Analysis On The Different Settlement Characteristic Of Highway Widdening Subgrde In Retarding Basin Soft Soil Subgrade Area

The biggest problem is the excessive differential settlement between new and old subgrade in freeway widening project. The excessive differential settlement can make road produce additional stress and cracking damage, and thus the safety and performance of the road are effected. Settlement mainly come from the ground in soft freeway widening project, and then reasonable and effective program must be taken to control the differential settlement. It has been found that pile-soil composite foundation can effectively alleviate this problem. However, widening foundation is a complex system of interaction among new subgrade, old subgrade and foundation. The effect of pile-soil composite foundation under load in widening subgrade on controlling settlement and settlement calculation are not clear. There are not any design specifications to follow, and they mainly rely on experience and technology, and so on. So this paper based on the actual highway projects of broaden soft foundation in detention areas to calculate the settlement as the goal, and different composite foundation treatment programs were as the main line. The treated options of road widening soft detention basin were evaluated and optimized by using the finite element simulation and field deformation observation. The main contents are as follows:(1) According to the investigation reports and soil test results, the physical and mechanical properties of Retarding Basin of Laowangpo, and differences of the soil body under the new and old subgrade were analyzed in order to provide the basis for numerical calculations.(2) The applicable conditions of two-dimensional model and three-dimensional model in finite element aiming at the road widening were analyzed, and the shortcomings of using traditional two-dimensional modeling in the soil pile composite foundation were discussed. A three-dimensional model of broaden subgrade was established by using finite element software, and the three-dimensional modeling processes based on the actual situation of the project site were introduced.(3) The ground treatment of detention areas of Laowangpo was made a deformation analysis by using the finite element method and numerical simulation results of the design scheme were obtained. The rationality of the foundation treatment plans were evaluated and optimized based on the calculation results of differential settlement.(4)According to the programs used in the detention process, the effects of pile length, pile diameter, pile spacing, affect change pile modulus, modulus of cushion on the differences settlement of widened subgrade were analyzed respectively.(5) The typical sections of retarding basin were selected to observe the deformation of the subgrade. According to the observed results, curve fitting was commonly used in settlement prediction to predict the final settlement of the observation point, and verify the effect of control settlement of CFG and numerical methods accuracy.