Field-Scale Quality Control of Lime-Cement Pillar in Conductive Clay Using Electrical Resistivity Tomography

Ground improvement with lime-cement pillars is becoming increasingly common in the Nordic countries for exploitation of areas with poor stability. However, there is no non-destructive method for quality control of the ground improvement. Significant changes in the electrical properties after mixing of the binders make electrical resistivity tomography (ERT) a potential method. In connection with lime-cement pillar trials for the Västlänken project in Gothenburg, Sweden, a series of different single borehole ERT measurements were performed. Three cases are compared in this paper: untreated ground, treated uncured ground and treated cured ground. The raw data pseudosections show a significant general drop in resistivity between the untreated and treated uncured data sets, while the curing process increase the resistivity significantly close to the borehole. Full 3D inversions have been carried out for all three cases. In model space the cured pillar is still causing a clear increase in resistivity around the borehole, while the decrease between the untreated and uncured case is less obvious than in data space. With the large contrast between the untreated and the treated uncured in data space it was expected to be visible in model space, improved inversion methods and settings could help resolve this.