Study On Differential Settlement And Treatment Technology At Bridge Approach Zone In Soft Soil Foundation

With the rapid development of Chinese national economy, the investment and construction of highway engineering have been promoted. However, during running process of highway, various diseases appear more and more frequently, and bridge approach bump is one of the most difficult problem to be solved. It is particularly remarkable in soft-soil foundation. The bridge approach bump not only seriously influences the safety and comfort of driving, but also consumes much maintenance cost. So it is significant for the engineering practices to take the effective measures to prevent and treat the bridge approach bump.In view of this mentioned above, in this paper, the differential settlement distribution is presented through the analysis of the field surveys at first, and the evaluation method and grade classification of bridge approach bump are also put forward; And next, the construction of bridge approach backfill is simulated with ABAQUS finite element software, and pore pressure in the ground, lateral earth pressure of abutment and post construction settlement are deeply analyzed with the different soft soil, pile length and backfill, and the optimum scheme, which combine the composited foundation and light weight backfill has been given for bridge approach backfill. In the final, the construction technology of new lightweight backfill and transversal bored-hole replacement is presented to control the differential settlement and treat the bridge approach bump. The research results and some conclusions can be summarized as follows:(1) In accordance to the analysis of survey data, one can conclude that in the transitional zone the different distresses results from the bridge approach settlement, which is mostly composed of post-construction settlement due to soft soil consolidation. According to the highway grade, design speed and comfortable index of driver and passenger, the allowable differential settlement are presented, and the evaluation method and grade classification of bridge approach bump are also given.(2) The results of numerical simulation indicate that the consolidation of soft soil include two phases:in or post the construction, and the factors are dominant for ground consolidation, which are the permeability of soft soil and the unit weight of backfills. The piles composed of gravel can improve the drain condition of soft soil and speed up its consolidation process or decease its post construction settlement. The post construction settlement is become less when the pile length is decreasing. The self-weight of backfills is the direct source of external forces. The additional stress, post construction settlement and earth pressure are become more when the unit weight of backfills is increasing. Therefore, with application of the reasonable pile length and light weight backfills, the post construction settlement can be effectively decreased.(3) Based on the engineering application and numerical simulation of the construction technology, on can draw some conclusions:the light weight backfills, which is mixed with the ashes of rice husk and fiber reinforced soil, can make recycled use of waste of crops such as rice husk and wheat straw, and decrease the self weight of backfills and prevent the bridge approach bump resulted from differential settlement. The transversal bored-hole replacement also can make cycled use of industrial waste such as dredged silt and fly ash. And it can be used to replace the subgrade soil with light weight backfills, which can expand and make a jack-up action on the upper soil and then decrease the differential settlement to treat the bridge approach bump.