Background
The Queens Hotel was opened in 1838 on the site formerly known as the Sherborne or Imperial Spa. The hotel is located on The Promenade, Cheltenham, Gloucestershire, GL50 1NN and was opened in 1838, it has been listed as a Grade II English Heritage building since 1955.
A large sinkhole was uncovered under the ground floor of the Regency Room, the hotel’s main function room, during regular maintenance checks by the Hotel. The void was approximately 4m across and 2.5m deep, and is approximately 1.5m from the internal face of the front façade of the hotel at the base of the excavation.
The sides of the hole were roughly vertical and some tension cracks were visible which indicated that further spalling of the ground around the sides of the void could have occured. The cause of the hole is unknown, but speculative assessments by previous ground investigations suggested a capped well had failed resulting in the sinkhole forming.
Customer alternatives
Mass filling the hole was considered, however, the depth of weak ground beneath the sinkhole could not be confirmed and access to the site was restricted. Furthermore, the mass void filling approach was not the customers ideal choice as this would mean the Regency room remained closed for months and the room was booked for wedding functions during this period. The edge of the void was also extremely close to the outside walls of the hotel this also raised concerns on invasive remedies further weakening the soils beneath the hotel foundations
Why Geobear
We were initially approached to see if our ground injection technique could be used to stabilise the weakened ground whilst further investigations were conducted. However, the proposal would have required further weeks of delay whilst the ground investigation company completed their assessment.
Following our own engineering assessment, and based on additional dynamic probe testing, it became clear that using a lightweight geopolymer to stabilise the base of the hole would provide the necessary ground strength for a subsequent lightweight fill material to be introduced. This process could be designed, engineered and delivered very quickly and enable the function room to be brought back into use several months ahead of time and enable wedding bookings to be honoured.
Geobear completed the dynamic probe testing that revealed the initial void to be 12m below ground level with an affected area of 25m2.
Geobear solution
Geobear’s team of engineers designed a proposal using two separate types of geopolymer material. The deeper segment of the works successfully and bearing in mind the potential presence of water and to also ensure that the injected Geo-polymer will be able to influence soils at considerable depth, Uretek have specified a Geo-polymer with a lengthy liquid phase, and a medium amount of swelling pressure required for expansion.
The total weight of the geopolymers are at least 30% the weight of the mass filling option
Natural expansion of the Geopolymers perfectly fill the irregular shapes of the void. Geobears works were completed on time and within budget in 3 days. The hotel remained fully open with a wedding reception taking place as planned the following weekend.
Customer testimonial
“I appreciate your help and assistance in this work being completed in a timely fashion.”
Alan Bickerton
Area General Manager
M Gallery Hotels UK
