Comparison of Tunnel Convergence Measurement Methods

Sammanfattning: When creating cavities below ground, movements occur in the surrounding soil due to disrupted equilibrium. In tunnel constructions these displacements are referred to as tunnel convergence. This report compares four dierent methods for monitoring tunnel convergence with regards to both measurement precision and method cost. Three of the methods are based on displacement measurements of optical targets placed at regular intervals in the tunnel. Presented is also a method using a combination of wireless tilt and distance sensors to monitor tunnel convergence. The overall conclusion is that measurement precision and cost are well correlated. However, important to consider is that tunnel convergence monitoring cost is faceted and not only the obvious cost of equipment and labour, but also the indirect cost from interfering with other activities in the tunnel. Measurement precision of the dierent methods was determined by applying the methods in a lab environment, congured to eliminate any possible movements, and analysing the distribution of the displacement demonstrated by each method. In addition, information regarding the labour eort required to prepare and perform the measurements was also collected. Based on the experiments and literature studies, the report discusses the criteria to consider when selecting a tunnel convergence monitoring method and presents a comparison of the four methods included in the study.