Study On Influence Of One Side Widening Uneven Settlement On Pavement And Its Treatment Techniques

In order to meet the increasing traffic demand,it is an economically reasonable plan to widen and rebuild on the basis of the existing high-grade highways.In the highway widening project,due to the difference in settlement between the old roadbed and the new roadbed,the new and old roadbeds will be unevenly settling,which will in turn reflect the upper structure and cause road surface damage and affect the normal use of the highway.At present,there are many researches on the uneven settlement characteristics of new and old roadbeds,but there are not many studies on the effect of uneven settlement on pavement structures.One-sided widening is an important widening method.It has the characteristics of full use of terrain,less demolition and less interference with traffic construction.The settlement characteristics of new and old roadbeds are different from those on both sides.In this paper,finite element analysis shows that the uneven settlement of unilaterally widened embankments of different heights is basically the same,and the uneven settlement of higher embankments is larger.Compared with the widening of both sides,the unilateral widening of the surface of old and new roadbeds is not.Even settlement is more.Based on the stress analysis of the pavement structure based on the uneven settlement of the old and new roadbeds,the stress of the pavement structure under different widening methods,different height embankments and different new roadbed filling modulus comparisons,and the simplified settlement patterns are compared.The results are shown.: In the actual subsidence form,the surface stress of the pavement structure at the joints of the old and new roadbeds is the largest,and the corresponding road arches have the largest increase in the lateral gradient,which is prone to tensile damage.When the lateral gradient of the local road arch increases by about 0.75%,the surface layer is first damaged by tension.Under the action of vehicle loads,the settlement of new roadbed,the increase value of the maximum roadway cross-slope,the maximum stress value of pavement structure,and the road surface deflection decrease with the increase of the new roadbed modulus.Gravel soil is a kind of filling material with excellent mechanical properties that can be widely used in subgrade filling.In this paper,compaction test and compressiontest were carried out by adopting the equivalent replacement method.It was found that after compaction under the optimum moisture content condition,the crushed stone has the characteristics of small settlement and large compression modulus.In the compression test,60% The unit sedimentation value of gravelly-weighted crushed stone is 38.1 mm/m,which is a unit settlement of 103.6 mm/m for clay,and a compression modulus of 33 MPa is 3 times that of clay for 9.77 MPa.Through finite element calculations,the new roadbed was filled with crushed stone,and the maximum settlement value of unilateral widening was reduced from 11.43 cm to 8.7cm,which reduced the settlement of the new roadbed.The convergence between old and new roadbeds is very important.The results of the FEM calculations indicate that by digging steps and laying geogrids on the slope of the old embankment,the differential settlement of the new roadbed can be reduced,and the maximum value of the maximum cross-section of the road arch on the surface of the old and new embankments can be reduced.In turn,the adverse effects on the road surface are reduced.However,in the process of step excavation,there may be insufficient compaction due to lack of roller compaction in the local soil of the step,thereby weakening the effect of step excavation and geogrid reinforcement,which is not conducive to the convergence of new and old roadbeds.The use of crushed soil as replacement for soils with insufficient local compaction can alleviate this problem to some extent.At the same time,gravel soil was used to fill in new roadbeds,excavation steps of old embankment slopes,and geogrid reinforcement measures.The settlement value was reduced from 11.43 cm to 7.01 cm,and the maximum value of the maximum cross-arch gradient was decreased from 1.03%.To 0.41%,the maximum surface stress value of the corresponding pavement structure surface layer is 0.32 MPa,and the maximum surface stress value of the base layer surface is 0.12 MPa,which is less than the corresponding allowable tensile stress,and the purpose of controlling uneven settlement of new and old roadbeds is achieved.