Study on Disintegration Characteristics and Response Laws of EICP-Treated Dam Slope Soil Under Complex Conditions

Earth dams’ upstream slopes suffer from reservoir water-level fluctuations and long-term immersion, triggering soil softening and disintegration and endangering structural safety. Enzyme-Induced Carbonate Precipitation (EICP) is an eco-friendly technique for enhancing clayey soil disintegration resistance, but its performance and multi-factor responses under complex service conditions are not fully understood. Using clayey soil from Bozhou embankment upstream slopes, we conducted laboratory immersion disintegration tests to simulate field service conditions. The effects of the number of surface-spraying applications, curing age and dry–wet cycle number on cumulative disintegration mass were analyzed. A Box–Behnken Design (BBD) quadratic regression model was established to evaluate main and interaction effects, and the water resistance mechanism was explored via surface-wetting tests and micro-structure observation. The results showed that after one dry–wet cycle, the cumulative disintegration mass of EICP-treated soil was only 1.71% of that of untreated soil. The influence degrees of the three factors were ordered as follows: number of surface-spraying applications> curing age > dry–wet cycle number. Five sprayings and ≥14 d of curing were recommended as optimal practical parameters, with 14 d serving as the minimum curing age balancing performance and construction efficiency, while 21 d curing yielded the minimum cumulative disintegration (1.4 g) mass within the investigated experimental range. Calcium carbonate precipitates filled soil pores and formed a vaterite protective layer, effectively blocking water infiltration. EICP mixing reinforcement combined with surface spraying significantly improved the disintegration resistance and water barrier capacity of embankment clay. The response surface model provides a technical basis for reinforcement design regarding earth dams’ upstream slopes.