Hilden Grange Preparatory School

The old pool

Hilden Grange Preparatory School in Hildenborough, Kent had an old dilapidated liner pool constructed from old asbestos sheeting lined with a domestic pool liner and very old and inadequate pipework connected to poor filtration, all of which required a substantial upgrade to meet current regulatory requirements

The decision

Ascot Pools were invited to inspect the pool and after a site meeting and discussions with the school and the owners, it was agreed that the existing school pool was beyond economic repair and that a new swimming pool would better serve the needs of the school in the long term.

Challenging access

In view of the severely restricted access to the pool site and the limited parking a carefully detailed action plan was drawn up.

Since the removal of the old pool and construction of the new swimming pool was to be undertaken during the school term so the timing of material deliveries. All plant ans machinery had to be carefully coordinated so that operations on site would not adversely affect the day to day activities of the school nor pose a hazard to the young pupils.

Removal of the old pool

The first task was to remove the existing swimming pool which was constructed from plywood, asbestos panels and steel wall supports.

When the water was drained from the pool, the old plywood pool walls collapsed - confirming our initial assessment was correct concerning the weakness of the old pool!

Hazardous materials

All the materials containing asbestos were handled in accordance with our risk assessment and the parts of the old pool containing asbestos was separated from the rest of the material, removed from site and taken to an approved site for the purpose.

The new pool

The new pool dimensions of 16 metres x 8 metres with a constant depth of 1.1 metres was larger than the original school pool, so an amount of additional excavation was required in order to accommodate the larger pool.

Excavation and preparatory work

Given the restricted access to the site only a small excavator could be used in conjunction with a skip loader dumper to take the excavated material from the swimming pool site and into the car park for removal by skip from the site.

The existing concrete floor from the old pool was broken up and removed from site.

The newly formed excavation was trimmed by hand and plywood was erected around the perimeter of the pool as shuttering in readiness for the construction of the new concrete pool shell.

The new concrete shell

Because of the limited access to the site it was agreed that a swimming pool shell using sprayed concrete using 'Shotcrete' rather than blocks would provide the quickest and most cost effective method of pool construction for this project.

The first stage using this type of pool construction is to form a steel reinforcement cage using high tensile steel.

Fabric reinforcement for the swimming pool walls is achieved by using high tensile rod tied horizontally and vertically with steel tying wire.

Steel reinforcement to the floor is double layer of mesh

All the pool fittings such as the underwater lights, skimmers, and inlets are set at the required position in the steel cage

Premixed concrete is fed to the pump from which it is sprayed at high pressure through flexible hoses to the gun held by the concrete spraying operative.

Speed of construction

The 'Shotcrete' sprayed concrete method of swimming pool construction is a very fast process of shell construction. This 16 metres x 8 metres swimming pool shell was completed in 7 hours!

As the shell is drying it is hand trimmed in readiness for the internal render.

After the new concrete shell has been completed it is ready to receive the waterproofed sand and cement render to finish the swimming pool shell to the required dimension.

The next stage of the construction was the fitting of the on - site lining system which we have used on a number of other large projects.

The Delifoil on site lining was completed in 3 days and the pool was filled immediately.

The pool may be enclosed with a building in the future so a structural foundation and a reinforced concrete surround formed around the swimming pool to meet Building Regulations together with a retaining wall.

The limited site access meant that the most cost effective way to form the concrete slab was by the use of a concrete pump.

Pool surround

The concrete raft was then applied with an anti-slip rubber finish running up to the pool edge; this surface eliminated the need for stone coping.

The rubber coating is free draining, soft on the feet and reduces the potential of slipping on the pool surround.

Filtration

In order to achieve the necessary safe circulation rate for a school swimming pool we installed a deep bed laminated polyester sand filter and commercial pool pump. This new filtration system increased the pool water turnover rate to 3 hours enabling a large number of pupils to swim in clean and healthy water throughout the school day.

Successful completion

The swimming pool for Hilden Grange School was completed on time and within the agreed budget with the minimum disruption to the school.