I am updating a calculation where the bearing pressure at the toe of a gravity dam is calculated in the usual way, depending on whether the resultant is in the middle third. Uplift is initially assumed to be a straight line from heel to toe and adjusted by iteration to full headwater pressure if a crack occurs at the heel. All of this makes total sense; however, the engineer who prepared the calculations (no longer with company) adds tailwater pressure to the calculated pressure at the toe. For example pressure at the toe per unit width with R in middle third is calculated as R/BASE LENGTH)(1+6e/BASE LENGTH) + tailwater pressure.

Does anyone agree that it is correct to add the tailwater pressure? Why? Is it a pore pressure thing?