Abstract:
The work presents a full-scale implementation of bio-grouting for sandstone consolidation in a zone affected by dissolution, fracturing and exfoliation as results of chemical weathering. A total area of 24 m2 is treated up to a depth of 3 meters using an environmentally friendly, low-viscosity grout to produce calcite binding minerals. The mineralized calcite is result of an organic enzymatic mechanism, reflecting a naturally occurring process, which is designed fit for purpose, with respect to the required strength and permeability parameters. Injection pressures as low as 0.3-0.5 bar are applied, which makes the whole approach very efficient and reduces the risk of unwanted ground deformations during injections. This bio-geo-chemical grouting approach is intensively monitored using geophysics. The findings reveal a general improvement of geotechnical properties, indicating the successful injection in line with the project specifications. In particular, seismic methods reflect a significant increase in the material’ s density due to the presence of newly mineralized calcite crystals. Electric tomography is used to monitor the penetrability of the injected bio-grout in real time. Significant variations in the sandstone’ s resistivity are captured and by comparing pre-, during and post-mineralization resistivity spectra a valuable, and so far unique, insight into the bio-cementation process is provided at the macro-scale. Overall, the findings of this work demonstrate the successful implementation of bio-grouting, in the form of calcite production, to consolidate a sandstone which lost its integrity and natural cementation due to weathering. The work aims to accurately capture and illustrate the contributing mechanisms of bio-cementation on different scales, benchmarking its general applicability for full-scale hazard mitigation measures based on environmentally friendly grouts.