Study On Mechanical Properties And Deformation Prediction For Coarse-grained Red Mudstone Improved Filler In Sbugrade Of Sichuan-tibet Railway

With the construction of a number of western railways such as the Sichuan-Tibet Railway,the utilization of redbed filler and settlement control of redbed subgrade have become an urgent engineering problems to be solved.There is a shortage of high-quality fillers in group A and B which meet the requirements of railway design code in southwest areas such as Sichuan Province.The redbed as subgrade filling is easy to weathering,softening when water is encountered,and the compactness of filling is very sensitive to water content.It belongs to Group C filling because of its bad engineering properties.For railway roadbed,the redbed filler with bad engineering properties should not be used in the subgrade bed and the embankment below the bottom layer of the subgrade bed.Because there is less experience in railway construction in red bed area,whether the settlement of soft soil embankment with red bed filler can meet the requirements of the control standard of design code,there is no corresponding theoretical basis for calculation,so it is necessary to carry out scientific research to guide engineering practice.The foundation coefficient K₃₀,the compaction coefficient K and the porosity n of improved fillers were measured by field construction test,and a reasonable construction compaction scheme was explored.Based on large-scale dynamic triaxial tests,the cumulative deformation,critical dynamic stress and dynamic strength of coarse-grained improved fillers in red-bed clay subgrade under cyclic train load are studied.A permanent deformation prediction model of improved red-bed subgrade is proposed,and the post-construction settlement of embankments at different heights after one year of operation is estimated.The main work of this paper and the results achieved are as follows:?1?Through a large number of geotechnical tests,the mineral composition,density,liquid-plastic limit,particle size distribution,compaction characteristics and compressive strength,shear strength and disintegration characteristics of red clay and red mudstone are studied in depth.The physical and mechanical characteristics of the composition of improved filler are mastered,which provides a scientific basis for improving the design of filler ratio.Based on the physical and mechanical properties of red clay and red mudstone,combined with the deformation and strength requirements of railway subgrade filler,three improved fillers blending schemes are designed.The improved fillers are well graded,the improved filler 1 and the improved filler 2 belong to the group A filler,and the improved filler 3 belongs to the group B filler.?2?The physical and mechanical properties of different proportions of improved fillers were compared by particle composition analysis,heavy compaction test,unconfined compressive strength test and large-scal direct shear test,and the optimum proportions and water content range were determined.The results show that when the moisture content of undisturbed red soil is 15%²0%and the moisture content of graded gravel of weak weathered mudstone is less than 5%,and when mixed with 50%⁶0%of graded mudstone gravel of 5 mm¹0 mm,10 mm²0 mm and 20 mm⁴0 mm in size range of 1:2:1 mass ratio,the improved filler has good strength and deformation resistance characteristics.It can be applied to the filling of the embankment below the bottom layer of the subgrade bed.?3?The cumulative deformation,critical dynamic stress and dynamic strength of coarse-grained improved fillers under cyclic train load are studied in depth by dynamic triaxial test.The results show that dynamic stress,confining pressure and water content have a significant effect on the cumulative deformation of the filler,while the dynamic stress and water content have a more significant effect on the cumulative deformation.The critical dynamic stress and dynamic strength increase with the increase of confining pressure.With the increase of water content,the critical dynamic stress and dynamic strength will increase first and then decrease,and reach the maximum at the optimal water content.At the optimum water content,the dynamic cohesion of the sample is 31.52 kPa and the dynamic friction angle is 32.30°.With the increase of water content,the dynamic shear strength index of the sample decreases sharply.?4?The experimental data were fitted by non-linear least squares method.AASHTO2002 model can better reflect the relationship between cumulative deformation and vibration times,and establish the relationship between water content,dynamic shear stress ratio,confining pressure,dynamic stress and model parameters.The settlement of embankment with different heights after one year of operation is estimated by reasonable calculation parameters.The results show that after 1 year of operation,the settlement of 2 m embankment is 4.58 mm,the settlement of 5 m embankment is 8.31 mm,the settlement of10m embankment is 13.00 mm,and the settlement tends to be stable,which meets the requirements for the standard settlement of less than 200 mm after construction.It can reliably guarantee the long-term safe and stable operation of the train.