Evaluation of Settlement Prediction Methods for Shallow Foundations on Cohesionless Soils

Shallow foundation on cohesionless soils is one of the most economic and technically simple alternatives for bridge foundations. Typically, deep foundations (e.g., piles, drilled caissons) are explored only if shallow foundations are not technically viable, which in most cases depend on foundation settlement. Geotechnical design standards often limit the magnitude of allowable settlement for shallow foundations (such as 25 mm). However, estimation of foundation settlement on cohesionless soils depends not only on soil and foundation properties but also on the empirical/semi-empirical or numerical methods used for settlement computation. This paper compares shallow foundation settlement using four empirical/semi-empirical methods: elastic half-space method, Hough method, Schmertmann method, and Christian and Carrier method. Computed settlements are compared with settlement monitoring data collected for two ramp bridges over Interstate 80 in Monroe County, Pennsylvania. It was observed that modulus of elasticity and influence depths are not the same for all these methods which affected computed settlements. A comparison of the measured and computed settlement was also performed using the same influence depth and the same modulus of elasticity in all of the four empirical/semi-empirical methods.