By Jason Pollard
The novel coronavirus pandemic has changed life as we know it. The economic impact has forced organizations in every industry, including the sports world, to evolve. The face of baseball and softball infields is changing, and so is the need for facility owners to reduce costs while continuing to properly maintain their fields. As designers, we have needed to explore new strategies to support safe fields for athletes that meet our end users’ expectations and budgets.
Many designers offer a good, better, and best approach to fulfill sports field requirements. If the best solution is used currently, it might be too costly in the future if reduced budgets and spending restrictions are applied. It’s essential to weigh additional options to ensure you can sustain the same high standards when maintaining your fields for the upcoming seasons.
Most of us appreciate grandma’s famous dish or a meticulously prepared dessert; two things comprised of a precise list and ratio of ingredients. One slip up or missed step could throw everything off. Baseball and softball field managers understand the comparison of a skinned infield mix to a delicate recipe. It takes time and repetition to perfect this material, and even then, you need to evolve alongside it. The infield mix is a blend of three simple soil components; sand, silt and clay. It seems basic on the surface, right? Well, that blend is very complex below the surface and has been giving field managers headaches for decades.
With 70 percent of the game played on the infield, it’s important to get it right. What do we recommend when it is clear the infield mix is not operating at maximum efficiency? The first question to ask is, “What is the biggest complaint about the field? Is it too hard, too soft/loose, is it poor at handling moisture, or are those pesky lips at the infield/outfield grass transitions causing a safety concern?” With restricted spending for many field owners, doing the best thing for our fields may not be financially practical in this economic climate. Instead of merely taking a stab at a remedy, we will always recommend getting the infield material tested. It is difficult to understand the soil mix needs until you know what it’s made of. Arguably, the most important test to run is a particle size analysis (ASTM 6913) on a representative sample to determine the individual percentages of sand, silt and clay and a breakdown of sand fractions from very coarse to very fine. This test is relatively inexpensive, but will definitely save the owner time and effort in the long term.
The typical infield mix should have an overall sand content between 60-75 percent and a silt/clay content between 25-40 percent. The recommended ratio depends not necessarily on the level of competition, but also on the availability of maintenance staff and water. The overall sand content of the material determines the level of maintenance required. More sand typically equals less maintenance. Clay is responsible for moisture retention, and silt binds the sand to the clay. Breaking this down further, the particle size and shape within the overall sand component is vital in determining the mix’s structural stability. The larger and more angular the sand particles, the more stable it can feel underfoot. Ideally, more than two-thirds of the sand should be medium and coarse. A larger portion of fine, silty sands can spell trouble for many types of soil, with infield mix being no exception. The ideal ratio of silt to clay (SCR) is 0.5 to 1.0 (silt/clay) to make everything work together.
After testing the infield mix, other important aspects to look at are the surface planarity, field slope, edge build-up (lips), and moisture management. Even the best material won’t perform to its highest potential without being graded appropriately to utilize surface drainage. It’s recommended that a 0.5-1.0 percent slope be provided from the middle of the infield toward the outfield and foul territory areas. Regarding planarity, otherwise known as surface smoothness, avoid any depressions greater than ¼ inch over a 10-foot span. Anything greater will increase the likelihood of birdbaths presenting after even moderate rain events. We recommend laser grading a baseball or softball infield once a year, if possible, to alleviate standing water. Regular checks along the edges or where the infield mix meets the grass are crucial to keeping your infield safe. The lips that form here are from improper dragging where extra material is thrown to the infield and outfield grass to build up over time. The drag should never move faster than a person can walk. Finally, water management is possibly the most important factor affecting the overall performance of skinned surfaces. The water content affects both the ball and player performance. Water is needed to soften fine soils (silt and clay) and firm those course, sandy soils. A typical guideline is to water the surface at a rate that allows for infiltration slowly into the skin and retention for a considerable amount of time. An infield mix’s optimal moisture content is between 4-12 percent, where the soil receives natural moisture binding by surface tension. This creates a damp soil consistency, which is ideal for athlete performance. A well-balanced infield mix will maintain this optimal level of moisture for the longest possible timeframe.
When the particle size test results come back, it’s time to analyze and attempt to develop a solution, keeping in mind that it’s not a “one size fits all” scenario. One field’s fix may not be another’s – even if the two fields have the same mix. Serious consideration must be put into the availability of maintenance, water and funds to manage the fields. Once you know where your field currently stands in terms of sand (overall and particle size), silt and clay content, you can start deciding where you want to end up. For a lot of facility owners, hiring a sports field consultant during this process is highly recommended. Others know where they want to be; they simply need to determine the correct method to get there.
There are three main options to improve the performance of your infield mix. The first option is to topdress with a conditioner, along with scarifying the existing soil. Calcined clay is one of the most common conditioners and made of montmorillonite clay heated to extremely high temperatures (1,200 degrees Fahrenheit) to form granules of clay that remain hard even when wet. They can absorb excess water, hold onto it, and then release it when conditions become dry. After scarifying the existing infield mix (up to 1/2 inch), a thin layer (1/4 inch) of calcined clay conditioner product could be applied as a topdressing. The advantage of this option is the lower cost and the ability to create a consistent playing surface. The disadvantages are that topdressings aren’t long-term fixes and can’t continue to be used year after year. Eventually, your infield elevation will get too high relative to the adjacent grass areas.
The second option is to amend the existing material using an engineered soil mixture and till to a depth of 2 to 3 inches for optimal blending. For a typical 90-foot baseball infield, roughly 4 to 5 tons of material would be necessary. To increase sand content, use soil with a sand content higher than your current levels. Just make sure the sand doesn’t contain high amounts of fine or very fine sand, and that you keep the silt to clay ratio between 0.5 and 1.0. To decrease sand content, use soil with a sand content lower than your current levels. To reduce the silt to clay ratio, use soil with more clay than silt. This is also a great time to laser grade your infield. The advantages of amending your existing soil are that it’s still an affordable option and can be done over time, tweaking the soil as needed. The disadvantages are that results may not be seen immediately, and the entire cross-section of the infield is not homogeneous. It’s highly recommended to obtain a follow-up soil test report a few weeks after your amendment to reveal the changes made. If any additional modification is required, repeat the process.
If it’s clear that adjustments to the skinned area aren’t producing the results you want, the third and most drastic option is to fully remove and replace your infield. This entails excavating roughly 6 inches of material, establishing a new properly sloped subgrade, and installing a new engineered infield mix. If you are considering this direction after realizing your field is too far gone, some field owners even contemplate replacing the natural skinned infield with a synthetic turf system. This last option would come at a high cost and could put the field out of play for a substantial period of time, but it can be a full fix if done correctly.
Each of these options should be carefully considered by the field owner, manager and designer once the existing infield is tested and analyzed. In this new environment we live in, with budgets in extreme focus, small decisions must be made with short- and long-term goals in mind. The “best” option today may not have been part of the plan just one year ago. The option that could best solve the underlying issue may not currently fit into the budget. Still, through creative maintenance strategies, we can extend the life of the field until finances allow. Those of us involved in sports field design have vital roles in the process of blending high-quality design with the needs of facility owners and the surrounding communities. We must all commit to our clients to listen to their goals, evaluate the options, weigh the costs, and develop thoughtful solutions that ultimately strike a happy balance.
Jason Pollard, PE, is a senior engineer at CHA Consulting with more than 12 years of experience in sports and recreation facility design, specializing in baseball/softball and track and field facilities throughout the country. His expertise includes campus master planning, project design/coordination, contract documents, and construction administration. You can contact him at email@example.com.