Experimental Study On Hydraulic Characteristics Of Subgrade Coal Gangue Filler

Coal gangue is widely distributed around the major coal mines in the country.As waste material generated during coal mining and washing,coal gangue is often used in roadbed filling.Coal gangue filler belongs to coarse granular soil and forms a dual-porosity structure during compaction,which usually leads to bimodal soil-water characteristic curves?SWCC?.SWCC is closely related to the permeability coefficient of unsaturated soils and has an important influence on the roadbed water migration.At the same time,the coal gangue has certain disintegration property,which has an important impact on the roadbed stability and long-term cumulated deformation.Therefore,it's of great significance to investigate the consolidation characteristics of coal gangue under the coupling action of load and wet-dry cycle for its application.In this paper,the common coal gangue fillers in central and southern China are considered.A series of experimental studies have been carried out on SWCC and consolidation characteristics.The contents are divided into the following four aspects:?1?The basic characteristic parameters of coal gangue filler were obtained through laboratory tests,including specific gravity test,X-ray diffraction test,grain size analysis test,liquid limit and plastic limit test,compaction test,consolidation test,permeability test,disintegration test and scanning electron microscopy test.The basic mechanical parameters of coal gangue filler were obtained.?2?A series of pressure plate tests were conducted on coal gangue samples to study the impacts of compaction degree,silt content and maximum particle size on the formation and step height difference of bimodal SWCC.The test results show that the step height difference of SWCC decreases with increasing the compaction degree,and the change of the second step's height was related to silt content of the compacted simples.When the silt content was 5%,the second step's height is basically the same,and coal gangue samples with different compaction degree all have bimodal SWCCs.When the silt content was 50%,the second step's height decreased slightly and the SWCCs changed from bimodal to unimodal.The bimodal phenomenon disappeared when the degree of compaction reached a peak value.As the silt content increased or the maximum particle size decreased,the step height d ifference of SWCC decreased,and the second step's height increased substantially the same value.?3?The V-G and the Bi-V-G formulas were used to fit the measured SWCCs,and the fitting effect was compared.The variation law of the model parameters with compaction degree,silt content and maximum particle size was analyzed.With the increase of compaction degree or silt content,the model parameters?₁,?₂?parameters related to the air-entry value?and n₁,n₂?parameters related to drainage degree?decreased gradually,that was,the air-entry values and the water holding capacity of both macro-pore part and micro-pore part increased.As the maximum particle size decreased,the parameters?₁,?₂ and n₁ increased,n₂ decreased,that was,the air-entry values of both macro-pore part and micro-pore part increase,while the water holding capacity of macro-pore part enhanced and of micro-pore part weakened.?4?A series of consolidation tests were conducted on coal gangue samples which were under the coupling action of load and wet-dry cycles.The dehumidification and humidification properties of the samples during the wet-dry cycles were studied,the influence of load and wet-dry cycles on the cumulative plastic deformation of coal gangue samples was also analyzed,and finally,the microstructure evolution of coal gangue filler was studied by laser grain size analyzer test,scanning electron microscopy test and mercury intrusion test.The results show that,with the increase of wet-dry cycles,the compressive modulus of coal gangue samples decreases gradually.Both axial load and wet-dry cycles have a significant impact on the cumulative plastic deformation of coal gangue samples,and the plastic deformation caused by the 1st wet-dry cycle is the most significant,the dry shrinkage deformation and swelling deformation became basically the same when wet-dry cycles reached about 4 times.With the increase of wet-dry cycles,the final moisture content of dehumidification and humidification decreased linearly.In descending section of e-w curve,the void ratio of coal gangue sample is basically constant when the skeleton pores and macro-pores drain,while decreases significantly in the process of continuous micro-pores drainage,and decreases slowly when the drainage of discontinuous micro-pores occurs.With the increase of wet-dry cycles,the volume of macro-pores and micro-pores decreases gradually,and the silt content of small size increases gradually.When the number of wet-dry cycle is high enough,the microstructure of coal gangue filler changes significantly,and the pore nearly disappears.During the wet-dry cycles,the smaller the axial load,the more significant the disintegration of aggregates.