Royton Wastewater Treatment Works, Oldham

Category: Geotechnical Design

Location: Greater Manchester, UK

Client: Farrans Construction

Sector: Water

As part of the Oldham Royton Integration Strategy (ORIS), Farrans Construction Ltd constructed a 25m x 50m Stormwater Detention Tank.

A formation level of up to 14m below existing ground level required a novel approach for stabilisation of the temporary batters. Typical solutions such as a secant pile wall or sheet pile wall were not appropriate due to the lack of flexibility to avoid existing infrastructure.

GROUND ENGINEERING AWARDS 2018

Technical Excellence Category – WINNER

Project Challenges

This was a particularly challenging project due to variable soil conditions, anthropogenic hazards and a high water table encountered at the site.

Live pipelines and a critical manhole chamber also had to be protected as part of the slope stabilisation works.

OGI proposed the Stable-Earth™ system which comprised groundwater engineering and management, slope reinforcement and erosion control.

This approach enabled OGI engineers to adjust placements and frequency of Platipus anchors, vary slope angles around restricted boundaries and account for variable loads and movement of plant at the top of the batters.

Modelling Analysis

To design the batters in accordance to Eurocode 7, finite element software was utilised in the form of PLAXIS 2D.

This software enables complex geometry to be assessed and can account for the failure mechanism of the soil around the anchors, strength of the cable and pre-stressing of the anchor. OGI prepared and analysed a number of models depending on the constraints around the perimeter of the tank and the anthropogenic hazards encountered.

The first output model was used to check displacements and show stability can be maintained for the load regime for that particular phase. The second output model was used to determine the factor of safety of the design.

Project Success

The Stable-Earth™ system was particularly well suited to the bridging over of existing infrastructure as shown below. With careful and meticulous design, live pipelines and a manhole were protected as part of the slope stabilisation works.

The continued support provided by OGI allowed Farrans to effectively manage the construction programme without relying on specialist contractors to install the slope stabilisation system.

The flexibility of the system enabled live infrastructure to be secured and could enable variable loads to be safely applied at ground level.
The use of OGI’s system for this large scale infrastructure project demonstrated the viability of using cost effective materials to stabilise steep batters for temporary excavation works.