Preliminary Geotechnical Exploration Armstrong Tract Rivers Avenue and Hanahan Road North Charleston, South Carolina S&ME Project No.

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1 Preliminary Geotechnical Exploration Rivers Avenue and Hanahan Road S&ME Project No Prepared for: Charleston Water System 103 Saint Phillip Street Charleston, South Carolina Prepared by: S&ME, Inc. 620 Wando Park Boulevard Mt Pleasant, SC February 22, 2016

2 February 22, 2016 Charleston Water System (Charleston Commissioners of Public Works) 103 St. Phillip Street Charleston, South Carolina Attention: Reference: Mr. Frank Crawford Preliminary Geotechnical Exploration Rivers Avenue and Hanahan Road S&ME Project No Dear Mr. Crawford: We have completed our preliminary geotechnical exploration of the at the intersection of Rivers Avenue and Hanahan Road in. Our services were performed pursuant to S&ME Proposal No dated January 14, The purpose of this preliminary geotechnical exploration was to determine the general site subsurface conditions at widely-spaced locations and evaluate the considerations these conditions will have on site development. This report presents our understanding of the proposed construction, the site and subsurface conditions encountered, and preliminary conclusions and recommendations. Project Information We understand plans are to develop the approximately 31-acre (TMS# ) located in the east quadrant of the intersection of Rivers Avenue and Hanahan Road in North Charleston, South Carolina. There are no definitive plans for site development at this time, only that the property is being considered by potential developers for the construction of multi-purpose structures. We assume potential structures will be of steel and masonry construction with soil-supported floor systems, and site development will consist of new paved parking and drive areas. Specific structural information was not provided. Based on our experience with similar projects, we assume maximum column and wall loads will be approximately 300 kips and 5 kips/ft, respectively. Grading information was not provided. We also assume cut and fill depths of 2 ft or less will be required to grade building and pavement areas. This project information was provided by Mr. Frank Crawford with Charleston Water System (Charleston Commissioners of Public Works) in s to Mr. Chuck Black, P.E. of our firm on January 9, Mr. Crawford provided additional project information during a telephone conversation with Mr. Aaron Brummitt, RPA on January 13, S&ME, Inc. 620 Wando Park Boulevard Mt Pleasant, SC p f

3 Preliminary Geotechnical Exploration Rivers Avenue and Hanahan Road S&ME Project No Methods of Exploration Our exploration included a site reconnaissance by a geotechnical engineer and the performance of two cone penetrometer test (CPT) soundings and one seismic cone penetrometer test (SCPT) sounding. The widely-spaced soundings were extended to a depth of approximately 40 ft below the existing ground surface. A 4-ft-deep hand-auger boring was drilled at each sounding to evaluate the near-surface soils. The borings were drilled by manually turning a steel auger into the ground, and the soils encountered were visually classified in the field using the Unified Soil Classification System (USCS). Upon completion of the borings, the bore-holes were backfilled with soil cuttings, and core holes were patched with coldpatch asphalt. In the CPT soundings, an electronically instrumented cone penetrometer was hydraulically pushed through the soil to measure point stress, pore water pressure, and sleeve friction in general accordance with ASTM D The CPT data was used to determine soil stratigraphy and to estimate soil parameters such as preconsolidation stress, friction angle, and undrained shear strength. In an SCPT sounding (sounding C-2), the travel times of shear waves generated by an impulsive force applied to the ground surface are measured by geophones mounted within the cone penetrometer. For each measurement, the distance traveled and travel time of the first shear wave arrival was determined. Interval velocities were calculated by dividing the distance between adjacent depths by the difference in travel times. The test locations were established in the field by S&ME personnel measuring distances and estimating right angles from existing site features. The approximate test locations are shown on the Test Location Plan in the Appendix. A more detailed description of our field testing procedures, the CPT Sounding Logs, and the Hand-Auger Boring Logs are also included in the Appendix. Site and Subsurface Conditions Site Conditions The approximately 31-acre site consists of four parcels (parcels 1, 2, B, and C) located in the east of the quadrant of the intersection of Rivers Avenue and Hanahan Road in. According to the provided property survey 1, parcels 1, 2, and B are bordered by Hanahan Road and Highland Park Avenue to the north and northwest, a railroad easement to the northeast, the Aichele Terrace subdivision to the southeast, and Rivers Avenue to the southwest. Brandt Street separates parcels 1 and 2 from parcel B. Parcel C is bordered by Hanahan Rd to the north and west, Highland Park Avenue to the south, and a railroad easement to the east. At the time of our exploration, the site consisted of grassed and moderately-wooded areas. Wooded areas consisted of mature trees, underbrush, and a ground cover of pine straw and leaf litter. The site also contained several utility easements within all the parcels, and parcels 2 and B contain an asphalt road that was partial overgrown 1 Zoning Exhibit for a Portion of The, owned by The Commissioners of Public Works of the City of Charleston, S.C. (TMS# ) dated March 14, February 22,

4 Preliminary Geotechnical Exploration Rivers Avenue and Hanahan Road S&ME Project No with grass in some areas. This road was several feet higher than adjacent grades. Low, wet areas were also observed primarily within parcel 2. Topographic information was not provided; however, at the time of our exploration, the ground surface appeared to be relatively flat, with the exception of the low, wet areas and the elevation change along the asphalt / grass covered road within parcel 2. Soil Survey Data We reviewed the Soil Survey of Charleston County, South Carolina (USDA SCS 1971) to determine the mapped soil type(s) at the site. The Soil Survey indicated the project site is located within an area of Charleston County that is not included in the Soil Survey because of its long history of urban development and filling/excavating operations, which have left the soil profile highly disturbed. Subsurface Conditions Details of the subsurface conditions encountered by the soundings and borings are shown on the logs in the Appendix. These logs represent our interpretation of the subsurface conditions based upon field data. Stratification lines on the logs represent approximate boundaries between soil behavior types 2 ; however, the actual transition may be gradual. The general subsurface conditions and their pertinent characteristics are discussed in the following paragraphs. The exploration initially encountered approximately 4 to 5 in. of organic-laden topsoil underlain by relatively clean (low percentage of silt and clay) sand, silty sand, and clayey sand. The near surface sands appear to be natural; however, it was difficult to discern between natural sandy soils and sandy fill at this site. The site has been previously developed (i.e. an asphalt road, utility easements, etc.). Based on our experience with similar sites in this area Charleston County, fill soils are like present throughout the site, especially within the vicinity of previously developed areas, and fill depths will vary. Beneath the topsoil and near surface sands, the exploration generally encountered very loose to medium dense sands with varying amounts of silt and clay to depths of approximately 22 to 25 ft followed by firm to stiff sandy clays and silts to the top of the Cooper Marl 3. Marl was encountered at depths of approximately 30 to 32 ft and continued to the deepest explored depth of 40 ft below the existing ground surface. 2 Soil Behavior Type is calculated based on empirical correlations with tip resistance, sleeve friction, and pore pressure. A CPT may define a soil based on its behavior as one type while its grain size and plasticity, the traditional basis for soil classification, may define it as a different type. 3 The Cooper Marl, locally referred to as marl, is an incompressible, thick ( 200 ft) stratum which underlies the area and is typically the bearing stratum for deep foundations in the Charleston area. February 22,

5 Preliminary Geotechnical Exploration Rivers Avenue and Hanahan Road S&ME Project No Subsurface Water Subsurface water was measured upon completion of the soundings and hand-auger borings at depths of approximately 3 to 5½ ft below the existing ground surface. Subsurface water levels at the sites will fluctuate during the year due to such things as seasonal and climatic variations and with construction activity in the area. General Geotechnical Considerations The preliminary analyses and conclusions submitted in this report are based, in part, upon data obtained from the widely-spaced test locations. Subsurface conditions between the test locations will vary, as will grading and construction details. Therefore, only general comments about the suitability of the site for the anticipated development can be provided. Once final site development plans have been established, additional geotechnical exploration and analysis will be required at specific project location(s) to provide design recommendations for site preparation and structural support. Based on the findings of the field exploration, the following preliminary comments and conclusions are provided: 1. Site Preparation. Site preparation should begin with the removal of any previous development including pavements, old foundations and slabs, subsurface utilities, and buried debris. Site preparation should continue with clearing and grubbing vegetation and roots, stripping organic laden topsoil, and undercutting unsuitable surface soils. Stumps, taproots, and buried debris should be completely removed, and voids created should be cleaned and backfilled with wellcompacted controlled fill. Prior to fill placement, the exposed subgrade in building and pavement areas should be evaluated as determined by the Geotechnical Engineer. This evaluation may involve manually probing, proofrolling, and/or hand-auger borings with dynamic cone penetrometer testing. Unstable areas can be undercut or stabilized as recommended by the Geotechnical Engineer. The site has been previously developed. Fill soils were not obvious during our exploration; however, fill soils are likely present on site and within previously developed areas such as roadway and subsurface utility easement areas. As such, thorough subgrade evaluations and proofrolling will be very important, and some undercutting and replacement of existing in situ soils should be anticipated. The extent and depth of any undercutting will heavily depend upon final grades, the climatic conditions during construction, the aggressiveness of the earthwork schedule, and the contractor s means and methods. 2. Controlled Fill. Controlled fill material is typical soil containing no more than 15% fines (material passing the No. 200 sieve) by weight, having a maximum dry density (ASTM D 1557) of at least 100 pcf. The soil should be relatively free of organics, deleterious matter, and elongated or flat particles susceptible to degradation. Soils are typically placed in uniform lifts of 10 in. or less (loose measure) and compacted to at least 95% of the modified Proctor maximum dry density (ASTM D 1557). February 22,

6 Preliminary Geotechnical Exploration Rivers Avenue and Hanahan Road S&ME Project No Seismic Considerations. A liquefaction 4 analysis based on the design earthquake 5 prescribed by the 2012 edition of the International Building Code (IBC 2012) indicates isolated sand zones across the site have the potential to liquefy during the design seismic event. Our preliminary analysis predicts a Liquefaction Potential Index (LPI) 6 greater than 15, which indicates the liquefaction risk is severe and foundation damage is likely. Additionally, up to 4 in. of free-field liquefaction-induced settlement are possible at this site. Section of the IBC 2012 classifies sites with the potential for liquefaction as Seismic Site Class F. However, the IBC 2012 allows the design spectral response accelerations for a site to be determined without regard to liquefaction provided structures have a fundamental period of less than or equal to 0.5 seconds and the risks of liquefaction are considered in design. Buildings should meet this criterion; however, this must be confirmed by the Structural Engineer. Based on the CPT data and an average shear-wave velocity >600 ft/sec, it is our interpretation the site may be considered a Site Class D to determine ground motions. 4. Foundations. Based on the preliminary exploration, the site soils appear suitable for supporting buildings using conventional shallow foundations if the risks associated with liquefaction are accepted or mitigated. Although the test locations are too widely spaced to provide final design values, it is anticipated maximum allowable bearing pressures ranging from 2,000 to 2,500 psf are feasible for conventional shallow foundations. The site contains some previous development, subsurface variations are probable, and undercutting unsuitable soils at isolated footing locations should be anticipated. The preliminary analysis indicates that total post-construction static settlement due to the assumed building loads (300 kip columns and 5 kips/ft walls) will be on the order of 1½ in. Static settlement should be more thoroughly assessed in a design geotechnical exploration tailored to the actual structural loads and the grading plans. Seismically-induced settlements are predicted to be 4 in., which can be 100% differential across building areas. If structures can be designed to accommodate this settlement and not suffer catastrophic failure, (i.e. collapse), the structures can be supported on shallow foundations. Otherwise, ground improvement or deep foundations will be required. 5. Excavation. Excavation to expected subgrade levels will encountered low to moderate consistency soils using typical equipment and techniques. Excavations will likely encounter groundwater. If encountered, the water level should be maintained at least 1-ft below excavations to help maintain bottom stability. Water can probably be controlled at the site by pumping from sumps located within the excavation. The effects of dewatering on nearby structures should be evaluated and are the responsibility of the designer of any dewatering system. 4 Liquefaction, the loss of a soil s shear strength due to the increase in porewater pressure resulting from seismic vibrations, is always a potential concern in coastal South Carolina. 5 The IBC 2012 design earthquake has a 2% probability of exceeding in 50 years. This is statistically equivalent to an event that occurs about once every 2,500 years. Our liquefucation analysis was based on an earthquake with a magnitude of 7.3 and ground surface acceleration of 1.01g. 6 Iwasaki et al. 1982, Toprak & Holzer (2003) February 22,

7 Preliminary Geotechnical Exploration Rivers Avenue and Hanahan Road S&ME Project No All excavations should be sloped or shored in accordance with local, state, and federal regulations, including OSHA (29 CFR Part 1926) excavation trench safety standards. The contractor is usually solely responsible for site safety. This information is provided only as a service, and under no circumstances should S&ME be assumed to be responsible for construction site safety. 6. Floor Slabs and Pavements. Subsurface conditions are adaptable for typical slab and pavement design with proper site preparation and fill placement and compaction. Some undercutting should be anticipated, and undercutting depths will be specific to individual areas. Based on the exploration data and our experience, a soil modulus of subgrade reaction (k), based on the 30-in. diameter plate method, on the order of 150 to 180 pci should be available for design. A vapor retarder may be required for the floor slabs, depending on the floor covering design. California Bearing Ratio (CBR) values on the order of 7 to 10% can be considered reasonable for conceptual design of flexible pavements with 2 ft of controlled fill. Flexible asphalt pavements typically are a minimum of 8 in. thick (2 in. of asphalt and 6 in. of graded aggregate base) for automobile parking areas. Areas subjected to heavy truck traffic are typically a minimum of 11 in. thick (3 in. of asphalt and 8 in. of graded aggregate base). Rigid concrete pavements for fire engine traffic or other heavy truck traffic areas are typically at least 11 to 12 in. thick (5 to 7 in. of concrete and 6 in. of graded aggregate base). Pavement thickness design is heavily dependent on the expected traffic type and volume, which are unknown at this point. Limitations of Report This report has been prepared in accordance with generally accepted geotechnical engineering practice for specific application to this project. The conclusions and recommendations contained in this report are based upon applicable standards of our practice in this geographic area at the time this report was prepared. No other warranty, express or implied, is made. The information provided in this preliminary report is considered sufficient for planning purposes; however, it is not adequate for geotechnical design purposes. When the project is further advanced with building design and locations determined, additional field and laboratory testing must be performed. The additional testing should include an appropriate amount of soil test borings, CPT soundings, test pit excavations, and laboratory testing that would be used to provide design level geotechnical information for individual building sites. February 22,

8 Preliminary Geotechnical Exploration Rivers Avenue and Hanahan Road S&ME Project No Closure We appreciate the opportunity to be of service on this project. If you have any questions concerning this preliminary report, please call. Sincerely, S&ME, Inc. Ronald C. Boller, P.E. Project Engineer Michael S. Ulmer, P.E. Principal Engineer / Project Manager RCB/MSU/taj February 22,

9 Appendix Test Location Plan (Figure 1) CPT Sounding Logs Hand-Auger Boring Logs Field Testing Procedures

10 C 3 C 2 C 1 LEGEND Approximate CPT Sounding / Hand-Auger Boring Location The site plan was adapted by S&ME, Inc., and the test locations are approximate. This plan should not be used for design or construction. S&ME Project No.: February 2016 Scale: Not to Scale TEST LOCATION PLAN Rivers Avenue and Hanahan Road Figure 1

11 Date: Estimated Water Depth: Rig/Operator: S&ME Project No: Jan. 26, ft Marooka / D. Oldal Cone Penetration Test C-1 Total Depth: 40.2 ft Termination Criteria: Target Depth Cone Size: 1.75 Depth (ft) 0 Tip Resistence q t (tsf) Sleeve Friction f s (tsf) Pore Pressure u 2 u 0 (tsf) Friction Ratio R f (%) Equivalent N SBT Bq MAI = 1 Depth (ft) Gravelly Sand to Sand CPT REPORT - STANDARD - SBT BQ CPT.GPJ S&ME.GDT 2/8/ Page 1 of 1 Electronic Filename: H26J1603C.ECP Sand Mixtures- to Sandy Silt Silt Mixtures-Clay Silt to Silty Clay Silt Mixtures-Clay Silt to Silty Clay Clays-Clay to Silty Clay C-1

12 Date: Estimated Water Depth: Rig/Operator: S&ME Project No: Jan. 26, ft Marooka / D. Oldal Cone Penetration Test C-2 Total Depth: 40.3 ft Termination Criteria: Target Depth Cone Size: 1.75 Depth (ft) 0 Tip Resistence q t (tsf) Sleeve Friction f s (tsf) Pore Pressure u 2 u 0 (tsf) Friction Ratio R f (%) Shear Wave Velocity V s (ft/sec) SBT Bq MAI = 1 Depth (ft) 0 5 >> CPT REPORT - STANDARD - SBT BQ CPT.GPJ S&ME.GDT 2/8/ Page 1 of 1 Electronic Filename: H26J1602C.ECP Sand Mixtures- to Sandy Silt Clays-Clay to Silty Clay Silt Mixtures-Clay Silt to Silty Clay Clays-Clay to Silty Clay C-2

13 Date: Estimated Water Depth: Rig/Operator: S&ME Project No: Jan. 26, ft Marooka / D. Oldal Cone Penetration Test C-3 Total Depth: 40.0 ft Termination Criteria: Target Depth Cone Size: 1.75 Depth (ft) 0 Tip Resistence q t (tsf) Sleeve Friction f s (tsf) Pore Pressure u 2 u 0 (tsf) Friction Ratio R f (%) Equivalent N SBT Bq MAI = 1 Depth (ft) Gravelly Sand to Sand Gravelly Sand to Sand CPT REPORT - STANDARD - SBT BQ CPT.GPJ S&ME.GDT 2/8/ Page 1 of 1 Electronic Filename: H26J1601C.ECP Sand Mixtures- to Sandy Silt Sand Mixtures- to Sandy Silt Clays-Clay to Silty Clay C-3

14 PROJECT: DATE STARTED: /17/16 DATE FINISHED: 2/17/16 HAND AUGER BORING LOG: C-1 NOTES: SAMPLING METHOD: Hand-Auger PERFORMED BY: R. Boller WATER LEVEL: Groundwater encountered at 3.75 ft at time of boring Depth (feet) GRAPHIC LOG MATERIAL DESCRIPTION ELEVATION (feet) WATER LEVEL Topsoil = 5 in. SLIGHTLY SILTY SAND (SP-SM) brown to yellowish brown, fine, moist 1 CLAYEY SAND (SC) brown to yellowish brown, fine, moist Reddish brown to yellowish brown Wet 4 Boring terminated at 4 ft 1. PENETRATION RESISTANCE IS THE NUMBER OF BLOWS OF A 10.1 LB HAMMER FALLING 22.6 IN., DRIVING A 0.79 IN. O.D. 60 DEGREE CONE 1.75 IN. Page 1 of 1

15 PROJECT: DATE STARTED: /17/16 DATE FINISHED: 2/17/16 HAND AUGER BORING LOG: C-2 NOTES: SAMPLING METHOD: Hand-Auger PERFORMED BY: R. Boller WATER LEVEL: Groundwater encountered at 3 ft at time of boring Depth (feet) GRAPHIC LOG MATERIAL DESCRIPTION ELEVATION (feet) WATER LEVEL Topsoil = 5 in. SLIGHTLY SILTY SAND (SP-SM) brown to yellowish brown, fine, moist 1 SILTY SAND (SM) brown to yellowish brown, fine, moist 2 CLAYEY SAND (SC) reddish brown to yellowish brown, fine, moist Wet 4 Boring terminated at 4 ft 1. PENETRATION RESISTANCE IS THE NUMBER OF BLOWS OF A 10.1 LB HAMMER FALLING 22.6 IN., DRIVING A 0.79 IN. O.D. 60 DEGREE CONE 1.75 IN. Page 1 of 1

16 PROJECT: DATE STARTED: /17/16 DATE FINISHED: 2/17/16 HAND AUGER BORING LOG: C-3 NOTES: SAMPLING METHOD: Hand-Auger PERFORMED BY: R. Boller WATER LEVEL: Groundwater encountered at 3.75 ft at time of boring Depth (feet) GRAPHIC LOG MATERIAL DESCRIPTION ELEVATION (feet) WATER LEVEL Topsoil = 4 in. SLIGHTLY SILTY SAND (SP-SM) dark brown, fine, moist Brown to yellowish brown SILTY SAND (SM) brown to yellowish brown, fine, moist 2 CLAYEY SAND (SC) reddish brown to yellowish brown, fine, moist Wet 4 Boring terminated at 4 ft 1. PENETRATION RESISTANCE IS THE NUMBER OF BLOWS OF A 10.1 LB HAMMER FALLING 22.6 IN., DRIVING A 0.79 IN. O.D. 60 DEGREE CONE 1.75 IN. Page 1 of 1

17 FIELD TESTING PROCEDURES Cone Penetrometer Test (CPT) Sounding The cone penetrometer test soundings (ASTM D 5778) were performed by hydraulically pushing an electronically instrumented cone penetrometer through the soil at a constant rate. As the cone penetrometer tip was advanced through the soil, nearly continuous readings of point stress, sleeve friction and pore water pressure were recorded and stored in the on-site computers. Using theoretical and empirical relationships, CPT data can be used to determine soil stratigraphy and estimate soil properties and parameters such as effective stress, friction angle, Young s Modulus and undrained shear strength. The consistency and relative density designations, which are based on the cone tip resistance, q t for sands and cohesive soils (silts and clays) are as follows: SANDS Cone Tip Resistance, q t (tsf) Relative Density SILTS AND CLAYS Cone Tip Resistance, q t (tsf) Consistency <20 Very Loose <5 Very Soft Loose 5 10 Soft Medium Dense Firm Stiff Dense Very Stiff >200 Very Dense >60 Hard CPT Correlations References are in parenthesis next to the appropriate equation. General p a = atmospheric pressure (for unit normalization) q t = corrected cone tip resistance (tsf) f s = friction sleeve resistance (tsf) R f = 100% * (f s /q t ) u 2 = pore pressure behind cone tip (tsf) u 0 = hydrostatic pressure B q = (u 2 -u 0 )/(q t -σ v0 ) Q t = (q t -σ v0 )/ σ v0 F r = 100% * f s /(q t - σ v0 ) I c = ((3.47-logQ t ) 2 +(logf r +1.22) 2 ) 0.5 N-Value N 60 = (q t /pa)/[8.5(1-i c /4.6)] (6) (6) Jefferies, M.G. and Davies, M.P., (1993), Use of CPTu to estimate equivalent SPT N60, ASTM Geotechnical Testing Journal, Vol. 16, No. 4

18 CPT Soil Classification Legend Robertson's Soil Behavior Type (SBT), 1990 Group # Description Ic Min Max 1 Sensitive, fine grained N/A 2 Organic soils - peats 3.60 N/A 3 Clays - silty clay to clay Silt mixtures - clayey silt to silty clay Sand mixtures - silty sand to sandy silt Sands - clean sand to silty sand Gravelly sand to dense sand N/A Very stiff sand to clayey sand (High OCR or cemented) N/A 9 Very stiff, fine grained (High OCR or cemented) N/A Soil behavior type is based on empirical data and may not be representative of soil classification based on plasticity and grain size distribution. Relative Density and Consistency Table SANDS SILTS and CLAYS Cone Tip Stress, qt (tsf) Relative Density Cone Tip Stress, qt (tsf) Consistency Less than 20 Very Loose Less than 5 Very Soft Loose 5-15 Soft to Firm Medium Dense Stiff Dense Very Stiff Greater than 200 Very Dense Greater than 60 Hard