Feasibility Study and Technical Report - Pretivm

18.2 GEOTECHNICAL18.2.1 OVERVIEWThe geotechnical designs and recommendations in this section are based on the resultsof site investigations and geotechnical assessments. Geotechnical site investigationswere undertaken in 2011 and 2012 to evaluate the subsurface conditions in the area ofthe proposed mill building. These investigations included geotechnical drilling andlogging, test pit excavations, laboratory testing of rock core and soil samples, installationof piezometers to measure groundwater pressures, and geophysical surveys. Detailsregarding the investigations are provided in BGC’s 2013 design report, “GeotechnicalAnalysis and Design of the Plant Site Foundations”. In general, the materialsencountered during the site investigations consisted of glacial till, ranging in thicknessfrom 1 to 8 m, overlying fair to good quality bedrock.18.2.2 FOUNDATIONSFor all buildings and facilities located within or adjacent to the mill building, foundationswill consist of conventional spread footings, strip footings, or other mass concretefoundation elements founded on good quality bedrock. For ancillary buildings locatedoutside of this area, foundations will consist of conventional spread footings founded oneither structural fill or bedrock. Recommendations were provided for allowable bearingpressures based on the results of the 2011 and 2012 site investigations, and theanticipated foundation types provided by Tetra Tech (BGC 2013). Allowable bearingpressures for foundation stratum were estimated − assuming a factor of safety of 3 −against bearing capacity failure and to limit total and differential settlements to thosespecified by Tetra Tech. Table 18.1 provides a summary of the recommended allowablebearing pressures for specific facilities.Table 18.1Recommended Allowable Bearing Pressures for Specific FacilitiesFacilityTypeFoundationDimensionsFoundationStratumAllowable BearingPressure(kPa)Surge Bin Mat Up to 8 m by 8 m Bedrock 600Spread Footings Up to 7 m by 3 m Bedrock 600Mill Building Mat Up to 13 m by 8 m Bedrock 600Strip Footings 2.5 m wide Bedrock 600Spread Footings Up to 5 m by 3.5 m Bedrock 600Tailings Thickener Mat Up to 29 m by 29 m Bedrock 600Spread Footings Up to 5 m by 5 m Bedrock 600Ancillary Buildings Spread Footings Up to 3 m by 3 m Structural Fill 200or BedrockNote: Foundations on structural fill assume a minimum embedment of 1 m below the surrounding grade.For the design cold year, the depth of frost penetration is estimated to be up to 5 m in fillmaterials and 4 m in bedrock. Exterior building foundations and interior footings ofPretium Resources Inc. 18-5 1291990200-REP-R0012-02Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC