Services via Gloucester as well as Bristol Parkway are affected.
Meanwhile, due to signalling upgrade work, no trains will run between Gloucester and Kemble or Yate on Saturday and Sunday, November 4 and 5.
Stations affected include Stonehouse, Stroud and Cam & Dursley.
In addition, track renewals will also mean that no train services can stop at Bristol Parkway on Sunday until after 5pm that day.
Replacement buses are planned between Gloucester and Kemble, Gloucester and Bristol Parkway on Saturday, or Gloucester and Bristol Temple Meads on Sunday.
- Trains between London Paddington and South Wales will be diverted via an alternative route – extending journey times by around 30 minutes.
- On Sunday these GWR services will stop at Patchway instead of Bristol Parkway up until 1700 – with connecting buses to/from Bristol Parkway
- Trains between London Paddington and Cheltenham Spa will run to Kemble instead of Cheltenham Spa – services will run between Swindon and Kemble on Sunday
- CrossCountry trains will be diverted via an alternative route between Cheltenham Spa and Bristol Parkway/Bristol Temple Meads – stopping at Gloucester and Newport
- Valid rail tickets can also be used on the Y1, Y2 and Y6 buses between Bristol and South Gloucestershire
Ben Scott, GWR Station Manager for the South Cotswolds area, said:
“These works form part of an ongoing programme of rail improvement works that will allow us to maintain services for customers travelling via Gloucester or Bristol Parkway.
“Some train services will be using a slightly different route from normal this weekend, in order to maintain connections.
“We will also provide replacement road transport, plus ticket acceptance on relevant bus services to enable customers to complete their journeys.”
Mark Parker, Network Rail project manager, said: “This is part of our continual work to make services safer and more reliable.
“Unfortunately, we do need to close the railway so our teams can work safely and most efficiently.
“We’re sorry for the disruption but the benefits will be felt for decades to come.”