The correct answer is: C. Both top and bottom faces perpendicular to wall
The main reinforcement in the heel of a T-shaped R.C. retaining wall is provided on both the top and bottom faces perpendicular to the wall. This is because the heel is the part of the wall that is subjected to the maximum bending moment. The main reinforcement is provided to resist this bending moment.
The top face of the heel is subjected to tension, while the bottom face is subjected to compression. The main reinforcement is therefore placed on both faces to resist these forces.
The main reinforcement is typically placed in two layers, with the top layer being placed in tension and the bottom layer being placed in compression. The reinforcement is also typically tied together with vertical ties to prevent it from buckling.
The main reinforcement in the heel of a T-shaped R.C. retaining wall is an important part of the structure, and it is essential to ensure that it is properly designed and installed.