ABSTRACT

A large LPG cavern in bedrock has been constructed in the oil industries area of Porvoo, southern Finland. Excavation works were finished in autumn 2016 and the rest of the construction works were finished by June 2017. The filling of the cavern was started in July 2017. The storage capacity of the cavern is about 163 000 m3 of liquid petroleum gas. The main cavern is situated about 100 m below the groundwater table. The cavern dimensions are: cross section 600 m2, width 22 m, height 30 m and length 275 m. The construction of the cavern was made by using the drilling and blasting method and it was supported by rock bolts and steel fiber shotcrete. Host rock of the cavern is of good quality which favors its large size. Rock conditions are known quite well on basis of the numerous previous cavern projects in the area during the past five decades. Rock quality of the site was controlled with investigation drill holes before starting of the construction. The optimum direction of the cavern was justified using elastic numerical modelling and key block analysis. Rock mass water conductivity around the cavern was found to be very low, even one magnitude lower than was expected on basis of the Lugeon tests made in the investigation drill holes. Sustaining of the water pressure around the cavern during operation is ensured with water curtain drill holes which were drilled above the cavern from the access tunnel. The groundwater table around the cavern and in the water curtain will be regularly monitored from boreholes during the operation of the cavern. No major rock mechanics or engineering problems were met during the construction of the cavern.

1. INTRODUCTION

A large new LPG cavern (Figure 1) has been built in the bedrock of Borealis Polymers production facilities in Porvoo, southern Finland. It is related to the total capacity increase of plants. Liquid propane and butane can be stored in the rock cavern, which Borealis uses as raw materials for the production of polyolefin plastics. Polyolefin plastics manufactured at the Borealis Porvoo plant are mainly used as raw material for water, gas and wastewater pipes, steel pipe coatings, electrical cables and packaging.

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