Groundwater will go where it wants to go and will exert hydrostatic pressure at the most inconvenient locations. Unchecked, groundwater can collapse tunnel boring machine entry and exit points; blow out shaft bottoms; carry soil along with it and cause sinkholes; and, basically, create a mess. Therefore, Effective groundwater control is one of the key factors to a successful tunneling project.

No two schemes are alike. But at their essence, groundwater control techniques operate either through extraction (pumping the groundwater out to control flow and pressure) or exclusion (using walls or barriers to keep the groundwater out). Or some combination of both.

North American specialty foundation contractor Malcolm Drilling has been installing innovative groundwater control systems for several decades. As tunneling and underground projects have become more complex, dewatering schemes have advanced in sophistication and effectiveness. Here’s what we’ve learned on three of our recent projects.

Groundwater control techniques, both through extraction and exclusion, are an essential component of most tunneling projects.

Today’s larger and more powerful ground improvement equipment have enabled a huge advance in ground improvement techniques. Larger elements, such as CSM panels, large-diameter drilled shafts, and groundwater extraction wells, can be installed more economically. Advances in quality control techniques offer more confidence that ground improvement systems are built and will perform as intended, reducing the risk to tunneling operations.

Every tunneling project is unique. The major takeaway is that tunnel owners and prime contractors should rely on their ground improvement subcontractor’s expertise to bring both innovation and proven techniques to bear when wrestling with groundwater conditions. For tunneling, it’s all about control.