Abstract：Expansive force is one of the important indicators of expansion potential responses.This paper selects the expansive soil of K25 + 000 section from Xiaoxita to Yaqueling first-class highway rebuilding engineering, mixing weathered sand to improve expansive soil.The basic swell-shrink experiment is carried out under different weathered sand contents, at the same time, deeply research on the influence of an initial moisture content on the growth speed and the size of the expansive force of weathered sand improved expansive soil.The test results show that:after incorporating weathered sand, the swell-shrink indicators of expansive soil are obviously improved and can reach the standards of subgrade filling; when incorporating the same weathered sand dosage, with the increasing of an initial moisture content, the expansive force is reduced gradually.The expansive force can use the power function of an initial moisture content to describe the correlation.The lower the initial moisture content, the greater the potential and the expansive force of the soil samples.The curve of the expansive force changing with time is steep.After flooding, the growth of the expansive force of the improved expansive soil is concentrated within one hour, and the speed of steady is faster.The comprehensive consideration for the influence of economy and the initial moisture content and weathered sand dosage on expansive force, the weathered sand dosage should be controlled between 30% and 40%, and the initial moisture content is controlled in a slightly larger than the best moisture content of 1% and 2%.At this time, the inhibition effect of expansive force is better.

Keyword：expansive soil;weathered sand;initial moisture content;expansive force;