Differential Settlement Of Subgrade In The Widening Of Highway And The Application Of Composite Foundation Of Sheet Piles On Soft Soil Foundation

In the widening of the highway subgrade on the soft soil foundation,the subgrade was prone to large differential settlement.In severe cases,the embankment was unstable and destroyed.Combined with the wide application of pile-slab composite foundation structure in the railway subgrade construction and the advantage of 3D laser scanner to judge the overall settlement,the two methods were introduced into the highway widening project which could effectively reduce the differential settlement.This paper was based on the reconstruction and expansion project of the Shi'an section of the Beijing-Hong Kong-Macao Highway,and the pile-plate composite foundation structure was applied,By observing the test section,the advantages of the 3D laser scanner on the overall settlement were clarified,and the effectiveness of the pile-slab composite foundation on the settlement control was also illustrated.On this basis,the numerical model of pile-slab composite foundation was set up,and its force and deformation characteristics under different working conditions were analyzed.Combined with the long-term settlement observation trend,the control index of differential settlement was proposed.The research results showed that:(1)During the construction process,it was necessary to focus on controlling the quality of the junction of the old and new embankments.The effect of pile-plate structure on reducing differential settlement gradually appeared in the construction stage of semi-rigid base layer,and the advantage of surface layer construction stage was obvious.(2)Compared with the cement mixing pile composite foundation,the pile-slab composite foundation had obvious advantages in controlling the differential settlement and lateral displacement of new and old embankments;(3)In the treatment of the pile-slab composite foundation,the pile-soil stress ratio was 12.075,and the pile load sharing ratio was 28.07%after the completion of the new embankment.In the treatment of cement mixing pile,the pile-soil stress ratio was 2.646,and the pile load sharing ratio was 7.87%,which indicates that the pile-plate structure could effectively bear the filling load,and the consolidation settlement was smaller.(4)Combined with on-site observation and wide-section mechanical response analysis,it was recommended that the pile spacing be 4.5?5.5 times the pile diameter;the pile length should be 4.5?5.0 times the pile spacing and the filling embankment modulus of the new embankment should not exceed 30 MPa.(5)It was recommended that the differential settlement control index based on the slope-increasing slope rate was 0.15%?0.35%.During the construction period,the new subgrade settlement control rate was 0.01?0.20mm/d,the old road shoulder daily settlement control rate was 0.01?0.10mm/d,and the old road central settlement control rate was 0.01?0.10mm/d.The monthly settlement control rate of the new road was 0.30?3.5mm/30d,the shoulder monthly settlement control rate of the old road was 0.25?2.5mm/30d and the central monthly settlement control rate of the old road was 0.15?2.0mm/30d.