Study On Designing Theory Of Pile Foundation-trimmer Beam-retaining Wall Structure

Pile foundation-trimmer beam-retaining wall is a new type of retaining structure. When the whole structure works collaboratively, the dynamical mechanism and the design theory are not perfect, which fall behind engineering practice. Combined with an engineering case in Chongqing, this thesis uses the method of combining theoretical analysis and numerical simulation to study the design theory of pile foundation-trimmer beam-retaining wall. The main results and conclusions can be expressed as follows.1. Without consideration for the interreaction of each part of pile foundationtrimmer beam-retaining wall, summarize the theoretical calculation system. Focus on the capacity properties considering the pile and joist as a whole, and the cross deflection formula of the beam and the regulation that the bending moment decreases and the shear force increases on the end of the pile are concluded.2. Establish a 3D finite element model, with using simple variable method, to study the change regulation of the stress of joist, the internal force of pile and the horizontal displacement of retaining wall, when joist thickness, pile gap, pile width and pile length change. Some conclusions are reached. The change of joist thickness, pile gap and pile width has little effect on the horizontal displacement of retaining wall. When pile length increases, the horizontal displacement of the bottom of the wall is well controlled. The maximum principal stress change regulation is that extremum appears at the supporting point of the pile, and the figure decreases from the supporting points of two piles to the middle between them. The change of joist thickness has little effect on stress distribution, so joist thickness can be abated when the bearing capacity of joist could meet the requirements. When the increase of pile length and width is beyond some range, the bending moment and the shear force will be influenced significantly. As for pile length and width, bigger is not always better.3. Use MIDAS GTS for numerical simulation for an engineering case to study the displacement change trend, stress distribution and internal force change regulation of each part of the structure. The conclusions are as follows. Horizontal displacement regulations of retaining wall, joist and pile are consistent. The displacement distribution of pile has direct effect on the displacement of joist and retaining wall. Internal force of joist is smaller than theoretical figure because of ignoring the counter force of the soil under joist, so this should be considered during design. The internal force and displacement of pile foundation are smaller than theoretical figures. When we design the structure, the size of pile or the reinforcement should be reduced properly while the retaining effect is guaranteed.4. Comparing and analyzing the theoretical calculation results and the numerical simulation results, a conclusion is reached that the regulations of soil pressure of retaining wall, internal force of joist and internal force of pile are basically consistent. The validity of theoretical calculation and the rationality of numerical simulation are proved.