Views: 0 Author: Site Editor Publish Time: 2026-06-08 Origin: Site
When people judge whether a sports field is good, they usually look at the visible parts first: how bright the track surface is, how flat the turf looks, or how clean the overall finish appears. That is understandable. But in reality, the real factor that determines the fate of a sports field lies underground, completely out of sight: the subgrade and foundation system.
Under World Athletics standards, the surface is only the face of the field. The subgrade and foundation are what truly determine safety, flatness, long-term performance, and service life. In practice, common problems such as bubbling, cracking, settlement, soft spots after rain, and wave deformation of the track are caused not by the surface layer itself, but by poor ground treatment, non-standard foundation structure, or insufficient compaction.
Whether it is a professional competition venue, a school playground, or a public fitness facility, standardized subgrade and foundation construction is the prerequisite for compliant acceptance, long-term durability, and safe athletic performance. Simply put, this is the most important hidden part of the entire sports field.
- Dual-layer core structure: the underground structure consists of the natural subgrade as the load-bearing layer and the artificial foundation as the structural layer. These two work together and neither can be omitted.
- Three critical indicators: bearing capacity, compaction, and flatness must be strictly controlled. Overall compaction should be at least 95%, 28-day compressive strength should be at least 25 MPa, and flatness deviation measured by a 3-meter straightedge should not exceed 3 mm.
- Standardized slope control: in line with World Athletics requirements, the longitudinal slope in the running direction should be no more than 0.1%, and the transverse drainage slope should be no more than 1.0%, balancing competition fairness and drainage performance.
- Zone-specific design: the running track, field event landing areas, turf infield, and throwing areas should be designed differently according to their loading conditions and functional requirements.
- Waterproof and frost-resistant design: anti-seepage, filtration, and buffering structures should be included as standard. In freezing regions, an additional geotextile buffer layer should be installed to prevent frost heave, reverse seepage, and settlement.
3. Analysis and Explanation
3.1 What Are the Subgrade and Foundation?
Subgrade and foundation work is one of the most critical parts of sports field construction. Many construction mistakes come from confusing their functions, which later leads to frequent field defects.
Natural subgrade (original bearing layer)
This is the original soil layer and the deepest structural base of the field. Before construction, topsoil stripping and site cleaning must be completed thoroughly, including the removal of weeds, mud, construction debris, and organic soil. Soft interlayers must not remain. If weak or low-lying soil is encountered, graded crushed stone replacement or dynamic compaction should be adopted. Replacement thickness should generally be no less than 50 cm, and load testing should be carried out to ensure the soil is uniform, stable, and free of voids or soft pockets.
Artificial foundation (structural support layer)
This layer is built above the natural subgrade and serves as the core structure that supports the surface and distributes sports loads. The two mainstream foundation types are asphalt foundation and cement-stabilized foundation. Asphalt is preferred for professional competition venues, while cement-based systems are often used for ordinary school or community fields. In all cases, layered spreading and layered rolling should be applied, and each layer should generally not exceed 30 cm in thickness to ensure structural integrity.
3.2 Which Foundation Type Should Be Chosen?
Asphalt foundation (preferred for competition venues)
A typical asphalt foundation adopts a double-layer structure with a total thickness of at least 80 mm. A common configuration is 50 mm of coarse asphalt base layer plus 30 mm of fine asphalt surface layer, combined with a graded crushed stone subbase. This system has strong flexibility and is less likely to crack.
Its main advantages are excellent shock adaptation for athletics, low cracking risk at low temperatures, good deformation resistance at high temperatures, and high flatness, making it well suited to World Athletics standards.
Its disadvantages are higher material and construction costs, sensitivity to oil market fluctuations, aging over time, and stricter construction control requirements regarding temperature and compaction.
It is suitable for sports grounds that require high flatness and comfort, including professional tennis, badminton, and table tennis courts, and is also widely used in school playgrounds and community sports venues.
Cement-stabilized foundation (common for general-use projects)
This foundation usually requires a thickness of at least 120 mm. Cement-stabilized crushed stone is compacted in layers to form a rigid and economical structure with relatively fast construction speed.
Its advantages include high compressive and tensile strength, good water stability, good frost resistance, and stable performance under different climates and seasons. It is generally more economical than asphalt.
Its disadvantages are lower flexibility and a greater tendency to develop fine cracks under temperature changes, so expansion joints and sealant protection are required.
It is suitable for venues with high load-bearing requirements, such as large track fields, sports grounds within industrial areas exposed to heavy vehicle traffic, and regions with complex climate conditions.
3.3 Hard Indicators for Construction and Acceptance
- Compaction standard: rolling should follow the process of light to heavy, slow to fast, and overlapping wheel tracks. Static rolling with a roller above 12 tons for two passes plus four passes of vibratory rolling is typically required. Final overall compaction must be at least 95%, with no looseness, sanding, or hollowing.
- Strength and flatness: after 28 days of curing, compressive strength must be at least 25 MPa. Using a 3-meter straightedge across the field, flatness deviation must not exceed 3 mm, with no visible high-low differences or wave-shaped surface.
- Precise slope control: the longitudinal running slope must be no more than 0.1%, and the cross slope for drainage must be no more than 1.0%, while remaining smooth and uniform.
- Waterproof and frost-resistant structure: anti-seepage geotextile and filtration layers should be installed at the bottom to block groundwater reverse seepage. In freezing regions, a geotextile buffer layer must be added between the crushed stone layer and the asphalt layer to prevent frost heave, cracking, and deformation.
Ideally, beneath 60 mm of asphalt macadam there should be at least 150 mm of free-draining collection space. In less favorable sites, a structural layer of 400-500 mm may be necessary. In regions where winter temperatures frequently fall below 0 degrees C, greater construction depth is needed to prevent frost-related heaving.
3.4 Different Zones Require Different Solutions
- Running track zones: focus on flatness and elasticity. The foundation must be uniform and slope control must be precise to ensure stable performance for sprinting, distance running, and hurdles.
- Field event landing areas: long jump, triple jump, high jump, and pole vault zones require reinforced subgrade and foundation to improve impact resistance and prevent local settlement.
- Throwing areas: shot put, discus, and hammer circles require hardened and reinforced ground treatment to avoid cracking or collapse under concentrated heavy loads.
- Turf infield: emphasis should be placed on permeability, anti-seepage performance, and settlement resistance, combined with a drainage structure that supports both turf growth and overall field stability.
3.5 What Does a Good Foundation Actually Deliver?
Athlete safety and competition fairness
From a biomechanical perspective, a flat and stable foundation is the real foundation of athlete safety. During running and jumping, large impact forces are generated at the moment the foot contacts the ground. If the base is uneven, force distribution becomes unbalanced, increasing the risk of slipping, ankle injury, and unstable landing. A well-built foundation helps distribute force more evenly and reduces avoidable sports injuries. Consistent slope and flatness are also prerequisites for competition fairness.
Longer service life
A high-quality foundation can effectively support the pressure transmitted from the surface layer. During use, the surface is subjected to repeated loads from athletes and equipment. If the foundation quality is poor, settlement, cracking, and hollowing can easily occur. These problems cause the synthetic surface or turf to lose stable support and eventually fail. A strong and uniform foundation spreads pressure evenly, reduces base-layer defects, and helps avoid surface failure caused by underlying structural problems. In practice, a high-quality foundation can extend field service life by 3 to 5 years, significantly reducing renovation and maintenance costs.
World Athletics certification and inspections by education and sports authorities all follow strict procedures and standards. In these acceptance processes, standardized subgrade and foundation construction is one of the core hard requirements. Even if the surface looks excellent, a field with a non-compliant base will not pass formal certification or regulatory inspection.
A complete waterproof, frost-resistant, and drainage foundation structure allows a field to resist rainwater infiltration, frost heave, and high-temperature exposure. In practical terms, this means the field can remain usable and stable under rainy, snowy, or hot-weather conditions, enabling reliable all-weather performance.
The subgrade and foundation of a sports field are the invisible skeleton supporting the entire venue. More importantly, they are the core hidden works that define field quality and determine service life. The surface layer is responsible for appearance and touch. The subgrade and foundation are responsible for safety, durability, and compliance. Both matter, but the latter is more fundamental.
Whether the project is a professional competition venue, a school playground, or a community sports ground, construction must strictly align with World Athletics and relevant national standards. Ground reinforcement, layered rolling, precise slope control, waterproofing, frost protection, and zone-specific construction must all be properly executed. Only then can common defects such as cracking, settlement, bubbling, and ponding be prevented at the source.
Only when the hidden works are built solidly can the field have a truly stable base to support high appearance, high safety, and high durability, enabling running, jumping, and throwing to take place smoothly and safely while ensuring compliance, long service life, and long-term operation.
Q1: If a running track shows bubbling, cracking, or wave deformation, is that a surface problem or a foundation problem?
A1: In most cases, it is a foundation problem. The surface layer itself does not provide structural bearing capacity. Cracks and wave deformation usually result from insufficient compaction, local settlement, or voids between layers. Large-area bubbling is often caused by the absence of an anti-seepage layer, which allows groundwater to build up beneath the surface. Repairing only the surface treats the symptom, not the root cause.
Q2: How should we choose between asphalt foundation and cement foundation? Which one is more durable?
A2: For competition venues and high-frequency-use fields, asphalt foundation is the preferred option because it has better flexibility, higher fatigue resistance, and lower cracking risk. For ordinary school fields or lower-frequency-use facilities, cement-based foundation offers better cost performance and faster shaping, but expansion joints and sealing protection must be done properly. Under compliant construction, asphalt is generally more durable.
Q3: Why must we wait 28 days after foundation construction before installing the surface layer?
A3: Twenty-eight days is the standard curing period. During this time, moisture evaporates and the structure stabilizes until the designed compressive strength of at least 25 MPa is reached. If curing time is insufficient, later settlement, cracking, and surface damage are much more likely.
Q4: What happens if foundation compaction is not sufficient?
A4: If compaction is below 95%, the soil layer remains loose and full of voids. After a period of use, uneven settlement will occur, leading to track depression, surface tearing, and joint cracking. Loose foundations also trap moisture easily, causing bubbling and delamination of the synthetic surface. This is one of the most serious quality risks in sports field construction.
Q5: Do rainy southern regions and cold northern regions require different foundation treatment?
A5: Absolutely. In rainy regions, anti-seepage design, drainage performance, and slope precision must be strengthened to prevent water accumulation and soaking. In cold regions, a geotextile frost-protection buffer layer is essential to prevent frost heave, foundation cracking, and surface damage.
Q6: A new field looks flat to the eye. Do we still need foundation testing?
A6: Yes. Visual inspection only shows the surface. Core indicators such as compaction, bearing capacity, internal hollowing, and slope precision can only be confirmed through testing. Sand cone compaction testing, 3-meter straightedge flatness testing, slope rechecking, and strength testing are all necessary. A field is only truly qualified when the data meets the standard.
