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# Piezo Surface

A Piezo Surface in RocSlope is a type of Water Surface which might represent Pore Pressure in a confined aquifer for example. A Piezo Surface is created by setting the Water Type = Piezometric Surface, when you add a water surface using the Add Water Surface or Add Water by Location options.

A Piezometric Surface is used primarily for Pore Pressure calculation.

• 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.

## Piezo Surface versus Water Table

For Pore Pressure calculation, a Piezometric Surface is identical to a Water Table. If you only require a Water Surface for Pore Pressure calculation, then a Piezometric Surface and a Water Table are interchangeable.

However, a Piezometric Surface CANNOT be used for Ponded Water. For modelling Ponded Water, you must define a Water Table.

In general, a Water Table refers to a Phreatic Surface (e.g., a water table in an unconfined aquifer) which represents a surface of zero pore pressure within the material.

A Piezometric Surface could represent Pore Pressure in a confined aquifer. In such cases, a Piezometric Surface might have an elevation above the ground surface. In this case, you would NOT want Ponded Water created by the Piezo Surface. This is why a Piezo Surface in RocSlope does NOT generate Ponded Water.

## Number of Piezometric Surfaces

There is no limit on the number of Piezometric Surfaces which can be defined in a RocSlope model.

This is in contrast to a Water Table - only ONE Water Table is allowed in RocSlope model. If you require more than one Water Surface for modelling groundwater you will have to use Piezometric Surfaces.