Abstract: The water conservancy and transportation projects in the expansive soil and rock formations are frequently damaged due to the expansion, contraction and multi cracks in these soil and rock formations. To fully utilize the local waste material resources mixed with a certain cement ratio is one of the effective methods to mitigate expansive soils and rocks. The weak expansive rock and soil in an area are selected as the study site, and the weak expansive rock and soil are physically modified by the excavated waste disintegrated sandstone and other rocks. Based on the free expansion rate test, the optimal mixing ratio is proposed, and the basic physical property test and expansion characteristic test of the soil samples modified by the physical modified material and cement are performed to evaluate the expansion deformation of the modified soil. The test results show that: (1) the optimal mixing ratio of the physical modified weak expansive soils with the disintegrated  sandstone rock and mudstone is 3:7 and 5:5 respectively; (2) The permeability coefficient k≤10^-4 cm·s^-1under 96% compaction and the permeability coefficient k≤10^-5 cm·s^-1 after the modification with 3% cement; (3) When the overburden pressure of the physically modified soil is 6.25 kPa, the expansion rate is less than 2.0%. After being modified with 3% cement, the unloaded expansion rate is less than 0.2%, and the expansion deformation of modified soil is significantly reduced.

Key words: Irrigation Channel Engineering, Weak Expansive Rock and Soil, Modified Soil, Laboratory Tests