Study On Evolution Law Of Cumulative Deformation State Of Gravel Crushed Bed Filler Under Cyclic Loads

In recent years,the development of high-speed railways in my country has been rapid,and the speed of high-speed trains has continued to increase,which has imposed more stringent requirements on the deformation and strength control of railway subgrades.The subgrade bed is the direct bearing structure of the dynamic load of the train,and also directly determines the safety and comfort of the train.It is an important structural layer that needs to be considered and carefully designed in the design of the high-speed railway subgrade.Therefore,the modified triaxial test system was used to carry out the dynamic triaxial test of the stepped loading of the graded crushed stone packing,the plastic deformation characteristics of the graded crushed stone under the action of dynamic stress were studied,and the cumulative deformation state with the change of the stress level was analyzed.The main research works and results are as follows:(1)In order to meet the test requirements,the existing GDS three-axis test system was independently designed and modified,mainly focusing on the expansion of the pressure chamber volume and the enhancement of the pressure capacity of the confining pressure controller.Since the original pressure chamber could not be tested for samples with a diameter of 150 mm and a height of 300 mm,the pressure was solved by adding flanges,connecting rods and large-size sample bases to respectively accept large-size pressure chambers and large-size samples expansion of the room;considering the problem that a single confining pressure controller still cannot reach the target confining pressure within the stroke,an infinite confining pressure switching system is added to achieve the purpose of alternately supplying confining water by switching between the two controllers.(2)The static triaxial test of the bed graded crushed stone packing was carried out,and the stress-strain relationship of the sample under different degrees of compaction,and the relationship between the peak strength and the degree of compaction were analyzed.The research shows that the stress-strain relationship of the samples under different degrees of compaction is strain-softening type,the volume of the sample increases continuously during the shearing process,and the sample has obvious shear expansion;the peak strength increases linearly with the degree of compaction.(3)The dynamic triaxial test of the bed graded crushed stone packing was carried out,and the development law of cumulative deformation of the graded crushed stone under dynamic stress,as well as the cumulative deformation and dynamic stress when the number of cyclic load action N=10000 times were analyzed.Studies have shown that under lower dynamic stress,the cumulative deformation is smaller and the curve shows a convergence trend;under larger dynamic stress,the cumulative deformation increases significantly and the curve shows a divergent trend.The cyclic partial stress level ? has a characteristic value ?v = 40%,which divides the cumulative deformation into stable and failure states.When ???v=40%,the cumulative deformation has a small deformation increment,the sample is in a stable state,the cumulative deformation development curve of the sample basically coincides under the same compactness,and the confining pressure has little effect on the cumulative deformation development law;When ?>?v=40%,the cumulative deformation increases significantly,and the sample is in a damaged state.(4)Use the negative power function to fit the cumulative deformation,obtain the deformation control parameter P value and deformation state influence parameter C value of the sample under different compaction degrees,and analyze the development law of the cumulative deformation rate and the changing law of P value and C value with dynamic stress.The results show the deformation rate decreases rapidly and tends to zero that under a small dynamic stress;the deformation rate increases rapidly under a large dynamic stress.On the whole,the deformation control parameters P and C values showed a decreasing trend with the increase of dynamic stress.(5)Further analyze the variation of the deformation control parameter P value with the cyclic partial stress level ? under different compaction degrees,and divide the cumulative deformation state characteristics of specimens with different compaction degrees under dynamic stress into fast stable,slow stable,slow failure and rapid failure.On the basis of comprehensive consideration of the degree of compaction,according to the shape of the P-? curve,the characteristic threshold of the deformation state of the graded crushed stone bed filler under dynamic stress is obtained.Among them,when P?2 or ??5%,the sample is in a fast stable state under dynamic stress;when 1<P<2 or 5%<?<40%,the sample is in a slow stable state under dynamic stress;When 0<P?1 or 40%??<80%,the sample is in a slow failure state under dynamic stress;when P?0 or ??80%,the sample is in a fast failure state under dynamic stress.