The mechanism analysed by Terzaghi is shown below.Note that it differs from the simple problem analysed above by having a transition region between the regions where the principal stresses are horizontal and vertical. Dr ..k. The shape of the footing also influences the bearing capacity.This can be allowed for by adjusting the terms in the bearing capacity equation. Fora continuous strip footing q=q,N。+YN,+cN Fora square footing qr =q,N 0.4y BN,1.3cN For a circular footing qr =q.N 0.6y BN,1.3cN. bove 4.2.1 Effective Stress Analysis Two situations can be simply analysed. The soil is dry.The total and effective stresses are identical and the analysis is identical to that described above except that the parameters used in the equations are c.Y rather than c.d.v If the water table is m ore than adepth of 1.5B(the footing with)belowthe base of the footing the water can be assumed to have no effect. .The soil below the base of the footing is saturated. IQ=qrBThe mechanism analysed by Terzaghi is shown below. Note that it differs from the simple problem analysed above by having a transition region between the regions where the principal stresses are horizontal and vertical. BEARING CAPACITY FACTORS [After Terzaghi and Peck (1948)] 60 50 40 30 20 10 0 20 40 60 80 N and N 0 10 20 30 40 ( d e g r e e s ) q c N  Nq N B D a b c d q=  D Qf f f Bearing capacity of a shallow foundation ULTIMATE BEARING CAPACITY OF CLAY ( = 0 only) (After A.W. Skempton) 0 1 2 3 4 5 D/B 5 6 7 8 9 N Circle or square Continuous c 5.14 B D N (for rectangle) = (0.84+0.16 ) N (square) L= Length of footing B L c q ult = cNc q = B N + cN + D N continuous footing 1 2 f  c  f q q = 0.4 BN + 1.3cN + D N square f  c  f q q = 0.6 RN + 1.3cN + D N circular f  c  f q qf = cNc + D c    Nc  BEARING CAPACITY THEORIES OF TERZAGHI AND SKEMPTON The shape of the footing also influences the bearing capacity. This can be allowed for by adjusting the terms in the bearing capacity equation. For a continuous strip footing q q N B f = s q + N + cNc   2 For a square footing qf = qs Nq + 0 BN + 13cNc .4  .  For a circular footing qf = qs Nq + 0 6 BN + 13cNc .  .  The analysis has been presented in terms of total stress. This can be used to evaluate the short term undrained bearing capacity. To evaluate the long term bearing capacity an effective stress analysis is required. This is very similar to the total stress analysis considered above. 4.2.1 Effective Stress Analysis Two situations can be simply analysed. • The soil is dry. The total and effective stresses are identical and the analysis is identical to that described above except that the parameters used in the equations are c´, ´, dry rather than cu, u, sat. If the water table is more than a depth of 1.5 B (the footing width) below the base of the footing the water can be assumed to have no effect. • The soil below the base of the footing is saturated. Df qs =  D Q = qf B u = uo