The installation of CMC columns induces significant changes in pore water pressure up to a distance of 7D from its axis. The contribution of further CMCs (distance between 7D and 15D) to the accumulated EPWP readings is less important (Fig.
8). However, a small effect of the columns drilled on the neighboring testing field (at distance of 30–40D) was still recorded (Fig.
9). This finding confirms the observations of Chandra and Hossain (
1993) and Robertson et al. (
1990) for driven piles, where the extent zone of 14–35D was observed in normally consolidated (NC) clays and McCabe and Lehane (
2003) for pile group in silt. The normalized maximum EPWP recorded with P-CPTU during the installation of columns is presented in Fig.
12 and compared to other measurement data. The figure considers the effect of CMC group installation with the shadow effect of already constructed columns. The comparison to other recorded data thus cannot be straightforward due to different measuring systems applied. However, one can make some general observations that the maximum EPWP is very similar to that recorded by McCabe and Lehane (
2003) for the pile group in silt. It is slightly higher than the general tendency observed by Poulos and Davis (
1980) for driven piles in low to medium sensibility clays, by Roy et al. (
1981) in the vicinity of the base of jacked piles in clayey silt, and by Meng et al. (
2015) for a single screw pile in clay. The observed EPWP values for a single pipe pile in slightly overconsolidated soft clay (
Xu et al. 2006), closed-ended pile in Young Bay mud (
Pestana et al. 2002), and a screw pile in soft sandy silt (
Suleiman et al. 2015) are significantly lower than recorded in the present study. These observations make our results consistent with previous measurements. The EPWP distribution in the soil at closer distance to the shaft was not possible to measure during the column installation. The CPTU data connection was lost during the installation of Column 8 (at 2D distance from the P-CPTU). Taking into account the measurements performed on instrumented piles (
Gavin et al. 2010;
Lehane 1992;
Roy et al. 1981), one can expect that EPWP will be higher at closer distance to the column shaft.