Study On The Mechanical Properties Of Dredger-filled Sand-Fly Ash Compound Soil

The wide use of fly ash in the construction of railway and highway subgrade can contribute to the green construction and turn waste into treasure.In recent years,with the development of hydraulic filling on the construction of roads,this technology is often used in road construction which along the rivers or lakes in northern China.Fly ash is also used as an additive and mixed with the hydraulic filled sand to fill the subgrade.This technology can reduce the use of earth filling so as to save land resources,and it can also reduce the freight costs.Meanwhile,it is also beneficial to the dredging of riverbeds.More importantly,fly ash used as an admixture can not only reduce costs but also be friendly to the environment.In this study,the hydraulic filled sand and flyash were mixed with different mass ratios to form compound soils,the optimum moisture contents and maximum dry densities of the soils with different mix proportions were determined by compaction tests.A series of triaxial tests were conducted to obtain the mechanical properties of the compound soils with different mix ratios under their optimum water contents.After comprehensive consideration of various mechanical properties,the optimum mix ratio was determined,which will provide some technical references for the practical road construction projects.Finally,the effects of freeze-thaw cycles on the mechanical properties of the compound soil under the optimum mix ratio were investigated.The main works and conclusions are as follows:(1)The hydraulic filled sand and flyash were mixed with different mass ratios,and the compaction tests were performed to determine the optimum moisture contents and maximum dry densities of the mixtures.According to the results of compaction tests,the compound soils with different mix proportions were prepared,on which triaxial tests were conducted and the mechanical properties of them were obtained.(2)The stress-strain curves,failure strengths,cohesion and internal frictionangles of compound soils with different mix ratios were compared and analyzed.The failure strength of the compound soil with a mix ratio of 1:9 is 10% higher than that of the pure sand specimens under 100 kPa confining pressure,and it is 9% and 7%under a cell pressure of 200 kPa and 300 kPa.Considering the factors such as failure strength and shear strength,the optimum mix ratio of the hydraulic filled sand and flyash is 1:9,and the addition of fly ash with 10% of the total mass can maximize the failure strength of the embankment.(3)The effects of freeze-thaw cycles on the mechanical properties of the compound soil under the optimum mix ratio were investigated.The variation of stress-strain curve,failure strength,elastic modulus,failure strain and shear strength with the increase of freeze-thaw cycles were obtained and analyzed.Regardless of the confining pressures,the stress-strain relationship of specimens is strong softening before the first three freeze-thaw cycles,and then it becomes weak softening until the7 th cycles after which the failure strength tends to be stable.The elastic modulus decreases with the increase of freeze-thaw cycles,while the failure strain shows a contrary trend.The cohesion decreases by 59% at the 13 th freeze-thaw cycle,while the effect of freeze-thaw cycles on the internal friction angle is relatively small.