of of

This curve can be used to estimate the values of a for piles with penetration lengths less than 30 m. As the length of the embedment increases beyond 30 m, the value of a decreases. Piles of such great length experience elastic shortening that results in small shear strain or slip at great depth as compared to that at shallow depth. Investigation indicates that for embedment greater than about 50 m the value of a from Fig 15.15 should be multiplied by a factor 0.56. For embedments between 30 and 50 m, the reduction factor may be considered to vary linearly from 1.0 to 0.56 (Dennis and Olson, 1983a, b)

Skin Resistance by A-Method Vijayvergiya and Focht (1972) have suggested a different approach for computing skin load Qjfor steel-pipe piles on the basis of examination of load test results on such piles. The equation is of the form

(15.40) where A = frictional capacity coefficient,

~ =mean effective vertical stress between the ground surface and pile tip. The other terms are already defined. A is plotted against pile penetration as shown in

Fig. 15.16. Eq. (15.40) has been found very useful for the design of heavily loaded pipe piles for offshore

structures.