A 15 ft Retaining Wall with a 16” thick footing (H=16.33’) has a point load surcharge of 4 kips at 21 ft setback (x=21’). Most designers will say X > H, so there is no surcharge influence.
Looking at the chart above, you can see 20 psf surcharge. While this is small influence, it does show that surcharges setback greater than 1H still impose lateral stresses on the wall. More surprising, if we were to look at the horizontal distribution, you can see 15 pound force at either side of the wall at 30 ft distance. It only diminishes (say 2 lbf) at 45 ft perpendicular distance from point of application. Look at the plan view below:
This means, you could have a surcharge 45 ft away from your wall, in another property line, but it still imposes lateral stresses. Earth pressure does not recognize property line boundaries. With SoilStructure Retaining Wall Software, you can see this value on the Table below:
In this case it is only 2 lbf and can be neglected. However, it is better to be aware of this phenomenon and quantify it. SoilStructure Retaining Wall program tell you this value.