Building a large community pool where land stability is an issue

January 16, 2017

By Greg Keller

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The new pools at Horace Mann Park were designed and built to appeal to a variety of pool goers.

How can a large community pool complex be constructed on land that is slightly unstable? In the case of the Horace Mann Pool in Rapid City, S.D., designers used 63 underground concrete piers (along with specially designed cardboard boxes under the floor slab) to accomplish this feat. This project was an engineering and construction marvel, to say the least. As recently as 30 years ago, this type of pool design and construction was not possible. Today, however, when posed with this challenge, these construction techniques are available to builders to make such a project a reality.

The existing site

There was an existing pool on-site; however, 
it was 43 years old and derelict at the time of decommissioning. It had outlived its average 30-year lifespan, as the pool suffered from an abundance of large cracks that were no longer feasible to fix, thus the need for the pier-design system to install the new pool. The facility had also outgrown its design, as pool goers today want more options than a basic rectangular basin of water, which is what was previously in place.

Therefore, the new design was to have an abundance of play features and modern pool amenities that would be sure to impress the people of Rapid City.

The piers

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There was an existing pool at the site; however, it was 43 years old and derelict at the time of decommissioning.

As previously mentioned, to design and construct this type of aquatic facility the pools had to be built on top of 63 underground concrete piers which reach down to solid ground. The piers range in diameter from 610 to 1067 mm (24 to 42 in.) depending on the needs of the specific location. The geotechnical report and design plans helped determine the size of the drilled piers required for each specific location.

For instance, the drilled piers around the perimeter of the lap pool are 610 mm (24 in.), while some are 1067 mm (42 in.) in diameter towards the centre of the pool. In total, 24 piers were required to build 
the lap pool: 18 at 610 mm (24 in.), five at 914 mm (36 in.), and one pier at 1067 mm (42 in.) in diameter. Thirty-seven piers needed to be installed to build 
the recreation pool: 20 at 914 mm (36 in.), 12 at 1067 mm (42 in.), and seven at 610 mm (24 in.) 
in diameter.

Each pier is created by drilling into the ground at the desired location to the required depth. If the soil is loose (i.e. caving in) a support/casing tube or drilling fluid is used. Then, a prefabricated steel reinforcement cage is dropped in place. Finally, concrete is poured into the hole and left to cure before construction can continue.

Next, a layer of cardboard forms are placed on areas that do not have piers. These forms allow the earth to expand up into them without cracking the concrete should there be any movement in the earth. These systems are not just any ordinary cardboard box. In fact, they are specifically manufactured for this use, as they have a precise wall thickness and construction type, along with specific thicknesses of the void in between the cardboard walls. They must be placed on a dry day to maintain their structural integrity, and then concrete must be poured on top of them immediately to avoid potential rain damage. If concrete pours cannot be performed on the same day as the cardboard forms are installed, they can be covered to protect them from any impending storms.

The builders

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The top of the drilled piers after concrete was poured into the hole and left to cure.

Acapulco Pools of Kitchener, Ont., worked with RCS Construction, a general contractor in Rapid City, to design/build this new facility. All construction crew members involved had to endure winter temperatures to complete the yearlong project which started in October 2014. Concrete was only poured when temperatures were above 4.4 C (40 F). While based in Canada, Acapulco Pools made good use of local workers as much as possible. It is impractical to send every worker to an out-of-country jobsite, while at the same time, it does not support the local economy where the project is located. That said, Acapulco Pools typically sends a foreman to oversee the project, and throughout the job sends other foreman specific to their trade and the work that needs to be performed at the time. Whether it is the plumbing system, tiling work, or general concrete labour, Acapulco Pools hires as many local trades as possible to help with the job. This is done by hiring through the local union hall, if one exists in the area, or by hiring workers on a temporary basis.

RCS Construction was responsible for the new pool house, housing the change rooms, lifeguard offices, mechanical room, etc. They also completed the demolition of the existing pool, as well as 
the construction of the drilled piers beneath the pool and landscaping. Once the drilled piers were completed, Acapulco Pools then started to construct the two new pool structures.

The pools

The new pools at Horace Mann Park were designed and built to appeal to a variety of pool goers. The lap pool is 25 m (82 ft) in length with a 3.6-m (12-ft) deep end which includes a diving board, rock-climbing wall, and waterslide plunge area. It is a gutter pool, which means the water flows over the top edge of the pool wall and down into a gutter or trench where it makes its way to the filtration and sanitizing systems.

The 25-m (82-ft) length is important, as it enables the pool to be used for competitive swim practices and competitions. While it is not a 50-m (164-ft) Olympic pool, it still adds value to the complex and provides some competitive venue features. Diving boards have long been a staple of a typical aquatic facility, and they will continue to be, as many can remember how fun and exhilarating it is to jump off into the pool. A 1-m (3-ft) dive stand and diving board were installed at this facility.

Climbing walls are a relatively new feature found in today’s aquatic facilities. Users climb up the mock rock wall as high as they are able, and then jump off into the water. These types of climbing walls are becoming increasingly popular for new pool construction, as well as being retrofitted to existing pools. All that is required of the pool is sufficient deck space and water depth, which most pools can accommodate. The lap pool also includes additional gaming features such as a removable basketball hoop and volleyball net. Permanent anchor points were embedded into the deck for these features which allow them to be easily installed or removed.

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The vortex pool is 7.3 m (24 ft) in diameter and is connected to the rest of the pool via an opening. It has water propulsion jets that create a vortex effect, letting bathers float around in a circle.

Finally, the waterslide plunge zone drops bathers 
2 m (6 ft) into the pool at the end of the waterslide. This may not sound like much of a drop, but it is just enough to put a bit of suspense into the riders’ hearts before they splash into the water. This is not a ride for those who are unable to swim on their own; however, it is one of those rides kids will strive to 
be able to go on. Two other waterslides were also installed that end with a runout which brings riders to a stop. These slides are suitable for non-swimmers.

The recreation pool also features a creative design approach when compared to the old rectangular pool. This pool’s footprint is the furthest thing from a rectangle. It uses curves instead and features a beach-entry design which gradually leads up to its deepest point of 0.3 m (1 ft) where a huge playground structure is located.

This is another common design trend amongst new pools for many reasons. It is great for young children who are new to walking and just learning about water.

Beach entries also permit those who are in a wheelchair to easily access these aquatic features without feeling alienated from their peers. A pool lift was also installed on the lap pool to easily transport bathers who may be in a wheelchair or unstable on their feet into and out of the pool.

The recreation pool also features a mountain slide suitable for preschoolers, and a splash 
pad feature where buckets fill with water that randomly empty onto unsuspecting children. Ground geysers and a side winder toy also spray water in a circular motion.

The other half of the recreation pool is geared toward older kids and adults, as it is deeper and includes in-pool benches and a vortex pool. The vortex pool is 7.3 m (24 ft) 
in diameter and is connected to the rest of the pool via an opening. It has water propulsion jets that create a vortex effect, letting bathers float around in a circle.

Behind the scenes

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Each pool system uses two horizontal high-pressure sand filters, stacked one on top of the other.

Each aquatic feature uses underground surge tanks to hold water that is displaced by bathers getting into the pool. Should 50 people get in, for example, there is a lot of water that is not needed at that moment to keep the pool filled (as bathers are taking up this space). The surge tanks help to conserve water by eliminating the need to refill the pool after all the bathers exit the water.

The facility’s waterslides use a similar holding tank; however, in this case it is called a balance tank. It functions by holding enough water to keep the pumps primed in addition to circulating enough water to fill the pipes and slide until it is recirculating at a level that will keep it running without damaging any pumping equipment.

The lap pool, recreation pool, and waterslides all have an independent filtration system. Each pool system uses two horizontal high-pressure sand filters, stacked one on top of the other. The waterslide system only requires one filter 
of the same design. Each of the two pool’s use a valve system, which enables the operator to switch the filters simultaneously into backwash mode.

All of the bronze-fitted, epoxy-coated, close-
coupled pumps use centrifugal suction and are equipped with stainless steel shafts, and totally enclosed fan-cooled, high-efficiency motors. Each pump is connected to a variable-frequency drive (VFD) control system, which acts as a transmission for the pump, allowing it to run smoother and at the proper speed for the task at hand. This conserves energy when full power is not necessary. The facility’s original pumps, which were typical of older commercial pools, operated at one speed. This meant they were either off, or constantly running at full-speed and using way more energy than necessary.

Each system also uses a custom chemical controller that is interlocked with the VFD control system. The flow rate of each system is shown on the chemical controller’s display screen and, based on the incoming water rates, each system adds the appropriate amount of chemicals needed to keep the water sanitized and within acceptable health code ranges.

Currently, the aquatic facility does not use ultraviolet (UV) sanitation, however, the system was designed to allow it be added at a later point. UV is still more popular for indoor public pools where eliminating chloramines in the air can be more problematic.

Keller_Headshot_1[6]Greg Keller is a service and sales representative at Acapulco Pools Ltd., a commercial pool builder and service provider based in Kitchener, Ont. He graduated from Conestoga College’s architecture–project and facility management program in 2011 and was hired by Acapulco upon graduation. He can be reached via e-mail at greg@acapulcopools.com.

Endnotes:
  1. [Image]: http://psm.poolspas.ca/wp-content/uploads/2017/01/IMG_6228e.jpg
  2. [Image]: http://www.poolspas.ca/wp-content/uploads/2017/01/IMG_6836.jpg
  3. [Image]: http://www.poolspas.ca/wp-content/uploads/2017/01/20141014_160822.jpg
  4. [Image]: http://www.poolspas.ca/wp-content/uploads/2017/01/IMG_6239.jpg
  5. [Image]: http://www.poolspas.ca/wp-content/uploads/2017/01/IMG_6213.jpg
  6. [Image]: http://psm.poolspas.ca/wp-content/uploads/2017/01/Keller_Headshot_1.jpg

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