{"id":6660,"date":"2026-10-05T05:45:16","date_gmt":"2026-10-05T05:45:16","guid":{"rendered":"https:\/\/www.pipetechservice.com\/?p=6660"},"modified":"2026-10-05T05:45:20","modified_gmt":"2026-10-05T05:45:20","slug":"microtunneling-shaft-sizing","status":"publish","type":"post","link":"https:\/\/www.pipetechservice.com\/ru\/microtunneling-shaft-sizing\/","title":{"rendered":"Microtunneling Shafts: How to Size Launch and Receiving Shafts"},"content":{"rendered":"

Microtunneling shafts are sized from the pipe outward, and the two types are sized differently: the launch shaft carries the thrust wall (the structure that provides the jacking reaction), the jacking frame and rams, the thrust ring, the jacking cradle and guide rails, the machine or the first pipe, the entry seal or gland, and the slurry and spoil lines, while the receiving shaft only has to receive the machine and the seal, so it is smaller.<\/strong><\/p>\n\n\n\n

This guide sets out the sizing sequence for both, the shaft type and depth envelopes published by the Pipe Jacking Association, how the thrust wall is sized for the maximum jacking force, and the base stability, uplift and flotation checks that decide whether a shaft works. Every dimension here is an input to project-specific design, not a value to copy.<\/p>\n\n\n\n

What Must Microtunneling Shafts Physically Hold?<\/h2>\n\n\n\n

A launch shaft is not a hole in the ground; it is a working chamber whose internal dimensions are fixed by the equipment inside it.<\/strong> The items below are the reason a shaft is almost always larger than a first estimate suggests, and they form the checklist that should be worked through before any excavation is priced.<\/p>\n\n\n\n

Item in the launch shaft<\/th>Why it sets the size<\/th><\/tr><\/thead>
Thrust wall<\/th>Carries the full jacking reaction and sits behind the frame; its depth and thickness consume one end of the shaft.<\/td><\/tr>
Jacking frame and rams<\/th>Sets the length of shaft needed behind the pipe, and the ram stroke sets the pipe section length that can be jacked.<\/td><\/tr>
Thrust ring<\/th>Spreads the jacking load around the pipe circumference and must be fully clear of the shaft walls.<\/td><\/tr>
Jacking cradle and guide rails<\/th>Set the launch line and grade and need clearance on both sides of the pipe for alignment and adjustment.<\/td><\/tr>
MTBM or first pipe<\/th>The machine or first pipe is lowered into the shaft and positioned before launch, so it must fit with lifting clearance.<\/td><\/tr>
Entry seal or gland<\/th>Seals the eye, retains annular lubricant and holds back groundwater; it occupies the front wall and must stay accessible.<\/td><\/tr>
Slurry and spoil lines<\/th>Feed and return lines, slurry pumps and the separation plant connection need routed space and maintenance access.<\/td><\/tr>
Safe access<\/th>Ladder or stair access, egress routes and the exclusion zone around the jacking frame all have to fit the chamber.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

In our design reviews, the size of microtunneling shafts is settled by three items more often than by the pipe diameter: (1) the length of one pipe section, (2) the depth of the jacking frame behind the reaction wall, and (3) the working space kept below the invert.<\/strong> When an owner fixes a shaft size before those are known, the shaft tends to come out either too small for the frame or larger than the drive needs.<\/p>\n\n\n\n

\"Section
Figure 1. A launch shaft is a working chamber. Thrust wall, jacking frame, guide rails and entry seal each take space, and the pipe section length usually governs the longest internal dimension.<\/figcaption><\/figure>\n\n\n\n

What Is the Sizing Sequence for a Launch Shaft?<\/h2>\n\n\n\n

The sizing sequence works outward from the pipe and downward from the invert, and each step adds a real dimension rather than a contingency.<\/strong> For a municipal sewer owner approving the budget, an EPC bidder pricing the excavation, and a third-party design consultant checking the geometry, the value to challenge first is whichever step is governing the internal dimension.<\/strong> If the question is how the internal dimensions are actually calculated, the answer is the outward sequence from the pipe outside diameter and downward from the invert, with the governing step identified before the excavation is priced.<\/p>\n\n\n\n