Project Description
The Townend development on South Side in Steeple Aston near Bicester is a collection of eight new homes that have been designed to blend perfectly into their village setting. As part of the enabling works a new entrance was required for site traffic and future residential access to the development.
The Challenge
Site operations revealed a weaker than anticipated subgrade strength, with a CBR value of less than 2.0%. The pavement at the entrance of the development subsequently needed to be re-designed to meet Section 278 of the Highways Act 1980 in order to obtain approval from Oxfordshire County Council. Methods for improving the subgrade, as outlined in the Design Manual for Roads and Bridges (DMRB) document CD225 revision 1 (2020), clause 2.7, Note 2, include excavating and replacing between 500 to 1,000mm of the soft subgrade with granular fill, mechanical stabilisation (using geogrids and/or geotextiles), and soil stabilisation.
The Solution
ABG Ltd was approached by MJA Consulting to provide a solution to meet the requirements under Section 278 of the Highways Act 1980 and to avoid unnecessary site delays.
ABG Engineers proposed a stabilised road foundation utilising geogrids to improve the stiffness of the unbound layers, thereby increasing pavement life and allowing for a reduction in pavement thickness. This proposal minimised additional excavation, reduced the amount of imported stone required, and decreased construction time, carbon emissions, and overall project cost.
Designed Pavement Section
The entire road construction design was developed using our in-house software, which integrated ABG geogrids to facilitate safe construction traffic and provide a stabilised foundation for the final road construction.
