Centrifugal Study On Sidewall Friction Of Caisson In Sandy Soil

Sidewall friction is a crucial factor that prevents a caisson sinking. This topic has been however less studied by scholars so far, though much experience has been obtained through numerous caisson projects. Inadequate data of distribution pattern of sidewall friction measured, particularly those satisfactory, is one reason. Another factor might be a dearth of well-established calculation methods. Experimental studies related are even rarer. In this dissertation, a caisson buried in different depths in homogenous sandy soil was modeled in centrifuge, and a clear distribution of soil pressure on sidewall was found. Strengthened by FEM analysis, some following conclusions are drawn:(1) Soil pressure reaches its maximum at a certain depth of caisson sidewall. The distribution shows a general upward trend before this depth, whereas pressure falls in the area deeper, with downward phase much close to linear development. Rational function is found suitable fitting this distribution.(2) Test results indicate the position of maximum pressure is at 40%～50% area of sidewall in depth. Pressure falls to 64.5% of maximum pressure at the 89% depth area near the bottom. FEM results point that soil pressure can fall to 55%～72% of maximum at the bottom.(3) The contact pressure beneath caisson was found highest at corners, followed by borders and center. A square area is proposed as corner area to calculate contact pressure in this paper, with side length equals to 1/6～1/5 of shorter edge of caisson sidewall. The average corner pressure equals to that at square center.(4) FEM analysis shows deformation in sidewalls can affect horizontal distribution of soil pressure. Shorter edge of caisson shows a higher pressure than long side. When compared at the same depth, the pressure is lowest at central line on the longer edge, and goes higher at the area close to border. Conversely, the highest value of soil pressure is found at central line on the shorter edge.(5) The average friction angle between sidewalls and surrounding soil, by calculation based on test and FEM results, is showed much closed to 2/3 of internal friction angle of test soil in value.