Question

1. An 8-m thick normally consolidated clay layer is doubly drained as shown below. (This means that a very pervious layer compared to the clay exists on top of and under the clay layer) The embankment applied an average vertical stress increase of 100 kPa to the clay layer. The water table is located at the mid depth of the sand layer. Assume the sand above the water table is dry 0 Pore water pressure, u (kPa) 20 40 60 80 100 120 140 160 180 200 7.-20 kN/m Sand 7-21 kN/m Soft clay Y. 22 kN/m e, -0.6 OCR-1 Ce-0.25 3x10 m/s Dense sand Depth (m) -24 kN/m a) Fill the table below, and estimate the excess pore water pressure (Au) remaining in the clay after 5 years for the depths in the clay layer of 0, 2, 4, 6, and 8 m. Show a sample caleulation for 2 m. Depth from ground surface (m) z (m) in the clay layer z/Har U. (9) Au (kPa) (t-Syears) 6 b) On the graph provided above, plot the initial pore water pressure before the load was applied (1-0) the pore water pressure after the load was applied (1-0), and the pore water pressure after 5 years (1-5 years). Use y 10 kN/m' for your calculation. e) Compute the primary (final or ultimate consolidation) settlement(s) to I decimal place in ſem Primary settlements (em) d) How much settlement would you expect to occur in 5 years to I decimal place in (cm)? Settlement (cm) 1-5 years

Answer 1

biven for initial effective Stress (=0.25, Co=0.6, Cu= 3x10 m/ AT = 100 kPa. Ho=8m. To = 8 d x2 + rsat x 2 + rsat x4 Jo=20x2 +21x2 + 22xU Jo = 170 kN/m² (c.) A H= C, Ho 1o go [Foto] Primary ltlo settlement. AH = 0.2588 Ito 6 AH = 0.25lm AM = 0.25 x 8 logio [170+100] 170+100 170 ř 25cm. (d) To Cut Tu= 3x10 - 8 x 5 x 365x24x60x60 Tu= 0.295 = 60% consolidat Tu= I UZ 0.295 - 7 8% so U% = 60% → 60% of 25cm = 15cm. settlement in 5 years. (e.) Tgs = Cut - 1.163 = 3x108 t t = 20 years. (8/2)² d 2

loc=0.04 Hoo H.-AH ColccHool Itloo t = 8 100 years - 8- 0.25 = 7.75 m tioo= 20 years 100=0.6 Secondary - settlement = 0.04 +7.75 10910 [1200 (+0.6 13.5 cm. So total settlement - 25+ 13.5 = 38.5cm. after 100 years

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