0003 Attachment 1 - Geotechnical Assessment - VA Anchorage Mental Health - Submitted.pdf

1120 Huffman Road

Unit 24 Anchorage, Alaska 99515

907.313.3370 www.centralgeotech.com

August 3, 2020

GDM Inc.

1401 W 34th Avenue Suite 200 Anchorage, Alaska 99503

Attention: Jim Blair (jim.gdmanc@ak.net)

Re: Geotechnical Assessment Department of Veterans Affairs Mental Health Clinic and Parking Lot 1201 N Muldoon Road Anchorage, Alaska

Dear Mr. Blair, Central Geotechnical Services, LLC is pleased to submit this Geotechnical Assessment Report for the proposed new mental health building and parking lot located in Anchorage, Alaska.

This report provides:

Ø An overview of the project site including information related to the regional geology of the area.

Ø Geotechnical information, based on findings during surface reconnaissance and subsurface explorations.

Ø General construction recommendations.

Ø Recommendations for additional work as needed.

A set of appendices can be found at the end of this document.

Thank you very much for the opportunity to work with you. If you feel obliged, we welcome referrals from our previous clients and would enjoy the opportunity to work with others in your professional and personal networks. Please feel free to call our office with questions about this report.

Respectfully, Central Geotechnical Services, LLC

Stephen Eagar, P.E.

Principal

Geotechnical Assessment:

Department of Veterans Affairs Mental Health Clinic 1201 N Muldoon Road Anchorage, Alaska

Prepared For:

December 29, 2019

Submitted by:

Anchorage, Alaska 99515

Geotechnical Assessment – GDM – AVAHS Mental Health Clinic

Page i of 67

Table of Contents

1.0 INTRODUCTION AND PURPOSE OF REPORT

1.1 Project Description

2.0 ASSESSMENT SUMMARY

2.1 Site Location and Surface Conditions

2.2 Site Geology

2.3 Tectonic and Seismic Setting

2.4 Liquefaction Hazard

2.5 Subsurface Soil Conditions

2.5.1 Fill

2.5.2 Holocene Alluvium

2.5.3 Glacioestuarine or Eolian Silt and Fine Sand

2.5.4 Lab Testing Results

2.6 Groundwater and Permafrost Conditions

2.7 Environmental Considerations

3.0 CONCLUSIONS AND RECOMMENDATIONS

3.1 Existing Undocumented Fill

3.2 Removal of Existing Fill

3.3 Site Preparation

3.4 Site Grading

3.5 Permafrost and Frozen Soils

3.6 Temporary Excavations

3.7 Utility Trenches

3.8 Engineered Structural Fill

3.9 Seasonal Frost

3.9.1 Building Foundations

3.9.2 Pavement Areas

3.10 Foundations

3.11 Slab on Grade Floors

3.12 Retaining Walls

3.13 Pavement Profiles

3.14 Drainage Considerations

3.15 Seismic Design Considerations

Anchorage, Alaska 99515

Page ii of 67

3.16 Additional Geotechnical Services

4.0 LIMITATIONS OF REPORT

5.0 SIGNATURES

APPENDIX A:

APPENDIX B:

APPENDIX C:

APPENDIX D:

Anchorage, Alaska 99515

1.0 INTRODUCTION AND PURPOSE OF REPORT

The purpose of this Geotechnical Assessment Report is to engage with the owner/developer and provide technical insight and analysis for the project based on various public data, local findings onsite, lab data of local soils, and experience.

After receiving direction from GDM Inc. and Hood River Engineering (HRE), Central Geotechnical Services (CGS) was requested to provide a Geotechnical Assessment, along with general recommendations for the design and construction of a new Mental Health building and parking lot development. The construction recommendations cover topics such as investigative soils data, allowable soil bearing pressure, lateral pressures, compaction requirements, foundation placement, pavement, and seismic considerations.

This report is intended to facilitate the preliminary focus of future development and initiate the requirements for the design and permitting of the proposed project.

1.1 Project Description

The proposed project involves the construction of a new Mental Health Building and nearby surface parking lot at the Department of Veterans Affairs Medical Center, located at 1201 N Muldoon Road in Anchorage, Alaska. We were provided with a preliminary site plan from the Final Campus Master Plan for the Alaska Veterans Affairs Healthcare System presentation completed June of 2018, which depicts the Mental Health Building on the southwestern corner of the existing VA building, and the parking lot on the western half of the nearby seven-acre parcel. After discussion with GDM and HRE, it is our understanding the Mental Health Building has been relocated to the southeastern corner of the existing VA building. The exact location of the new building is still undecided.

From discussions with the design team, it was indicated to our office that this structure, though connected to a healthcare facility, is not considered to be a critical structure for seismic design. As such, no additional shear wave velocity data or seismicity analysis was to be completed as part of our scope of work.

We expect the project will include only limited site grading that would largely consist of excavations and temporary road construction for contractor equipment access, localized site improvements and for restoration of the site to pre-construction conditions. No site grading plans have been provided to Central Geotech at this time.

The proposed Mental Health Building is planned to be a single-story building and be approximately 20,250 square feet in size. It will be located near the southeastern corner of the existing Alaska VA Healthcare System building. We understand that the proposed Mental Health Building is planned to be constructed as a one-story building, with the potential for a second story addition in the future.

The parking lot is proposed to be approximately one-acre and from bituminous asphalt pavement with various locations occupied by landscaped areas surrounded or partially surrounded by curbs.

Anchorage, Alaska 99515

At the time of this report, no retaining walls have been proposed for this construction.

A site grading plan has not yet been prepared. We expect that the parking lot will be constructed at an approximate elevation of 229 feet, close to the elevation of existing pavement on Zuckert Avenue.

We were provided with the following guidance documents outlining the requested scope of geotechnical assessment and design information needed for our Geotechnical Assessment.

1. Final Campus Master Plan for the Alaska Veterans Affairs Healthcare System, Slideshow Presentation from Department of Veterans Affairs, JBER Team, and Hood River Engineers, dated June 6, 2019, pages 1-50.

2. Statement of Work, Project No. 463-301, New Mental Health Building and Parking Lot, undated, pages 1-11.

3. Meeting Minutes – Master Site Plan Study for the Alaska Veterans Administration Health Care System, Project 36C26019Q0262 – Master Site Plan Study for the Alaska Veterans Administration Health Care System, March 19, 2019

4. Meeting Minutes – JBER – Bartlett – VA Permit Modification Design Review, Project 36C26019Q0262 – Master Site Plan Study for the Alaska Veterans Administration Health Care System, March 27, 2019.

5. Specifications for New VA Outpatient Clinic and Regional Office at VAMC Alaska Anchorage, Alaska, Spec. Vol. II of V, Project. No. 463-500, Livingston Slone, Inc. March 23, 2019.

6. A Site Utility Map with suggested boring locations from Hood River Engineers and the Joint Base Elmendorf Richardson Planning dated November 2019.

Anchorage, Alaska 99515

2.0 ASSESSMENT SUMMARY

2.1 Site Location and Surface Conditions

The proposed building development site is located at the northwest corner of the intersection of North Muldoon Road and Zuckert Avenue in Anchorage, Alaska. It is our understanding through discussion with GDM Inc., HRE, and members of the design team that the proposed building has been relocated from the preliminary plans to the southeastern corner within the landscaped area and parking lot of the existing VA Building.

The proposed parking lot site is located at the northeast corner of the intersection of North Muldoon Road and Zuckert Avenue in Anchorage, Alaska. Preliminary plans for the new one-acre parking lot depict its location on the western half of the seven-acre forested area.

Along the western area of the parking lot area, and nearby to our boring location, is a drywell and drainage ditch system surrounded by what appears to be an area of raised fill material. This drywell can be found on referenced utility locates not included in this report, and should be considered during design.

An area map of the site is shown in Figure 2-1.

Figure 2-1: Area map of project site (Source: USGS The National Map)

The site is located in the Anchorage plains on a broad alluvial plain with gentle topography at an approximate elevation of 229 feet above sea level. The site lies about 2,000 feet south of alluvial lowland associated with Ship Creek, about 20 feet vertical above the creek channel.

SITE

Anchorage, Alaska 99515

The area for the proposed Mental Health Clinic is currently to the southeast of the existing Alaska VA Healthcare System building. The area for the proposed parking area is currently an undeveloped forested area. The surrounding area is developed with commercial, light industrial, and residential buildings.

The general topography of the proposed development area is shown in Figure 2-2. The location of our exploratory borings was directed and placed solely by Hood River Engineers. Figure 2-3 depicts these locations.

Figure 2-2: Draft of Topographic Survey of the project site completed by Lounsbury and Associates .

(Provided by GDM Inc. dated December 18, 2019)

2.2 Site Geology

The geology beneath Anchorage is a result of the complex interplay of glacial, fluvial, stillwater, and colluvial depositional processes during the last 1.6-million years (Quaternary Period). The resulting sediment wedge ranges in thickness from zero where it abuts metamorphic rocks of the Chugach Mountains to the east at an elevation of about 1,000 ft (300 m), to about 1,600 ft (500 m) thick where it overlies Tertiary sandstone beneath Pt. Campbell in the westernmost part of the city.

During latest glaciation period approximately 75,000 to 11,000 years ago (Wisconsin time), glacial ice advanced over the Anchorage area several times from the northeast, northwest, and south, first leaving deposits of hard till of widely varying thickness over the bedrock. As these glaciers retreated, they left

Anchorage, Alaska 99515 complex deposits of washed ice-contact sediments. Later advances did not cover the entire lowland area with glacial ice and instead impounded water that at times was turned brackish by contact with marine waters of lower Cook Inlet. Sediments that filled this basin grade from relatively clean glaciodeltaic sand and gravel along the basin margins to thick deposits of glacioestuarine silt and clay in the basin interior, part of which underlies downtown Anchorage.

The last major glaciation to affect the Anchorage area was the Elmendorf advance from the northeast, estimated to be approximately13,500 years ago. This advance reached as far as Elmendorf Air Force Base, about 3 mi (5 km) northeast of present-day downtown Anchorage. Gravelly outwash from this advance blankets most of northern Anchorage, including the downtown area, to a thickness of up to several tens of feet.

During the last 12,000 years (Holocene Epoch), the Anchorage lowland was dissected by several small streams, which left alluvial fans along the mountain front and partially filled their incised valleys with alluvium.1

2.3 Tectonic and Seismic Setting

The Cook Inlet basin is a northeast-trending forearc basin above the Aleutian subduction zone in southern Alaska. The geologic history and tectonic setting within Cook Inlet is composed of complex, discontinuous structures with variable shape and vergence that probably developed by right-transpressional deformation on oblique-slip faults extending downward into Mesozoic basement beneath the Tertiary basin.

The most recent episode of deformation may have been as early as late Miocene time, but most of the deformation occurred after deposition of much of the Pliocene Sterling Formation. Deformation continued into Quaternary time, and many structures are probably still active. One structure, the Castle Mountain fault, has Holocene fault scarps, an adjacent anticline with flower structure, and historical seismicity. If other structures in Cook Inlet are active, blind faults coring fault-propagation folds may generate Mw 6–7+ earthquakes. Tectonic activity near the Cook Inlet is understood to be driven by coupling between the North American and Pacific plates along the Alaska-Aleutian subduction zone, and by lateral escape of the forearc to the southwest, due to collision and indentation of the Yakutat terrane 300 km to the east of the basin2.

The Anchorage Basin is underlain by a thick section of unconsolidated sediments, and when introduced to long periods of shaking can cause damage to buildings similar to the damage experienced in the 1964 earthquake. Typically, areas underlain by a deep section of unconsolidated sediments tend to experience longer periods of shaking in contrast to shallow bedrock area.

1 Combellick, R.A., 1999, Simplified Geologic Map and Cross Sections of Central and East Anchorage, Alaska, State of Alaska Department of Natural Resources, Division of Geological and Geophysical Surveys, Preliminary Interpretive Report 1999-1, August 1999.

2 Haeussler, P.J., Bruhn, R.L., and Pratt, T.L., 2000, Potential seismic hazards and tectonics of the upper Cook Inlet basin, Alaska, based on analysis of Pliocene and younger deformation: Geological Society of America Bulletin, v. 112, no. 9, p. 1414-1429.

Anchorage, Alaska 99515

The seismic setting of this region is highly relied upon the geologic and tectonic setting rather than historical records like many portions of the world. Prior to the 9.2 MW earthquake in 1964, only two seismograph stations were in operation in the area.

The 1964 earthquake is believed to represent the probable maximum earthquake for the southern Alaskan region. The shaking intensities that were experienced in the Anchorage area during this event are believed to be the maximum expected ground intensity in future earthquakes.3

Quaternary age (last 1.6 million years) crustal faults inventoried in the USGS National Fault and Fold Database that lie within 40 miles of the site are the Wasilla St No. 1 Needham, Pitman, and Big Lake North Anticlines about 17.2, 20.9, and 24.3 miles to the north, the Castle Mountain Fault about 28.5 miles to the northwest, the Stump Lake and Ivan River Anticlines about 32.6 and 35.4 miles to the west, and the Swanson River Anticline about 39.7 miles to the southwest.

The contribution of potential earthquake-induced ground motion from all known sources, including the folds and faults described above, are provided by the seismic design parameters for the project site presented in the recommendations section of this report.

2.4 Liquefaction Hazard

Strong seismic shaking can result in ground failure due to the phenomenon known as liquefaction. Soil liquefaction occurs when saturated soil temporarily loses strength and behaves as a fluid in response to seismic shaking. Liquefaction is generally limited to loose, granular, cohesionless soil located below a shallow water table. Various types of ground deformation can occur including but not limited to slope movement, lateral spreading, sand boils, settlement, ground oscillation and cracking.

A regional assessment of seismically induced ground-failure susceptibility of Anchorage, Alaska was completed by the Alaska Division of Geological and Geophysical Surveys and the Municipality of Anchorage4. This study designates the site vicinity as having a very-low susceptibility to liquefaction.

3 Winterhalder, E.C., Williams, T.L., England, J.M., 1979, Geotechnical Hazards Assessment Municipality of Anchorage, Alaska, Harding- Lawson and Associates, p. 21-40.

4 Weems, S.M., Combellick, R.A., 1997, Seismically induced ground-failure susceptibility of Anchorage, Alaska; Alaska Division of Geology and Geophysical Surveys in Cooperation with the Municipality of Anchorage, Miscellaneous Publication 32, Weems and Combellick, scale 1:25,000.

Anchorage, Alaska 99515

Figure 2-3: Existing site conditions with exploration locations, scale is approximate.

(Imagery from Google Earth)

2.5 Subsurface Soil Conditions

We completed a program of subsurface exploration at the site that included drilling two geotechnical borings (B-1 and B-2) as requested in the scope of work by Hood River Engineers, at the approximate locations shown in Figure 2-3, above. We utilized hollow-stem augers for the geotechnical borings.

The soil and groundwater conditions encountered are described in the following sections. Field exploration procedures, summary logs of the explorations, and Soil Classification and Description Guidelines are presented in Appendix A.

2.5.1 Fill

Based on our observations and at the locations explored, both of the sites are covered with a layer of fill.

This material was found to be variable in composition. Generally, it consists of medium-dense to very-dense, brown, gray, and red, damp to moist, silty Gravel with sand. The gravel and sand is angular to sub rounded. Based on correlations between standard penetration resistance and soil strength, the encountered fill was mostly medium-dense to very-dense with N-values generally ranging between 17 and 100+. We encountered topsoil in the upper foot, and then fill extended to approximate depths of 9

Exploration Locations – AVAHS Mental Health Facility & Parking Lot

1201 North Muldoon Road, Anchorage, Alaska

N

Key

Geotechnical Borings

50 100 200 ft

B-2

Geotech Notes:

• Geotech Exploration was completed on 12/2/2019

• Geotech borings were drilled in depts and locations requested by the Project Civil Engineer via email correspondence.

• Geotechnical borings were completed with a Geoprobe 7822DT Combo Rig using Hollow Stem Augering operated by Discovery Drilling.

B-1

Anchorage, Alaska 99515 feet in B-1, and 6.5 feet in B-2. We expect that there may be additional areas of thick fill onsite in the areas that extend beyond our explorations.

Laboratory testing of samples collected from this unit indicate the moisture content (ASTM D2216) of the fill ranges from 3 to 40 percent.

2.5.2 Holocene Alluvium

Directly beneath the fill, we encountered a very-dense well-graded GRAVEL (GW-GM) with Silt and Sand belonging to the Holocene Alluvium. The field-tested density of the well-graded GRAVEL was very-dense with N-values generally ranging between 89 and 100+ in our explorations. The well-graded GRAVEL extended to depths of 19 feet bgs in B-1, and to 24 feet bgs in B-2.

Beneath the well-graded GRAVEL, we encountered primarily gravelly SAND (SM) with silt belonging to the Holocene Alluvium. In general, the deposit is well-graded with grain sizes ranging from cobbles, gravel and coarse- to very-fine sand. The gravel is generally subrounded, while the sand is generally subangular. Gravel sizes up to 2-inches in diameter were recovered from the drill cuttings. The deposit contains trace silt and clay.

At approximately 28-32 feet deep, the driller identified what appeared to be heaving sands against the equipment at that depth. This should be noted in the case of deep excavations and foundations, and that heave is probable at other depths.

Based on Standard Penetration Tests in borings, the sandy GRAVEL (GW) is very-dense to dense with N-values ranging from 74 to 100+. The SAND and GRAVEL extended below the maximum depth explored of 24 feet bgs in B-1. The sandy GRAVEL extended to depths of 39 feet bgs in B-2.

Laboratory testing of samples collected from this unit indicate the moisture content (ASTM D2216) of the fill ranges from 3 to 22 percent. Sieve analysis (ASTM C136) of a grab sample from B-1 at a depth of

17.5 feet yielded a gravel content of 58%, a sand content of 32%, and a silt or clay content of 10%. The grain size of the sand varies from fine to coarse.

2.5.3 Glacioestuarine or Eolian Silt and Fine Sand

Directly beneath the Holocene Alluvium, we encountered a very-dense silty SAND (SM) and trace gravel belonging to the Holocene Alluvium. The field-tested density of the silty SAND was very-dense with N-values generally ranging between 94 and 100+ in our explorations. The silty SAND extended below the maximum depth explored of 51.5 feet in B-2.

Laboratory testing of samples collected from this unit indicate the moisture content (ASTM D2216) of the fill ranges from 10 to 15 percent.

Anchorage, Alaska 99515

2.5.4 Lab Testing Results

Geotechnical lab tests were performed on selected samples of the soils encountered in subsurface exploration, including grain size sieve analysis (ASTM C136), washed sieve analysis of material passing the No. 200 sieve (ASTM D1140), and moisture content (ASTM D2216).

The results of the laboratory tests are shown on the boring logs. Detailed lab reports, including a percentage plot of each grain size constituent, are presented in Appendix B.

2.6 Groundwater and Permafrost Conditions

We encountered groundwater in both of our hollow-stem auger explorations at an approximate depth of 21 feet bgs in B-1, and at approximately 24 feet bgs in B-2 during our exploration on December 2, 2019.

The Geotechnical Report from DOWL Engineers also found the groundwater to be between 22 to 25 feet bgs during their subsurface explorations in 20055.

No Permafrost was encountered in any of the test borings during our exploration in early December. In addition, no abnormal temperature changes were noted in the soils observed during sampling.

2.7 Environmental Considerations

Environmental testing and analysis was not part of the scope of this work. Samples from our exploration were taken by a representative from Hood River Engineers from boring B-1 during the initial segments of drilling for lab testing.

Although design has not yet been developed for the parking lot area, we anticipate additional information may be required involving the existing drywell along the western edge of the parking lot area if plans to drain to this well or decommissioning are in the development plans.

5 Kampsen, M.E., 2006, Subsurface Exploration Veteran’s Affairs Outpatient Clinic Elmendorf Air Force Base, Alaska, DOWL Engineers,

p. 7.

Anchorage, Alaska 99515

3.0 CONCLUSIONS AND RECOMMENDATIONS

Based on the results of our geotechnical assessment, we consider the site to be suitable for the development as proposed. The building may be supported on shallow foundations designed and constructed in accordance with our recommendations. We expect a minimum excavation depth of 36 inches will be necessary to reach subgrade suitable for footing support and to remediate for frost depths.

Additional depth of excavation may be required to remove unsatisfactory soils or existing uncontrolled fills, or to reach depths as needed for frost remediation. See below sections for details.

The following sections present our conclusions and recommendations for project design and construction.

3.1 Existing Undocumented Fill

Based on the results of our geotechnical assessment, there is significant thickness of fill in both locations of exploration. In B-1, we encountered a fill thickness of approximately 9 feet within the area for the proposed parking lot, and in B-2, we encountered a fill thickness of 6.5 feet within the area for the proposed Mental Health Clinic.

The existing fill will not be suitable for support of structures due to variable consistency and the possible presence of voids, deleterious materials or poorly-compacted pockets. Fill encountered in boring B-1 consisted primarily of medium-dense, silty sand with trace amounts of fine organics; however, the boring appeared to encounter large-sized concrete debris with possible voids at the base. The fill may be susceptible to future settlement.

The lateral limits of the fill mass in the subsurface are not well constrained due to the wide spacing between exploratory borings and may affect a large portion of the parking lot area. Additional geotechnical exploration should be considered in order to better define the subsurface boundaries of the fill. The location of B-1 (the parking lot) especially appears to be in a local area of increased fill, based on the surrounding topography and ground features. Less fill may be present further to the “center” of the parking lot, however, additional exploration would be required to better ascertain fill depths across the site.

3.2 Removal of Existing Fill

Removal of all undocumented fill will be required at the building location. Replacement of material is described in below sections.

We offer the following options for mitigation of the existing undocumented fill on the parking site.

Option 1 is to remove all of the existing undocumented fill from beneath all structural areas and replace it with new imported fill material compacted to engineered structural fill specifications as outlined in Section 3.5 Engineered Structural Fill.

Anchorage, Alaska 99515

If fill is discovered to be deeper or consistent with the findings of our boring location, Option 2 is to remove and replace the upper portion of the existing fill and evaluate how much of the lower portion of the fill may remain in place during site grading as necessary. Proof-roll performance tests in conjunction with visual assessment would be utilized to determine the suitability of the lower portion of the fill for structural support prior to placement of engineered structural fill.

In either approach, close geotechnical observation would be necessary during construction. Removal of materials may coincidentally be inclusive of all fill onsite if the excavation requirements beneath pavement push past the depth of existing fill.

For preliminary planning purposes, we expect that the minimum depth of removal and replacement beneath the pavement section would three feet or more. We expect that localized areas that yield under applied proof roll loads or that contain pockets of excessive deleterious materials (organics, voids, debris, etc.) would need to be over excavated deeper than three feet and replaced with compacted imported granular fill. The actual recommended minimum depth of removal would be determined in construction.

Proof-roll performance testing would be conducted under the observation of CGS with a loaded dump truck. Once the subgrade is sufficiently evaluated and stabilized, a cap of engineered structural fill will be placed to provide an even, stable base for the placement of rock anticipated for pavement construction. The replacement fill should consist of imported fill material as approved by CGS. The contractor should submit samples of the proposed fill material for suitability assessment and Proctor testing prior to being imported to the site. The replacement fill should be compacted to engineered structural fill specifications as outlined in Section 3.5 Engineered Structural Fill.

If Option 2 is employed, the potential for future settlement during the life of the pavement would be reduced to a level that may be considered acceptable, but there would still be a potential for settlement damage during the lifetime of the pavement.

The potential for settlement damage would be further reduced with the placement of a thickened geotextile reinforced pavement section in the area underlain by existing fill. We recommend a thickened pavement section consisting of 18 inches of crushed rock with two layers of geotextile reinforcement.

Geotextile reinforcement should consist of Tensar TX140 Geogrid (or approved alternative) placed at the base and middle of the crushed rock section. Geogrid should be placed in accordance with manufacturer recommendations. The minimum overlap between geogrid panels is 12 inches. Geogrid should be laid smooth and pulled taut prior to burial.

The options presented in this report should not be considered to be an exhaustive list, and a competent contractor should be consulted in order to optimize costs for the construction methods. Other options, such as soil-cement amendment may be feasible and can be evaluated upon request.

3.3 Site Preparation

Any existing structures or utilities on the site should be demolished and all debris removed from the site.

Subsurface structures, such as existing footings and abandoned utilities, should be removed and the excavations backfilled utilizing only an approved granular material, placed and compacted in

Anchorage, Alaska 99515 accordance with Section 3.4 Engineered Structural Fill. Removal of undocumented backfill adjacent to demolished and excavated structures is recommended. Excavation should employ benching of the side walls so that backfill can be properly placed.

In preparation for construction, all existing asphalt and concrete should be removed from future structural areas. In vegetated areas, mulch and the heavily rooted topsoil zone should be stripped and removed from the site in all proposed structural areas and for a minimum 2-foot margin around such areas. Based on our explorations, the minimum depth of stripping will be approximately 4-8 inches or more. Greater removal depths may necessary in isolated areas to remove tree stumps, root balls, excessively rooted zones, or undocumented fills. Stripped material should be transported off-site for disposal or stockpiled for use in landscaping areas.

After stripping and the required site cutting has been completed, we recommend the areas be observed by a member of our geotechnical staff who will evaluate the subgrade by probing or other applicable means. Existing compacted fill beneath the asphalt may remain provided that CGS evaluates it to verify adequate compaction. The evaluation should be performed by proof-rolling with a loaded dump truck or similar vehicle, and should be observed by CGS. If soft or other unsatisfactory areas are identified, the material should be excavated and replaced with compacted engineered structural fill.

It is likely that unrecognized areas of undocumented fill may be encountered on the site during construction. It is recommended that all uncontrolled fill soils be removed completely in preparation for foundations or other construction and be replaced with engineered structural fill in accordance with Section 3.8 Engineered Structural Fill.

3.4 Site Grading

We expect that the project may include limited site grading to construct pavement areas and storm water facilities. Site grading should be designed and performed in accordance with Appendix J of the International Building Code (IBC). Permanent cut and fill slopes should not exceed a grade of 2H:1V (Horizontal to Vertical). Slopes that will be maintained by mowing should not be constructed steeper than 3H:1V. CGS recommends that fill slopes be overbuilt by about 3 feet and trimmed back to finish grade in order to construct a stable slope face that is resistant to shallow sloughing and erosion. Structures and paved surfaces should be located at least 5 feet horizontal from the slope face. Finish slope faces should be planted with appropriate vegetation to provide protection against erosion. Surface water runoff should be collected and directed away from slopes steeper than 3H:1V to prevent water from running down the slope face.

3.5 Permafrost and Frozen Soils

We did not encounter any permafrost or frozen soils during our explorations. If frozen soils are encountered during the construction process, do not place fill or any foundations or pavement subgrade atop frozen soils.

Anchorage, Alaska 99515

3.6 Temporary Excavations

The stability of temporary excavation slopes is a function of many factors, including soil type, soil density, slope inclination, slope height, the presence of groundwater, and the duration of exposure. The likelihood of slope failure increases as the cut is deepened and as the duration of exposure increases.

Temporary slope safety should remain the responsibility of the contractor, who is continually present at the site and is able to monitor the performance of the excavation and modify construction practices and shoring methods to reflect varying conditions. All excavations should be made in accordance with applicable Occupational Safety and Health Administration (OSHA) and State regulations.

Native soils at the site are characterized by low cohesion such that near vertical excavation faces including utility trench walls will likely experience moderate to severe caving. Shoring or widening of trenches should be expected to construct underground utilities.

Regardless of inclination, temporary slopes should be protected from surface runoff of storm water. This can typically be accomplished using berms or swales located along the top of the slope, and by placing plastic tarpaulins over the slope.

3.7 Utility Trenches

Utility trench construction in this region is especially susceptible to damaging frost action. At no time should native material be placed in utility trenches as backfill due to the susceptibility of frost heave.

Utility trench backfill in structural areas should consist of granular fill limited to a maximum particle size of 1¼ inches. Granular trench backfill should be compacted to at least 95% of the maximum dry density as determined by ASTM D1557. Placement of a clean drain rock (1” angular rock) may be placed in a section of the backfill area (depending on trench depth) to help drain the surface backfill of water and to prevent upward capillary action of perched water reaching the frost zone. During design, it is imperative to have CGS review all utility trench and backfill designs and be onsite during construction.

Excavator-mounted, vibratory-plate compactors are typically the most efficient for compaction of trench backfill. Lift thicknesses should be evaluated based on field density tests and material type; however, care should be taken when operating vibratory compactors to prevent damage to pipes. An initial lift thickness over pipe may be increased to protect the pipe from damage during compaction. Depths of this increased area vary due to utility type and excavation depths.

Native materials should only be used for trench backfill in non-structural areas where a soft trench and future settlement or heave of the backfill can be tolerated. This practice is not generally recommended.

3.8 Engineered Structural Fill

Structural fill is any fill material used for support of foundations, retaining walls, slab-on-grade floors, sidewalks, embankments, pavements, and similar features. Upon approval by our office, the on-site soil

Anchorage, Alaska 99515 may be suitable for use as structural fill provided it can be separated from unsuitable material, be properly moisture conditioned, and compacted to the specified density as determined by standard testing in a soils lab. The on-site soil used as structural fill should be placed in lifts with a maximum uncompacted thickness of eight inches.

Imported granular material should be used for engineered structural fill if the on-site material cannot be properly processed and moisture conditioned. Imported granular fill should consist of crushed aggregate that is fairly well-graded between coarse and fine material and have less than 5 percent by weight passing the U.S. Standard No. 200 Sieve. Use of alternative granular fill material such as pit-run or quarry-run rock or sand should be evaluated for suitability by CGS prior to its use, but is unlikely to be approved.

Engineered structural fill is to be placed in lifts with a maximum uncompacted thickness of eight inches, compacted lifts of six inches, and tested for compaction at elevations, distances, and imported fill volumes in accordance with US Department of Veterans Affairs specifications and guidelines. Minimum compaction testing at each lift of compacted fill should be completed, and at each 50 horizontal feet for broad areas, or at each footing location for foundation-specific areas. The most conservative compaction guidelines found in this report or found in other public specifications utilized for this construction will serve as standard.

All engineered structural fill is to be compacted to at least 95% of the maximum dry density determined by the Modified Proctor ASTM D1557 or equivalent. CGS should perform density testing of engineered structural fill to verify that adequate compaction is achieved. All nuclear densometer testing will be performed against specifically conducted lab test results of the material recently (within one week of production) taken from the granular fill producer. No previous Proctor results are to be admitted as optimum. In the case of reuse of onsite material as fill, the material will be tested at each 50 cubic yards of placed material in order to avoid soil inconsistencies during processing efforts.

Proof-rolling with a loaded dump truck or water truck may be allowed in certain circumstances under the guidance of CGS onsite to evaluate fill compaction, but should not be construed as the site standard.

Regardless of material or location, structural fill should be placed over firm, unyielding subgrade prepared in accordance with the "Site Preparation" section of this report. The condition of the subgrade should be verified by a CGS representative before backfilling or construction begins.

3.9 Seasonal Frost

This region is especially susceptible to frost permeating the soils below the surface, causing frost heave, reduction of bearing capacities, uplift, and other problems associated with construction. For this site, we expect frost depths to penetrate up to 6-8 feet or more below the exposed ground surface during winter months.

Remediation efforts generally include maintaining either a frozen or unfrozen state in the underlying bearing soils to prevent damage due to uplift or loss of bearing capacity. Construction of subgrade, especially of that involving pavement, will not be applicable to conventional practices in areas of no frost penetration.

Anchorage, Alaska 99515

Remediation can include several applied methods during design. Some of these include air exposure, refrigeration, or subgrade rock placement that includes free-draining material with high void ratios to allow water to drain away from the structure both laterally and vertically. Some structures may also be designed to account for heavy uplift or settlement. Based on the apparent construction type and soils found onsite, CGS should be consulted to provide ongoing recommendations for frost protection throughout design phases, and be retained onsite to perform observation of foundation material placement.

3.9.1 Building Foundations

We recommend allowing heat from the building to keep the underlying soils from freezing during the winter months, applicable throughout the life of the building. No floor insulation is recommended.

However, for perimeter foundations, placement of footings to below frost depths and/or placement of proper insulation along the exterior of footings, and extending insulation foam upwards along the perimeter of the new building and outwards horizontally from the building is recommended. In addition, overlap between the exposed exterior wall of the foundation and interior insulation is recommended.

The above recommendations have many variations during design, but the main concept is to provide an adequate wrapping of insulation around the concrete foundations, both interior and exterior to prevent freeze-thaw cycles and frost heave from pushing into the foundation concrete, and to focus building heat downward into the foundation subgrade.

3.9.2 Pavement Areas

Frost penetration and ice lens formation beneath pavement in this region is difficult to control without sometimes taking uneconomical precautions, such as insulation placement and/or thick subgrade sections. Heave and settlement is most noticeable in areas where trenching has been completed. For details regarding pavement sections and depths of subgrade, see Section 3.13: Pavement Profiles. For details regarding utility trench placement, see Section 3.7: Utility Trenches.

To help limit differential frost heave, we recommend installing a layer of insulation within the pavement section in an attempt to reduce the depth of frost penetration. An expanded width trench may also be introduced, beginning with standard width surrounding the pipe and at the base of the trench, and then becoming increasingly wider as the trench moves upward to the surface. This can help to alleviate soil inconsistencies surrounding trench construction, as the underlying trench bedding can better blend into the surrounding pavement subgrade rock material and compaction level. It may also be considered by the Department of Veterans Affairs to perform a series of periodic inspections surrounding the pavement construction, paying special attention to trenchlines, and then performing maintenance as needed to help maintain pavement integrity throughout the lifespan of the paved surfaces.

Anchorage, Alaska 99515

3.10 Foundations

In our opinion, the proposed building and associated structures can be supported on shallow, spread footings bearing on an 8-inch thick layer of engineered structural fill, placed and compacted as described in this report, underlain by approved, undisturbed, native soils. Foundation design, construction, and setback requirements should conform to the International Building Code (IBC) and other governing codes as applicable, with additional consideration regarding frost susceptibility in this region.

We recommend an allowable soil bearing pressure of 4,000 pounds per square foot (psf) be used for footing design. The recommended allowable bearing pressure applies to the total of dead plus long-term live loads. The allowable bearing pressure may be increased by a factor of 1.33 for short-term loads such as those resulting from wind or seismic forces. Additional seismic design parameters should be considered for this project, as this area lies within an active seismic zone.

Total static settlement of footings founded as recommended is expected to be less than 1 inch.

Differential settlement is estimated to be less than ¾ inches over a horizontal span of 20 feet. Most of the settlement will occur during construction as the loads are applied. These estimates are based on maximum wall loads of 3,000 pounds per lineal foot and a maximum column load of 50 kips. For heavier loads, CGS should be consulted.

We understand from meetings and conversations with the VA and with GDM and HRE that there is a likely possibility of expanding the building to two stories. Additional consideration should be brought to the forefront of design regarding the possible vertical expansion of the building. We recommend that the loadings of a two-(or even) three-story building be used when designing footing types and sizes to account for the increased loads in future years or expansion.

Excavations adjacent to footings should not extend beneath a 1H:1V plane projected downwards from the bottom edge of the footing.

Footing excavations should be trimmed neat and carefully prepared. Loose, wet or otherwise softened subgrade should be removed from footing areas prior to placing forms and reinforcing steel. In wet weather conditions, we recommend an additional eight-inch layer of granular material (typically 5/8”-0 or 3/4” – 0 crushed aggregate) be placed at the base of footing excavations. The granular material reduces water softening of subgrade soils, reduces subgrade disturbance during placement of forms and reinforcement, and provides a cleaner environment for reinforcing steel. To be effective, the granular material should be placed on firm, well-drained subgrade and compacted until well-keyed using a small vibratory plate compactor.

Throughout the construction process, we recommended that CGS observe the foundation excavation subgrade and perform compaction testing prior to placing structural fill, formwork, or reinforcing steel to verify subgrade support conditions are within recommended specifications.

Anchorage, Alaska 99515

3.10.1 Lateral Resistance

Lateral loads on the proposed structures imposed by wind or seismic forces can be resisted by a combination of sliding resistance on the base of footings and passive earth pressure on the sides of footings. We recommend an ultimate coefficient of friction of 0.35 for footings bearing on undisturbed, native sandy silt, and 0.5 for footings bearing on structural granular fill.

Passive earth pressures on the sides of buried footings may be calculated using an allowable equivalent fluid pressure of 300 pcf per foot of embedment. For this value, backfill against the footing should be compacted to at least 95% of the maximum dry density of obtained from ASTM D1557. The upper foot of embedment should be neglected unless protected by pavement or concrete slabs on grade.

3.11 Slab on Grade Floors

Satisfactory subgrade support for lightly-loaded building floor slabs can be obtained on undisturbed native soil or on newly placed structural fill. The modulus of subgrade reaction for design of floor slabs may be taken as 100 pounds per cubic inch.

In addition to fill removal depths, a minimum 8-inch-thick layer of imported granular material should be placed and compacted over the prepared subgrade to assist as a capillary break and blanket drain.

Imported granular material should consist of clean crushed rock or sand that is fairly well-graded between coarse and fine, contains no deleterious materials, has a maximum particle size of 1¼ inches, and less than 5 percent by weight passing the U.S. Standard No. 200 Sieve. The imported granular material may be placed in one lift and should be compacted until well-keyed, about 85 percent of the maximum dry density as determined by ASTM D 1557.

A vapor retarder manufactured for use beneath floor slabs should be installed above the base rock and according to the manufacturer’s recommendations. Careful attention should be made during construction to prevent perforating the retarder, and to seal edges and utility penetrations. We recommend following ACI 302.1, Chapter 3 with regard to installing a vapor retarder.

3.12 Retaining Walls

The preliminary plans do not contain any retaining walls for the project. Because the project is in the preliminary design phase, it is unclear whether structural retaining walls will be included. Lateral pressures presented in this report are to be considered as general guidelines, should retaining walls be included. CGS should be consulted for feature-specific recommendations.

Lateral pressures are determined from measured or assumed soil parameters of the soils found onsite.

The design engineer of retaining walls must take into consideration the state at which the soil retention walls will be placed, whether under active, passive, or at-rest pressures. The possibility of additional non-seismic surcharge loading should also be considered.

Our recommended lateral earth pressures for design of retaining walls are presented below. The design

Anchorage, Alaska 99515 parameters shown below are to be used for well-drained backfill conditions with no hydrostatic pressures. Walls that may deflect by at least 0.01 times their height are to be designed with active earth pressures. Walls that may not deflect are to be designed with at-rest pressures.

With assumed granular backfill, a wet density of retained soils at 135 pounds per cubic foot, a friction angle of 35 degrees and a level slope condition above the wall, the at-rest, active, and passive equivalent fluid pressures may be taken as 50, 35, and 300 pounds per cubic foot, respectively. The seismic surcharge may be taken as 10 pounds per cubic foot.

A layer of compacted aggregate that is a minimum of one-foot-thick should be placed behind all retaining walls to be constructed on the site to allow for proper drainage, and placed utilizing the compaction recommendations as described in this report. All structural retaining walls should be backfilled with an imported, free-draining granular material such as ¾”-0 crushed rock with no more than 5% passing the No. 200 sieve.

Near the base of the layer of aggregate, a 3- or 4-inch-diameter, perforated gravity drain pipe wrapped in clean, angular drainrock, and contained within geotextile fabric should be installed to divert water from retaining structures. Consideration should be given to additional drainage placed at both the “inside corner” of the cantilevered portion of the wall and at the innermost base of the retaining wall to assure the best possible drainage scenarios.

3.13 Pavement Profiles

The recommendations for the design of the traffic sections of this report are to be governed by frozen ground conditions rather than on assumed values of resistance to anticipated pressures and traffic loadings.

The main problematic soil behavior involved with pavements is frost heave, especially in locations near utility trenches (See Section 3.7: Utility Trenches). Design in this region still typically results in difficulty preventing frost heave even when taking proper construction measures to help alleviate the condition.

Frost heave and cracking should be considered inevitable and should be expected due to the harsh climate conditions. Cracks should be filled each spring to maintain the integrity of the pavement sections and subgrade.

We were not given specific information on the frequency and type of vehicles that will use the facility.

For design purposes, we have assumed post-construction traffic conditions will average no more than five heavy trucks per day. Our pavement recommendations are based on a typical subgrade density for sandy silt with gravel using a California Bearing Ratio value of 10.

We recommend the minimum pavement section profiles presented in Table 3-1, below, to support the anticipated traffic loads and to help alleviate some frost heave conditions by deepening the distance from the surface to the underlying, more frost-susceptible soils and to allow drainage of water away from the surface. The AC pavement thickness should be increased as shown in the areas where garbage trucks or heavy vehicles (such as armored trucks) typically travel. Thicker sections might also be considered in

Anchorage, Alaska 99515 vehicle drop-off areas, delivery drop-off areas,…