When a structure applies the load on a footing, total and effective stress increases in the soil mass. If you  like to consider the effect of surcharge loads on soil liquefaction assessment (read more here), click on Input→ Surcharge Loads menu to access this page:

 

 

To activate this feature, simply click on "Footing Size and Loading" checkbox and enter footing (surcharge) size and the bearing pressure. If you uncheck this checkbox, the effect of surcharge will not be considered in soil liquefaction analysis.