Numerical Evaluation on Dynamic Response of Existing Underlying Tunnel Induced by Blasting Excavation of a Subway Tunnel

In Southwest China, most regions are mountainous, where traditional drill-and-blast method is adopted to excavate relatively harder rocks. However, blasting would cause vibration to adjacent structures and might result in damage or even failure. This paper considers a case where subway tunnel is overlying an existing railway tunnel, while the excavation requires blasting method. Vibration and stress distribution are calculated via Dynamic Finite Element Method (DFEM) for both full-face excavation and CD method. Result shows that vibration induced by CD method is only 28% of that caused by full-face blasting with same distance. Peak vibration is located on the lining facing the blasting source, while peak tensile stress is on the other side of the contour due to the reflection of stress wave on strata boundary. And peak value of tensile stress induced by full-face blasting is capable of causing lining failure; thus full-face blasting is not suggested within 40 m beyond the underlying tunnel axis. However, CD method has shown much advantage, since blasting within 25 m is also considered safe to the underlying tunnel. But when the blasting source is as near as 12 m within the underlying tunnel, the CD method is no longer safe.

Bearing Board's Force Analysis of the Rodless Drilling Set and its Prototype Test

To solve the problem of the traditional drill rig in its designs and applies, the concept of the rodless drilling rig was put forward. The working and structural principles of the rodless drilling set were introduced. The three-dimensional models of the rodless drilling rig and rodless drilling set were built based on virtual prototype technology. A detailed analysis of the rodless drilling sets force was made, and the force statuses of one bearing board of the rodless drilling set in all directions were given out. By the rodless drilling sets prototype test, the displacement curve was achieved, which indicates the working and structural principles of the rodless drilling set are correct, and its operation is reliable as well.

Tick-tack-four

Children are intrigued by numbers and their relationships to one another. If we, as teachers, use this curiosity, it is possible to develop many games and activities in arithmetic which can serve as replacement for traditional drill.