Field-scale performance improvement of ammonia-soda white mud as a waste-derived geomaterial through dewatering and preloading

Abstract

Ammonia-soda white mud (ASWM) is a high-water-content industrial residue generated during soda-ash production. Its large-volume reuse as a backfill geomaterial could reduce long-term stockpiling and the consumption of conventional fill materials; however, its high compressibility, low permeability, and low initial strength restrict direct engineering application. Unlike previous ASWM reuse approaches based mainly on blending, cementitious incorporation, or chemical stabilization, the present study investigated the in situ physical improvement and direct large-volume reuse of an already placed, high-water-content ASWM deposit. This study compared three field-scale dewatering-consolidation pathways for an artificially backfilled ASWM deposit in a coastal port area of Bohai Bay, China: vacuum preloading, surcharge preloading, and surcharge preloading combined with well-point dewatering. Three approximately 2,500 m 2 test zones were monitored using surface settlement, layered compression, pore-water pressure, and groundwater-level measurements. Changes in moisture content, wet density, dry density, void ratio, cone tip resistance, and sleeve friction were also evaluated. All three pathways induced consolidation and improved the physical-state and penetration-resistance characteristics of ASWM. Vacuum-induced settlement developed mainly during the first 15–20 days and stabilized at approximately 600 mm, whereas final settlements under surcharge preloading and combined treatment reached approximately 1,260 and 1,670 mm, respectively. The combined treatment produced a maximum layer compression ratio of 13.32%. In the 0–6 m interval, it reduced moisture content from 219.2% to 199.1% and void ratio from 5.264 to 4.700, while increasing dry density from 0.38 to 0.412 g cm -3 . Cone tip resistance and sleeve friction increased from 217.8 to 419.9 kPa and from 7.81 to 12.78 kPa, respectively. Under the tested field conditions, surcharge preloading combined with well-point dewatering produced the greatest overall improvement in consolidation response, physical state, and CPT-based penetration resistance among the three evaluated pathways. This site-specific finding supports the field-scale conversion of high-water-content ASWM into a more serviceable waste-derived geomaterial. Environmental safety, long-term durability, energy demand, cost, and life-cycle benefits should be evaluated before broader implementation.