This lecture is demonstrating a new technique of supporting a shaft bulge-out used the first time when constructing shaft bulge-out of coal mine General Blumenthal in Germany. It differs from convential design by a step by step supporting of the newly exposed rock face by shotcrete, supporting rings, and rock bolt anchoring fixed to the rock throughout by GD-Topac anchoring system.
The coal mining enterprise General Blumenthal in Germany intends to drive a 6.5 m diameter tunnel between two shafts. It is foreseen due course that a full face tunneling machine shall commence the drive in the shaft number 8 at a depth of about 1000 m. In preparation of the scheme the shaft had to be widened from 7.6 m diameter to 15 m. Further requirements are two wing-like excavations necessary, projecting 17 m laterally from the bulge-out on opposite sides. The central portion of the configuration is 21 m high, whereas the recesses have a threshold height of 13 m. In the vertical direction the total alteration of the original shaft measures 31.5 m overall. About 4800 cubic meters of rock had to be removed. The sprayed concrete lining of the exposed rock covers an area of 1700 square meters approximately.
The Department for Construction Methods and Construction Management of the Ruhr- University Bochum was commissioned to proceed with the consulting engineering work for the scheme which is perhaps the first of its kind. It differs from the conventional design concept through the stipulation that the newly exposed rock face should be lined with step by step sequences of sprayed concrete support rings and anchor supports. Traditionally there would have been first the drilling and blasting programme to ensure that the new shaft bulge-out has the correct shape. Then either brick lining or steel arches and concrete panels would be built in as necessary. The new concept, by contrast, is a noteworthy break of the local mining traditions.
As a result of technical consultations with the Local Mining Authority a single shell lining system was approved. This decision was favorably influenced by the outcome of an investigation programme for this depth and previous mining operations on similar conditions which had shown that the rock was strong and had resisted convergence movements. The approved shaft bulge-out support construction, by contrast, has now been installed in the form of a single shell lining of 200 to 250 mm thick shotcrete. It has steel bar reinforcements, cut and bent on site. At the transition edges between the shaft bulge and the lateral extensions the reinforced concrete thickness has been doubled to 400 mm and attached to the rock at intervals of 1 m by means of 5 m long anchors. The other anchors of the support system are 3.5 m long and have been installed in a pattern of one anchor per square meter due to the safety regulations of the Mining Authorities.