AussoisApr05 Petersen

Large Excavations in the US : Large Excavations in the US Lee Petersen, CNA Consulting Engineers Presented by Chang Kee Jung, SUNY Stony Brook NNN05 Conference


Topics : Topics DUSEL sites Site characteristics important for large excavations Rock engineering Relative importance of site characteristics Megaton detector feasibility


DUSEL Site Locales : DUSEL Site Locales


Solicitation 2 Sites : Solicitation 2 Sites Cascades-Icicle Creek, WA Greenfield escarpment site andamp; nearby railroad tunnel Henderson Mine, Empire, CO Operating molybdenum mine since mid 1970s Homestake Mine, Lead, SD Former operating gold mine Kimballton Mine, Giles Co., VA Limestone mine andamp; adjacent subsurface


Solicitation 2 Sites : Solicitation 2 Sites San Jacinto, CA Greenfield escarpment site Soudan Mine, Soudan, MN Operating lab at former iron mine, expansion into adjacent subsurface SNOLAB, Sudbury, Ontario Operating lab in operating nickel mine WIPP, Carlsbad, NM Operating lab in operating low-level waste facility


Characteristics for Large Excavations : Characteristics for Large Excavations What site characteristics are important for large excavations? Depth / shielding capacity Rock type / rock chemistry Rock quality / In situ stress Access / rock removal Will review each characteristic for each site All comments that follow are for large excavations, not DUSEL in general


Depth / Shielding Capacity : Depth / Shielding Capacity


Rock Type / Rock Chemistry : Rock Type / Rock Chemistry


Rock Quality / In situ Stress : Rock Quality / In situ Stress No site has sufficient experience to be sure that a megaton detector is feasible! Summary of available information about site rock quality.


Rock Engineering 101 : Rock Engineering 101 Rock 'material' — strong, stiff, brittle Weak rock andgt; Strong concrete Strong in compression, weak in tension Postpeak strength is low unless confined Rock 'mass' — behavior controlled by discontinuities Rock mass strength is 1/2 to 1/10 of rock material strength Discontinuities give rock masses scale effects


Rock Engineering 101 : Rock Engineering 101 Massive rock Rock masses with few discontinuities, or Excavation dimension andlt; discontinuity spacing


Rock Quality : Rock Quality


Rock Engineering 101 : Rock Engineering 101 Jointed or 'blocky' rock Rock masses with moderate number of discontinuities Excavation dimension andgt; discontinuity spacing


Rock Quality : Rock Quality


Rock Engineering 101 : Rock Engineering 101 Heavily jointed rock Rock masses with a large number of discontinuities Excavation dimension andgt;andgt; discontinuity spacing


Rock Quality : Rock Quality


Rock Engineering 101 : Rock Engineering 101 Rock stresses in situ Vertical stress  weight of overlying rock ~27 KPa / m  35.7 MPa at 1300 m Horizontal stress controlled by tectonic forces (builds stresses) andamp; creep (relaxes stresses) At depth, v  h unless there are active tectonic forces


Major Rock Features : Major Rock Features Examples Geologic contacts Joint swarms Shears and faults Effects Reduced rock quality Reduced strength Locus for rockburst / seismic activity


Effect of Major Rock Features : Effect of Major Rock Features


Numerical Modeling : Numerical Modeling Rock engineering equivalent of bridge or building structural analysis Develop understanding of the critical physical parameters Rock characteristics Rock stresses Cavern shape Rock support andamp; reinforcement Common types Continuum Discontinuum


Simple example : Simple example Continuum model FLAC 2D 60 x 60 x 180 meters (length not modeled) Curved roof andamp; straight walls Depth 1300 meters Stresses  depth Example rock properties Sequential excavation Rock reinforcement Model permits rock failure


Sequential excavation : Sequential excavation


Effect of Rock Strength : Effect of Rock Strength


Cablebolt Forces : Cablebolt Forces


Rock Mass Characterization : Rock Mass Characterization Stages Choose the best site Find best location at the chosen site Prove rock conditions at chosen location Volume of rock necessary Technical objectives Provide design basis Choose proper design and construction techniques Reduce risk of differing site conditions Basis for cost estimating Basis for defining baseline, i.e. contractor bidding


Access / Rock Removal : Access / Rock Removal


Conclusions about important features : Conclusions about important features Depth / shielding capacity All sites appear adequate Rock type / rock chemistry All sites appear adequate, but salt at WIPP may be problematic (due to creep andamp; solubility) Rock quality / In situ stress All sites are potentially suitable, but none are guaranteed feasible Access / rock removal All sites are potentially suitable, but horizontal access is beneficial


What is MOST important? : What is MOST important? Rock type / rock chemistry Creep andamp; solubility are the principal issues Rock quality / In situ stress Commonly influences costs by a factor of 2 to 4, could make a site unfeasible Access / rock removal Can influence costs significantly, but is very site dependent


Rock Engineering 101 : Rock Engineering 101 What are the implications for large cavern construction? Find a site with excellent rock Characterizing the rock mass is JOB ONE Avoid tectonic zones andamp; characterize in situ stresses Select size, shape andamp; orientation to minimize rock support, stress concentrations, etc. Soudan 2 andamp; MINOS caverns


Cost & Risk vs. Site Investigation : Cost andamp; Risk vs. Site Investigation


Questions? : Questions?


Concluding Remarks : Concluding Remarks Is a megadetector feasible? Qualified yes What are the qualifications? Rock conditions andamp; depth Best location at the best site, not too deep Enlightened funding agencies Understand andamp; manage the risks, cost uncertainties Site factors Rock removal, competing demands for resources Contractor Chosen on cost andamp; qualifications