The Application of Sand Technology for
Turf Systems
by Charles R. Dixon
(former President of Turf Diagnostics & Design)
Printed in part by Sports Turf Magazine June 1994

    The development and the proper application of defined sand technology has resulted in a general acceptance of the substantial benefits of high performance sand based systems. What follows is a technical explanation of the application of this technology based on Turf Diagnostics & Design's experience as an agronomic consultant to leading sports complex architects, and as a recommended consultant by the National Football League, National Association of Professional Baseball Leagues and the PGA Tour.

    Sand is used to modify soils and construct turf systems for various sports turf applications to promote proper air and water management. Without a doubt sand is the most extensively used amendment on a weight basis to modify turf systems. The use of sand has been extensively reviewed by the United States Golf Association (USGA) in regards to putting green construction. A wide range of sports turf applications such as football, baseball, race tracks and soccer, are utilizing the concepts of the USGA putting green construction guidelines to design and build turf systems for high performance demands. Not all sports programs have the budget for sand based sports fields and will utilize sand in other ways to improve the performance of a field.

    Sand is often used in conjunction with the native soil in what is known as a by-pass system. The Cambridge™ system is a commercially available system that uses sand in trenches and for creating a permeable sand cap over the trenches to remove water during periods of high rainfall. There are several designs that use a by-pass approach with sand. We are often approached about mixing sand with native soils to improve permeability and to lower excessive water holding values. The mixing of sand with soil is not as effective as some are led to believe. If the proper sand particle size is used and the correct amount of sand is added, some benefit can be realized. Usually the amount of sand necessary to increase the overall sand content of the rootzone is so great, that the money and energy is better spent on by-pass approaches or maintenance.

    The amount of sand particles in relation to the size of the particle is very important to how a sand will function in various implementations. Most people are familiar with a particle size analysis. It is important to understand the definition of particle sizes and how they are determined. To accurately assess the particle size distribution of a sand or soil, a full mechanical analysis should be performed. A full mechanical analysis involves extracting the silt and clay from the sample and sieving the resulting sand fraction. By removing the silt and clay, the sand distribution is accurately assessed. If a sieve analysis (known as a drop sieve) is performed without the removal of silt and clay, small aggregates of silt and clay can be perceived as sand particles and a false impression of the material may be generated. If you are in the market for a sand for any agronomic purpose, make sure a full mechanical analysis has been performed.

    Most sand suppliers provide contractors with materials that meet some building construction codes. Sand is used in asphalt, concrete, and filtration media. The definition of sand size and silt and clay will vary according to end user. There are three common definitions of sand size as well as silt and clay in this country. Regional regulations may add to the definition but the basic definition sources for building and road construction will be from the American Society for Testing and Materials (ASTM). In agriculture, the United States Department of Agriculture (USDA) has definitions on how soil is classified in regards to crop production and soil conservation. In the March/April issue of the USGA Green Section Record another sand size definition has been published that pertains to the USGA putting green construction recommendations (USGA 1993). Prior to the recent USGA definition, the USDA criteria and methodology had been used to evaluate materials for determining suitability in turf systems. The USGA and USDA definitions are very similar in sand size criteria as well as the silt-clay size range. The ASTM definition is quite different especially in regards to how silt and clay are defined. Since clay and silt can have a profound impact on the drainage characteristics of a sand, the definition used is very important to making a good decision.

Table 1 Definition of USGA and USDA Sand Sizes

Table 2 ASTM Particle Size Definition

    If material selections are being made for turf systems, you definitely want to have an analysis that accurately assesses the sizes of materials and is also based on agronomic definition such as the USGA or USDA size scheme. Since the publishing of the new USGA recommendations and lab testing protocol, there is an adequate definition and test method available for most field designers and turf managers.

    Since we now have definition concerning the size range of various particles, the concentration of sizes can be examined in relation to sand selection criteria. The new USGA recommendations are a good start for systems that are designed in concept like USGA putting greens. For use in selection of sands in a by-pass system or topdressing of native fields, it may be too specific.

Table 3 Particle Size Distribution of USGA Root Zone Mix.

* Gravel plus Very Coarse should not exceed 10% total.

    The particle size ranges listed in Table 3 are designed for a specific purpose and are a good guide for putting greens. For use in sports field construction additional parameters should be considered. We have found the criteria published by Dr. George Blake to be helpful in adding to the USGA criteria or for offering a less stringent guide for sands to be used as a topdress for native fields or to be used in by-pass systems.

Table 4 Dr. G. Blake's Selection Criteria

George R. Blake (1980) Proceedings of Third International Turfgrass Research Conference Amer. Soc of Agronomy

    The Fineness of Modulus (Fm) and Uniformity Coefficient (Cu) are determined from a graph of the concentration of particles versus size. The grain size graph is a useful tool in comparing sands and also determining the Fm and Cu. Grain size graphs are used to design and select materials for drain systems. Most sand suppliers that work with concrete or Department of Transportation (DOT) specifications determine the Fm. We have found the Fm value to be useful in communicating the general class of sand that we are looking for. The Cu of a sand along with the particle size analysis has been the most useful information we have in regards to estimating performance.

    The Cu is a numeric estimate of how a sand is graded. The term graded relates to where the concentration of sand particles are located. A sand with all the particles in two size ranges would be termed a narrowly graded sand and would have a low Cu value. A sand with near equal proportions in all the fractions would be termed a widely graded sand and would have a high Cu value. The Cu is a dimensionless number or in other words it has no units. Filtration sands for water treatment will have a low Cu to promote movement of water. Concrete sands usually have a high Cu to pack and offer strength and stability. For turf applications, the Cu values we are looking for range from 1.8 to 4.0.

    Widely graded materials usually offer firm turf surfaces and will be less prone to developing divots and ruts. Soccer pitches are firmer with higher Cu materials. The goal is to balance physical stability with the desired drainage characteristics. The materials with higher Cu values also have a more tortuous path for water to move through and will have lower infiltration rates or permeability. Usually the water retention is greater with sands that have a higher Cu.

    We recently performed a study using a plastic fiber for Synthetic Industries Corporation. The goal of the study was to examine the effect of the fibers in three different sands representing three divergent Cu values. The idea was to promote good drainage as is found in low Cu sands and offer stability with the fiber. The grain size graph in Figure 1 shows the three very different curves and their Cu values. The particle size distribution data is presented also in Table 5. The Cu is calculated from the grain size graph by determining the diameter in millimeters at which 60% (D60) of the material passes through the sieve and at which 10% (D10) of the material passes.

Cu = D60/D10
Figure 1 Grain Size Graph for Synthetic Industries Study
 

Table 5 Sand Particle Size Distribution for Synthetic Study

    The information we are presenting will require some thought to fully understand. It may not be as important to know how to determine the values as it is to know the process and the impact of the numbers generated. Because of the value of the Cu in making material selection in relation to a specific application, we have been routinely generating the Cu data on particle size determinations for sand.

    The performance data for each sand was generated in the lab using the USGA protocol. The sands and a sand-peat mix were evaluated. The 90:10 sand-peat mix (90% sand to 10% peat volume basis) was also mixed with the Synthetic Industries fibers and physically evaluated. Table 6 presents the data from the physical evaluation.

Table 6 Physical Performance Data for The Various Cu Values

    The value of the Cu has an obvious impact on the infiltration rate as well as the bulk density. Sports fields that are sand based need higher Cu values to have firmer surfaces (higher bulk density). The infiltration rate is dramatically impacted by the Cu. Sands that are intended for use in French drains and water by-pass systems will need lower Cu values than sands to be used as the complete growing medium and surface. Placing a layer of sand over a native soil that has a slope has been used to allow a faster rate of water movement to catch basins. Sands that depend on lateral movement should have lower Cu values to promote drainage. Sands have different physical attributes and should be evaluated in the lab for suitability for the intended application. The Cu is one component that should be determined as well as basic physical performance criteria. Most lab generated data, if properly interpreted, supports an assessment to attain the anticipated performance expectation.

    Evaluations we have performed concerning the additions of soil to sand increased the Cu of a rootzone well above the 4.0 level. Often these mixes have been reported to us as poorly drained, hard and difficult to maintain turf cover. We have often seen implemented field designs that placed a sand-soil mix with low permeability and compaction problems over an extensive and expensive drain system. The drain system was rendered useless by the compacted impermeable rootzone above. Every evaluation we have performed on these types of fields had Cu values well above 30. One facility spent $100,000 for a field with full under drains that is hard and that has no drainage. The money would have been better spent to make a sand cap and cut drains into the field at an interval based on cost. It is sad to have had such an elaborate design with little hope of achieving the desired performance.

    It is not how much you spend that is important, it is how you spend what is available. Whether you manage a small baseball complex for Tee Ball or take care of fields for the pro-athlete, there is a liability associated with the performance of the field. To make the best use of money and achieve your stated objectives, you must have technical information that will accurately assess the performance of the field design. The technical information is also utilized in the development of the turf management program for the completed turf system.

    The single most important tool available to a turf manager is a properly performed particle size analysis because it is the foundation on which we build the technical platform for the assessment of turf systems. The price of the particle size analysis data is irrelevant given the interpretive ability of the data for the construction of agronomically sound turf systems. However, the data must be generated using accepted testing protocols that are relevant to supporting agronomic decisions, otherwise, the testing is worthless.

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