2D Tutorial 16: Freeze pipes in tunnel construction

20 May 2017

This tutorial illustrates change in coupling of groundwater flow and thermal flow as a result of ground freezing. A tunnel is constructed with the use of freeze pipes. By first installing freeze pipes in the soil, the soil freezes and becomes watertight so that tunnel construction can take place. This method of construction requires a lot of energy for the cooling of the soil, so by being able to model the cooling behaviour while groundwater flow is present an optimal freezing system can be designed.

In this tutorial a tunnel with a radius of 3.0 m will be constructed in a 30 m deep soil layer. A groundwater flow from left to right is present, influencing the thermal behaviour of the soil. First the soil will be subjected to the low temperatures of the freeze pipes, and once the soil has frozen sufficiently, tunnel construction can take place. The latter is not included in this tutorial.

Because groundwater flow causes an asymmetric temperature distribution, the whole geometry needs to be modelled,  where in previous examples only half of the geometry was sufficient.

Objectives:

  • Modelling soil freezing, coupling between thermal flow and groundwater flow
  • Modelling unfrozen water content.
  • Using the command line for structure definition.

Figure 1. Temperature distribution for a transient calculation


This exercise requires the PlaxFlow module and Termal module in order to be able to perform transient groundwater flow calculations in combination with thermal calculations.

The attached file LineCoordinatesCommands.txt contains all the commands to generate heat pipe lines

The other attached *.p2dxlog file contains all the commands to generate the model. With a PLAXIS VIP licence, you can use the commands runner to open the *.p2dxlog file and to execute all commands in one go, see also this instruction.

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