Comparison of Bearing Capacity of Shallow and Deep Foundations Based on Sondir (DCPT) Data: A Case Study of Office Building Rehabilitation in Medan City

Abstract

Foundation design requires accurate knowledge of subsurface soil bearing capacity, particularly for building rehabilitation projects where structural loads may change. This study evaluates and compares the bearing capacity of shallow and deep foundations based on Dutch Cone Penetrometer Test (Sondir/DCPT) data collected during the rehabilitation of the BKKBN Regional Office Building on Jl. Gn. Krakatau, Medan, North Sumatra. Two sondir points (S-1 and S-2) were tested using a 2.5-ton capacity cone penetrometer following ASTM D3441 procedures, reaching maximum depths of 5.40 m and 4.60 m with cone resistance (CR) values of 209 kg/cm² and 205 kg/cm², respectively, both classified as very dense soil. Shallow foundation bearing capacity was calculated using the general Meyerhof approach (Qa = CR/40) for footing widths ranging from 125×125 cm² to 200×200 cm², while deep foundation bearing capacity was calculated using the De Beer method for driven piles and bored piles with diameters of 20-60 cm. The results show that at a depth of 3.00 m, the allowable bearing capacity of a 200×200 cm² shallow footing reaches 82,000 kg (S-1) and 61,000 kg (S-2), while a single driven pile of 40 cm diameter at the maximum tested depth provides 94,082.77 kg (S-1) and 92,156.91 kg (S-2), consistently 7-8% higher than a bored pile of the same diameter due to soil densification during pile driving. The comparison indicates that shallow foundations are technically adequate for this project given the shallow occurrence of very dense soil, while deep foundations remain preferable where higher loads, groundwater interference, or long-term settlement control are governing design considerations.