MICP treatment techniques for sandy soil stabilization through shear wave velocity monitoring

This research investigates the application of Microbially Induced Carbonate Precipitation (MICP) as a sustainable ground improvement technique for enhancing the mechanical behavior of dry sandy soils. A biocement solution comprising 250 mM urea, 250 mM calcium chloride (CaCl2), and 20% (v/v) soybean-derived urease was utilized to promote calcium carbonate (CaCO) precipitation within the soil matrix. Two treatment methods were evaluated: surface percolation and subsurface injection. Surface percolation was conducted using three regimes (a) a single application at a rate of 157.5 mL/h, (b) continuous dripping at 3.3 mL/h, and (c) periodic dosing at 13.5 mL/h (79 mL/day) for four days. A fourth method employed periodic injection through a porous pipe to facilitate uniform distribution of the biocement and mitigate bioclogging, which commonly affects both the top and bottom layers of treated soil columns. A real-time monitoring system incorporating horizontally mounted bender elements was employed to measure shear wave velocity (Vs) and compute the initial shear modulus (G0), thereby enabling continuous evaluation of stiffness development during biocementation. Results demonstrated that periodic application (method c) and the injection technique produced the most uniform improvements in Vs and G0 across cross-sections, with the injection method achieving a peak G0 of 81.18 MPa on the X–X′ plane equivalent to a 211% increase over untreated conditions. Scanning Electron Microscopy (SEM) revealed widespread CaCO3 deposition bridging sand grains, while X-ray Diffraction (XRD) confirmed the presence of calcite as the primary crystalline phase. The study highlights the synergistic benefits of using soybean-derived urease and optimized dosing protocols to accelerate MICP reactions within one week, offering both practical and environmental advantages. These findings support the viability of enzyme-accelerated MICP as a scalable and low-impact soil stabilization method. The proposed injection technique, in particular, demonstrates strong potential for field applications requiring deep and homogenous ground improvement, such as roadbeds, embankments, and pipeline corridors in arid or semi-arid regions.