Roadside Active-Passive MASW Surveys to Evaluate Soil Grouting: Fid-Bau Portal

Roadside Active-Passive MASW Surveys to Evaluate Soil Grouting

Park, Choon / Cirone, Alessandro / Rodrigues, Roger

Soft soils are often improved through a grouting technique that injects grout at multiple ground locations. Soils surrounding the injected areas are displaced and compressed and the subsequent consolidation provides additional reinforcement within the soil structure. The overall soil stiffness is hence improved. Although various methods have been traditionally used to evaluate the improvement of the soil stiffness, for example, SPT, CPT, and pressuremeter test, they all provide local results highly dependent on test location. On the other hand, the seismic surface-wave (MASW) method can provide a macro-scale assessment of grouting effectiveness by analyzing wave propagation characteristics that respond to bulk elastic properties. In addition, an MASW survey can produce a cross section of subsurface shear-wave velocity (Vs), which is scientifically the most relevant indicator of material stiffness. Multiple MASW surveys were conducted over an area near Navegantes, Santa Catarina, Brazil, where the Federal highway was being duplicated and soft soils existing in the region were being improved by a special grouting technique locally developed. The survey results showed that, compared to the virgin soil, the Vs increase at grouting depths (2–8 meters below surface) is up to 200 m/sec, which corresponds to approximately 80 MPa and 240 MPa in shear modulus and Young's modulus, respectively. Some key aspects in data acquisition and processing steps are explained that included an active-passive combined survey followed by data analysis using a special algorithm for a full utilization of advantages from both type of MASW surveys.