YPEP 3D vegetation net~ Problems of ecological restoration of urban mountain slopes
I. Project overview: Problems of ecological restoration of urban mountain slopes
Project location: Upper slope along Pok Fu Lam Road, Hong Kong Island.
Project History: This slope was created during previous road widening work. Its surface consists of a mixture of highly weathered rocks and residual soil, with a slope of approximately 1:1 (45°). In a subtropical monsoon climate, the slope faces two main problems. First, intense rainfall during the monsoon season causes severe soil erosion and the risk of shallow surface landslides. Secondly, the exposed surface of the earth and rocks contrasts sharply with the surrounding dense mountain forest, which negatively affects the ecological landscape of the city. The main goal of the project is to quickly restore vegetation cover while ensuring slope stability, thereby restoring its ecological function and landscape value.
Solution: Instead of traditional rigid slope protection methods such as rubble stone masonry with mortar joints or wire mesh gunite, the project used flexible environmental technology combining “3D grass planting mats with hydraulic gunite.” This approach involves laying down a layer of three-dimensional plastic mesh mats that provide a stable base for soil and vegetation, providing a seamless combination of engineered protection and ecological restoration.
II. Project proposal: multi-layer composite environmental protection system
The essence of the design proposal is to create a functional structural layer that runs from the inside to the outside in successive tiers.
Cleaning the slope and preparing the base:Remove dangerous rocks and loose material from the slope surface. Perform appropriate excavation and backfill to level the surface, creating a straight, uniform slope that facilitates proper adhesion of the grass planting net. For locally unstable areas, install simple anchor rods for reinforcement.
3D grass mesh selection and functional design:
Material selection:use a 3D vegetation net made of black polyethylene (PE). This material is corrosion-resistant, aging-resistant, and its black color absorbs heat, promoting early seed germination. Model EM4 was selected with a mass per unit area of approximately 350 g/m², a thickness of ≥14 mm and a longitudinal and transverse tensile strength of ≥2.0 kN/m, which provides sufficient mechanical support.
Mechanism of action:The multi-layer structure of the three-dimensional mat effectively holds the soil and prevents erosion. More than 90% of its space can be filled with soil, providing a three-dimensional environment for seed germination and root growth. Plant roots can penetrate the mat and extend 30-40 cm into the underlying soil. Ultimately, the mats, roots and soil are tightly intertwined to form a durable green composite protective layer that is more than twice as resistant to erosion as conventional turf.
Design of the nutrient layer of the substrate:The mesh will be covered with a layer of a special soil mixture (consisting of planting soil, organic fertilizers, water retaining agents and binding agents) at least 12 mm thick to provide the plants with constant nutrition for growth.
Plant ratio design:Given Hong Kong's climatic conditions, Bermuda grass (Cynodon dactylon) was chosen as the primary species (approximately 70%), supplemented with fast-growing, nutrient-tolerant tall fescue (20%) and native shrub seeds (10%). This combination ensures rapid soil coverage and long-term ecological balance.
III. Installation and construction: standardized processes and key controls.
Construction strictly follows a standardized work process:"Preparation - laying the net - fastening - covering with soil - sowing - care."
Preparation for construction:Dig support trenches at the ridge and base of the slope, approximately 30 cm deep.
Laying and applying the grass mesh:
Laying direction:Install vertically along the slope surface from top to bottom, following the ridge line.
Overlapping method:Use the overlapping technique. To ensure continuous protection and strength, the overlap width between adjacent rolls is strictly controlled at 10 cm in both the longitudinal (up/down) and transverse (left/right) directions. During installation, ensure the mats lie flat against the slope surface without any suspended folds.
Anchor fastening:Use a combination of primary mount and secondary mount approach.
Use U-shaped steel rods (diameter ≥6mm, length about 20-30cm) as main anchors, staggered at intervals of about 1.5m to firmly anchor the mesh into the soil.
On slabs and uneven areas, use 25cm bamboo stakes or U-shaped iron nails for additional fixing.
The top edge of the mesh lining should be buried in the ridge trench, and the bottom edge in the footing trench. Backfill and compact to complete the sealing of the ends.
Soiling and sowing:
Immediately after securing the mesh liner, spread the pre-mixed growing medium evenly over the mesh liner until the entire mesh space is filled.
Using a hydraulic sprayer, evenly apply a suspension containing grass seed, fertilizer, binder, wood fiber, and water to the entire slope surface. This method provides high efficiency and uniform coverage, making it suitable for challenging slopes.
Coating and care:
Immediately after spraying, cover the area with non-woven fabric to retain heat and moisture and prevent erosion. Frequent misting is required initially to maintain humidity. Remove the non-woven fabric when the seedlings reach 5-6 cm in height and resume regular care.
IV. Summary of the main advantages of 3D grass planting grids
Compared with traditional methods such as soil spraying and turf laying, 3D grid grass planting technology demonstrated comprehensive advantages in this project.
| Comparison parameter | 3D geomat technology for eco-protection | Traditional turf laying |
|---|---|---|
| Protection efficiency | Comprehensive, permanent protection. The mat and plant roots form a "reinforced soil" composite, providing high resistance to erosion and long-term slope stabilization. | A temporary, surface covering. The turf's root system is weakly connected to the underlying soil, making it susceptible to complete loss under the impact of rainfall. |
| Ecological effect | In-situ ecosystem restoration. Plants grow naturally, their developed root systems integrate into the surrounding ecosystem, and have high biodiversity potential. | Ecological isolation. Reminiscent of a "green carpet," the weak connection to the ground results in a relatively isolated and fragile ecosystem. |
| Construction and adaptability | High adaptability. Slope surface flatness requirements are relatively low, and the technology is applicable to a variety of complex and steep slopes. High mechanization ensures rapid construction. | Significant limitations. A level slope surface is required; anchoring on steep slopes is difficult, as there is a high risk of slippage. Large volumes of high-quality topsoil are required, and this is highly dependent on site conditions. |
| Resources and Cost | Land and water savings. No need to occupy farmland for sod cultivation, preventing damage to arable land. Water requirements on-site are significantly lower than those for irrigation after sod installation. | High resource consumption. Growing turf requires large areas of arable land, and soil removal is damaging. Long-distance transportation costs are high. Abundant watering is required after installation to ensure establishment. |
| Long-term cost-effectiveness | Low overall costs, long service life. One-time construction work ensures long-term results. The combined effect of vegetation and matting results in extremely low long-term maintenance requirements, approaching "near-zero maintenance." | High repeat investment. Turf is susceptible to degradation and bald spots and requires frequent seeding, irrigation and fertilization, which leads to high long-term maintenance costs. |
Conclusion:
The successful application of 3D grid technology for grass planting in the Pok Fu Lam Road slope restoration project in Hong Kong demonstrates its exceptional value in addressing soil erosion and ecological restoration problems on steep urban slopes. It goes beyond simple “greening” and achieves the triple goal of ensuring engineering stability, ecological restoration and landscape enhancement. Its outstanding advantages - construction efficiency, high adaptability, environmental friendliness and long-term economic efficiency - make it the preferred solution for the development and renewal of environmental infrastructure in complex urban geological and climatic conditions, which is fully consistent with the principles of sustainable development.
