Monitoring of Underground Construction Processes

Underground construction is being increasingly adopted to provide infrastructure solutions, such as tunnels, shafts and deep excavations, particularly in urban and other sensitive environments. Underground construction processes are often tightly constrained in terms of both programme and cost, however there are several uncertainties that limit how accurately these factors can be controlled. One of the most important areas is the structural interaction with the ground, in particular the contact stresses exerted on structures by the surrounding soil. The development of excessive frictional contact stresses can have a major impact on processes such as tunnelling and caisson shaft sinking.
The ability to predict or calculate soil-structure contact stresses during design is still relatively poor and the understanding of ground conditions prior to construction can be limited. As a result, it is desirable to have the ability to accurately monitor soil-structure interaction during construction. To achieve this, it is required to instrument underground construction projects with suitable monitoring systems. The underground environment presents a number of challenges to traditional instrumentation, such as electrical sensors. Many of the measured quantities undergo very small variations in magnitude, meaning sensors with a high resolution are required. Furthermore, monitoring systems are often subject to significant electromagnetic interference and are required to operate in harsh conditions.
The key aim of this work is to provide better understanding of the interface between the soil and structure during construction. This research will endeavour to demonstrate an improvement on current monitoring capabilities, by developing advanced, intelligent systems to monitor soil-structure interaction. It is hoped that this can be exploited to actively inform the construction processes, leading to improvements in both efficiency and safety. This research will also extend current experience of installing instrumentation on live projects. This can help to address some of the technical and logistical challenges, including installation, data acquisition and providing real-time feedback. Furthermore, information obtained from the developed systems should offer significant scope to improve the design on future projects. This could include validating design assumptions, leading to opportunities for optimising future designs and reducing design risks.
The methodology for this research will seek to pursue novel technologies to facilitate accurate measurement of the soil-structure normal and frictional contact stresses. New transducers will be developed using fibre optic sensing technology, namely fibre Bragg gratings (FBGs). Optical fibre systems and FBGs overcome some of the issues faced when using traditional instrumentation, including immunity to electromagnetic interference and durability in harsh environments. Whilst these technologies have been applied to force sensors previously, they have mainly been confined to industries such as robotic control and minimally invasive surgery. A review of these applications will be undertaken, before designing, building, calibrating and testing the new transducers. These will then be integrated into intelligent, automated underground monitoring systems, for deployment onto live construction projects. The addition of more sophisticated contact stress information will help these systems to provide more detailed feedback and predictions during the construction process. The fibre optic nature of the sensors will also help to improve the robustness and dependability of the systems.
Current EPSRC strategies for the area Ground Engineering include addressing complex SSI to prevent failure of critical infrastructure as well as integrating intelligent technologies into industry. This research is therefore completely aligned with these targets.