June 23, 2010
SoilVision Systems Ltd. is proud to announce the implementation of tunnel objects in the latest release of SVFlux™ and SVHeat™. The tunnel objects extend the current capabilities of the software to the modeling of irregular but linear 2D and 3D objects beneath the ground. The implementation of tunnels opens up new types of numerical models which can be solved by geotechnical and hydrological consultants.
Tunnel objects may be easily described as a series of internal lines in a numerical model to which internal boundary conditions can be applied. Tunnel objects can be comprised of multiple line segments and can be at any orientation. They can also intersect and cross existing geo-strata in any fashion.
Rate, head, or review-by-pressure boundary conditions can be placed on tunnel objects. Rates or heads can also be entered as constants or as functions of time specified through data tables. The tunnel properties dialog can be seen in the following figure.
Tunnel Properties dialog
Tunnel objects are managed through the Tunnel Manager dialog, found as shown in the following screenshot.
Tunnel menu item
It should be noted that the tunnel objects makes use of an exponential decay function to apply the internal boundary condition to not only the nodes on the tunnel, but the nodes immediately surrounding the Tunnel object. This greatly stabilizes the numerical calculations and avoids the creation of excessively steep gradients next to tunnel objects. The exponential decay function still preserves the mass of either energy or water which is added to or extracted from the numerical model.
If high gradients develop around tunnel objects, then the software can also make use of automatic mesh refinement to increase the accuracy of the resulting numerical calculations.
There are a number of applications of this type of technology, such as:
- Pumping from angled wells,
- Numerical modeling of dewatering of mine shafts,
- Influence of angled thermosyphons,
- Earth dam sideslope dewatering.
A few simple example problems will illustrate the use of this feature.
Pumping from Angled Wells
This example is a very simple model where tunnel objects are applied into a slope. The pumping rate is then applied to each tunnel object, and the result on the water table can be calculated. The geometry of the numerical model can be seen in the following figure.
Tunnel Example, found in Tunnels > Tunnels
Once the numerical model is solved, the impact on the water table can be seen. What is also interesting to note is the automatic mesh refinement which improves the calculation of results right next to the tunnel objects. The high gradients next to the tunnel object necessitate the addition of nodes to the mesh such that the calculations remain stable and accurate. The final location of the water table and the final mesh used to create the solution may be seen in the following figure.
Dewatering Mine Shafts
Calculating the pumping capacity required for mine shafts which are under the groundwater table is a useful analysis for which SVFlux™ can be applied. This particular model can be found in the distribution models under Tunnels > Tunnels_m_layer. The front end visualization of the numerical model can be seen in the following figure. It can be seen that an angled shaft cuts through the model with several side shafts. Even though it is unrealistic, the shaft is set to cut through several geologic layers to illustrate the point that this can be done successfully in the numerical model, despite being a challenging part of the analysis. The next figure shows the results of the numerical model; the depression of the water table around the mine shafts and the resulting pumping rates can be calculated with the numerical model.
Dewatering Example Results
Earth Dam Sideslope Dewatering
This particular application examines the use of a tunnels object to de-water the downstream side slope after an earth dam. It is desired to study the pumping rate and the relative influence on the groundwater table of installing a small drainage tunnel. Proper drainage in such a situation can also influence the stability of the downstream slopes. The geometry of the model may be seen in the following figure, found in the distribution models as Tunnels > EarthDamDrainageTunnel_2:
The solution of this numerical model may be seen in the following figure. Note the resulting impact on the pumping rate of the tunnel, as seen in the drainage results shown below:
Tunnel objects are also useful for modeling thermal effects. Refer to our article on Open Pit Modeling for several examples of thermal siphons installed under a pond, with results demonstrating their influence on the thermal regime surrounding them.