2020-01-13 斜面安定13 tanθ=H/B, B=H/tanθ sinθ=H/L, L=H/sinθ W=γBH/2=(γH^2/2)/tanθ N=Wcosθ→σ=N/L=Wcosθ/(H/sinθ) =(γH^2/2)/tanθ・cosθ/(H/sinθ) =(γHHcosθ)cosθsinθ/sinθ/2/H =γH/2cosθ×cosθ