Assume that a frictionless retaining wall 15 ft high having a vertical backface supports a sandy soil with a unit weight of 118 pcf and an angle of internal friction of 34°. The soil backfill is...

Assume that a frictionless retaining wall 15 ft high having a vertical backface supports a sandy soil with a unit weight of 118 pcf and an angle of internal friction of 34°. The soil backfill is level. Calculate the difference in the lateral force imposed onto the wall (per foot of wall length) when the at-rest lateral pressure condition applies compared to when the active lateral pressure condition applies (express the difference as a percentage increase related to the active pressure condition).