Study On Bearing Characteristics Of Coal Gangue Modification And Filling Roadbed

Coal gangue is a kind of black and grey rock waste produced in the process of coal mining,washing,etc.Air pollution,water pollution and soil pollution and some other problems caused by the accumulation of large amounts of coal gangue have a great impact on the ecological environment and people’s lives.Therefore,how to rationalize the comprehensive use of waste gangue is particularly important.Coal gangue have characteristics such as a loose texture,poor bonding,low strength and easy to swell in water,etc.Physical and chemical modification of coal gangue can improve its physical and mechanical properties hence used as roadbed filling material.In addition,in the gangue roadbed vibro-rolling construction,rolling effect is affected by a variety of factors.A reasonable rolling plan can improve the efficiency of the roadbed rolling and save construction costs.This paper relies on a highway project from Jinan to Weishan and uses a combination of physical and mechanical tests,theoretical analysis and numerical simulation to carry out research on the load-bearing characteristics of gangue modified and filled roadbeds.The main research contents and results are as follows:（1）Research on the physical and chemical properties of the project section of the disposed coal gangue and road performance research.Analysing the physical and chemical properties through the gangue chemical composition,loss on ignition,liquid-plastic limit and plasticity index,immersion expansion amount,disintegration resistance,crush value test and combined with the gradation test,moisture-density test,California bearing ratio test on the gangue road performance to carry out research.The test results show that the gangue used in this study meets the basic requirements for filling the roadbed.In order to improve the bearing capacity of the gangue road base to meet the higher level of road base design requirements,the gangue needs to be physically-chemically modified.（2）Taking moisture-density test,unconfined compressive strenth test,compression resilient modulus test,direct shear test and California bearing ratio test for 10%,20%,30%and 40%P₂（under 2 mm size of gangue）content gangue to analyse the effect of particle grade on the mechanical and road performance of gangue,revealing the change law of physical and mechanical indexes with P₂ mixture,and finally determining 30%P₂ mixture as the optimal ratio.（3）Testing on the effect of SAHP compound curing agent doping（0.2%,0.4%,0.6%,0.8%）on 30%P₂ gangue and natural gangue 7 d and 28 d road performance parameters（unconfined compressive strength,compressive resilient modulus,California bearing ratio,cohesion and internal friction angle）is carried out.The results show that:0.2%curing agent under the amount of gangue 7 d compressive rebound modulus and California bearing ratio have met the specification requirements;gangue 7 d and 28 d road performance with the amount of curing agent increase are on an upward trend;the 30%P₂ gangue of distributed grain size with curing agent has better properties than natural gangue with curing agent.The curing mechanism of the gangue was studied based on X-ray diffraction analysis（XRD）,scanning electron microscope（SEM）and energy dispersive spectrum（EDS）.Under the joint action of the ettringite skeleton,silicic acid gel and the curing agent’s own hydroxypropyl methylcellulose and polyacrylamide,the mechanical properties of the gangue were significantly improved,and the properties were continuously enhanced with the increase in the amount and age of the curing agent.（4）A single-degree-of-freedom vibration model combined with compaction energy was used to establish the relationship between vibratory force,vibration frequency,self-weight of the rolling wheel,travel speed and compaction settlement.Based on the PFC 2D discrete element software,the vibration rolling simulation was carried out on 30%P₂ gangue after the addition of curing agent.The relationship between vibratory force,vibration frequency,self-weight of the roller and compaction effect is positive,and the relationship between driving speed and lay-down thickness and compaction effect is negative.Through orthogonal tests and using range analysis,it was found that the most critical factor affecting the settlement rate of rolling is the lay-down thickness,followed by the vibration force and the self-weight of the rolling wheel,while the influence of the driving speed and the vibratory frequency on the settlement rate of rolling is relatively small.The optimum compaction solution was finally determined for a lay-down thickness of 30 cm,a compaction weight of 12 T,a travelling speed of 2 m/s,a vibration frequency of 50 Hz and a vibratory force of 200 kN.