Shrewd Temporary Works Solutions Enable Safe Transport Of 650T Elements Through Live Fuel Refinery

Movement of large and heavy modules for a new plant through a constrained space in a live oil refinery required engineers to solve a complex temporary works design challenge using a combination of “off the shelf” products.

ExxonMobil’s Fawley Fast project involves the construction of a new ultra-low sulphur diesel plant at its Fawley refinery on the western shore of the Solent in Hampshire. The project is now in its testing and commissioning phase after several years of construction.

The plant’s main components are 18 large prefabricated modules. The biggest weighs 650t and the dimensions of the various pieces are up to 15m in width, 40m in length and 22m in height.

The modules arrived via cargo ship from China at the nearby docks before being transported 6.5km via a circuitous heavy haul road route through an active industrial site to the required location in the centre of the existing refinery.

Creation of this route and enabling the transport of the modules over numerous obstacles required extensive preparation, monitoring and temporary works ingenuity from contractor Taylor Woodrow and its specialist consultancy business Taywood Engineering.

From sea to land

“The main challenge of this project was the scale of the load that had to be transported,” explains Taylor Woodrow engineering and digital director Millan Martin.

Not only did this make it an engineering challenge, but it meant that the safety of the team was even more at the top of mind in all designs, solutions and operations than usual.

This was a consideration from the point that the elements arrived via cargo ship to the dock. To transport them, they were first jacked up while still on the barge so that the self-propelled modular transporter (SPMT) could drive underneath, take them on board and carry them onward.

To convey them off the barge, Taylor Woodrow created a bridge directly from the barge to dry land, into an area known as The Knuckle.

“We used The Knuckle because the modules were too large to pass through the normal offloading dock,” Taylor Woodrow head of temporary works and technical services Jonathan Rushton says. “There were also buried existing structures here we had to avoid.”

However, The Knuckle had different complications. “It is an area of very soft clay surrounded by an existing reinforced concrete sea retaining wall and the water table was less than a metre below ground level,” Martin says.

“This is also an SSSI [Site of Special Scientific Interest], so additional approvals were required to build the abutments,” Rushton adds.

It’s one of the most expert clients in the world in terms of this kind of energy and it really wanted us to meet all the most stringent standards, especially within the behaviours of all our people

The bridge from the barge to land spanned the sea wall. However, the sea wall still had some load induced on it, and the risk of collapse due to poor ground conditions, lack of historic information and very heavy imposed loads meant it was a potential risk to safety, programme and cost.

A concrete slab was required, which transferred the load to a 1.3m thick layer of type 1 material, which was partially embedded into the surrounding clay.

“We had to monitor it with tilt sensors just to see whether it was going to sink or not,” Martin recalls. The engineers received continuous real time monitoring data from the sensors, which transmitted via Bluetooth, but no issues were detected throughout.

“It went really smoothly,” Martin says. “The modules were balanced; they were not tilting – the manoeuvre was done as planned.”

With the prefabricated modules shipped to the site, a bridge was installed to transport them from the cargo ship to dry land

Heavy haul road

When it came to the heavy haul road, there were several constraints that had to be overcome, especially considering the size of the elements and the enormous imposed pressure from the SPMTs on the ground by their weight.

“The ground in that area is not the most competent. It is very soft clay with a high water level,” Martin says. “So, we needed very detailed assessments about the bearing capacity of the soil, the most efficient ways to create this haul road and the amount of material that we needed to put in place.”

Rushton describes the route as “snaking through the refinery” due to the number of constraints and assets that it had to be designed around. This was compounded by the narrowness of the haul road, with a clearance of only 100mm from the nearest structure at its thinnest point.

The height of the modules was also an issue. “Due to the overhead lines above clashing with the top of the modules, we diverted the SPMT route into a neighbouring field where we dug a cutting to ensure we could pass underneath,” Rushton says.

The modules’ height also meant they couldn’t pass under existing service bridges. Taylor Woodrow had to devise a route that included four bridges to take the SPMTs over live utilities for the petrochemical complex, which included fuel, chemical and oxygen lines, along with associated assets.

Usually for a bridge that is to carry loads of this scale, a traditional concrete cast in situ solution with deep foundations is used to create the abutments. This is what was outlined in the concept design for the haul road, but as the abutments would have to be quickly removed after the work was done, this was not an ideal approach. Additionally, Taylor Woodrow and the client wanted to reduce embodied carbon, time and costly skilled labour, while improving safety.

“What we needed was something that we could place and remove very quickly, without having to pile in the area, which would require bringing big rigs into the refinery,” Martin says.  “What we managed to do is use Legato blocks as temporary abutments.”

These interlocking concrete blocks are 1.6m wide, 0.8m high and 0.8m deep, weighing 2.4t. They are usually used for structures that carry much smaller loads, such as footbridges or retaining walls. However, the project team believed they could be used in this project and commissioned

settlement calculations and assessments to check the suitability for loads over 650t. It was found to be a viable solution.

Taylor Woodrow placed the blocks on a compacted type 1 material base constructed directly onto the existing ground. “The thickness of the base and the number of Legato blocks varied depending on the span of the bridge, with the largest base utilising up to 48 blocks,” Martin says.

We couldn’t build a permanent bridge because we didn’t have enough time, it’s not cost effective and it would have caused a lot of disruption in the live environment. We had to find a hybrid solution which allowed us to utilise elements to create a solution where the entity of the system is permanent

The slopes up onto the bridges were also an issue due to the constricted space on either side. Usually, earthworks slopes of this kind have three-by-two ratio shoulders to ensure stability, but this was not possible in this space.

Taylor Woodrow engaged reinforced earthworks specialist Tensar to use its TensarTech TR2 system, which allowed near vertical side slopes (up to 85°).

“The use of the TensarTech TR2 system was to reduce the footprint of the bridge, primarily to reduce interfaces with the refinery assets,” Rushton says. “We were still so limited for space that we had to decrease the edge exclusion zone to 500mm to allow for the SPMT route to pass up the embankments and onto each bridge.”

“This was the first time that Tensar had used this system with such high loadings,” Martin says. “However, we managed to validate the design and reduce the exclusion zone to 0.5m from the edge, therefore reducing our footprint further.”

Taylor Woodrow arranged for representatives from Tensar to hold training sessions with its workforce and supervise the construction of the first embankment to ensure that they were able to use the system correctly.

This ensured they would get it right first time without any quality issues, which could have had “dire consequences”, according to Martin.

The bridges were all 9.6m wide and varied in span from 11.8m to 30m. They were constructed using a Sarens modular system featuring bridge beams lifted into position by crane and topped with timber bridge deck mats. The largest was made of seven beams and had a total weight of 340t.

“We couldn’t build a permanent bridge because we didn’t have enough time, it’s not cost effective and it would have caused a lot of disruption in the live environment,” Martin says. “We had to find a hybrid solution which allowed us to utilise elements to create a solution where the entity of the system is permanent.”

To validate the design, Taylor Woodrow carried out load testing through placing gradually increasing volumes of ballast on top of an SPMT and driving it across. It started at 20% of the weight of the design load and went up to 110% (715t).

“To support the load testing, we installed settlement monitoring on the abutments to ensure that any undue movement was identified and suitable control measures could be implemented,” Martin says. “This ensured that the system behaved as expected prior to taking delivery of the modules.”

Changes in groundwater levels were identified as the biggest risk to the stability of the structures, according to Martin, so standpipes were installed near the abutments and were monitored in case groundwater rose above the defined critical levels.

The elements arrived at the neaby dock via cargo ship

Ensuring smooth transportation

The contractor used a mix of technologies across different stages of the project to identify the optimal transportation route for the modules.

During the design phase of the heavy haul road, accurate swept path analysis was carried out to ensure the feasibility of transporting the modules through the route. “This was done to ensure that the structures were in the correct location and of the correct size, and to set the horizontal and vertical alignments,” Rushton says.

To create this, a drone carried out a point cloud survey of the route outside the refinery, while data from topographical surveys was used to provide information within it. This was combined by Taylor Woodrow to create a 3D model.

The swept path was then overlaid onto the model using Autoturn software to detect obstructions.

On site, a handheld Avus augmented reality visualisation device attached to a smartphone provided further detail. This device used the smartphone’s camera to create an image and enabled the engineers to plot the SMPT route over the real-world environment. The Avus device visualised both the wheel alignment and the module overhang, enabling the team to check the road condition and overhead clashes.

“This was done well in advance of the SPMTs arriving so that we could make any modifications and ensure that they would fit down the road,” Rushton says.

The result

The project moved from the design of the heavy haul road in December 2022 to construction in February 2023. Construction took place over nine months and the first module used the route in November 2023.

The SPMTs travelled at roughly 0.8km/h, so it took them each approximately six hours to reach their destination, if uninterrupted. However, this varied depending on space, storage areas within the refinery and the sequencing of the final location.

“All module movements outside the refinery happened at night and predominantly all day within the refinery,” Martin recalls. “The main module movements were completed by May 2024. However, extra module movements were identified, so other items used the heavy haul road until June 2024.”

He describes the performance of the road as “absolutely perfect”.

Additionally, the innovative solutions used to create the haul road saw significant carbon savings on the project.

The Legato blocks for the abutments meant that 250t of reinforced concrete was removed from the design. Additionally, the 217 blocks used for the abutments were reused on site by the client as part of the permanent works, therefore maximising the circular economy.

The combination of existing proprietary solutions – the Legato blocks, the Sarens bridge decks and the Tensar TR2 system – meant that off-site manufacturing was maximised. This saw labour costs reduced by £75,000 and the volume of imported fill material slashed.

The use of the Tensar system for the bridge slopes saved up to 18m width from the haul road’s footprint, removing approximately 12,000t of material that would have been used in a traditional method.

What material was used for the haul road was almost entirely saved, with 85% of it reused on site, while 14% was recycled and only 1% went to landfill. This reduced the lifecycle carbon cost of the project.

With the project now nearing completion, Martin credits the “very high” standards of the client with driving the results.

“It’s one of the most expert clients in the world in terms of this kind of energy and it really wanted us to meet all the most stringent standards, especially within the behaviours of all our people,” he says. “We thank the client; it helped us to do a great job in terms of carbon and safety and was very clear on all the industrial regulations for our construction site and all the interfaces, because this is not somewhere we would normally work in civil engineering.”

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