Stability Evaluation And Comprehensive Treatment For The High Steep Shore Rock Slope Near The Tianshengqiao Reclic

Tianshengqiao Bridge and Yanzhi River in Lishui Strict of Nanjing,which were formed by river excavation in Ming dynasty,have over 600 years of history,and they are key cultural relics protected by Jiangsu Province.A large degree of differential weathering happened in the rock mass of the high steep shore rock slope around bridge,leading to the appearance of several perilous rocks which may threat the tourists in the scenic spot and destroy the valuable cultural relics as well.So in this article,the weathering characteristics of the rock mass along the river bank were analyzed;the failure modes of the shore perilous rocks were proposed;the calculation models for the perilous rock stability were established;the geological analysis method and numerical simulation method were adopted to evaluate the stability of the rock slope;at last,some suggestions for the slope treatment were put forward based on the principals of cultural relic protection.The main achievements of this article are as follows.(1)Firstly,the engineering geological analyses of the western shore slope were conducted.The rock mass was divided into three regions.In region Ⅰ,the rocks were well cemented and mainly affected by chemical erosion,resulting in small karst grooves and caves.In region Ⅱ,the siltstone was affected by strong weathering,forming weathered grooves.While a part of rock mass has slipped down in this region,on which a perilous rock of cantilever type came into being.The conglomerate in region Ⅲ was affected by weathering and river scouring simultaneously so that deeper weathered grooves were formed.(2)Based on the comprehensive environmental geological analysis,the factors affecting the weathering of rock mass were given.The internal factors include characteristics of lithology and structural planes,while the external factors include the rain and freeze,river and vegetation.Furthermore,the weathering rates of different parts of rock mass were calculated based on the time of the cultural relics and the depth of the weathering grooves.The maximum weathering rate of the siltstone in region II is 0.33 m per century,while that of the conglomerate in region III is 0.66 m per century.(3)The integrate stability of the rock slope was qualitatively analyzed by stereographic projection method.The failure modes of local perilous rocks were classified into three types,including crack mode,toppling mode and single-plane sliding mode,and then the calculation formulas of stability coefficients were derived by establishing the mechanical equilibrium equations.(4)A software applying discrete element method 3DEC was used to study the formation mechanism of the perilous rocks along with the process of weathering.The formation mechanism of the perilous rocks on the slope was studied.The relationship between the rock stability and the location of the structural planes and the depth of the weathered grooves was revealed.It was predicted that overall failure of the rock slope might happen when the weathering grooves in region II is up to 2.5m and that in region Ⅲ is up to 5m.(5)Slope safety,cultural relic protection,suitable treatment and drainage were proposed as the principles of the rock slope treatment.According to the different conditions in different areas of the slope,appropriate treating methods were suggested to guarantee the appearance consistency between the slope and the environment around so that the cultural relics could be protected.