400 kV Switchyard at Yeramarus TB-332-607-016 REV-02 document.xls Page 1 DESIGN OF CABLE TRENCH SECTION 1-1 For detail of section TB 0 332 316 004 Design of cable trench wall Min depth of trench wall below ground level 1.625 m Assuming max. length of trench as 55m with longitudinal slope of 1 : 750 (length upto section 1-1&4-4) Depth of trench wall due to slope 55 / 750 = 0.073 m Max depth of trench Wall(from GL) 1.625 + 0.073 1.698 m (MAX.) Max. Total Height of cable Trench wall 1.823 Surcharge pressure q = 2000 Soil density 1800 Angle of internal friction 0 Coefficient of internal friction Ka = (1-sin0)/(1+sin0) = 1.000 Weight of tray+cable +connector(w1) (refer email dated 26.06.13) 80 kg/m length of wall Width of tray 0.75 m No. of trays 5 Lateral stress over the wall due to uniform surcharge pressure( Ka x q) = 2000.00 Total active thrust due to surcharge(P 2000.00 x 1.70 = 3396.67 kg/m 0.5*1800*1*1.698^2 = 2595.90 kg/m Total active thrust (Pa) 3396.67 + 2595.90 = 5992.6 kg/m 5992.57*y=3396.67*1.698/2+2595.9*1.698/3 y = 0.727 m Bending moment at the base of wall 5992.6 x 0.727 = 4353.91 kg-m/m ( Considering 1m length of wall) Moment from tray (Connected from wall) 80 x ( 0.75 )/2x5 150.00 kg-m Total moment 4353.91 + 150.0 = 4503.91 kg-m Design moment, Mu1 1.50 x 4503.91 = 6755.86 kg-m Concrete grade M 25 Depth of water 1.698 = 1.698 m Active thrust due to water 0.5 x 1000 x 1.698 ^2 1442.168 kg/m Bending moment at the base of wall 1442.168 x 1.698 /3 816.43 kg-m/m ( Considering 1m length of wall) Design moment, Mu2 1.50 x 816.43 = 1224.64 kg-m 250 GL B GL P1 1698 1.698 P2 750 y H/3 H/2 A Design moment for wall 6755.9 kg-m Required thickness of wall ( 6755.86 *25*1000)^0.5 139.94 mm Providing, D 400 mm Effective depth, d 400 -40-5 = 355 mm Reinforcement 6755.86 1000 x 355 0.54 Required % of steel, Pt = 0.152 (Refer SP16,tab Table 1) Required area of steel ( 0.152 x 1000 x 355 )/100 540.84 kg/m 2 g = kg/m 3 f = o CASE-I : When no water in the trench and soil outside the wall kg/m 2 Active thrust due to Backfill (P2=1/2*Ka*g*H^2) Pa acts at a distance 'y' above A and acts horizontally. Taking moment about A CASE-II : When water in the trench and no soil outside the wall * 10 4 / 0.138 d = (Mu / .138x fck x b) 0.5 Mu/bd 2 = x 10 4 / 2 mm 2