Question

Describe how you would prepare the site has the following properties for use within 8 months. A soft clay deposit with Su= 20 kPa (from qu tests) is 9 m thick and is underlain by a dense sandy gravel. The site is to be used for oil storage tanks. The water table is approximately at ground surface. The area is 400 X 500 m. Other soil data include the following: kh = 3.8 × 10-6 m/s , L.L = 60%, PL = 31% , wn = 55%, Gs = 2.60 , ch= 3cv and cv = 8.64 × 10-4 m2/day. The tank pressure loading including tank and oil is 135 kPa. The tank has a diameter of 10 m, and it is desirable that the tanks not settle over 20 mm additional from the preload position when filled. How would you control the anticipated settlement in the clay prior to installing the storage tanks?

Note: assume reasonably any data you may need.

Answer 1

   = 16.27 kN/m³

= 16.27 x 4.5 = 73.215 kPa at centre of clay layer

= 135 kPa

   = 0.756 m

= 756 mm > 20mm

Therefore ground improvement should be done such as installing stone columns and vertical drains to increase the rate of consolidation by radial drainage.