188 Ground improvement by deep vibratory methods
the columns. The capability of stone columns to provide also additional
excess pore water dissipation was conservatively neglected in the foundation design. More interesting details can be found in the papers already
mentioned above.
The block of stone columns below the downstream buttress was 76.30 m
long and extended over the whole width of the dam. In total 55,000 lin.m
of stone columns were installed using 81,000 ton of crushed rock resulting
in an average column diameter of 100 cm.
The dry bottom feed method was used to install the stone columns to
depths of 9.00–29.00 m. It is not surprising that the large column diameters together with the high replacement ratios selected for this project
and the densification to be achieved in the alluvial deposits could only be
accomplished using capable stone columns construction equipment (Keller
S-340 vibrators) operated by experienced personnel. The responsible engineer concluded that “some level of design uncertainty in the effectiveness
of stone column densification is unavoidable. A thorough geotechnical
investigation throughout the site area can help minimize that uncertainty”
(Lawton et al., 2004). In addition, the high standard QA/QC program
together with a real-time data acquisition system provided at all times during construction an additional back-up security to detect zones in the foundation soil requiring different treatment than anticipated.
the columns. The capability of stone columns to provide also additional
excess pore water dissipation was conservatively neglected in the foundation design. More interesting details can be found in the papers already
mentioned above.
The block of stone columns below the downstream buttress was 76.30 m
long and extended over the whole width of the dam. In total 55,000 lin.m
of stone columns were installed using 81,000 ton of crushed rock resulting
in an average column diameter of 100 cm.
The dry bottom feed method was used to install the stone columns to
depths of 9.00–29.00 m. It is not surprising that the large column diameters together with the high replacement ratios selected for this project
and the densification to be achieved in the alluvial deposits could only be
accomplished using capable stone columns construction equipment (Keller
S-340 vibrators) operated by experienced personnel. The responsible engineer concluded that “some level of design uncertainty in the effectiveness
of stone column densification is unavoidable. A thorough geotechnical
investigation throughout the site area can help minimize that uncertainty”
(Lawton et al., 2004). In addition, the high standard QA/QC program
together with a real-time data acquisition system provided at all times during construction an additional back-up security to detect zones in the foundation soil requiring different treatment than anticipated.