Question

Question 3 A 10 m square and 7.5 m deep pit is to be excavated in a soil with a unit weight of 20 kN/m2. What is the stress relief at 2 m. 5 m and 10 m below the centre point of the bottom of the excavation? b. The circular flexible area is uniformly loaded (q 320 kN/m2). Determine the change in vertical stress: i. at point A At a point 2 m below point A 4 m A Plan Ao 14m Cross-section [15+ 10 Marks] FIGURE QU 3b Variation of / r/R z/R 0.2 0.4 0.6 0.8 1.0 1.000 1.000 1.000 1.000 1.000 1.000 0.1 0.999 0.998 0,996 0.970 0.922 0.860 0.796 0.732 0.674 0.619 0.484 0.468 0,999 0,976 0.890 0.793 0.987 0.963 0.2 0.3 0.992 0,976 0.991 0.973 0.451 0,920 0.435 0.4 0,949 0.943 0.712 0.869 0.5 0.911 0.902 0.646 0.417 0.814 0.756 0.852 0.798 0.743 0.591 0.400 0.367 0.366 0.348 0.332 0.300 0.256 0.864 0.6 0.811 0756 0.701 0.646 0.546 0.424 0.286 0.200 0.545 0.7 0.699 0.504 0.467 0.8 0.644 0.570 0.688 0,9 1.0 1.2 15 0.633 0.535 0.416 0.591 0.501 0.392 0.525 0.434 0.377 0.308 0.447 0.355 0.248 0.286 0.197 0.145 0.086 0.268 0.224 0.196 2.0 2.5 0.167 0.127 0.191 0.180 0.151 0.135 0.082 0.141 0.118 0.146 0,087 3.0 0.085 0,080 0,075 4.0 3 of 4

Answer 1

Salu hon unit wt. a Seil Excavutrd 75m Ti tal Wt Excuvated =-20 x 7.5X10 X10 =-15000 KN -15000 --150 KN/m^ gntenity Jo m Can using Fadum D1ag10m, Stresses 5PM at Corner Hence diding found be to fuus bloc K Avea Jo m lo m 5m as Shau in F5m - 5m At dfpth o2m below Excavatrd Area Thjulen Foc tor dr?end on .h늘들. Sfrom Fadum Dagten) 5 2.5 Stre Relife 4 = -150xo. 2 4 dup to onr A 36 KN/m* veSign haw Stre Rehf) O24 kN/m2 Totul Stre Relifr due * 4 Block At depth o5m Ag n 5 m= - -150 x o.175 o.175 Stress Rhfr. 26. 25 K/m At Depth f lo m n 5 O.5 o.5 0.08 4 %e = - 150 xo.085 =4x (-12.15 51 KNM2

b 320 kJm Ит A Veshcal Shyei Changr .Ro Point A At Plan в Чт R. 6.33 A 2m O..332X 320 l06.24 kNm2 At Poin t below Point A suy Peint z 6m 1.5 R. и Aa O. 256 X 3 20 81.yR km. .AB