# Liner Type: Standard

In the Define Liner Properties dialog, choose Liner Layer Type = **Standard**. The **Standard** liner type can be used to model a liner which has flexural rigidity (i.e. resistance to bending), such as a shotcrete or concrete liner. A Standard liner is made up of 2-dimensional plate elements which can respond to flexural, axial (compressive or tensile) and transverse shear loads. For information about the numerical implementation of liner support in *RS3* see the Beams and Plates document in the *RS3* Theory section. Enter the properties described below.

## Geometry

For a **Standard** liner there are two ways of defining the liner cross-section: Thickness or Area and Moment of Inertia.

Thickness

If your liner has a constant cross-section, and uniform properties (e.g. a shotcrete layer), then you can simply define the liner Thickness. The liner axial and flexural properties will then be based on a cross-sectional area = Thickness x 1 (unit width).

Area and Moment of Inertia

If your liner has a more complex cross-section (e.g. reinforced concrete), then you can define the liner cross-section by entering an equivalent Area and Moment of Inertia. These values must be normalized per unit width of excavation.

## Elastic Properties

For a Standard liner, you must define the following **Elastic Properties**:

- Young's Modulus
- Poisson's Ratio

Liners are assumed to have isotropic Elastic Properties, therefore only a single Young’s Modulus and a single Poisson’s Ratio can be entered.

## Strength Parameters

For a Standard liner, the following **Strength Parameter** options are available:

Material Type: Elastic

If the liner Material Type = **Elastic**, then strength parameters are not considered. The liner will only respond elastically to loading, and there will be no upper limit to the loading which can be sustained by the liner.

Material Type: Plastic

If the liner Material Type = **Plastic**, then you may enter the transverse shear strength, and the peak and residual compressive and tensile strength parameters, which will be used in the analysis. Liners defined as Plastic will yield if the peak strength is reached. The plasticity calculation uses the "layering" method presented in Owen and Hinton (1986), in which the cross-section of the liner is partitioned into layers. If the stress in a given layer exceeds the peak strength (compressive or tensile), the layer yields.

## Include Weight in Analysis

By default the forces due to the weight of a liner are NOT included in the finite element analysis (i.e. the liner has zero weight).

If your Liner has a substantial thickness (e.g. a thick concrete or shotcrete liner), you may wish to account for the Liner weight in the stress analysis. To do this, select the **Include Weight in Analysis** checkbox, and enter the **Unit Weight** of the Liner material.

*RS3* will then use the Liner Geometry (Thickness or Area) and the Liner Unit Weight, to determine the total weight of the liner (i.e. the weight of each plate element), and include the resulting forces in the finite element analysis.

## Stage Liner Properties

The properties of a **Standard** liner can be modified at different stages of a multi-stage model, by using the **Stage Liner Properties** option in the Define Liner Properties dialog. This could be used, for example, to model the increase in strength and stiffness of shotcrete or concrete liners after initial placement. By selecting **Define relative change based on the install stage** allows for the factor to change relative to their installation stage. This would be used to define changes in strength and stiffness of a liner as it is applied in a stage excavation of a tunnel.

Most of the parameters entered in the Define Liner Properties dialog can be increased or decreased by user-defined factors at different stages. For details about staging liner properties, see the Stage Material Properties topic, as the general procedure for staging properties is the same.