Geotechnical Investigation

Transcription

1 Geotechnical Investigation Prepared for: Precision Approach Engineering, Inc. Corvallis, Oregon January 16, 2017 Professional Geotechnical Services Foundation Engineering, Inc.

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3 GEOTECHNICAL INVESTIGATION ALBANY MUNICIPAL AIRPORT RUNWAY EXTENSION & APRON REHABILITATION ALBANY, OREGON BACKGROUND The is planning improvements that will include extending Runway and rehabilitating the main apron west of the runway. We understand the runway extension will incorporate the existing blast pad/overrun pavements on both ends of the runway and will also include the construction of new connector taxiways at both ends. The project location is shown on Figure 1A (Appendix). A layout of the improvement areas is shown on Figures 2A through 4A (Appendix A). Precision Approach Engineering, Inc. (PAE) is the prime engineering consultant and will provide pavement and civil design services. PAE indicated the design for both the runway extension and apron rehabilitation will be completed in Construction for the apron rehabilitation is currently planned for 2017, while construction for the runway extension is planned for Foundation Engineering, Inc. was retained by PAE to perform the subsurface investigation, conduct laboratory testing, and provide recommendations for subgrade preparation and design parameters associated with the pavement improvements. We have completed multiple investigations for different projects at the airport, which include the Runway rehabilitation project (circa 2010) and the access road (i.e., Aviation Way SE) rehabilitation and north taxiways project (circa 2000). Information from those investigations has been used to supplement the current work, where applicable. The following sections summarize our work. SITE CONDITIONS AND LOCAL GEOLOGY The airport is located on a relatively flat alluvial plain, ±¾ mile east of the Willamette River. Topographic relief is typically limited within the airport and the surrounding area. A small drainage provides the southern boundary to the site and connects Timber-Linn and Swan Lakes on the east and west sides of the airport. Vegetation within the airport is primarily limited to short grass and scattered weeds. Local geologic mapping (e.g., Wiley 2006) indicates the airport is underlain by Willamette Silt and Linn Gravels. The Willamette Silt may contain mixtures of silt, sandy silt, and silty clay. Our previous and current explorations at the airport encountered mixtures of silt, clay, and sand at shallow depths, consistent with the Willamette Silt. We have also completed deeper borings immediately north and west of the airport for a previous project. Those borings encountered medium dense to very dense gravel at depths ranging from ±0 to 15.5 feet. January 16, 2017 Geotechnical Investigation 1 Project Precision Approach Engineering, Inc.

4 FIELD EXPLORATION Pavement Cores Twelve pavement cores (C-1 through C-12) were completed at the site on December 21, 2016, using a 5-inch diameter core drill and trailer-mounted drill rig. C-1 was cored at the north end of Taxiway A, near the planned north taxiway and runway extension. C-2 through C-10 were cored within the main apron and its connecting taxilanes. C-11 was cored within the overrun pavement at the south end of Runway and C-12 was cored near the south end of Taxiway A (west of C-11). The approximate core locations are shown on Figures 2A through 4A. The exploration at C-10 was limited to the depth of the asphaltic concrete (AC) core only. At the other explorations, the AC cores were removed and the base rock and underlying subgrade was excavated using a solid-stem auger or hollow-barrel drilling attachment. Drilling extended to maximum depths ranging from ±2 to 5 feet below the paved surface. The core holes were logged to delineate the thickness of the AC and the base rock, and to identify the subgrade conditions. The core hole logs are included in Appendix B. Dynamic Cone Penetrometer (DCP) testing was performed on the base rock and subgrade in each core hole. The DCP testing is described in a subsequent section of this report. Following the completion of the explorations, the core holes were backfilled with the excavated materials, placed and compacted in thin lifts, and capped with granular fill and AC cold patch. Test Pits Three test pits (TP-1 through TP-3) were excavated on December 21, 2016, using a CASE 580 Super N backhoe. The test pits were dug to help document the soil conditions across the site and to obtain bulk subgrade samples. TP-1 was dug north of Taxiway A, near the planned connector for the north runway extension. TP-2 was dug in a grass area adjacent to the main apron. TP-3 was dug where a connector taxiway is planned near the south end or the runway. The approximate test pit locations are shown on Figures 2A through 4A. Each of the test pits extended to a depth of ±5 feet. The soil profiles were logged and disturbed soil samples were retained for possible laboratory testing. Upon completion, the excavated materials were placed back into the test pits and the ground surface at each location was graded relatively smooth. The test pit logs are included in Appendix B. January 16, 2017 Geotechnical Investigation 2 Project Precision Approach Engineering, Inc.

5 DISCUSSION OF SUBSURFACE CONDITIONS The following sections provide a summary of the subsurface conditions encountered in the explorations. More specific details are provided on the logs (Appendix B). Photos of the pavement cores are also provided in Appendix B. Pavement Cores Pavement Section The pavement cores encountered ±3 to 6 inches of AC. Consistent with the available pavement inventory (e.g., Pavement Consultants, Inc. 2015), several of the cores showed at least one previous overlay. The observed overlay thickness varied between cores and typically included a non-woven paving fabric between the overlay and the original wearing course. Additional details are provided in the logs and the pavement core photos (Appendix B). The AC is underlain by base rock that varies with location. At most of the explorations, the base material consists of ±1.5 or 2-inch minus crushed gravel with varying sand and silt content. Some of the cores (C-2, C-5, C-9, and C-12) encountered base material consisting of unprocessed (i.e., uncrushed) gravel or sandy gravel. The exploration at C-11 (completed in the south blast pad/overrun pavement) encountered base material that included ±4 inches of AC millings and crushed gravel over an additional ±4 inches of crushed gravel. Unified Soil Classification System (USCS) Classifications for the base materials include GW, GP, and GP-GM. The base rock thickness ranged from ±4 to 16 inches in the explorations. The total thickness of the pavement sections (including the AC and base rock) ranged from ±9 to 20 inches. Pavement section thicknesses are summarized on Table 1B (Appendix B). Subgrade The subgrade underlying the pavement section varies with location. Consistent with previous investigations at the airport, most of the explorations encountered brown to dark brown, low plasticity silty clay to silt with some clay, sand and gravel. These soils were encountered in C-1, C-2, C-3, C-7, C-9, and C-11. Silty to sandy gravel was encountered beneath the fine-grained subgrade in most of the above-noted locations at depths ranging from ±2 to 3.5 feet. The gravel stratum was encountered directly below the pavement section in C-12 and within a few inches below the pavement section in C-8. The gravel stratum appears to be shallower towards the south end of the airport. Grey, medium to high plasticity clay or silty clay was encountered towards the middle of the apron in C-4, C-5, and C-6. At these locations, the clay extended to the maximum depth of the explorations (±5 feet). Similar soil was also encountered in C-8, but to only a few inches below the pavement section. We also encountered grey, high plasticity clay in one exploration (TP-2) completed for the north taxiways project in That test pit was located near the hangars at the northwest corner of the airport. January 16, 2017 Geotechnical Investigation 3 Project Precision Approach Engineering, Inc.

6 We interpreted the approximate limits of clay within the apron based on where it was encountered in the recent explorations. The limits are represented as yellow dashed lines in Figure 3A. However, the extent of the clay may be more variable than what is shown in Figure 3A since it was also encountered further north during a previous investigation. Test Pits The test pits encountered varying subgrade conditions, similar to the pavement cores. TP-1 and TP-2 encountered dark brown, low plasticity silty clay or silt with some clay, sand and gravel extending below the ground surface. This stratum was encountered to ±3 feet in TP-1 and to ±1.5 feet in TP-2. The fine-grained soil is followed by medium dense silty or sandy gravel that extended to the bottom of the test pits (±5 feet). The fine-grained soil was not encountered in TP-3. Instead, the exploration encountered silty to sandy gravel for the full depth of the exploration (±5 feet). Medium to high plasticity clay, similar to that observed in C-4, C-5, and C-6, was not encountered in the test pits. Ground Water Ground water infiltration was observed in the explorations completed near the north and south ends of the runway. At the north end, moderate to rapid seepage was observed in TP-1 at a depth of ±2.5 to 3 feet. Moderate seepage was also observed in C-1 at ±3 feet. At the south end, moderate seepage was observed at ±3 feet in TP-3 and C-11. Ground water was not observed in the other explorations. However, the subgrade was typically moist at shallow depths across the site. Similar conditions were observed during our previous explorations at the airport. Given the close proximity of the airport to the surrounding Timber-Linn and Swan Lakes, and the Willamette River further west, we anticipate the local ground water remains relatively shallow throughout the year and closely corresponds to the water level in the lakes. During periods of prolonged rainfall, perched ground water conditions are also likely to develop at shallower depths where the low permeability fine-grained soils (i.e., silts and clays) are present. FIELD AND LABORATORY TESTING DCP Testing Dynamic Cone Penetrometer (DCP) testing was completed on the base rock and subgrade within each of the core holes (except C-10). The DCP test consists of driving the cone of the DCP apparatus into the soil and recording the penetration versus blow count (mm/blow) as the DCP value. The Oregon Department of Transportation (ODOT) Pavement Design Guide (2011) provides a correlation for estimating the in-situ resilient modulus from results of the DCP testing. A summary of the DCP test results and the correlated in-situ subgrade and base rock modulus values are summarized in Table 1C (Appendix C). January 16, 2017 Geotechnical Investigation 4 Project Precision Approach Engineering, Inc.

7 In-situ modulus values ranging from ±7,739 to 22,565 psi were calculated for the base rock, with an average value of ±16,674 psi. The relatively low modulus values are likely due, in part, to thin base rock sections being influenced by the underlying subgrade. In-situ modulus values ranging from ±3,219 to 12,435 psi were calculated for the subgrade, with an average value of ±5,131 psi. The FAA Airport Pavement Design and Evaluation Circular (2016) recommends estimating the subgrade modulus based on the following correlation with laboratory California Bearing Ratio (CBR) tests: E = 1,500 x CBR Based on the above equation, we back-calculated in-situ CBR values ranging from ±2.1 to 8.3 for the subgrade, with an average value of 3.4. Significantly higher subgrade modulus values were observed where gravel was encountered (C-8 and C-12). At those locations, the calculated modulus value ranged from ±6,309 to 12,435 psi, with back-calculated CBR values ranging from 4.6 to 8.3. The remaining explorations with predominantly silt or clay subgrade had calculated modulus values ranging from ±3,219 to 6,309 psi, and back-calculated CBR values ranging from 2.1 to 4.2 (with an average value of 2.7). Laboratory Testing Index Tests The laboratory work included natural water content determinations, Atterberg limits tests, and mechanical sieve and hydrometer analyses to classify the soils and estimate their overall engineering properties. The test results are summarized on Table 2C and Figures 1C through 6C (Appendix C). The Atterberg limits tests were completed on two bulk samples from TP-1 and TP-2 (S-1-1 and S-2-1) and four samples from the pavement cores (C-3-2, C-5-2, C-6-2, and C-11-2). The samples were selected to represent the range in plasticity observed in the subgrade soils. Most of the test results fall on or near the dividing line between USCS classifications CL and ML (i.e., low plasticity clay or silt). Therefore, we used a dual classification to characterize most of the subgrade. Sample C-6-2 (from core hole C-6) was an outlier, with USCS classification CH (i.e., high plasticity clay). The Atterberg limits results are generally consistent with the range of values from previous projects at the airport. Figure 1C provides a summary of the Atterberg limits test results from the current project and previous projects. As noted in Figure 1C, most of the test samples fall close to the dividing line between CL and ML soils. Two samples, C-6-2 from the current study and S-2-2 from the Access Road & Taxiways project (2000), have significantly higher plasticity and are classified as CH soils. Sieve and hydrometer gradation curves were completed on the bulk samples from TP-1 and TP-2 (Figures 2C and 3C). The results are consistent with the Atterberg limits, indicating primarily silt and clay-sized particle with some sand and gravel. A January 16, 2017 Geotechnical Investigation 5 Project Precision Approach Engineering, Inc.

8 sieve analysis on the bulk sample from TP-3 (S-3-1) indicated the subgrade at that location consists of primarily gravel with some sand and silt, and a USCS classification of GM. Sieve analyses were also completed on two samples of the base rock from the apron at C-4 and C-5 (samples C-4-1 and C-5-1). Both samples contain primarily gravel-sized particles with fines contents ranging from ±5.8 to 7 percent, and resulting USCS classification of GW-GM. Moisture-Density and CBR Testing Moisture-density curves (ASTM D698) were developed for bulk samples obtained from TP-1 (S-1-1) and TP-2 (S-2-1). The individual test results are summarized in Figures 7C and 9C (Appendix C). The results are also summarized in Table 3C (Appendix C). The test results indicate a maximum dry density of pcf at an optimum moisture content of 16.2% for S-1-1, and a maximum dry density of pcf at an optimum moisture content of 14.2% for S-2-1. Both moisture-density test curves were modified using an oversize correction factor since the samples included greater than 5% gravel content. California Bearing Ratio (CBR, ASTM D1883) tests were completed on samples S-1-1 and S-2-1 using the results from the compaction tests. The individual CBR results are summarized in Figures 8C and 10C (Appendix C). The results are also summarized in Table 3C. At 95% relative compaction (with oversize correction), the test results indicate a CBR value of 8.9 for sample S-1-1 and a CBR value of 4.3 for S-2-1. The test results indicate a wide range in CBR values for similar soils. The CBR value of 8.9 for S-1-1 is high for predominantly silt and clay soils. Therefore, we believe the gravel in sample S-1-1 (±23.7% gravel; see Figure 2C) likely skewed the results. A CBR value of 4.3 for sample S-2-1 is more typical for these soils. Moisture-density and CBR test results for the current project and previous projects at the airport are summarized in Table 3C. Additional scattered in the CBR values is apparent from Table 3C. Some of this additional scatter can be attributed to the varying soil conditions. For example, the lowest CBR value of 1.4 was from a test complete on a sample of high plasticity clay (USCS classification CH). We note consistent CBR values of 4.3 for two samples of silty clay or clayey silt (USCS classification CL). Additional discussion and recommendations for design CBR values are provided in the following section. DISCUSSION OF GEOTECHNICAL CONSIDERATIONS AND DESIGN REQUIREMENTS The following sections discuss geotechnical considerations and recommendations for the proposed runway extension and apron rehabilitation. We anticipate PAE will evaluate options that include full depth reconstruction or overlay of the existing apron and the overrun pavements where the runway will be extended. New pavement sections will be required to provide connector taxiways between the lengthened runway ends and Taxiway A. January 16, 2017 Geotechnical Investigation 6 Project Precision Approach Engineering, Inc.

9 Discussion of Subgrade Conditions The pavement subgrade varies across the site, but typically consists of silty clay and/or silt with some clay, sand and gravel. Corresponding USCS classifications range from CL to ML. Appendix A of the 2016 FAA Airport Pavement Design and Evaluation Advisory Circular (AC 150/5320-6F) indicates that soils designated as CL or ML are fair to good as a foundation material when not subject to frost action. Frost-susceptibility is discussed in a subsequent section of this report. A portion of the apron is underlain by high plasticity clay with corresponding USCS classification CH. The FAA Pavement Advisory (2016) characterizes this soil as poor to very poor. The estimated limits of the high plasticity clay are shown in Figure 3A. Silty gravel (with corresponding USCS classification GM) was encountered at shallow depths in some of the explorations. The FAA Pavement Advisory (2016) characterizes these soils as good as a foundation material. The gravel may be shallowest towards the south end of the airport. However, the depth to gravel appears to vary across the site. Therefore, we do not recommend predicating any portion of the pavement design on the gravel subgrade. Parameters for Pavement Overlay If rehabilitation of the apron includes pavement overlay (or mill and inlay), we recommend the following design parameters: Subgrade If pavement overlay is planned, the subgrade will remain in its present condition. Therefore, the results of the DCP testing are most suitable for evaluating the subgrade. Excluding the DCP test on gravel subgrade, which was only encountered at two locations, the tests indicated a mean resilient modulus of 4,116 psi (CBR value of 2.7) with a standard deviation of 900 psi. The mean minus one standard deviation is 3,216 psi, which correlates to a CBR value of ±2.1. Therefore, we recommend assuming a CBR value of 2.1 for design. This value is recommended across the site, regardless if the subgrade is classified as CL/ML or CH. Base Rock The existing base rock consists of crushed and uncrushed gravel with varying silt and sand content. The DCP tests indicated an average base rock modulus of ±16,674 psi. Default modulus values for unreinforced base material in FAARFIELD are significantly greater, ranging from 40,000 psi (P-154) to 70,000 psi (P-209). We anticipate the relatively low modulus values correlated from the DCP testing are due to the quality of the existing base rock and the relatively thin base rock section over weak subgrade. We recommend assuming a base rock modulus of 15,000 psi to evaluate a pavement overlay. January 16, 2017 Geotechnical Investigation 7 Project Precision Approach Engineering, Inc.

10 Existing AC We recommend assuming a modulus value of 200,000 psi to represent the existing AC to evaluate the pavement overlay. A modulus value of 200,000 psi is consistent with the FAARFIELD default for existing surface AC that will be overlain. If all or portions of the existing pavements remain in place, methods should be evaluated to mitigate the risk of existing cracks propagating through the new AC. Mitigation techniques typically include milling the existing AC, placing fabric and sealants over the existing AC prior to paving, and/or providing a relatively thick overlay. When milling to repair existing pavement damage, FAA requires leaving at least 2 inches of AC in place unless the entire section is removed. Subgrade Preparation and Parameters for New Pavement Design For new pavements and/or full-depth reconstruction, the appropriate subgrade parameters and preparation will depend, in part, on location since the subgrade varies across the airport. As discussed above, three general soil types were identified at the subgrade elevation, which include: low plasticity silty clay or silt with some clay (CL or ML soils), medium to high plasticity clay (CH soil), and silty gravel (GM soil). The extent of the silty gravel at the subgrade elevation is variable and appears to be limited. Therefore, we recommend the pavement design be predicated on either the CL/ML soil or the CH soil. Recommendations for these two soil types is provided below. Low Plasticity Silty Clay to Silt, some Clay (CL/ML Soil) Low plasticity silty clay to silt, some clay (CL/ML soil) was encountered in most of the explorations within the improvement area, except the mid-section of the apron (see Figure 3A). Therefore, the recommended soil parameters and preparation described below should be suitable for most of the planned pavement improvements. The laboratory testing indicated a range of CBR values for the CL/ML soil that varied for reasons discussed above. A CBR value of 4.3 (indicated by two test results) is within the typical range for these soils. Therefore, we recommend assuming a design CBR value of 4 for the CL/ML subgrade soils where new pavements and/or full-depth reconstruction is planned. This is consistent with the recommended CBR value for the Runway Rehabilitation project completed in The recommended CBR value assumes the subgrade will be moisture-conditioned, as required, and compacted to a minimum of 95% relative compaction (based on the maximum dry density of ASTM D698) prior to placing subbase and base rock. Multiple moisture-density curves and careful inspection of the soils will be required to evaluate the relative compaction of the subgrade because of the varying moisture-density test results that have been observed. This includes allowing for an over-size correction where the subgrade has greater than 5% gravel content. January 16, 2017 Geotechnical Investigation 8 Project Precision Approach Engineering, Inc.

11 The subgrade is moisture-sensitive. Therefore, we recommend compacting it at or slightly dry of optimum moisture to reduce the risks of pumping. The prepared subgrade should be backfilled with base rock or subbase as soon as practical to limit moisture fluctuations (i.e., wetting or drying). Medium to High Plasticity Clay (CH Soil) Medium to high plasticity clay (CH soil) was encountered near the mid-section of the apron (see Figure 3A). Laboratory test results from a previous project indicated a CBR value of 1.4 for this soil (see Table 3C). In-situ DCP tests during the current investigation indicated subgrade modulus values ranging from ±3,564 to 4,441 psi (i.e., CBR values ranging from ±2.4 to 3.0). Based on these results, we recommend assuming a design CBR value no greater than 2 for this material for designing new pavements. The FAA Pavement Advisory (AC 150/5320-6E) indicates a CBR of 3 (i.e., subgrade modulus of 4,500 psi) is the lowest value recommended for design of new pavements. For subgrade with a CBR below 3, subgrade stabilization or other means to improve the CBR value is recommended. FAA also requires stabilization for subgrade with swell greater than 3% and high potential for moisture fluctuation. The previous CBR test on CH soil from the airport indicated a swell of at least 3.4%. Options available for subgrade improvement include mechanical and chemical stabilization. Given the relatively limited treatment area, which includes only a portion of the apron, we anticipate the most cost-effective solution will be partial overexcavation and replacement where the clay is present. For completeness, additional options are also discussed briefly below. Mechanical Stabilization. Mechanical stabilization typically includes overexcavating and replacing soft soils, and bridging the soft areas with a thick lift of large, open-graded aggregate. The clay subgrade encountered in the explorations was typically medium stiff to stiff. Therefore, we do not anticipate needing an overly-thick layer of stabilization material to facilitate construction. Rather, the stabilization layer would be used to mitigate the long-term pavement performance due to low CBR value and swell potential and the clay. If overexcavation and replacement is selected, we believe it would be reasonable to assume a nominal overexcavation and replacement depth 1 foot below the planned subgrade elevation. This will provide a suitable treatment depth to mitigate swelling soils per FAA requirements and provide a working platform for placing new base rock and subbase. The excavation should extend to medium stiff to stiff, relatively undisturbed subgrade and the overexcavated material should be replaced with granular material (e.g., additional base rock or subbase) underlain by a separation geotextile. If these two requirements are met, it is our opinion a CBR of 3 may be used for flexible pavement design to represent the combination of imported fill within the overexcavated zone and the underlying native soils. January 16, 2017 Geotechnical Investigation 9 Project Precision Approach Engineering, Inc.

12 Geogrid reinforcement could also be used to improve the strength of the pavement section to compensate for the low subgrade strength. The relative improvement is highly dependent on the selected geogrid and may be proprietary to particular geogrid manufacturers. Therefore, the design of a geogrid-reinforced pavement section would require consultation and analysis from selected geogrid manufacturer(s). Chemical Stabilization. Chemical stabilization includes mixing cement, lime, or other additives into the subgrade to improve its strength. Cement stabilization would provide an additional, stabilized layer within the pavement section. It also would provide a working surface to facilitate placement of the granular base course. If this option is desirable, additional testing would be required to evaluate the required application rate to meet durability requirements, as well as a design CBR value for the treated layer. For preliminary evaluation of costs, we recommend assuming a nominal treatment depth of 12 inches and a cement application rate of ±12% by weight based on the subgrade soils at the site. The underlying subgrade (below the treatment depth) should remain relatively undisturbed. FAA s recommends selecting the design CBR value for chemically-treated subgrade as one standard deviation below the mean CBR value from the laboratory testing. For the underlying, untreated and uncompacted subgrade, we recommend assuming a CBR of 2. Frost Considerations Most of the subgrade consists of silty clay or silt with some clay (CL to ML soil) with plasticity index (PI) values typically less than 12. This material corresponds to a FAA frost group classification of FG-4, suggesting most of the subgrade is highly frost-susceptible. The high plasticity clay (CH soil) that was encountered in the mid-section of the apron has a corresponding frost group classification of FG-3. Complete mitigation of the risk of detrimental frost heave requires overexcavation and replacement of the soils below the depth of frost penetration. The local building code for Linn County indicates a frost penetration depth of ±12 inches in the vicinity of the airport. Given the limited frost depth, we expect frost mitigation will not be an issue in the design of new pavements. Site Drainage The 2016 FAA Pavement Advisory (AC 150/5320 6E), Appendix A, indicates soil classified as CL or ML can have drainage characteristics ranging from fair to practically impervious. Soil classified as CH generally has very low permeability. The 2013 FAA Surface Drainage Design Advisory Circular (AC 150/5320-5D), Figure G-3, suggests a coefficient of permeability, k, for these soils in the range of 10-7 cm/sec to cm/sec, which corresponds to practically impermeable soil. Given the high clay content of the subgrade, we recommend assuming a k value no higher than 10-8 cm/sec for evaluating drainage alternatives. January 16, 2017 Geotechnical Investigation 10 Project Precision Approach Engineering, Inc.

13 Construction Considerations Site Stripping Where new pavements are planned (i.e., connector taxiways), we recommend assuming a nominal stripping depth of 4 inches to remove sod, roots, and/or other organics. Construction Timing The airport site is relatively flat and underlain by low permeability soils. As such, rainfall perches on the site in the wet winter and spring months. The perched water typically disappears in the summer months, where the soil is exposed to dry weather (i.e., outside existing paved areas). However, it has been our experience that subgrade covered by existing pavements can remain wet of optimum year-round. Therefore, where complete reconstruction is planned, wet subgrade should be anticipated beneath the existing pavements regardless of the construction season. As such, the construction schedule should include ample time to aerate and moisture-condition the soils prior to compaction. We anticipate moisture-conditioning will require ripping and aerating the soils to a depth of ±12 inches. We recommend completing the earthwork during the dry summer months (typically July through September), when it should be practical to adjust the moisture content of the soil to near optimum and compact the subgrade. The contractor may still experience pumping problems and have difficulty achieving adequate compaction in the summer if the soils have not adequately dried. If the construction schedule does not allow enough time for soil aeration, overexcavation and replacement of wet soils should be anticipated. Where wet soils are overexcavated, a thickened subbase and/or base rock section over a separation geotextile is typically required to protect the moisture-sensitive soils and limit the risk of subgrade pumping from repeated construction traffic. A fill thickness of ±18 to 24 inches is typical required. The actual fill thickness will depend on the stiffness and moisture content of the exposed subgrade. Reclamation of Existing Materials The existing base materials are variable and likely will not meet the requirements for re-use as P-209 (base course). However, it may be possible to re-use the base material as P-154 (subbase course) for reconstructed pavement sections if it is mixed with reclaimed AC (ground to 3-inch minus particle size) or combined with cleaner imported granular fill. AC millings and reclaimed base rock could also be used in areas where overexcavation of poor subgrade is required (e.g., CH soil in the apron). Fill Materials and Compaction The base rock for new pavements should consist of 1 or ¾-inch minus, clean (i.e., less than 5% passing the No. 200 sieve), well-graded, crushed gravel or rock conforming to FAA P-209 requirements. Subbase material should consist of January 16, 2017 Geotechnical Investigation 11 Project Precision Approach Engineering, Inc.

14 free-draining sand, gravel, rock, asphalt grindings, or mixtures of the above that conform to FAA P-154 requirements and are free of plastic clay and organic matter. All fill should be placed in level lifts not exceeding 12 inches and compacted to a minimum of 95% relative compaction. The maximum dry density of ASTM D698 should be used as the standard for estimating relative compaction of the fill. The moisture content of the fill and subgrade should be adjusted to within ±2% of its optimum value prior to compaction. Imported granular fill will compact most efficiently with a smooth-drum, vibratory roller. Efficient compaction of fine-grained subgrade (where practical) will typically require the use of a tamping foot or kneading roller. Field density tests should be run frequently to confirm adequate compaction of the base rock, subbase, and subgrade. Adequate compaction of fill materials, which are too coarse or variable for density testing, should be evaluated by observation of the compaction method and proof-rolling with a loaded dump truck or other approved heavy construction vehicle. DESIGN REVIEW/CONSTRUCTION OBSERVATION/TESTING We should be provided the opportunity to review all drawings and specifications that pertain to site preparation and fill placement. Site preparation for new pavements will require field confirmation of the subgrade conditions. Mitigation of pumping subgrade and fill will also require engineering review and judgment. That judgment should be provided by one of our representatives. We recommend we be retained to provide the necessary construction observations. VARIATION OF SUBSURFACE CONDITIONS, USE OF THIS REPORT AND WARRANTY The analysis, conclusions, and recommendations contained herein assume the soil profiles encountered in the pavement cores and test pits are representative of the site conditions. The above recommendations assume we will have the opportunity to review final drawings and be present during construction to confirm the assumed subgrade conditions. No changes in the enclosed recommendations should be made without our approval. We will assume no responsibility or liability for any engineering judgment, inspection, or testing performed by others. This report was prepared for the exclusive use of Precision Approach Engineering, Inc. and their design consultants for the Runway Extension and Apron Rehabilitation project in. Information contained herein should not be used for other sites or for unanticipated construction without our written consent. This report is intended for planning and design purposes. Contractors using this information to estimate construction quantities or costs do so at their own risk. Our services do not include any survey or assessment of potential surface contamination or contamination of the soil or ground water by hazardous or toxic materials. We assume those services, if needed, have been completed by others. Our work was done in accordance with generally accepted soil and foundation engineering practices. No other warranty, expressed or implied, is made. January 16, 2017 Geotechnical Investigation 12 Project Precision Approach Engineering, Inc.

15 REFERENCES ASTM, 2014, Standard Test Methods for CBR (California Bearing Ratio) of Laboratory-Compacted Soil: American Society for Testing and Materials (ASTM), Standard D1883, vol ASTM, 2012, Standard Tests Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12,400ft-lbf/ft 3 (600kN-m/m 3 )): American Society for Testing and Materials (ASTM), Standard D698, vol FAA, 2016, Airport Pavement Design and Evaluation Advisory Circular: AC No. 150/5320-6F, Federal Aviation Administration. FAA, 2013, Subsurface Drainage Design Advisory Circular: AC No. 150/5320-5D, Federal Aviation Administration. FAA, 2014, Standards for Specifying Construction of Airports Advisory Circular: AC No. 150/ G, Federal Aviation Administration. ODOT, 2011, ODOT Pavement Design Guide, Oregon Department of Transportation (ODOT), Pavement Services Unit. Wiley, T.J., 2006, Preliminary Geologic Map of the Albany Quadrangle, Linn, Marion and Benton Counties, Oregon: Oregon Department of Geology and Mineral Industries, Open-File Report O January 16, 2017 Geotechnical Investigation 13 Project Precision Approach Engineering, Inc.

16 Appendix A Figures Professional Geotechnical Services Foundation Engineering, Inc.

17 North Albany Albany SITE Source: ODOT City Maps Database

18 No Scale

19 Approximate limits of CH Clay No Scale

20 No Scale

21 Appendix B Test Pit and Core Hole Logs and Core Photos Professional Geotechnical Services Foundation Engineering, Inc.

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24 Comments Depth, Feet Sample # Location Class Symbol Water Table C, TSF Symbol Soil and Rock Description Surface: Short grass. Fine roots extend to ±9 inches. 1 S-1-1 SILT, some clay, sand, and gravel (ML); dark brown, low plasticity, moist to wet, medium stiff, fine to coarse sand, fine to coarse subrounded gravel, (alluvium). 2 Moderate seepage at ±2.5 feet. Rapid seepage at ±3 feet. 3 S-1-2 Silty GRAVEL, some sand (GM); grey to brown, low plasticity silt, wet, medium dense, fine to coarse sand, fine to coarse subrounded gravel, (alluvium). 4 5 BOTTOM OF EXPLORATION Project No.: Surface Elevation: Date of Test Pit: Test Pit Log: TP-1 N/A (Approx.) December 21, 2016 Comments Depth, Feet Sample # Location Class Symbol Water Table C, TSF Symbol Soil and Rock Description Surface: Short grass. Fine roots extend to ±4 inches. S-2-1 Silty CLAY, some sand and gravel (CL); dark brown, low plasticity, moist, medium stiff, fine to coarse sand, fine to coarse subrounded gravel, (alluvium). 1 2 Sandy GRAVEL, trace to some silt (GP-GM); brown to grey, damp, medium dense, fine to coarse sand, fine to coarse subrounded gravel, (alluvium). S No seepage or ground water encountered to the limit of excavation. 5 BOTTOM OF EXPLORATION Project No.: Surface Elevation: Date of Test Pit: Test Pit Log: TP-2 N/A (Approx.) December 21, 2016

25 Comments Depth, Feet Sample # Location Class Symbol Water Table C, TSF Symbol Soil and Rock Description Surface: Short grass and weeds. Fine roots extend to ±3 inches. S-3-1 Silty, sandy GRAVEL (GM); grey to brown, low plasticity silt, moist, medium dense, fine to coarse sand, fine to coarse subrounded gravel, (alluvium). 1 2 Sandy GRAVEL, scattered cobbles (GP); grey, wet, medium dense, fine to coarse sand, fine to coarse subrounded gravel, subrounded cobbles up to ±6 inch diameter, (alluvium). Moderate seepage at ±3 feet. 3 S BOTTOM OF EXPLORATION Project No.: Surface Elevation: Date of Test Pit: Test Pit Log: TP-3 N/A (Approx.) December 21, 2016

26 Comments Depth, Feet Sample # Location Class Symbol Water Table C, TSF Symbol Soil and Rock Description Core includes ±2-inch overlay over original wearing course. 1 C-1-1 ASPHALTIC CONCRETE (±4 inches). CRUSHED GRAVEL (GW) (±16 inches); grey, damp, dense, ±1½-inch minus, angular to subrounded gravel, (base rock). 2 Sandy SILT, some clay (ML); dark brown, low plasticity, moist to wet, soft to medium stiff, fine to coarse sand, (alluvium). C-1-2 Moderate seepage at ±3 feet BOTTOM OF EXPLORATION Project No.: Surface Elevation: Date: Core Hole Log: C- 1 N/A (Approx.) December 21, 2016 Comments Depth, Feet Sample # Location Class Symbol Water Table C, TSF Symbol Soil and Rock Description Core includes 3 lifts: 2.25-inch with geotextile fabric/1.75-inch/2-inch 1 C-2-1 C-2-2 ASPHALTIC CONCRETE (±6 inches). GRAVEL (GP) (±4 inches); grey, damp, medium dense, coarse subrounded gravel, (base rock). Silty CLAY to SILT, some clay, sand, and gravel (CL to ML); dark brown, low plasticity, moist, medium stiff, fine sand, (alluvium). 2 C-2-3 Silty GRAVEL, some sand (GM); grey to brown, low plasticity silt, moist, medium dense, fine to coarse sand, fine to coarse subrounded gravel, (alluvium). 3 4 Sandy GRAVEL, trace silt (GP); grey, damp to moist, dense, fine to coarse sand, fine to coarse subrounded gravel, (alluvium). No seepage or ground water encountered to the limit of excavation. 5 BOTTOM OF EXPLORATION Project No.: Surface Elevation: Date: Core Hole Log: C- 2 N/A (Approx.) December 21, 2016

27 Comments Depth, Feet Sample # Location Class Symbol Water Table C, TSF Symbol Soil and Rock Description Cored on surface crack that extended through the core. ±1.75-inch overlay with geotextile fabric over original wearing course. 1 C-3-1 ASPHALTIC CONCRETE (±4 inches). CRUSHED GRAVEL, some sand and silt (GW-GM) (±11 inches); grey to brown, damp, ±1½-inch minus, (base rock). Base rock is minimally processed with few fractured faces. 2 C-3-2 Silty CLAY to SILT, some clay, sand, and gravel (CL to ML); dark brown, low plasticity, moist, medium stiff, fine to coarse sand, fine subrounded gravel, (alluvium). 3 C-3-3 Silty GRAVEL, some sand (GM); grey to brown, low plasticity silt, moist, medium dense to dense, fine to coarse sand, fine to coarse subrounded gravel, (alluvium). No seepage or ground water encountered to the limit of excavation. 4 BOTTOM OF EXPLORATION 5 Project No.: Surface Elevation: Date: Core Hole Log: C- 3 N/A (Approx.) December 21, 2016 Comments Depth, Feet Sample # Location Class Symbol Water Table C, TSF Symbol Soil and Rock Description Irregular surface on the bottom of the core. Reported AC thickness of 5 inches is the thickest portion of the core. 1 C-4-1 C-4-2 ASPHALTIC CONCRETE (±5 inches). CRUSHED GRAVEL, some sand and silt (GW-GM) (±9 inches); grey, damp, dense, ±1½-inch minus, angular to subrounded gravel, (base rock). CLAY (CH); grey, high plasticity, moist, medium stiff, (alluvium) No seepage or ground water encountered to the limit of excavation. 5 BOTTOM OF EXPLORATION Project No.: Surface Elevation: Date: Core Hole Log: C- 4 N/A (Approx.) December 21, 2016

28 Comments Depth, Feet Sample # Location Class Symbol Water Table C, TSF Symbol Soil and Rock Description Core includes ±1.75-inch overlay with geotextile fabric over original wearing course. 1 C-5-1 C-5-2 ASPHALTIC CONCRETE (±5 inches). Sandy GRAVEL, some silt (GW-GM) (±6 inches); grey to brown, moist, medium dense, fine to coarse sand, fine to coarse subangular to subrounded gravel, (base rock). Silty CLAY (CL to ML); grey, medium plasticity, moist, medium stiff to stiff, (alluvium) No seepage or ground water encountered to the limit of excavation. 5 BOTTOM OF EXPLORATION Project No.: Surface Elevation: Date: Core Hole Log: C- 5 N/A (Approx.) December 21, 2016 Comments Depth, Feet Sample # Location Class Symbol Water Table C, TSF Symbol Soil and Rock Description Core includes ±2.5-inch overlay with geotextile fabric over original wearing course. Lower AC lift is fractured. 1 C-6-1 ASPHALTIC CONCRETE (±4 inches). CRUSHED GRAVEL (GW) (±8 inches); grey, damp to moist, dense, ±1½-inch minus, angular to subrounded gravel, (base rock). CLAY (CH); grey, high plasticity, moist, stiff, (alluvium). C No seepage or ground water encountered to the limit of excavation. 5 BOTTOM OF EXPLORATION Project No.: Surface Elevation: Date: Core Hole Log: C- 6 N/A (Approx.) December 21, 2016

29 Comments Depth, Feet Sample # Location Class Symbol Water Table C, TSF Symbol Soil and Rock Description 1 C-7-1 ASPHALTIC CONCRETE (±3.75 inches). CRUSHED GRAVEL, some sand (GW) (±13.25 inches); grey, damp, dense, ±1-inch minus, angular to subrounded gravel, (base rock). 2 C-7-2 Gravelly SILT, some clay (ML); brown, low plasticity, moist, medium stiff, fine subrounded gravel, (alluvium). 3 4 Silty GRAVEL, some sand (GM); grey to brown, low plasticity silt, moist, medium dense, fine to coarse sand, fine to coarse subrounded gravel, (alluvium). No seepage or ground water encountered to the limit of excavation. 5 BOTTOM OF EXPLORATION Project No.: Surface Elevation: Date: Core Hole Log: C- 7 N/A (Approx.) December 21, 2016 Comments Depth, Feet Sample # Location Class Symbol Water Table C, TSF Symbol Soil and Rock Description Core includes ±½-inch overlay with geotextile fabric. Irregular surface on the bottom of the core. Reported AC thickness of ±4.5 inches is the thickest portion of the core. Practical drilling refusal at ±2.5 feet on coarse gravel or cobble. No seepage or ground water encountered to the limit of excavation C-8-1 C-8-2 C-8-3 ASPHALTIC CONCRETE (±4.5 inches). CRUSHED GRAVEL, some sand (GW) (±4.5 inches); grey, damp, medium dense, ±2-inch minus, angular to subrounded gravel, (base rock). CLAY, trace gravel (CH); grey, high plasticity, moist, stiff, (alluvium). Silty GRAVEL, some sand (GM); grey to brown, low plasticity silt, moist, dense, fine to coarse sand, fine to coarse subrounded gravel, (alluvium). BOTTOM OF EXPLORATION 4 5 Project No.: Surface Elevation: Date: Core Hole Log: C- 8 N/A (Approx.) December 21, 2016

30 Comments Depth, Feet Sample # Location Class Symbol Water Table C, TSF Symbol Soil and Rock Description Core includes ±2.5-inch overlay with geotextile fabric over original wearing course. 1 C-9-1 C-9-2 ASPHALTIC CONCRETE (±6 inches). Sandy GRAVEL (GP) (±7.5 inches); grey, damp, dense, fine to coarse sand, fine to coarse subrounded gravel, (base rock). SILT, some clay, trace gravel (ML); dark brown, low plasticity, moist, medium stiff, fine subrounded gravel, (alluvium). 2 Practical drilling refusal at ±3 feet on coarse gravel or cobble. No seepage or ground water encountered to the limit of excavation. 3 Silty GRAVEL, some sand (GM); grey to brown, low plasticity silt, moist, medium dense, fine to coarse sand, fine to coarse subrounded gravel, (alluvium). BOTTOM OF EXPLORATION 4 5 Project No.: Surface Elevation: Date: Core Hole Log: C- 9 N/A (Approx.) December 21, 2016 Comments Depth, Feet Sample # Location Class Symbol Water Table C, TSF Symbol Soil and Rock Description Limited to AC core only. ASPHALTIC CONCRETE (±3 inches). BOTTOM OF EXPLORATION Project No.: Surface Elevation: Date: Core Hole Log: C-10 N/A (Approx.) December 21, 2016

31 Comments Depth, Feet Sample # Location Class Symbol Water Table C, TSF Symbol Soil and Rock Description Moderate seepage at ±3 feet C-11-1 C-11-2 C-11-3 ASPHALTIC CONCRETE (±4 inches). CRUSHED GRAVEL and ASPHALTIC CONCRETE GRINDINGS, trace sand and silt (GW) (±4 inches); grey to black, damp, dense, ±2-inch minus, angular to subangular gravel, (base rock). CRUSHED GRAVEL, trace silt and sand (GP) (±4 inches); grey, damp, dense, ±1½-inch minus, angular to subrounded gravel, (subbase). Silty CLAY to SILT, some clay and gravel (CL to ML); dark brown, low to medium plasticity, moist to wet, medium stiff to stiff, fine subrounded gravel, (alluvium). Clayey GRAVEL, some silt and sand (GC); brown, medium plasticity clay, wet, medium dense, fine to coarse sand, fine to coarse subrounded gravel, (alluvium). 4 5 BOTTOM OF EXPLORATION Project No.: Surface Elevation: Date: Core Hole Log: C-11 N/A (Approx.) December 21, 2016 Comments Depth, Feet Sample # Location Class Symbol Water Table C, TSF Symbol Soil and Rock Description Core includes ±2.25-inch overlay with geotextile fabric over original wearing course. Practical drilling refusal at ±2 feet on coarse gravel or cobble. No seepage or ground water encountered to the limit of excavation. 1 2 C-12-1 C-12-2 ASPHALTIC CONCRETE (±5 inches). Sandy GRAVEL, trace silt (GP) (±5 inches); grey to brown, damp to moist, dense, fine to coarse sand, fine to coarse angular to subrounded gravel, (base rock). Sandy GRAVEL, some silt (GW-GM); grey to brown, low plasticity silt, moist, dense, fine to coarse sand, fine to coarse subangular to subrounded gravel, (possible fill). BOTTOM OF EXPLORATION Project No.: Surface Elevation: Date: Core Hole Log: C-12 N/A (Approx.) December 21, 2016

32 Foundation Engineering, Inc. Project Photo 1. Pavement Core C-1 Photo 2. Pavement Core C-2

33 Foundation Engineering, Inc. Project Photo 3. Pavement Core C-3 Photo 4. Pavement Core C-4

34 Foundation Engineering, Inc. Project Photo 5. Pavement Core C-5 Photo 6. Pavement Core C-6

35 Foundation Engineering, Inc. Project Photo 7. Pavement Core C-7 Photo 8. Pavement Core C-8

36 Foundation Engineering, Inc. Project Photo 9. Pavement Core C-9 Photo 10. Pavement Core C-10

37 Foundation Engineering, Inc. Project Photo 11. Pavement Core C-11 Photo 12. Pavement Core C-12

38 Foundation Engineering, Inc. Project Table 1B. Summary of Pavement Thicknesses 1 Exploration 1 Location 2 Asphaltic Concrete Thickness (in.) 3,4,5 Base Rock Thickness (in.) Total Pavement Section (in.) C-1 Taxiway A (north) C-2 Apron at north Taxiway A access C-3 Apron C-4 Apron C-5 Apron C-6 Apron C-7 Apron C-8 Apron at A C-9 Apron C-10 5 C-11 Taxilane south of apron South blast pad/ overrun pavement /4 12 C-12 Taxiway A (south) Notes: 1. See Figure 2A for approximate pavement core locations. 2. Pavement core photos are included in Appendix B. 3. Base rock varied in the explorations, typically consisting of either 1.5 to 2-inch minus CRUSHED GRAVEL or sandy GRAVEL. USCS Classifications include GW, GP and GP-GM. 4. Exploration C-10 was limited to the asphaltic concrete (AC) core only and did not measure the entire pavement section. 5. Exploration C-11 encountered ±8 inches of base material that appeared to include ±4 inches of AC millings and gravel over ±4 inches of sandy gravel. See pavement core log for additional details.

39 Appendix C Field and Laboratory Test Results Professional Geotechnical Services Foundation Engineering, Inc.

40 Foundation Engineering, Inc. Project Table 1C. Summary of DCP Test Results Exploration C-1 C-2 C-3 C-4 C-5 C-6 C-7 C-8 Notes: Initial Test Depth (inches) Soil Description 1 Average DCP (mm/blow) 2 Average Mr (psi) 3 Corrected Mr (psi) 4 Correlated CBR Value 4 CRUSHED GRAVEL (GW) ,046 16, Sandy SILT, some clay (ML) ,198 3, GRAVEL (GP) ,482 7, Silty CLAY to SILT, some clay, sand and gravel (CL to ML) CRUSHED GRAVEL, some sand and silt (GW-GM) Silty CLAY to SILT, some clay, sand and gravel (CL to ML) CRUSHED GRAVEL, some sand and silt (GW-GM) ,311 3, ,650 16, ,377 3, ,846 17, CLAY (CH) ,183 3, Sandy GRAVEL, some silt (GW-GM) ,344 13, Silty CLAY (CL to ML) ,688 4, CRUSHED GRAVEL (GW) ,103 21, CLAY (CH) ,081 4, CRUSHED GRAVEL, some sand (GW) Gravelly SILT, some clay (ML) CRUSHED GRAVEL, some sand (GW) Silty GRAVEL, some sand (GM) ,615 15, ,249 3, ,110 13, ,911 6, DCP (mm/blow) based on the average readings from the initial test depth. 2. Mr value based on average DCP value at the test depth and the ODOT recommended correlation: Mr = 49,023 (DCP) Values may vary slightly due to rounding. 3. Corrected Mr value is based on the ODOT recommended correction factors of 0.62 for base rock and 0.35 for subgrade. 4. Correlated CBR value for subgrade is based on the FAA recommended correlation of MR = 1,500*CBR.