Pretty good work man. You explaind it pretty well and took some conservative assumptions, which is always on the safe side. I just want to say, you forgot the shear checks. Never forget that shear, is a fragile mechanism and should be not neglected!
The textbook forgot the shear check 😛 but yes do remember to check shear however in my experience, shear is hardly ever critical and retaining wall design is governed by bending and deflection.
Regarding the passive resisting force against the heel beam @4:30 why isn't the formula [Hp=Yf x 0.5KpPg(aH)]? - 'aH' as opposed to 'a2' . Why isn't the fill above the base slab being taken into account? Wouldn't the fill above be placing pressure on the soil at the heel beam level via the base slab? or is the pressure from the fill above not being transferred through the base slab? Genuine question.
What is the allowable ground pressure for this problem? If the permissible pressure is 100 kN/m2, then it is necessary to increase the area of the base?
Thank you for the upload. Do you stick with Eurocodes predominantly or do you ever use British standards? What would you recommend for upcoming engineers to use?