Mechanical Properties Of Modified Loess Under Freeze-thaw Cycles

The modified loess is widely used as roadbed filler while the choice and ratio of the modifier is usually based on the strength index and impermeability indicators. Loess roadbed in seasonal frozen soil areas often suffers from intense freeze-thaw cycles which therefore must be considered when discussing the choice and ratio of loess modifier. This paper investigates the changes of frost-heaving ratio, unconfined compressive strength, permeability coefficient and microstructure of modified loess under different ratios of cement, lime and fly ash before and after the freeze-thaw cycles. According to the comprehensive strength, permeability and freeze-thaw resistance performance of the modified loess, this thesis proposes the optimal ratio of the modifier and discuss the influence of freeze-thaw in practical application. The results show that in considering with freeze-thaw cycles, loess with4%—5%of cement,6%of lime and10%of fly ash can not only have higher compressive strength (over3MPa after cyclic freezing and thawing), lower permeability coefficient (around10-/cm/s order of magnitudes after the freeze-thaw cycles) and lower frost heave ratio of volume (below5%of its total volume after the cycles), but can also avoid the decreasing of its ability resisting the freeze-thaw caused by its over-rigid. The micro experiment also indicates that needle-like and other gel-type hydration products of cement, lime and fly ash bonded the loess particles together in the form of large grain aggregates, and this improvement of microstructure didn’t seem to vanish after the freezing and thawing. The three modifiers together visually change the arrangement and links of soil particles, decrease the porosity, thus ameliorate the compression and impermeability of modified soil.