Department of Civil Engineering, Indian Institute of TechnologyRoorkee, Roorkee,

Abstract

Experimental investigations on ultimate lateral load capacity of helical anchor piles embedded vertically in sand have been presented in this study. A brief literature review depicts the consolidated view of the work done by the previous investigators. Two sets of model helical anchor piles, each comprising of single, double and triple helical anchor plates have been used in this investigation. The only difference between the two sets is the diameter of helical plate, first set having 50 mm diameter helical plate and second set having 80 mm diameter helical plate. Tests with first set were conducted by varying embedment ratio (L/d = 14, 18 & 22), the number of helical plates (n = 1, 2 & 3) and eccentricity (e), the vertical distance between the soil surface and the point of application of lateral load (e = 90 mm, 120 mm & 150 mm). Tests using other set have been conducted by varying the above parameters in the same manner except eccentricity which has been taken as 90 mm and 120 mm. only. The helical anchor piles were pre-installed in test tank. Sand was weighed in batches and was laid in the test tank in 50 mm thick layers, around the pile, which was held in position in the centre of the tank. The unit weight of sand at relative density of 80% was calculated and maintained by compacting each layer with a drop weight tamper. The results indicate that the ultimate lateral load capacity of helical anchor piles increases with increase in embedment length, number of helical plates and decreases with increase in eccentricity. An analytical analysis has been developed to predict the ultimate lateral load capacity of helical anchor pile embedded in dry sand. The analysis is based on equilibrium of forces. A best fitted equation based on the test results has also been developed. The validity of equation has been checked by conducting some field tests on full scale helical anchor pile. The results of the field tests showed the equation to be on safer side. A comparison between the experimental values of ultimate lateral load from the data given by Prasad and Narasimha Rao and the theoretical values of ultimate lateral load capacity calculated from the equation developed in this study has shown good agreement. Other comparisons also point towards acceptable pattern of the results.