Behavior of buried box culverts on fill soil

Abstract

When reinforced concrete (RC) box culverts are located under heavy over-burden soil pressure, the overlying soil loading may produce 'beam bending like' effect in the longitudinal direction. This bending effect can induce considerable pressure on the culverts causing excessive deformations and cracks. So far there is no clear suggestion or provision available in the current codes and specifications to consider such influence of soil-structure interaction on the stresses developed in the direction of stream, except the provisions for the minimum reinforcement or distribution reinforcement. Analysis and design based on the 2-D plane strain condition is incapable of recognizing such stresses. In the present study, the 3-D finite element technique has been effectively used to analyze for stresses in the direction of stream under soil pressures considering soil-culvert interaction. The FE model developed in this study can be successfully used to investigate the effect of soil structure interaction on the stresses developed in the direction of stream. A detailed sensitivity analysis is carried out to consider the influence of different parameters on the soil-culvert behavior. The sensitivity analysis shows that soil fill height, length of culvert in the direction of stream, side slope, culvert size etc. have significant influence on the stresses developed in the direction of stream. Parameters like coefficient of friction of soil with concrete has little effect on the maximum bending moment originated at the mid span of the culvert. But it has considerable effect on the frictional drag along the culvert i.e. on the axial force in the direction stream. There is no significant change in stresses developed in the culvert when the extent of soil on both sides of the culvert is more than twice of the width of the culvert. Based on the findings of the sensitivity analysis, a semi-empirical equation has been developed to calculate the mid-span moment that may be readily used for design purpose without going through complicated numerical FE analysis. The validity of the proposed equation has been established by comparing predicted moments with those obtained from the FE analysis and it has been found that the proposed equation predicts moments with reasonable accuracy.