Chittaranjan Patra

The deformation behaviour of footing under the load from the superstructure is fundamental to foundation design consideration. The deformation of footing changes when subjected to moment along with the central vertical load. The application of moment on footing can be derived as a load eccentricity from the central axis. Due to the load eccentricity (moment), the footing is subjected to rotation (tilting) along with settlement. The average settlement of footing along the central axis also increases with the increase in load eccentricity for a constant load. In these circumstances, the deformation of the footing can be decreased by adding a circumferential skirt around the footing. A series of model tests have been conducted in dense sand on a square footing of 10 mm width (B). The skirt length (L) varies from 0 to 1B, and load eccentricity (e) ranges from 0 to 0.15B. The effect of the skirt length, footing embedment, and load eccentricity on the behaviour of load–settlement and moment–rotation curves have been presented. Based on the model test, empirical formulations have been developed to predict the settlement and rotation of skirted footings.

The present study focuses on the development of an Artificial Neural Network (ANN) model equation to estimate the average ultimate load of shallow circular foundation on a sand layer of limited thickness underlain by a rigid rough base subjected to an eccentrically inclined load. The model is developed using the 260 number of data points obtained from extensive laboratory model tests. The input parameters considered are depth of embedment (D_f/B) of the foundation, thickness of the sand layer to diameter of foundation ratio (H/B), eccentricity ratio (e/B), and load inclination to friction angle ratio (α/ϕ) to estimate the reduction factor RF as output. The RF is the ratio of the ultimate eccentrically inclined load on a sand layer of limited thickness to the ultimate eccentrically inclined load on a sand layer, which is extending to a great depth. Importance of input parameters, which reflect the output, is studied using Pearson’s correlation and Spearman’s rank correlation. The sensitivity analyses are carried out using Variable Perturbation methods and Weight methods. It has been professing that H/B ratio is the most important input parameter.

An empirical non-dimensional reduction factor has been developed in this paper using 192 laboratory model test results of the previous studies made by authors for a strip foundation supported by sand and subjected to eccentrically inclined load for both types of loading, i.e. line of load application inclined towards the centre line of the foundation (partially compensated case) and away from the centre line of the foundation (reinforced case). The reduction factor is the ratio of the ultimate inclined load per unit area of the foundation subjected to an eccentrically inclined load (i.e. partially compensated or reinforced loading) to the ultimate bearing capacity of the same foundation subjected to a centric vertical load at the same embedment ratio, D _f/B. The developed reduction factor has been compared with those based on the earlier bearing capacity studies in this area available in the literature. The comparison seems to be reasonably good.)