Page 427 - Trenchless Technology Piping Installation and Inspection

Planning and Safety Considerations for Trenchless Installation Methods 377

To be feasible, a prospective alignment must have adequate jack-
ing and receiving shaft/pit locations available. In addition, prospec-
tive jacking and receiving shaft/pit sites must be spaced at distances
that are compatible with specific trenchless technology technique.
The maximum distance a pipe can be installed with a proposed
trenchless installation method is dependent on parameters such as
pipe size, structural capacity of the pipe, possible use of intermediate
jacking stations, thrust capacity of the thrust block and the main jacks,
soil conditions, effectiveness of the lubrication system, and specific
project conditions such as operator’s skills in steering the cutterhead
or the tunnel boring machine (TBM).
Providing adequate space for staging construction operations is
important so that pipe installation can be completed in an efficient
manner. Construction access to the jacking shaft/pit must be pro-
vided for hauling spoils, pipe sections, and tunneling/drilling equip-
ment. In urban areas, traffic control requirements must be evaluated
in selecting and laying out jacking shaft/pit sites. A typical jacking
shaft/pit site needs enough space for the jacking shaft/pit, slurry
tanks, a crane, pipe storage, and support facilities and equipment
(e.g., as a generator, power pack, and bentonite lubrication unit), and
operator’s trailer. The jacking shaft/pit should be a sufficient distance
from overhead electrical lines to avoid hazards in operating the crane,
although in some areas a gantry system can be used instead of a crane
for smaller pipe sizes.
The jacking equipment arrangement is quite flexible and space
requirements can be reduced for smaller sites, if necessary. Frequently,
jacking shafts/pits have been located in the parking strip along the
edge of a street with the equipment setup in a linear arrangement.
Similar linear arrangements have also been used to stage trenchless
technology operations from the median of wider, more heavily trav-
eled streets without significantly impacting traffic flow. Staging area
requirements can be further reduced by using same machine location
to install two drives, one in each direction (see Fig. 9.1). This approach
further minimizes the environmental impacts of construction by
reducing the number of jacking shaft/pit locations. Using pipe
sections with smaller lengths, and indexing jacking equipment with
several strokes, may allow smaller shafts/pits.

9.2.8 Accuracy and Tolerances Including Settlement
and Heave
As with other details of the planning phase, the question of settle-
ment and heave will be greatly impacted by many project-specific
conditions and ground conditions. Trenchless technology has
advanced so that pipe installation can successfully be performed in
difficult ground conditions.