References

Two LNG tanks have been built on the site of the Hazira LNG plant in India, with 85,000 m3 capacity each.
Made of prestressed concrete, with a diameter of 82 m and a height of 34 m, each tank applies high loads on its foundations, with an acceptable differential settlement limited to 3.3/1000°.
The soil is composed of 8 to 10 meters of dense sand laying on a series of sandy, silty and clayey levels on 7 m.  The bedrock is a compact sandy clayey material.

The preliminary studies showed that a shallow foundation on slab was possible with respect to the settlements criteria, but that a risk of liquefaction of the sandy levels existed under earthquake conditions. Several solutions have been analyzed (pre-loading, deep foundations, dynamic compaction), and finally it was decided to use soil reinforcement with stone columns.

The design of the grid of stone columns was carried out using a finite element model, which showed that settlements in the center of the tank could be reduced by a factor 2 (from 24 to 12 cm), with a differential settlement between the center and the edge of the tank lower than 1.5/1000°. The liquefaction risk has been evaluated using the method by NCEER (Youd & Idriss) based on the CPT tests (static penetrometer).
Finally, the design led to 1500 stone columns (800 mm diameter), under each tank (substitution ratio of 8.7%).

After this design stage, Terrasol was entrusted with the on-site follow-up of the installation of the 3000 stone columns, with a real-scale test on 12 columns (checking of all the  parameters of installation and soil density, with the execution of CPT tests before and after installation of the columns).
Finally, the hydrotest carried out with water filling on 20 m height confirmed the settlements predictions, with approximately 12 cm settlement in the center and 8 cm on the edge of the tanks.

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