APPENDIX D GEOTECHNICAL ENGINEERING RECOMMENDATIONS

Transcription

1 APPENDIX D GEOTECHNICAL ENGINEERING RECOMMENDATIONS

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3 USKH Juneau International Runway 8/26 Rehabilitation Prepared For: Prepared By: 11/27/2013 PND No November 2013

4 TABLE OF CONTENTS Page No. 1. INTRODUCTION Purpose and Scope Project Description BACKGROUND FIELD INVESTIGATION AND LABORATORY TESTING Field Investigation Drilling Methods/Procedures Dynamic Cone Penetrometer ANALYSES PAVEMENT DISTRESS PND-1, Station PND-2, Station PND-3, Station PND-4, Station PND-5, Station PND-6, Station PND-7, Station PND-8, Station PND-9, Station PND-10, Station PND-11, Station RECOMMENDATIONS Overall Recommendations Specific Recommendations at Distress Sites Investigated OTHER DESIGN AND CONSTRUCTION CONSIDERATIONS CLOSURE REFERENCES Page 1 of 2

5 LIST OF TABLES Table 3-1. Summary of DCP test data. DCP was driven continuously to depth up to 5.5in. below top of subgrade Table 4-1. BERG2 Analysis Parameters for Frost Depth... 4 Table 5-1. Summary of Pavement Core Distress... 7 Table 6-1. Recommendations for Pavement Distress Locations Investigated... 9 LIST OF FIGURES Figure 3.1 Core Barrel... 2 Figure 3.2 DCP Test Operation... 3 LIST OF APPENDICES Appendix A- Site Plan and Sampling Locations Appendix B- Bore Hole Logs Appendix C- Lab Test Results Appendix D- DCP Test Data Appendix E- FAARFIELD Analysis LIST OF ABBREVIATIONS a.c. Asphalt Concrete AC Advisory Circular CBJ City and Borough of Juneau CBR California Bearing Ratio CDF Controlled Density Fill DCP Dynamic Cone Penetrometer FAA Federal Aviation Administration FOD Foreign Object Debris HMA Hot Mix Asphalt I.D. Inner Diameter of split spoon sampler JNU Juneau International Airport PFC Porous Friction Course SP Poorly Graded Sand SP-SM Poorly Graded Sand with Silt STA. Station SW Well Graded Sand Page 2 of 2

6 1. INTRODUCTION 1.1 Purpose and Scope This report presents the results of a limited geotechnical field investigation performed for USKH in support of the evaluation of the Juneau International Airport (JNU) Runway 08/26 Rehabilitation. The scope of services summarized in this report includes: A drilling and sampling program that spanned the length of the airport runway, excluding the recent Runway 08/26 extension; Laboratory testing on represented samples to determine general soil index properties; Engineering recommendations; Preparation of this report. PND Engineers, Inc. (PND) received authorization to obtain security clearance and perform initial field work for this investigation in August PND received Notice to Proceed for the remaining laboratory testing, office analysis and report preparation on September 30, Project Description The CBJ is planning to rehabilitate the a.c. paving for the runway at the Juneau International Airport. As part of the rehabilitation project, USKH performed a visual pavement inspection program that identified and characterized a variety of pavement asphalt distresses along with their approximate locations along the runway. These distress locations were provided to PND to perform further geotechnical investigations in support of rehabilitation recommendations. One particular pavement distress type, of concern to the runway rehabilitation project, is longitudinal cracking in the pavement surface. The longitudinal cracking is categorized into groups as defined by USKH, depending on the length, concentration and degree of severity. One group of longitudinal cracks, span the entire length of the runway and in our opinion are considered to be related to construction joints from a runway pavement rehabilitation project performed in A second grouping of longitudinal cracks is more enigmatic and exists in discontinuous zones bounded by existing runway pavement construction joint cracks. PND, under the direction of USKH, performed a drilling and sampling program during September 16-19, 2013 with the objective of obtaining the information necessary to evaluate the pavement distresses, and to provide recommendations in support of the design work to be completed by USKH. 2. BACKGROUND Historic background information on paving and rehabilitation, specific to the JNU Runway, was obtained from previous reports provided by USKH. For purposes of discussion, the JNU Runway is divided into two geographical subdivisions, a west end and an east end. The west end/east end boundary is equivalent to the present day Sta near Taxiway E shown on the Existing Site Plan in Appendix A, Sheet 1. The following provides a brief description of the construction history: 1942: Original construction of the JNU airport : Various expansion projects of the JNU airport. The west end comprises the originally constructed runway and dimensions approximately 480 feet in width and 4,969 feet in length. The east end is comprised of two separate extensions onto the west end with dimensions of approximately 268 feet in width and 3,488 feet in length. The two divisions combine for a total of 8,456 feet in length. 1982: The upper layer of the entire runway was surfaced with a porous friction course of approximately 3 inches in thickness. Page 1 of 11

7 1997: Approximately 2.75 inches of the entire runway surface was milled to remove the PFC layer and replaced with the same thickness of a.c. The rehabilitation plans reveal that the inside 9 feet (out to the lights) was milled and overlaid. Prior to installation of the new a.c. pavement existing transverse cracks were repaired and overlaid with a non-woven geotextile centered over the cracks to minimize potential of reflection cracks through the new surface. To date the west end region consists generally of surface a.c. thicknesses of 6 to 8 inches overlaying asphalt emulsion sand. The east end region consists generally of surface a.c. with thicknesses ranging from 10 to 12 inches over a subgrade. Approximately 6 feet of sand, comprising the bulk of the subgrade material, underlays the composite a.c. layers of the entire runway. The runway shoulders vary in thickness from 1.5 to 3 inches. 2011: FAA conducts inspection of the JNU airport a.c. pavement. The inspection results indicate the runway pavement surface is deteriorating and producing foreign object debris (FOD) that potentially could be dangerous to airplane traffic and public safety and is in need of repair. The inspection also revealed longitudinal and alligator cracking spanning the entire length of the runway and 2013: Emergency repairs were performed on the middle sections of the runway to mitigate the production of FOD. In October 2012, an a.c. patch of 15 feet in width and spanning the entire runway length is placed on each side of the runway centerline. In June 2013, a similar a.c. patch of 7 feet in width and spanning the entire runway length was rehabilitated. In both a.c. patch placements, 2-foot bands on each side of the runway centerline are left untouched to avoid interference with the runway centerline lights (see runway sections provided in Appendix A). 3. FIELD INVESTIGATION AND LABORATORY TESTING 3.1 Field Investigation The geotechnical field investigation was originally designed to consist of a prioritized combination of eleven pavement coring locations and eight borehole drilling and soil sampling locations. Airport runway closures from 10:30 p.m. to 5:00 a.m. allowed work crews to conduct drilling operations on a night shift. Due to time restrictions and some delays from medevac flights, however, the program was modified in coordination with USKH and CBJ. It was decided to reprioritize pavement coring locations, and eliminate three previously planned boreholes. Borehole drilling and soil sampling was eliminated at Station 5+25, Station 16+00, and Station 46+00; only asphalt coring was performed in these locations. Additionally, DCP tests were performed on the pavement surface and in select locations of the base material. The drilling locations were identified using pictures, runway alignment stationing, and paving lane assignments provided by USKH. The runway alignment stationing at the specified sampling locations was surveyed and marked by PND s surveyors. The locations of the asphalt coring and borehole drilling are shown in Appendix A. The split spoon blow counts presented in the bore logs are uncorrected. Figure 3.1 Core Barrel Page 2 of 11

8 3.2 Drilling Methods/Procedures Asphalt coring and soil sampling was completed using a CME-75 truck mounted drill. The drilling was performed using equipment owned and operated by Denali Drilling, Inc. of Anchorage, Alaska. A 6-inch-diameter diamond tooth core barrel was used in combination with water to cut pavement cores. Soil sampling included driving oversize split spoons continuously up to 9 feet below the pavement surface. A 340-lb. hammer with a 30-foot drop advanced a 2.5-inch I.D. oversize split spoon to retrieve samples. Each sample retrieved was visually classified in the field based on the USCS and ASTM visual classification methods per ASTM D Samples were occasionally photographed. Once sample logging procedures were completed, the sample was sealed, and labeled. A representative group of samples were sent to the laboratory to determine the grain size distribution of the different types of soils encountered. 3.3 Dynamic Cone Penetrometer Figure 3.2 DCP Test Operation The DCP Test is used to correlate the rate of penetration of a cone tip with the CBR. It uses a 17.6-lb weight dropping 22.6 inches onto an anvil to drive the tip into the ground. By recording the penetration over a given number of drops the CBR can be calculated. The method presented in ASTM D 6951 is used for correlating mm/blow to CBR as suggested by the US Army Corps of Engineers. The DCP tests were also performed in general conformance with ASTM D DCP readings taken on underlying base and subgrade material at select locations are presented in Appendix D. The results of the DCP test and resulting CBR values calculated from the data are presented in Table 3-1. Some of the data points have CBR values equal to 100%. This may occur when the tip of the DCP encounters a larger bearing surface, such as a piece of gravel and is momentarily restricted from advancing. As a result the DCP test will interpret the encounter with the gravel as a very dense layer. Such data points skew the data and are not included in the averages below. The subgrade appears dense and in good condition. A conservative CBR of 30% is used in the FAARFIELD analysis. Table 3-1. Summary of DCP test data. DCP was driven continuously to depth up to 5.5in. below top of subgrade. Station Average CBR 65% 49% 55% 58% 55% 65% 4. ANALYSES To supplement the information gathered in this investigation, analyses were performed to calculate the necessary thickness of the runway pavement and the anticipated frost depth into soil underlying the existing pavement. To calculate frost depth, a computer program, BERG2, was used. BERG2 uses the Modified Berggren method to calculate freeze and thaw depths in different regions based on the soil type, air freezing index, and air thawing index. The inputs and results of the BERG2 analysis are shown in Table 4-1. The City & Borough of Juneau Building code recommends using a 32-inch frost depth. The calculated depth of freezing was 5.3 feet beneath the surface. This analysis used sandy gravel to simulate what the frost depth will be if the subgrade is replaced with non-frost susceptible material. Page 3 of 11

9 Table 4-1. BERG2 Analysis Parameters for Frost Depth Location Freezing Index Thawing Index Mean Temp. Soil Type Moisture Content Thaw Depth Freeze Depth (ft.) Juneau, AK 1609 F-Days* 3,920 F-Days 40.0 F* Sandy Gravel 6 % 12.7 ft. 5.3 ft. *Values from NOAA AFI-pubreturn.xls spread sheet. In analyzing the structural section for the pavement rehabilitation, PND used the FAA software FAARFIELD version 1.305, which meets requirements in AC 150/5320-6E Airport Pavement Design and Evaluation. In this analysis the subgrade was assigned a CBR of 30%. The traffic loading used to calculate total HMA thickness needed for a 20-year design life was based on the annual departures at Juneau International Airport. Based on the analysis the following was calculated: Assuming the subgrade material is left in-place an a.c. pavement thickness of 11.9 inches is required for the structural section. Additional FAARFIELD analysis was performed and revealed if 5 inches of HMA installed base material is would need to consist of 4 inches of P-209 crushed aggregate base and 5.5 inches of P-154 subbase for traffic loading/frequency for a 20-year design life. A third FAARFIELD analysis was performed showing 5 inches of HMA surface, and 9.0 inches of P-209 crushed aggregate is needed for the traffic loading and design life discussed above. This analysis does not consider a subbase with P PAVEMENT DISTRESS The following narrative describes PND s assessment of distress at each location along the runway. 5.1 PND-1, Station Pavement coring and soil sampling were performed at Station (see location defined in the plan view drawing of Appendix A, Figure 2) to evaluate a 14-foot-wide by 30-foot-long area defined by USKH as a sink box. A 10.5-inch surface core was recovered representing the total a.c. pavement thickness at this location. It is PND s understanding that this area has had the asphalt surface move up and down at different times of the year. PND observed no visible cracks in the core that were significant. Soil conditions at the site reveal poorly graded, dry SAND with Silt and Gravel directly beneath the pavement. The soil contains 11.5 percent fines and is classified as Frost Group F2 and extends to a depth of approximately 2.8 feet. Beneath this layer is a dry, well-graded SAND (SW) extending to approximately 4.9 feet in depth with 5 percent fines and with Frost Group F2. Based on the subgrade frost classification, visible observations of the area and the distress it is PND s opinion that cracks are a result of freeze/thaw of the frost susceptible subgrade soil. 5.2 PND-2, Station A pavement core was taken at Station to evaluate possible reflection cracking. Soil sampling was not performed at this location. An 11-inch surface core was recovered representing the total a.c. pavement thickness at this location. A longitudinal crack extended down 3 inches through the top paving layer. The pavement has a horizontal fracture 3.5 inches from the surface. In PND s opinion, the upper portion of the pavement appears to consist of past rehabilitation work. It appears this upper layer has delaminated from the underlying pavement and cracks are probably a result of deflection of the structural section after delamination occurred. Page 4 of 11

10 5.3 PND-3, Station A pavement core was taken at Station to evaluate possible reflection cracking. Soil sampling was not performed at this location. An 11-inch asphalt core was recovered representing the total a.c. pavement thickness at this location. The longitudinal crack extended vertically 2.5 inches into the pavement from the surface. There is a horizontal fracture at a depth of 7 inches. The core barrel used during the drilling had some oscillation which resulted in a mechanical fracture of the core at this location. In PND s opinion, the cracks are surficial in the upper layer of past rehabilitation work, possibly from laydown operations. 5.4 PND-4, Station A pavement core was taken at Station to evaluate a long reflection crack. Soil sampling was not performed at this location. An 11 inch core was recovered representing the total a.c. pavement thickness at this location. The vertical crack extended 2.5 inches into the top paving layer. The vertical crack terminated where a horizontal crack began. The horizontal crack is 2.5 inches beneath the top of pavement. In PND s opinion, the upper portion of the pavement appears to consist of past rehabilitation work. It appears this upper layer has delaminated from the underlying pavement and cracks are probably a result of deflection of the structural section after delamination occurred. 5.5 PND-5, Station Pavement coring and soil sampling was performed at Station to evaluate a 14-foot by 20- foot section with possible alligator cracking. A 9-inch core was recovered. Three inches were not recovered by the core drilling but was recovered as part of soils sampling operations. Total pavement thickness measured was 12 inches. Soil conditions at the site reveal poorly graded SAND with Gravel (SP) that was oil stained directly beneath the pavement and extending from to 1-foot in depth. Beneath this layer was a dry, poorly graded GRAVEL with Silt (GP-GM). The material has 7 percent fines and a Frost Group Class classification of F1. Oversize split spoons were driven continuously to a depth of 8.25 feet. The subgrade is dense to medium dense GP-GM with frost classification F1 (low). Based on review of the core sample, soil conditions, and visible observations of crack patterns it is PND s opinion that surface cracks are a result of deflection from subgrade conditions. 5.6 PND-6, Station Pavement coring and soil sampling was performed at Station to evaluate an area of 14- by 20-foot with block cracking. A 7.5 inch core was recovered during coring operations. Two additional inches were recovered from split spoon sampling. Total pavement thickness is 9.5 inches. Soil conditions at the site reveal poorly graded SAND with Gravel (SP) that is oil stained and extends 3 inches beneath the pavement. Beneath this material is a poorly graded SAND with Gravel (SP). The material contained a trace of fines. Based on review of the core sample, soil conditions, and visible observations of crack patterns it is PND s opinion that surface cracks are a result of deflection from subgrade conditions. Page 5 of 11

11 5.7 PND-7, Station A pavement core was taken at Station to evaluate the condition of the left center patch. A 17.5-inch core was recovered. One horizontal crack, at a depth of 5.75 inches, was found in the core. The core barrel used during the drilling had some oscillation which resulted in a mechanical fracture of the core at this location. Limited soil sampling was performed at this location and revealed well-graded SAND with Gravel (SW) with a trace of fines. In PND s opinion, the surface distress appears to likely be surficial. PND did not see any evidence of subgrade failure. The pavement is much thicker than other areas of the runway. The distress may be due to some near-surface delamination similar to other locations noted, however, the coring was not performed through the crack so this could not be confirmed. 5.8 PND-8, Station Pavement coring and soil sampling was performed at Station to evaluate the condition of the left center patch. A 10.5-inch core was recovered. Total pavement thickness is 10.5 inches. Over size split spoons were driven to a depth of about 8.5 feet. The top 3 inches of asphalt appears to be pitted and deteriorating. Soil conditions at the site reveal poorly graded, oil-stained Sand with Gravel (SP) followed by dry Silty SAND with Gravel to a depth of 2.3 feet. This material has a fines content of 12.3% and Frost Group classification of F2. Beneath this layer is a dry, poorly graded SAND (SP) with 4.8% fines and Frost Group classification of F2. In PND s opinion this distress is more surficial in nature similar to other locations evaluated. Subgrade failure does not appear to have occurred at this site. Although fines contents are high frost heave does not appear to be a factor in distress noted. 5.9 PND-9, Station 5+25 Pavement coring and limited soil sampling was performed at Station 5+25 to evaluate possible alligator cracking. A inch core was recovered. Minimal distress was found in the core sample. Though, there is surface distress in the proximity of where the core was taken. Minimal soil sampling was performed at this location and revealed a thin, dry, well-graded SAND with Gravel (SW) with a trace of fines. No subsurface information is available that would provide reasons for alligator cracking. Based on review of core samples, soil conditions, and visual surface distress it is PND s opinion there are two possible causes: 1) subgrade failure resulting in deflection, or 2) delamination of the upper surface similar to other sites. The fact that inches of pavement are present at this site with what appears to be suitable underlying material would indicate that the more likely cause is delamination. However, this cannot be confirmed with information available. Page 6 of 11

12 5.10 PND-10, Station Pavement coring and thin soil sampling were performed at Station to evaluate possible reflection cracking. A 16-inch core was recovered. Total pavement thickness is 16 inches. The crack evaluated propagates at an angle into the pavement creating a wedge on the top of the core. It is unclear how deep this crack extends into the pavement. The crack leaves the core at a depth of 2.5 inches. It could possibly continue further into the pavement. Although based on the distress found in the other cores, it is likely that the crack remains in the top paving rehabilitation previously noted. Soil conditions beneath the asphalt consist of loose to medium dense, well-graded SAND with Gravel (SW) with a trace of fines. In PND s opinion, the distress is likely to consist of issues in the top 3 inches of pavement and likely is related to delamination observed in this layer similar to other locations PND-11, Station Pavement coring and soil sampling were performed at Station to evaluate possible alligator cracking. A 17.5-inch core was recovered representing the total pavement thickness at this location. The horizontal fracture at a depth of 7.5 inches appears to be from a mechanical fracture during coring operations. Oversize split spoons were driven to a depth of 7.5 feet. The underlying base consists of dry, medium dense, poorly-graded SAND with Silt and Gravel (SP-SM). The material has 7 percent fines content and a Frost Group classification of F2. PND found minimal distress in the pavement core. A review of visual surface distress revealed alligator cracking is not present at this location. In PND s opinion, the likely cause of surface cracks is similar to other locations in which delamination of the upper material has resulted in vertical cracks extending through the upper 3 inches of previous rehabilitation work. Table 5-1. Summary of Pavement Core Distress Hole Number Station Total Pavement Thickness Length of Vertical Crack from Surface Measured Depth from Surface to Horizontal Crack PND in. - - PND in in in. PND in in in.* PND in in in. PND in. - - PND in. - - PND in in.* PND in. - - PND in - - PND in in in.* PND in in.* *It is PND s opinion that mechanically developed horizontal cracks occurred at these locations as a result of diamond core barrel oscillations while coring. Page 7 of 11

13 6. RECOMMENDATIONS Based on the information gathered during this geotechnical investigation, PND is providing both overall and specific recommendations for the JNU runway rehabilitation. The recommendations for paving and construction considerations are described in more detail below. 6.1 Overall Recommendations USKH has proposed a number of options for rehabilitation of the runway. One of these options is milling and removal of the upper 3 inches from the rehabilitation conducted in 1997 and replacement with 5 inches of new a.c. pavement overlay. This results in the runway surface being higher than its current surface. In order to accomplish this, a transition to taxiways must be constructed. The advantage of this option over the replacement of the entire a.c. section is there is less impact to the centerline lighting thereby reducing costs considerably. Calculations indicate approximately 11.9 inches of a.c. pavement is required if subgrade material is left in-place based on the plane configurations, loads and frequencies. This assumes a CBR of 30- and a 20-year design life for the rehabilitation. Calculations also indicate an anticipated frost depth of up to 5.3 feet based on climatic records for the region. PND s recommendations for the overall runway rehabilitation are as follows: Mill a minimum of 3 inches and confirm loose material is removed prior to installation of 5 inches of new P401/P403 HMA. Use of scraper and blade to remove any delaminated areas after milling Restore final surface to desired grade and cross slope free of humps, ruts and other surface imperfection. The runway surface should be prepared to maximize friction and minimize potential for hydroplaning by grooving meeting FAA requirements. Provide suitable grade transitions from runway to threshold Install new Runway Centerline Lighting System (RCLS). Use joint adhesive at transitions from runway to taxiway at edges of milling to minimize water infiltration into HMA joints. It should be noted the calculated frost depth is up to 5.3 feet. In PND s opinion, there are several areas where frost heave or subgrade failure may be present and these areas are addressed in more detail in the following section. However, it is PND s opinion that frost heave does not appear to be a prevalent problem for the existing runway. It would not be cost effective to completely remove all existing pavement and replace underlying frost susceptible materials to achieve a 20 year design life. The condition of the JNU runway is somewhat variable over the entire length of runway with variability in a.c. pavement thickness, pavement type, base, subbase, and subgrade. USKH has performed a visual assessment of the runway and found that primary distress points are located at the areas PND has been asked to evaluate as part of this study. PND s assessment of core samples, soil conditions, and other factors lead us to the opinion that the proposed plan to mill 3 inches of the existing asphalt for the runway and repave with 5 inches of P401/P403 HMA provides a substantial improvement that will provide an improved structural section. The approach also has the added advantage that minimal disturbance to the majority of utilities, including lighting, occur thereby reducing costs for this rehabilitation method considerably. The overall thickness of the runway will be increased and will provide improved pavement performance. Milling and repaving of the runway (milling 3 inches and repaving with 5 inches) will result in the need to modify approach grades on the adjacent taxiways and blastpads. Consideration will need to be given to the amount of milling that must be conducted in these areas as well; the transition zones from new pavement to old and water infiltration at the boundary of new to existing pavement. It is recommended that consideration be given to milling three inches in depth at these transition zones as well and repaving with a variable thickness from 3 to 5 inches to account for several pavement layers required during the laydown process and to minimize potential for Page 8 of 11

14 future delamination. Consideration should also be given to installation of an adhesive at the boundary from old asphalt to new to prevent water infiltration. 6.2 Specific Recommendations at Distress Sites Investigated USKH has requested PND investigate specific distress locations along the runway as previously described in this report. We have expressed an opinion on the likely cause of distress at each of these locations and recommendations for each location are described in Table 6-1. Recommendations for Pavement Distress Locations Investigated. It should be noted the area of distress is approximate and based on preliminary information provided by USKH. The actual beginning and ending stations and distance from centerline has not been provided at this time. As such, dimensions are only included where PND has been provided this information. Shown in this table is a recommended dimension for saw-cutting and removal of asphalt when subgrade soils are recommended to be removed and compacted base installed. These dimensions should provide sufficient room to excavate and compact. Select areas require replacement of subgrade. In these locations there are two rehabilitation options: 1. Replace section with minimum 5 inches P-401/P-403 HMA, underlain by P-209 crushed aggregate to a minimum depth of 32 inches below top of new a.c. surface. 2. Replace section with minimum 5 inches P-401/P-403 HMA, over minimum 4 inches P-209 crushed aggregate, underlain by P-154 uncrushed aggregate to a minimum depth of 32 inches below top of new a.c. surface. Table 6-1. Recommendations for Pavement Distress Locations Investigated Distress Location Approx. Station Dimensions of Distress Saw-cut Dimensions Required PND x x 34 PND Area provided by USKH 2 past distress location Recommendation Saw-cut asphalt and remove to dimensions shown or as required for distress area. Replace subgrade per option 1 or 2 described above. Compact subgrade, base and subbase to 100% per ASTM D1557, Method D. Mill an additional 1 (4 total) to penetrate delamination at 3.5. The milling should extend the entire length of the longitudinal crack and over the entire width of paving lane 1 left (approximately 14 feet in width). PND n/a n/a Mill 3, repave 5 per general recommendations. PND n/a n/a Mill 3, repave 5 per general recommendations. PND x x 24 Saw-cut asphalt and remove to dimensions shown or as required for distress area. Replace subgrade per option 1 or 2 described above. Compact subgrade, base and subbase to 100% per ASTM D1557, Method D. PND x x 24 Saw-cut asphalt and remove to dimensions shown or as required for distress area. Replace subgrade per option 1 or 2 described above. Compact subgrade, base and subbase to 100% per ASTM D1557, Method D. PND n/a n/a Mill 3, repave 5 per general recommendations. PND n/a n/a Mill 3, repave 5 per general recommendations. PND Area provided by USKH 2 past distress location Saw-cut asphalt and remove to dimensions shown or as required for distress area. Replace subgrade per option 1 or 2 described above. Compact subgrade, base and subbase to 100% per ASTM D1557, Method D. Page 9 of 11

15 PND n/a n/a Mill 3, repave 5 per general recommendations. PND n/a n/a Mill 3, repave 5 per general recommendations. In general, construction specifications should be developed meeting the Airport Construction Standards identified in AC 150/ , Standards for Specifying Construction of Airports. 7. OTHER DESIGN AND CONSTRUCTION CONSIDERATIONS The primary work elements of the project include milling, asphalt removal, saw-cutting, excavation of existing base, subbase, oil impregnated sand, and subgrade consisting of sand with varying amounts of silt and gravel. After milling and excavation work is complete, work will require compaction of the subgrade, installation of compacted base/subbase, installation of a.c. paving, and sealing of joints to prevent water intrusion. Work may also require construction of new centerline lighting and edge lighting and wiring as part of this work effort. Depending on milling method, centerline light cans may not need to be removed. If areas of excavation encounter utilities then additional utility work may be required along with possibly other miscellaneous activities as part of construction. Juneau is located in an area with significant precipitation that can occur at any time. Construction activities must be completed during late spring, summer, and fall in periods when temperatures allow construction to occur meeting the requirements of AC 150/ , Standards for Specifying Construction of Airports. In addition to these standards the Designer and Contractor may wish to consider specific issues that may occur as part of construction work progression: Milling, saw-cutting, and removal of a.c. pavement must be accomplished. Material extracted by either method considered hazardous waste unless used for recycled asphalt or similar purposes. The Contractor will need to dispose of materials at a legal upland location. Juneau is located in an area that has rain forest conditions at times resulting in considerable precipitation that may occur at any time. The Contractor will need to plan activities to minimize infiltration of precipitation and groundwater into excavations as work progression occurs. It may be necessary to pump water from excavations. If water is mixed with mill cuttings this may require special disposal. Pumps may be necessary to control infiltration into excavations both prior to and during fill placement and compaction. Fill should not be placed directly into ponded water within the excavation as it is likely optimum moisture may be exceeded resulting in difficulty achieving compaction. In these instances material may have to be removed and dried to optimum to achieve compaction or wasted. Stock piles of aggregate base and subbase should be covered to prevent infiltration prior to placement in the excavation. Excess moisture entering stockpiles may result in difficulty in maintaining optimum moisture to achieve required compaction. A relatively short construction window exists during the late spring, summer, and fall that will allow placement of earthwork and more importantly to achieve air temperatures suitable for paving operations. The Contractor will need to plan construction activities to meet allowable construction windows and project specifications. Positive drainage should be provided during construction. Softening of subgrade may occur as part of the construction process. If this occurs the Contractor should be prepared to compact subgrade or verify the subgrade is in a dense state prior to placement of any base or subbase material. Saw-cuts may result in 90 degree angles which may cause difficulty in achieving compaction at corners. If this occurs varying the type of construction compaction equipment may be necessary to achieve the desired compaction or changing construction techniques to minimize this issue. Page 10 of 11

16 Construction joints should have an adhesive applied to minimize water intrusion. 8. CLOSURE This geotechnical evaluation of pavement distress and pavement rehabilitation recommendations is based on historic record review, PND s on-site geotechnical investigation of asphalt cores, and soil conditions and communications with USKH. Actual subsurface conditions may vary in some areas as a detailed investigation for the entire runway has not been performed. This report has been prepared to aid in the design and construction of the pavement rehabilitation for the runway. This report and drawings are not to be used in any manner that would constitute a detriment directly or indirectly to PND. The ASFE publication Important Information about your Geotechnical Engineering Report is included in Appendix F for your information and contains additional information relative to what is presented in this report. 9. REFERENCES American Society of Testing and Materials (2003). Use of the Dynamic Cone Penetrometer in Shallow Pavement Applications, Designation D City & Borough of Juneau (2000). CBJ Permit Center Handout No.10, Building Code Data pg.1. Federal Aviation Administration (1995). Airport pavement design and evaluation, Advisory Circular No. 150/5320-6D. Federal Aviation Administration (2010). FAARFIELD 1.305, Computer Program for Airport Pavement Thickness Design. Federal Highway Administration (2006). Geotechnical Aspects of Pavements, Publication number NHI , Figure National Oceanographic and Atmospheric Administration (2012). Air Freezing Index Return Periods and Associated Probabilities Excel Spread Sheet AFI-pubreturn.xls. W. Alan Braley, Billy Connor (1989). BERG2, Microcomputer Estimation of Freeze and Thaw Depths and Thaw Consolidation. Prepared for Alaska Department of Transportation and Public Facilities. Page 11 of 11