Experimental Study and Reliability Analysis of ESSC–FA–WESS Foamed Lightweight Soil

This study developed ESSC–FA–WESS foamed lightweight soil using early-strength supersulfated cement (ESSC), fly ash (FA), and waste engineering slurry sediment (WESS), and evaluated its performance and reliability. Twelve mixtures combined water-to-binder ratios of 0.55, 0.60, and 0.65 with wet densities of 700–1000 kg/m3. Fluidity, 7 d and 28 d unconfined compressive strength (UCS), and durability were tested. Individual failure probabilities for the softening coefficient (Ks), freeze–thaw strength reduction rate (δf), and wet–dry strength loss rate (Ldw) were estimated using Student’s t-distribution; system reliability was evaluated using a series system. Weakly bound water in WESS could be converted into free water. Fluidity increased with water-to-binder ratio and wet density. UCS and durability improved with wet density; with increasing w/b, UCS and durability first improved and then declined, both peaking at 0.60. All 12 mixtures met the fluidity criterion, and 11 met the 28 d UCS criterion. Four mixtures satisfied all three durability criteria in terms of average values, and A8 achieved the highest system reliability (97.30%), with Ks being the most critical factor limiting overall system reliability. A8 (1000 kg/m3, w/b = 0.60) is recommended for high-reliability engineering applications. This study provides a practical route for utilizing waste engineering slurry in foamed lightweight soil.