Soil and Compaction
Improvement of Different Grounds
Based on a grain size analysis a soil can be judged for its compactability:
Soils in zones A and B can be compacted by the deep vibratory compaction method Vibro Compaction (also called “Vibroflotation”), while soils of zones C and D cannot be compacted by vibration alone.
Soils in zone C are often found on sites where liquefaction due to earthquakes is of concern. These soils can be compacted during the installation of Stone Columns.
Soils in zone D are not compactable by vibration, but can be substantially reinforced, stiffened and drained by installing Stone Columns.
Requirements for the soil to achieve good compaction by vibration :
- The soil must be permeable enough to allow rapid drainage of the pore water during the compaction process. The permeability is high enough for all granular soils with less than 10 % fines smaller than sieve #200 (0.074 mm) AND less than 2 % clay.
- The friction angle of the soil must be high enough to permit the passage of the compacting shear waves. This requirement is usually satisfied if the soil is well graded.
- The sand or gravel should not be easily crushable (carbonate content in form of shells) or contain very platy mica minerals that would increase soil compressibility.