Question

Question 3 (70) Design an isolated rectangular footing of dimension 4m x 5m. The gross pressure acting at the base of the footing is 150 kN/m2. Choose the depth of foundation such that the factor of safety is exactly 3 against shear failure. Also check against the permissible settlement (75mm) to ensure that the design is safe from the settlement criterion too. If the design is not safe against settlement criterion, then choose the proper dimension and depth to ensure that design is safe against both the criterions. Take pore water correction factor as 0.7. Use Skempton's bearing capacity equation for clay soil. Take E = 600cu and u = 0.5. The soil profile is shown below. G.L 0 m Layer - 1. Silty clay 4-2 Um y-19 m CM1+) -0.016 -3.5 m WT .4.0 m Layer-11. Şilty clay -2.5m y 18 tm? C/(1+0) -0.05 -8. Om Layer - III. Silty clay - 5 m y 19 t/m C/(1+0) - 0.06 -11.5 m Hard Soil

Please assist with Geotechnical engineering

Answer 1

As own CNC NOTE: amera end om Hence raus 8 Now per Skempton que elbibelle not pressur C - Cohesion Mo for o las footing [14 0.2DF + [1+ 0.23 B=44 L=5m Df = ? soil SPT value ie is to be given in the question hence . essuming or is Thien for finding depth of footing Depth (Base) of foundation is between ym Vsuy = re-ru [ 3.5+1-8) +(0.541-8) + Cux(1.8-9) = 1.34375 t/m3 we have gross presson or the box of booting so calculating het pression [(iso kulus?) (1.343040p)] Now equations, 15-(1,34306) have to find Cars = 2,25 3 [1s - (1,34307]] = 2.25 [12 0.38) (1.4)*5 - 6.094m Thence assump umption is correct, to check whether frosting is under allowable settlement or not hence not pressun -CNC Also we L Fos NOW

lorslit Dw 13 DA 713 By using IS Code method Va(net) = 0.88 NS Cw . settlement in mm In kW/m2 soil SPT Done on Depth of 1.5 to 2B Below foundation level N=15 (assumed) , Dw = Depth of water telle helow foundation in questions it is o Of = Depth of foundation B = width level and our case 11 Valmet) - 20143 t/m3 o 204.3 kN/m3 hence 204.3 = 0,88 x 15 x 's too [lt 0+3] DE+B Hience s = 38 mm The Foothing is safe.