G-8 E-1

Example Problem:

1.     A footing of 3.6x3.6 size for a tower carries 700t load and rest on a 6 m dense sand layer overlying by 3m clay layer. The depth of foundation foundation is 2m at 2:1 load distribution. Liquid limit of soil is 56% and void ratio is 1.08 . The saturated unit weight of sand and clay are 1.8 g/cc and 1.7 g/cc respectively.

i.                  What is the ultimate consolidation settlement of clay layer?

ii.               What is the Max. effective stress at center of clay layer at the end of consolidation

Ans:

Consolidation settlement  

               

               Cc  = 0.009 x (W_L-10)

                      = 0.009 x (56-10)

                      = 0.414

                  H = 3 m

                 e_o = 1.08

     

                                         = 5.85 t/m²

For 1:2 load distribution, the change in stress stress is

It is a square footing So..

                            

     

                                                 

                                                Sf= 0.187 m 

2.     In a laboratory the clay sample of thickness 25mm drained at top only.50% consolidation occurs in 11 minutes. Assume                           T₅₀=0.19                                  T₇₀ = 0.405.

i.     Find the time required Corresponding clay layer in field of 3m thick and drained at top and bottom to undergo 50% consolidation.

Ans:

              H₀ = 25mm       ;   U= 50%           ; t= 11 min

             T₅₀ =0.197          ;  T₇₀ =0.405      ;

      

ii.The clay layer loaded for 4 years and the settlement was found to be 50mm. The ultimate settlement expected as 300mm. Estimate the settlement in 6 years.

Ans: