Abstract：In-situ full-scale tests on stress characteristics of composite foundation with sparse T-shaped rigid piles were carried out under the condition of experimental section of Shanghai—Nanjing Expressway widening project. Based on the test data，the level and distribution of pile-soil stress were analyzed；and the pile-soil stress ratios calculated with different methods were studied. The results indicate that pile-stress concentration effects are related to the embankment height and the sites of piles. Pile-stress concentration effects can be found if the height of embankment constructed with soil mixed with fly ash and lime is larger than 120 cm；and they will not be encountered under the embankment slope near slope-foot. The pile-stress concentration effects of the piles in the middle of composite foundation are greater than those of the piles at the range of composite foundation. The bearing capacity of soils under the pile-cap works only when pile-stress concentration effects are great；and the difference between the stresses on the caps and those under the caps all indicate that the soils under the caps are nearly separated from the caps. Pile-soil stress will be adjusted continuously during embankment construction；and the observed pile-soil stress ratios range from 1 to 12. The observed pile-soil stress ratios can not correctly reflect the stress characteristics of composite foundation with sparse T-shaped rigid piles under widening embankment；and it is suggested that pile-stress concentration effects should be evaluated with pile-site stress ratio.
