ABSTRACT
This chapter presents a practical and intuitive method of finding all unsafe areas on tunnel surfaces. The unsafe areas consist of the faces of 3-d key blocks. The algorithms for locating the primary loops and maximum key block loops are non repeating deletion algorithms. The number of removable blocks is indefinite and tends to be infinite when the joints are long and dense. In the unrolled map, the removable blocks are overlapped and nested. The sum of removable blocks of the same joint pyramid (JP) is finite and removable; therefore, it is also a removable block of this JP. All removable block areas of a given JP can be connected to form a maximum removable block and all of the maximum key block areas are separated. The boundaries of all maximum removable block areas of a JP are individual loops without intersections.
