Strength Properties and Evaluation Method of Composite Modified Carbonaceous Mudstone Soil-rock Mixtures

The application of carbonaceous mudstone soil-stone mixtures (CM-SRM) in embankment engineering is limited due to its poor mechanical properties. This study aims to enhance the strength properties of CM-SRM by modifying it with guar gum, fly ash and red clay. Unconfined compressive strength (UCS) tests and triaxial compression tests were carried out using orthogonal design methods to systematically analyze the mechanical properties and modification mechanisms of modified CM-SRM. The results indicated that the modified CM-SRM exhibited failure modes such as single-shear, single-shear-bulging, double-shear, and double-shear-bulging, with fly ash and guar gum dosages significantly affecting both failure modes. Unconfined compressive strength and cohesion increased post-modification, with minor changes in friction angle. Orthogonal analysis reveals that guar gum dosage significantly effects on UCS and shear strength indexes, whereas the effect of fly ash is comparatively weaker. Based on the test results, a shear strength evaluation method based on linear and nonlinear models is proposed. The study shows that the composite modification mechanisms of red clay, fly ash, and guar gum on CM-SRM mainly includes bonding and filling effects, cation exchange, and gel aggregation. The suggested dosage combination is 10% red clay, 5% fly ash, and 4% guar gum.