Water Table

A Water Table in RocTunnel3 is a type of Water Surface which represents a phreatic surface. A Water Table is created by setting the Water Type = Water Table, when you add a water surface using the Add Water Surface or Add Water by Location options.

A Water Table is used primarily for pore pressure calculation but also has several other possible uses. A Water Table can be used for the following purposes in RocTunnel3:

• Pore Pressure - if the Groundwater Method = Water Surfaces then you can assign a Water Surface (e.g., Water Table, Piezo Surface) to calculate the Pore Pressure for a Material. Pore Pressure is proportional to the vertical distance from the Water Surface. For joints assigned with a Joint Property using Material Dependent Water Pressure Method, any portion of the joint which passes through the material will take on the pore pressure effects of the material.
• Joint Pressure - if the Water Pressure Method = Water Surfaces then you can assign a Water Surface (e.g., Water Table, Piezo Surface) to calculate the Water Pressure inside the Joints. Pressure is proportional to the vertical distance from the Water Surface. The selected Water Surface is used to compute the water pressure over the entire joint.
• Ponded Water - if a Water Table is defined above the excavation surface, then Ponded Water is automatically created. The weight of Ponded Water is accounted for in the stability analysis, acting on the Free Surface of the block.

Assigning Water Surfaces

To use a Water Surface in the calculations, you must assign it to Materials in the Water Parameters tab of the Define Materials dialog or assign it to Joint Properties in the Water Parameters tab of the Define Joint Properties dialog.

Ponded Water

For any Groundwater Method (i.e., Water Surfaces, Ru, Water Grids) a Water Table can be used to define Ponded Water. When you define a Water Table with elevation above the ground surface, ponded water is automatically created and used in the stability analysis, regardless of:

• The Groundwater Method or Water Surface assignment in Define Materials dialog
• The Water Pressure Method or Water Surface assignment in Define Joint Properties dialog

Number of Water Tables

Only ONE Water Table entity can be defined for a RocTunnel3 model. If you have defined a Water Table, you will notice that Water Table can no longer be selected as the Water Type for any new water surfaces. If you already have a Water Table defined and you wish to define a new water table, then you will first have to delete the existing Water Table or use a Piezo Surface.

If you require more than one Water Surface for modelling groundwater you will have to use Piezometric Surfaces.

Water Table versus Piezo Surface

For Pore Pressure calculation, a Water Table is equivalent to a Piezo Surface in RocTunnel3. However, there are several additional features associated with a Water Table (e.g., Ponded Water) which are not available for a Piezometric Surface - see the Piezo Surface topic for details.