Add Pre-Load

The Pre-Load option allows you to define a polygonal load representing a fill material, where the load magnitude is defined by the Fill Height and the unit weight of the fill material. The Pre-Load option can be used in two different ways:

• The primary purpose of the Pre-Load option is to use as a back analysis option, allowing you to determine the required fill height necessary to achieve a particular settlement at a given stage.
• The Pre-Load option can also be used to directly define the fill height, without using the back analysis option.

A Pre-Load represents a uniform load (i.e. the fill height is assumed to be constant over the area of the pre-load).

Due to the requirements of the back-analysis computation, only a single Pre-Load can be defined.

To add a pre-load:

1. Select Loads > Pre-Load
2. In the Plan View, enter the vertices of the polygon as described in Entering Coordinates. To close the polygon boundary, after all vertices are entered, right-click and select Close, or you can type c and Enter in the prompt line.
3. You will see the Define Pre-Load dialog:
• Enter the Fill Unit Weight, Installation Stage and Removal Stage (if the pre-load is to be removed).
• Back Analysis - to calculate a fill height for a required settlement, select the Calculate Height from Settlement checkbox (this is on by default). Enter the desired settlement value, the stage of the desired settlement, and a reference stage (if you want to enter relative settlement between two stages).
• User-Defined Fill Height - to enter a user-defined Fill Height, turn off the Calculate Height from Settlement checkbox, and enter the Fill Height.
4. When you are finished entering the information, select OK. The pre-load will be added to the model.
5. A Point Query is automatically added at the center of the pre-load and results will be displayed. See below for details.

Pre-Load Results

When you add a pre-load, a Point Query is automatically created at the center of the pre-load.

This is the location at which the back-analysis computation is carried out. If the Calculate Height from Settlement checkbox was selected, the results of the back analysis (i.e. fill height for desired settlement) will be displayed in a text box beside the pre-load.

If the specified settlement cannot be achieved at the specified stage, for any value of fill height, the results will indicate Preload Height: Outside Limits. This may occur, for example, if the settlement you have entered has already occurred prior to the specified stage.

After computing a back-analysis, if you turn off the Calculate Height from Settlement checkbox, the computed fill height will automatically be entered as the Fill Height.