Sheet15.1 Design of Sanitary Wastewater ManholesPurpose of Calculation : The purpose of this calculation is to determine the size of manholes,thickness of wall, cover slab and base slab.Assumptions:1. Assume water table is 1 meter below finish grade.Diagram:TwBTwTsTwHWTwTbPLANSECTIONAssume manhole sizeB =1.20mTs =0.25mW =1.20mTw =0.30mH =2.20mTb =0.30mDesign ParametersUnit weight of concrete ( yc )=24kN/m3Unit weight of submerged soil ( ys )=10.5kN/m3Unit weight of dry soil ( ys1 )=18kN/m3Unit weight of water ( yw )=10kN/m3Soil Bearing Capacity ( SBC )=100kN/m2Angle of internal friction ( f )=30degCoefficient of friction bet soil & conc ( m )=0.4Compressive strength of concrete ( f'c )=27.58MPaYield strength of rebars ( fy )=414MPaLive load surcharge ( s )=10kN/m2Vertical Loads ( Wt )Wmh =Weight of manhole = W1 + W2 + W3W1 =Weight of slab=( yc ) ( B W Ts ) =8.64kNW2 =Weight of walls=( yc ) [ ( 2 B H Tw ) + ( 2 W1 H Tw ) ] =95.04kNW3 =Weight of base slab=( yc ) ( B1 W1 Tb ) =23.33kNWmh =127.01kNWw =Weight of water=( yw ) ( B W H ) =31.68kNWt =158.69kNActual soil bearing pressure ( qa ) ( Full of water )qa =Wt / AA =W1 B1 =3.24m2qa =48.98kN/m2 1.2 ( SAFE )=48.60kNDesign of slabConsidering 1 meter strip of slabDL =yc Ts =6.00kN/mLL =3.60kN/m2 =3.60kN/mwu =1.4 DL + 1.7 LL =14.52kN/mMu =wu L2 / 8L =1.20m=2.61kN-mRequired Depth ( d )d =Muf =0.90f b Rub =1000mmRu =r fy [ 1 - 0.59 ( r fy / f'c ) ]f'c =27.58MPar =0.75 rbfy =414MParb =0.85 f'c b 600 =0.0284803333b =0.85fy ( 600 + fy )r =0.02136025rmin =1.4 / fy =0.00338