Study On The Regulation Of Compactness Of Graded Gravel Fill And Its Road Performance

As a kind of flexible base,graded gravel base has low cost,simple construction,and has certain drainage function,which can reduce the pavement water damage.However,due to the discrete material and irregular shape of the graded gravel,it is difficult to compact and poorly stable during construction.As a result,the graded grave pavement structure has some problems,such as low bearing capacity and poor resistance to permanent deformation.Therefore,this study focuses on solving the problem that graded gravel is difficult to be compacted during construction.The study is carried out from the perspective of stabilizing the bond without losing its characteristics,exploring the method of upgrading the graded gravel and the mechanical strength and road performance changes of the graded gravel base after the upgrading.To provide some theoretical basis and experimental demonstration for spreading and applying graded gravel base.In this paper,SRX water-based polymer and 2% cement were used as stabilizing materials for the disposal of graded gravel,respectively.A CBR test to determine the range of singlestage throughput rates of the key sieve holes of the graded gravel to optimize the two skeletal dense gradations;In addition,the compactness results of the graded gravel(easily compacted graded gravel mixes)after easy-density disposal were evaluated with the aid of the height method,the image method and the maximum pressure method in relation to the base graded gravel mixes.On this basis,the variation of mechanical properties of easily compacted graded gravel mixes was analyzed by CBR test,unconfined compressive strength test and splitting strength test.A CBR prediction model for easily compacted graded gravel mixes was also developed with the aid of machine learning methods.Finally,the pavement performance of the easily compacted graded gravel was investigated by means of water stability tests and freezethaw tests.A comparative analysis with the pavement performance of the benchmark graded gravel base and cement stabilized gravel base was also carried out.The main work and conclusions are as follows:(1)The physicochemical properties of SRX water-based polymer stabilized materials were analyzed using adhesion tests and infrared scanning.It was found that the chemical properties of SRX polymer were stable and the adhesion was good after being heated.To summarize the range of graded gravel specified by domestic standards and take the graded gravel with the maximum particle size of 31.5mm as the primary grading scheme.With throughput rates of the key sieve holes of the graded gravel as independent variable and CBR strength as evaluation index,it was optimized and determined that the key sieve throughput rate of graded gravel0.075 mm should be controlled at 1%-6%,4.75 mm at 34%-54% and 13.2mm at 63%-78%.Two skeletally dense G1 and J2 gradations are preferred within the optimized gradation of the graded gravel mix.The results of the change in compactness of the graded gravel mix after easy compacting disposal are evaluated by the height method,the image method and the maximum pressure method in relation to the base graded gravel mix.It was found that the use of SRX water-based polymer and 2% cement for the disposal of graded gravel can effectively improve the compactness of graded gravel.The compactness of 2% cement-stabilized graded gravel mixture is better than that of SRX polymer.The gradation will affect the denseness of the graded gravel mix regulation effect,coarse and fine aggregates more uniform skeleton dense type of mix easier to dense.(2)A study of easily compactable mixes disposed of with SRX water-based polymer and2% low admixture cement.CBR tests were conducted to analyze the effect of material type,material admixture,grading and age of maintenance on the strength of CBR.At the same time,the time of strength formation of easily compacted mixes was clarified by testing the height variation of CBR specimens.It was found that the CBR values of the J2 graded mixes are all higher than those of the G1 after easy densification disposal.The CBR strength of SRX polymer stabilized compacted mixture increases with the increase of SRX content,and the reasonable content of SRX polymer stabilized material is recommended to be 0.5%.As the age of maintenance increases,the CBR value of easily compacted gravel mixture increases rapidly first,then slowly,and finally tends to be stable.Based on the results of the CBR specimen height variation,it is recommended that SRX polymer stabilized easily compacted mixes be maintained naturally for 10 d to 15d;6d to 9d natural curing of easily compacted mixes stabilized with 2% low admixture cement.72 sets of CBR intensity test results were used as machine learning samples to build CBR intensity prediction models using four deep learning methods: random forest,Adaboost,BP neural network and support vector machine.It was found that the CBR intensity prediction models built using the random forest method and Adaboost method had good generalization ability and prediction accuracy.The strength variation of easily compacted graded gravel mix was studied with the aid of unconfined compressive strength tests and splitting strength tests.As the amount of SRX is increased,the unconfined compressive strength and splitting strength of the G1 graded easily compacted mix stabilized with SRX polymer is significantly greater than that of the J2.(3)A mix of SRX polymer at 0.5% and a 2% low cement stabilized graded gravel mixes was selected.The influence of water stability and freeze-thaw resistance of stabilized materials and graded easily compacted graded gravel mixes was analyzed by means of water immersion CBR tests and freeze-thaw splitting tests.The results show that the water stability of the SRX polymer-stabilized compacted mixture is not as good as that of the 2% low content cement stabilized graded macadam mixture;the water stability of J2-graded compacting mixture is better than that of G1.Compared with cement stabilized material with low content,SRX polymer stabilized gravel mixes has poor freeze-thaw resistance.The differences of pavement performance between easy compacted graded mixture,ordinary graded gravel base and cement stabilized gravel base were compared and analyzed.It was found that the water stability and freeze-thaw resistance of the compact gravel base treated with SRX polymer and 2% low content cement are better than those of the benchmark graded gravel base.