Geogrid

2. Construction Steps

2.1 Subgrade Preparation

• Compaction Degree: The compaction degree of the subgrade should be ≥ 96% of the standard Proctor density (AASHTO T180) to ensure the stability of the subgrade.

• Flatness: The flatness of the subgrade surface should be ≤ 5cm when detected by a 3m straightedge to provide a smooth base for geogrid laying.

• Removal of Sharp Objects: All sharp objects, such as stones with a particle size > 5cm, should be removed from the subgrade surface to prevent damage to the geogrid.

2.2 Geogrid Installation

• Layout and Positioning: Lay the geogrid along the longitudinal direction of the expressway (perpendicular to the driving direction). Accurate positioning should be carried out according to the design drawings.

• Lap Width: The longitudinal lap width should be ≥ 20cm, and the transverse lap width should be ≥ 40cm to ensure the connection strength between geogrid sheets.

• Tensioning and Fixing: Use U-shaped nails to anchor the geogrid. The spacing of U-shaped nails is 1.5m × 1.5m. In special areas such as slopes, additional anchor trenches (depth 40cm × width 20cm) should be set up to enhance the stability of the geogrid.

• Joint Treatment:

• For plastic geogrid, adopt hot melt welding, and the welding temperature is 380 ± 20℃.

• For steel-plastic geogrid, use special connecting fasteners to ensure reliable connection.

2.3 Fill Placement

• Layer Thickness: The fill should be placed in layers, and the thickness of each layer should be ≤ 30cm. After each layer of fill is placed, it should be compacted with a vibratory roller.

• Particle Size Control: For the base course fill, the maximum particle size of the fill material should be ≤ 8cm; for the subgrade soil fill, the maximum particle size should be ≤ 15cm.

• Compaction Degree: The compaction degree of the base course should be ≥ 98%, and the compaction degree of the subgrade soil fill should be ≥ 96%.

3. Quality Control

• Laying Position: Use a total station to measure the laying position of the geogrid, and the allowable deviation is ± 5cm.

• Lap Width: Use a tape measure to detect the lap width of the geogrid. The allowable deviation is + 10cm / - 0cm.

• Anchor Strength: Conduct a pull-out test on the anchor points, and the anchor strength should be ≥ 1.2kN/anchor point.

• Fill Compaction Degree: Use a nuclear density gauge to detect the compaction degree of the fill, and the compaction degree should be ≥ 2% of the design value.

4. Special Applications for Expressway

4.1 Soft Ground Treatment

• Composite Foundation: Combine geogrid with gravel piles to form a composite foundation. This can increase the CBR value of the subgrade by 2-4 times, effectively improving the bearing capacity of the soft ground.

• Settlement Control: Through the reinforcement of the geogrid, the differential settlement of the subgrade can be reduced, and the differential settlement should be controlled within ≤ 2cm/10m.

4.2 Transition Zone Treatment

• Lap Length: At the transition zones such as the connection between bridges and subgrades or culverts and subgrades, the lap length of the geogrid should be ≥ 8m.

• Slope: Set a gradual transition slope of 1:3 to ensure the smooth transition of the subgrade structure and reduce the occurrence of uneven settlement.

5. Performance Advantages

• Post-Construction Settlement: For expressways with geogrid reinforcement, the post-construction settlement is ≤ 3cm/year, while for traditional expressway subgrades, the post-construction settlement is 6-10cm/year.

• Dynamic Stiffness: The dynamic stiffness of the subgrade with geogrid reinforcement can be increased by 30% compared with the traditional subgrade, which can better resist the dynamic loads generated by vehicles.

• Maintenance Cycle: The maintenance cycle of expressways with geogrid reinforcement can be extended to 6-8 years, while the maintenance cycle of traditional expressways is 2-4 years.

6. Construction Precautions

• Avoid Direct Rolling of Machinery: Before rolling the fill, a 20cm protective layer should be laid on the geogrid to prevent direct rolling of machinery on the geogrid, which may cause damage to the geogrid.

• Suspend Welding in Bad Weather: In rainy, snowy or windy weather, welding operations should be suspended to ensure the quality of the geogrid connection.

• Long-Term Design Consideration: When designing the geogrid reinforcement for expressways, the long-term service life of the geogrid should be considered, and the geogrid should be able to withstand at least 1 million times of vehicle load cycles.

7. Standards Compliance

• GB 50164-2011 (Code for Acceptance of Construction Quality of Concrete Structures): Ensure the quality of the subgrade and related structures.

• EN 15381 (Geosynthetics for Civil Engineering): Provide standards for the performance and application of geosynthetics.

• AASHTO LRFD Bridge Design Specifications: Refer to relevant regulations for the design and construction of expressway bridges and related structures.

8. Technical Services

• Finite Element Modeling and Analysis: Use finite element software to model and analyze the stress and deformation of the expressway subgrade with geogrid reinforcement to optimize the design scheme.

• Dynamic Load Testing: Conduct dynamic load testing on the expressway after construction to evaluate the dynamic performance of the subgrade and geogrid reinforcement system.

• Full Life Cycle Cost Assessment: Evaluate the full life cycle cost of the expressway with geogrid reinforcement, including construction costs, maintenance costs, and social costs, to provide a reference for decision-making.