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Killingholme Caverns (1983)

During my year in industry, between the second and third year of my degree, I undertook my first site job for Fairclough Civil Engineering, developing underground gas caverns in Killingholme near Illingham, the first project of its kind in the UK.

I remember it vividly as it was around the time of the miners’ strike, so we were working alongside a lot of the former coal miners, who were tough men working 12-hour shifts, day and night, to get the job done.

The caverns were built for the purpose of storing liquified petroleum gas (LPG), which was a lot safer and more economical to complete underground rather than with above ground tanks.

Located 200m below ground level in Grade A chalk, the caverns could store up to 60,000 tonnes of LPG and were designed to cope with high demand throughout the year, due to its popular use in heating. Of course, with it being the UK’s first ever gas cavern storage scheme, the pressure was on, quite literally, to ensure the substance was safely stored beneath Humberside.

The main challenge came from drilling the chalk itself, as the ground was much harder than first expected and transporting the necessary equipment down to the site wasn’t an easy task! The original plan had been to excavate with two large Titan Roadheaders, but due to the hard and less fractured chalk, drill and blast became the method of choice instead.

As you can imagine, dismantling and lowering the equipment through 2m diameter access shafts was easier said than done, and we had to cut certain pieces in half then weld them back together underground, just to ensure their safe arrival.

From a technical perspective, the site’s main feature was its 230m thick band of Northern Province chalk, which was calculated to have a vital mix of geotechnical and hydrological properties that allowed it to host large unsupported caverns, capable of safely containing pressurised gas.

It wasn’t all plain sailing however, as one of the steel lined access shafts suddenly flooded, which cost an additional £500,000 to fix, while setting the project back 18 weeks, which could have been a major issue given the strict schedule of the project.

While the use of explosives was originally ruled out during the tender stage for the fear of disturbing the jointing systems, it was later tested and confirmed as a safe alternative that allowed us to recover lost time. Establishing the complex shaft bottom with separate bays for rock testing and equipment assembly was however a lengthy process, made more difficult due to restricted access.

Six months into the year-long programme, we were maintaining a steady progress of 4m per 12-hour shift, but this improved as time passed and we gained more experience.

A vital requirement of the caverns was that the pressure of water in the chalk was slightly greater than that of the gas being stored, with the slow ingress of self-replenishing water around the perimeter ensuring there would be no future gas leak.

A project of such magnitude obviously required a lot of technical planning and consultation, so above ground, engineers carried out an independent audit of the geological survey and proposed design, guaranteeing the safety of the project and its workforce.

With the caverns successfully mined into rock that acted as a solid amorphous mass at a depth twice that required to balance the pressure of propane, it was a revolutionary first experience that reaffirmed my love for the career I would embark on for the next three decades.

Although the project was challenging at times, it was the camaraderie between engineers and workers that ensured all aspects were delivered safely and on time – principles that we pride ourselves on today at PDMA.