Abstract: The engineering technology that expansive soil embankment, cutting and canal slope were reinforced with geogrids has been successfully applied to highway, railway and hydraulic projects in the recent years. But the strength and deformation characteristics of reinforced expansive soil are not yet researched thoroughly. This paper presents the results of CD triaxial tests of a middle-class rxpansive soil under different confining pressures and different reinforcing patterns (horizontal reinforcing with one layer/three layers, vertical reinforcing and un-reinforcing) for evaluating the reinforcing effects. The test results indicate that: (1) Reinforced-geogrids in expansive soil provide the drainage passageways, which accelerate the consolidation of expansive soil and are conducive to the stability of expansive soil slope. (2) Reinforced-geogrids reduce the strain softening of expansive soil, so the stress-strain curves of expansive soil possess strain hardening characteristics. (3) Reinforced-geogrid restrains the development of shear zone, which results in the changing of failure models of soil sample. (4) The internal friction angle of the reinforced expansive soil only changes a little under different reinforcing patterns, but the cohesion obviously increases. (5) Evaluating according to coefficient of reinforcing effect(R), reinforcing effects are all enhanced except horizontal reinforcing with one layer, among them, the effect of vertical reinforcing pattern is the best.

Key words: expansive soil, horizontal reinforcing, vertical reinforcing, stress-strain characteristics, strength index, coefficient of reinforcing effect