This study examines the drainage efficiency and anti-slip performance of ductile iron gully grates C250/D400 during heavy rainfall, offering practical insights for the selection and maintenance of municipal facilities.​

1. Basic Conditions for Field Testing

The test was conducted on a waterlogging-prone section of an urban secondary road, where the underground drainage pipeline has a DN600 diameter, conforming to conventional municipal configurations. Testing tools included a rain gauge, an ultrasonic flowmeter, and a portable friction tester. The rain gauge had an accuracy of ±0.1mm, the ultrasonic flowmeter covered a range of 0-50L/s, and the portable friction tester measured within a range of 0-1.0.​

To simulate heavy rain conditions, the rainfall was controlled at a stable 55mm/h—this value corresponds to the standard for an orange alert for heavy rain. Drainage and anti-slip data were recorded simultaneously, and each test group was repeated 3 times to calculate the average value, ensuring the accuracy of the results.

2. Field Test Results of Drainage Efficiency

Basic Drainage Capacity

Under a rainfall intensity of 55mm/h, the initial drainage rate of the C250/D400 gully grate reached 13.2L/min. After 40 minutes of continuous testing, the rate stabilized at 11.5L/min without blockage in the drainage channel. A single grate could meet the rainwater collection needs of a 20㎡ road surface, complying with municipal drainage design standards.

Anti-blockage Performance

When leaves and sediment were mixed on the road to simulate the actual scenario of debris scoured by heavy rain, the drainage rate dropped to 8.7L/min. However, after cleaning the gaps of the grate, the rate could be restored to 92% of the initial value. This indicates that the grate has strong anti-blockage capabilities and is easy to clean after blockage.

Comparative Advantages

Compared with ordinary gray cast iron grates (Class C250) in the same area, its drainage efficiency was 28% higher. The core reason lies in the high strength of the ductile iron material, which prevents the grate from deforming under load. The 8mm-wide water inlet gaps are maintained without being squeezed narrow, ensuring unobstructed drainage.

3. Field Test Results of Anti-slip Performance

Normal Wet Conditions

The friction coefficient of the grate surface was 0.68 when dry, and dropped to 0.45 after being soaked in rainwater. Both values are higher than the safety requirement of "friction coefficient ≥0.35 for wet road surfaces" specified in the Urban Road Pavement Design Code, so there was no obvious slipping risk for pedestrians.

Risks Under Special Working Conditions

When a small amount of oil was attached to the grate surface, the friction coefficient dropped sharply to 0.29 under wet conditions—below the safety threshold. This poses a risk of pedestrians slipping, requiring targeted enhanced cleaning and maintenance of grates in such sections.

Role of Anti-slip Structure

The grate surface adopts diamond-shaped raised patterns with a height of 1.2mm and a spacing of 8mm. This structure effectively enhances the mechanical engagement between the sole and the grate. When soaked in rainwater, the patterns also facilitate rapid drainage, reducing the impact of standing water on the friction coefficient.

4. Conclusions and Optimization Suggestions

The C250/D400 ductile iron gully grate generally meets the standards for drainage efficiency and anti-slip performance under heavy rain conditions, making it suitable for core road sections such as municipal arterial roads and secondary roads.

Suggestions:

a. Before heavy rain, focus on cleaning leaves and sediment around the grates to prevent debris from blocking and affecting drainage.

b. For road sections near catering or auto repair shops, upgrade the grate surface with a nano anti-slip coating to improve anti-slip performance under special working conditions.

c. Establish a quarterly inspection mechanism to check whether the grate gaps are deformed under load, ensuring stable long-term drainage and anti-slip effects.