The solid the enclosure created is perfectly fine. However, it's a massive solid (fills through the pipe) and it's not possible to subtract the outer boundary of the pipe from it using the combine tool. I only get the message "Unable to intersect bodies" when trying to do so. The problem it causes in Mechanical is related to the meshing because of the intersection between the concrete block and the pipe (in addition to being physically incorrect, of course).


When trying your alternative suggestion the solid is not split correctly. It divides the concrete block in two: One piece remains as the complete block, while the other solid consists only of the intersecting volume between the block and the pipe. This is illustrated in the attached screenshot.