Study On Mechanical Properties And Microscopic Mechanism Of Rice Husk Ash-lime Modified Coastal Soft Soi

The coastal soft soil produced by foundation pit excavation has high water content and poor engineering properties.After solidification treatment,it can be used as subgrade filler in road works to achieve reasonable absorption of construction waste.The random accumulation of rice husk ash destroys the soil acid-base balance,pollutes water areas and occupies land.Because it contains a large amount of active silica,it can replace the traditional curing agent.Based on the concept of "carbon neutralization",this paper uses rice hull ash lime to improve coastal soft soil,and realizes the resource utilization of construction waste soil and biological waste rice hull ash.Taking 5% lime soil as the benchmark group,the unconfined compressive strength test,triaxial shear test and California bearing ratio(CBR)test were carried out on the modified soil mixed with 1%,2%,3%,4% and 5% rice husk ash to study the unconfined compressive strength,water stability,energy dissipation,shear strength and its shear resistance index,secant modulus,CBR strength value of the modified soil,and the lime was replaced equally under the optimal amount of rice husk ash.The influence of rice husk ash on the macro mechanics and micro mechanism of lime soil was analyzed by means of XRD and SEM.The research conclusions of this paper are as follows:(1)The unconfined compressive strength test shows that the unconfined compressive strength increases with the increase of rice husk ash content under 7d standard curing.With the increase of curing age,the optimum content of rice husk ash is 3% at 28 d,and the strength is increased by 52.0%.Under the conditions of 6d and 27 d standard curing+1d immersion curing,the strength first increases and then decreases with the increase of rice hull ash content,reaching the maximum value at 3% content,which is significantly lower than the strength of standard curing samples.Rice husk ash can improve the water stability of lime soil,and the test results meet the requirements of subgrade use specifications.(2)The triaxial shear test shows that rice husk ash can effectively improve the shear strength and shear resistance index of lime soil.Under different confining pressures,the peak strength first increases and then decreases with the increase of rice husk ash content,and the strength of the sample decreases after immersion,showing a similar general law.At the age of7 days,the secant modulus reached its maximum when the content of rice hull ash was 3%,which was 143.44%,79.20%,77.16% and 48.60% higher than that of the reference group,respectively.The increase amplitude gradually decreased with the increase of confining pressure;At 28 days of age,the secant modulus reached its maximum value when the content of rice hull ash was 4%,which increased by 61.7%,59.1%,69.2% and 58.1% respectively.(3)Under the optimum amount of rice husk ash,the effect of replacing lime equally: when the sample is not immersed in water,the compressive strength and shear strength of 5% lime+3%rice husk ash and 8% lime are basically the same.After the sample is immersed in water,the5% lime+3% rice husk ash sample is significantly higher than the 8% lime sample.The effect of rice husk ash on total energy consumption and energy dissipation rate is higher than that of8% lime sample.The curing environment and curing age have a greater impact on total energy consumption.With the increase of age,the brittleness of the sample increases significantly.The CBR values of 5% lime,5% lime+3% rice husk ash and 8% lime are 52.2%,71.6% and 60.1%respectively.Rice husk ash can effectively improve the CBR value of lime soil,and it is better than the same amount of lime.(4)The microscopic test shows that when rice husk ash is added to the lime soil,the diffraction peaks of some calcium hydroxide disappear,the pH value of the soil decreases,and the diffraction peaks of hydrated calcium silicate increase.The sheet and flocculent hydration products in the soil are obviously increased,and a large aggregate structure appears.Under the joint action of the cementation of the hydration product CSH and soil particles and the filling effect of rice husk ash,the soil pores are continuously reduced,and the sample porosity is negatively correlated with the unconfined compressive strength.Although more hydration products are generated in the sample after immersion,the structure is relatively dispersed and it is difficult to form larger aggregates.