection with State Route 78. Each of the borings drilled along the Gecko Road encountered these dune sand deposits.

Figure 2: Geologic Map (Strand 1962, no scale)

5. SITE CONDITIONS

5.1 Terrain and Vegetation

Gecko Road is within the western portion of the Imperial Sand Dunes complex. The dunes are bordered by the Coachella Canal and adjacent flat lands that border the western margin of the dunes, and lie about ¼ to ½ mile west of Gecko Road. The eastern edge of the dunes, about 6 miles east of Gecko Road, are bordered by a terrace type feature referenced as Pilot Knob

Mesa, and furthered by the Chocolate and Cargo Muchacho Mountains.

The dunes are active within only sparse vegetation consisting of occasional shrubs, and relatively heavy off-highway recreational vehicle use. The ground elevation along Gecko Road undulates through the dunes between approximately elevation (el.) 175 and 287 feet, generally increasing in elevation southward from Highway 78. Grades within the Gecko Campground access range from approximately el. 270 to 294 feet.

5.2 Climate

The climate data (www.usclimatedata.com) for Brawley, California (located approximately 20 miles west of the Gecko Road area, reports an average annual rainfall at of 3.15 inches. The majority of the rainfall is reported to occur between August and October (monsoon season) and during the winter months between December and March. The reported monthly average temperature ranges from a low of 70 degrees for December and January to a high of 107 degrees in July.

5.3 Existing Pavement Surface Condition

Figure 3: Typical Surface Pavement Conditions along Gecko Road left to right: Sta. 101+00, Sta. 157+00, Gecko Camp Access, Sta. 266+00

The exposed pavement surface along Gecko Road consisted of asphalt concrete with a seal coating of 3/8-inch chips in a rubberized asphalt binder. The overall roadway was in fair condition with a posted limiting speed of 35 mph. There was extensive high severity block cracking throughout the project. It appears that crack sealing has been has been performed as part of roadway maintenance. The pavement surface conditions along Gecko Road are notably consistent with highly developed block cracking (Distress Type ACP 2) observed along the entire alignment, and along the side roads at the Gecko and Roadrunner campgrounds.

Pavement drop off was observed in some areas where wind blow sand appears to have eroded from the edge of the pavement. Typical surface pavement conditions observed along Gecko

Road are show in photos on Figure 3.

http://www.usclimatedata.com/

6. SUBSURFACE CONDITIONS

Subgrade soils encountered in the pavement borings consisted of materials associated with the existing pavement structural section for Gecko Road, overlying artificial fill and dune sand. The approximate locations of the drill holes are shown on the Boring Location Plan and noted on the logs in Appendix A. A description of the units encountered is summary below.

Existing Pavement. The existing structural section generally consisted variable thicknesses of asphalt concrete overlying cemented treated sand or aggregate base. The base materials were underlain by sandy subgrade soils composed of artificial fill derived from dune sand. A summary of the thicknesses encountered in each of the drill holes is presented below:

Table 1: Existing Pavement Conditions Encountered

Drill Hole No.

and Station

Asphalt Thickness

(inches)

Base Thickness

(inches) Base Material

Subgrade soil and

AASHTO1 Comment

15P-101 104+02, 6’ rt.

4.75 4 Cement treated sand Sand A-3(0)

Cement treated soil is fine sand

15P-102 130+20, 5’ rt.

3.25 4.5 Cement treated sand Sand

A-3 (0)

15P-103 156+83, 6’ rt.

3 5 Cement treated sand Sand

A-3 (0)

15P-104 183+86, 5’ rt.

3.75 6 Cement treated sand Sand A-3

15P-105 211+65, 5’ rt.

3.75 8 Cement treated sand Sand

A-3 (0)

15P-106 237+96, 5’ rt.

3 6 Cement treated sand Sand

A-3 (0)

15P-107 266+58, 5’ rt.

3 6 Cement treated sand Sand

A-3 (0)

15P-108 293+40, 5’ rt.

3.5 6 Cement treated base Sand

A-3 (0) CTB has nominal ¾” aggregate size

15P-109 321+80, 6’ rt.

3.5 6 Cement treated base Sand

A-3 (0)

15P-110 352+99, 5’ rt.

3.75 9 Cement treated base Sand A-3(0)

15P-111 378+25, 8’ rt.

3 7 Cement treated base Sand

A-3 (0)

15P-112 401+60, 5’ rt.

2.5 5.5 Cement treated base Sand A-3(0)

Geotextile over subgrade

15P-113 421+75. 23’ rt.

3 5.5 Cement treated base Sand A-3(0)

Road Runner loop.

Geotextile over subgrade

15P-114 1283+50, 8’ lt.* 3 4

Cement treated sand

Sand A-3 (0)

Gecko Camp access

15P-115 1298+97, 7’ lt.* 3.25 7

Cement treated sand

Sand A-3(0)

Gecko Camp access

1 AASHTO symbol may be based on manual classification of soil.

*changed station reference 9/9/2015

Subgrade Conditions. Subgrade soils encountered below the existing structural section generally consisted of medium dense to very dense sand and sand with silt. The subgrade soils primarily consisted of embankment fill associated with the construction of the existing Gecko

Road network that appear to have been derived from local dune sand, and natural dune sands that are predominant throughout the project area. Where the existing fill and compacted subgrade soil was penetrated, the underlying dune sand typically consisted of medium dense sand.

Subgrade Properties. Laboratory test results for drive samples taken at a depth of 1.5 feet below the pavement surface had moisture contents ranging from approximately 1.5 to 2.7 percent and dry unit weights that ranged from approximately 104 to 112 pounds per cubic foot

(pcf). Laboratory tests results for two drive samples taken at 4 feet below the pavement surface had moisture contents of approximately 2.1 and 3.8 percent, and dry unit weights of approximately 100 and 102 pcf. Modified Proctor tests performed on bulk samples recovered from borings 15P-102 and 108 had an estimated maximum dry unit weight of approximately 111 pcf at an optimum moisture content for compaction of 11 percent.

The percentage of fines (passing through the No. 200 sieve) from wash samples and mechanical sieve analyses ranged from approximately 1 to 4 percent for 15 of 17 samples that were tested, and from 6 to 11 percent for two bulk samples recovered from P15-101 and 115.

Unconfined compression tests performed on samples cut from blocks of the cement treated sand exposed along the existing edge of pavement had compressive strengths of 1,360 and

1,720 pounds per square inch. A summary of the subgrade soil properties associated with the

CBR test results is presented in Table 2.

Table 2: Subgrade Soil Properties Test Summary

Boring No. Station

Molding Water

Content (%) CBR2 AASHTO USCS Classification

15P-101 104+02, 6’ rt. 12.3 36 A-3(0) Poorly graded SAND (SP)

15P-112 401+60, 5’ rt. 12.7 25 A-3(0) Poorly graded SAND with silt (SP-SM)

15P-112 401+60, 5’ rt 12.7 15 A-3 (0) Poorly graded SAND with silt and gravel (SP-SM), (with 30% AC grindings)

15P-115 1298+97, 7’ lt.* Gecko Camp

13.1 22 A-3(0) Poorly graded SAND with silt (SP-SM)

2 Samples were remolded at 2 percent above optimum moisture content for testing.

7. GEOTECHNICAL CONSIDERATIONS FOR DESIGN AND CONSTRUCTION

Geotechnical engineering related conditions that could affect design and construction include compaction the subgrade soils, construction operation within a loose dune sand environment, and the presence of cement treated materials, geosynthetic material, relatively deep pulverization depths that could impact the proposed full depth reclamation (FDR) of the existing pavements, and working in the desert environment. Special recommendations to address freeze thaw or groundwater considerations are not needed for this project.

7.1 Compaction

The dune sand is typically a poorly graded granular soil containing few fines and should be relatively easy to compact. The samples tested had a relatively low moisture content (less than about 3 percent). Compaction of the subgrade should be performed using suitable equipment for the sandy soil conditions, such as smooth drummed rollers and/or vibratory compaction.

Pulverization of the asphalt pavement will increase the fines content and the sensitivity of the soil to moisture.

Control of compaction layer thickness, moisture content, and providing an adequate amount of compactive effort will be necessary to achieve the minimum specified compaction. The use of heavy rollers or vibratory type compaction equipment, good processing and control of moisture content will be necessary to provide the recommended compaction within a single 10- to 12-inch thick lift of FDR material.

7.2 Desert Conditions

The project is within a desert area of California. Low humidity and high temperatures can make maintaining soil moisture difficult. Samples of the subgrade soils tested were typically at a moisture content 9 to 10 percent below the estimated optimum needed for compaction.

Although moisture conditions vary seasonally, water will likely need to be added to the soil to provide a moisture content suitable for compaction. The use of palliatives or prime coat and continued water application should be provided to help maintain moisture and avoid loosening of the compacted surface prior to paving. A brief discussion regarding water availability is provided in Section 9 of this report.

7.3 Loose Dune Sand

The Gecko Road project is within an active sand dune and dry desert type environment. Dry surface soils within the sand dunes will be loose, and may not support construction vehicles that may attempt to traffic over uncompacted sand. The addition of water to provide a water content near the optimum, and compaction of the sand should allow for stabilization of the subgrade and provide adequate support for earthwork operations.

7.4 Pulverization for FDR

The existing structural section for Gecko Road includes cement treated sand. Unconfined compressive strength tests cut from block samples of the cement treated sand were 1360 and

1720 psi. The pulverization for FDR should consider the presence of the cement treated soil having strengths similar to concrete, particularly for those areas north of the Gecko Camp

Access. Pulverization should extend through the existing structural section and to at least 1 inch below the existing structural section

Depth of Pulverization. Pulverization to a typical depth of 10 inches will be needed to penetrate the thickness of the existing structural section encountered in the borings; however, equipment should be capable of pulverization to a depth of at least 12 inches to penetrate the existing structural section encountered in some areas and to extend at least 1 inch into the underlying subgrade.

Paving Fabric. A paving fabric/geotextile was encountered within the existing asphalt concrete encountered in selected borings, particularly in the area of the Road Runner campground loop.

The fabric appears to have been used in association with past subgrade stabilization or pavement overlays. Fabric can become bound up or trapped within pulverization equipment and may cause delays to remove those materials. The presence of the fabric and associated delays should be considered for the construction of this project.

8. PAVEMENT DESIGN RECOMMENDATIONS

The minimum design thickness for the new Gecko Road network is recommended based on pavement design standards provided in Chapter 11 of the CFLHD Project Development and

Design Manual (PDDM) and the AASHTO (1993) Guide for the Design of Pavement Structures.

Preliminary pavement structural sections were evaluated and presented in the Yeh (2015c) memorandum. The concept to use full depth reclamation (FDR) with a hot mix asphalt pavement overlay was selected as being the appropriate alternative for this project, and to remove the upper 4 inches of the FDR and replace that material with aggregate base in areas where the CTS will be pulverized. The spreadsheet calculations for our recommended traffic loading and thickness recommendations are presented in Appendix C. The memo presenting our evaluation of the draft structural sections is presented in Appendix D.

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8.1 Design Traffic Volume and Subgrade

The design traffic volume was estimated using the average daily traffic (ADT) volume and vehicle distributions presented in the Atkins (2014) Trip Report and procedures in the Federal

Lands Highway Project Development and Design Manual (FHWA 2008). Atkins reported that the current seasonal daily traffic for the Gecko Road network is approximately 320 vehicles per day, with an annual average daily traffic (ADT) of approximately 184 vehicles per day. The traffic is reported to be composed of 2 percent trucks, 5 percent buses and 85 percent recreational vehicles (RV). These data were used to estimate the number of 18-kip equivalent single axle loads (ESALs) considering a design life of 20 years. This design ESAL value was

1,112,830 for the Gecko Road network. The design ESAL for the apron that will provide a pullout into various camp pads along Gecko Road was assumed to be no more than about 5% of the mainline traffic volumes or approximately 55,642 ESALs.

The dune sand encountered along Gecko Road generally classified as A-3(0) and is considered excellent subgrade support for the roadway. CBR values obtained from dune sand ranged from approximately 25 to 36 percent at 0.2 inches, and about 15 percent for a sample remolded with

30 percent asphalt chips obtained from the drilling. The recommended structural section thicknesses were estimated considering a resilient modulus (Mr) of 23,200 psi for the sandy subgrade soils encountered.

8.2 Structural Section

A summary of our recommended structural sections is presented in Figure 4. The roadway structural section for the Gecko Road network should consist of at least 3 inches of hot mix asphalt concrete pavement (HACP) placed over either compacted FDR material or 4 inches of aggregate base (AB). The AB layer would be placed following pulverization and removal of the upper 4 inches of the FDR material where CTS was encountered within the existing structural section: within the Gecko Campground and on Gecko Road north of the campground. If needed to maintain the vertical profile of the road, the AB can be placed on either FDR or compacted subgrade after removal and/or regrading of the FDR material.

Full Depth Reclamation. FDR should consist of pulverizing and compacting the existing asphalt pavement, cement treated base material, and subgrade to a typical depth of 10 inches in accordance with FP-14 Section 304, Method 2. Equipment used for pulverization should be capable of pulverizing to a depth of at least 12 inches to provide pulverization of the existing structural section thickness encountered in the borings and to penetrate at least 1 inch into the

1 1 underlying subgrade. The recommended depth of pulverization is based on the necessity for the pulverization equipment to extend below the cement treated materials and into the underlying subgrade. Where the base course will consist of only FDR, the structural section should provide a minimum thickness of 8 inches of compacted FDR material below the HACP.

Aggregate Base Layer. The structural section that includes 4 inches of AB does not require

FDR material to provide structural support for the new pavement. Grading or excavation and reuse of the FDR material may be performed to control the vertical grade of the new roadway, provide a new super elevation, or to provide fill for wider sections of the roadway or

Figure 4: Structural Section placed with FDR or AB

1 2 embankment. Where the base course will include AB, the AB can be placed on either FDR or directly on the compacted subgrade with no FDR material below the AB. The upper 9 inches of the subgrade below the AB should be scarified to a depth of 9 inches, moisture conditioned, and compacted to at least 95 percent relative compaction.

Campground Apron Transition areas. A transition apron will be provided to allow turnouts onto camp pads located along Gecko Road and into turnouts for camp access roads. The structural section for the transition apron can consist of 3 inches of new HACP placed over the existing aggregate base. We recommend that the existing aggregate base within the transition be pulverized and compacted in-place to a depth of at least 9 inches prior to placing the asphalt pavement for the apron. The FDR material should be moisture conditioned and compacted in-place to at least 95 percent relative compaction in accordance with Section 304, Method 2 of

FP-14.

Shoulder Backing. Shoulder backing materials should be placed along the new edge of pavement (NEP) to support the pavement edge, reduce the potential for wind to erode sandy embankment materials and dune sand from beneath the structural section, and reduce the potential for edge cracking of the pavement. Similarly, the transition from the pavement to gravel surface within the camp pad area should include the placement of additional base along the edge of the pavement and a smooth transition to the gravel surface. Shoulder backing should consist of at least a 3-inch thickness of Grading D base conforming to Section 703.05 of

FP-14 placed at the NEP.

8.3 Binder and Mix Recommendations

The State of California (Caltrans 2012) has adopted a program of Asphalt Binder Grade

Selection which classifies this project area as a Desert Region. The recommended binder for this area based on Caltrans data is PG 70-10.

This project is in a relatively remote location and we understand the location of existing commercial asphalt plants may result in relatively long haul distances to the construction site

(see discussion in Section 9 of this report). Loss of temperature and segregation of the hot asphalt mix can occur during long distance transport. We recommend the project specifications require the use of a material transfer device at the point of placement to provide uniform temperature and reduce the potential for segregation of the mix during placement.

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8.4 Subgrade Stabilization

Subgrade stabilization should be provided in areas where unsuitable material or soft subgrade conditions are encountered that will not allow for proper compaction of the subgrade or FDR materials, or where the subgrade is composed of organic or other deleterious materials that will not provide suitable foundation support for the new roadway. Subgrade stabilization can consist of removing the existing soil to a depth at least 1 foot below the bottom of the structural section or to the bottom of the unsuitable material, whichever is deeper. If the subgrade is wet or yielding, subexcavation should be performed using backhoe type equipment such that construction equipment will not operate on the exposed subgrade during excavation.

A geotextile for stabilization should be placed over the undisturbed subgrade in accordance with

Section 207 of FP-14. The geotextile should be placed without gaps or wrinkles and conform to

Section 714.01 of FP-14 for Class 1 Geotextile, Type E. Gravel for stabilization should consist of uniformly graded 3/8 to 1.5-inch gravel conforming to Section 703.6, Crushed Aggregate, of

FP-14. The aggregate should be fully encased in the geotextile to reduce the potential for the overlying base course or adjacent sand dune soils to erode into the gravel.

The project specifications should include a quantity of 500 cubic yards for stabilizing the subgrade for the roadway, if needed, and for increasing, decreasing for deleting the quantity based on the conditions encountered during construction. The geotechnical professional should review the subgrade conditions encountered at the time of construction to evaluate whether or not stabilization of the subgrade is needed, and to recommend the depth and limits of the subexcavation and stabilization.

8.5 Pavement Maintenance

The pavement condition should be periodically evaluated to help plan and scope the need for maintenance and rehabilitation following the initial construction of the pavement. Maintenance of asphalt concrete pavements should typically include periodic fog, chip or slurry seals to reduce the potential for weathering, or overlaying with additional HACP when needed to strengthen and further the life of the pavement. Deflection surveys can be performed to evaluate the structural capacity of pavements and the need for future overlays.

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8.6 Earthwork Design

8.6.1 General Grading

The recommendations of this report assume that pavement and fill materials will be placed in general accordance with Standard Specification FP-14. Compliance with those specifications is needed for the recommendations in this report to remain applicable.

All site grading should conform to the applicable sections of FP-14. Fill materials should not contain organic matter or other deleterious material. On-site soil removed from excavations consisting of sand and sand with silt (SP, SP-SM) can likely be used as borrow for general embankment fill and non-critical areas of construction. Existing base or excess FDR should be reviewed by the Engineer during construction prior to reuse as shoulder backing material or fill.

Excess fill or cut material should be hauled offsite for proper disposal, unless an onsite location has been specifically identified for placement of excess fill on the project plans. Temporary excavations should conform to OSHA requirements.

The dune sand is highly erosive. Existing drainage is generally by sheet flow from Gecko Road running directly to the edge of pavement. Surface drainage should be maintained similar to existing conditions and without concentrated flows or runoff.

8.6.2 Graded Slope Design

Grading is generally expected to consist constructing FDR within the prism of the existing roadway and minor widening of the embankment slopes. Unreinforced cut and fill slopes should be graded at 1 Vertical to 3 Horizontal (1V:3H) or flatter. The existing embankment slopes are composed of dune sand, unprotected from erosion and generally without vegetation. Where the embankment will be widened, the new fill should be keyed into the existing slope such that at

Figure 5: Typical Embankment Widening

1 5 least the outer 1-foot of the existing embankment is removed. The keying can be performed in association with placement of the new fill, and such that the soil excavated from the existing embankment slope is simultaneously incorporated into the layer of the compacted fill that is being placed. The excavated material should be scarified and blended with the new fill to provide uniformity of material and moisture that is suitable for compaction.

8.6.3 Earthwork Factors

As previously discussed in this report, the holes drilled for the Gecko Road improvements were drilled through the existing pavement and sampled at depths of approximately 1.5 and 4 feet below the pavement surface with a driven split spoon samplers. Drive samples taken at a depth of 1.5 feet below the pavement surface had dry unit weights that ranged from approximately 104 to 112 pcf. Drive samples taken at the 4-foot depth had dry unit weights of approximately 100 and 102 pcf. The maximum dry unit weight of the sand estimated from Proctor tests was approximately 111 pcf.

It is recognized that disturbance to drive samples occurs due to compaction of samples during driving, and loosening of soils when recovering the sampler from the drill hole and during trimming in the laboratory. Differences in soil density likely occur in areas where the existing pavement subgrade and embankment fill materials were compacted, deposition of sand occurred on the winward versus the leeward side of the dunes, compaction along off-road vehicle paths and routes through the dunes, and inherent differences in soil type and consistency.

The estimated earthwork factors3 do not account for losses for removal of vegetation or unsuitable material. An earthwork factor of 1 can be used considering the pulverization and compaction of the existing structural section. An earthwork factor of 0.96 can be used for areas where the subgrade will be compacted outside the limits of the existing structural section, or the

FDR will be grade to a final thickness of less than 1 foot. An earthwork factor of 0.92 can be used for on-site borrow or compaction of the subgrade for embankment widening. The

3 The earthwork factor represents the ratio of the existing in-situ unit weight of the soil before construction to the unit weight of the same soil after compaction. For example, an earthwork factor of 0.95 represents a 5 percent loss in the volume of soil following compaction. An earthwork factor of 1.05 represents a 5 percent gain in volume of the soil or pavement following compaction due to bulking of a relatively dense material.

1 6 earthwork factors are approximate, and should be checked and adjusted as-needed as the grading work progresses.

9. MATERIAL SOURCES

The main material requirements for this project are likely to provide hot mix asphalt and aggregate base that will be placed following full depth reclamation of the existing roadway.

Gecko Road is located approximately 20 miles east of Brawley, California and about a 1 hour drive from Yuma, Arizona.

Hot Mix Asphalt Concrete Pavement. There are few asphalt plants located in close proximity to the project site. Relatively long haul distances will make it necessary to monitor truck hauling and standby times, and to check mix temperatures arriving at the site and during placement.

The following commercial material sources advertise as having the closest asphalt plants to the site. Yeh contacted these plants only to confirm that the suppliers are in business and available to provide hot mix asphalt for state and/or federal projects:

BLT Co, 3515 E Gila Ridge Rd, Yuma, AZ 85365. As of March 2015, BLT does not provide trucking to California but have a plant in Yuma that can provide hot mix asphalt concrete. Route from plant to Gecko Road is about 63 miles (I8-Olgilby-CA78).

Pyramid Construction, 839 Dogwood Rd, Heber, CA 92249. Reports that plant can provide hot mix asphalt for Caltrans and federal projects. Route from plant to Gecko

Road is about 42 miles (CA111-CA115-CA78).

Granite Construction Company, 2095 CA-111, El Centro, CA 92243. A call to their office in March 2015 reports that Granite does not have an operating hot mix asphalt plant in

El Centro at this time.

This report is not a statement that these potential suppliers are pre-approved nor implies that the plants will meet quality control and material compliance for the project or materials to be placed at the site.

Aggregate. Various aggregate suppliers that can supply base course or other aggregate types that may be associated within Brawley, El Centro and Yuma, including those listed above for supplier of asphalt.

General Borrow. Onsite soils and excess material from FDR should be suitable for reuse as general borrow. Existing aggregate base, FDR materials, and aggregates consisting of durable

1 7 particles should be suitable for use as shoulder backing material or parking aprons with the campground areas. There are various active and abandoned mining operations near-by the site; however, it is not anticipated that the project will require significant quantities of imported borrow that would make specific consideration of those potential sources necessary for design.

Water. The subgrade soils encountered were relatively dry, 9 to 10 percent below the optimum needed for compaction. Water sources at the site are limited and will likely not be available for construction (personal communication with Neil Hamada, May 27, 2015). The contractor may have to truck water or obtain permits from local purveyors or other sources for construction.

10. LIMITATIONS

This study has been conducted in general accordance with currently accepted geotechnical practices in this area for use by the client for design purposes. The conclusions and recommendations submitted in this report are based upon the data obtained from field reconnaissance, drilling and sampling, and our understanding of the proposed project and type of construction described in this report. If there are any changes in the project or site conditions, Yeh should review those changes and provide additional recommendations, if needed. Any modifications to the recommendations of this report or approval of changes made to the project should not be considered valid unless they are made in writing. The report and drawings contained in this report are intended for design-input; and are not intended to act as construction drawings or specifications.

Site conditions will vary between points of observation or sampling, seasonally, and with time.

The nature and extent of subsurface variations across the site may not become evident until excavation is performed. If during construction, fill, soil, or water conditions appear to be different from those described herein, Yeh should be advised and provided the opportunity to evaluate those conditions and provide additional recommendations, if necessary. The geotechnical professional should observe portions of the construction and site conditions, such as excavations, exposed subgrades and earthwork, to evaluate whether or not the conditions encountered are consistent with those assumed for design, and to provide additional recommendations during construction, if needed.

11. REFERENCES

American Association of State Highway and Transportation Officials (AASHTO), AASHTO

Guide for Design of Pavement Structures, Washington D.C., copyright 1993.

1 8

Atkins North America, Inc. (Atkins 2014), Federal Highway Administration, Central Federal

Lands Highway Division, Federal Lands Transportation Program, Trip Report, Bureau of

Land Management, Imperial Sand Dunes Recreation Area, El Centro, California, CA FTBL

67110 (1) Gecko Road, unpublished consultant report prepared for FHWA CFLHD, for trip dates of May 6 to 8, 2013.

Atkins North America, Inc., Preliminary Plan and Profile for: CA FTBL 67110(1) Gecko Road, 33 sheets, dated February 13, 2015.

California Department of Transportation (Caltrans), Highway Design Manual, Topic 632.2, Performance Factors, Sacramento, California, issued May 7, 2012.

Federal Highway Administration, Federal Lands Highway Project Development and Design

Manual, Chapter 11 – Pavements, U.S. Department of Transportation, issued March 2008.

U.S. Department of Transportation, Federal Highway Administration, Project Development and

Design Manual (PDDM), Chapter 11 – Pavements, Government Printing Office, Washington

D.C, March 2008.

U.S. Department of Transportation, Federal Highway Administration, Standard Specifications for

Construction of Roads and Bridges on Federal Highway Projects FP-14, U.S.

Yeh and Associates, Inc. (2015a), Geotechnical Field Investigation Plan for Gecko Road

Network, CA FTBL 67110(1), Imperial County, California, memorandum prepared for Atkins

North America, Inc., YA Project No. 215-013, submitted January 29, 2015.

Yeh and Associates, Inc. (2015b), Geotechnical Field Investigation Summary for Gecko Road

Network, CA FTBL 67110(1), Imperial County, California, memorandum prepared for Atkins

North America, Inc., YA Project No. 215-013, submitted February 26, 2015

Yeh and Associates, Inc. (2015c), Draft Pavement Structural Sections for Gecko Road Network, CA FTBL 67110(1), Imperial County, California, memorandum prepared for Atkins North

America, Inc., YA Project No. 215-013, submitted March 27, 2015.

APPENDIX A - BORING LOGS

miles km

FIGUREPROJECT NAME:

PROJECT NUMBER: DATE:

Notes:

1. All boring locations noted by pins and drill number were advanced throught the existing pavement.

2. See boring logs for station, o�set and elevation of the drill hole locations.

Gecko Camp

Roadrunner Camp to Brawley

GECKO ROAD NETWORK

Imperial Sand Dunes Recreational Area Imperial County, CA

215-013 2015

Boring Location Plan

Page A-1 of 20

Page A-2 of 20

Page A-3 of 20

Page A-4 of 20

Page A-5 of 20

Page A-6 of 20

Page A-7 of 20

Page A-8 of 20

Page A-9 of 20

Page A-10 of 20

Page A-11 of 20

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Page A-13 of 20

Page A-14 of 20

Page A-15 of 20

Page A-16 of 20

1 *

Page A-17 of 20*changed station reference 9/9/2015

1 *

Page A-18 of 20

FIGUREPROJECT NAME:

PROJECT NUMBER: DATE:

Asphalt Concrete

Asphalt Concrete

Cement Treated Sand

(CTS)

Aggregate Base/Fill

~3.5 ft.

Notes:

1. Test pit located at southbound edge of pavement near drill hole 15P-107.

(lat. 32.94117, long. -115.14442).

2. Hand excavated on February 17, 2015 by Yeh and Associates. Logged by S. Boone and J. Blanchard.

3. CTS is: Poorly graded fine SAND (SP), light brown, dry, strongly cemented

4. AB is: Well graded GRAVEL with silt and sand (GW)-GM), light brown, dry, clasts to 3 inches

5. Artificial Fill is: Poorly graded fine SAND with gravel (SP), light brown, dry, likely sourced from local Dune Sand

Cement Treated Sand

(CTS)

GECKO ROAD NETWORK

Imperial Sand Dunes Recreational Area Imperial County, CA

215-013 2015

Test Pit 15T-107

Page A-19 of 20

FIGUREPROJECT NAME:

PROJECT NUMBER: DATE:

Asphalt Concrete

Cement Treated Base

Asphalt Concrete

Cement Treated Base

(CTB)

Aggregate Base

(AB)

1.5” Crack

1” Crack

Dune Sand

~2 ft.

~8 ft.

Notes:

1. Test pit located at southbound edge of pavement about 100 ft. north of drill hole 15P-111.

(lat. 32.91892, long. -115.12130).

2. Hand excavation on February 17, 2015 by Yeh and Associates. Logged by S. Boone and J. Blanchard.

3. CTB is: Well graded GRAVEL (GW), light brown, hard, dry, strongly cemented, grooves to ~1/4” with hammer, 3/4” gravel typical.

4. AB is: Well graded GRAVEL (GW-GM) with silt and sand, grayish brown, dense, dry, trace cobble sized clasts, subangular to angular, dense with 1 to 2 inches of sand cover

5. Dune Sand is: Poorly graded fine SAND (SP), light brown, dry, loose, subangular to subrounded

GECKO ROAD NETWORK

Imperial Sand Dunes Recreational Area Imperial County, CA

215-013 2015

Test Pit 15T-111

Page A-20 of 20

APPENDIX B - RESULTS OF LABORATORY TESTING

Project Name Project No.

Tested By Testing Date

15P-101 15P-102 15P-103 15P-104 15P-105 1 1 1 1 1

1.5 1.5 1.5 1.5 1.5

SP-SM SP SP SP SP

2.60 2.60 2.60 2.60 2.60 lig ht b ro w n, m oi st , f in e lig ht b ro w n, m oi st , f in e lig ht b ro w n, m oi st , f in e lig ht b ro w n, m oi st , f in e lig ht b ro w n, m oi st , f in e

1 1 1 1 1

432.84 451.69 450.67 454.11 445.25

49.20 49.20 49.20 49.20 49.20

101.13 101.10 101.10 101.10 101.10

106.84 106.84 106.84 106.82 106.83

ST-3 ST-40 ST-100 ST-35 ST-33

101.00 100.14 102.01 100.60 101.28

161.82 171.25 162.59 169.94 159.21

160.79 169.59 161.25 168.57 157.68

1.7% 2.4% 2.3% 2.0% 2.7%

1.696 1.794 1.789 1.807 1.761

1.667 1.752 1.749 1.771 1.714

105.8 112.0 111.6 112.7 109.9

104.0 109.3 109.2 110.5 107.0 8.0% 12.8% 12.1% 11.2% 13.6%

0.56 0.48 0.49 0.47 0.52

0.36 0.33 0.33 0.32 0.34

Gecko Road Network 215-013

Sample No.

DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING

Moisture and Density Measurements Test Methods: ASTM D2488, 2216, 2937

ND 2/28/2015

SPECIMEN ID AND CLASSIFICATION

Boring No.

Dish ID

Sample Depth (ft) Group Symbol Estimated Specific Gravity

Soil Description:

DIMENSIONS AND MASS

Number of Rings Mass of Moist Sample + Rings (g) Specimen Diameter (mm) Specimen Height (mm) Total Ring Mass (g)

WATER CONTENT

Porosity

Mass of Dish (g) Mass of Moist Soil + Dish (g) Mass of Dry Soil + Dish (g)

RESULTS

Water Content Total Density (Mg/m3) Dry Density (Mg/m3) Total Unit Weight (lbs/ft3) Dry Unit Weight (lbs/ft3) Saturation Void Ratio

Page B-1 of 19

15P-106 15P-107 15P-108 15P-109 15P-110 1 1 1 1 1

1.5 1.5 1.5 1.5 1.5

SP SP SP SP SP

2.60 2.60 2.60 2.60 2.60 lig ht b ro w n, m oi st , f in e lig ht b ro w n, m oi st , f in e lig ht b ro w n, m oi st , f in e lig ht b ro w n, m oi st , f in e lig ht b ro w n, m oi st , f in e

1 1 1 1 1

451.54 446.89 449.80 443.76 452.14

49.20 49.20 49.20 49.20 49.20

101.10 101.10 101.10 101.10 101.10

106.85 106.85 106.85 106.85 106.85

ST-48 ST-11 5 ST-34 ST-37

100.59 100.84 30.74 101.91 101.98

160.49 160.92 108.97 175.41 164.12

158.97 159.80 107.26 174.14 162.86

2.6% 1.9% 2.2% 1.8% 2.1%

1.793 1.769 1.784 1.753 1.796

1.748 1.736 1.745 1.723 1.760

111.9 110.4 111.3 109.4 112.1

109.1 108.3 108.9 107.5 109.8 13.9% 9.9% 11.9% 9.0% 11.3%

0.49 0.50 0.49 0.51 0.48

0.33 0.33 0.33 0.34 0.32

Gecko Road Network 215-013

Sample No.

DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING

Moisture and Density Measurements Test Methods: ASTM D2488, 2216, 2937

ND 2/28/2015

SPECIMEN ID AND CLASSIFICATION

Boring No.

Dish ID

Sample Depth (ft) Group Symbol Estimated Specific Gravity

Soil Description:

DIMENSIONS AND MASS

Number of Rings Mass of Moist Sample + Rings (g) Specimen Diameter (mm) Specimen Height (mm) Total Ring Mass (g)

WATER CONTENT

Porosity

Mass of Dish (g) Mass of Moist Soil + Dish (g) Mass of Dry Soil + Dish (g)

RESULTS

Water Content Total Density (Mg/m3) Dry Density (Mg/m3) Total Unit Weight (lbs/ft3) Dry Unit Weight (lbs/ft3) Saturation

Page B-2 of 19

15P-111 15P-112 15P-112 15P-113 15P-113 1 1 2 1 2

1.5 1.5 4.0 1.5 4.0

SP SP SP SP SP

2.60 2.60 2.60 2.60 2.60 lig ht b ro w n, m oi st , f in e lig ht b ro w n, m oi st , f in e lig ht b ro w n, m oi st , f in e lig ht b ro w n, m oi st , f in e lig ht b ro w n, m oi st , f in e

1 1 1 1 1

445.61 448.58 422.05 458.23 433.86

49.20 49.20 49.20 49.20 49.20

101.10 101.10 101.10 101.10 101.10

106.85 106.85 106.85 106.85 106.85

ST-5 ST-30 208 ST-47 58

100.34 100.22 30.19 100.77 30.46

156.59 173.51 115.35 169.28 107.88

155.69 172.45 113.60 167.97 105.06

1.6% 1.5% 2.1% 1.9% 3.8%

1.762 1.778 1.640 1.828 1.701

1.734 1.752 1.606 1.793 1.639

110.0 110.9 102.3 114.1 106.2

108.2 109.3 100.2 111.9 102.3 8.5% 7.9% 8.8% 11.3% 16.8%

0.50 0.48 0.62 0.45 0.59

0.33 0.33 0.38 0.31 0.37

Gecko Road Network 215-013

Sample No.

DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING

Moisture and Density Measurements Test Methods: ASTM D2488, 2216, 2937

ND 2/28/2015

SPECIMEN ID AND CLASSIFICATION

Boring No.

Dish ID

Sample Depth (ft) Group Symbol Estimated Specific Gravity

Soil Description:

DIMENSIONS AND MASS

Number of Rings Mass of Moist Sample + Rings (g) Specimen Diameter (mm) Specimen Height (mm) Total Ring Mass (g)

WATER CONTENT

Porosity

Mass of Dish (g) Mass of Moist Soil + Dish (g) Mass of Dry Soil + Dish (g)

RESULTS

Water Content Total Density (Mg/m3) Dry Density (Mg/m3) Total Unit Weight (lbs/ft3) Dry Unit Weight (lbs/ft3) Saturation

Page B-3 of 19

15P-114 15P-115 1 1

1.5 1.5

SP SP

2.60 2.60 lig ht b ro w n, m oi st , f in e lig ht b ro w n, m oi st , f in e

1 1

456.29 452.33

49.20 49.20

101.10 101.10

106.85 106.85

ST-00 ST-50

100.35 101.66

166.05 155.75

164.82…