Rubber tyred gantry cranes (RTGs) are widely used in manufacturing yards, precast concrete plants, logistics centers, construction sites, and outdoor material handling operations. A 20-ton RTG crane, in particular, offers the ideal balance between lifting capacity, mobility, and operational flexibility. However, unlike rail-mounted cranes that operate on fixed steel tracks, rubber tyred gantry cranes rely entirely on ground contact for stability, traction, and safe load handling. This means that ground conditions directly influence the actual capacity, performance, safety, and operating reliability of a 20-ton RTG crane.
Understanding how soil characteristics, surface quality, foundation strength, moisture conditions, and terrain affect crane performance is essential for operators, engineers, and buyers. This article explores the key ways ground conditions impact a 20-ton rubber tyred gantry crane for sale and provides best practices for evaluating and preparing work surfaces.
1. Why Ground Conditions Matter for RTG Cranes
The fundamental characteristic of an RTG crane is mobility on rubber wheels. Its entire structural load – including self-weight, dynamic forces from lifting, and the weight of the lifted load – is transferred directly onto the ground.
This creates a clear relationship:
Ground Conditions → Stability → Safe Rated Capacity → Performance Efficiency
Weak or uneven ground can introduce several risks:
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Loss of crane stability
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Wheel sinkage
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Uneven wheel loads
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Increased structural stress
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Reduced rated capacity
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Skidding or traction issues
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Premature tire damage
In extreme cases, poor ground conditions can cause crane tipping or catastrophic structural failure. Therefore, evaluating ground conditions is a vital step before operating any RTG crane, especially a 20 ton gantry crane unit designed for moderately heavy loads.
2. Types of Ground Conditions That Influence Crane Capacity
Ground conditions vary significantly depending on the site environment. The following are the most important factors that influence a 20-ton RTG crane’s operational capacity and safety.
2.1 Soil Bearing Capacity
The soil’s bearing capacity determines how well it can support the pressure exerted by the crane wheels. When the ground has low bearing strength—such as loose gravel, soft clay, or sandy soil—the risk of wheel sinkage increases.
Impact on capacity:
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When soil strength is insufficient, the effective lifting capacity decreases.
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Excessive sinkage causes uneven distribution of wheel loads, leading to torque imbalances.
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Operators may be required to reduce the safe working load (SWL) to avoid tipping risk.
2.2 Surface Type: Asphalt, Concrete, Gravel, or Earth
Different surfaces provide different levels of stability:
Concrete
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Offers the best stability, minimal deformation, and excellent load distribution.
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Ideal for achieving maximum rated capacity.
Asphalt
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Supports moderate loads but can deform under heavy wheel pressure, especially in hot climates.
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Load capacity may need adjustment.
Gravel
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Provides fair support but may shift unevenly.
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Can cause wheel slip or unpredictably varying support.
Natural Earth or Soil
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Highly variable; prone to settling, erosion, and moisture changes.
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Usually requires reinforcement before use.
2.3 Moisture Content and Water Drainage
Water significantly alters soil strength. Wet or waterlogged ground becomes softer, reducing load-bearing capacity.
Effects include:
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Wheel rutting and sinkage
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Reduced traction
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Increased risk of lateral sway
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Reduced safe lifting capacity
In rainy or coastal environments, drainage design becomes critical.
2.4 Ground Levelness and Surface Flatness
A 20-ton RTG crane’s stability depends on maintaining equal wheel loads. Even small inclines or surface irregularities can introduce risk.
If the ground is:
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Uneven → crane structure twists or leans
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Sloped → higher risk of tipping during movement or lifting
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Rutted → sudden load shifts increase structural stress
Uneven ground can require derating the gantry crane capacity to maintain safe operations.
2.5 Hardness and Compaction
Highly compacted surfaces distribute loads better. Poorly compacted soil compresses under crane weight, and continuous operation worsens the condition.
Soft or loose ground:
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reduces rated capacity
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damages tires
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increases rolling resistance
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leads to unstable crane movement
3. How Ground Conditions Influence Crane Performance
Ground conditions affect more than capacity. They also influence traction, speed, maneuverability, and long-term maintenance of a 20-ton rubber tyred gantry crane.
3.1 Traction and Mobility
RTG cranes rely on tire-to-ground friction. Poor traction increases:
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wheel slip
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difficulty maintaining straight movement
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overuse of steering or drive systems
Wet grass, sand, and soft clay significantly reduce friction, requiring operational adjustments.
3.2 Tire Wear and Damage
Uneven or abrasive ground accelerates tire wear. Running a 20-ton RTG crane over:
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sharp gravel
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poorly maintained asphalt
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uneven concrete expansion joints
can lead to premature tire cracking, blowouts, or tread deformation.
3.3 Steering and Multi-Directional Maneuvering
Advanced RTG cranes often support steering modes such as:
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90° transverse steering
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diagonal movement
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360° pivot steering
These steering functions require stable, level ground. Poor surfaces restrict maneuverability and increase mechanical stress on the steering cylinders and drive motors.
3.4 Structural Stress and Fatigue
When the gantry crane travels over uneven or unstable ground, the frame experiences continuous torsional forces. Over time, this contributes to:
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fatigue cracks in the structure
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misalignment of long-travel mechanisms
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premature mechanical wear
A stable, level surface greatly extends crane lifespan.
4. How Ground Conditions Affect Rated Capacity
A 20-ton RTG crane is designed to lift its maximum rated load under ideal ground conditions. When the ground is compromised, operators must derate the lifting capacity to avoid instability.
Capacity may be adjusted based on:
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soil testing results
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load charts provided by the manufacturer
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engineering calculations
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on-site safety rules
A typical reduction scenario might be:
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Soft clay → reduce capacity by 20–30%
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Unpaved gravel → reduce capacity by 10–15%
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Uneven ground → reduce capacity until inclinometer readings are safe
Capacity derating ensures stability and prevents tipping.
5. Evaluating Ground Conditions Before Crane Operation
To ensure safe and efficient operation, the following assessments should be performed:
5.1 Soil Bearing Capacity Test
Geotechnical testing determines whether the soil can support the crane.
5.2 Ground Compaction Assessment
Check whether the surface has been compacted to industrial yard standards.
5.3 Flatness and Levelness Measurement
Laser leveling or ground survey ensures acceptable tolerances.
5.4 Seasonal Ground Change Review
Freeze–thaw cycles, rain seasons, or storms can alter conditions dramatically.
6. Best Practices for Preparing Ground for a 20 Ton RTG Crane
To optimize performance and minimize risks:
6.1 Reinforce Work Areas
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Use concrete pads
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Install temporary steel plates
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Lay compacted gravel bases under heavy-use areas
6.2 Improve Drainage
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Build slope gradients for water runoff
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Install drainage channels
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Avoid low-lying areas
6.3 Maintain a Regular Surface Inspection Schedule
Check for:
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cracks
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rutting
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uneven patches
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loose debris
6.4 Follow Load Charts and Operational Guidelines
Always consider manufacturer recommendations for ground conditions.
Conclusion
Ground conditions play a significant role in determining the safe rated capacity and overall performance of a 20-ton rubber tyred gantry crane. Soil strength, surface flatness, moisture content, compaction, and traction all contribute to how well the crane can operate and how much load it can safely handle. By understanding and managing these factors – through proper ground preparation, testing, and maintenance – operators can ensure safer, more efficient, and more reliable crane operations.