TENAX logo International web site
  International web site Geosynthetics Soil reinforcement Case histories Archive  
sitemap contact us
  Soil reinforcement  

Reinforced pulverised fuel ash embankments, Newton Cap Viaduct, England



TENAX reinforced pulverised fuel ash embankments




TENAX TT geogrids


A689 Newton cap viaduct, Northern
England. South approach embankments


Bullen Consultant (now AECOM)

Main contractor:

John Mowlem Construction Plc
(now Carillion)


Durham County Council

TENAX distributor:

Tenax UK Ltd



Existing structure

The existing viaduct and approach embankments were constructed between 1854 and 1857 as part of the Bishop Auckland branch line of the North Eastern Railway’s branch linking Darlington, Bishop Auckland and Durham.


It stands one hundred feet high with sixty foot spans. After closure in 1968 it became part of the Brandon - Bishop Auckland Railway Walk but in 1995 was re-decked for road traffic and now is converted into a road bridge carrying the A689 highway across the River Wear.


Widened by 13 feet with footpaths to either side, concrete was used on top of the stone deck. The viaduct is a Grade 2 listed protected structure.



Approach embankments

The existing southern embankment was constructed on the sloping valley side and gradually increased in height from the original ground level to a maximum of 15m adjacent to the viaduct.


The embankment had a crest width of 10-12m approximately and a total length of 120m. The side slopes were generally 1 vertical to 1.5 horizontal (33.70 to the horizontal).


The specifications required that the embankment at the southern end be widened, but the toe of the new slopes would have been very near the adjacent houses.


The Consulting Engineer, Bullen Consultants therefore decided to reconstruct the embankment at the southern end of the viaduct by the reinforced soil technique, using lightweight materials as the reinforced fill, thus keeping the net increase in loading to a minimum.


In order to achieve this the Consultant proposed a conceptual design with clay shoulders and a lightweight core of expanded clay balls. To meet the Consultants main criteria for the design, and for reasons of economy, Contractor John Mowlem Construction Plc proposed the use of Lightweight pulverized fuel ash (PFA) as the fill material.


Extensive site investigation was carried out for the project in order to determine the geotechnical properties of the underlying foundation soils and the location of the ground water table.


Modified embankments

The reconstruction of the south approach embankment, involved the raising and widening of the existing embankment to suit the requirements of the new highway.


The overall weight of the modified embankment was designed to be approximately equal to the existing in order that the overall stability of the valley side was not reduced.


The distribution of the weight longitudinally was also made similar to the existing embankment. The design included removal of the existing embankment material down to the assumed foundation level and replacement with pulverised fuel ash (PFA) fill.


All surfaces of the modified embankment were covered with plants and grasses to form permanent ground cover and were designed to be drought resistant.


The reinforced earth slopes were designed to resist erosion during their design life. The design also ensured protection against fire, chemical spillage, ultra violet light and wilful damage.


Also, an overall stability analysis was carried out to ensure its stability against a deep seated failure.


This project has demonstrated how embankments can be constructed in urban areas where landtake is virtually impossible, by the use of a geogrid reinforced technique, by:

  • The use of lightweight fill such as (PFA), in order to minimise net increase in loading.
  • Minimising the size of the embankment by the construction of reinforced steep slopes.
  • Providing basal reinforcement to the embankment, thus increasing the factor of safety against deepseated failure.

reinforced earth embankment construction


reinforced earth embakments


reinforced pulverised fuel ash embankments







TENAX reinforced pulverised fuel ash embankments, Newton Cap Viaduct, England


Slope crest enlargement

  TENAX © 1995-2014 All rights reserved