Project

For the Hazira LNG Terminal Project two liquid gas tanks were constructed' each 84 m in diameter and with a filling level of approx. 35 m. The site is located at an estuary on the coast of the Khambhat Gulf in India.

The subsoil at site consists of loose to medium dense silty sand up to a depth of 16 m b.G.L. The upper 4 to 5 m were recently reclaimed material. The fines content of the sand was in the range of 15% on average' sometimes slightly higher. Very dense sand with SPT>50 was encountered below.Stone columns of 1 m diameter and 16 m long were installed on a square grid spacing of 2.4 m using the conventional wet installation method.

a) Settlement Reduction
The expected settlement for the tank centre under the full tank load of 230 kN/sqm was in the range of 12 cm' well below the allowable values.

b) Mitigation of Liquefaction
A peak ground acceleration (PGA) of a=0.25 g for the SSE case was assumed in the calculations. The design was carried out using the method of PRIEBE (1998) and for safety reasons used the initial in-situ density conditions as encountered before start of the soil treatment works. An additional strip of SC-treatment was carried out around the outside of the tank to provide additional stability to the surrounding area in case of a seismic event.

A SC-trial with Pre- and Post-CPT was performed at site. Although not part of the contractual requirement for quality and performance' the post-treatment results in the sand zones have almost doubled and are well above the initial in-situ density condition. At a few levels lenses of cohesive soils reduced the test results to values below the target line. However these lenses are not susceptible to liquefaction.