Transcription of Vertical Stress in a Soil Mass - University of Waterloo
1 1 Vertical Stress in a soil MassForces that Increase Vertical Stress in soil Mass Weight of soil (effective Stress ) Surface loads Fill large area Point loads: Hydro pole, light stand, column, etc Lines loads Rack or rail loading, strip foundation Rectangular area Raft or rectangular footing Circular area tank Earth embankment Road, railway, fill, ice, or Surcharge over Large AreaCASE I No flow and no surcharge = 18 kN/m3 = 20 kN/m310m20mFill or surcharge over large areaCASE II 10m of fill added = 18 kN/m3 = 20 kN/m310m20m10mFill = 22 kN/m33 Fill or Surcharge over large area fill= fillH = Note: fill= constant with depthGlaciers over during ICE AGE increased Vertical Stress in soil and rock. This Stress is now gone. Boussinesq 1885 Point load Solution Uses elastic theory to get change in Stress with depth below point load Solution based on.
2 Linear elastic, homogeneous, isotropic medium with semi-infinite depth4 Point LoadPIntegration of area at a given depth must equal the applied surface areaWith depth peak gets smaller however Stress spreads over larger areaPoint Load5 Point LoadPoint Load67 Line LoadLine Load8 Strip Load9 Strip Load10 Below centre of uniformly loaded circular area11 Rectangular Loaded AreaB is always shortest dimension12 Fadum Chart = q I2131415 Newmark s Influence ChartNewmark sChart16 Boston Rule (Approximate method) For uniform footing (B x L) we can estimate the change in Vertical Stress with depth using the Boston Rule Assumes Stress at depth is constant below foundation influence areaBoston Rule (Approximate Method) z= qo(BxL) /(B+z)(L+z)=P/(B+z)(L+z)Actual Stress distributionBoston Rule assumed Stress distributionz/217 Stress Influence AreaNote: after 2B Stress increase due to q is very smallFoundation Stress Influence Stress overlap due to both foundations18 2004 Brooks/Cole Publishing / Thomson Learning Embankment LoadingInfluence value I for embankment loading(after Osterberg, 1957) 2004 Brooks/Cole Publishing / Thomson Learning z= 2I q0
