Numeric Analysis For U-Shaped Abutment And The Study Of Crack Mechanism

With the rapid development of the base establishments,a new tide of traffic construction has been raised all round the country in last decades.A lot of huge gravity abutments(also called U-shaped abutment)have been constructed,because the high-grade highways were limited in road base width and pavement level,In the China western,huge abutments were becoming the popular due to the special geology and geography.The huge abutments mentioned in this paper are which the width and height are more and more larger than the common abutments' dimension.However,the abutments often happened to crack during the usage stage and the process of the building.The investigation has been indicated that the cracks of abutments present the regularity,such as the cracks took place in the joint of forward and lateral wall,the cracks located in the middle of the forward wall,the cracks developed in the process of filling the soil,furthermore,the width development of the cracks was so fast,etc. Because the most of cracks happened in process of filling the soil,it indicates that abutments are suffered to soil pressure induced by abutments padding.According to current specifications,abutment padding is reckoned in the abutment gravity,which used for calculating the whole stability of the abutments and carrying capacity of the ground fill but checking computations of soil pressure.Based on correlative research on abutments' crack problem being collected intensively and sorted,the influences of soil pressure on the abutments should be accounted into during abutment designed and constructed.Firstly,the soil pressure formula of lateral wall was deduced in this paper, which could be applied when the soil cracking face behind lateral wall is limited by another lateral wall.Secondly,we have performed the calculations,which included n number of various U-shaped abutments by the FEM(finite element method numerical analysis).Thirdly,the crack mechanics and causes have been analyzed by contrast of non-reinforced and reinforced abutments with various width and height.Lastly,the improved design method and reinforcement measures were put forward,which could be used as the theory guideline for further revising bridge criterions.The main research work in the paper includes,1)Based on the correlative data of researching huge abutments' destroy problems existed in domestic and foreign abutments,the research status of U-shaped abutments and problems existed during construction were analyzed.2)According to Coulomb theory,the calculation formula of soil pressure on lateral wall and applied conditions were given,when the soil cracking face behind lateral wall is limited by another lateral wall.3)We have performed the calculations with FEM procedure-MSC.NASTRAN software for the different dimensions of the abutments,and have analyzed the influences on abutments mechanism because of the changes of the widths and heights.4)Reinforcement methods,such as chamfered,pre-stress strand,and so on,were put forward in this paper.Comparing the variety orderliness of displacements and stresses for the reinforced abutment or improved abutment with that of non-reinforced abutments by MSC.NASTRAN software.The reinforcement effects were validated.5)Suggestions on design and construction of U-shaped abutments were brought forward,which could be as theory guide and references.