Agenda - 06-21-2011 - 8e - Laserfiche WebLink

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Report of subsurface Exploration and Geotechnicai Engineering Services 2M1 Acre Parcel - Carrboro, North Carolina EC5 Projoct Number os:1829z June 3, 2011 EXECUTIVE SUMMARY S~~t S ~~ t o~ ~ ECS Carolinas, LLP (ECS) has completed a report of subsurtace exploration and geotechnical engineering services for the 2.691 acre parcel located at 210 Hillsborough Street in Carrboro, North Carolina. This summary should not be considered apart from the entire text of the report with ail the qualifications and conditions mentioned herein. A structure consisting of aslab-on-grade, steel frame. metal stud, and brick veneer building is planned at the site. In addition, parking and drive [apes and a bio-retention pond are planned for the site. Building biding and grading infaniiation has not been provided at this time; however, we have assumed maximum column and wall bads would be on the order of 200 kips end 3 kips per linear foot, respectnrelp. We anticipate existing site grades would be maintained with iriinirnai cut and fill, no more than 4 feet. Seven soil test borings were pertormed at the site (B-1 though B-7}. Residual soils consisting of sandy and/or silty CLAY (CH} and sandy and/or clayey StLTS (ML) were encountered in the borings. The SPT N-values of the residual- soils ranged from 6 to 77 -blows per foot. High plasticity clays and- silts were encountered in Borings B-1 and B-3 through B-6 to depths ranging from approximately 3 feet below existing grades. Partially weathered rock (PWR), classified as material with SPT blow counts greater than 50 blows per ~ inches of penetration, was encountered in the borings below the residual soils at depths ranging from 3 to 13 feet below existing grades. Auger refusal, interpreted as intact bedrock, was encountered at depths ranging from 1 Z to 16 feet below existing grade. Groundwater was not encountered during subsurface exploration. Cave-in depths ranged from approximately 6 to 14 feet below existing ground surtace. Moderately to highly plastic clays were encountered- in the upper approximately 3 feet of Borings B-1 and- B-3 through B-6. These. soils may require moisture adjustments, localized undercutting and replacement or other appropriate remedial activities if they exist at Ehe finished subgrade elevation in building and pavement areas. It is desirable to maintain! at least 2 to 3 -feet of separation between the bottom of foundations, slabs and pavement sections to help reduce the potential far premature distress of as-built-construction as a result- of volumetric changes in the soil due to variations in its moisture content. Altemat[vely, the footings could be extended below the high plastic soils. Provided the recommendations presented in this report are followed, the proposed structures may be supported on conventional shallow footil~lg foundations and ground-supported floor slab. A design soil bearing pressure of 3,000 psf- is recommended for footings supported on approved residual soils or engineered fill materials. Based on Section 1615 of the 2006 North Carolina Building Code, the site has a Site Classifcation of C. Grading operations at this site wilt be more economical if performed during the drier periods of the year (typically April io November). However, during the wetter periods of the year, wet soils probably can be dried by using discing or other drying procedures, such as lime or cement stat~i[ization, to achieve moisture contents necessary to achieve adequate degrees of compaction. Due to the PWR and bedrock, difficult excavation should be anticipated for deep excavations into the PWR and bedrock. 14