Using the enzyme-induced carbonate precipitation (EICP) technique to solidify rubber and clay mixtures as lightweight backfill is a feasible way to reduce waste tire impacts and boost rubber recycling in geotech engineering. In this study, a comprehensive laboratory investigation, including triaxial compression, oedometer, permeability, and nuclear magnetic resonance (NMR) tests, was conducted on EICP-reinforced rubber particle solidified clay (hereafter referred to as EICP-RC solidified clay) to evaluate the effects of rubber particle content and size on the mechanical behavior of the improved soil under various solidification conditions and to elucidate the solidification mechanism. The results show that although rubber particles inhibit EICP, they significantly enhance the mechanical properties of the samples. The addition of 5% rubber particles (rubber A) increased cohesion by 11% and the internal friction angle by 18% compared to EICP-treated clay without rubber. Additionally, incorporating smaller-sized tire particles facilitated pore filling, resulting in lower compression and swelling indices and reduced permeability coefficients, making these materials suitable for use behind retaining walls and in embankment construction.

The ecological restoration of rock slopes has long been a challenging endeavor. The success of rock slope recovery largely depends on the artificial ecological substrate layer. This study presents a new ecological substrate developed by combining enzyme-induced carbonate precipitation (EICP) and phosphogypsum (PG). To determine the optimal substrate composition and evaluate the influence of each component, the mechanical properties and water stability were systematically investigated using an orthogonal experimental design. Range analysis was then used to evaluate the contribution of each component. Subsequently, the vegetative performance of the proposed substrate was validated through experimentation. Based on the analysis of the mechanisms of modification, it was concluded that the incorporation of EICP and PG significantly enhanced the substrate’s mechanical strength, with the cohesion and internal friction angle increasing by approximately two-fold and 1.7-fold, respectively, compared to the untreated samples. Water stability improved markedly, as evidenced by a reduction in the permeability coefficient by a factor of ten and a significant delay in the disintegration process. The substrate provides a favorable growth environment for ryegrass and meets slope protection requirements within one month of seeding. This strengthening is attributed to the multiphase synergy within the ‘plant–urease–stabilizer’ system. The optimal formulation was found to be a mixture containing 0.2% water-retaining agent, 6% rice husk charcoal, 3% adhesive, 20% PG and 20% EICP solution.