Development of a Distributed Optical Fibre Sensor NetworkBased Condition Monitoring System to Alert Road Collapse

Dr. Madhubhashitha Herath
Senior Lecturer, Department of Engineering Technology, Faculty of Technological Studies, Uva Wellassa University, Badulla, Sri Lanka 

Prof. Jayantha Epaarachchi
Associate Professor, School of Engineering, Faculty of Health, Engineering and Sciences, University of Southern Queensland,  Australia. 

Abstract: Road infrastructure is a crucial public asset that contributes to economic development and growth while bringing critical social benefits. It connects communities and businesses and provides access to education, employment, social and health services. Heavy rains, floods and hurricanes cause roads to collapse, resulting in life-threatening catastrophes and road closures. Emergency repair costs are estimated to be ten times that of planned maintenance. Therefore, condition monitoring and preventive maintenance will have significant cost and safety advantages for road infrastructure. The rapid rise in pore water pressure can be adduced as the key root cause of road collapse.

This research introduces a monitoring technique based on distributed optical fibre sensors to facilitate early warning for road infrastructure. Laying subterranean distributed optical fibre sensors along a road offers unique advantages for spatially distributed measurements for hundreds of kilometres. By analyzing the dynamic strains, road conditions can be measured in real-time. The evolution of the strain fields can relate to road collapse dynamics with an unprecedented resolution for early warning.

The proposed sensor system is designed in segments to measure the pore water pressure, and vertical and horizontal ground movements. The concept and the mechanical design were developed with the aid of computer simulations and Computer-Aided Design software. Initially, the first version of a pore water pressure sensor array was tested under laboratory conditions to investigate the water pressure-measuring performance by measuring strain readings through an Optical Backscatter Reflectometer. Afterwards, the second version of a pore water pressure sensor array was tested systematically to calibrate and build the relationship between water pressure and strain readings. The third version of the sensor consisted of all three components, including the pore water pressure sensor and vertical and horizontal ground moment-sensing components. The performance of the entire sensor system will be demonstrated in a physical model that has been constructed to date.

It was proven that the proposed sensor has the potential to precisely measure pore water pressure, and it was revealed that the measured strain readings were proportional to the applied hydrostatic pressure. The real-time measurements indicating the combined subterranean conditions of the roads can be obtained frequently from a remote locations as the optical fibres can transmit the measured data over long distances. The established system will be introduced to road development authorities for condition monitoring and to alert them about road collapses at an early stage. A model combined with water pressure sensing and land properties can be developed in the future to address any developing geohazards in water-prone areas. The developed condition monitoring and early warning system will be proposed for implementation in a high-risk road section in Sri Lanka and Australia.