Several studies until now have been carried out on the variance of strength when curing concrete is subjected to Vibration. But the vibration sources considered on these studies were impact, shaking table and surface blasting Mortar lining model with cylindrical shape was made for laboratory tests and real concrete wall and bottom lining model was built in tunnel for field test. The results of the laboratory test showed that vibration with 2cm/sec increased P-wave velocity of mortar lining model and vibration with 5cm/sec could decrease P-wave velocity. The results of field test showed that compressive strength of all lining concrete subjected to blast-vibration below 2.5cm/sec for curing period was increased. The critical value of blast-vibration on concrete after 5 hours of casting was 3–4cm/sec, which can decrease the strength of concrete from small-scaled test blasting on concrete lining. This result was in accordance with the result when compared with P-wave velocity.
Mostly, the lining-concrete at tunnel site has been poured after the blasting work for the excavation of rocks in Korea. To do these two works simultaneously can reduce working hours for tunneling, but blast-vibration generated by blasting work can cause damage of curing lining-concrete. Damages of curing lining-concrete mean the strength decrease of concrete or occurrence of cracks at lining, so many studies to determine the effect of blast-vibration on curing lining-concrete in tunnel are necessary. The strength of concrete is increased gradually after casting. Therefore early aged concrete is more dangerous by blast-vibration. Lining-concrete poured in tunnel is subjected by blast vibration of which dominant frequency is over 150Hz. But the dominant frequency of vibration in several studies conducted to determine the effect of vibration on curing concrete until now was mostly below 100Hz. Also vibration source in these studies was not tunnel blasting but was shaking table, impact hammer or surface blasting (Bastian, 1970; Howes, 1979; Desai et al, 1984; Lim et al, 1994; Hulshizer, 1996). Therefore, in this study impact hammer test at laboratory and blast-vibration test at tunnel site were conducted to determine the effect of vibration of which dominant frequency is in the range of 150–300Hz on curing lining concrete. We measured the strength and elastic wave velocity of concrete specimen at 28 days after casting and the variance of strength and elastic wave were analyzed according to magnitude of vibration that subjected to lining concrete.
The structure of this model is similar to that of concrete lining in tunnel site. Two types of hexahedral rock block were used. The size of 30B block is 300 x300x300mm, and that of 50B block is 300x300x500mm. A cylindrical hole to copy tunnel was built by coring at the center of each rock block. The diameter of cored hole at each rock block is about 100mm and the thickness of mortar lining model is about 12mm.