Design, construction and performance of chalk trackbed for High Speed One

High Speed One (HS1/CTRL) required the design and construction of the first high speed 300 km/hr track bed in the UK, with about 40km of its length built through chalk geology. With the imminent commencement of the detailed design of High Speed 2, the authors thought it would be prescient to draw together, review and summarise this track bed knowledge into a single paper. To deliver the UK’s first high speed track bed in chalk, there was much to learn and compare with our high speed colleagues in France. We tested and evaluated the cyclic behaviour of the resilient modulus of our English chalk and went back to first principles with the international railway earthworks design code to extrapolate track bed design up to high speed. There was also innovation in regard to chalk earthworks, developing a new chalk earthworks specification, controlling chalk earthworks primarily by moisture content (with periodic secondary intact dry density testing) for construction of embankments suitable for high speed trains. The acceptance testing of the track bed during construction adopted the French plate load tests. The track bed design and construction also succesfully dealt with extensive solution features under trackbeds. The paper also discusses the performance of the chalk earthworks track bed on HS1 over the last decade.