Question

A new concrete water tank (unit weight= 24 kN/m3) with inner diameter of 13.8 m with 0.1 m wall thickness, and 9.0 m high is proposed for construction to cover the water shortage of government officers’ quarters that located near to an existing 6.0 m high concrete water tank with similar diameter. The existing water tank sits on a concrete foundation of diameter 15.0 m and thickness of 0.6 m which is below the finished surface level. The existing water tank has fully loaded to its capacity up to a height 5.8 m (unit weight = 9.81 kN/m3) during the construction of the new tank. The new water tank is located at a distance of 4.0 m centre-centre to the existing concrete tank. The new tank sits on a similar foundation as the former. The foundation bottom is 0.6 below the finished surface elevation. The soil consists of 5m thick soft, overconsolidated silty clay and overlain by 1.0 m silty sand. The clay layer sits above a very thick layer of completely weathered mudstone, more than 10 m thick. The groundwater level is 0.6 m below the surface level.

The geotechnical data of the soft clay gave Cc = 0.28, Cr = 0.06, Cv = 40% we = 7.427x10-5 m2 / day, sand = 30% and OCR = 8. The specific gravity of sand and clay are 2.6 and 2.7, respectively. Assume Poisson ratio, v=0.35. W clay

Please make any additional reasonable assumptions that you feel necessary and please state its resource clearly.

a) Estimate the immediate settlement under the centre of new tank just after the construction with both tanks full.

b) After 6 months of service having both tanks are full, estimate the primary consolidation settlement of the clay layer under the centre of new tank.

c) As an engineer, comment on the impact of the soil total settlement due to both tanks considering allowable settlement is 25 mm in this construction.

Answer 1

New tank (2) Existing tonko om 4m Im 13.8m 13.8 6 m Finished duism prithm_ja loom surface GWT Tm Silty Sand 47:26 5m soft clay 6 9 2.7 Gliveu, C = 0.28, G = 0.06, C = 7.427 xio'm m² 1 day OCR = 8 Self weight of of existing took 0 Wt & foundation (15)?x0.6x24 - Ascax height x Unitwt. 254 4.7 KN wt of tank wall = 7 1 14² 13-8/² x 6 x 24 = 628.82 KN Total weight of tank along with foundation E 3173.5 KN Similarly weight of New tank@ = x(142-13.82) x9x24 wt. of tunk wall 943.2 KN Total weight of Neue tank with foundation = 943-2 + 2514.7 3487.9 KN =

When water is full in both tank. 0.2 m arcuming 14. of water in front tunk = free boat. WA Vox KR²h - 9-81x 18(13:9965-8 - 8 510.3 KN wt of water in New tank when fully filled Yux ap²h = 9.81 x x 8.8 ax | 13:5.)?* 12912:2 KN q ܀ = Wt. per Unit area o below the new tank, 1 2912.2 + 3487.9 KN Area of foundation 16400 92.8 kN/m2 115) @ initial settlement below. New foundation q* B 11-02) It Si E I = influence facter, for cisular. If = 0.8 Where Given V: 0:35 & Eef Silty Sand = 12x106 kN/m2 Si = 92.8 x 15*(1-0-352) * 0.8 12 x10+ 0.0081432 mm initial settlement below new tank : 8.143 mm

After six month AH = Cc Ho of Service. lte. logu (5.0*05) 4m TS ism 62.6, wa zor. 0.4 e 0.78 2.5 day 2.9 2.9 Se W61 G: 27 eo - D•4x2.2 W: 40Y S-1007 clay . 108 The above diagram in 1:1 (1:14) Load disperssion belowe the soil and the existing tank's poossure bulb not affecting the the pressure bulbs of new tank, up to the mid layer depth of clay. Vw Crse) siH - ite Yout of sih = 9.81(2.67 0:48) 18.62 KNIm - 1.78 Vset of clay = Yw 1697 se.) 14. = 9-81 | 2711:08) 1 +1:08 = 17.82 kN/m. 29 Ő at the mid layer of clay = 0.418:62 + 1762*: = 23.56 kN/m2 9x115) = 48.26 kN/m2 91 + 15+2x29)?

AH H.Gc log lo Tim ) Iteo 5x0.28 11:08 log 23.56 +18.26 23.56 :0 0.03258 m :: Total Selllemet 003258 m final settlement more than 25mm As from above calculations the ix Coming as Iwe should Modifie the Design. SO

● So tank have 14 m outer diameter and 13.8 m inner diameter beacuse it have thickness of 0.1 m both sides.​​​​​

Thank you.