Trant Engineering contracts manager Dean Heaphy discusses challenges related to the foundation pour and concrete mix on a major construction project at an oil refinery in south west Wales.

Valero’s Pembroke Refinery in Milford Haven is one of the largest, most complex oil refineries in western Europe. It processes around 250,000bbl/d of crude oil to produce gasoline, diesel, jet fuel, heating oil and low sulphur fuel oil.

The refinery was importing some 41MW of electricity, and Valero decided to invest £127M in a combined heat and power (CHP) cogeneration plant capable of generating 45MW of electricity and supplying the refinery with steam.

Valero’s Cogeneration (Cogen) project was the first to receive planning permission as a Development of National Significance under the Planning (Wales) Act. The engineering, procurement and construction contract for the CHP plant, which consists of a combustion turbine generator (CTG) together with a heat recovery steam generator (HRSG), was awarded to Fluor.

The civil works were undertaken by Trant Engineering, which has a 20 year history of working on the Pembroke Refinery, and a long relationship with Valero, having upgraded fuel bunds and containment at its Avonmouth and Cardiff oil terminals.

Trant commenced enabling works, covering site security and access, temporary bridges, welfare facilities and setting down areas, in January 2019. Next, it moved onto the civil engineering works for the Cogen project, which included foundations, earthworks and backfill, pipe supports, substation foundations, retaining walls, piling, security fencing, ducting, landscaping and utility pipework. Steelwork was fabricated by Trant’s in-house offsite manufacture and assembly department.

The main civils were completed in November 2020, with Trant finishing on site mid last year.

The CTG foundation was nearly 500m3, and it became apparent that the initial proposed large pour concrete design was outside the normal criteria for ready-mix concrete. There was concern that it could result in early age cracking of the concrete due to the heat generated from the chemical reaction in this large mass of concrete.

To overcome these problems, the concrete specification had to meet a number of specific requirements for strength, core heat targets and aggregate type. Having dealt with such requirements for ready-mix concrete previously, Trant’s design team was able to propose a solution to Fluor with a concrete mix that had not been used in the UK before.

Trant worked closely with ready mixed concrete supplier GD Harries & Sons to develop initial concrete mix designs with 80% ground granulated blast furnace slag (GGBS). These were trialled at GD Harries & Sons’ local laboratory with results that they believed were exceptional in terms of strength. The local in-house aggregate sources worked well with the CEM1 and high percentages of GGBS together with a combination of Oscrete UK’s admixtures.

Trant involved Hanson Cement’s technical team to assist with core temperature calculations, mass pour monitoring plans and concrete core temperature recording using thermocouples for the large slab pour. It was agreed that, to obtain the maximum comparable results on site, the structural formwork would be totally insulated for 28 days together with thermocouples installed through the rebar into the centre of the slab for temperature monitoring.

The pour would be more than 480m³, and the team decided to test for slump, or workability, at every 24m³ with simultaneous test concrete cube manufacture. Hanson Cement installed the thermal couples together with data logging to monitor the core temperatures over a 28 day period.

Trant and Harries worked 24 hours continuously on site to ensure that the foundation was completed, with no impact on the original programme. This required the concrete to be supplied continuously, and Harries agreed to produce the special mix at two of its plants, at Bolton Hill and Narbeth. Deliveries were organised in sequence so as not to congest the busy working site, with due time allowance made for on site PPE in accordance with Trant’s health and safety plan.

“We started the large pour at six o’clock in the morning,” says Harries ready-mix technical manager Garry Batte, “and the last truck left the site at 4.30pm having delivered a total of 483m³. The logistics were testing, particularly ensuring the consistency of the mix and coordinating deliveries from two plants using 16 ready-mix trucks each doing four trips, but it all went without a hitch.”

Subsequent test results for the hardened concrete showed that all was in accordance with the design, and thermocouple data confirmed that the core temperatures remained as low as predicted. Trant said that this crucial part of the contract was completed on time and to programme.

Want to read more? Subscribe to GE’s enewsletters and follow us on Twitter and LinkedIn

Tagged with: concrete Fluor foundations Hanson UK Trant Engineering Wales

Van Elle completed its largest and most technically challenging project for the…

Lack of data, back to front decision making and wrangles about risk…

HS2’s Old Oak Common station is set to be the biggest to…

National Grid has introduced flood defence improvements at its Walham substation as…

Sign in or Register a new account to join the discussion.

Business news, Project news, Industry news and Top Stories