Research On Cracking Resistance Of Lower Layer Based On Differential Settlement Between New And Old Subgrade

Since the reform and opening up,my country’s economy has developed rapidly,and the traffic volume of expressways has increased rapidly.Many expressways that have been in operation for many years cannot meet the current heavy traffic volume and the requirements of social development,and urgently need to be rebuilt and expanded.The reconstruction and expansion of expressways will be an important issue facing my country’s infrastructure construction now and in the future.Although many expressway reconstruction and expansion projects have been completed at home and abroad,and some valuable experience has been obtained,they lack theoretical results and do not have complete specifications.The study and comparison of surface cracking caused by the differential settlement of new and old subgrades in reconstruction and expansion projects Lack,need to strengthen research.Based on the reconstruction and expansion project of Liunan Expressway in Guangxi,this paper uses theoretical analysis and numerical simulation to study the cracking and anti-cracking of the lower layer based on the differential settlement of the old and new subgrades.The main research contents and results of this paper are as follows: The theoretical analysis of the settlement of the roadbed was carried out,and the basic principle of the differential settlement of the new and the old roadbed was obtained.Combined with the research results at home and abroad,the manifestation of the differential settlement and the method that can reasonably express the amount of the differential settlement were obtained.Based on the basic theory of fracture mechanics,theoretical analysis of the cracking process of asphalt pavement and the development of cracks.Combined with the actual engineering experience,with the aid of the large-scale finite element simulation software ABAQUS modeling analysis,the pavement’s bearing capacity for the differential settlement of the subgrade is studied.With the increase in the differential settlement of the new and old roadbeds,there are three main stages of pavement structure failure: the first stage is the yield stage of the subbase material,which generally occurs when the differential settlement of the new and old roadbed is 5cm;the second stage is the yield stage of the base material.This stage generally occurs when the differential settlement of the old and new subgrade is 10-20cm;the third stage is the emptying stage of the pavement structure and the subbase,which is accompanied by the first and second stages.The influence of the thickness and material parameters of each structure layer of the pavement on the cracking of the surface layer is studied by the controlled variable method.Increasing the surface layer material modulus will cause the maximum stress of the surface layer to increase.Under the same differential settlement,the void range between the bottom surface of the subbase and the roadbed becomes larger,but the yield speed of the base material becomes slower due to the stiffness of the surface layer.Both strong base and thick base can improve the pavement’s ability to withstand the differential settlement of the roadbed.Research several typical asphalt pavement widening methods,namely,four-lane widening,sixlane,eight-lane,and ten-lane,respectively,to withstand the differential settlement.With the increase of differential settlement,the smaller the widening width,the easier it is to produce voids between the subbase and the roadbed.Finally,combined with the actual project,the research results are applied to the engineering practice,and the reasonable control standards for the differential settlement of the old and new subgrades are proposed for different road widening forms.For road sections where the differential settlement of the old and new subgrades is difficult to control within the standard,anticracking measures are proposed based on the actual situation for different differential settlements.