Attachment 04 CRRD Work Center Geotechnical Report.pdf

Report of Subsurface Exploration and Geotechnical Engineering Evaluation

Chattooga River Work Center U.S. Forest Service 9975 Highway 441 S Lakemont, Georgia Geo-Hydro Project Number 222708.20

Prepared for Croft & Associates, Inc.

November 22, 2022

400 Chastain Center Boulevard, Suite 430 • Kennesaw, Georgia 30144 o: 770.426.7100 • f: 770.426.5209 • www.geohydro.com

Mr. Anthony Iorillo, R.A. November 22, 2022

Croft & Associates, Inc.

3380 Blue Springs Road

Kennesaw, Georgia 30144

Report of Subsurface Exploration and Geotechnical Engineering Evaluation

Chattooga River Work Center

U.S. Forest Service

9975 Highway 441 S

Lakemont, Georgia

Geo-Hydro Project Number 222708.20

Dear Mr. Iorillo:

Geo-Hydro Engineers, Inc. has completed the authorized subsurface exploration for the above referenced project. The scope of services for this project was outlined in our proposal number 222708.P0 dated

October 28, 2022.

PROJECT INFORMATION

The project site is located at 9975 Highway 441 South in Lakemont, Georgia. Figure 1 in the Appendix shows the approximate site location.

The project will include a new single-story work center building encompassing 3,900 square-feet, heavy- duty pavement, and new utility infrastructure north of the existing facility parking lot. The construction documents provided to us indicate that the building will have a structural wood frame with a concrete slab-on-grade floor with foundation turndowns. Based on our experience with similar projects, we have assumed that column loads will not exceed 25 kips with wall loads no greater than 2 kips per lineal foot.

The project site currently includes grassed areas and a gravel parking lot and storage yard. The ground surface within the building footprint and associated parking and gravel yard slopes down from east to west with a total change in elevation of about 9 feet within the project area. Based on a relative finished floor elevation of 140.40 feet, we expect site grading to involve no more than

3 feet of mass excavation and structural fill placement. The annotated aerial photograph to the right shows the approximate site limits and current site conditions.

Planned Construction

Area

N

Chattooga River Work Center 9975 Highway 441S • Lakemont, Georgia Project Number 222708.20

November 22, 2022 | 2

EXPLORATORY PROCEDURES

The subsurface exploration consisted of four machine-drilled soil test borings performed at the approximate locations shown on Figure 2 included in the Appendix. The test borings were located in the field by Geo-

Hydro using a hand-held GPS unit (Garmin GPS Map 64S) with preloaded boring coordinates and by measuring angles and distances from existing site features. The ground surface elevations shown on the test boring records were interpolated from the topographic information provided to us (Grading Plan –

Drawing Number C-300 by Croy Engineering dated May 5, 2017) and the information is not certified as correct by this engineer. Users of the data do so at their own risk. In general, the boring locations and elevations should be considered approximate.

Standard penetration testing, as provided for in ASTM D1586, was performed at select depth intervals in the soil test borings. Soil samples obtained from the drilling operation were examined and classified in general accordance with ASTM D2488 (Visual-Manual Procedure for Description of Soils). Soil classifications include the use of the Unified Soil Classification System described in ASTM D2487

(Classification of Soils for Engineering Purposes). The soil classifications also include our evaluation of the geologic origin of the soils. Evaluations of geologic origin are based on our experience and interpretation and may be subject to some degree of error.

Descriptions of the soils encountered, groundwater conditions, standard penetration resistances, and other pertinent information are provided in the test boring records included in the Appendix.

REGIONAL GEOLOGY

The project site is located in the Blue Ridge Geologic Province of Georgia. Soils in this area have been formed by the in-place weathering of the underlying crystalline rock, which accounts for their classification as "residual" soils. Residual soils near the ground surface, which have experienced advanced weathering, frequently consist of red brown clayey silt (ML) or silty clay (CL). The thickness of this surficial clayey zone may range up to roughly 6 feet. For various reasons, such as erosion or local variation of mineralization, the upper clayey zone is not always present.

With increased depth, the soil becomes less weathered, coarser grained, and the structural character of the underlying parent rock becomes more evident. These residual soils are typically classified as sandy micaceous silt (ML) or silty micaceous sand (SM). With a further increase in depth, the soils eventually become quite hard and take on an increasing resemblance to the underlying parent rock. When these materials have a standard penetration resistance of 100 blows per foot or greater, they are referred to as partially weathered rock. The transition from soil to partially weathered rock is usually a gradual one, and may occur at a wide range of depths. Lenses or layers of partially weathered rock are not unusual in the soil profile.

Partially weathered rock represents the zone of transition between the soil and the indurated metamorphic rocks from which the soils are derived. The subsurface profile is, in fact, a history of the weathering process which the crystalline rock has undergone. The degree of weathering is most advanced at the ground surface, November 22, 2022 | 3 where fine grained soil may be present. And the weathering process is in its early stages immediately above the surface of relatively sound rock, where partially weathered rock may be found.

The thickness of the zone of partially weathered rock and the depth to the rock surface have both been found to vary considerably over relatively short distances. The depth to the rock surface may frequently range from the ground surface to 80 feet or more. The thickness of partially weathered rock, which overlies the rock surface, may vary from only a few inches to as much as 40 feet or more.

SOIL TEST BORING SUMMARY

Starting at the ground surface, borings B-1, B-2, and B-4 encountered approximately 4 inches of gravel.

Detailed measurements necessary for quantity estimation were not performed for this project, and the thickness of materials should be expected to vary. For planning purposes, we suggest assuming a thickness of 6 inches for surface materials.

Beneath the surface materials or starting at the ground surface, all borings encountered residual soils typical of the Blue Ridge Region. The residuum was classified as silty sand. Standard penetration resistances recorded in the residual soils ranged from 10 to 49 blows per foot.

Partially weathered rock was encountered in borings B-1, B-2, and B-3 at depths ranging from about 3 to

17 feet. Partially weathered rock is locally defined as residual material having standard penetration resistance values greater than 100 blows per foot.

At the time of drilling, groundwater was not encountered in the borings. The borings were backfilled with soil cuttings upon completion. It should be noted that groundwater levels will fluctuate several feet depending on yearly and seasonal rainfall variations and other factors and may rise in the future.

For more detailed descriptions of subsurface conditions, please refer to the test boring records included in the Appendix.

Summary of Subsurface Conditions

Boring Ground Surface

Elevation

Bottom of Fill Groundwater* Top of PWR Auger Refusal Boring

Termination

Depth (feet)

Elev.

Depth (feet)

Elev.

Depth (feet)

Elev.

Depth (feet)

Elev.

Depth (feet)

Elev.

B-1 139 NE --- NE --- 12 127 NE --- 20 119

B-2 140 NE --- NE --- 17 123 NE --- 20 120

B-3 141 NE --- NE --- 3 138 NE --- 10 131

B-4 138 NE --- NE --- NE --- NE --- 10 128

All Depths and Elevations in this Summary Table are Approximate NE: Not Encountered PWR: Partially Weathered Rock Elev.: Elevation Groundwater level measured at time of drilling

November 22, 2022 | 4

EVALUATIONS AND RECOMMENDATIONS

The following evaluations and recommendations are based on the information available on the proposed construction, the data obtained from the test borings, and our experience with soils and subsurface conditions similar to those encountered at this site. Because the test borings represent a small statistical sampling of subsurface conditions, it is possible that conditions may be encountered during supplemental explorations or construction that are substantially different from those indicated by the test borings. In these instances, adjustments to the design and construction may be necessary.

Geotechnical Considerations

The following geotechnical characteristics of the site should be considered for planning and design:

• Fill materials were not encountered in the borings. However, we expect that any fill encountered on site during construction will be of variable consistency, and it is likely that some management of poor-quality or loose fill will be necessary during construction. Where encountered, such loose or unstable soils should be excavated and replaced with structural fill placed in accordance with the

Structural Fill section of this report.

• Partially weathered rock was encountered in three of the four borings at depths ranging from about 3 to 17 feet. Excavation of partially weathered rock typically requires large equipment capable of ripping.

Due to the leverage required to pre-loosen partially weathered rock, it is often impractical to rip partially weathered rock in trench excavations, on sloping terrain, or in wet conditions.

The soil test borings indicate generally favorable conditions within the anticipated excavation limits.

Residual soils should be readily removable using conventional soil excavation equipment such as loaders and backhoes.

• It is important to note that the depth to rock or partially weathered rock may vary drastically over relatively short distances, and it would not be unusual for rock or partially weathered rock to occur between or around some of the soil test borings.

• At the time of drilling, groundwater was not encountered in the test borings. Based on our understanding of the project and the results of the test borings, we do not expect groundwater to be a major hindrance to design or construction. Regardless of groundwater conditions, the contractor should be prepared to manage surface runoff during rain events, and subsurface drainage will be required behind all below-grade structures including foundation walls.

• Based on the results of the test borings and following the calculation procedure in the 2018 International

Building Code (Chapter 20, ASCE 7-16), the seismic Site Class for the site is C. The mapped and design spectral response accelerations are as follows: SS=0.272, S1=0.105, SDS=0.218, SD1=0.118.

• At the time of this report, we have not been provided structural loading information for the project.

Assuming that column loads will not exceed 50 kips and wall loads will be no greater than 5 kips per

November 22, 2022 | 5 lineal foot, and contingent upon proper site preparation and thorough evaluation of the foundation excavations, it is our opinion that the proposed building can be supported using conventional shallow foundations and concrete slab-on-grade floors.

• The project plans provided to us indicate that an allowable soil bearing pressure of 2,000 psf was used for design. The subsurface exploration indicates that the design allowable bearing pressure should be available. If from an economic standpoint redesign is advantageous, an allowable bearing pressure of

3,000 psf would be suitable for foundation design. However, the foundation loads for the single-story building are relatively light, and redesign of the current foundation system may yield little or no construction cost savings. The monolithic foundation turndowns should bear at least 18 inches below the prevailing ground surface to avoid potential problems due to frost heave.

The following sections provide recommendations regarding these issues and other geotechnical aspects of the project.

Existing Fill Materials

Fill materials were not encountered in the test borings. However, we expect that any fill encountered on site during construction will be of variable consistency, and it is likely that some management of poor-quality or loose fill will be necessary during construction. There are several important facts that should be considered regarding existing fill materials and the limitations of subsurface exploration.

• The quality of existing fill materials can be highly variable, and test borings are often not able to detect all of the zones or layers of poor-quality fill materials.

• It is likely that fill materials will be encountered during construction in areas not directly explored.

Variations within the fill should be expected, and poor-quality or loose fill material may be encountered during construction.

• Layers of poor-quality fill materials that are less than about 2.5 to 5 feet thick may often remain undetected by soil test borings due to the discrete-interval sampling method used in this exploration.

• The interface between existing fill materials and the original ground surface may include a layer of organic material that was not properly stripped off during the original grading. Depending on its relationship to the foundation and floor slab bearing surfaces, an organic layer might adversely affect support of footings and floor slabs. If such organic layers are encountered during construction, it may be necessary to “chase out” the organic layer by excavating the layer along with overlying soils.

• The construction budget should include funds for management of poor-quality existing fill materials at this site.

• Subsurface exploration is simply not capable of disclosing all conditions that may require remediation.

November 22, 2022 | 6

General Site Preparation

Topsoil, roots, trees, gravel, and other deleterious materials should be removed from the proposed construction area. All existing utilities should be excavated and removed unless they are to be incorporated into the new construction. Additionally, site clearing, grubbing, and stripping should be performed only during dry weather conditions. Operation of heavy equipment on the site during wet conditions could result in excessive rutting and mixing of topsoil and debris with underlying soils. All excavations resulting from demolition of underground structures or rerouting of underground utilities should be backfilled in accordance with the Structural Fill section of this report.

We recommend, wherever possible, that areas to receive structural fill be proofrolled prior to placement of structural fill. Areas of proposed excavation should be proofrolled after rough finished subgrade is achieved. Proofrolling should be performed with multiple passes in at least two directions using a fully loaded tandem axle dump truck weighing at least 18 tons. If low consistency soils are encountered that cannot be adequately densified in place, such soils should be removed and replaced with well compacted fill material placed in accordance with the Structural Fill section of this report. Proofrolling should be observed by Geo-Hydro to determine if remedial measures are necessary.

For planning purposes, we suggest considering that approximately 20 percent of the aggregate planned building and pavement footprints will require undercutting and replacement extending to an average depth of 1½ feet. The suggested site preparation approach is intended only as a tool to estimate a cost associated with managing unstable subgrade conditions. Ground stabilization may be accomplished by in-place densifications, treatment with geosynthetics (grid or fabric) and crushed stone, or a combination of methods. The need for, extent of, location, and optimal method of stabilization should be determined by

Geo-Hydro at the time of construction based on actual site conditions.

Water wells, if encountered during construction, must be abandoned in accordance with the requirements of the Georgia Water Well Standards Act of 1985. The owner of the property is responsible for plugging the well in accordance with the requirements outlined in Circular 13, “ Grouting and Plugging of Domestic

Water Wells in Georgia” published by the Georgia Department of Natural Resources, Environmental

Protection Division and the Georgia Geologic Survey. A water well contractor licensed to practice in

Georgia must perform the actual work of plugging the well. Additionally, any existing septic systems and drain fields must be removed, and the resulting excavation should be backfilled in accordance with the recommendations in the Structural Fill section of this report.

During site preparation, burn pits or trash pits may be encountered. All too frequently such buried material occurs in isolated areas which are not detected by the soil test borings. Any buried debris or trash found during the construction operation should be thoroughly excavated and removed from the site.

November 22, 2022 | 7

Groundwater

At the time of drilling, groundwater was not encountered in the test borings. It is important to note that groundwater levels will fluctuate depending on yearly and seasonal rainfall variations and other factors and may rise in the future. Based on our understanding of the project, we do not expect groundwater to be a major hindrance to design or construction.

Regardless of groundwater conditions, the contractor should be prepared to manage runoff during wet weather conditions and subsurface drainage will be necessary behind all below-grade structures including foundation walls.

Excavation Characteristics

The soil test borings indicate generally favorable excavation conditions within the anticipated excavation limits. For construction bidding and field verification purposes it is common to provide a verifiable definition of rock in the project specifications. The following are typical definitions of mass rock and trench rock:

• Mass Rock: Material which cannot be excavated with a single-tooth ripper drawn by a crawler tractor having a minimum draw bar pull rated at 56,000 pounds (Caterpillar D-8K or equivalent) and occupying an original volume of at least one cubic yard.

• Trench Rock: Material occupying an original volume of at least one-half cubic yard which cannot be excavated with a hydraulic excavator having a minimum flywheel power rating of 123 kW (165 hp);

such as a Caterpillar 322CL, John Deere 230C LC, or a Komatsu PC220LC-7; equipped with a short tip radius bucket not wider than 42 inches.

The foregoing definitions are based on large equipment typically utilized for mass grading. Excavations for building foundations, retaining walls, and underground utilities are often performed with smaller equipment such as rubber-tired backhoe/loaders or even mini-excavators. Contractors will often request additional payment for mobilizing larger equipment than that which was anticipated during preparation of their construction bid. The amount of additional compensation, if any, and the minimum equipment size necessary to qualify for any additional compensation should be defined before the start of construction.

Reuse of Excavated Materials

Based on the results of the test borings, the residual soils at the project site are suitable for reuse as structural fill. Routine adjustment of moisture content will be necessary to allow proper placement and compaction.

It is important to establish as part of the construction contract whether soils having elevated moisture content and/or high plasticity will be considered suitable for reuse. We often find these issues to be a point of contention and a source of delays and change orders. From a technical standpoint, soils with moisture contents wet of optimum as determined by the standard Proctor test (ASTM D698) can be reused provided that the moisture is properly adjusted to within the workable range. Likewise, soils with liquid limits above

November 22, 2022 | 8

50 can also be reused provided they are blended with lower plasticity soils as needed to reduce their liquid limit. From a practical standpoint, wet soils can be very difficult to dry during periods of extended wet weather and low temperatures. Blending soils to reduce their plasticity also requires extra handling and effort. Such difficulties should be considered during planning and budgeting. A clear understanding by the general contractor and grading subcontractor regarding the reuse of excavated soils will be important to avoid delays and unexpected cost overruns.

Structural Fill

Materials selected for use as structural fill should be free of organic debris, demolition debris, and other deleterious materials. The material should not contain rocks having a diameter over 4 inches. It is our opinion that the following soils represented by their USCS group symbols will typically be suitable for use as structural fill and are usually found in abundance in the Piedmont: (SM), (ML), and (CL). The following soil types are typically suitable but are not abundant in the Piedmont: (SW), (SP), (SC), (SP-SM), and

(SP-SC). The following soil types are considered unsuitable: (MH), (CH), (OL), (OH), and (Pt).

Laboratory Proctor compaction tests and classification tests should be performed on representative samples obtained from the proposed borrow material to provide data necessary to determine acceptability and for quality control. The moisture content of suitable borrow soils should generally be no more than 3 percentage points below or above optimum at the time of compaction. Tighter moisture limits may be necessary with certain soils.

Suitable fill material should be placed in thin lifts. Lift thickness depends on the type of compaction equipment, but a maximum loose-lift thickness of 8 inches is generally recommended. The soil should be compacted by a self-propelled sheepsfoot roller. Within small excavations such as in utility trenches, around manholes, above foundations, or behind retaining walls, we recommend the use of “wacker packers” or “Rammax” compactors to achieve the specified compaction. Loose lift thicknesses of 4 to 6 inches are recommended in small area fills.

We recommend that structural fill be compacted to at least 95 percent of the standard Proctor maximum dry density (ASTM D698). The upper 12 inches of floor slab subgrade soils should be compacted to at least 98 percent of the standard Proctor maximum dry density. The upper 12 inches of pavement subgrades should be compacted in accordance with Georgia DOT requirements to at least 100 percent of the standard

Proctor maximum dry density (ASTM D698). Additionally, the maximum dry density of structural fill should be no less than 90 pcf. Geo-Hydro should perform density tests during fill placement.

Earth Slopes

Temporary construction slopes should be designed in strict compliance with OSHA regulations. The exploratory borings indicate that most soils at the site are Type B as defined in 29 CFR 1926 Subpart P.

This dictates that temporary construction slopes in residual soils for excavation depths of 20 feet or less above the groundwater level should be no steeper that 1H:1V. Temporary construction slopes should be closely observed on a daily basis by the contractor’s “competent person” for signs of mass movement:

November 22, 2022 | 9 tension cracks near the crest, bulging at the toe of the slope, etc. The responsibility for excavation safety and stability of construction slopes should lie solely with the contractor.

We recommend that extreme caution be observed in trench excavations. Several cases of loss of life due to trench collapses in Georgia point out the lack of attention given to excavation safety on some projects.

We recommend that applicable local and federal regulations regarding temporary slopes and shoring and bracing of trench excavations be closely followed.

Formal analysis of slope stability was beyond the scope of work for this project. Based on our experience, permanent cut or fill slopes should be no steeper than 2H:1V to maintain long term stability and to provide ease of maintenance. The crest or toe of cut or fill slopes should be no closer than 10 feet to any foundation or to the edge of any pavement that will support truck traffic. The crest or toe should be no closer than 5 feet to the edge of any pavements supporting cars or light truck traffic or parking. Erosion protection of slopes during construction and during establishment of vegetation should be considered an essential part of construction.

Earth Pressure (Cast-In-Place Structures)

Three earth pressure conditions are generally considered for retaining wall design: "at rest", "active", and

"passive" stress conditions. Retaining walls which are rigidly restrained at the top and will be essentially unable to rotate under the action of earth pressure (such as basement or foundation walls) should be designed for "at rest" conditions. Retaining walls which can move outward at the top as much as 0.5 percent of the wall height (such as free-standing walls) should be designed for "active" conditions. For the evaluation of the resistance of soil to lateral loads the "passive" earth pressure must be calculated. It should be noted that full development of passive pressure requires deflections toward the soil mass on the order of

1.0 percent to 4.0 percent of total wall height.

Earth pressure may be evaluated using the following equation:

ph = K (DwZ + qs) + Ww(Z-d) where: ph = horizontal earth pressure at any depth below the ground surface (Z).

Ww = unit weight of water

Z = depth to any point below the ground surface d = depth to groundwater surface

Dw = wet unit weight of the soil backfill (depending on borrow sources). The wet unit weight of most residual soils may be expected to range from approximately 115 to 125 pcf.

Below the groundwater level, Dw must be the buoyant weight.

qs = uniform surcharge load (add equivalent uniform surcharge to account for construction equipment loads)

K = earth pressure coefficient as follows:

November 22, 2022 | 10

Earth Pressure Condition Coefficient

At Rest (Ko) 0.5

Active (Ka) 0.33

Passive (Kp) 3.0

The groundwater term, Ww(Z-d), should be used if no drainage system is incorporated behind retaining walls. If a drainage system is included which will not allow the development of any water pressure behind the wall, then the groundwater term may be omitted. The development of excessive water pressure is a common cause of retaining wall failures. Drainage systems should be carefully designed to ensure that long term permanent drainage is accomplished.

The above design recommendations are based on the following assumptions:

• Horizontal backfill

• 95 percent standard Proctor compactive effort on backfill (ASTM D698)

• No safety factor is included

For convenience, equivalent fluid densities are frequently used for the calculation of lateral earth pressures.

For "at rest" stress conditions, an equivalent fluid density of 63 pcf may be used. For the "active" state of stress an equivalent fluid density of 42 pcf may be used. These equivalent fluid densities are based on the assumptions that drainage behind the retaining wall will allow no development of hydrostatic pressure; that native sandy silts or silty sands will be used as backfill; that the backfill soils will be compacted to

95 percent of standard Proctor maximum dry density; that backfill will be horizontal; and that no surcharge loads will be applied.

For analysis of sliding resistance of the base of a retaining wall, the coefficient of friction may be taken as

0.4 for the soils at the project site. This is an ultimate value, and an adequate factor of safety should be used in design. The force which resists base sliding is calculated by multiplying the normal force on the base by the coefficient of friction. Full development of the frictional force could require deflection of the base of roughly 0.1 to 0.3 inches.

Foundation Design

After general site preparation and site grading have been completed in accordance with the recommendations of this report, it is our opinion that the proposed building can be supported using the planned monolithic slab-on-grade with foundation turndowns. The project plans provided to us indicate that an allowable soil bearing pressure of 2,000 psf was used for design. The subsurface exploration indicates that the design allowable bearing pressure should be available. If from an economic standpoint redesign is advantageous, an allowable bearing pressure of 3,000 psf would be suitable for foundation design. However, the foundation loads for the single-story building are relatively light, and redesign of the current foundation system may yield little or no construction cost savings. The monolithic foundation turndowns should bear at least 18 inches below the prevailing ground surface to avoid potential problems due to frost heave.

November 22, 2022 | 11

The allowable bearing pressure used for design or an updated allowable bearing pressure of 3,000 psf should yield an estimated maximum total foundation settlement no greater than approximately 1 inch, with differential settlement between adjacent columns not exceeding about ½ inch. If the architect or structural engineer determine that the estimated total or differential settlement cannot be accommodated by the proposed structure, please contact us.

Foundation bearing surface evaluations should be performed in all footing excavations prior to placement of reinforcing steel. Geo-Hydro should perform these evaluations to confirm that the design allowable soil bearing pressure is available. Foundation bearing surface evaluations should be performed using a combination of visual observation, hand augering, and portable dynamic cone penetrometer testing

(ASTM STP-399).

Because of natural variation, it is possible that some of the soils at the project site may have an allowable bearing pressure less than the design value. Likewise, existing fill materials can be highly variable, and may have an allowable bearing pressure less than the recommended design value. Therefore, foundation bearing surface evaluations will be critical to aid in the identification and remediation of these situations.

Remedial measures should be based on actual field conditions. However, in most cases we expect the use of the stone replacement technique to be the primary remedial measure. Stone replacement involves the removal of soft or loose soils, and replacement with well-compacted graded aggregate base (GAB) meeting

Georgia Department of Transportation specifications for gradation. Stone replacement is generally performed to depths ranging from a few inches to as much as 2 times the footing width, depending on the actual conditions. For budgetary purposes, we suggest considering that as much as 15 percent of the foundation excavations will require overexcavation and stone replacement extending to a depth of 2½ feet below bearing elevation. The actual quantity of stone replacement will be different and may exceed the provided estimate.

Seismic Design

Based on the results of the test borings and following the calculation procedure in the 2018 International

Building Code (Chapter 20, ASCE 7-16), the seismic Site Class for the site is C. The mapped and design spectral response accelerations are as follows: SS=0.272, S1=0.105, SDS=0.218, SD1=0.118.

Based on the information obtained from the soil test borings, it is our opinion that the potential for liquefaction of the residual soils at the site due to earthquake activity is relatively low.

Floor Slab Subgrade Preparation

Slab-on-grade support is often disturbed during foundation excavation, plumbing installation, and superstructure construction. We recommend that the floor slab subgrade be evaluated by Geo-Hydro immediately prior to beginning floor slab construction. If low consistency soils are encountered that cannot be adequately densified in place, such soils should be removed and replaced with well-compacted fill material placed in accordance with the Structural Fill section of this report or with well-compacted graded aggregate base (GAB).

November 22, 2022 | 12

Assuming that the top 12 inches of floor slab subgrade soils are compacted to at least 98 percent of the standard Proctor maximum dry density, we recommend that a modulus of subgrade reaction of 120 pci be used for design of floors supporting light loads (no more than 150 psf) and transient loads. If the monolithic floor slab with turndown foundations will support relatively heavy floor loads or permanent or semi-permanent floor loads such as storage racks, we recommend using modulus of subgrade reaction of 70 pci for design purposes.

Moisture Control for Concrete Slabs

To prevent water vapor transmission from adversely affecting the concrete slab-on-grade floor in the apartment buildings, we recommend that slab-on-grade floors be underlain by a minimum 4 inches of #57 stone. The stone must be covered by a vapor retarder. We suggest polyethylene sheeting at least 10 mils thick as a minimum vapor retarder.

For floor areas that will be subjected to relatively heavy wheel loads from heavy equipment, forklifts, or other vehicles, we recommend that slab-on-grade floors be underlain by a minimum 5-inch thickness of

GDOT compliant graded aggregate base (GAB) compacted to at least 100 percent of the modified Proctor maximum dry density (ASTM D1557). The GAB must be covered by a vapor retarder. We suggest polyethylene sheeting at least 10 mils thick as a minimum vapor retarder.

Pavement Design

The construction documents provided to us (Sheet C-400 – Construction Details) show three pavement sections as presented below. Based on our understanding of the project, we concur with the gravel and concrete pavement sections as presented. However, we suggest considering the use of GDOT compliant graded aggregate base (GAB) as the Gravel Section surface instead of #57 stone. GAB should be compacted to at least 100 percent of the modified Proctor maximum dry density (ASTM D1557). Using

GAB will allow for better grade control and a more stable surface for support of truck and equipment traffic.

Similar to other unpaved surfaces, routine maintenance will be required to fill in ruts and repair any damaged areas.

November 22, 2022 | 13

Pavement Materials Testing

To aid in verifying that the pavement system is installed in general accordance with the design considerations, the following materials testing services are recommended:

• Density testing of subgrade materials.

• Proofrolling of pavement subgrade materials immediately prior to placement of graded aggregate base

(GAB). This proofrolling should be performed the same day GAB is installed.

• Density testing of GAB and verification of GAB thickness. In-place density should be verified using the sand cone (ASTM D1556) or Nuclear Density Gauge method (ASTM D6938).

• Coring of the pavement to verify thickness and density (asphalt pavement only).

• Preparation and testing of beams and cylinders for flexural and compressive strength testing (Portland cement concrete only). The total number of test specimens required will depend on the number of concrete placement events necessary to construct the pavement.

We appreciate the opportunity to work with you on this project and are prepared to provide any additional services you may require. If you have any questions concerning this report or any of our services, please call us.

Sincerely, GEO-HYDRO ENGINEERS, INC.

Jacob O. Congrove, E.I.T. Luis E. Babler, P.E.

Staff Engineer Chief Engineer jcongrove@geohydro.com luis@geohydro.com

APPENDIX

Figure 1: Site Location Plan

Approximate Scale, Miles

0 0.25 0.5 1 1.5

Chattooga River Work Center 9975 Highway 441S Lakemont, Georgia

Site

B-3

B-2

B-1

B-4

Approximate Scale: 1"=30'

Figure 2: Boring Location Plan

15 30 60 90

LEGEND: Soil Test Boring

Chattooga River Work Center 9975 Highway 441S Lakemont, Georgia

Symbols and Nomenclature

Symbols ▐ Thin-walled tube (TWT) sample recovered

Thin-walled tube (TWT) sample not recovered

● Standard penetration resistance (ASTM D1586)

50/2” Number of blows (50) to drive the split-spoon a number of inches (2)

65% Percentage of rock core recovered

RQD Rock quality designation - % of recovered core sample which is 4 or more inches long

GW Groundwater

Water level at least 24 hours after drilling

Water level one hour or less after drilling

ALLUV Alluvium

TOP Topsoil

PM Pavement Materials

CONC Concrete

FILL Fill Material

RES Residual Soil

PWR Partially Weathered Rock

SPT Standard Penetration Testing

Penetration Resistance Results Approximate Number of Blows, N Relative Density Sands 0-4 very loose

5-10 loose 11-20 firm 21-30 very firm 31-50 dense Over 50 very dense

Approximate Number of Blows, N Consistency Silts and 0-1 very soft Clays 2-4 soft 5-8 firm 9-15 stiff 16-30 very stiff 31-50 hard Over 50 very hard

Drilling Procedures Soil sampling and standard penetration testing performed in accordance with ASTM D 1586. The standard penetration resistance is the number of blows of a 140-pound hammer falling 30 inches to drive a 2-inch O.D., 1.4-inch I.D. split-spoon sampler one foot. Rock coring is performed in accordance with ASTM D 2113. Thin-walled tube sampling is performed in accordance with ASTM D 1587.

Gravel (Approximately 4 inches) Loose red-brown silty fine to medium sand (SM) with rock fragments (RESIDUUM)

Very firm to dense black and brown to light brown micaceous silty fine sand (SM)

Partially weathered rock sampled as light brown silty fine to medium sand (SM)

Boring Terminated at 20 feet

50/5"

50/2"

E le v.

(F t)

0 30 40 100

S ym bo l

Test Boring Record D ep th

(F t)

G W

T

GWT at Drilling: Not Encountered

50 70

Date: 11/3/22

GWT at 24 hrs: N/A: Boring Backfilled Logged By: BGS

Method: HSA- ASTM D1586

Project No: 222708.20Project: Chattooga River Work Center - U.S. Forest Service

Location: 9975 Highway 441S - Lakemont, Georgia

Remarks:

Standard Penetration Test (Blows/Foot)

B-1

G.S. Elev: 139

Description

Driller: GCD (Auto-Hammer)

N

T E

S T

B O

R

IN

G R

E C

O R

D L

O G

S .G

P J

G E

O H

Y D

R O

.G D

T

/2

2/

Very firm to dense tan-brown micaceous silty fine sand (SM) with rock fragments

(RESIDUUM)

Partially weathered rock sampled as tan silty fine sand (SM)

Boring Terminated at 20 feet

50/2"

E le v.

(F t)

0 30 40 100

S ym bo l

Test Boring Record D ep th

(F t)

G W

T

GWT at Drilling: Not Encountered

50 70

Date: 11/3/22

GWT at 24 hrs: N/A: Boring Backfilled Logged By: BGS

Method: HSA- ASTM D1586

Project No: 222708.20Project: Chattooga River Work Center - U.S. Forest Service

Location: 9975 Highway 441S - Lakemont, Georgia

Remarks:

Standard Penetration Test (Blows/Foot)

B-2

G.S. Elev: 140

Description

Driller: GCD (Auto-Hammer)

N

T E

S T

B O

R

IN

G R

E C

O R

D L

O G

S .G

P J

G E

O H

Y D

R O

.G

Very firm tan silty fine to medium sand (SM) with rock fragments (RESIDUUM)

Partially weathered rock sampled as tan-brown silty fine sand (SM)

Boring Terminated at 10 feet

50/1"

50/2"

50/3"

E le v.

(F t)

0 30 40 100

S ym bo l

Test Boring Record D ep th

(F t)

G W

T

GWT at Drilling: Not Encountered

50 70

Date: 11/3/22

GWT at 24 hrs: N/A: Boring Backfilled Logged By: BGS

Method: HSA- ASTM D1586

Project No: 222708.20Project: Chattooga River Work Center - U.S. Forest Service

Location: 9975 Highway 441S - Lakemont, Georgia

Remarks:

Standard Penetration Test (Blows/Foot)

B-3

G.S. Elev: 141

Description

Driller: GCD (Auto-Hammer)

N

T E

S T

B O

R

IN

G R

E C

O R

D L

O G

S .G

P J

G E

O H

Y D

R O

.G

Dense tan silty fine to medium sand (SM) with rock fragments (RESIDUUM)

Boring Terminated at 10 feet

E le v.

(F t)

0 30 40 100

S ym bo l

Test Boring Record D ep th

(F t)

G W

T

GWT at Drilling: Not Encountered

50 70

Date: 11/3/22

GWT at 24 hrs: N/A: Boring Backfilled Logged By: BGS

Method: HSA- ASTM D1586

Project No: 222708.20Project: Chattooga River Work Center - U.S. Forest Service

Location: 9975 Highway 441S - Lakemont, Georgia

Remarks:

Standard Penetration Test (Blows/Foot)

B-4

G.S. Elev: 138

Description

Driller: GCD (Auto-Hammer)

N

T E

S T

B O

R

IN

G R

E C

O R

D L

O G

S .G

P J

G E

O H

Y D

R O

.G