Earlier this year a sinkhole had developed due to a failure of a Thames Water asset. This sinkhole created a number of complications and as such it was urgent that a solution was found quickly.

To meet this need Riddwood Consulting Engineers and Pro Rail Services Ltd teamed up, combining our skills, talents, and experience to provide Network Rail with a rail drainage design.

What Is A Sinkhole?

Sometimes referred to as a swallow hole or a doline, sinkholes are large holes in the ground that seemingly appear out of nowhere'. They can sometimes be large enough to consume buildings in a few moments. They happen in nature, but they can also be caused by human activities such as groundwater pumping or construction. However, whilst it may seem like the 'appear from nowhere', this is not true. They only form in specific situations when specific criteria is met.

There are numerous different types of sinkholes, one such type is the cover-collapse sinkhole which is arguably one of the most dangerous forms of sinkhole. This type of swallow hole can cause catastrophic damage because over time sediments spall into a cavity which grows until it causes a proof collapse, which creates a sudden sinkhole.

Another type of sinkhole is a dissolution sinkhole. This as its name suggests is caused by a solid substance being dissolved into a solvent. For example, if a limestone surface is dissolved by ponding water, a sinkhole can be created over time.

Did You Know? Sinkholes can also happen underwater. However, when they occur underwater, they are often called blue holes. This form of sink hole have been found in areas such as the Bahamas, which is where the deepest known sinkhole is located; it is called Dean's Blue Hole.

The Sinkhole At Hersham Station

The sinkhole in question was positioned at the toe of a 7 meter embankment which was approximately 6 meters away from the up slow on the main Waterloo line. The distress call was received at 15:30 on the day of the incident and by 18:30, a mere three hours later Pro Rail Services Ltd and Riddwood had sent a senior civil/structural engineer, a surveyor, and a track handback engineer to provide their expert services to remedy the situation.

The Plan - Reactive Works At Hersham Station

Subsequent to meetings with representatives on site from Network Rail, a proposal was put forward in order to manage the situation until the root cause of the sinkhole could be stabilised. This plan included the following.

  • The placing of an emergency speed restriction on the section of the track.
  • The placement of track movement gauges on the track adjacent to the sinkhole, the gauges were monitored hourly to establish if the track was subject to any form of vertical movement or “bouncing".
  • The establishment of a grid of survey points on the embankment and fence line adjacent to the sinkhole. This enabled the monitoring of the position of the track in both the X and Y axes therefore indicating any movement of the track either vertically or horizontally. The baseline reading was recorded by 20:45.
  • The implementation of a Track Monitoring Plan, the plan was generated and authorised by 14:00.

The Project - Reactive Works At Hersham Station

During the early stages of the reactive works, Network Rail requested that the survey area be extended. However, the positioning of survey points in the proposed additional areas proved challenging. This was due to the locations being populated by numerous mature trees. As such, Network Rail requested the removal of the trees to facilitate and accurate comprehensive survey of the greater area.

Too meet the needs of the client, Pro Rail Services Ltd mobilised a de-vegetation team which included tree climbers and arborists, and as such the site was cleared and all arisings were removed from the site within just 72 hours.

With regards to Riddwood Consulting Engineers and the role we played in the reactive works, we surveyed the control points every four hours and readings were checked against preceding readings by a senior engineer. This was to establish if any significant movement has occurred.

Rail Engineering Services From The Riddwood Team

The Riddwood team of rail engineers have over 40 years experience providing their services. We have managed and delivered numerous multi-million pound rail projects across the world, including surveys, track monitoring, and a full spectrum of design and engineering solutions.

In addition to our recent work at Hersham Station, we have also provided rail drainage design services to renew an existing drainage design near Minster Station, Kent.

If you would like to learn more about the consulting and civil engineering services that our team have provided in the past, please visit our Case Studies page. It's filled with valuable information about previous projects which could provide you with valuable insight into our engineering skills. This includes case studies working with clients such as London Underground, UKDN Waterflow, and many more.

Interested? Give Our Team A Call And Make An Enquiry Today

If you would like to make an enquiry, please do not hesitate to get in touch with a member of staff. Our friendly team of experts will be happy to assist you and answer any questions you have regarding our services.

You can contact us using one of the following methods:

  • You can contact us by telephone using the following number, 0118 978 7930.
  • You could contact our team using Email. Please send your questions/enquiry to us at, info@riddwood.co.uk.
  • You can also contact us by filling in our contact form.
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