Box Jacking Trenchless TechnologyBox jacking is a well-established means of engineering culverts or tunnels under rail embankments orwaterways to accommodate road or rail traffic. It is a way of overcoming or circumventing geophysicalimpediments in order to build road or rail networks. Many tunnels of note around the world have beenbuilt using the box jacking process and though technology has improved greatly in recent times theengineering capacity has been around for quite a while. From a technical viewpoint the box jackingprocess begins with the excavation of a launch area or sink pit where a secure backdrop can beconstructed to facilitate the hydraulic jacking rams that will push the pre-cast concrete box sections intoplace. These large concrete boxes are custom constructed on site to suit the size of the tunnel. Oncebuilt they are hydraulically jacked into position with an excavator digging out the spoil at the face andremoving it for disposal. As the excavation proceeds the concrete section is pushed slowly into positionto form the roof, floor and sides of the tunnel.Box jacking requires high pressures to push the concrete boxes into place and a series of hydraulic ramsis used to accomplish the task. Large cutting heads such as are used with tunnel boring machines do notform part of the box jacking procedure. The excavator performs the task of removing the clay soil orrock from the face as the concrete section is rammed slowly forward to form the tunnel casing. Thebackdrop against which the jacking rams rest is constructed with concrete filled sheet pile shuttering.This ensures a strong enough backdrop against which the jacking rams can operate to jack the concretesections into place. This procedure is used for larger tunneling projects and can be performed quitequickly once the concrete sleeve or box has been constructed on site. Box jacking requires a minimalnumber of operatives and is therefore cost-effective from a labor point of view.
Box jacking as a form of underground tunneling is preferred in many cases to overhead bridges fordifferent contextual reasons. It can be more expensive than building bridges in given locationsdepending on environmental and geophysical considerations. Very often where building a bridge mightcause an obstruction to traffic, such as river traffic, there is no alternative but to construct anunderground tunnel using box jacking techniques to accomplish the task.The positive features of box jacking a tunnel include non interference with existing ground surfaceservices such as rail or road links and no disruption to pedestrian or automotive traffic.The non-intrusive nature of box jacking tunneling makes it an obvious choice as regards observing verysensitive environmental concerns. It complies with all European directives regarding protecting theenvironment and this is a big plus for the whole concept of box jacking tunneling for thosecommissioned with the task of installing new infrastructure to accommodate rail and road traffic.Box jacking will undoubtedly continue to be the most propitious method of installing undergroundinfrastructure for whatever purpose it is required.