Study On The Influence Of Fly Ash,Rice Husk Ash And Polypropylene Fiber On Physical And Mechanical Properties Of Expansive Soil

Expansive soil is one of the most serious problems in civil engineering.Due to the significant compressibility and weak shear resistance of expansive soil,which may cause soil shrinkage or swelling,building on expansive soil carries a great risk of damage or collapse.Fly ash and rice husk ash are used to improve the properties of expansive soils.The effects of fly ash and rice husk ash on the stability of expansive soil from Ergun city,Inner Mongolia were studied through a number of laboratory tests such as sieve analysis,compaction test,triaxial test,consolidation test,swelling test,California bearing ratio test,scanning electron microscopy(SEM)and X-ray diffraction(XRD).The changes of physical parameters,mechanical properties,microstructure and mineral composition of expansive soil before and after solidification of fly ash and rice husk ash were compared and analyzed.The results show that the plasticity index of the soil decreases with the increase of fly ash and rice husk ash content,which improves the stability and workability of expansive soil.The increase of fly ash content increased the MDD of expansive soil,but the increase of rice husk ash content decreased the MDD of expansive soil.The OMC index is directly proportion to fly ash and inverse proportion to rice husk ash.The internal angle friction(Φ)of the expansive soil increased slightly when the fly ash increased and increased considerably when the rice husk ash increased,while the cohesion C decreased overall with increased of fly ash and decreased and then increased with increased of rice husk ash.The results show that the use of fly ash is more effective than rice husk ash to improve the properties and properties of expansive soil,mainly because the porosity and density of rice husk ash are lower than that of fly ash and untreated soil,and the optimal modifier ratio of fly ash is 16%.The polypropylene fiber is also used to improve the properties of expansive soils.The present study considers the effect of adding different percentage of polypropylene fiber(PF)(0.75%,1.5%,2.25%and 3%)on the properties of expansive soils.The expansive soil selected for this project is from Ergun City,Inner Mongolia,northern China,and is studied through a number of laboratory tests,such as sieve analysis,compaction test,triaxial test,consolidation test,swelling test,California bearing ratio test,and microstructure analysis for treated soil with polypropylene fiber and untreated soil.The odometer test was used to study the swelling test and carried out under surcharge pressure.The results show that the compaction,shear strength,consolidation and California bearing ratio of the polypropylene fiber stabilized clay are improved.With the increase of polypropylene fiber content,the maximum dry density increases and the optimal water content decreases.The swelling potential is directly proportion to cohesion coefficient and inverse proportion to Angle of internal friction.The void ratio,consolidation coefficient and permeability coefficient decreased simultaneously.Compared with the clay stabilized by 3%polypropylene fiber,the void ratio,consolidation coefficient and permeability coefficient of soil are all reduced.By combining fly ash with rice husk ash and polypropylene fiber,the bearing ratio of fly ash can be improved.The effects of soil weight on the consolidation,permeability coefficient and California bearing ratio(CBR)of expansive soils were analyzed,and the scanning electron microscopy(SEM)-energy dispersive X-ray(EDX)analysis was performed.The results show that the void ratio,consolidation coefficient,permeability coefficient and CBR value are all improved.The optimum FA,RHA,and PF content were determined to be 4%FA,3%PF,and 16%RHA by the weight of the soil,as this quantity resulted in the best improvement in soil properties.The research results can provide a suitable basic application method for the treatment of expansive soil,provide a new idea for improving expansive soil conditions in infrastructure construction,and also provide a reference for the design and construction of expansive soil project in Ergun City,Inner Mongolia.