CA_FTBL_67113(1)_Grays_Well_Road_Pavement_Engineering_Rpt_Final.pdf

PAVEMENT ENGINEERING REPORT

CA FTBL 67113 (1)

GRAYS WELL ROAD NETWORK

IMPERIAL SAND DUNES RECREATION AREA

IMPERIAL COUNTY, CALIFORNIA

YEH PROJECT NO.: 215-012

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 67113 (1)

GRAYS WELL ROAD NETWORK

IMPERIAL SAND DUNES RECREATION AREA

IMPERIAL COUNTY, CALIFORNIA

YEH PROJECT NO.: 215-012

JUNE 8, 2015*

Prepared by:

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

Independent Reviewer:

Robert F. LaForce, P.E.

Sr. Materials Engineer

*revised station references 9/9/18

* Errata sheet C-2

Pavement Engineering Report Yeh Project No. 215-012 Grays Well 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 GRAYS WELL ROAD

FIGURE 4: SUMMARY OF STRUCTURAL SECTION RECOMMENDATIONS

List of Tables

TABLE 1: EXISTING PAVEMENT CONDITIONS ENCOUNTERED

TABLE 2: SUBGRADE SOIL PROPERTIES TEST SUMMARY

List of Appendices

Page Appendix A – Boring Logs

Boring Location Plan .............................................................................................................................. A-1 Fence Diagram for Grays Well Road Boreholes ....................................................................................... A-2 Legend for Symbols used on Borehole Logs ............................................................................................ A-3 Borehole Logs for 15P-01 to 10 ..................................................................................................... A-4 to 13

Appendix B – Results of Laboratory Testing Moisture and Density Measurements .................................................................................................... B-1 Percent Passing No. 200 Sieve ................................................................................................................ B-2 Mechanical Sieve Analysis ...................................................................................................................... B-3 Proctor Compaction ........................................................................................................................ B-4 to 5 California Bearing Ratio ................................................................................................................... B-6to 8

Appendix C – Pavement Design Calculations AASHTO (1993) Spreadsheet calculations ........................................................................................ C-1 to 2

Appendix D – Draft Pavement Structural Sections memorandum (2 pages)

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

Grays Well 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 Grays Well 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 Grays Well Road network were presented in a memorandum submitted to Atkins in April 2015 (Yeh 2015). Based on review of the alternatives, Yeh has recommended to pulverize and recompact existing the roadway using full depth reclamation

(FDR) with an overlay of new hot mix asphalt concrete pavement (HACP).

Figure 1: Project Location Map (no scale)

Grays Well Road is located within the Imperial Dunes south of Interstate Highway 8 and approximately 40 miles east of El Centro, California. The existing roadway is two lanes, paved with asphalt concrete. The road runs about parallel to I-8 from the end of the off ramp at the

Buttercup Ranger Station for approximately 4 miles to the west where the pavement ends and a dirt extension of the road continues. Luis Aguilar Road intersects with Grays Well Road at the ranger station, and runs for approximately 0.5 miles east providing access to camp pads and terminating in a paved turnaround (approximately 175 feet in diameter). The Midway

Campground with an unpaved road network is located approximately 2.6 miles west of the ranger station. The historic Plank Road turnoff is located 3.2 miles west of the ranger station.

Plank Road is approximately 0.1 miles long and ends at a paved parking area and the Plank

Road historic marker. 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, NS 24 feet on Luis Aguilar

Road. The roadway is mostly constructed on embankment or near adjacent grade. The embankment fill ranges in thickness up to about 15 feet with typical 1:3 (vertical to horizontal) 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 10 borings in Grays Well Road on February 19, 2015. Memoranda describing the field exploration program 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 was 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 the 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. Test 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, and California Bearing Ratio (CBR were performed as part of this program. The results of laboratory tests are presented in Appendix B. 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, Figure 2) as Holocene-aged unconsolidated eolian deposits (Qs-Dune Sand) and alluvium (Qa-Alluvium). The Imperial Sand

Dune Recreation Area is mostly within the Algodones dune field that stretches for 43 miles from east of Calipatria to south of the US-Mexico border. The dune field has a generally uniform width, ranging from 4 to 7 miles 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.

Gray Well Road runs generally east-west within the southern part of the dunes, crossing the western margin of the active Algodones Dunes and the mapped trace of the San Andreas fault just beyond and west of Midway Campground. Localized areas of relatively flat interdunal depressions are mapped as alluvium within the dune complex, such as is shown along Luis

Aguilar Road. However, in all cases the borings drilled for this report encountered sandy fill material or dune sand that either concealed or could not be differentiated from the alluvium.

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, exposing large areas of former lakebed allowing sandy nearshore sediments to be blown southeast by the prevailing westerly and northwesterly winds.

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

5. SITE CONDITIONS

5.1 Terrain and Vegetation

Grays Well Road is within the undulating topography of the Imperial Dunes, and flat terrain to the west of the dunes beyond the Plank Road turnout. The dunes are active within only sparse vegetation consisting of occasional shrubs, and relatively heavy off-highway recreational vehicle use. Vegetation is more prevalent within alluvial areas mapped west of Plank Road. The ground elevation along Grays Well Road undulates through the dunes between approximately elevation (el.) 162 feet at the western terminus of the project, el. 172 feet at the Buttercup

Ranger Station, and with a high of approximately el. 235 feet near the Midway Campground.

The terrain west of Plank Road is relatively flat and ranges between approximately el. 162 and

165 feet, as is the terrain along Luis Aguilar Road that undulates at approximately el. 172 feet.

5.2 Climate

The climate data (www.usclimatedata.com) for Yuma, Arizona (located approximately 15 miles east of the Grays Well Road area, reports an average annual rainfall at of 3.09 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 high temperature ranges from a low of 69 degrees for December and January to a high of 107 degrees in July.

5.3 Existing Pavement Surface Condition

The exposed pavement surface along Grays Well Road consisted of asphalt concrete, with local recent overlays. The overall roadway was in poor to fair condition with a posted limiting speed of 35 mph. The pavement surface conditions observed along Grays Well Road were generally distressed shoulder to shoulder by a raveled and disintegrated pavement surface. Highly developed block and transverse cracking (Distress Type ACP 2) were typical along the alignment, with areas of secondary cracking up to 12 inches wide along some transverse joints.

As a result, chunks of the pavement were dislodged and localized low to moderately severe potholing was observed along some block and transverse cracks. A low to moderate level of reflective cracking was observed along block joints where the pavement was overlaid in or about 2008 (Grays Well Road Improvement Project, NDR080004). The Plank Road turnoff was paved in 2014 (personal communication with Neil Hamada, BLM, during 2015 site work), and the parking area was widened by placing about 4 inches of new asphalt over a compacted sand subgrade.

The pavement surface along Luis Aguilar Road had less severe raveling and moderate block cracking. It appears that crack sealing and filling has been performed as part of roadway maintenance. Typical surface pavement conditions observed along Grays Well 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 Grays Well 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 of variable thicknesses of asphalt concrete overlying asphalt or cemented treated base materials and aggregate base.

The thicknesses of the various layers are variable that may be associated with differences in past phases of roadway construction, subgrade repair with additional base material, overlays, and seal coatings. The base materials were underlain by sandy subgrade soils composed of

Figure 3: Typical Surface Pavement Conditions along Grays Well Road Top left to right: ~Sta. 106+00, Sta. 167+50, Sta. 176+00

Bottom left to right: Sta. 189+00, Sta. 281+50 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-01

106+07, 7’ lt.

Fabric

-- -- Sand

A-3(0)

15P-02 139+39, 12’ lt.

Fabric

-- -- Sand

A-3 (0)

15P-03 167+78, 4’ rt.

Fabric 12” ATB Sand

A-3 (0) 15P-04

189+55, 9’ lt.

4.5

Fabric 6.5 CTB Sand A-3 2008 overlay

15P-05 220+00, 8’ lt.

4.5 Fabric 8 ATB Sand

A-3 (0) 2008 overlay

15P-06 249+48, 9’ lt. 4 13 AB Sand

A-3 (0) 15P-07

281+59, 8’ lt. 3 33 AB Sand A-3 (0)

15P-08 309+21, 5’ lt. 12 -- -- Sand

A-3 (0) 15P-09

1320+85, 8’ rt. * 2 10 AB Sand A-3 (0) Luis Aguilar Road

15P-10 144+17, 175’ rt. 11 -- -- Sand

A-3(0) 2014 overlay

AB – aggregate base, ATB – asphalt treated base, CTB – cement treated base

Subgrade Conditions. Subgrade soils encountered below the structural section in each of the borings generally consisted of loose to medium dense sand and sand with silt. The subgrade soils consisted of embankment fill associated with the construction of the existing Grays Well

Road network that appears to be derived from local dune sand, and natural dune sands that are predominant throughout the project area.

Subgrade Properties. Laboratory test results for drive samples had moisture contents ranging from approximately 0.8 to 6 percent and dry unit weights that ranged from approximately 100 to

108 pounds per cubic foot (pcf). Modified Proctor tests performed on bulk samples recovered from borings 15P-03 and 05 had estimated maximum dry unit weights of approximately 116 and

109 pcf with an optimum 11 percent moisture content for compaction.

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

*changed station reference 9/9/2015

The percentage of fines (less than No 200 Sieve) from wash samples and mechanical sieve analyses ranged from approximately materials ranged from 1 to 6 percent. 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-02 139+39, 12’ lt. 13.0 21 A-3(0) Poorly graded SAND with silt (SP-SM)

15P-06 249+48, 9’ lt. 12.8 24 A-3(0) Poorly graded SAND (SP)

15P-06 249+48, 9’ lt. 13.0 8 A-3 (0) Poorly graded SAND with gravel (SP), (with 50% AC grindings)

7. GEOTECHNICAL CONSIDERATIONS FOR DESIGN AND CONSTRUCTION

Geotechnical engineering related conditions that could affect design and construction include compaction the subgrade soils, and construction operation within a loose dune sand 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.

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

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.

7.3 Loose Dune Sand

The Grays Well Road project is within an active sand dune and dry desert type environment.

Dry surface soils within the sand dunes and the subgrade soil 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 Grays Well Road includes a deep section of asphalt, asphalt treated and cement treated base, and aggregate base. The pulverization for FDR may need to address a variable thickness and composition of those materials. 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 depth of 14 inches is recommended to extend below the thickness of the asphalt encountered in the borings; however, equipment should be capable of pulverization to a depth of at least 18 inches to account for potential variability in the pavement thickness.

Compaction of FDR material. The recommended depth of pulverization is generally thicker than what would be considered suitable for compaction in a single layer. The upper 6 to 8 inches of the pulverized material should be removed and replaced to allow the FDR material to be compacted in two lifts, and to achieve compaction within the deeper portions of the pulverized material.

Paving Fabric. A paving fabric/geotextile was encountered within the existing asphalt concrete encountered in selected borings. The fabric appears to have been used in association with past pavement overlays. Fabric can become bound up or trapped within pulverization equipment and

1 0 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 Grays Well 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. 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.

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 Grays Well Road is approximately 155 vehicles per day, with an annual average daily traffic (ADT) of approximately 105 vehicles per day. The traffic is reported to be composed of 2 percent trucks, 5 percent buses and 85 percent recreational vehicles (RV). The ADT was 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 635,039 for the

Grays Well Road network. =

The dune sand encountered along Grays Well 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 21 and 24 percent at 0.2 inches. The recommended structural section thicknesses were estimated considering a resilient modulus (Mr) of 23,200 psi for the sandy subgrade soils encountered and the range of the CBR results considered.

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8.2 Structural Section

The roadway structural section for the Grays Well Road network should consist of at least 3 inches of hot mix asphalt concrete pavement (HACP) placed over compacted FDR material. A summary of the structural section recommendations is shown in Figure 4.

Figure 4: Summary of Structural Section Recommendations

Full Depth Reclamation. FDR should consist of pulverizing the existing asphalt pavement, cement treated base material, and subgrade to a typical depth of 14 inches or 1 inch into the subgrade in accordance with FP-14 Section 304, Method 2. The 14-inch typical depth should penetrate the estimated thickness of the existing asphalt pavements and treated base materials encountered in the borings. The FDR material may be regraded in some areas to provide for the new superelevation and minor widening of the roadway. A minimum thickness of 6 inches of compacted FDR material should be provided below the asphalt layer to provide for the design traffic loading and subgrade conditions. FDR material should not be compacted in lifts greater than 10 inches thick. Where the thickness of FDR will be greater than 10 inches, the upper 6 to

8 inches of the FDR should be removed to allow for compaction of the FDR in at least two lifts.

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 and storm runoff to erode of the sandy embankment materials and dune sand from beneath the edge of 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

1 2 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 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.

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 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, Class 1, Type E Geotextile, of FP-14. Gravel for stabilization should consist of uniformly graded 3/8 to 1.5-inch 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 yard 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

1 3 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, and 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.

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 Grays Well

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 of FDR within the prism of the existing roadway and minor widening of the embankment slopes. 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

1 4 widened, the new fill should be keyed into the existing slope such that at 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 content that is suitable for compaction.

8.6.3 Earthwork Factors

As previously discussed in this report, the holes drilled for the Grays Well 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. The subgrade generally consisted of loose to medium dense sand. Drive samples had dry unit weights that ranged from approximately 100 to 108 pcf. The maximum dry unit weight of the sand estimated from Proctor tests was approximately 109 to 116 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 the soil density likely occur in areas where the existing pavement subgrade and embankment fill materials were compacted, deposition of sand 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 0.92 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 0.90 can be used for on-site borrow or compaction of the subgrade for embankment widening. The earthwork factors are approximate, and should be checked and adjusted as-needed as the grading work progresses.

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.

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9. MATERIAL SOURCES

The main material requirements for this project are likely to provide hot mix asphalt that can be placed following full depth reclamation of the existing roadway. Smaller quantities of aggregate base and general borrow may also be needed. Grays Well Road is located approximately 40 miles east of El Centro, California and about 20 miles west of 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 pavement. Route from plant to Grays Well Road is about 23 miles (I-8 corridor).

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

Well Road is about 47 miles (Heber-CA111-I-8).

• Granite Construction Company, 2095 CA-111, El Centro, CA 92243. A call to their office in March 2013 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 particles should be suitable for use as shoulder backing material. There are various active and abandoned mining operations near-by the site; however, it is not anticipated that the project will

1 6 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.

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

1 7

67113 (1) Grays Well 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 67113(1) Grays Well

Road, 18 sheets, dated March 11, 2015.

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

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.

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, 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 Grays Well Road

Network, CA FTBL 67113(1), Imperial County, California, memorandum prepared for Atkins

North America, Inc., YA Project No. 215-012, submitted January 28, 2015.

Yeh and Associates, Inc. (2015b), Geotechnical Field Investigation Summary for Grays Well

Road Network, CA FTBL 67113(1), Imperial County, California, memorandum prepared for

Atkins North America, Inc., YA Project No. 215-012, submitted February 26, 2015

Yeh and Associates, Inc. (2015c), Draft Pavement Structural Sections for Grays Well Road

Network, CA FTBL 67113(1), Imperial County, California, memorandum prepared for Atkins

North America, Inc., YA Project No. 215-012, revised and resubmitted March 31, 2015.

APPENDIX A - BORING LOGS

miles km

FIGUREPROJECT NAME:

PROJECT NUMBER: DATE:

Notes:

1. All boring locations noted by pins and drill numbers were advanced through the existing pavement.

2. See boring logs for station, offset and elevation of the drill hole locations.

I-8/Grays Well Rd. Interchange

Buttercup Ranger Station

Luis Aguilar Road

Plank Road

Midway Camp

< to El Centro

GRAYS WELL ROAD NETWORK

Imperial Sand Dunes Recreational Area Imperial County, CA

215-012 2015

Boring Location Plan

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1 *

Page A-12 of 13*changed station reference 9/9/15

Page A-13 of 13

APPENDIX B - RESULTS OF LABORATORY TESTING

Project Name Project No.

Tested By Testing Date

15P‐02 15P‐03 15P‐05 15P‐06 15P‐08

1 1 1 1 1

1.5 1.5 1.5 1.5 1.5

SP‐SM SP SP SP SP‐SM

2.60 2.60 2.60 2.60 2.60 lig h t b ro w n , m o is t, f in e lig h t b ro w n , m o is t, f in e lig h t b ro w n , m o is t, f in e lig h t b ro w n , m o is t, f in e lig h t b ro w n , m o is t, f in e, sl ig h tl y ce m en te d

1 1 1 1 1

426.69 433.39 441.43 418.84 431.01

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‐38 A‐3 A‐5 A‐4 91

101.80 8.46 8.51 8.46 30.74

158.17 69.26 61.79 71.49 112.37

156.92 68.70 61.35 70.90 111.27

2.3% 0.9% 0.8% 0.9% 1.4%

1.664 1.699 1.741 1.623 1.687

1.627 1.683 1.726 1.608 1.664

103.8 106.0 108.6 101.3 105.2

101.5 105.0 107.7 100.3 103.8

9.9% 4.4% 4.3% 4.0% 6.3%

0.60 0.54 0.51 0.62 0.56

0.37 0.35 0.34 0.38 0.36

Grays Well Road Network 215‐012

Sample No.

DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING

Moisture and Density Measurements

Test Methods: ASTM D2488, 2216, 2937

ND 3/1/2015

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 8

Washed

Boring Sample Depth ft Tin ID

Tin Mass, g Tin+Soil g

Tin+Dry

Soil, g

Tin+Dry

Soil, g

Passing

No. 200

Water

Content

15P‐02 1 1.5 ST‐38 101.8 158.17 156.92 153.6 6.0% 2.3%

15P‐05 1 1.5 A‐5 8.51 61.79 61.35 59.98 2.6% 0.8%

15P‐06 1 1.5 A‐4 8.46 71.49 70.9 70.17 1.2% 0.9%

Prewash

DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING

Percent Passing No. 200 Sieve

Test Method: ASTM D1140, D2487

Project Name Grays Well Road Network Project No. 215‐012

Tested By ND Testing Date 2/28/2015

SPECIMEN ID AND MEASUREMENTS

Classification

Poorly‐graded SAND w/ silt (SP‐

SM): lt. brn., moist, fine

Poorly‐graded SAND (SP): light brown, moist, fine

Poorly‐graded SAND (SP): light brown, moist, fine

Page B-2 of 8

Project No.

Testing Date

15P‐06 Sample No. A Depth (ft) 1.5‐4.0

Soil Description

Dish ID ST‐51 177.01 Water Content 0.9%

Dish Mass (g) 102.71 176.36 Dry Post‐Wash (g) 72.15

Sieve No. Size, mm Mass Retained (g) % Retained % Passing

3 in 76.2 0.0% 100.0%

2 in * 50.8 0.0% 100.0%

1 in * 25.4 0.0% 100.0%

3/4 in * 19.1 0.0% 100.0%

1/2 in * 12.7 0.0% 100.0%

3/8 in * 9.50 0.0% 100.0%

No. 4 * 4.75 0.00 0.0% 100.0%

No. 10 2.00 0.16 0.2% 99.8%

No. 20 0.84 0.31 0.6% 99.4%

No. 40 0.425 0.89 1.8% 98.2%

No. 60 0.250 4.75 8.3% 91.7%

No. 100 0.150 37.19 58.8% 41.2%

No. 200 0.075 28.80 97.9% 2.1% Pan ‐‐ 0.19 Sieve Continuity 99.8%

72.10 72.29

0.00

0.16

0.47

1.36

6.11

43.30

0.00

0.00

0.00

0.00

0.00

0.00

Poorly‐graded SAND with silt (SP): light brown, moist, fine

SIEVE MEASUREMENTS

Moist Soil + Dish (g)

Dry Soil + Dish (g)

Cumulative Retained (g)

Tested By ND 3/1/2015

SPECIMEN ID AND CLASSIFICATION

Boring No.

DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING

Mechnical Sieve Analysis

Test Method: ASTM D6913, D2487

Project Name Grays Well Road Network 215‐012

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.010.1110100

P as si ng

Particle Diameter (mm)

Gradation Curve

Cu=2.1 Cc=0.03

Page B-3 of 8

Boring No. 15P-03 Sample No. A Depth (ft) 1.5-4.0 Soil Description

Test Method (D698/D1557) D1557 Ram. Mass (g) 4530 # of Lifts 5 Mold Volume (cm3) 943 Mold Mass(g) 2001 Blows/ Lift 25

Mass of Soil + Mold (g) 3821 3888 3945 3916 Dish ID ST-9 ST-40 ST-33 ST-100 Mass of Dish (g) 100.15 100.15 100.16 102.04 Mass of Moist Soil + Dish (g) 680.24 680.63 714.11 738.39 Mass of Dry Soil + Dish (g) 649.48 636.74 652.56 664.12

Water Content 5.6% 8.2% 11.1% 13.2%

Dry Density (Mg/m3) 1.828 1.850 1.855 1.794

Dry Unit Weight (lbs/ft3) 114.0 115.4 115.7 111.9

Lab Max. Dry Density (Mg/m3) 10.9%

Lab Max. Dry Unit Wt. (lbs/ft3)

EQUIPMENT AND PROCEDURE

DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING

Proctor Compaction Test Method: ASTM D698, D1557

Grays Well Road Network 215-012

ND 3/11/2015

SPECIMEN ID AND CLASSIFICATION

Poorly-graded SAND (SP): light brown, moist, fine

DENSITY AND MOISTURE MEASUREMENTS

RESULTS

1.858 Optimum Water Content (%)

115.9

2% 6% 10% 14% 18% 22% 26% 30%

D ry

U ni t W ei gh t

(lb s/ ft3 )

Water Content (%)

Compaction Curve

ZAV Curve (Gs=2.6)

Page B-4 of 8

Boring No. 15P-05 Sample No. A Depth (ft) 1.5-4.0 Soil Description

Test Method (D698/D1557) D1557 Ram. Mass (g) 4530 # of Lifts 5 Mold Volume (cm3) 943 Mold Mass(g) 2001 Blows/ Lift 25

Mass of Soil + Mold (g) 3724 3758 3838 3840 Dish ID 4 10 31 8 Mass of Dish (g) 1,048.67 1,046.20 723.75 952.78 Mass of Moist Soil + Dish (g) 1,374.83 1,433.08 1,180.78 1,497.57 Mass of Dry Soil + Dish (g) 1,355.42 1,402.22 1,133.14 1,430.34

Water Content 6.3% 8.7% 11.6% 14.1%

Dry Density (Mg/m3) 1.718 1.715 1.745 1.709

Dry Unit Weight (lbs/ft3) 107.2 107.0 108.9 106.7

Lab Max. Dry Density (Mg/m3) 11.6%

Lab Max. Dry Unit Wt. (lbs/ft3)

EQUIPMENT AND PROCEDURE

DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING

Proctor Compaction Test Method: ASTM D698, D1557

Grays Well Road Network 215-012

ND 3/11/2015

SPECIMEN ID AND CLASSIFICATION

Poorly-graded SAND (SP): light brown, moist, fine

DENSITY AND MOISTURE MEASUREMENTS

RESULTS

1.745 Optimum Water Content (%)

108.9

2% 6% 10% 14% 18% 22% 26% 30%

D ry

U ni t W ei gh t

(lb s/ ft3 )

Water Content (%)

Compaction Curve

ZAV Curve (Gs=2.6)

Page B-5 of 8

DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING

Test Method: ASTM D1883, T193

Project No.

Testing Date

15P‐02 Depth (ft)

4530 5

Mold + Soil Mass (g) 11399 25

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

Dry Unit Weight (lbs/ft3)

Molding Water Content (%) 13.0%

REMARKS

Surcharge (lbs) 105.2

1001.79

Dish ID Dish ID T‐4 1048.77 1389.47

1348.96

# of Lifts

Blows/ Lift

Ram. Mass (g)2124

AFTER TESTMOLDING

California Bearing Ratio

Project Name

Tested By

Grays Well Road Network

ND

COMPACTION AND WATER CONTENT

Soil Description Poorly‐graded SAND with silt (SP‐SM): light brown, moist, fine

SAMPLE ID AND CLASSIFICATION

Boring No. A 1.5‐4.0

215‐012

3/12/2015

CBR at 0.2 inches (%) 21%

Sample soaked prior to penetration.

RESULTS

CBR at 0.1 inches (%)

Mold Volume (cm3)

17%

Swell During Soak (%) Post‐Test Water Content (%)

N/A 13.5%

Sample No.

Mold Mass (g)

T‐23 630.74 1049.98

0 0.1 0.2 0.3 0.4 0.5

St re ss O n P is to n , p

Penetration, inches

Page B-6 of 8

Project No.

Testing Date

15P‐06 Depth (ft)

4530 5

Mold + Soil Mass (g) 11306 25

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

Dry Unit Weight (lbs/ft3)

Molding Water Content (%) 12.8%

REMARKS

Surcharge (lbs) 102.1

1396.02

Dish ID Dish ID T‐2 956.65 1403.98

1352.06

# of Lifts

Blows/ Lift

Ram. Mass (g)2124

AFTER TESTMOLDING

California Bearing Ratio

Project Name

Tested By

Grays Well Road Network

ND

COMPACTION AND WATER CONTENT

Soil Description Poorly‐graded SAND (SP): light brown, moist, fine

SAMPLE ID AND CLASSIFICATION

Boring No. A 1.5‐4.0

215‐012

3/12/2015

CBR at 0.2 inches (%) 24%

Sample soaked prior to penetration.

RESULTS

CBR at 0.1 inches (%)

Mold Volume (cm3)

20%

Swell During Soak (%) Post‐Test Water Content (%)

N/A 13.1%

Sample No.

Mold Mass (g)

T‐3 951.09 1452.99

0 0.1 0.2 0.3 0.4 0.5

St re ss O n P is to n

Page B-7 of 8

Project No.

Testing Date

15P‐06 Depth (ft)

4530 5

Mold + Soil Mass (g) 11410 25

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

Dry Unit Weight (lbs/ft

7%

Swell During Soak (%) Post‐Test Water Content (%)

N/A 12.7%

Sample No.

Mold Mass (g)

T‐30 636.96 1383.86

A 1.5‐4.0

215‐012

3/12/2015

CBR at 0.2 inches (%) 8%

Sample soaked prior to penetration.

RESULTS

CBR at 0.1 inches (%)

Mold Volume (cm3)

California Bearing Ratio

Project Name

Tested By

Grays Well Road Network

ND

COMPACTION AND WATER CONTENT

Soil Description Poorly‐graded SAND with gravel (SP): light brown, moist, fine, w/ 50% grindings

SAMPLE ID AND CLASSIFICATION

Boring No.

# of Lifts

Blows/ Lift

Ram. Mass (g)2124

AFTER TESTMOLDING

1298.01

Dish ID Dish ID T‐5 1049.27 1464.58 1417.9

Molding Water Content (%) 13.0%

REMARKS

Surcharge (lbs) 108.6

0 0.1 0.2 0.3 0.4 0.5

St re ss O n P is to n

Page B-8 of 8

APPENDIX C - PAVEMENT DESIGN CALCULATIONS

Flexible Pavement Thickness Design - Spreadsheet

Client Name: Atkins Project Number: 215-012 Project Name: Grays Well Road Network Improvements Date:

Case: HACP on 14" pulverized

Ref.

FHWA, Federal Lands Highway Project Development and Design Manual , Chapter 11 – Pavements, U.S. Department of Transportation, issued March 2008.

Mr Correlation: 2

(a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) (l) (m) (n) (o) (p) (q)

Case R-value Wt18, EDAL's Design Life Reliablility (3) Req'd SN(1) W18 log(W18) ZR

Std. Dev.

So

(2) po pt ∆psi S1

MR

(psi) log(W18) difference

Grays Well Road 40.0 87 20 75 1.88 635039 5.803 -0.674 0.49 4.2 2.0 2.2 -- 23200 5.803 0.000

1) find req'd SN by using goal-seek to set "difference" column to zero by changing the value in the "SN" column in the same row

2) per FHWA (2008) PDDM, Ch. 11 use 0.49 for flexibile pavement design, use 0.39 for rigid pavement design

3) per FHWA (2008) PDDM, Ch. 11 use 75% for < 2,500 ADT; 85% for 2500-5000 ADT, 90% for >5000 ADT (CFL uses 75%)

II. AASHTO Conversion and data summary:

Select a design R-value for roadbed: Sample: 2A 6A Reliability ZR

Soil: SP-SM SP SP-SM+AC 50 0 R-value 40 CBR 21 24 8 60 -0.253 CBR = 15 MR = 1500xCBR (psi): 31500 36000 12000 70 -0.524

MR (psi) 23200 Equivalent R-value: 55 63 20 75 -0.674 Equations/Definitions: 80 -0.841

Col. (f), Req'd…