Establishment of a Procedure for Blast Mining During Construction of New Highway in the Vicinity of Treska River Spring

The waters of Treska river come from a fractured and karstified aquifer. A new highway route running over the aquifer has been designed for this area. Unfortunately, the construction of the new highway demands a series of mining blasts for the purpose of laying out the route.  Therefore, it was necessary to investigate whether the blasts could damage the aquifer and affect the water flow or its quality. To that effect, the capacity (flow) and the quality (purity, clarity of water, possible muddiness during and after trial mining) of water were monitored. A procedure had to be established for the purpose of investigating the influence of the blast waves on the rock medium in which the aquifer is embedded. The geological structure of the terrain along the route is represented by Triassic dolomite limestone that is cracked on the surface and karstified. Since our country doesn’t have any standards that cover the field of blasts and explosions, the Swiss standard (SWISS 640312:2013) was used.The main objective was  to evaluate the effects of blasting works on a cut in the zone of the Treska river spring, along the new highway route, namely subsection 2 of Kichevo – Ohrid motorway, in respect to the geological and hydrological characteristics of the terrain of the Treska river spring, define a methodology for performance of trial blasting, evaluate the effect of trial blasting, draw conclusions and provide  recommendations of measures and further activities.

Three trial blasts were performed on three trial fields according to the “far to close” principle and using  low destruction blasting technology with continuous monitoring of the velocity of blast waves as well as monitoring of the quantity and quality of the water (possible muddying) flowing from the spring.

The trial blasts were performed in sequences, on blasting fields with a radius of effect of 50 m and using quantities of explosives causing vibrations that are lower than the allowed ground vibration limit. According to the results obtained from the trial blasts, it can be concluded that the trial blasts in the vicinity of Treska river spring performed under good control and high quality monitoring of the blasting process will not have negative effect upon the spring flow regime. Also, the results obtained from the conducted geophysical surveys do not point to important changes of the physical-mechanical characteristics of the terrain structure after the trial blasts. In these zones, local disturbances as those during the referent measurements were defined. It is recommended to follow the same procedure for mining the rock medium during the construction works.