Settlement Behaviour of Heinenoord Tunnel

Abstract

The 1st Heinenoordtunnel is an immersed tube which has been open for service in the Netherlands since 1969. Over the past 50 years, a large and increasing settlement has been measured along the tunnel alignment. The greatest value of settlement (65 mm) occurs in tunnel element 1 from 1978 to 2018. The maximum differential settlement has reached 30 mm between element 1 and 2 which causes a potential threat to the tunnel serviceability. In addition, Distributed Optical Fiber Sensors (DOFS) was used to measure daily joint deformation of immersed tunnel. The result of DOFS has shown a periodic settlement under tide.
The aim of this thesis is to investigate the long-term and daily settlement behavior of Heinenoordtunnel. The study starts with the geological information investigation, followed by settlement analysis using 2D Finite Element Modeling. Both long-term settlement and daily cyclic settlement are simulated and compared with the monitoring data.
In long term settlement analysis, the results show that the consolidation settlement of tunnel element is trivial (<0.5mm) over the 50 years operation. The calculated result does not match with the monitoring data under a constant load assumption over the operational period. Therefore, three additional factors are considered which can be the possible causes of the excessive settlement. Those factors are the growth of traffic volume, fluvial deposition on riverbed and secondary compaction on the foundation. The main results are summarized as follows:
(1) The settlement due to extreme traffic growth is between 10 and 20 mm which increases gradually from 1979 to 2018.
(2) The fluvial deposition causes an average settlement of 1.68 mm over the past 40 years of operation.
(3) The secondary compaction result is in between 5.30 and 10.70 mm, while the exact value depends on the selection of creep parameter.
(4) The combined settlement is in between 18.27 and 30.62 mm that is significantly less than the monitoring data.
Based on the above findings, the combination of those three factors cannot provide a sound explanation on monitoring data. Hence, a sensitivity analysis will be conducted in the final stage of the research.
In the daily settlement response simulation, a coupled flow simulation is applied on both traverse and longitudinal direction under tidal fluctuation. The summary of results is indicated as below:
(1) A phase delay of excess pore water pressure occurs for soil under the low permeable layer. This causes periodic rebound and settlement on the tunnel element
(2) The amplitude of tunnel cyclic settlement is in between 0.143 and 0.215 mm
(3) The deformation of intermediate immersion joint is under 0.059 mm
Since the difference between calculation and monitoring results is over 0.2 mm in joint 6, it is important to conduct sensitivity analysis on the Plaxis model.
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To verify the importance of soil variability, the sensitivity analysis is conducted by reducing the stiffness parameter with two standard deviation value in long term settlement analysis and one standard deviation value in daily settlement analysis. The long-term settlement become twice as the initial value after the parameter adjustment. The difference between monitoring data and Finite Element result reduces by 30 to 192 percent of the original value. On the other hand, the daily settlement of tunnel reduces by 4 to 17 percent under the one standard deviation increment. The daily response of tunnel is closer to the monitoring data after parameter adjustment.
In conclusion, the three factors considered in this research causes a significant change on the total settlement of immersed tunnel. The periodic response of tunnel settlement is verified from the coupled flow mode. Finally, some recommendations are made for future study.