Control criteria for differential settlement of widened road

The additional stress imposed on different pavement structures with differential settlement between the new and old foundations of a widened road is studied. By the use of a large-scale ground differential settlement simulator, full-size model tests are performed to study the strain response and the deformation behavior of pavement layers. The results show that under the effect of differential ground settlement, the asphalt cement wearing course is subjected to tensile stress. Plastic deformation will develop in both layers when the differential settlement reaches a value of 14 cm, which is recommended as the critical control standard for ground differential settlement. On the basis of the model test results, and with the differential settlement at the bottom of pavement as the constraint condition, a two-dimension finite element model is established for the uncoordinated deformation of the subgrade, which is used to study the stress variation of different pavement layers in response to differential settlements of varying magnitude. The results indicate that when the differential settlement at the bottom of pavement reaches 1 cm, the maximum additional stress in the surface of the base course will surpass the maximum splitting tensile strength for the cement-stabilized base materials specified in the current specifications. Therefore, 1cm is recommended as the critical control standard for the differential settlement at the bottom of pavement. In addition, an approximate formula is deduced to calculate the critical control standard of ground differential settlement (S_c) which is expressed as S_c=1000λ(16.8l²-30.4l+17.1), in which λ is the rate of the reverse slope of the pavement and lis the ratio of the width of the new road to that of the original one.