Study On The Pile Force And Settlement Influence By Pile Length Of Rigid Pile Composite Foundation In Saturated Soft Soil

The application of rigid piles shows significant effectiveness and economic value in foundations that pales in capacity and settlement behavior, which can be frequently seen in ocean construction where soil is soft around piles. While the studies on calculation methods of piles-soil interaction and bearing ratio are temporarily inadequate, leading to less developed use of rigid piles. In this dissertation, the rigid piles bearing and settlement behaviors affected by pile length is studied. The conclusions are obtained by use of centrifuge tests along with numerical and theoretical analysis:1. The piles on the edge of the applied load present a smaller axial stress and accounts for40%of inner piles. The neutral point depth of one second at pile length is observed at these marginal piles, much deeper than inner piles, and the larger total negative skin friction of marginal piles is seen. The data captured during the centrifuge tests also shows the pile bottom and pile top axial stress ratio is above50%, therefore pile length effects on settlement is smaller than that from load.2. The further study on bearing and settlement behavior of composite foundation enforced by rigid piles is then presented in this dissertation. The consolidation of soil between rigid piles and its compressive settlement cause the constant existence of negative skin friction on piles top. For a single pile unit, the unit load is firstly undertaken by shaft resistance and rest part is then shared by pile top and the surround soil on the top.3. The calculation model for pile-soil interaction with uniform load effect is established in accordance with the bearing and settlement performance of rigid pile composite foundation. Based on cavity expansion at pile bottom, this dissertation proposes the formula for bearing behaviors of pile. By the use of iteration, axial stress distribution on the pile and penetration in the soil are then obtained. The calculated result indicated a13%maximum deviation compared with test data and14%with numerical method.4. The shaft resistance distribution along the pile is concluded:An inverted triangle shaped distribution is observed at the part of pile above the neutral point, while a different tends is shown below the neutral point at which the value increases at first and then remains unchanged. 5. The increase in pile length can result in a better bearing and settlement performance of composite foundation in that when the total shaft resistance increases, the small penetration at pile bottom causes obvious stress at pile end, therefore the further penetration is significantly restricted.