Bearing Capacity of Expanded‐Base Piles with Compacted Concrete Shafts

A data base of 70 loading tests on expanded‐base piles with compacted concrete shafts has been collected to develop empirical design correlations based on standard penetration N‐values. Both shaft and point resistances, $f_s$ and $q_p\text{,}$ were found to increase with depth and with increasing N‐value. It appears that limiting values of $f_s$ and $q_p$ might be approached for initially loose sands at D/B ($D_b/B_b$) ratios greater than 12; however, at greater relative densities, both $f_s$ and $q_p$ continue to increase with depth, but at a decreasing rate, indicating an important scale effect. A modification to traditional bearing capacity theory is used to show that the so‐called scale effect arises because the bearing capacity factor $N_q\text{,}$ which is a function of the friction angle of the soil, decreases with depth or increasing effective overburden pressure; consequently, point resistance increases with depth at a decreasing rate. About 40% of the data base was used as an independent means of evaluating the accuracy of the empirical correlations developed.