EFFECT OF VIBRATIONS ON SKIN FRICTION IN PILES

Abstract

The behaviour of friction piles subjected to vertical vibration has been studied in this investigation. Pulling resistance of friction piles depends upon a number of factors. The effect of frequency and acceleration of vibrations, the number of revolutions, the diameter of piles and the relative density of sand has been studied. In the present investigation three R.C.C. piles models were tasted of 2.25 cm, 3.5 cm and 5.5 cm diameter each 60 cm in. length. The relative density of sand deposit was 13.5% ; 25% and 80%. Tests were performed in a tank of 30 cm x 30 cm x 75 cm Mounted on the vertical vibration Table. The required amount of sand was deposited in tank and vibrated to the required density. The static resistance for each case was found out. A fixed percentage of static resistance was applied and the pile vibrated till it was pulled out 2 cm. The number of revolutions were noted. An expression for the dynamic resistance has been established in terms of all the variables studied. It agrees well with the observed value's. It has been observed that the dynamic resistance to pulling increases with increasing frequency of vibration, (x) diameter of pile and the relative density. It is found to decrease with increasing acceleration of vibration and .number of revolutions. The coefficient of lateral earth pressure 'K' has been calculated and compared with Rankine's value. It has been found that 'K' is very nearby equal to Rankine's passive value in case of medium and dense sand. But in the case of loose sand, this value is low, nearby 1/4th of Rankine passive case. This reveals that before the full shearing resistance of the soil could be developed around the pile, a slip occurred between sand and pile. After the dynamic test was observed, in most of the cases, this resistance was less than the original one which shows that there was no increases in the density of sand after dynamic test. This is due to fact that the energy imparted during compaction was more than that during the dynamic test.