Experimental Study on Static Triaxial Test of Fly Ash Modified Red Mudstone Filler

The water absorption and softening and volume expansion characteristics of the red mudstone are prone to cause the phenomenon of slurry mud and uneven settlement of the roadbed and other diseases, so it should be improved when used as highway roadbed filler. In this paper, fly ash was chosen as an improver to analyze the compositional composition and ionic content of red-bedded mudstone and fly ash through indoor X-ray diffraction tests, chemical composition tests and easily soluble salts. The physical and mechanical properties of the specimens before and after improvement were analyzed by unconfined compressive strength tests, indoor variable head penetration tests and consolidation tests. The effects of different fly ash admixtures on the shear stress-strain gauge shear strength of the modified specimens were investigated by conventional triaxial UU tests; the effects of the age of maintenance on the shear strength parameters of the modified tests when the fly ash admixture was 10% were analyzed. The results show that the red mudstone in the area is a low liquid-limit clay with the highest SO₄^2- ion content and alkaline pH in its labile salt solution. In triaxial shear test, both modified and unmodified specimens showed plastic damage, and both the amount and age of fly ash admixture of the specimens contributed to the increase of shear strength of the specimens, and the increase of cohesion was much larger than the internal friction angle. The cohesive force of the specimens at the age of 28 d with 10% fly ash was 37.9% and 6.9% higher than that of the unmodified unmaintained specimens and 10% unmaintained specimens, respectively, and the internal friction angle increased by 1.2° and 0.7°. The hydrostatic experiments of the specimens all verified the reliability of the fly ash improvement.