Structural solutions for highways
by Craig Roberts, on June 23, 2020
Reinforced (sometimes called mechanically-stabilised) soil is becoming a standard way of forming cost-effective walls and bridge abutments on highways, instead of the more traditional options frequently involving piling and reinforced concrete.
Load-bearing reinforced soil walls can cut construction costs by up to 75% and halve build times, compared with traditional solutions, while being robust and low-maintenance. Systems use layers of geogrid to reinforce soil, increasing bearing capacity and increasing resistance to differential settlement. Reinforced soil structures have lower bearing pressures, which can eliminate the need for expensive foundations.
Geogrid layers are mechanically connected to a range of facings, including modular blocks, concrete panels, gabions and crib walls, depending on the aesthetic requirements of the project. This creates strong, durable structures, requiring minimal maintenance, with design lives of up to 120 years, that are covered by HAPAS BBA certificates.
In many cases, all of a bridge’s bank seat loading can be carried by a reinforced soil abutment. As I discussed in my blog on temporary highways structures, Tensar has designed load-bearing abutments using our TensarTech systems that can support loads of more than 500kN/m. And, if piling is needed, then the piles can be incorporated easily into the abutment fill.
Also, as we discussed last week, a big advantage of using Tensar’s durable HDPE geogrids is that they work with a wide range of materials, including non-standard fills (such as selected site-won fill) and waste products such as pulverised fuel ash. This versatility can save time and money on projects, as well as reducing their carbon footprint.
Loads of support on the A21
The TensarTech TW3 modular block reinforced soil system was the ideal solution for building the load bearing bridge abutments and wing walls for overbridges at two new grade separated junctions between Tonbridge and Pembury on the A21 in Kent.
We worked with WSP to design the retaining structures for the main contractor. The abutments were built using Department of Transport Type 6I/J aggregate, designed to meet bank seat loads of up to 566kN/m and to resist horizontal loads of up to 54kN.
TW3 was used to build a total of 194 linear metres of abutments and 80 linear metres of wing walls up to 7.6m high. It was also used to build a 60m long, 3.6m high retaining wall on the route.
Aside from technical performance, the main contractor chose TW3 because traffic flow had to be maintained throughout the works. TW3’s modularity meant it could be built in the limited space available, without heavy lifting equipment or propping, and with minimal disruption to road users.
Download the A21 Tonbrige to Penbury case study to find out more.
Tensar's TensarTech Wall and Slope Systems
With over 30 years of construction knowledge, design experience and innovative geogrid products, our TensarTech permanent and temporary retaining wall and slope systems provide a number of facing types and construction options to suit the structure’s end use, location and required design life.