Question

1. A 2 m high road embankment is to be constructed in order to raise the level of a road above the potential flood level. Consider the data shown on Figure 1 and determine the vertical effective stress (ov) at Points X and Y (which are at the centre of the two soil layers) (i) before the road is constructed, (ii) immediately after construction of the road embankment and (iii) many years later. . . . . . . . . . . . . . . 2 m · New road embankment unit weight of fill (Y) = 18 kN/m3 Groundwater level V 2 m V Soil A: Yan= 16 kN/m3, = 19 kN/m3 0.5 m coefficient of permeability (k) • Point X = 1x10-3 m/s - - - - - - - - - - - - - . . 3 m • Point Y Soil B: y = 21 kN/m2, k = 1x109 m/s - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Figure 1 You may have to refer to Notes on Topic 11 to understand permeability values. 2. Considering the initial condition before the embankment is built recalculate the ov' at Points X and Y assuming the 0.5 m of dry soil becomes saturated by water under capillary pressure. Would you be concerned about this change from a practical design viewpoint?

Answer 1

Bil 18 kN/m3 18x2=36 kN/m2 Там — Т . 736 kN/m² 12m 40.5m 2m at X, 5= 16X0.5 + 1980s © before the road re-19=0] ① immediately after construction s=o-u 8 Ydryx 0.5+ (Ysat-Yw) x0.5 = 16X0.5+ (19-9.812*0,5 + 36 = 12:595 kN/m² = 53.5 kN/m2 U= Li +36 = 9.87X0.5 og's YaryX0.5+ (Ysat 1 - Yw) xl-5 +36 - 40.905 + Ysat)2* 1.5 rls 53.5-40.905 = 16X0.5+ (19-9.813x1,5 = 12.595 kN/m + 21x1.5-9.81X15 (so no change) - Seven knim ♡ similarly at y 38.51 No change ♡ after long time o2 Sep 23 KNM o's 5-4 at , sr 16x0.5+ 18x0.5 +36-53.5 kN/m2 4,5 30 9.81405+0 = 4.905 Knimi ola 48.595 kN/m2 at 8,51680 5+ 19x15 +2131:5+36- 104 kwimu 9.81x3: 2943 Oleo-45 104-29.843 = 74.57 km de = 38.57

4-9.84*0.5 9.81805 at o X and Y , tgoet Pore water press. remains same. only total stress change. as Ydre Ysat ③ at BY 1① Atx - 19x2 +21X1, us 9.81X3 re 19x1 = 19 Knim u=9.81X0.5 olo 40.07 kN/me 5= 14.055 kome = 29.43 a 69.8 KNIML