Got it! Here is my result from camera view showing only the hole:
The first thing I did was flip all normals by keying Tab to enter Edit Mode, T to toggle open/close the Toolshelf, going to Toolshelf > Shading/UVs tab > Shading dropdown and clicking Flip Normals. This ensures that the textures display properly on the inside of the tube.
Second and lastly, I modified your node setup to this:
For the Image Textures, red_rock is still on top and brown_dirty on the bottom. I did not change how the color is integrated, but they now have bump mapping for each that is averaged by a Converter > Vector Math node. The additional Separate XYZ and other top nodes add the Ambient Occlusion shadows. Separate XYZ makes the darkness align to the local Z-Axis. The Gradient Texture mostly serves to convert the z vector to a Fac: value for the ColorRamp, which decides how much black and color there is. The MixRGB's bottom color input actually decides what color appears in the tube.
Here is the .blend file: