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Abstract In order to protect the cultural relics of Mogao Grottoes in Dunhuang and to reduce potential safety hazards，the following engineering measures were planned：grotto cliff strengthening，repairing and rebuilding of the plank road on the grotto cliff，and comprehensive prevention of wind-blown sand hazards. Among the above measures，drilling vibration in the process of cliff strengthening will have the strongest impact on the safety of the grottoes. In order to understand the propagation of drilling vibration and its impact on grotto safety，the tests dynamic parameters and drilling vibration behavior of the grotto rock mass were carried out. The results show the following：(1) longitudinal wave velocity in the country rock of the Mogao Grottoes is between 1 100 and 1 930 m/s；(2) the sympathetic vibration frequency of the rock mass is between 75 and 90 Hz；(3) longitudinal wave velocity is greatly affected by the spatial distribution of grottoes；(4) the peak values of vibration speed tested at a distance of 1，2，and 3 m from the borehole are mostly between 0.1 and 1.0 mm/s；and(5) the highest vibration speed recorded during high-pressure impact drilling is 6.01 mm/s. If the strict protection standard of 0.1 mm/s is used to evaluate the effect of drilling vibration on the grottoes，it is clear that drilling vibration will have a harmful impact on the grottoes. Therefore，low-pressure(0.8～0.9 MPa) and low-speed(≤0.4 m/min) drilling and appropriate protective measures must be adopted to reduce or eliminate the harmful effect of drilling vibration on the grottoes.
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Received: 08 November 2008
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