Zili Li obtained his Bachelor's degree in Civil Engineering at Tongji University in 2010 with a First Class Honors. He joined the Geotechnical & Environmental Engineering Research Group at the University of Cambridge in October 2010 as a PhD student under the supervision of Professor Kenichi Soga. Zili was offered the 'Cambridge Oversea Trust International Scholarship', to carry out his research work. He is a member of Jesus College.
Departments and Institutes
Zili's research topic is " Modelling and monitoring of London underground cast-iron cross passage structures".
The London Underground has a history of more than 100 years, still possessing one of the busiest underground metro system in the world. Deep tube tunnel lines several hundred miles of the London Underground system and many of which is comprised by cast-iron jointed linings. In particular, the engineering performance of cross passages between adjacent cast-iron tunnels is considered to be critical by recent assessment conducted by Tube Lines. The tunnel openings are entrances and exits for cross-passages and other adits by removal of several segments of lining. The number of deep tube tunnel openings over the London Underground system is several thousand and hence understanding of the behavior of cast iron lining is very important.
A common way to evaluate the structural performance of civil infrastructures is to acquire field data using a monitoring system. An innovative wireless sensor network (WSN) is emerging as an efficient technique for monitoring ageing underground infrastructure. Research on this topic started only a few years ago but has since then attracted worldwide attention. Previous tests in this area show certain advantages of WSN over traditional methods, for example, significant cost savings, rapid deployment and flexible adjustment. However, there has been limited work on their use in underground metro structures, and many challenging issues of which are still required to be investigated.
In Zili's PhD research, a wireless sensor network developed in the University of Cambridge will be deployed in the cross passages in London underground tunnels, where some movement has been observed. This monitoring system consists of gateways, strain gauges and displacement gauges with thermistor installed for temperature correction. The measurements will be sent to a computer server via a mobile phone network and made available on a web page in real time for structural analyses. Radio modules, power consumption and other issues will also be discussed to prove the feasibility of wireless sensing in a cast iron tunnel structure. The long-term monitoring data will present important findings on the lining performance to validate the results derived from numerical models.
To evaluate the behaviour of cross passage structures, Zili modelled a cast iron segmental lining using 3D-FEM. Numerical modelling on cast-iron segmental joints was first conducted and validated against a set of full-scale tests, carried out by a previous researcher. Based on this verified model, the influence of structural features (e.g. caulking groove and bolt pre-tension) on the segmental joint was studied and a set of spring models were then proposed to simulate the structural behaviour of the joints under bending and shearing forces. After that, large-scale numerical modelling of tunnel structures was performed to develop a detailed structural assessment on cast-iron cross passages in London underground. Based on the FE model and the comparison with the field data, the engineering features of the tunnel and their influence on the stability of the structure were studied. As a further study, an advanced soil model for London Clay was introduced and contributed to the understanding of long-term cross-passage tunnel validated against the field measurement.