Browney Curve Landslide

  • Location: County Durham
  • Client: Story Contracting Ltd - On Behalf of Network Rail
  • Year: Ongoing
  • Sector: Rail |
  • Specialisms: Geotechnical Engineering |

The Browney Curve site is located on and adjacent to the East Coast Main Line (ECML) approximately 3 miles south of Durham. The East Coast Mainline along this section is on an embankment up to 12m in height and crosses side long ground impacted by a series of active landslides for a length of over 500m.

The site has been facing slope stability problems ever since the embankment was built in the 19th Century. Due to issues with the track line and level along the embankment, several rounds of ground investigation have been conducted on the site since the late 1960s. Various remedial works have also been carried out, with most of the focus on draining the slope above the embankment and channelling water beneath the embankment via undertrack crossings. This water is eventually discharged into the River Browney at the foot of the slope.

The hillside and embankment have continued to experience slope movements despite attempts at remedial work. In 2012, Pell Frischmann was brought in to investigate the drainage system and propose solutions to limit ground movement at the site.

What we are doing

In 2017, our Geotechnical team created a plan to fix the drainage system at a site. This plan helped slow down ground movements, which made it easier to maintain the track line and level. It also gave time to come up with a long-term solution for the issue. In the same year, an investigation was carried out and added to the existing data collected over the last 147 years, which included 320 exploratory holes. To manage all this data, the information was entered into geotechnical database software called Holebase SI. Using CAD Civils 3D exploratory hole location plans, geological cross sections, and a 3D ground model, a complete picture of the site was created, as seen in the image below.

By utilising 50 years’ worth of data on ground movement and groundwater monitoring, the ground model was able to map out the known failure surfaces in the ground. This allowed for the identification of two landslides: one affecting the hillside above the railway embankment (landslide 2) and a second, deeper-seated landslide affecting the railway embankment and hillside between the embankment and River Browney (landslide 1).

Outcomes so far

After reviewing the ground investigation data, preliminary geotechnical parameters were used to conduct slope stability analyses. This helped us back-calculate material parameters and refine the ground model to accurately represent the modes of failure observed on site.

Further slope stability analyses were then carried out to determine factors of safety on the existing slope. Our findings found that out-of-balance forces had caused slope movement and displacement of the ECML embankment and rail infrastructure. To ensure the long-term stability of the hillside and embankment, we identified the shear resistance required to balance these out-of-balance forces.

Next, 3D finite element analyses were utilised to determine the optimal location, length, diameter and spacing for shear restraint. Spaced piles were decided on to limit the deflection of the ground beneath the railway tracks and enable the structural design of the piles. Our remedial design proposals included the use of over 500 spaced piles in multiple rows to stabilise Landslide 1. Our plan involved a variety of measures to control the groundwater level and minimise the impact of Landslide 2 on the railway. This also included planting trees, implementing slope drains, repairing drainage systems and utilising sheet piling.

We have designed the construction of the proposed remedial works to ensure that rail traffic on the East Coast Mainline is maintained. Work is scheduled to commence in Autumn 2023 with construction support and monitoring of the performance of the remedial works to be provided by Pell Frischmann into 2025.

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