Geobear was contacted by J Brown Construction to provide an emergency solution for a project they were completing for Thames Water.

The overall project scope was to replace a section of leaking water pipe beneath Hadley Green Road in Barnet. Over the decades, gradual degradation had led to the victorian era pipe cracking, which resulted in water leaking into the surrounding soils. The pipe needed replacing to prevent any potential for a sinkhole in the road and subsequent subsidence occurring in the area.

Following the excavation of the site, a large void was discovered 10m below ground, around the area of the victorian pipework. The leaking water had caused a major washout of the soils surrounding the pipe and a sinkhole formed in a 2m radius. The project had to be stopped immediately due to safety concerns and a solution sought.

To complete the pipe replacement works the road needed closing for several days, but the discovery of the void could have meant a lengthy closure unless an urgent solution was delivered.

 

Geobear solution

Geobear on-site at Hadley Road

The contractor discovered the void on a Thursday morning, and J Brown subsequently contacted Geobear to provide a proposal for emergency works. The Geobear engineering team promptly assessed the reports and designed a solution using one of Geobear’s lightweight, highly expansive structural fill materials. The proposal was accepted, and we were on-site within 24hrs to deliver the works on Saturday morning.

The solution involved the installation of a geopolymer material directly into the voided area, which would also surround the existing pipe. The expansive force of the material would fill the 2m3 void and provide stability around the location of the pipe. This stability would ensure a completely stable and safe working area to continue the main scope.

A qualified Geobear technician installed the geopolymer material via a hose from the Geobear mobile unit stationed on site. The hoses can be used up to 100metres from the mobile unit and material is introduced to the site via a pump housed within the self-contained Geobear unit. 

Our geopolymer material was pumped into the void, filling it and completely encasing the existing pipeworks. This method was used to ensure a completely safe and stable environment for the works to continue. The next stage would see the client remove segments of the geopolymer fill material and access the pipe to complete replacement. Due to the fast curing nature of the geopolymer, the replacement could be completed within hours, thus reducing a further delay to the project.

 

Why Geobear

There are several critical reasons for using a Geobear solution, firstly the nature of the material we use for filling voids. The material is lightweight, so no further weight is added to the depleted soils; this prevents the likelihood of any new movement at depth. It also has strong structural properties, comparable to that of foam concrete. 

Secondly, the geopolymer we use is easy to remove; this meant the client could cut through and remove the required material to access the area of pipe within an hour.

Thirdly, we use minimal plant and our installation process through the use of pumps and hoses enabled us to fill the difficult to access void competently. Furthermore, on receiving the original instruction, we could design and deliver a solution within 48hrs.

 

Alternatives 

The only viable alternative was for a foam concrete product to be poured into the maintenance hole to fill the void below. Foam concrete is a much heavier material, and there would be risks associated with adding weight to an already unstable area of soil. 

Had foam concrete been used to fill the void, access to replace the pipe would have been extremely difficult. There would have been a delay while the concrete set and then its subsequent removal would have added days to the project.

Outcome

Geobear successfully filled the void with geopolymer, and the client was able to complete the pipe replacement for Thames Water without requiring a lengthy road closure, which would have affected the local community greatly.