ATTACHMENT 2 - Soil Properties_Profile_CHP Plant.pdf

BASIS OF DESIGN REPORT CHP AND NEW STEAM GENERATION PLANT

ATLANTA VA MEDICAL CENTER

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Accessible parking: The project does not include additional parking. Parking and accessible parking is addressed throughout the campus and in the six parking structures.

Handicapped van parking: The project does not include handicapped parking. Parking and accessible parking is addressed throughout the campus and in the six parking structures.

Surface and structured parking allotment: The project does not include parking. Parking and accessible parking is addressed throughout the campus and in the six parking structures.

1.3 SITE DEVELOPMENT NARRATIVE

The project site is a portion of the Atlanta VAMC facility located on 26 acres in the City of Decatur in DeKalb County, Georgia. The project site is currently developed, irregular in shape, and occupies approximately 0.30 acres on the north side of the campus. The project area currently includes Loading Dock C, eleven paved parking spaces, and typically paved surfaces. The average elevation is about 880 feet above mean sea level. The site is fairly flat however there is an existing paved ramp that slopes down toward Loading Dock C. A recent underground utility survey of the site area performed by LandAir Surveying Company indicates that there are a number of utilities located within the proposed building footprint. These utilities include, water, sewer, stormwater, gas, and fuel pipes. Other utilities include power lines and an abandoned air handling unit and grease trap next to the Building D. All of the existing utilities will have to be removed or relocated to outside of the proposed building footprint except an electrical duct bank that traverses the site. This duct bank cannot be damaged or taken out of service. The referenced duct bank will be protected and left in operation during the entire construction period.

Other than the relocation of the existing utilities, there will be considerable other demolition work such as curb and gutter, asphalt and concrete pavement, bollards, light pole bases, Loading Dock C, air handling unit, and an grease trap, etc.

The storm drainage system will primarily consist of pipes connecting the roof drains leaders to storm drain structures located within the project site. In order to comply with the water quality requirements, a structural Best Management Practices is proposed to address source pollutant runoff load.

The CHP building will cover a large portion of the proposed site minimizing the amount of new pavement that will be required. Areas around the project site that are disturbed as part of the installation or relocation of utilities will be repaved with concrete.

1.4 FLOODPLAIN (100-YEAR) AND FLOODWAY

The area proposed for the new CHP Plant is located within the DeKalb County’s special flood hazard AE- Zone boundaries. AE-Zone refers to areas of special flood hazard area where base flood elevations have been established. This matter was confirmed by review of the Federal Emergency Management Agency (FEMA) FIRM (Flood Insurance Rate Map) panels with Effective date of May 16, 2013.

DeKalb County has jurisdiction over the floodplain requirements and the related permitting process. URS has confirmed that a Flood Compliance Study is needed to confirm that minimum DeKalb County floodplain ordinance requirements are met. Verification of no-rise conditions, flood storage volumes, and flow characteristics have been analyzed using a step-backwater method to meet these requirements. The ordinance also requires full compensation for flood storage capacity such that the net change in the flood storage capacity is zero. This requirement is achieved by proposing an underground storage vault and removing certain existing structures from limits of the floodplain.

1.5 EXISTING SOIL CONDITIONS

A geotechnical investigation was completed as part of the Design Development phase of this project. The objective was twofold, namely:

to provide an assessment of subsurface conditions; and, to provide design data for foundation support and associated site development.

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The findings of the Geotechnical Investigation Report (dated October 28, 2013) are summarized below.

The complete Report is provided under separate cover.

1.5.1 Soil Profile

The soil profile observed in the borings is consistent with the weathering profile observed in residual soils in the metropolitan Atlanta area. The soil/rock within the limits of this exploration are a sequence of residual soils, generalized for the purposes of this report, as follows:

Unit 1, Fill/Pavements. The site is covered by asphalt/concrete pavement, related base materials and a thin veneer of fill, ranging in thickness from 5 to 6 feet below land surface (bls).

Unit 2, Residuum. Below the fill the site is underlain by naturally occurring residual soils - silty sand of loose to very dense consistency. The layer includes weathered rock fragments and lenses.

Unit 3, Transition Soils/Partially Weathered Rock (“PWR-inch). Layer 2 is underlain by partially weathered rock, sampled as very dense silty fine to coarse sands with lenses of solid rock and weathered rock. Unit 3 includes thin (to about 3 feet thickness) zones of relatively unweathered, fractured rock that refused the auger. Borings encountered this rock at 18 feet and 25 feet depths (about elevations +873 ft. and +856 ft. MSL).

Unit 4, Unweathered Rock. The bedrock was penetrated by coring following the occurrence of “auger refusal-inch at the top of Unit 4. Bedrock is fine-grained biotite gneiss (a granite-like material). The unweathered rock is characterized by unconfined compressive strengths in excess of 6,000 psi (the strength of high quality concrete).

Testing of rock from this site indicated an unconfined compressive strength of 6,360 psi.

Boring 1 encountered this rock at 37 feet and 41 feet depths (about elevation +854 feet and +840 feet MSL).

1.5.2 Soil Strength

Published information regarding the strength of residual soils in the Piedmont (the Layer 2 Residuum) indicates that soil shear strength is developed due to cohesion and the angle of internal friction.

The apparent cohesion observed in the residual soils is thought to be due to the mineral bond of the original rock which remains in the residual soils, and averages about 400 pounds per square foot (psf) for soils in the downtown area. The angle of internal friction appears to be the result of both particle interlocking and true friction, and may be presumed to be about 34 . In general, published results of the testing of residual soils of the Piedmont indicate that these soils exhibit strength with little confining pressure and a significant increase in strength with increasing confining pressure.

1.5.3 Liquefaction Potential

“Liquefaction-inch refers to the loss of soil strength during a seismic event. The phenomenon is observed in saturated (below the water table) coarse grained (sandy) soils of loose to medium dense consistency as the ground motions creates high pore water pressures which causes the soils to lose strength.

Because of the finer grained nature of the soils, the relatively high in situ density of the soils, the relatively deep depth to the static groundwater table, the high preconsolidation pressures, the geologic age of the soils, and the relatively low anticipated ground motion levels from earthquakes, the potential for “liquefaction-inch of soils during a seismic event is considered to be extremely low to non-existent.

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1.5.4 Soil Profile Classification for Seismic Design

The Soil Profile Type should be “C- Very Dense Soil/Soft Rock-inch after Table 1615.1.1 of IBC 2009.

1.5.5 Groundwater and Surface Water

Groundwater was encountered during this exploration. At the time of this work, groundwater occurs at about elevation +870 feet MSL, approximately 10-feet below grade.

It should be noted that the observed levels will change due to seasonal/weather-related influence.

The levels observed are likely representative of a relatively wet period. These levels may be expected to decrease somewhat (perhaps one to two feet) during dry periods.

No surface water was evident on the site at the time of URS’ work.

Table 1-1. Field Investigation Summary

Boring Number 1

Approximate Surface

Elevation (feet, MSL) 2

Boring Depth

(feet, bgs)

Depth to 3

Groundwater (feet, bgs)

Groundwater Elevation

(feet, MSL)

Depth to Rock

(feet, bgs)

Rock Elevation

(feet, MSL)

B-1 880.9 61 10.6 870.3 41 839.9

B-2 881.1 47 NM NM 37 844.1

B-3 879.6 32 NM NM NM NM

B-4 878.0 21 7.1 870.9 NM NM

B-5 877.9 25 7.5 870.4 NM NM

1 Borings are located on Figure 3-1, logs of the borings and representative cross sections are included in Appendix A

2 Boring Elevations are as was reported by Lowe Engineers 3 indicates depth to groundwater is approximate bgs – below existing ground surface.

NM – Not measured.

Figure 1-3. Typical Residual Soil and Rock Profile in the Piedmont Physiographic Region

(Reference: O’Brien and Norton, 2001, Economics of Deep Foundations in the Piedmont Physiographic Province)