- Chemical Resistance
- Safety Data Sheets (SDS)
- Material Properties
- PRO Systems
- PE Pressure Pipe
- PE Pipe Selection
- MAOP for PE Pipes
- Temperature Influences
- Selection of Wall Thickness for Special Applications
- Hydraulic Design for PE Pipes
- Surge and Fatigue
- Slurry Flow
- Pneumatic Flow
- Expansion and Contraction
- External Pressure Resistance
- Allowable Bending Radius
- Thrust Block Support
- Conductivity, Vibration and Heat Sources
- Polyethylene Jointing
- Handling and Storage
- Trench Preparation for Buried Pipes
- Relining and Sliplining
- Pipeline Detection
- Above Ground Installation
- Accommodation of Thermal Movement by Deflection Legs
- Service Connections for PE Pipes
- Concrete Encasement
- Fire Rating
- Testing and Commissioning
- PVC Pressure Pipe
- PVC Pressure Pipe Standards
- Pressure Considerations
- PVC Temperature Considerations
- Mine Subsidence
- Water Hammer
- Thrust Support
- Air and Scour Valves
- Soil and Traffic Loads
- Bending Loads
- PVC Pipe Jointing
- Jointing Components with Ductile Iron Flanged Joints
- Service Connections for PVC Pipe
- PVC Pipe Handling and Storage
- Below Ground Installation
- Above Ground Installation for PVC Pipe
- Testing and Commissioning for PVC Pressure Pipe
- Detecting Buried Pipes
- FLUFF – Friction Loss in Uniform Fluid Flow
- Technical Notes
Thrust Block Support
PE pipes and fittings joined by butt welding, electrofusion, or other end load bearing joint system do not normally require anchorage to withstand loads arising from internal pressure and flow.
Thrust blocks are only required for Vinidex PE pipes in pressure applications where the joint types do not resist longitudinal loads. For non end-load resisting joints, thrust blocks must be provided at all changes in direction and other points of potential pull-out forces, e.g., bends, valves, tees etc. In addition, anchorage support must be provided for fabricated fittings which incorporate welded PE pipe segments.
All fittings and heavy items such as cast iron valves must be independently supported in order to prevent excessive shear loads being transferred to the PE pipe. In addition, where valves are used, the torque loads arising from the opening/closing operations must be resisted with block supports.
Where concrete blocks are used, the contact points between the PE pipe, or fitting and the thrust block must be protected to prevent abrasion of the PE. Rubber or compressible PE or geotextile sheeting may be used for this purpose.
The velocity thrust is generally small in comparison to the pressure thrust. The pressure used in the calculations should be the maximum working, or test pressure, applied to the line.
R = Resultant thrust (kN)
P = Pressure (MPa)
A = Area of pipe cross section (mm2)
φ = angle of fitting (degrees)
For blank ends, tees and valves:
The velocity or kinetic thrust applies only at changes in direction.
w = fluid density (kg/m3)
A = area of pipe cross section (mm2)
V = flow velocity (m/s)
The velocity thrust is generally small in comparison with the pressure thrust. The pressure used in the calculation should be the maximum working or test pressure applied to the line.
The thrust developed must be resisted by the surrounding soil. The indicative bearing capacities of various soil types are tabulated below:
The figures in the table below are for horizontal thrusts, and may be doubled for downward acting vertical thrusts. For upward acting vertical thrusts, the weight of the thrust block must counteract the developed loads.
In shallow (<600mm) cover installations or in unstable conditions of fill, the soil support may be considerably reduced from the values tabulated, and a complete soil analysis may be needed.
|Soil Type||Safe Bearing Capacity (N/m2)|
|Rock and sandstone (hard thick layers)||100 x 105|
|Rock- solid shale and hard medium layers||90 x 104|
|Rock- poor shale, limestone||24 x 104|
|Gravel and coarse sand||20 x 104|
|Sand- compacted, firm, dry||15 x 104|
|Clay- hard, dry||15 x 104|
|Clay- readily indented||12 x 104|
|Clay/Sandy loam||9 x 104|
|Peat, wet alluvial soils, silt||Nil|
- Establish the maximum pressure to be applied to the line
- Calculate the thrust developed at the fitting being considered
- Divide (2) by the safe bearing capacity of the soil type against which the thrust block must bear.
What bearing area of thrust block is required for a 160 mm PN12.5 90° bend in hard, dry clay?
- Maximum working pressure of PN12.5 pipe is 1.25 MPa. Test pressure is 1.25 x WP = 1.56 MPa.
- Bearing area of thrust block