(1. Institute of Geotechnical Engineering，Zhejiang University，Hangzhou，Zhejiang 310058，China；2. Key Laboratory of Soft Soils and Geoenvironmental Engineering，Ministry of Education，Zhejiang University，Hangzhou，Zhejiang 310058，China； 3. Zhejiang Electric Power Design Institute，Hangzhou，Zhejiang 310014，China)
Abstract Two groups of tests have been conducted in a large-scale model chamber，and each group contains four uplifting tests with embedment ratios(embedment depth to enlarged base diameter) of 1，2，3 and 5，respectively. One group of tests was conducted in unsaturated slit with degree of saturation of 49% and the others in saturated silt soil. The effects of soil saturation and embedment ratios on the ultimate bearing capacity and the failure patterns of the enlarged base piles are discussed. It is found that the uplift ultimate bearing capacities of the enlarged base piles decrease 30%–50% while the degree of saturation of silty soils increases from 49% to 100%，but 8 and 12 times larger while embedment ratios increase from 1 to 5 in unsaturated slity soil and saturated slity soil，respectively. The failure pattern of the soil around the pile changed from inverted truncated cone slip-surface to local failure around the enlarged base with the increase of embedment ratio.
