Study On The Mechanism And Design Method Of Ram-compacted Piles With Bearing Base

In the construction process of the Puwanxinqu, the project encountered a complex geological condition. In this case, the ordinary precast piles and driven cast-in-place piles are both not up to the bearing capacity requirements. According to this case, a new type of piles, ram-compacted piles with bearing base, is adopted in engineering.Ram-compacted piles with bearing base have great differences with general piles. Ram-compacted piles with bearing base are typical end-bearing piles, carrying load by pile end mainly. The load carried by pile end accounts more than 80 percents of that carried by the entire pile. Ram-compacted piles with bearing base are more different from pedestal pile. In the procedure of pedestal pile construction, some high strength crushed stone was added, and after dynamic compaction, a dense structure was formed,thus an extended carrier structure was formed. The mechanical behavior of ram-compacted piles with bearing base also differs from general piles. Based on this situation, research in this thesis started.From the field trials, piles' Q-s curve, and the value of the ultimate bearing capacity of the piles are gained.According to the Q-s curve.a better check can be made for ABAQUS simulation. The value calculated by the bearing capacity characteristic number of ram-compacted piles with bearing base according to norm, is smaller than the value got in field trial. That is reasonable, because data calculated according to norm is conservative. The ultimate bearing capacity of ram-compacted piles with bearing base is more than three times than that of driven cast-in-place piles calculated in the same condition according to norm. Obviously, the ram-compacted piles with bearing base improve the bearing capacity of pile foundation in a large scale. In addition, to prepare for the simulation in next chapter, estimate the diameter of the expanded pile head of ram-compacted piles with bearing base using norm. At last, reasonable pile spacing is obtained by researching the optimal pile spacing of ram-compacted piles with bearing base, which coincides with pile spacing in construction drawing relatively.Using ABAQUS to simulate on Q-s curve build two models, ram-compacted piles with bearing base and general driven cast-in-place piles. They are based on the same conditions, the same geological conditions, the same pile diameter, and the only difference is the support section of ram-compacted piles with bearing base. Through simulation, two different settlement curves were obtained, and found that the Q-s curve of ram-compacted piles with bearing base is a slowly varying type according to the field trial and a large number of other tests. In Mechanical behavior, the force of ram-compacted piles with bearing base differs from general driven cast-in-place piles, showing a more uniform stress distribution around the support section of ram-compacted piles with bearing base. There is a common stress concentration phenomenon around general driven cast-in-place piles, which generates a great difference in the entire force system.Finally, the formul y=1-e-Ax A?(-0.00133,0.00108) was gained by curve fitting to the Q-s curves of ram-compacted piles with bearing, which can be use as a simple formula for on-site design and construction.