Technical Information
Design Considerations
With proper planning and execution, the grouting of the Danby Liner can be accomplished without damage to the liner. The second significant design consideration with Danby is concerned with the strength of the composite structure after the grout has set and its ability to withstand expected loads while in service. Although small, isolated grout voids will not significantly affect the load carrying capacity of the composite structure (PVC liner-grout-pipe), it must be assumed that these ungrouted PVC arches will be exposed to any ground water present and must be capable of withstanding such hydrostatic pressure.
Hydrostatic pressure load tests (NCSU, 1989) on the grouted Liner with several different percent voids have shown good agreement with the following equation (Timoshenko and Gere, 1961) for critical buckling strength of the ungrouted arch whose half-angle is Ø:
Pc= 8EI (k² –1) psi
D³
Sin kØ Cos Ø= k Sin Ø Cos kØ
Where k is found by iteration for given value of Ø.
Long Term Critical Buckling Pressure for Ungrouted Arch
Internal Diameter Pc
| Unlined (mm) | Lined (mm) | Danby (psi) |
| 1000 | 950 | 44 |
| 1200 | 1150 | 39 |
| 1350 | 1300 | 34 |
| 1500 | 1450 | 31 |
| 1675 | 1625 | 28 |
| 1800 | 1750 | 26 |
| 2000 | 1950 | 24 |
| 2150* | 2100 | 22 |
| 2300* | 2250 | 20 |
| 2400* | 2350 | 18 |
* Diameters larger than 2150 mm may require thicker material
NOTES
1 Includes safety factor = 2.0;
2 E (long term) = 200,000 psi; I = 0.004 in4 /in
3 Assumes 150 mm grout void in all diameters
For man-entry pipes (=900mm), 100% grout fill can be accomplished in the annulus due to the ease of access to multiple grout injection points. Obviously, the structural characteristics of the composite structure (PVC liner-grout-pipe) will depend primarily on the character of the grout. Fortunately, due to the ease of access to multiple grout injection points, most any grouting material appropriate can be used without undue restrictions due to flow characteristics.
Where appropriate, high strength cementious grout or light-weight foam grouts can be used with compressive strengths of 8,000 psi down to 150 psi and with Young’s moduli of 4,000,000 psi down to 300,000 psi respectively.
The grout will tend to fill holes and cracks in the old pipe (fill in where bricks and mortar are missing in brick lines) and generally rehabilitate the existing structure while “tying” the liner to the old pipe, and adding load-carrying wall thickness of similar material in rigid pipes. The composite structure is a rigid structure and should be designed using rigid pipe design principles.