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Pipe Bursting Large Diameter Pipe - Class C Pipe Bursting
8th In A Series From The IPBA
This article primarily focuses on replacement of large diameter sewer mains as that makes up the majority of large diameter pipe bursting. Proper project planning is critical to success and as pipe sizes increase the calculations required to manage the installations become more complex. A project team must have a clear understanding of the forces required to install pipe with bursting technology. The primary calculation is the force required to install a new pipe from point A to point B. Pipe bursting is accomplished in three steps that are all occur simultaneously as the pipe is installed. These steps are represented in the following equation as A, B and C.
A. The amount of energy required to burst or split the existing pipe -- plus (a) the amount of energy required can increase in areas where pipe repairs were made, or there are some types of pipe joints or other factors with the existing pipe material.
B. The energy required to expand the existing soil to +/-20 percent larger than the OD of the newly installed pipe – (b) this is a volumetric calculation and the displaced volume is directly related to the difference from the ID of the existing pipe and the OD of the expander head. The energy required to expand the existing soil will vary with changes in soil conditions or original trench construction.
C. The drag that is placed on the new pipe as it is pulled into place – (c) drag can increase as the installations get longer, soil conditions or groundwater table causes the annulus to revert the pipe contact state, or a number of other factors.
Also, another factor that must be consider is lubrication (L) which is often used on Class C pipe bursting projects to reduce pipe drag by maintaining hole stability or friction caused by the existing soils contacting the new pipe. Lubrication mixtures are often similar to that of horizontal directional drilling mud. However, the project team must have a true understanding of fluids in order to truly manage drag forces and maintain a safety factor. This is generally the amount of power that is desired to be in reserve during normal conditions.
All this equates into the following formula: (A) x (a) + (B) x (b) +(C) x(c)-(L) = Required Force + (safety factor %) = Equipment Required.
The biggest difference between a small diameter and large diameter burst is that the expansion force is a volumetric displacement formula which is directly related to the amount of soil that must be displaced and the energy required to do so.