Category Archives: Construction

Expansion and Contraction in PVC Pool Piping

In the commercial swimming pool industry, the overwhelming choice for pool piping material selection is Polyvinyl Chloride (PVC). The use of such materials can provide security, as it is non-corrosive, and if installed properly, some would say this pipe material can provide an almost infinite life span. But, in comparison to other pipe material selections, such as cast-iron, ductile iron, steel and concrete, PVC has a much higher coefficient of thermal expansion. This coefficient considers the amount of expansion or contraction that will occur due to the temperature range your pipe will endure and the length of pipe you are calculating. Thus, the design and installation of PVC pipe must consider how to accommodate such changes in pipe length.
For pools located in areas with seasonal temperature changes that utilize long runs of straight pipe sections, consideration should be given to accommodating expansion and contraction of the pipe. The ASTM Standard 2774 Underground Installation of Thermoplastic Pressure Piping, contains specific information on the topic of expansion and contraction in pool piping. A science-based formula for determining the expected change in pipe length due to expansion and contraction is:

By knowing the amount of expansion or contraction that will occur in your piping system, you can adjust the design as needed. These accommodations can range from changes in vertical or horizontal direction of your piping system, to the use of mechanical expansion and contraction joints. Changes in pipe direction using expansion loops, offsets and bends are ways to accommodate the expected changes in pipe length within your system. Considering that pool piping systems often have changes in direction due to the inclusion of supply inlets, main drains and feature supplies, the design and installation of the underground pool piping system naturally accommodates expansion and contraction. However, there are times when pipe runs become quite lengthy without changes in direction, and considerations for the inclusion of an expansion loop or mechanical joint will be needed.

Mechanical expansion joints come in many different types. Their primary purpose is to provide a means of flexibility in the piping network for expansion and contraction. They often work by allowing the pipe to slide into or out of itself like a piston. Installation of mechanical expansion joints for underground piping is critical. If the mechanical expansion joints, along with the materials used for backfill around the joints, are not properly installed, the effectiveness can be compromised. For example, backfill materials can make their way into the mechanical joint and hamper pipe movement. If backfill materials are a concern, it is recommended to boot the joint for protection.

In most installations, the straight pipe runs are not excessive enough or the design of the piping network will already include many bends or turns in the pipe. However, for those occasions where environmental factors result in expansion and contraction of pool piping, or straight pipe runs 100 feet or more exist, the design and installation must have allowances for the changes in pipe length that will occur. Without these provisions, the underground piping will be susceptible to potential damage, which will result in leaks to your pool piping system.

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Springboard Diving

As a full-service aquatic consulting firm, we strive to design facilities that meet the needs of all user groups. While many aquatic sport facilities revolve around competitive swimming, we certainly do not want to neglect diving. While most university and high school teams only have 5-10 divers on their roster, they can be a secret weapon to propel a team over the competition. For instance, Purdue University finished in 13th place at the 2017 NCAA Championships with a final score of 106.5. The Boilermakers, Purdue’s diving team, scored 94.5 of the total 106.5 score for Purdue. Without the diving team, Purdue would have finished tied for 32nd place. Clearly, consideration should be given to a facility’s diving amenities.

Coincidentally, Purdue has one of the premier diving training facilities in the country, which includes a separate warm water diving pool with a massive 1-meter, 3-meter, 5-meter, 7.5-meter, and 10-meter diving tower. This facility has even attracted athletes like Olympic platform diving medalists Steele Johnson and David Boudia to train and compete at the university. While not every facility has the capacity or need for a platform as elaborate as Purdue’s, there are subtle ways to make your facility stand out when it comes to springboard diving.

There are two ways to mount a 1-meter or 3-meter springboard: on a stand or on a concrete platform. We tend to see a prefabricated, manufactured stand more often than anything else. These stands are made of heavy-duty aluminum and anchored to the deck using bronze deck anchors. The stands include handrails on both sides, as well as a ladder at the rear end of the board.

Shelby Bartlett, the four-time NCAA Zone qualifier and recently-appointed head diving coach at Saginaw Valley State University said that she prefers concrete platforms.

“They provide a more stable surface. Manufactured stands sometimes tend to shake, especially if they are older. And if the hand railings extend past the fulcrum, you can sometimes hit your hand on your walk down the board,” said Bartlett.

While manufactured stands are a good solution for low-level competition, Counsilman-Hunsaker has found that most high-level competitors prefer the more permanent solution that concrete platforms provide. These platforms also tend to be safer to travel up and down on.

Concrete platforms can be customized depending on the number and type of boards needed. Typically, we recommend providing two of each type of board to allow for multiple divers to practice simultaneously. Reinforcement for concrete platforms is designed by a structural engineer and is tested under both static and dynamic loads. A manufactured short stand is mounted to the concrete platform using bronze anchors and can come with or without handrails. If owners would prefer no handrails, they can be moved to surround the outside concrete platform to provide additional security on the elevated surface. This eliminates the risk of hands hitting the rails during divers’ approaches. In some jurisdictions, the concrete stairs leading to platforms fall under the design requirements of the International Building Code (IBC), which states that a maximum riser height for stairs is 7” with a maximum tread width of 11”. Both measurements are lower than that of most codes.

Counsilman-Hunsaker’s designed concrete stands have two intermediate steps bridging the elevation difference from the deck to the top of the one meter diving board surface.  There is a 10” riser difference between the deck and the first step, as well as between the first and second steps.  Between the second step and the top of the diving board, there is a 19-3/8” difference. Also, each step only has a “tread” depth of 4-3/8” at the deepest point.

While manufactured stands do not fall under the IBC, Counsilman Hunsaker can design custom stands to fit the gutter profile and meet requirements to provide a safer springboard experience.

Being leaders in aquatic design means presenting clients with all of their aquatic sport facility options. Determining the right diving amenities for you is just one of the many decisions we help make during the programming phase of design. Counsilman-Hunsaker has the tools to help guide your aquatic design to meet all user group needs.

How can geotechnical issues affect my pool structure?

Certainly one of the least conspicuous but most critically important design considerations for an on grade or in-ground commercial swimming pool structure are the geotechnical conditions (soil conditions). Variations in geotechnical conditions can drastically influence the design approach for the pool structure, pool shell construction methods, and in some cases the pool maintenance protocol as well.  Soil properties can dictate the difference between a simple slab-on-grade design and a more elaborate structural solution requiring deep foundations, over-excavation, soil conditioning, subsurface drainage, piping encasement, or some combination of the like.  This blog post will provide a brief introduction into the basic geotechnical considerations influencing pool shell design.

An early step in the design process for any earth supported structural system – be it a building foundation, swimming pool, or bridge design – is to study the geotechnical conditions of the project site. This must be done by a qualified geotechnical engineer who will provide data on the soil properties and recommendations to be used in structural design of the foundation system.  This study is done by analyzing soil samples taken from borings drilled on the project site.  For swimming pool design, it is typically recommended that one boring be taken for each 5,000 SF of pool area, and if multiple pools are included in the project, the borings be located accordingly with at least one taken for each pool.  Required boring depth is determined by the geotechnical engineer based on soil conditions, but in any case should not be less than 5 feet below the greatest excavation depth of the swimming pool.

Data collected from boring samples will be used to determine subgrade soil properties, including but not limited to soil gradation, density, bearing capacity, shrink and swell potential, plasticity, lateral earth pressures, and groundwater conditions. This information is then utilized to determine the most appropriate method of pool shell structural design.  One of the most critical considerations influencing the structural design approach is the swell potential of the soil.  Soil that exhibits high swell potential is known as “expansive soil” and can pose a iStock_000004621785Mediumgreat threat to the performance of an in-ground pool structure if not adequately addressed.  Expansive soils are generally made up of clayey materials which have the ability to absorb water.  These soil types swell or shrink dependent upon the moisture content of the soil.  For certain highly expansive soil types, a volume change of up to 30% may be possible.  As you might imagine, even a minimal volume change of soil supporting an in-ground structure can be catastrophic for a swimming pool shell.  Soil movement can cause cracking of the pool shell, uneven heaving or settlement, and damage to below grade piping systems.

Some common design solutions in dealing with expansive soils are over-excavation of the site to replace expansive material with more suitable soil, and/or structurally supporting the pool shell with deep foundations. When over-excavation is necessary, the geotechnical engineer will recommend the depth to which high plasticity or expansive soils must be removed from the site to limit swell potential.  The soil material that is used to replace the expansive material is known as “select fill”.  The select fill must exhibit the necessary soil properties to limit swell potential and to support whatever structural design approach will be utilized for the pool shells.  It is also very important that the fill material be properly placed and compacted to achieve the density necessary to support the foundation system.

When the structural solution requires deep foundations, such as drilled piers or friction piles, the pool structure is often constructed over a void space designed to allow for soil swell to take place without influencing the pool slab. The deep foundations serve the purpose of supporting the pool shell by distributing the load vertically or by bearing on subgrade material of greater capacity, such as bedrock.  When a void space is utilized, the expansive soil layer is then free to exhibit volume change without exerting pressure on the structure above.  Of course, with this structural solution, the design of the below grade pool piping system must be carefully considered such that soil movement does not affect buried piping beneath the shell.  Structural encasement of PVC piping is a common solution in this design scenario.

Another perhaps slightly less common approach to dealing with swell potential of expansive soils is to moisture condition the soils in order to minimize the possibility of volume change occurring during or following construction. The goal with this method is to saturate the expansive soils prior to construction and maintain the moisture content throughout not only the project, but theoretically the life of the facility as well.  This is only appropriate for certain soil types and generally only those that do not exhibit extreme shrink/swell potential.  Moisture conditioning can take on several forms and may involve injecting water into the native soils; excavating, conditioning, and compacting native soils in a series of lifts; or a combination of these approaches to achieve optimum moisture content.  Once the conditioning has taken place and moisture content of the soil established, it is critical that this be maintained.  Maintenance of moisture content may involve limitations on duration that excavations remain open, capping conditioned soil with select fill or paving to retain moisture, and even irrigation of landscaped areas.

While expansive soils are one of the more challenging soil properties and often one of the first to be considered when determining a design approach, there are many other geotechnical conditions 125509297_e7b05d82bdthat influence the pool shell. The pool wall design – whether it be a cast-in-place concrete wall, pneumatically applied concrete wall, or a stainless steel panel wall and buttress system – must take into account not only the pressure of water acting on the interior face of the pool walls when the pool is full, but also the pressure of the soil or backfill materials acting on the exterior side of the pool walls as well.  This force that the soil exerts in the horizontal direction is known as lateral earth pressure.  The measured or calculated lateral earth pressure conditions based on soil properties will dictate the pool wall structural design and the excavation and backfill requirements behind the pool walls.  This criteria, along with the type of soil, may influence preferred construction methods for the pool shell.  For example, shotcrete or pneumatically applied concrete construction methods for pool walls are most efficient when a vertical cut excavation can be supported and the concrete materials shot against earth.  When very sandy or soft soil is present, supporting a vertical cut to the full depth of the pool excavation may not be feasible.  When this is true the pool excavation must be “laid back” at an angle to prevent the excavation from caving in and pool wall construction will involve formwork for placement of concrete, or a stainless steel panel and buttress system, or a combination of the two depending on the depth of the pool.  The anticipated construction methods based on geotechnical conditions will have an impact on the cost of the pool construction, and also sequencing of the construction among trades, especially for indoor pools where adjacent building foundations are involved.

Another very important geotechnical consideration is the presence of groundwater. We have already discussed in this article the effects of moisture content on certain types of soil, but regardless of expansive soil, subsurface water must be considered in the design of a pool structure as well.  The design must consider naturally occurring groundwater relative to the water table in the area, and also the possibility of surface water infiltration on the site.  If groundwater is present at excavation depth, dewatering methods will be necessary to facilitate construction.  Once the pool is in place, groundwater levels that are above the lowest elevation of an in-ground pool structure will exhibit buoyant forces on the pool shell.  If the pool structure has not been designed to counteract buoyant forces due to hydrostatic pressure, there is risk that an empty pool shell may literally “float” out of the ground causing significant damage or catastrophic failure of the pool system.  If groundwater levels are naturally high on the site relative to the foundation elevation, a subsurface drainage system to remove groundwater from the soil surrounding the pool shell may be necessary.  The subgrade preparation for the pool slab and in some cases the backfill material for the pool walls must be designed to allow for drainage of subsurface water when build-up of hydrostatic pressure is a possibility.  Groundwater levels can fluctuate significantly in certain areas of the country or on certain project sites.  A pool owner or operator must have an understanding of how the pool structure has been designed to perform and whether or not it is safe to drain the pool for cleaning or maintenance.  A method of observing or monitoring groundwater level relative to the pool slab should be provided, such as a sight well or piezometer.  If a permanent subsurface drainage system is installed, it must be ensured that this system is functioning properly before making a decision to drain the pool, especially if the system involves the use of pumps to remove water.  Hydrostatic relief valves in the pool floor are another fail-safe against the effects of hydrostatic pressure on an empty pool shell.

While this post just barely “scarifies” the surface on the subject of how geotechnical conditions can influence the design and performance of a swimming pool, I hope that it has introduced some of the broad topics that must be considered when planning a new pool or even when evaluating issues with an old pool. As discussed, it is critical that a qualified geotechnical engineer be consulted to determine the soil properties on any project site.  Soil properties can vary quite dramatically in some areas, so just because the existing structure on the adjacent site employed a certain design approach does not mean that same solution will be appropriate for your pool project.  Each site must be evaluated according to the project type, and the design solution developed with project goals in mind.  This process of establishing design criteria for the pool structure will ensure expectations are met with regard to cost of the pool shell construction, long term performance of the pool shell, and maintenance requirements.  Simply put, several small holes in the dirt are required to determine how best to fill a big hole in the dirt with water.

NEWSFLASH: The 1st Edition of the long-anticipated Model Aquatic Health Code (MAHC) has officially been released.

Click here to download a copy.

As the MAHC now moves into the next phase, local and state health jurisdictions will be able to implement all or portions of the code as seen fit.  The CDC will work with national partners to periodically update the MAHC to ensure it stays current with the latest industry advances and public health findings.

Conference for the Model Aquatic Health Code:

The Conference for the Model Aquatic Health Code (CMAHC; www.cmahc.org) is a non-profit organization and will be the vehicle for recommending code modifications to the MAHC moving forward.  The CMAHC will be suggesting MAHC revisions as well as identifying research opportunities for the CDC’s final determination.

The CMAHC’s role will include:

  • Collecting, assessing, and relaying national input on needed MAHC revisions back to CDC for final consideration for acceptance
  • Advocating for improved health and safety at aquatic facilities
  • Providing assistance to health departments, boards of health, legislatures, and  other partners on MAHC uses, benefits, and implementation
  • Providing assistance to the aquatics industry on uses, interpretation, and benefits of the MAHC
  • Soliciting, coordinating, and prioritizing MAHC research needs

The CMAHC members will meet biennially to gather, assess, and decide on the need for proposed changes to the MAHC. This first meeting is planned for October 2015, which will be 1 year after CDC’s release of the MAHC 1st Edition.

Individuals and organizations can become a member or sponsor the CMAHC and help the organization become the driving force for improved health, safety, and fun at the nation’s public swimming facilities.

MAHC Background:

The Model Aquatic Health Code (MAHC) effort began in February 2005 with the 1st Edition now being completed and published in August 2014.  The MAHC will have a significant impact on the aquatic industry and we strongly encourage all industry members to take an active role in supporting the effort, identifying opportunities for improvement, as well as areas that could benefit from future research as this will be a living document.

The first industry standard was issued in 1958. In the subsequent 50 years, there have been at least 50 different state codes and many independent county and city codes. What was required in one jurisdiction may be illegal in another. It is clear that this historic approach is not working. Thus, the National Swimming Pool Foundation took a leadership position and provided funding to the Center for Disease Control (CDC) for the creation of the MAHC and now supporting the legacy and implementation efforts through sponsorship of the CMAHC. The MAHC is intended to transform the patch work of industry codes into a data-driven, knowledge-based, risk reduction effort to prevent disease, injuries and promote healthy water experiences.

 

Natatorium Acoustics

Consideration must be given to acoustical problems that develop in a natatorium.  Structural features and finish materials should be selected that will absorb sound and reduce noise levels.  In this regard, it is recommended that acoustical building materials be used on the walls and in the ceiling of the natatorium and that other noise dampening features be included, if possible. 

Ceiling decks have been successful when a perforated epoxy coated galvanized structural steel panel is used.  Further acoustical enhancement occurs if the panel is backed with polyethylene encapsulated fiberglass or closed cell styrofoam battens. Ithaca College Professional (3)

A different approach for enhancing acoustics for a concrete roof system is hanging acoustical baffles between the concrete beams or T’s.  Suspended acoustical panels made of fabric- covered fiberglass, aluminum, closed cell rigid plastic foam board or a combination of these are functional.  Not only do these units serve a technical purpose but they can also add color to the space.  All must be corrosion resistant. 

As with other materials in a natatorium, acoustical wall and ceiling must be corrosion resistant and interface with a vapor barrier, if necessary.