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Abstract Based on the uniaxial creep experiment with step-loading，the long term strength of pillar rockmass before grottoes No.9，10，20 at the world culture heritage Yungang Grottoes is studied and the long term mechanical properties is also evaluated. The results show that：(1) the pillar rockmass mainly composed of sandstones is with a good geological environment such as a single type of rock and good structure without developed joint. (2) the long term strength of the medium coarse-grained sandstones is lower than that of the medium-grained and medium fine-grained sandstones. The reasons for these are that the medium coarse-grained sandstone is argillaceous cementing and it contains montmorilonites which easily make reactions with water molecules resulting in the rockmass joints relatively developed. and (3) under condition of high moist content，the long term strength of the medium coarse-grained sandstones is about 20.22 MPa dropping 44.31% than that under condition of low moist content，and the safety stability factor of the pillar rockmass is 15.4 if the maximum stress numerical value(1.31 MPa) occurs on the upper of the western pillar of the grotto No.10. It is suggested that the rehabilitating should be implemented as soon as possible for the protection of the grottoes from the rain erosion and weathering. The maximum quality the pillar rockmass can bear can be a reference for related departments of architectural design and relics protection. The study results and suggest possess guiding significance for protecting Yungang Grottoes.
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Received: 07 November 2008
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