PENETRATION OF VERTICAL PILES UNDER LOW FREQUENCY LONGITUDINAL VIBRATIONS

Abstract

The vibratory method of pile driving is relatively of recent origin which is proving more economical under certain conducive conditions. The large miter of variables involved in the phenomenon make the study complicated and hence not amenable to mathematical formulation at this stage. Experimental work reported in this field is mostly limited to snail scale model tests which have yielded only qualitative results (Kodner and Edwards 1960, Bernhard 1968 and Schmid 1969). Ghumman (1985) has reported model study on relatively large size model, but the influence of various parameters has not been studied. The experimental data has been analysed on the basis of non-dimensional approach. Analytical approach proposed by Hejazi (1963) is based on certain idealized conditions. The proposed equations are lengthy and complicated. A unique solution of the equation is not possible. Present study deals with the penetration behaviour of vibro-pile driving in dry sand on the test set-up developed by Ghumman (1985). To study the various parameters in.fluencing pile penetration behaviour four different diameters of piles and different materials (three steel piles diart 3.1 cm, 4.9 cm and a RCC pile of diameter 6.0 am) are chosen. These piles are driven under four different vibratory conditions (f 10,20,30, 40 cps and FiFs = 48.6/30, 63.9/30, 80.7/30, 114.9/30) in three different states of compactness of sand (Dr= 39.2, 54.8 and 62.6 7.). Analysing the data obtained from various tests it is Observed that under low frequency longitudinal vibrations the pile initially penetrates suddenly into the sand (termed as Ys), then continues to penetrate at a slow rate (termed as Ym) and finally keeps on osc illating without any further penetration. Thus, the total depth of pile penetration, Yu could be considered to be made up of two parts namely Ys and Yu. The pile penetration Ysterm and Yu decrease as diameter of pile increases and also relative density of sand increases. The maximum depth of penetration is noted at 20 cps which probably is close to the resonant frequency in the present conditions. Ym, the time —dependent penetration and the decaying part of its tima— penetration curve can be simulated by an equation of exponential form involving a constant, K which is an index of measure of pile penetrati