Optimizing Uniformity and Mechanical Performance of Sandy Soil Through MICP Enhanced by n‐Butyl‐Thiophosphoryl Triamine (NBPT) as a Urease Inhibitor

Microbially induced calcium carbonate precipitation (MICP) has emerged as a sustainable approach for sandy soil stabilization, though its practical implementation is frequently hindered by nonuniform calcite distribution and premature pore occlusion near injection zones. In this study, the application of n‐butyl‐thiophosphoryl triamine (NBPT) as a urease inhibitor was systematically investigated to regulate MICP reaction kinetics, with dual objectives of enhancing mechanical performance and spatial homogeneity in treated sandy soils. A comprehensive experimental program involving solidified sand column specimens treated with NBPT concentrations spanning 0% to 1% (w/w urea) was conducted. Mechanical characterization through triaxial consolidated drained (CD) shear tests, hydraulic conductivity assessments, and stratified calcium carbonate quantification revealed critical dose‐dependent effects. Optimal enhancement was achieved at 0.1% NBPT concentration, yielding a maximum shear strength of 2.8 MPa and a three‐order‐of‐magnitude permeability reduction from 3 × 10 −4 to 2 × 10 −7 m/s. The spatial homogeneity of cementation products was substantially improved, as evidenced by a 121% increase in calcium carbonate content within the bottom section (from 3.8% to 8.4%) and a reduced spatial disparity to below 5% across vertical sections. Conversely, hyperinhibition effects were observed at elevated NBPT concentrations (1%), manifesting as suppressed microbial activity and compromised cementation integrity. These findings establish NBPT as an effective biochemical modulator for addressing MICP’s intrinsic heterogeneity limitations while concurrently enhancing geomechanical performance, offering critical guidance for field‐scale implementations in liquefaction mitigation and general erosion resistance. However, applications requiring ultra‐low permeability may necessitate supplementary treatment to meet stringent design thresholds.