Utilizing Targeted and Varied Ground Improvement Solutions during Trenchless Boring/Tunneling in Challenging and Unexpected Geologic Conditions along the Front Range of Colorado

As the population of the front range continues to increase, the growth continues to stimulate development requiring new utility installations in challenging conditions around already existing infrastructure. Trenchless boring of utilities across, next to, and under existing infrastructure is done to minimize disruption to existing infrastructure and the public in such urban environments. In larger diameter tunnel applications, ground improvement can be performed before or simultaneously during tunnel advancement. Although less common, ground improvement techniques are also utilized in smaller diameter trenchless boring where ground conditions dictate. Pre-tunneling ground improvement can stabilize raveling or weak soils which serves to reduce or eliminate settlement potential, promote the use of more economical tunneling methodologies, control water infiltration, and protect adjacent infrastructure. Ground improvement can also be utilized during and post tunneling to address actual settlement. This paper will review some available and common ground improvement techniques for tunneling and discuss two recent smaller diameter case studies completed along the front range to illustrate the benefits of ground improvement as implemented in challenging and/or unexpected geotechnical conditions. The paper will conclude with considerations that should be evaluated when approaching similar projects prior to and during the RFP and contracting process.