Background This work aims to study the improvement effect of quicklime and cement on expansive soil and provide important theoretical support and technical basis for the construction of terraces in southern Shaanxi.

Methods Taking typical expansive soil as the object, the expansive soil was mixed with certain proportion of quicklime and cement(2%, 4%, 6%, and 8%), then the mixed soil was compacted with a compaction density of 1.65 g/m³ under the condition that the soil moisture was 22%. The traditional soil physical methods were used to determine the disintegration resistance, soil anti-scour ability, and the mechanical strength of the expansive soil terraces.

Results 1) As the proportion of added quicklime or cement increased, both the expansive rate and expansive force of the expansive soil decreased significantly. When the addition proportion exceeded 4%, the expansive rate and expansive force reduced. 2) After adding 2% quicklime and cement, expansive soil collapsed the fastest. After adding more than 4% quicklime and cement, the disintegration speed of the expansive soil began to be gradually reduced, especially the performance was the best while adding 6% quicklime and 8% cement. 3) With the proportion of quicklime and cement added, the impulse resistance of the expansive soil gradually increased. After adding 2% of quicklime and cement, the impulse resistance of the expansive soil was greatly enhanced, and with the increase of the adding proportion, the impulse resistance of the expansive soil was not significant. 4) With the proportion of quicklime and cement increased, the water stability of the expansive soil gradually increased, and when the proportion of quicklime increased to 8%, the water stability of expansive soil began to decrease.

Conculsions Adding cement and quicklime to the expansive soil way reduce the expansive rate of the expansive soil, and improve the anti-disintegration, impulse resistance and water stability of the soil. Under the premise of considering the economic benefits of the terrace construction, adding 4% quicklime and 6% cement can achieve the construction effect of the optimal expansion of the terraced fields.