Hedge and Sitharam (2015), Studies on Tough-Cell Protection of Buried Pipelines and Underground Utilities , Geotextiles and Geomembranes
Research shows that Neoloy Tough-Cell/geogrid reinforcement enables pipelines and utilities to be buried at a shallow depth, providing long-term protection that prevents damage and reduces maintenance – and significant cost savings.
The safety of buried pipelines and underground utilities has become of paramount importance to avoid the social, economic and environmental impacts of damage of pipeline and conduit failure. It is proposed that reinforcement from Neoloy Tough-Cells combined with geogrids can enable pipeline construction at shallow depths and provide long-term reliable protection to prevent damage and maintenance.
Laboratory plate load tests simulating tire pressure were conducted on 75 mm diameter and 1.4 mm thickness PVC pipes buried in Neoloy Tough-Cell combined with geogrid reinforced soils in a test box. The test bed soils were sand and natural silty clay, while dry sand was used to fill the Tough-Cells. The secant modulus of the pipe material at 2% axial strain was 3.1 GPa. Pressure cell and strain gauges measured the performance. Tests of pipe were conducted at different depths at 1B, 1.5B and 2B where B is the width of the loading plate.
Schematic Diagram of Test Setup
Experimental results were validated with FLAC numerical analysis software. The measured pipe strain values were in good agreement with the numerical analysis. The numerical studies show that wide lateral distribution of stress reduces pressure on the pipe.
Hedge (2015) Experimental and Numerical Studies on Protection of Buried Pipelines
Results show that reinforcement with the geocell mattress and geogrid considerably reduce deformation of piping compared to other reinforcement solutions. Observed pressure and strain values indicate that Neoloy Tough-Cells significantly reduces the depth of placement of pipes.
The figure below shows the pressure settlement responses of the unreinforced vs various configurations of the reinforced foundation bed. Punching shear failure of the unreinforced bed is evident, as the curves become almost vertical. The reinforced foundation bed had no failures, as the 3D geocell layer acts as a slab that spreads applied loads over a wider area, while the 2D geogrid resists download movement of soil. The hybrid reinforcement system of Neoloy Tough-Cell + geogrid reduced strain on the pipe by more than 50% compared to an unreinforced pipe.
Variation of Bearing Pressure with Plate Settlement for Different Reinforcements
Bearing capacity improvement factor increased with the increase in footing settlement. The improvement factor increased with the decrease in the depth of the pipe placement. 1-g model tests were scaled up to the prototype case of shallow buried pipelines below pavement using the appropriate scaling laws.
Benefits – Robust and cost effective
Laboratory plate tests of pipes buried in geocell/geogrid reinforced soft clay bed showed the efficacy of using geosynthetic reinforcement to protect buried underground utilities from trafficking and accidental damage:
- Reduces deformation of pipe – reduces pressure by 40% and strain by 60%; values increase with depth
- Lateral stress distribution enables shallow placement of the pipe underground – is huge construction cost savings
- Reinforcement improves durability, reduces maintenance
- Prevent pipe breakage, economic costs and pollution/environmental damage